Berry Fruit: Value-Added Products for Health Promotion (Food Science and Technology)

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Berry Fruit

Value-Added Products for Health Promotion

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FOOD SCIENCE AND TECHNOLOGY Editorial Advisory Board Gustavo V. Barbosa-Cánovas Washington State University–Pullman P. Michael Davidson University of Tennessee–Knoxville Mark Dreher McNeil Nutritionals, New Brunswick, NJ Richard W. Hartel University of Wisconsin–Madison Lekh R. Juneja Taiyo Kagaku Company, Japan Marcus Karel Massachusetts Institute of Technology Ronald G. Labbe University of Massachusetts–Amherst Daryl B. Lund University of Wisconsin–Madison David B. Min The Ohio State University Leo M. L. Nollet Hogeschool Gent, Belgium Seppo Salminen University of Turku, Finland John H. Thorngate III Allied Domecq Technical Services, Napa, CA Pieter Walstra Wageningen University, The Netherlands John R. Whitaker University of California–Davis Rickey Y. Yada University of Guelph, Canada

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Berry Fruit

Value-Added Products for Health Promotion edited by

Yanyun Zhao

Boca Raton London New York

CRC Press is an imprint of the Taylor & Francis Group, an informa business

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CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2007 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Printed in the United States of America on acid-free paper 10 9 8 7 6 5 4 3 2 1 International Standard Book Number-10: 0-8493-5802-7 (Hardcover) International Standard Book Number-13: 978-0-8493-5802-9 (Hardcover) This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. A wide variety of references are listed. Reasonable efforts have been made to publish reliable data and information, but the author and the publisher cannot assume responsibility for the validity of all materials or for the consequences of their use. No part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www. copyright.com (http://www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC) 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Library of Congress Cataloging-in-Publication Data Berry fruit : value-added products for health promotion / editor, Yanyun Zhao. p. ; cm. -- (Food science and technology ; 168) Includes bibliographical references and index. ISBN-13: 978-0-8493-5802-9 (hardcover : alk. paper) ISBN-10: 0-8493-5802-7 (hardcover : alk. paper) 1. Berries. I. Zhao, Yanyun, Dr. II. Title. III. Series: Food science and technology (Taylor & Francis); 168. [DNLM: 1. Fruit. 2. Food Analysis. 3. Food Handling. 4. Nutritive Value. W1 FO509P v.168 2007 / WB 430 B534 2007] QP144.F78B47 2007 634’.7--dc22 Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com

2007001325

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Table of Contents Part I

Bioactive compounds of berry fruit ....................................................1

Chapter 1 Berry crops: Worldwide area and production systems............3 Bernadine C. Strik Chapter 2 Chemical components of berry fruits........................................51 Stephen T. Talcott Chapter 3 Berry fruit phytochemicals ..........................................................73 Luke R. Howard and Tiffany J. Hager Chapter 4 Natural pigments of berries: Functionality and application ...........................................................................................105 M. Monica Giusti and Pu Jing Chapter 5 Antioxidant capacity and phenolic content of berry fruits as affected by genotype, preharvest conditions, maturity, and postharvest handling .................................147 Shiow Y. Wang Chapter 6 The potential health benefits of phytochemicals in berries for protecting against cancer and coronary heart disease ................................................................................................187 Rui Hai Liu Part II Quality and safety of berry fruit during postharvest handling and storage.................................................................................205 Chapter 7 Quality of berries associated with preharvest and postharvest conditions ......................................................................207 Elizabeth Mitcham Chapter 8 Microbial safety concerns of berry fruit.................................229 Mark A. Daeschel and Pathima Udompijitkul

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Chapter 9 Postharvest handling, storage, and treatment of fresh market berries ............................................................................ 261 Cynthia Bower Part III Processing technologies for developing value-added berry fruit products ...................................................................................289 Chapter 10 Freezing process of berries ..................................................... 291 Yanyun Zhao Chapter 11 Dehydration of berries ............................................................ 313 Fernando E. Figuerola Chapter 12 Commercial canning of berries...............................................335 Hosahalli S. Ramaswamy and Yang Meng Chapter 13 Berry jams and jellies .............................................................. 367 Fernando E. Figuerola Chapter 14 Utilization of berry processing by-products....................... 387 Yanyun Zhao Index ..................................................................................................................... 411

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Preface Berries are highly valued fruit crops for their unique flavors, textures, and colors. In recent years, berries have been shown to provide significant health benefits because of their high antioxidant content, vitamins and minerals, fiber, folic acid, etc. In addition to fresh consumption, berry fruits are widely used in beverages, ice cream, yogurt, milkshakes, jams, jellies, smoothies, and many other food products. This book covers the basic functional chemicals (bioactive compounds), significant health benefits, shelf life, and microbial safety concerns associated with postharvest handling and storage, technologies to develop value-added berry products with high quality, and significant nutraceutical benefits. This book is divided into three parts: bioactive compounds of berry fruit and their health benefits, quality and safety of berry fruit during postharvest handling and storage, and processing technologies for developing valueadded berry fruit products. Each chapter in this book is written by an international expert (or experts), presenting information on the scientific background, research results, and critical reviews of the relevant issue, including a comprehensive list of recently published literature, and case studies, thus providing valuable sources of information for further research and development of berry fruit for the food industry.

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Editor Dr. Yanyun Zhao received her Ph.D. in food engineering from Louisiana State University, Baton Rouge, Louisiana, in 1993 and is now an associate professor in the Department of Food Science and Technology at Oregon State University, Corvallis, Oregon, with formal responsibilities in extension, research, and teaching. Dr. Zhao’s research efforts are in the area of valueadded food products development, with an emphasis on using novel food processing and packaging techniques for developing fruit- and vegetablebased functional foods. Dr. Zhao’s extension activities include providing leadership in identifying educational needs and creating, delivering, and evaluating educational programs and materials in value-added fruit and vegetable products. Dr. Zhao teaches “Fruit and Vegetable Processing” and “Functional Foods” courses. Dr. Zhao has published more than 40 journal articles and 8 book chapters, holds 6 patents, and has received more than 10 U.S. Department of Agriculture (USDA) competitive grants totaling about $1.5 million. Dr. Zhao serves on the editorial board of the Journal of Food Processing and Preservation, on advisory boards of several industrial organizations, is an expert reviewer for several peer-reviewed journals and USDA competitive research grant programs, and is an active member of the Institute of Food Technologists (IFT).

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Contributors Dr. Bernadine C. Strik Department of Horticulture Oregon State University Corvallis, Oregon Dr. Stephen T. Talcott Department of Nutrition and Food Science Texas A&M University College Station, Texas Dr. Luke R. Howard Department of Food Science University of Arkansas Fayetteville, Arkansas Dr. Tiffany J. Hager Department of Food Science University of Arkansas Fayetteville, Arkansas Dr. M. Monica Giusti Food Science and Technology The Ohio State University Columbus, Ohio Dr. Pu Jing Food Science and Technology The Ohio State University Columbus, Ohio

Dr. Shiow Y. Wang Fruit Laboratory, Beltsville Agricultural Research Center, U.S. Department of Agriculture Beltsville, Maryland Dr. Rui Hai Liu Department of Food Science Cornell University Ithaca, New York Dr. Elizabeth Mitcham Department of Pomology University of California Davis, California Dr. Mark A. Daeschel Department of Food Science and Technology Oregon State University Corvallis, Oregon Pathima Udompijitkul Department of Food Science and Technology Oregon State University Corvallis, Oregon

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Dr. Cynthia Bower U.S. Department of Agriculture Agricultural Research Service Subarctic Agricultural Research Unit, University of Alaska– Fairbanks Fairbanks, Alaska

Dr. Hosahalli Ramaswamy Department of Food Science and Agricultural Chemistry McGill University, Ste. Anne de Bellevue Quebec, Canada

Dr. Fernando E. Figuerola Tecnología de Alimentos Instituto de Ciencia y Tecnología de los Alimentos (ICYTAL) Universidad Austral de Chile Valdivia, Chile

Dr. Yang Meng Department of Food Science and Agricultural Chemistry McGill University, Ste. Anne de Bellevue Quebec, Canada

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Part I

Bioactive compounds of berry fruits

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chapter 1

Berry crops: Worldwide area and production systems Bernadine C. Strik Contents 1.1 Introduction ...................................................................................................4 1.2 Worldwide berry crop production ............................................................. 5 1.2.1 Strawberry ......................................................................................... 5 1.2.2 Raspberry........................................................................................... 8 1.2.2.1 Red raspberry..................................................................... 8 1.2.2.2 Black raspberry .................................................................. 9 1.2.3 Blackberry.......................................................................................... 9 1.2.4 Blueberry ......................................................................................... 11 1.2.4.1 Lowbush blueberry ......................................................... 11 1.2.4.2 Highbush blueberry ........................................................ 12 1.2.5 Cranberry......................................................................................... 13 1.2.6 Gooseberry and currant ................................................................ 13 1.2.7 Miscellaneous minor berry crops ................................................ 14 1.2.7.1 Lingonberry ...................................................................... 14 1.2.7.2 Hardy kiwifruit................................................................ 14 1.2.7.3 Other berry crops ............................................................ 15 1.3 Growth and development .........................................................................16 1.3.1 Strawberry ....................................................................................... 16 1.3.2 Raspberry and blackberry ............................................................ 17 1.3.2.1 Raspberry .......................................................................... 17 1.3.2.2 Blackberry ......................................................................... 18 1.3.2.3 Raspberry-blackberry hybrids....................................... 19 1.3.3 Blueberry ......................................................................................... 20 1.3.4 Cranberry......................................................................................... 21 1.3.5 Gooseberry and currant ................................................................ 22

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Berry fruit: Value-added products for health promotion 1.3.6

Miscellaneous minor berry crops ................................................ 23 1.3.6.1 Lingonberry ......................................................................23 1.3.6.2 Hardy kiwifruit................................................................ 24 1.4 Berry crop production systems ................................................................ 24 1.4.1 Strawberry ....................................................................................... 25 1.4.1.1 Annual production systems........................................... 25 1.4.1.2 Protected culture systems .............................................. 26 1.4.1.3 Perennial production systems ....................................... 27 1.4.2 Raspberry......................................................................................... 28 1.4.2.1 Summer-bearing red raspberry ..................................... 28 1.4.2.2 Primocane fruiting raspberry ........................................ 31 1.4.2.3 Off-season production systems ..................................... 31 1.4.2.4 Black raspberry ................................................................ 32 1.4.3 Blackberry........................................................................................ 32 1.4.3.1 Semierect blackberry .......................................................33 1.4.3.2 Erect blackberry ............................................................... 34 1.4.3.3 Trailing blackberry .......................................................... 35 1.4.4 Blueberry ......................................................................................... 36 1.4.4.1 Highbush and rabbiteye blueberry .............................. 36 1.4.4.2 Lowbush blueberry ......................................................... 38 1.4.5 Cranberry ........................................................................................39 1.4.6 Gooseberry and currant ................................................................ 42 1.4.7 Miscellaneous minor berry crops ................................................ 43 1.4.7.1 Lingonberry ...................................................................... 43 1.4.7.2 Elderberry .........................................................................43 1.4.7.3 Hardy kiwifruit................................................................ 44 References.............................................................................................................. 45

1.1 Introduction In 2005, there were more than 1.8 million acres of berry crops worldwide producing 6.3 million tons of fruit. The major berry crops grown, excluding grapes, are strawberries, black currants, blueberries, red raspberries, gooseberries, cranberries, and blackberries. Other minor berry crops are also grown commercially, including black raspberries, hardy kiwifruit, chokeberries, elderberries, saskatoons, and lingonberries. In addition, harvesting of some berries from the wild, including blueberries, blackberries, raspberries, cranberries, and lingonberries, contributes significantly to the worldwide availability of berry fruit. Berry crops are grown and sold via one of three marketing channels: (1) direct marketed through U-pick (customer harvested) or on-farm sales (grower harvested); (2) fresh sales via local stores or shipped to more distant markets; and (3) processed as frozen fruit, puree, dried, or juice—processed fruit may be sold directly to consumers in small retail packages, but it is often purchased by food manufacturers to make other products such as ice cream, yogurts, jams, jellies, juice blends, baked goods, cereals, and wines, for example.


Chapter 1:

Berry crops: Worldwide area and production systems

5

Production systems vary depending on whether the main market is for processed or fresh fruit. However, farms that have a fresh market focus may process a portion of their production that does not meet fresh fruit grade standards, when fresh prices are too low, or when there is a demand for processed fruit. Thus many growers access more than one marketing channel and grow a range of berry crops (and other crops as well) to diversify and improve their chances of success and minimize risk. Growers who are targeting large fresh or processed markets often work with a local wholesaler (fresh shipper or processing plant or “packer”) who sets prices and provides guidelines for harvesting and packaging. Some wholesalers provide the proprietary cultivars grown. Most berry crops are grown with conventional or integrated pest management practices. However, there is an increasing market demand for organically grown berry crops and thus organic acreage is increasing. This chapter details current berry crop acreage and production worldwide. The botanical classifications and growth and development of the major and many of the minor berry crops are described to provide the necessary fundamentals. The most common production systems are described by crop, with any differences among regions noted.

1.2 Worldwide berry crop production 1.2.1

Strawberry

There were more than 600,000 acres and 3.9 million tons of strawberries produced worldwide in 2005 (Table 1.1). More than half the acreage was in Europe, with Poland, Serbia and Montenegro, Germany, Ukraine, and Italy Table 1.1 Production of Major Berry Crops Worldwide, in Descending Order of Area Planted, 2005 Berry crop Strawberries

Red and black currants

Region Africa Asia Central America Europe Middle East North America Oceania South America World total Asia Europe Oceania World total

Area (acres) 16,264 134,670 1,142 327,205 35,360 75,664 4,643 14,685 609,633 179,222 219,069 3,855 402,146

Production (tons) 207,130 721,566 10,869 1,241,718 225,475 1,299,600 33,547 131,964 3,871,869 445,417 486,675 7,826 939,918 (Continued)


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Berry fruit: Value-added products for health promotion Table 1.1 (Continued) Production of Major Berry Crops Worldwide, in Descending Order of Area Planted, 2005 Berry crop

Region

Blueberries—Highbush

Africa Asia Europe North America Oceania South America World total North America World total Africa Asia Europe North America Oceania South America World total Asia Europe World total Asia Europe North America South America World total Africa Asia Central America Europe North America Oceania South America World total Asia North America World total

Blueberries—Lowbush Red raspberries

Gooseberries

Cranberries

Blackberries

Black raspberries

Area (acres) 741 1,754 9,736 74,585 2,434 18,039 107,289 172,840 280,129 163 100,428 104,069 21,164 927 25,950 252,701 42,056 54,520 96,576 26,687 247 46,245 1500 74,679 247 3,830 4,052 19,007 17,690 734 3,939 49,499 50 1,300 1,350

Productions (tons) 350 1,445 19,535 152,350 3,650 17,500 194,830 100,750 295,580 143 131,468 230,918 82,783 761 57,320 503,393 67,847 83,050 150,897 36,927 551 377,056 3000 417,534 220 29,051 1,753 47,386 65,170 4,023 6,975 154,578 250 235 485

Source: United Nations Food and Agriculture Organization (FAO) (strawberry, currants, gooseberries); Strik and Yarborough1 (Brazelton, D., personal communication; blueberries); Strik et al.2 (blackberries); FAO and academic colleagues (red raspberry).

being the leading producers. In fact, 40% of the acreage in Europe is in Poland, with most of their production being processed. There is strong year-round demand for high-quality fresh strawberries in Europe. Fresh strawberries are produced in southern Spain and Italy from February to May and are exported to countries in north and central Europe. Traditional cropping systems are


Chapter 1:


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used to produce fresh fruit in northern Europe and Scandinavia from June through August. Protected culture using greenhouses and tunnels is used in many European countries to provide “out-of-season” fresh fruit for 11 months of the year (from end of February until mid-January) in temperate climates. The next largest production region for strawberries is Asia (Table 1.1), where 65% of the acreage is in the Russian Federation, 14% each in Korea and Japan, and 5% in Kazakhstan. The United States had 51,595 acres of strawberries and 1.1 million tons, making it the largest producer in North America (Table 1.1). In the United States, 63% and 13% of the total acreage is in California and Florida, respectively, where strawberries are produced using annual production systems and more than 75% is fresh marketed. Fresh strawberries are available year-round using traditional annual and perennial production systems. Other states in the United States produce strawberries predominantly using perennial production systems, with the third largest producer, Oregon (6% of acreage), processing more than 95% of their production. It is difficult for states like Oregon, that produce high-quality processed strawberries, to compete with processed fruit produced at lower cost in Mexico and California. For example, strawberry acreage in Oregon has declined from 7800 acres in 1988 to 2200 acres in 2005. Most of this decline can be attributed to competition from processed fruit produced elsewhere, particularly in California. Historically California strawberry production is about 75% fresh marketed; however, they still produce more than 250 million pounds of processed fruit. While this processed fruit is considered inferior to that from cultivars bred specifically for processing produced in Oregon and other areas of the Pacific Northwest, it is a by-product and is sold at lower cost. In addition, yield in the annual production system used in California is up to six times higher than in the perennial systems used in the Northwest. These higher costs of production have made it difficult for Oregon growers to compete. It is likely that certain manufacturers will always demand premium quality fruit for certain products, so the future for a small, niche market industry in Oregon, for example, seems good. Mexico produced 165,632 tons of strawberries on 13,378 acres using annual production systems. Mexico typically exports about 30,000 tons/year, of which 70% is processed and 30% is fresh. Most of the exports are to the United States, but fruit is also shipped to Canada, Japan, and Europe. In 2005, Canada had more than 10,600 acres producing strawberries in perennial production systems for local fresh markets and processing. More than 72% of the strawberries in the Middle East (Table 1.1) are grown in Turkey. Other strawberry-producing countries in this region are Iran (21%), Israel (3%), Lebanon, Palestine, Cyprus, and Jordan. Strawberry production in Turkey has increased considerably over the last 10 years. Strawberries are produced in most areas of Turkey, mostly on small family farms. Egypt and Morocco accounted for 84% of the total acreage in Africa (Table 1.1). There is also some strawberry production in South Africa, Tunisia, and Zimbabwe. Production in most areas uses Californian cultivars in annual


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Berry fruit: Value-added products for health promotion

production systems. Fresh fruit from Egypt is exported mainly to the United Kingdom. In South America (Table 1.1), strawberries are planted in Chile (27% of acreage), Peru (24%), Columbia (13%), Venezuela and Brazil (7%), Paraguay (5%), and Ecuador (3%). Annual production systems using Californian cultivars are common. Nearly 60% of strawberries in South America are produced between June and November, with the remainder produced between November and May. About 50% to 70% of the strawberries are shipped fresh, while 30% to 50% are shipped frozen. There is also some strawberry production in Central America, mainly in Guatemala and Costa Rica, and in Oceania, with 79% of the acreage in Australia (Table 1.1). Currently it is not easy to obtain acreage information on organic strawberry production. However, there is some organic production in most regions. In California, where accurate statistics are reported, there were 965 acres of organic strawberries in 2006 (3% of the total acreage). Fresh strawberries are most commonly shipped in clamshell containers. Strawberries are processed as individually quick frozen (IQF), bulk frozen, sliced and sugared (“4 + 1”; 4 pounds fruit + 1 pound sugar), freeze-dried, pureed, or juice/concentrate.

1.2.2

Raspberry 1.2.2.1 Red raspberry

In terms of area planted, red raspberries are the fourth most important berry crop in the world (Table 1.1). Europe accounts for the largest portion of red raspberry acreage. Serbia and Montenegro (40% of the acreage) and Poland (34%) are the largest red raspberry producers in Europe, together producing more than 161,500 tons in 2005, mainly for processing. Other countries producing red raspberries in Europe are the United Kingdom (4%), France (3%), Hungary (3%), Spain (3%), Bulgaria (3%), Germany (3%), and Belgium, Croatia, Czech Republic, Estonia, Finland, Norway, Portugal, Romania, Switzerland, Sweden, Slovakia, The Netherlands, Italy, Ireland, and Denmark. More than 60% of the total production in most western European countries is fresh marketed. Asia accounts for about 40% of world acreage (Table 1.1); however, most (81%) of Asia’s production is in the Russian Federation. More than 12,350 acres were reported in the Ukraine, but an additional 30,000 acres of wild raspberries are harvested. The next largest raspberry producer in Asia is Korea, with 3212 acres; much of their production is locally used to produce wine. Other countries in Asia with red raspberry acreage are the Republic of Azerbaijan, the Republic of Moldova, and China. Chile is the only country in South America with significant red raspberry acreage (Table 1.1). Only 7% of Chilean production is for domestic use, the rest is exported, mainly (85%) as processed product. Frozen red raspberries from Chile are exported to Europe, the United States, Canada, and Australia.


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North America produces 16% of the red raspberry tonnage in the world (Table 1.1). The United States has about 14,826 acres, mostly in Washington State, but significant production also occurs in Oregon and California. Canada has 5560 acres, mostly in British Columbia, and most of this fruit is processed. The 778 acres in Mexico are mainly grown for the fresh export market. In Oceania, most of the acreage is in New Zealand (80%). Zimbabwe and Morocco produce red raspberries in Africa (Table 1.1). Red raspberries for the fresh market are most commonly sold in clamshell containers. Raspberries are processed as IQF, bulk frozen, freeze-dried, puree, or juice/concentrate.

1.2.2.2 Black raspberry The only countries reporting significant acreages of black raspberries are China and the United States, for a total world production of 485 tons from 1350 acres (Table 1.1). Korea has substantial new, but unreported, acreage being used for the production of berries for liqueur. In the United States, 99% of the black raspberry acreage is in Oregon, with almost all of the production processed as bulk frozen, puree (seedless), freeze-dried, or juice/ concentrate.

1.2.3

Blackberry

Blackberry acreage worldwide has increased an estimated 45% in the last 10 years. In 2005, there were about 49,498 acres of blackberries planted and commercially cultivated worldwide (Table 1.1). Blackberries are now more available to consumers. In 1990, most of the blackberry production in the eastern United States was U-pick or direct marketed and less than 2% was processed.3 In contrast, in 1990 more than 90% and 50% of the trailing blackberry crop in Oregon and California, respectively, was processed. Blackberries were not found on grocery store shelves in the eastern United States, and only rarely in the western United States in 1990.4 However, in the late 1990s, Chester Thornless became a major shipping blackberry, as it was found to have good fruit firmness. Navaho, from the University of Arkansas, was found to have excellent shelf life and could be shipped. These and other cultivars contributed to a major shift in the production outlook for blackberries from that of a locally marketed crop to one shipped for retail marketing.4 Also, the shipping of blackberries from Chile, Guatemala, and Mexico to the United States provided fresh blackberries during the “off-season” autumn, winter, and spring months and increased consumer awareness of this berry crop and consequently increased sales of U.S.-produced “in-season” fruit. Wild blackberries, not included in Table 1.1, still make significant contributions to worldwide production, and although accurate data are hard to obtain, there were an estimated 19,770 acres of wild blackberries harvested in 2005 with a total reported production of 14,837 tons.2 In some regions, the fruit harvested from wild blackberries may negatively impact sales of commercially grown fruit.


10


Worldwide blackberry production was 154,578 tons in 2005, not including the wild production mentioned above (Table 1.1). The largest blackberry production region is Europe, with Serbia accounting for 69% of the blackberry acreage in Europe. Ninety percent of Serbia’s production is processed and exported. Hungary was the next largest producer in Europe, with 3950 acres (21% of the total area) and 13,227 tons. Countries in Europe with 250 acres or more are the United Kingdom, Romania, Poland, Germany, and Croatia. The area in Poland has doubled in the last 10 years. There were 550 tons produced in 2005, with 80% processed, and most of this was exported, as was most of their fresh production. The United States accounted for 67% of the blackberry acreage in North America, the second largest in the world, after Serbia. The area planted in the United States increased 28% from 1995 to 2005. The United States had the highest production—35,099 tons—in the world in 2005. Sixty-five percent of the blackberries cultivated in the United States are planted in Oregon— 7755 acres. More than 95% of the total production of 25,185 tons was processed, with the remaining marketed fresh, and all for domestic use. The next largest blackberry-producing state in the United States is California, with 700 acres and 2600 tons in 2005. Most of the blackberry production in California is now located on the north-central coast and has a fresh market focus from mid-May through August. Other blackberryproducing states are Texas, Arkansas, and Georgia.5 Mexico accounts for 32% of the planted area in North America, with 5683 acres. Blackberry production in Mexico has increased from 568 acres in 1995 and is projected to grow to at least 12,355 acres by 2015. Most of the Mexican production targets fresh export markets to the United States. In 2004, Mexico exported 8245 tons to the United States, more than double their export volume in 2002. In Central America (Table 1.1), Costa Rica (3830 acres) and Guatemala (222 acres) reported commercial production. Of the 1653 tons produced in Costa Rica, less than 15% was exported. Currently most is used for local processing and fresh consumption. Guatemala is the main country in Central America that ships fresh blackberries to the United States. Ecuador accounts for 53% of the planted area in South America (Table 1.1), with 2100 acres. There was an estimated 30% growth in planted area from 1995 to 2005, but little growth is projected for the next 10 years. Only 15% of their estimated 1421 tons of production is exported for the fresh market, mainly due to the soft fruit of the species they grow (Rubus glaucus Benth.) and the Mediterranean fruit fly (Ceratitis capitata Wiedemann). Chile has 1111 acres of commercial blackberries with a total production of 4275 tons, not including the 6393 tons harvested from wild plantings and exported as a processed product. The area planted increased 50% from 1995 to 2005 and is projected to be 1975 acres in 2015, provided competition from Mexico in the fresh market does not adversely affect the cost of production and competitiveness in the processed portion of their industry. In 2004, Chile exported 10,670 tons of processed fruit (55% to 65% was harvested from introduced wild species) and 210 tons of fresh fruit. Their fruiting season is


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from November to March. Brazil had 617 acres and produced 860 tons in 2005, with only 15% exported. China accounted for all of the production in Asia (Table 1.1). Most of China’s production is in the Jiangsu Province, but the newest regions, the Liaoning, Shandong, and Hebai Provinces, are projected to grow the most in the next 10 years, when China is expected to have 5436 acres. Most of the production in China is processed, with 70% of processed fruit and 10% of their fresh production exported. Most of the blackberry area in Oceania (Table 1.1) is planted in New Zealand, which had 640 acres and 3690 tons in 2005. The area in Oceania is projected to grow by about 35% in 10 years. The fruiting season in New Zealand is from November through April, with almost all of their blackberry production consisting of trailing types, mainly Boysen. Almost all of their production is processed, with 55% of that exported. South Africa is currently the only African country with blackberry production (Table 1.1). However, no fresh fruit is exported because of the distance to the major markets of Europe. Projections for the greatest growth in the next 10 years are in Romania (900%), Poland (200%), Mexico (117%), Chile (76%), Hungary (50%), China (42%), and the United States (20%). There may be 66,797 acres of commercial blackberries worldwide, not including production from harvested wild plants, in 2015.2 Blackberries for the fresh market are most commonly sold in clamshell containers. Blackberries are processed as IQF, bulk frozen, puree (with or without seeds, depending on the cultivar), freeze-dried, or juice/concentrate.

1.2.4

Blueberry

Blueberries have become a major crop worldwide. Strong markets for processed and fresh fruit have resulted in good returns for growers and an increase in planted area. The growth in markets and production is related to the positive health benefits of blueberries. These benefits have been used in marketing campaigns since 1997. Over the last 10 years, demand for blueberries has exceeded supply. New cultivars, better adapted to “nontraditional” growing areas, have expanded production worldwide. From 1995 to 2005, worldwide highbush blueberry acreage increased by 90%. In many areas of the world, wild species of blueberries are harvested for personal and commercial use. Data on total production are often difficult or impossible to obtain. For example, Vaccinium uliginosum L. is harvested in China, Vaccinium myrtillus L. in Europe, and various species in the United States, often marketed as “huckleberries.” I will not include information on the production of any native Vaccinium species here, other than the lowbush blueberry.

1.2.4.1 Lowbush blueberry Lowbush blueberry fields consist mainly of native clones of Vaccinium angustifolium Ait. with some clones of Vaccinium myrtilloides Mich. mixed in, depending


12


on the region. In Canada and the United States, native stands are managed and harvested for commercial production. Fruit are often marketed as “wild blueberries,” with more than 97% of the total production being processed. In 2003, processed lowbush blueberry fruit accounted for 68% of the total processed fruit (all types of blueberries) produced in North America and they are expected to continue to account for a significant share of this market. In 2003, the total area of lowbush blueberries managed in North America was 172,845 acres, a 33% increase from 10 years earlier.1 Since lowbush blueberries are native, this increase in area reflects a larger portion of native stands being managed for harvest because of the strong blueberry market. There were 65,442 acres of lowbush blueberries in the United States, mainly in Maine, and 107,404 acres in Canada, mainly in Quebec, Nova Scotia, and New Brunswick. Only half of the total area of lowbush blueberries is harvested annually because of alternate-year pruning practices.5 Total lowbush blueberry production in North America in 2003 was 111,058 tons, with approximately 99% sold for processing. The managed area of lowbush blueberries in North America is expected to increase by 10% by 2013.1 The major limitation for expansion of this industry is finding native stands that can be economically brought into production.

1.2.4.2 Highbush blueberry In 2005, there were an estimated 107,289 acres of highbush blueberries (Vaccinium corymbosum L.) planted worldwide with a total production of 196,900 tons, a 20% and 51% increase in acreage and production, respectively, from what was reported in 2003.6 North America accounted for about 70% of the planted area and 77% of the total highbush blueberry production in the world (Table 1.1). Acreage in North America increased an average of 2535 acres/year from 2003 through 2005. Most of the North American acreage was in the United States—60,975 acres—but there were 13,500 acres in Canada, mainly in British Columbia, and about 180 acres in Mexico in 2005. South America accounted for about 17% of the world area in 2005 (Table 1.1). Fruit is harvested by hand from the end of September through April, depending on the country and region. Most of the fruit is exported to markets in the Northern Hemisphere. Blueberry production in South America started in Chile, which still accounts for 62% of the area planted and 80% of the total production. The remaining blueberry production is in Argentina. In Europe, 95% of the total production (Table 1.1) is marketed in Europe. There were an estimated 3954 acres in Poland, 3954 acres in Germany, 741 acres in France, 852 acres in The Netherlands, 593 acres in Spain and Portugal, 445 acres in Italy, and 49 acres in the United Kingdom. Oceania accounted for about 2% of the world’s blueberry area in 2005 (Table 1.1), with about half the area in each of New Zealand and Australia. South Africa had 741 acres and produced 350 tons of blueberries in 2005 (Table 1.1). There is tremendous interest in blueberries in Asia. Plantings are expected to increase steadily in this region. Japan has about 1112 acres and


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China 642 acres (Table 1.1). However, interest in planting blueberries is strong in both countries. For example, in China there may be more than 1500 acres planted by 2008. Total highbush blueberry production in the world in 2005 was 194,830 tons, with approximately 63% sold for the fresh market. Blueberries for the fresh market are most commonly sold in clamshell containers. Blueberries are processed as IQF, bulk frozen, freeze-dried, pureed, or juice/concentrate. Many areas producing highbush blueberries have some limitations to expansion of the area planted, particularly in North America and Europe. These limitations include cold winter climate and insufficient cold hardiness of the present cultivars, lack of suitable soils, insufficient planting stock, pressures for urbanization, and the cost of establishment. Still, many project significant growth in the planted area of highbush blueberries in the next 5 to 10 years. The markets for fresh and processed fruit will need to continue to be strong to support the projected increase in supply.

1.2.5

Cranberry

There were a reported 74,679 acres of cranberries harvested worldwide in 2004 (Table 1.1). The United States is the world’s largest producer, with 39,200 acres of the large-fruited cranberry (Vaccinium macrocarpon Ait.) and 74% of total world production. In the United States, Wisconsin and Massachusetts have the largest cranberry acreage, accounting for 80% of the total. Other states producing cranberries are New Jersey, Oregon, and Washington. Belarus has the second largest area, with 19,768 acres, but the yield of the small-fruited cranberry (Vaccinium oxycoccos L.) they produce is relatively low, with a total production of 25,353 tons. In comparison, Canada had the second highest production in the world, harvesting 68,556 tons of large-fruited cranberry from 7045 acres. The area in Europe is currently reported as 247 acres, all in Romania; however, there are commercial cranberry plantings in Ireland and Poland that are not yet reported in official statistics. Other countries producing the small-fruited cranberry are Ukraine, Latvia, and the Republic of Azerbaijan in west Asia. In South America, the only country producing the large-fruited cranberry on established beds is Chile, with 1500 acres (Table 1.1). The majority of cranberry production worldwide is processed. In the United States, 94% of total production was processed in 2004. Cranberries are processed for juice and sauces, and are dried. Chile exported 40 tons of fresh cranberries in 2004; however, fresh cranberries in the Northern Hemisphere are typically only sold during Thanksgiving (October in Canada and November in the United States) and Christmas. Fresh cranberries are stored from harvest (September or October) until the time of sale.

1.2.6

Gooseberry and currant

There were 96,576 acres of gooseberries (Ribes uva-crispa L.) and 402,146 acres of red and black currants (Ribes rubrum L. and Ribes nigrum L., respectively) worldwide in 2005 (Table 1.1). Currants are produced mainly in Europe and


14


Asia, with black currants being the most common type grown; black currants are mainly processed into juice, but they are also used for jams, jellies, liqueurs, and colorings.7 Almost all of the currant acreage in Asia is planted in the Russian Federation. In Europe, countries with currants are Poland (47% of acreage), Germany (23%), Ukraine (5%), and the United Kingdom, Austria, the Czech Republic, France, Estonia, Denmark, and Finland, all with 2% to 3% of European acreage. The predominant acreage of red currants is in Poland and Germany, with lesser acreages in Belgium, France, Holland, and Hungary.7 Red currants are used mostly for juices and other processed food items, often in combination with other fruits. White currants are used in parts of Europe for baby food and in Finland for sparkling wines.8 Ninety percent of the acreage in Oceania is in New Zealand. Although some commercial acreage of gooseberries and currants exists in North and South America, it is relatively small and scattered. For example, currants are produced for the fresh market in Chile and for the fresh and processed markets in the United States (Oregon). Gooseberries are mainly grown in Asia and Europe (Table 1.1), with the largest area, 42,000 acres, in the Russian Federation and 30,885 acres in Germany. The next largest producer is Poland, with 8400 acres. Although some commercial acreage of gooseberries exists in North America, it is relatively small and scattered. Gooseberries are grown for the fresh market and processing, mainly canning, in Oregon. Worldwide, gooseberries are processed mainly for jams and are sold to a limited extent for the fresh market.

1.2.7

Miscellaneous minor berry crops

1.2.7.1 Lingonberry The commercial acreage of lingonberries in established plantings is estimated at 70 acres worldwide. Actual production statistics for this crop are difficult to obtain. Most of the lingonberry production worldwide is harvested from wild stands.

1.2.7.2 Hardy kiwifruit Kiwifruit is native to Southeast Asia. There are more than 50 species in the genus Actinidia, and many have commercial potential. The most common kiwifruit species grown commercially is Actinidia deliciosa cv. Hayward. Consumers are very familiar with this brown, fuzzy fruit. Hayward is grown commercially in New Zealand, Italy, Japan, France, Australia, Greece, Chile, and California. Hardy kiwifruit [Actinidia arguta (Siebold & Zucc.) Planch. ex Miq], however, are much more limited in their production and, unlike Hayward, are often marketed along with other berry crops. Ananasnaya is the most widely grown cultivar of hardy kiwifruit in the world and may also be known or marketed under alternate names including “baby kiwifruit,” “grape kiwi,” “wee-kee,” and “cocktail kiwi.” In 2003, about 250 acres of Ananasnaya were grown commercially worldwide, in the United States, New Zealand, Canada, Chile, Italy, France, Germany, and


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The Netherlands9 more than one-third of this acreage was in Oregon. Fresh fruit of Ananasnaya have been well received in the San Francisco and Los Angeles, California, markets and in Japan, fetching high prices. In addition, private industries are working on developing processed products. The commercial acreage has been limited mainly by marketing factors, such as development of fresh markets for this relatively unique fruit, the range in fruit size, the limited ripening period, and the relatively short storage and shelf life compared to fuzzy kiwifruit. The continued development of processed markets likely will strengthen this industry.

1.2.7.3 Other berry crops Every culture around the world has native crops that are important locally and some of these have become important berry crops.10 Other berry crops grown commercially include the elderberry (Sambucus canadensis L.), in North America and its counterpart Sambucus nigra L. in Europe. The purplishblack berries, about 1/4 in. in diameter, are produced on large cymes up to 1 ft in diameter. The stems of the American elder have long been used for musical flutes and pipes for conducting liquids. North American Indians and early pioneers adapted the hollow stems for use as a tap to draw sap from sugar maple trees. Tannin in the bark and roots of elderberry was used in tanning leather. The leaves, flowers, and fruit provided dyes for leather, baskets, and other articles made by North American Indians. The berries and oil pressed from seeds have been used to flavor wine. All parts of the elderberry have been used in medicine, and the powdered, freeze-dried, encapsulated fruit of S. nigra is a major use for this crop. At present, elderberry fruit is used for various culinary purposes: in sauces, alone or combined with other fruit in tarts and pies, fruit juice, jelly, and red wine.11 Saskatoons, also called juneberries or serviceberries (Amelanchier alnifolia Nutt.), are grown commercially mainly in Alberta and Saskatchewan, Canada. Various species of Amelanchier are used as ornamentals for their showy flowers and edible, dark purple fruit that look like blueberries. However, this plant does not produce true “berries”; botanically, this species produces a pome fruit. The fruit was used by North American Indians in making pemmican, a semidry mixture of fruit and meat. Early pioneers used this as a major source of fruit. The fruit can be eaten fresh, in pies or other baked desserts, canned, frozen, or made into wines, jellies, or syrup. The chokeberry [Aronia melanocarpa (Michx.) Elliott] is grown commercially as a processed fruit product in eastern Europe and to a limited extent in North America. Plants produce dark purple berries, about 1/4 in. in diameter, that are used mainly for juice production. Some wild blueberries, commonly called “huckleberries,” are not only harvested from wild stands, but are planted and commercially cultivated. An example of this is the “evergreen huckleberry” Vaccinium ovatum Pursch.), grown to a very limited extent in established plantings in Oregon. The small, dark blue to purple fruit are processed and mainly used for “huckleberry” jam.


16


1.3 Growth and development Vegetative and reproductive growth of berry crops is influenced by environment, particularly photoperiod and temperature, soil type, and cultural practices such as fertilization, irrigation, and production systems. This chapter highlights the stages of growth and fruit development. Cold hardiness is not covered here, but is well reviewed in other publications.8,12–18

1.3.1

Strawberry

The cultivated strawberry (Fragaria × ananassa Duch., family Rosaceae) is a perennial plant adapted to a wide range of climates. There are many other species of Fragaria found worldwide, however, the only other species grown commercially to any extent are Fragaria vesca L., the wood or alpine strawberry, and Fragaria chiloensis (L.) Mill., the beach strawberry. The strawberry plant has trifoliate leaves arranged spirally around a compressed stem, called a crown.19 Buds in the axils of each leaf may develop into a branch crown, inflorescence, a runner, or remain dormant. Branch crowns tend to develop under short day length (less than 10 hours), whereas runners are promoted under long days (more than 10 hours). Runners consist of an aboveground stem with a new daughter plant produced at the second node. Daughter plants may also produce runners, thus leading to a runner “string.” The original plant established is often called the “mother plant.” Some types or cultivars of strawberry produce more runners than others. Runner production may also be manipulated through chilling received in cold storage, as is done in the California production system. Roots arise from the base of the crown, with 90% of the root system found in the upper 6 in. of soil.20 The two main types of strawberry grown worldwide are short-day types (called “June bearers” in the northern hemisphere) and day-neutral types. Short-day cultivars initiate flower buds when the day length or photoperiod is less than 14 hours, whereas day-neutral cultivars typically initiate buds every 6 weeks throughout the growing season.13 However, at low temperatures (about 50°F to 59°F) most cultivars initiate flowers regardless of the photoperiod, while at high temperatures (about 77°F), flower bud initiation is almost inhibited.13 The impact of light intensity and temperature on strawberry plant growth is well reviewed by Darnell.13 Strawberry inflorescences often produce a terminal flower (primary), two secondary, four tertiary, and eight quaternary flowers.20 However, as breeding programs have selected for larger fruit, they have selected for much simpler inflorescences that commonly contain only one to three flowers. Individual flowers typically have 10 sepals (calyx), 5 petals, 20 to 30 stamen, and 60 to 100 pistils, depending on the flower order.21 The flowers are mainly pollinated by bees. The strawberry is an aggregate or accessory fruit composed of a fleshy, red receptacle with achenes (fertilized ovules, often called “seeds”) arranged spirally on the outside of the receptacle. Growth of the receptacle depends


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on the successful fertilization of the ovules and the size and shape of the mature fruit is a function of the number and arrangement of achenes formed.22 Fruit development from pollination to ripe fruit ranges from 20 to 50 days, depending on the cultivar and temperature. The primary fruit ripens first and produces the largest fruit (“berry”), then the secondary, and so on.

1.3.2

Raspberry and blackberry

The red raspberry (Rubus idaeus L.), the black raspberry (Rubus occidentalis L.), and the blackberries (Rubus sp.) belong to the family Rosaceae. This group or genus (Rubus) is collectively called “brambles” in eastern North America and “caneberries” in western North America. Most blackberries and raspberries have spines, although spine density can vary considerably among cultivars, with some being genetically thornless. Raspberry and blackberry plants have perennial root systems and crowns (base of the plant). However, the canes are biennial, living for only 2 years. Cane growth (increases in length) occurs only in the first year, when canes are called primocanes. In year two, canes are called floricanes. These canes flower, fruit, and then die after fruiting. In any year, except the planting year, there are both cane types present.

1.3.2.1 Raspberry The red raspberry (R. idaeus) is commonly divided into two types based on fruiting habit: “summer bearers” or floricane fruiting types (e.g., Tulameen, Meeker, Glen Ample), and “primocane fruiting” types (e.g., Heritage, Autumn Bliss, Polka). The only black raspberry harvested commercially is R. occidentalis (e.g., Munger). Purple raspberries (e.g., Royalty), hybrids between red and black raspberries, are grown to a very limited extent, mainly in eastern North America. Yellow-fruited R. idaeus, in which the fruit color is due to a recessive mutation, is also grown in small quantities for specialty markets. Wherever raspberry species are found, they have been harvested from the wild; however, several species have interest beyond their area of origin.10 Raspberry species harvested in the wild include Rubus chamaemorus L., the cloudberry, and Rubus arcticus L., the arctic raspberry, both native to alpine and circumpolar regions and having a dwarf, herbaceous, annual bearing habit. Hybrids of the European R. arcticus and the American Rubus stellatus are marketed in northern Europe.23 Primocanes are produced from buds at the base of floricanes at the crown or from buds on roots in red raspberry. Black raspberries only produce new primocanes from buds on the crown. Generally, in summer-bearing red and black raspberries, primocanes are vegetative the first year and fruit the second year on the entire length of the floricane. Primocane fruiting raspberries produce a relatively large crop at the tip of the primocane and will produce a floricane crop on the base of the second-year cane. Raspberries have an extensive root system. Roots start growing in the spring after bud break. If water is adequate, most root growth occurs in midsummer and growth continues in the fall after top growth has stopped.


18


In summer-bearing raspberries, flower bud initiation for next year’s crop occurs as the day length shortens and temperatures start to cool in late summer. Flower bud development starts at the tip of the cane and progresses basipetally. Flower bud initiation in primocane fruiting cultivars is not dependent upon photoperiod or cooler temperatures, but rather is based on the physiological age of the cane, starting at the tip.24,25 Carew et al.26 reviewed how the growth cycles of summer-bearing and primocane fruiting raspberries are controlled by the environment, the cultivar, and cultural practices. Once plants enter dormancy, a certain number of chilling hours (temperatures between 32°F and 45°F) are required before the plant can grow normally. Although the exact chilling requirements of many cultivars are not known, many of the summer-bearing red raspberries grown in the northern hemisphere have a chilling requirement of 800 to about 1400 hours. Primocanes overwinter as dormant canes and become floricanes when growth starts the following spring. Buds break along the floricane producing fruiting laterals, the lengths of which are cultivar dependent. Cultivars that are suited to machine harvesting generally have fruiting laterals that are not too short or too long and are not brittle. The range in flower opening time along the fruiting lateral, coupled with a slightly earlier emergence of laterals at the tip of the cane, leads to a range in fruit ripening time within a cultivar. Most summer-bearing cultivars have a ripening season of about 30 days, although some have a season as long as 55 days. Raspberry flowers have five sepals, five petals, many stamens, and many pistils arranged spirally around a receptacle. Commercial red and black raspberries are self-fertile, in that a cross pollinator is not required. However, they do require insect/bee transfer of pollen to the pistils. Insufficient pollination or fruit set within a flower leads to the development of crumbly fruit. Some viruses, such as raspberry bushy dwarf virus, may lead to symptoms of crumbly fruit.17 It takes about 30 to 35 days for raspberry fruit to mature after pollination. Individual fruit typically weigh from 2.5 to 5 g, depending on the cultivar. For maximum productivity, flavor, and sweetness, fruit must reach full maturity and full size before harvest. However, fruit firmness decreases in the later stages of fruit maturation. Fruit firmness is also cultivar dependent. The “berry” is an aggregate fruit consisting of many drupelets, each of which contains a pyrene (seed). The drupelets are spirally arranged around a white-colored receptacle. When picked, the berry separates from the receptacle, or “torus,” yielding a hollow, thimble-shaped fruit. The ease of fruit removal when ripe is cultivar dependent, with those suited for machine harvesting requiring easy fruit removal.

1.3.2.2 Blackberry Blackberries are often classified according to their cane architecture into three types: erect, semierect, and trailing.27 Erect blackberries produce primocanes


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from buds at the base of floricanes at the crown or from buds on roots, whereas trailing and semierect types only produce new primocanes from buds on the crown. With the exception of the primocane fruiting erect types, primocanes are vegetative the first year and fruit the second year on the entire length of the floricane. Blackberries have an extensive root system. Primocanes emerge in the spring, with rapid growth under suitable temperature conditions. Erect and semierect blackberries produce primocanes that grow upright, with vigor dependent on the cultivar and growing conditions. The primocanes of trailing blackberry are not self-supporting and will grow along the ground. Canes will continue to grow in length until cold weather in the fall limits their development. In general, flower bud initiation in blackberry occurs under short day length and low temperature. However, the time of flower bud initiation and the pattern of development on the cane can vary with the growing location and the blackberry type or cultivar.28,29 Primocane fruiting blackberries produce fruit on the top one-fifth or so of the cane during the latter part of the growing season. The chilling requirement of blackberries has been reported to range from 200 to more than 900 hours, depending on the type and cultivar.30,31 Weather, specifically low winter temperatures, limits where blackberries can be grown.32 In general, erect blackberries can survive much lower winter temperatures (less than 5°F) than trailing types, and thorny cultivars are more winter hardy than thornless types.33 Blackberry flowers and fruit have a similar morphology to raspberries. The “berry” is an aggregate fruit consisting of many drupelets, each of which contains a pyrene (seed). The pyrenes of most trailing blackberries are much smaller or thinner than those of erect and semierect blackberry. In all blackberry fruit, the receptacle or “torus” separates from the plant when picked and is part of the fruit that is consumed. The ease of fruit removal when ripe is cultivar dependent, with those suited for machine harvesting requiring easy fruit removal. It takes from 40 to 60 days for blackberry fruit to mature after pollination. Individual fruit typically weigh from 3 to 12 g, depending on the cultivar. Many blackberry fruit are not at their optimum flavor until they change from glossy black to dull black in color. For maximum productivity, flavor, and sweetness, fruit must reach full maturity and full size before harvest. However, fruit firmness decreases in the later stages of fruit maturation. Fruit firmness is also cultivar dependent.

1.3.2.3 Raspberry-blackberry hybrids Hybrids of red raspberry and blackberry are grown commercially. These are considered trailing blackberry types due to their growth habit. While Boysen and Logan have historically been very important commercially, the acreage of these, particularly Logan, has declined over the last 10 years. Other hybrids that are occasionally sold include Tayberry and Tummelberry.


20

1.3.3


Blueberry

There are about 400 species of blueberry (Vaccinium sp., family Ericaceae). The most important blueberries cultivated worldwide are the northern highbush (V. corymbosum), southern highbush (complex hybrids based largely on V. corymbosum and V. darrowi Camp.), and rabbiteye blueberry (V. ashei Reade), all native to eastern North America.34 The lowbush blueberry in northeastern North America (mainly V. angustifolium) is harvested from managed native stands. Various other species are harvested from the wild in many regions of the world. Like other ericaceous plants, blueberries thrive in acid soils with a pH between 4.2 and 5.5. All commercial blueberry species are deciduous and have a typical bush height at maturity of 1 foot in lowbush blueberry, 6 to 8 feet in highbush, and 12 feet in rabbiteye blueberry. The roots of highbush and rabbiteye blueberries are very fine, fibrous, and lack root hairs.35 Lowbush blueberries produce roots adventitiously from rhizomes, or below-ground stems. Thus lowbush blueberries are maintained in solid beds without aisles, whereas highbush and rabbiteye types are planted in fields with aisles between rows of plants. The fine, fibrous roots of the blueberry require an open, porous soil. Most blueberry roots are found within the drip line of the bush and in the upper 18 inches of soil. Blueberries produce simple buds—vegetative buds, producing a leafy shoot, and flower buds, producing only an inflorescence. Flower buds are large and almost spherical, whereas vegetative buds are pointed, small, and scalelike. Buds are found mainly on 1-year-old wood, with latent buds also occurring on older wood. Shoot growth occurs in two or more flushes per season, depending on the cultivar and the length of the growing season. The impact of light intensity and temperature on blueberry plant growth is well reviewed by Darnell.14 New canes develop from the crown (base) of the blueberry plant in early spring or from older wood higher up in the bush. These shoots, usually called “whips,” are extremely vigorous and often are the “renewal” wood for subsequent years’ production. Flower bud initiation occurs under short day length in late summer and early fall,36,37 usually on the tip of the current season’s shoot. Initiation proceeds basipetally, with the number of floral buds per shoot affected by the cultivar, climate, and production practices. Flower bud development continues until temperatures become too cool in fall. Both flower and vegetative buds require a period of dormancy, from 800 to 1200 hours between 32°F and 45°F in northern highbush blueberries, before growth begins again the following spring.15 However, flower bud differentiation in southern highbush blueberries may occur through the winter without a dormant period.38 Blueberry plants flower in spring, with flowers at the tip of 1-year-old wood and the tip of the cluster opening first. The length of the bloom period varies with the cultivar, but can be affected by climate. Each flower bud contains from 8 to 16 potential flowers.15 Flowers consist of sepals (calyx),


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petals (a four- or five-lobed, urn-shaped corolla), 10 stamens, and a pistil.39 Commercial growers usually use honeybees for pollination. Although blueberries are often self-fertile, cross-pollination increases fruit set and fruit size for many cultivars.40–42 The blueberry fruit is a true berry, consisting of an ovary with up to 100 seeds. The fruit of some species, particularly rabbiteye blueberries, contain stone cells, that contribute to fruit grittiness.14 Ripe fruit are generally blue, blue-black, or purple in color, but have a surface wax layer, the “bloom,” which may make the berry appear lighter in color. The fruit development period ranges from 42 to 90 days for northern highbush,43 55 to 60 days for southern highbush,44 70 to 90 days for lowbush,45 and 60 to 135 days for rabbiteye blueberry,46 depending on the cultivar, weather, and plant vigor. The sugar content of the fruit will increase during maturation to about 15% when the fruit is ripe. Fruit size continues to increase after the fruit turns blue, due mainly to water uptake. Individual fruit typically weigh from 0.5 to 3 g, depending on the cultivar. Fruit flavor, much of it associated with the skin, increases during ripening, but not after harvest.

1.3.4

Cranberry

The large-fruited American cranberry (V. macrocarpon, family Ericaceae) is a low-growing, trailing, woody, broadleaf, nondeciduous vine. This species of cranberry is native to eastern North America. The small-fruited cranberry (V. oxycoccos) is not commercially cultivated in North America, but is harvested in eastern Europe and Asia. Like blueberries, cranberries are adapted to acid soils and are best grown at a pH of 4.2 to 5.5. Cranberry roots are very fine, fibrous, and lack root hairs. Roots are readily formed on decumbent stems when covered with a moist medium such as sand. Plants produce various types of shoots. Runners are horizontal stems ranging from 1 to 6 feet in length and spread profusely over the bed or canopy. The short, vertical branches in cranberry are called uprights. Uprights originate from axillary buds on the runners or from older uprights and grow for several years. Uprights are typically 2 to 3 inches long, but length is affected by light intensity and nutrition. Uprights can be either fruiting or vegetative (nonfruiting). In the Pacific Northwest, from 150 to 700 uprights per square foot have been documented in Stevens cranberry beds, with 10% to 65% of these being fruiting uprights. Cranberry uprights produce one of two types of buds at their tip: flowering (fruit) and vegetative. Flower buds may contain from one to seven flowers, as well as leaves and a growing point. Axillary buds located at a leaf node either on the runner or on an upright are the source of new uprights or runners. Bud break in cranberry typically occurs in early April, depending on weather conditions and vine nutrition. In April and May, some vegetative growth, including the development of new leaves, occurs. At the “hook”


22


stage, the flower pedicels are visible on fruiting uprights. At this stage, the curve of the slender flower stem with the still-closed flower is said to resemble the neck and head of a crane, thus suggesting the name “craneberry,” which was shortened to cranberry. Bloom begins around the first part of June and lasts from 3 to 6 weeks, depending on the growing region. Each flower is borne individually, with one to seven flowers per upright. Normally, vegetative growth continues beyond the flowers. The normal flower consists of an inferior ovary with four cells, a calyx of four sepals, and a corolla of four petals that are pinkish white in color and deeply cleft. Eight stamens surround the pistil.47 The cranberry is self-fertile, however, some evidence indicates that cross-pollination may improve fruit set and berry size. Mixtures of cranberry cultivars, or off-types, are not unusual in commercial beds, although this is not desired from a management perspective. Honeybees are used for pollination in commercial plantings. The ovary and calyx fuse to form a true berry that varies in shape and color. The berry consists of a relatively thin epidermis and four locules containing from 0 to 50 seeds, depending on seed set. A waxy cuticle covers the epidermis and contributes to the ability of the cranberry to resist moisture loss after harvest. Although the thickness of this waxy cuticle has been found to differ among cultivars, it is not related to the keeping quality of the fruit. A typical fruit weight is about 1 to 1.5 g. Cranberry fruit go through several stages of color development, from green to white to red. Berries reach physiological maturity about 80 days after fruit set. After harvest, the cranberry vine enters dormancy and requires more than 1000 hours of chilling before normal growth resumes the following spring.

1.3.5


There are about 150 species of gooseberries and currants (Ribes sp., family Grossulariaceae) worldwide; approximately 18 of these have been used to develop modern cultivars. In addition to several species that have ornamental landscape value, five subgenera of Ribes are grown for their fruit: black currants (R. nigrum), red currants (R. rubrum), white currants (variants of R. rubrum), gooseberries (R. uva-crispa), and jostaberries (Ribes × nidigrolaria Bauer), hybrids of black currants and gooseberries.8 Cultivated gooseberries and currants are woody, perennial, deciduous shrubs that normally grow from 3 to 5 feet tall. Jostaberries can grow to 8 feet tall. Plants develop root systems about 3 feet in diameter, with most of the roots in the top 16 inches of soil. Roots near the surface are especially abundant in root hairs. Ribes produce simple buds, either vegetative or floral. Vegetative buds produce short shoots—spurs—in all except black currants, or longer shoots that have strong apical dominance, particularly in currants. Vigorous new shoots also originate from the base of the plant, providing an important source of renewal wood for future production. Leaves, arranged alternately


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along shoots, are lobed and are high in phenolic and terpenoid compounds. Black currant leaves and buds are used as medicinal herbs.48 Flower bud initiation for most Ribes occurs with short days and cool temperatures. Flower bud development is completed about 7 to 10 days before the flowers open. In black currants, flower bud development starts at the base of current-season shoots, progressing acropetally. In red and white currants, most jostaberries, and gooseberries, some flower buds are initiated on current-season shoots, but most are initiated on spurs, located on 1- to 3-year-old wood. Thus the flowers of black currants are produced on 1-year-old wood, whereas all other Ribes grown commercially produce flowers mainly on spurs of 2-year-old or older wood—this affects pruning practices. Once canes enter full dormancy, they must go through a period of chilling—800 to 1600 hours—before growth can resume the following spring. Gooseberries and currants are among the most cold hardy fruit crops, tolerating −22°F to −31°F when fully dormant. Currants and gooseberries can bloom early, making them susceptible to frost damage in northern production areas. Currants produce flowers on racemose inflorescences called “strigs.” Gooseberry and jostaberry flowers are borne in clusters of one to three, sometimes called fascicles. Ribes flowers are greenish yellow or red and are pollinated by bees and other insects. Although most red and white currants and gooseberries are considered self-fruiting, some black currant cultivars are considered partially or completely self-sterile. The degree of self-fertility may differ with the cultivar, growing region, and perhaps other factors. Thus many recommend planting a pollinizer in commercial black currants.8 Red and white currant berries have a thin epidermis that tears when the fruit is picked from the pedicel. Thus these crops are harvested by picking the entire strig when all the berries are ripe. Black currants are more firm and can be stripped from the strig as individual fruit or entire clusters can be picked by hand.

1.3.6

Miscellaneous minor berry crops 1.3.6.1 Lingonberry

Lingonberries (Vaccinium vitis-idaea L.) belong to the family Ericaceae and are thus closely related to blueberries and cranberries. Lingonberries are native to the circumpolar boreal region, including Scandinavia, Europe, Alaska, and northern Canada, but are not widely cultivated. The lingonberry is known by many other common names, including lingon, alpine cranberry, dry-ground cranberry, foxberry, moss cranberry, mountain cranberry, northern mountain cranberry, cowberry, partridgeberry, red whortleberry, and rock cranberry. Lingonberry is a low-growing, woody, perennial, evergreen plant that spreads by below-ground stems called rhizomes. Plants are typically 1 foot tall and produce urn-shaped, white or pink flowers. Flower morphology is similar to that of the blueberry. The fruit is a small, red berry ranging from 0.17 to 0.45 g in size.


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Lingonberries flower on 1-year-old wood, similar to blueberries. However, lingonberries are native to areas with very short summers, and when they are grown in environments with longer summers, some cultivars will have two bloom periods, March to April and July to August, with two potential fruit harvest seasons. A pollinizing cultivar is required for fruit set and good fruit production.

1.3.6.2 Hardy kiwifruit Hardy kiwifruit are vining, cold hardy plants native to China, Russia, and Japan. Ananasnaya is the most widely grown cultivar of hardy kiwifruit [A. arguta (Siebold & Zucc.) Planch. ex Miq] in the world. The mature plant is very midwinter hardy, tolerating temperatures of 30°F. However, Ananasnaya has a relatively low chilling requirement and may be injured due to fluctuating temperatures in late winter or early spring. The flowers of Ananasnaya are small, less than 1/2 inch in diameter, and are female, bearing a multibranched stigma and nonfunctional stamens. The flowering period lasts for about 10 days. The flowers of Ananasnaya must be cross-pollinated for successful fruit production. Male selections of A. arguta can serve as pollinizers. Male selections of A. deliciosa (A. Chev.) C.F. Liang & A.R. Ferguson may also be used as pollinizers, but they are not considered sufficiently cold hardy to be recommended as males for commercial plantings in northern temperate areas.49 Flower bud initiation in hardy kiwifruit occurs the year before flowering as day length shortens. Flowers are borne in leaf axils either singly or more commonly as three flowers in a small cyme on shoots from 1-year-old canes. The fruit of Ananasnaya is a medium size, ovoid, 1.5 inches long × 1 inch wide berry. Fruit weight ranges from 2 to 14 g, averaging about 7 g per fruit.50 Ananasnaya produces a green to red blushed berry with a smooth, edible epidermis. The smooth skin is bright green on immature fruit and develops a red blush later in the maturation phase, particularly in sun-exposed fruit, with the green color darkening and the fruit softening as it ripens. The flesh is light green, juicy, and has a sweet-tart taste with a rich, aromatic flavor that has been compared to ripe pineapple, strawberries, bananas, European gooseberries, overripe pears, or rhubarb. Fruit mature in late summer to autumn, 100 to 110 days after flowering, depending on the region, with firmness decreasing in the later stages of ripening.49,51

1.4 Berry crop production systems Berry crops are grown in various types of perennial and annual production systems. Typical production methods are briefly described below for each berry crop, with major variations by production region mentioned. In most studies involving berry crops, experimental treatment effects on fruit quality have generally been described as changes in fruit size or weight, uniformity of shape, color, fruit firmness, texture, percent soluble solids (°Brix), pH, titratable acidity, and anthocyanins. These fruit quality attributes and yield


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can be affected by disease, insufficient or excess irrigation (or rain), nutrient deficiency or excess fertilization, poor pollination/fertilization, and fruit exposure to light. There is now considerable interest in identifying whether cultural practices, beyond cultivar selection, can impact the beneficial health properties of berry crops. The first step is identifying which compounds are most important in each crop. Then research is required to see how much these attributes are affected by cultural practices such as pruning/training, irrigation, fertilization/plant nutrition, production in tunnels, etc. We may thus see additional fruit quality attributes described in future research. However, to date, there has been relatively little published research on the impacts of cultural practice on the nutraceutical properties of fruit. In general, most fruit for the fresh market is harvested directly into the final container, often clear plastic clamshells. Flats are usually supported on specially constructed wire or wooden stands and are not allowed to contact the ground. Pickers are monitored to ensure high quality. In ideal situations, fruit is harvested in the early morning, after the dew is off the berries and temperatures are cooler, for best quality. Field heat is often removed using forced-air cooling, where large, high-powered fans pull cold air through pallets of fruit to lower fruit temperature to 32°F to 34°F within 2 hours of picking. Relative humidity within the refrigerated rooms is maintained at 85% to 95%, although free moisture on the berries or in the containers must be kept to a minimum. Unlike some other fruits, fresh market berries are not washed or cooled in water (hydrocooling) after picking and before shipment to consumers. To reduce fruit rot, the berries must be kept dry. It is not possible to cover production systems for all berry crops in great detail in this chapter. There are general textbooks on berry crops,52 blueberries,15,53,54 raspberries and blackberries,32 strawberries,55 cranberries,16 and gooseberries and currants.8 Nitrogen fertilization recommendations are not provided here, but can be found in various local publications.56–59 Pest problems and suggestions for management are not covered here, but are well reviewed in other publications.8,12,17,18

1.4.1

Strawberry

Strawberries are grown in annual or perennial production systems in the field or are planted in soilless media in tunnels or greenhouses to target “off-season” markets.

1.4.1.1 Annual production systems Most of the strawberry acreage worldwide is planted in the annual hill production system. In this system, strawberries are planted and cultivated, fruit is harvested, and the plantings are removed annually. Many of the cultivars grown worldwide were bred in public or private breeding programs in California. Common short-day cultivars include Camarosa, Strawberry Festival, Elsanta, Darselect, Marmolada, Addie, Korona, and Honeoye.


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Common day-neutral cultivars include Diamante, Albion, Seascape, and Selva. There are also proprietary cultivars grown in annual production systems. The cultivars grown can shift relatively quickly compared to other berry crops, as there are many breeding programs worldwide producing cultivars for annual production. As growers try to remain competitive with newer, better cultivars, plantings are changed annually. The annual strawberry production system is rather complex, with many variations. Plantings are established with fresh-dug plants, partially or fully chilled dormant plants, or plug plants. Dormant plants can be stored for 1 to 9 months at 32°F to 34°F and are commonly used in off-season production systems. Planting dates vary from summer through winter. By altering the use of short-day and day-neutral cultivars, the amount of chilling, and the planting date, growers are able to produce fruit 11 months of the year in California, for example. Late fall to winter planting of fresh, short-day nursery plants (fresh dug or partially chilled in cold storage) for late winter through early summer fruit production is the dominant cultural practice worldwide. Summer planting, using cold-stored (“frigo”), short-day plants, is used to a more limited extent to extend the season. For example, large cold-stored plants can be planted in sequence from April until mid-July, with fruiting starting about 8 weeks after planting. Production in the summer is also achieved by planting day-neutral cultivars (e.g., Selva) in the spring, with fruit harvest from July to October. Growers in all production areas with mild winters are thus able to target higher priced fresh market niches. Typically, annual strawberries are grown on raised beds covered with plastic, with fumigation occurring prior to planting. Drip irrigation, under the plastic, is typical. Fertilization through the drip system is common. Plants grown in annual production systems, particularly on sandy soil, benefit from fertilization with nitrogen. Plants are often established in a double-row hill system, with plants spaced 8 to 12 inches apart and the double-row centers 36 to 40 inches apart. Runners are removed every few weeks to keep plants as individuals and to encourage good fruit production and ease of harvest. The fruit is picked by hand for the fresh market or processing. The average yield per acre ranges from 12 to 45 tons, depending on the planting date, cultivar, and production region.

1.4.1.2 Protected culture systems In the last decade, there has been a considerable increase in programmed out-of-season production systems in several European countries. This is being accomplished, in part, by using several cultivars with different fruiting seasons, but mainly by sequential planting in the field of cold-stored plants (described above) and by growing strawberries in plastic-covered tunnels and in greenhouses. Tunnels can be used to protect a day-neutral cultivar from adverse weather; in this way, fruit harvest can continue well into the autumn. Protection of the crop from rain, wind, and hail improves the ease of fruit harvest and fruit quality. Often, domestic strawberries bring premium prices early and late in the season compared to imports.


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Production in tunnels and greenhouses requires a higher investment of capital, and more skill and technical knowledge from growers. There are more than 32,000 acres of strawberries grown in tunnels worldwide, much of them in Europe, particularly in Spain. On a large proportion of this acreage, strawberries are grown in soil using the traditional annual production systems described above. Growing strawberries in tunnels can advance the harvest by 3 weeks compared to an unprotected crop. Additional heating can advance the crop further and allow harvest long into the autumn. Substrate (no soil) culture is used on a small scale in tunnel and greenhouse production systems. There are about 500 acres of strawberry greenhouses in Belgium and 270 acres in The Netherlands.60 The most common cultivars are Elsanta, Lambada, Darselect, and Gariguette. There are smaller areas of greenhouse production in France, the United Kingdom, and Switzerland. In substrate culture, strawberry plants are grown in buckets, bags, and containers filled with a peat mixture, pine bark, and perlite or on rock wool slabs. In Belgium and The Netherlands, two or three crops can be harvested in greenhouses per year. Sophisticated computerized irrigation/fertilization (fertigation) systems and climate control, carbon dioxide (CO2) enrichment, and artificial lighting are common cultural techniques. Containers filled with strawberry plants are placed in the greenhouse in November at a plant density of about one per square foot. Fruit harvest is from late winter through spring, depending on the cultivar, with a yield ranging from 0.5 to 1.2 pounds per square foot. A second planting can go in the greenhouse after the first planting’s harvest is done, and a third is also possible.

1.4.1.3 Perennial production systems In perennial production, short-day cultivars most commonly are grown in flat or raised-bed systems in the open field using mainly “matted rows.” Plantings are established in the spring, with the first major fruiting season being the year after planting, from June to August, depending on the production region. Plantings are kept for 3 to 5 years. Perennial production is the most common system in Scandinavia, Poland, the northwest and northeast United States, and Canada. Common cultivars include Senga Sengana (Scandinavia, Poland), Korona and Jonsok (Scandinavia), Honeoye (Scandinavia and the eastern United States), Totem (western North America), and Allstar, Earliglow, Glooscap, and Jewel (eastern North America). Cultivars suited to perennial production systems must runner well, have good winter hardiness (particularly in more northern climates), and have higher levels of resistance to specific pests and diseases than those grown in annual systems. Cultivars tend to be adapted to the region in which they were developed. Plants are typically set at relatively low densities (8,000 to 20,000 plants per acre) in spring using dormant, cold-stored plants, and matted rows are created when the runner plants root and fill in the row. Aisles are maintained using cultivation. The year after planting, the original “mother” plants and well-rooted daughter plants (runners) flower and fruit. Matted rows typically


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produce yields of 5 to 12 tons per acre, depending on the cultivar, fruiting season, and production region. The yield and berry size decline, primarily due to infection by viruses, as plantings age from the first through the third fruiting season. For processing, berries are picked in the early morning. Cultivars ideal for processed markets can be picked without the cap or calyx. Plantings are irrigated using overhead sprinkler systems or drip irrigation. Weed management is very important to maintain good plant growth and fruit production. Strawberries are renovated after each fruiting season to prepare for next year’s crop. Renovation includes mowing off the foliage of short-day cultivars (to stimulate faster regrowth), weed management, narrowing of matted rows, fertilization, and irrigation. In colder climates, straw mulch is applied to the top of matted rows in winter to protect plants against cold injury. In all production regions, overhead irrigation is used to protect flowers against frost injury in the spring. Growers with drip irrigation systems can use row covers for frost protection.

1.4.2

Raspberry

Raspberries are most commonly grown in perennial production systems that generally have a life of 10 to 20 years for red raspberries and 5 to 10 years for black raspberries. Red raspberries are also forced in tunnels for off-season production. Fresh market raspberries can be stored for 2 to 3 weeks using controlled atmosphere storage. The best soils for raspberry production are deep and well-drained, with a sandy to loamy texture and a pH between 5.6 and 6.5. The most common planting stock used is dormant, bare-root, certified, disease-free plants or tissue-cultured plants. Rows are run in a north-south direction to maximize canopy light exposure.

1.4.2.1 Summer-bearing red raspberry The largest share of red raspberry acreage worldwide is planted to summerbearing types. Most of the raspberry acreage in northwestern North America and Serbia is planted with Meeker, as well as about 8% of the acreage in Chile. Meeker is well suited for processing, as is Willamette. Fresh market cultivars grown worldwide include Tulameen, Glen Ample, Glen Lyon, Chilliwack, and some proprietary cultivars. Summer-bearing red raspberries can be grown in either hedgerows or hill systems. In mature hedgerows, individual plants are not distinguishable because canes run continuously down a row. Hedgerows are best established by planting rooted plants or root cuttings about 2 feet apart in rows spaced 10 feet apart. The hedgerow width, 1 foot, is maintained through hand pruning, mowing, or rototilling along the row edge. Overly dense canopies increase pest and disease problems and can reduce flower bud development due to shading. Hedgerow systems are common in hand-harvested fields or plantings that are for U-pick or direct markets. However, hill systems are


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much more common in machine-harvested fields and larger commercial plantings for the fresh market. A trellis is required to support the floricanes and primocanes. The most common trellis used has two moveable lower wires at about 2.5 to 3 feet high to train new primocanes and two top wires at 5.5 to 6 feet to “pinch” the floricanes or keep them trapped in the row when they are fruiting. Generally canes are not tied to the wires in winter. In hill systems, individual plants can be distinguished. Plantings are generally established with 2.5 feet between plants in the row and 10 feet between rows on raised beds or flat ground. The overwintering canes are trained by tying them together in bundles and tying them to a trellis as described above. The bundled canes are topped at 6 feet or are left untopped and are arched and tied to the trellis. Topping canes reduces yield, but can increase average fruit size by 10% depending on the cultivar.61 In general, summer-bearing raspberries are pruned by removing the dead floricanes anytime from after fruit harvest through autumn. The remaining primocanes are thinned in some production systems to a certain number per foot of row or per hill, weak or diseased canes are removed, and the remaining canes are trained to the trellis, as described above. The prunings are typically left in the field, between rows, and are flailed or chopped. Thus the nitrogen in the prunings will ultimately be returned to the plant system.62 In some production systems, growers practice primocane suppression (also called cane burning), where the first flush of new primocanes is cut off or chemically suppressed when primocanes are about 6 inches tall. The subsequent flush of canes is then retained for next year’s crop. This practice is only used in vigorous cultivars and has the benefits of improving the current season’s yield of floricanes, machine-harvest efficiency, and next year’s yield. Plantings are irrigated with overhead or drip systems, depending on the production region. Growers commonly fertilize through drip systems. Weeds are usually managed using herbicides, with diseases and insects controlled as needed or with preventative pesticide applications. The impact of nitrogen fertilization on growth, yield, and fruit quality of raspberries has been reviewed.62 The nitrogen concentration of ripe fruit of fertilized plants ranges from 1.4% to 1.7%.63 In a 5-year study, nitrogen fertilization decreased the total soluble solids of red raspberry fruit.64 There are no conclusive data on the impact of the nitrogen fertilization rate on fruit nitrogen concentration and any related impacts on fruit quality. The harvest season for summer-bearing types grown in open fields lasts for about 3 to 8 weeks, depending on the production region and cultivar. For example, in Oregon, the season for Meeker is from about June 20 to July 20. Raspberries are fragile, have a short shelf life, and the berries ripen over several weeks, so frequent harvests are necessary. Once picked, the berries must be kept as cool as possible and transported quickly to processors or refrigerated facilities to prepare them for processing or fresh packaging and shipment.


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About 90% of the red raspberry acreage for processing in North America is harvested by machine. In contrast, only 5% of the Chilean acreage, also for processing, is harvested by machine. This difference can mainly be attributed to labor costs. In North America, labor for hand harvesting can be hard to obtain and is relatively expensive. Hand harvesting can account for up to two-thirds of the total labor cost of fruit production. A typical mechanical harvester with one operator and four field graders can do the work of 80 to 85 people hand harvesting. Aside from decreased labor costs, mechanical harvesting has other advantages. Machine harvesters can be operated at night when hand picking is not practical. The lower night temperatures help keep fruit quality high. Compared with hand-harvested fruit, machine-harvested raspberries may also be more uniformly ripe. This translates into berries that are larger, with better color, lower acidity, and higher total soluble solids—ideal for processing. However, there are some important considerations with mechanical harvesting: • Mechanical harvesters are expensive to purchase and maintain. • Row spacing and trellises must be designed for machine harvesting. • Alleys must be maintained so as to support the harvester’s wheels without excessive compaction. • Irrigation must be managed so as to avoid creating muddy alleys that could interfere with harvester movement and operation. • Cultivars must be suited to mechanical harvesting; insect management is critical, as even beneficial insects that end up in the harvested product are a contaminant. • Mechanically harvested raspberries are not suited for the fresh market. A variety of mechanical harvesters are commercially available, although most are self-propelled, over-the-row machines. Rows of flexible horizontal bars or “fingers” on each side of the crop row gently shake the fruiting laterals, trellis wires, and canes, causing the ripe fruit to drop off. Inclined catch plates about 12 to 15 inches above the ground collect the falling fruit. From the plates, the berries travel on conveyor belts across screens where fans remove some contaminants. The fruit is then carried across a short inspection belt, where graders remove additional contaminants, and then into flats or other containers. Harvesters usually travel at about 1 mile per hour down the row. Summer-bearing red raspberries are machine harvested every 2 to 3 days to minimize the loss of ripe fruit. Thus there may be 10 to 15 harvests per season, depending on the cultivar and climate. Waiting too long between harvests increases fruit losses on the ground. Research has shown that typical losses for machine harvesting are 16% of the total yield over the length of the season.61 There are also losses when raspberries are hand picked—many estimate these to be 5% to 10% of the total yield. Hand harvesting is common on small farms and larger operations that focus on high-quality, fresh market fruit or high-quality IQF fruit for


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processing. The picking interval varies with the stage of harvest, cultivar, and weather conditions. Five or 6 days may pass between the first and second pickings, with 2 to 3 days being more common during the peak of the season or warmer temperatures. However, in some regions, such as Chile, fruit for the fresh market is hand harvested before it is fully mature—this underripe fruit is more firm and can be more easily shipped to distant fresh markets. Fruit that is not considered ideal for the fresh market is processed. In Chile, they often harvest daily and on some farms, twice a day. The average yield of summer-bearing raspberries is from 2.5 to 4.5 tons per acre, but this varies greatly with the cultivar, growing region, and method of harvest.

1.4.2.2 Primocane fruiting raspberry There are many primocane fruiting raspberry cultivars grown worldwide. The red-fruited Heritage, however, accounts for 82% of the total acreage in Chile (more than 21,000 acres) and a significant portion of the primocane acreage in North America. Other primocane fruiting cultivars grown, in addition to many proprietary cultivars, are Polka, Josephine, Caroline, Autumn Bliss, Amity, and Anne (yellow). Primocane fruiting raspberries are typically grown in hedgerows that are maintained to a width of 1 to 1.5 feet. This type of raspberry can be managed to produce one or two crops per year—an early crop on the base of the floricane and a later crop on the tip of the primocane. The portion of the primocane that fruited in late summer/fall dies in the winter. This cane can be pruned to remove the dead portion and it will fruit the following year on its base (floricane) early in the summer, at about the same time as a summer-bearing type. These floricanes die after harvest and are removed during dormant pruning. Primocane fruiting raspberries can easily be grown to produce just a primocane crop by mowing all the canes to about 1 to 2 inches high in late winter. New primocanes emerge in spring, flower in summer, and fruit in late summer, producing one crop per year. In Chile, most Heritage plantings are managed to produce both types of crops. In some warm climates, the primocanes are summer pruned to affect the harvest season. Primocane fruiting raspberries can be grown free standing, but are often supported on a simple trellis to keep the canes from bowing out into the alleys. Plantings are irrigated and otherwise maintained similarly to those mentioned for summer-bearing raspberry. Average yield tends to be lower, 2 to 4 tons per acre, and almost all are hand harvested for the fresh market or processing.

1.4.2.3 Off-season production systems Covers, often polyethylene, are used in many production regions to protect fruit from the weather and thus maintain quality. Shade cloth is also used for this purpose, as fruit exposed to high ultraviolet light levels can be less firm and may develop white drupelets. Shade cloth can also be used to delay


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the fruiting season somewhat, depending on when it is applied. The fruiting season of field-grown floricane fruiting types can be advanced and primocane fruiting types extended using polyethylene-covered tunnels. Specialized off-season production systems have been developed to target specific, high-value fresh markets. Plants are established in soil under high tunnels or in pots for use in tunnels or greenhouses. In floricane fruiting cultivars, special nurseries produce “long-cane” raspberries. These nursery plants consist of a rooted floricane, 3 to 5 feet long, that has been exposed to the right conditions for good flower bud set and has received adequate chilling to satisfy dormancy requirements. High-density plantings (about 12,000 canes per acre) are staggered to target specific fresh fruit marketing seasons, similar to what was described for off-season strawberry production systems.

1.4.2.4 Black raspberry The most common cultivar grown is Munger, which accounts for almost all of the acreage in Oregon. Plantings of black raspberries (also called “blackcaps”) are established in spring using plants produced by tip-layering or tissue culture. Plants are usually placed 2.5 to 3 feet apart in rows with 10 feet between rows. Although black raspberries can be grown without a trellis, an inexpensive support structure of some kind, such as metal posts with twine running on each side of the row, is commonly used in Oregon. Black raspberries are summer pruned to tip the new primocanes to a height of 2 to 3 feet to encourage branching. In winter, plantings are typically pruned by machine to shorten the primocane branches. This is done using tractor-mounted sickle bars that run along the top and one side of each row. Some branches are thus pruned shorter than others. However, this system is inexpensive and still produces good quality fruit for processing. The floricanes fruit in early summer, generally with a 4-week fruiting season. After fruit harvest, the floricanes die. Growers may remove dead floricanes when pruning in winter; however, most growers in Oregon leave the dead floricanes in the row, as they eventually break off at the soil level and fall into the aisles. Fruit is sometimes harvested by hand for processing markets and for local fresh markets, but harvesting by machine, similar to that described for red raspberry, is most common. Fruit is harvested in two to three pickings, with a total average yield of 1.5 tons per acre being common. Fruit is taken very quickly from the field to the processing plant. Purple raspberries are grown to a very limited extent, mainly for local processed markets. This type of raspberry is grown similar to black raspberry.

1.4.3

Blackberry

Blackberry plantings generally have a life of 15 to 20 years. Plantings are established in the spring using plants propagated by tissue culture or root cuttings, depending on the type of blackberry. Blackberries are tolerant of a


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wide range of soil pH (4.5 to 7.5) and soil types, although growth is better when soil drainage is good. Rows are usually planted in a north-south direction to maximize canopy exposure to light. The impact of nitrogen fertilization on growth, yield, and fruit quality of blackberries has been reviewed.62 The nitrogen concentration of ripe fruit from fertilized plants ranges from 1.4% to 1.6%. The nitrogen fertilization rate had little effect on fruit pH, titratable acidity, and soluble solids in Thornless Evergreen and had no consistent effect on fruit firmness.65 In Arapaho, increasing nitrogen fertilization rates increased fruit nitrogen concentrations and pH, but had no effect on the percent soluble solids, titratable acidity, and sugar:acid ratio.66 Fruit are a strong sink for fertilizer nitrogen.67,68 There are no conclusive data on the impact of nitrogen fertilization rate on fruit nitrogen concentration and any related impacts on fruit quality. Most blackberries are grown using a combination of cultivation and herbicides for weed management and pesticides for disease and insect control. In 2005, there were 6246 acres grown using organic production systems, mostly in Ecuador and Costa Rica.2 Plastic-covered tunnels are being used on about 775 acres of blackberries worldwide, mainly to protect against adverse weather.2 Tunnels or greenhouses to advance or delay the fruiting season, in addition to protection against the elements, are being used in Spain, The Netherlands, Italy, Romania, and South Africa. The use of tunnels is expected to increase, particularly in Mexico. In 2005, 50% of the cultivars grown worldwide were semierect, 25% were erect, and 25% were trailing types. In general, erect and semierect cultivars are grown predominantly for the fresh market—these types produce fruit that is more firm, has a longer shelf-life, and is better suited to shipping. Trailing types are mainly used for processing. These cultivars, like Marion, are known for having highly flavored, aromatic fruit, with small seeds. The fruit of most trailing cultivars available today is not firm enough for long-distance shipping. Still, there are a few cultivars of trailing blackberry that are relatively new and are suited for the fresh market—Siskiyou and Obsidian are.

1.4.3.1 Semierect blackberry Thornfree, Loch Ness, and Chester Thornless account for 60% of the semierect blackberry acreage and Dirksen Thornless, Hull Thornless, and Smoothstem account for 30%. The only other cultivar grown on more than 5% of the worldwide semierect acreage is Cˇ acˇanska Bestrna, grown in Serbia. The planting density for semierect blackberries varies with the production region. In Serbia, plants are generally established at an in-row spacing of 3 to 4 feet with 8 to 10 feet between rows. In the United States, plants are typically placed 5 to 6 feet apart in rows that are 10 to 12 feet apart. In most fields in China, the planting density is very high, with 1 to 1.5 feet between plants and 3 feet between rows. In almost all regions, primocanes are tipped during the growing season at about 5 to 6 feet high to encourage branching. In the winter, the dead


34


floricanes are removed and the branches of the new canes are pruned to about 1.5 feet in length or left unpruned. Canes are either trained on a multiple wire trellis with an undivided canopy or are trained to a “double-T” system. In most regions, plantings are irrigated using drip, overhead, or microjet systems. However, in China, fields are commonly flood irrigated. The average yield is 3.5 to 20 tons per acre, with all fruit hand picked every 3 to 5 days for the fresh market. The fruiting season in the northern hemisphere ranges from July to October, depending on the cultivar and production region. Excess fruit are processed, usually as a seedless puree. Semierect blackberries are considered relatively cold hardy, although cold injury is still considered the most important production problem in Serbia. In China, canes are buried in winter to avoid cold injury.

1.4.3.2 Erect blackberry Brazos is by far the most common erect blackberry grown worldwide, accounting for almost half of the erect acreage. However, Brazos is rapidly being replaced by Tupy in Mexico. Other cultivars accounting for 5% or more of the erect acreage are Tupy, Navaho, Kiowa, and Cherokee.2 In the more traditional production system for erect blackberries, plants are established 3 to 4 feet apart in rows 10 feet apart. During the growing season, primocanes are tipped at a height of 3 to 4 feet, depending on the production region, to encourage branching. Growers will go through the plantings on several occasions to catch all of the primocanes. After fruit harvest, or in the winter, dead floricanes are removed by pruning. In some production regions, such as Oregon, dead floricanes are left to save labor costs; they will eventually break off and fall into the rows. In winter, the primocane branches are usually shortened to about 1.5 feet. In Oregon, however, where hedging primocanes in winter using a machine is common, branch length may vary. Erect blackberries are grown without a trellis in some regions. However, as the canes are prone to breaking off at the soil level with wind, a trellis is sometimes used to support canes and minimize cane loss. Usually a simple two- to four-wire trellis is used. Fruit is harvested by hand, primarily for the fresh market, every 3 to 5 days. The fruiting season of erect floricane fruiting cultivars is about 4 weeks long, from May through July, depending on the production region. Yields range from 3 to 4 tons per acre. In Mexico, production systems are modified to extend the season for Tupy and other erect cultivars. About 5 to 7 months after primocane emergence, a chemical defoliant is applied two to three times to induce endodormancy. A growth regulator is used about 3 weeks after defoliation to promote bud break. The plants are then pruned. Fruit harvest begins about 90 to 100 days after defoliation. After the first crop is finished, many growers prune again, removing the portion of the canes that fruited, and repeat the defoliation process to obtain multiple crops. Growers then mow the canes to the ground level to repeat the cycle. Often plants are grown in tunnels to protect the


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fruit from adverse weather conditions. Using these methods, the Mexican fruiting season extends from mid-October to June. A new type of erect blackberry, one that produces a significant crop on the primocanes, is now available. The first cultivars of this type to be released were Prime-Jan and Prime-Jim. Similar to primocane fruiting raspberry, this type can be grown for a double crop (floricane in early summer plus primocane in late summer through autumn) or a single crop (primocane only). These blackberries are not yet grown commercially to any significant extent. However, it appears that primocane fruiting blackberries must be tipped during the growing season for maximum fruit production.69 Primocane fruiting blackberries show great promise for improving the availability of fresh market blackberries worldwide using off-season production systems.

1.4.3.3 Trailing blackberry Marion is the most important trailing blackberry grown, accounting for just over half of the worldwide acreage of trailing types; more than 90% of the Marion acreage is located in Oregon. Other important trailing blackberry cultivars are Boysen, Thornless Evergreen, and Silvan. Trailing types are typically grown in every-year production systems at an in-row spacing of 3 to 6 feet with 10 feet between rows. Most are grown on trellises, with the canes wrapped around two wires (with the first at 4.5 feet and the top at 6 feet). Trailing blackberries can be grown in every-year or alternate-year production systems. In every-year production, new primocanes are trained along the ground, under the canopy, while the floricanes are on the wire producing the current season’s crop. After fruit harvest, the dead floricanes are removed and the primocanes are trained onto the trellis wires in August or February. Most growers train primocanes in February, leaving canes more protected from cold through most of the winter. In alternate-year production systems, plants fruit every other year. In the “on year,” floricanes produce a crop and primocanes are not managed. In October, the dead floricanes and the primocanes are pruned at the crown. The following “off-year” primocanes are trained to the trellis as they grow. The yield of an alternate-year field is about 85% of an every-year field over a 2-year period.70 Research has demonstrated that primocanes following an off-year in an alternate-year system are more cold hardy than primocanes that grew in the presence of floricanes in an every-year system.71,72 There is also less cane disease in alternate-year production systems than in every-year systems. More than 60% of the trailing blackberry acreage in Oregon is grown in alternate-year production systems. Most of the trailing blackberry production worldwide is processed, with machine harvesting used on more than 75% of the acreage. The fruiting season of most trailing cultivars lasts for 4 to 5 weeks, starting in late June or early August, depending on the cultivar. Growers begin machine harvesting when the primary fruit, those that are first to ripen, are fully mature. Fruit is gently shaken from the plants using the same machine harvesters as


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described for red raspberry. However, blackberries are harvested less frequently, about every 5 days, depending on the cultivar and temperature, and are typically harvested at night when they are more easily removed. Machine-harvested fruit is more uniform in maturity, having greater aroma and flavor, and higher percent soluble solids than hand-harvested fruit. It is more difficult to visually distinguish ripeness by color in blackberry than in raspberry. Typical yields range from 4 to 8 tons per acre. In addition to the possible insect contaminants mentioned for red and black raspberry, thorns can be a serious contaminant in thorny cultivars that are machine harvested. Research has helped growers minimize this risk by using machine harvesters equipped with brushes to remove potential contaminants.73 Plant breeders consider the development of high-quality, thornless trailing blackberry cultivars a high priority and have recently released several thornless cultivars.

1.4.4

Blueberry 1.4.4.1 Highbush and rabbiteye blueberry

Northern highbush is the main type of blueberry planted in the northern regions of the world. The most common cultivars are Bluecrop, Jersey, Blueray, Rubel, Elliott, Duke, Bluejay, Earliblue, Reka, Draper, Aurora, and Liberty. Southern highbush blueberries are the most common type planted in warmer regions of the Northern and Southern Hemispheres. Common southern highbush blueberry cultivars are O’Neal, Bluecrisp, Reveille, Southern Belle, Star, Bladen, Emerald, Jewel, Sharpblue, Misty, Windsor, and Jubilee. Ozarkblue and Legacy, with northern highbush in their parentage are commonly planted. Rabbiteye blueberries are less widely planted than northern or southern highbush types, but offer a late fruiting season that is an advantage for targeting key high-priced fresh markets.1 The cultivars Climax, Tifblue, Brightwell, Premier, and Powderblue are common, with Ochlockonee, Alapaha, Columbus, Maru, and Rahi showing promise. Blueberries grow best on well-drained soils, high in organic matter, and with a pH of 4.2 to 5.5. However, in many regions blueberries are successfully grown through modification of traditional cultural practices. For example, in the relatively new production regions of California and southwestern Europe, blueberries are often grown on sandy soil, with or without organic material incorporated, using acidified irrigation water. In most production regions, blueberry plants are grown on raised beds about 1 foot in height to improve soil drainage in the root zone. Many mature blueberry plantings in North America were established at an in-row spacing of 4 feet with 10 feet between rows. However, long-term research experiments conducted in Oregon74,75 and subsequent positive grower experience have led to a change to higher density plantings worldwide; the most common in-row spacing is now 2.5 to 3 feet with 10 feet between rows. Plantings are established, usually with 2-year-old container-grown plants, but


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in many regions with younger plants, in autumn or spring. Organic material, commonly sawdust, is often incorporated prior to planting and applied as a surface mulch after planting; this layer is maintained for the life of the planting. In some production regions, a weed barrier that is permeable to water or black plastic may be used. However, there are many successful plantings in which no mulch or weed barrier has been used. Most fields have a permanent grass cover in the aisles between rows. Blueberries are shallow rooted and are thus subject to drought injury. Drought conditions during fruit ripening will reduce fruit size and may affect flavor. A uniform and adequate supply of moisture is essential for optimum plant growth. Water use efficiency is greater in high-density blueberry plantings. Water requirements vary by the cultivar, with the greatest need for water occurring during the fruit development stage.76 Research has shown there is no long-term cumulative yield advantage to producing fruit in the planting year or the year after planting, and in some cultivars there can be a disadvantage to “early cropping.”75 However, some growers allow plants to produce fruit earlier than the third year after planting to recover some of the high plant establishment costs.77 To prevent early cropping, growers prune the fruit buds at planting and in the dormant period prior to the second growing season. Blueberries are pruned annually in most production regions, with severity varying depending on type of blueberry grown and the amount of vegetative vigor. In Oregon, unpruned plants had the highest yield after 3 years, but also had smaller fruit, a later fruiting season, poorer fruit color (unpublished), and bushes that could not be machine harvested.78 Others have shown that fruit matures later, with lower percent soluble solids, when fruit is in shade compared to fruit well exposed to the sun.79,80 Dormant pruning of highbush blueberries is demonstrated in a DVD produced by Oregon State University.81 Plants to be machine harvested are pruned to a more upright habit with a narrow crown to allow close fitting of the machine harvester’s catcher plates, thus improving machine-harvesting efficiency and minimizing fruit loss. For hand harvesting, plants are pruned to maintain branches within easy picking height and low fruiting branches or canes are removed. In most northern production regions, highbush blueberries are pruned annually, mainly during the dormant season, with little, if any, summer pruning. Southern highbush blueberries, however, are often pruned after harvesting by hand or machine (hedging), especially in areas with a long growing season. Rabbiteye blueberries are often pruned in summer by tipping vigorous shoots on several occasions to stimulate the production of fruit buds for next year’s crop. In North America, most highbush blueberry fruit destined for the processed market is harvested by machine. A change in the last 10 years has been the increased use of machine harvesting for fresh market fruit; this trend is expected to continue in most production regions of North America due to the high cost and limited availability of labor.


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Most of the machine harvesters used are an over-the-row rotary type, similar to what was described for red raspberry. However, blueberry harvesters tend to be longer to minimize fruit loss on the ground. For fields that are harvested entirely by machine, losses have been measured as high as 24% of total yield in untrellised plantings.74 In many production regions, blueberries that may be harvested by machine are now trellised. Research has shown an added recovery of 3% to 8% of total yield when blueberry plants are kept more narrow to fit the “throat” of over-the-row machine harvesters.74 The trellis usually consists of wire posts in the row with two wires, one of each side of the row, that are moved higher as the bushes age. The blueberry plants are not trained or tied to the trellis wires. Trellises are used in some hand-picked fields as well. With a properly adjusted rotary machine and selection of cultivars, growers may fresh market machine-harvested fruit; however, at present, this fruit is sold to less distant markets, as it has a shorter shelf life than hand-picked fruit. In many production regions in North America, a large portion of the fruit destined for processed markets is picked by hand. Hand pickers are paid per pound of fruit harvested. In other areas of the world, production systems are similar to those in North America. However, in Europe and South America, most fruit is hand picked and the fresh market is dominant. Production on nontraditional substrates and off-season production in tunnels is quite common in parts of Europe. Not much is known, at present, about the effect of tunnels on fruit quality. Cultivated blueberry plants usually require 6 to 8 years to reach full production. Yields for highbush blueberries vary with the production region. In North America, typical yields for well-managed, mature highbush blueberry fields were reported as 3 to 4 tons per acre for the northeastern, southern, and southwestern regions, 4 to 4.5 tons per acre for the midwestern region, and 9 tons per acre for the northwestern region, where yields are considered the highest in the world. Yields among fields within a region are extremely variable due to the effects of microclimate, cultivars, and management practices.1 Fruit for the fresh market may be either packed into its final container in the field or picked into larger containers (often buckets) and then transported quickly to a cleaning, sorting, packing, and storage facility. Mechanical color sorting or hand sorting is done to remove any underripe or damaged fruit. Fruit is quickly cooled using forced air. For longer term storage, berries are kept in a controlled atmosphere. Most berries for the fresh market are now sold in clamshells and are shipped via refrigerated truck, airplane, or by ship to distant markets. Fruit for processing is transported quickly to a processing plant where it is either individually quick frozen, bulk frozen, pureed, juiced, or freeze-dried, depending on the facility and the end use or market.

1.4.4.2 Lowbush blueberry Although there are a few named cultivars of lowbush blueberry, these are not used to establish new stands, but are available in a few nurseries for the


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home garden. Commercial lowbush fields consist mainly of native clones of V. angustifolium and some V. myrtilloides. Native stands of these species are brought into commercial production through management practices that improve planting density. The cultural management of lowbush blueberries has changed significantly in the last 10 years, including increased use of fertilization, irrigation, beehives for pollination, herbicides for weed management, and management of soil pH, all of which have led to increased yield. Thus total lowbush blueberry production has increased almost 4-fold over the last 20 years, while managed area has only increased 1.5-fold.5 The use of herbicides allowed the addition of fertilizer to improve wild blueberry plant growth without stimulating weeds and reducing yield. Growers typically use monoammonium or diammonium phosphate fertilizers to increase yield. The soil pH is monitored and maintained, preferably below 4.5, to help manage weeds. Currently Maine is the only lowbush blueberry production region that has invested significantly in irrigation systems, with resulting increases in yield per acre. There were an estimated 300 to 500 acres of lowbush blueberries produced organically in 2003; this area is expected to increase in the near future. Only half of the total area of lowbush blueberries is harvested annually because of alternate-year pruning practices.5 Most growers mow the field to about 1/2 inch above soil level in winter. In the following growing season, straight shoots grow and produce flower buds; these yield the following year. Some growers still burn fields to prune in winter, which offers some advantages for pest control, but has a higher cost than mowing. Average yields are 1.5 tons per acre, but in a well-managed field yields of 5 tons per acre can be achieved. Machine harvesting of lowbush blueberries has increased to 40% in Maine and 25% to 80% in Canada, depending on the province. The use of machine harvesters is expected to increase in lowbush blueberry production as well.1 The most common type of machine used is a Bragg (Doug Bragg Enterprises, Collingwood, Nova Scotia, Canada) reel-type harvester.5

1.4.5

Cranberry

Commercial cultivation of cranberries began in the 1800s using selections from the wild. As certain selections gained notoriety, they were given a cultivar name. The most important cultivars grown today are Stevens, Crowley, Ben Lear, Bergman, and Pilgrim, from breeding programs in the United States, and Early Black, Howes, Searles, and McFarlin, selections from the wild. New cultivars continue to be developed through hybridization, but Stevens is still the most common cultivar planted. Cranberries are grown in beds or bogs surrounded by perimeter ditches and dike systems with adjacent water storage areas. In many sites in eastern North America, stands of native cranberries, growing in peat bogs, have been modified to increase yield and facilitate management. However, new plantings have been established on suitable sites. Cranberries are best grown


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at a pH of 4.2 to 5.5. In the Pacific Coast region of the United States, cranberry beds are commonly established on mineral soil, which is naturally acidic, with a semipermeable subsoil and added sand that allows for water flood management of established beds.82 Cranberry farms are divided into a number of beds ranging in size from 2 to about 40 acres. Each bed is surrounded by drainage ditches and dikes used as roads. A good source of high-quality water and a reservoir to hold enough water for management of the fields is needed. A permanent sprinkler irrigation system is used to supply water for plant needs as well as for frost protection in late winter and spring. Planting is done from January to May, depending on the production region. While tissue-cultured, rooted material may be used to establish plantings, it is more common to use cuttings or vine material that are spread over the surface of the planting (up to 2 tons per acre) and then mechanically pushed into a wet sand layer to a depth of 2 to 4 inches. Planting material originates from prunings of established beds or from beds that are mowed or renovated. Since cranberry beds are established from cuttings of hundreds (if not thousands) of different plants, there is the potential for a lack of genetic uniformity when the bed is planted. Therefore, growers must research the planting material, its source, its trueness to type (cultivar), and its quality very carefully. The cranberry bed is kept moist to enhance rooting of the cuttings, which usually occurs in 2 to 4 weeks. The surface of the bed is usually well covered by runners and plants by the end of the second year. A small yield may be harvested the year after planting, but year 3 is more typically the first production year, with production increasing until the bed is mature in year 5. Weed management is critical in cranberries. Weeds compete with the shallow-rooted cranberry plants, may shade vines, and can reduce the efficiency of pruning and harvesting equipment. Water is used in many ways in cranberry production. Sprinkler irrigation is used to satisfy the water requirements of the crop, for frost protection in late winter and spring, and for evaporative cooling of the vines on hot days. Flooding is used in several ways. In eastern production regions, a winter flood or ice is used to protect plants against cold injury. Flooding for short periods of time is used in all production regions as a pest management tool. Finally, many cranberry plantings are harvested using flooding, also called “wet harvesting.” Berries can be harvested with (wet harvested) or without (dry harvested) the use of flooding. In wet harvesting, the cranberry bed is flooded to just above the top of the plant canopy. A water reel or “egg beater” machine is driven through the flood to agitate the water, forcing berries to pop off the vine. Once the beating of a bed is completed, the floating berries are corralled using booms and are then moved into a truck with a conveyor belt or a berry pump. Dry harvesting has evolved from the hand scoops used in the early 1900s to several variations of small combine-like machines that are currently being used. Typically in dry harvesting, the bed is pruned and harvested concurrently.


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The Furford picker has horizontal knives to prune mainly runners and tines or rakes to pick fruit. Prunings and fruit are collected, commonly in burlap bags. Plant material is separated from berries on a mechanical shaker and the fruit is transported to a storage or packing facility. Dry harvesting is less common than wet harvesting. Harvesting of mature cranberry fruit occurs from September to November, depending on the cultivar and production region. Growers sometimes receive a bonus for fruit high in anthocyanin—this is promoted in regions with cool nights, such as western North America, and with later harvesting. However, in some eastern regions there is added risk of frost damage with later harvesting. In some areas, cranberries are harvested when they are immature, before most of the red color develops, for the white cranberry juice market. Growers are paid a premium to compensate for the lower yield at this stage of fruit development. Cranberry yield is still measured in barrels (bbl), the containers used in early production. One barrel weighs 100 pounds. The average yield ranges from 95 to 210 barrels per acre, but yields as high as 700 barrels per acre have been documented. Light reaching the uprights and fruit affects flower bud development for next year and fruit color.83 Dense canopies with overgrowth of runners may have reduced fruit set if flowers are below runners, reduced harvest efficiency, and less red fruit color. Vines are typically pruned in winter to remove mainly horizontally growing runners, but also to thin uprights. Cranberry pruning machines have vertical knives, the depth of which can be controlled by the operator. The knives move through the canopy cutting off excess runners and some uprights. Pruning severity can be adjusted by the depth of pruning and the speed of the machine. Pruning lightly in alternate years has been found to produce the highest yield and best fruit quality in Oregon.83 Sanding involves the application of a thin (1/2 to 1 inch) layer of sand to an existing cranberry bed to stimulate new rooting of stems closer to the fruiting zone. Sanding can help control weeds, stimulates the production of new uprights, and can be used to fill any low areas in the bed and stimulate new vine growth. Yield may be reduced, however, if too deep a sand layer is applied.84 Many growers sand beds every 3 to 4 years. Berries in most states are transported directly from the growers’ fields to large, centrally located receiving stations operated by handlers. Berries are cleaned, sorted to remove decayed and damaged fruit, and placed in containers for storage. Fruit destined for processing is shipped to freezer storage, where it can be held for months without deterioration. Fruit for the fresh market is air dried (if wet harvested) and stored in ventilated crates at about 40°F. In Oregon, some fresh market growers are storing fresh fruit “on the vine” and use delayed harvesting to target later market windows for fresh fruit. The fruit is graded for size (in some markets) and for soundness. Fruit for the fresh market is packed in polyethylene bags or in clamshells. About 94% of the North American cranberry crop in 2004 was processed.


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1.4.6



Ribes prefer soil with a pH between 5.5 and 7 and good drainage. Organic materials such as sawdust, manure, and bark are usually incorporated into the soil before planting. Planting distances for gooseberries and currants range from 2 to 4 feet in the row, with 10 feet between rows. Black currants may be grown at higher densities in hedgerows and cropped in an alternateyear production system. If a pollinizer is required, plantings are established with blocks of 10 rows of each cultivar or with the pollinizer interspersed throughout the planting. An irrigation system that supplies about 1 inch of water per week during the growing season is needed. There are a large number of cultivars of gooseberry and currant grown commercially. Cultivar performance varies a great deal from one site or growing region to another. Various factors need to be considered when selecting a cultivar, including performance and yield, fruit quality, pest and disease resistance, growth habit, and suitability for machine harvesting. Barney and Hummer8 provide the characteristics of many cultivars. Gooseberries are less widely grown commercially than are currants, due mainly to the susceptibility of this crop to powdery mildew (Sphaerotheca mors-uvae (Schw.) Berk & Curt and Sphaerotheca macularis (Wallr.:Fr.) Lind.) and the high labor requirement for hand harvesting. Most gooseberries do not machine harvest well, as the spines damage the fruit. In Russia, the cultivars Russkij, Szemena, Kohoznig, and Rekord are grown. Gooseberries popular in European countries include Weise Triumphbeere, Rote Triumphbeere, Weise Voltragenda, Lady Delamere, Hoennings Fruheste, Triumphant, and Green Giant.48 Gooseberries for processing are generally harvested when they are not fully ripe and are very firm and tart. Fully ripe berries are soft and sweet, and are used for the fresh market. Black currants are widely grown in Europe, although damage to flowers from spring frosts has resulted in variable yields in some regions. Baldwin, highly susceptible to spring frost, formerly accounted for 80% of the acreage in the United Kingdom,48 but it has been replaced with more cold tolerant cultivars including Ben Lomond and Ben Nevis. Ojebyn is popular in Scandinavia and Poland, with Titania and some cultivars from the Scottish Crop Research Institute (SCRI) increasing in popularity. Countries in the former Soviet Union grow many cultivars, including Golubka, Narjadnaja, Brodtorp, Vystavochnaja, and Stakhanovka Altaja.8 Tenah and Tsema are popular in The Netherlands, and Magnus, Blackdown, and Topsy are being replaced with cultivars from the SCRI in New Zealand. The most popular red currant cultivar in northern Europe is Jonkheer van Tets, with yields of 4.5 to 7 tons per acre.8 Other cultivars grown in Europe are Rondom, Rovada, Rosetta, Rotet, Jonifer, Laxton no. 1, Red Lake, Stanza, and Laxton’s Perfection. In Russia, Red Dutch is common. White currants are mainly grown in Germany and Slovakia and are primarily processed for baby food. The leading cultivars are Werdavia, Zitavia, Meridian, and Victoria. In Britain, White Versailles is popular, but newer cultivars from The Netherlands are replacing some older ones in Europe.8


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There is very little commercial production of jostaberry worldwide. The main cultivars available are Josta, Jostagranda, and Jostaki. Plantings are typically mature in their third year and last for 10 to 20 years. Mulching with an organic material may be done in some plantings to help manage weeds. Annual fertilization with nitrogen at rates of 35 to 90 pounds of nitrogen per acre, depending on the planting age, is typical. Yields of currants and gooseberries range from 2 to 6 tons per acre, depending on the type and cultivar.

1.4.7

Miscellaneous minor berry crops 1.4.7.1 Lingonberry

Common lingonberry cultivars are Erntedank, Erntekrone, Ida, Koralle, Sanna, Scarlet, and Splendor. Pollinizer cultivars include Red Pearl and Sussi. Lingonberries are best grown in light, well-drained, acid soil that is high in organic matter. Some plantings are established on raised beds to improve drainage and organic matter is often incorporated into the soil before planting. Plants are established 8 to 18 inches apart in rows 2 to 3 feet apart. Plants fill in the rows, as they spread by rhizomes, forming dense matted rows in 4 or 5 years. An organic mulch, such as sawdust, is often added to the soil surface after planting and replenished as needed. Berries can be once-over harvested when they are light red to dark red. Berries that ripen in summer will senesce if not harvested before the fall crop is mature. Lingonberries are most commonly harvested by hand, using a rake similar to that used for lowbush blueberries. Machine harvesting is possible, but is not common at the present time. Yields range from 0.5 to 15 tons per acre.85 Lingonberries can be stored for 3 to 5 weeks under refrigeration. Overripe berries do not store well. Worldwide, 10% of the crop is sold for juice concentrate.

1.4.7.2 Elderberry There is limited commercial production of elderberries in the United States, Chile, Canada, Austria, and Italy. Cultivars of S. canadensis include Adams I, Adams II, Johns, York, Nova, and Kent. While there are many ornamental S. nigra cultivars (e.g., Guincho Purple, Black Lace, Golden), examples of cultivars grown for fruit include Sampo, Haschberg, and Korsor. Plants will grow under a wide range of soil conditions, but are most vigorous in fertile, silt loam soils with irrigation. Plant spacing ranges from 5 to 7 feet in the row, with 10 to 13 feet between rows. Very little, if any fertilizer is recommended, particularly in the planting year. Pruning involves removing canes that are more than 3 years old, leaving a total of 7 to 9 canes per plant. Full production of up to 15 pounds of fruit per plant usually occurs in the third or fourth year. In mature, vigorous plantings, yields of up to 6 tons per acre are possible. Fruit mature from mid-August to mid-September, depending on the cultivar and growing region. Clusters ripen over a period of 5 to 15 days.


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Entire fruit clusters are harvested by clipping the peduncle for later stripping of individual berries and immediate processing or freezing. Clusters may be frozen, with the berries knocked off later.

1.4.7.3 Hardy kiwifruit Actinidia arguta is a vigorous perennial vine that must be trained to a support structure. The most common trellis used worldwide is the pergola; however, many growers feel that Ananasnaya is more easily pruned when trained to a “T-bar” system.49 In heavily shaded canopies, growers have observed premature fruit softening with a relatively low percent soluble solids, making the fruit unmarketable—this problem is much reduced when canopies are well pruned to improve the fruit’s light exposure. Vines are trained to a 6 foot or higher trunk so workers can walk under the plant canopy for harvesting and pruning. Plants are most commonly established at a spacing of 15 feet × 15 feet, equal to 194 total plants and 172 female plants per acre. Plants are dioecious, meaning they are either male or female, so the flowers of the female Ananasnaya must be cross-pollinated with male selections of A. arguta planted as pollinizers, with a planting ratio of one male vine for every 6 to 10 female vines. Honeybees are the predominant pollinators with 4 to 5 hives recommended per acre. Kiwifruit vines grow best on deep, well-drained soil with a pH between 5.5 and 6.0. Commercial growers often plant in raised beds to help avoid problems with phytophthora root rot (Phytophthora cryptogea Pethybr. & Lafferty). Young kiwifruit shoots are very sensitive to frost and wind injury. Growers install irrigation for frost protection to protect plants after bud break and install windbreaks to reduce wind damage to shoots and fruit. Kiwifruit vineyards need frequent irrigation during the growing season, so a supply of good quality irrigation water is required for production. Kiwifruit vineyards must be pruned annually for consistent production of quality fruit. About 70% of the wood that grew the previous season is removed. Vines are normally pruned to a bilateral cordon with about twenty 2-foot long spurs in the “T-bar.” Female vines are pruned in the dormant season, whereas male vines are shaped in the dormant season and most pruning occurring after bloom in early summer.49 Commercially, fruit are generally once-over harvested by hand at an average 8 to 10 °Brix, which typically occurs in September. At harvest, most fruit is still green and firm, although a small percentage (generally less than 4% of the total yield) are very soft and unusable.86 Fruit cannot be harvested vine ripe, as it is then too soft to handle or store. Vine-ripened fruit continue to increase in °Brix to 21% to 23%, depending on the cultivar.87 After harvesting, the fruit is immediately cooled to 33°F to 35°F and sorted, with culls (usually scarred or small fruit) removed and the remaining marketable fruit sorted by size. Packing varies by shipper, but typically clamshells are used. Low-vent packages reduce desiccation of the fruit compared to the traditional vented clamshells used for berry fruit. Fruit harvested


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at 9 °Brix and treated with an edible coating (SemperFresh) had reduced weight loss and a more favorable appearance or glossiness to the fruit.88 The fruit remain in cold storage, under relatively high humidity, with ethylene gases scrubbed to retard ripening. The fruit can be stored for 4 to 8 weeks, depending on the storage conditions (temperature, ethylene and oxygen levels, and humidity). Variable fruit quality (fruit size, °Brix, firmness, and subsequent flavor), relatively short storage life compared to A. deliciosa Hayward, short harvest season, and desiccation during shipping and in stores are the major problems related to fresh marketing hardy kiwifruit. Variability in fruit size can be reduced with good pruning and ensuring good pollination. Total yields of Ananasnaya in Oregon range from 30 to 100 pounds per vine in 4- to 5-year-old commercial vineyards. Vines are not considered mature until year 7 or 8. Total yields of mature Ananasnaya range from 66 to 160 pounds per vine (6 to 14 tons per acre).87 Yield and fruit size are very much affected by pruning severity.

References 1. Strik, B. and Yarborough, D., Blueberry production trends in North America, 1992 to 2003 and predictions for growth, HortTechnology, 15, 391, 2005. 2. Strik, B.C., Clark, J.R., Finn, C., and Ba¯nados, M.P., Worldwide production of blackberries, Hortech., 2007 (in press). 3. Clark, J.R., Blackberry production and cultivars in North America east of the Rocky Mountains, Fruit Var. J., 46, 217, 1992. 4. Clark, J.R., Changing times for eastern United States blackberries, HortTechnology, 15, 491, 2005. 5. Yarborough, D.E., Factors contributing to the increase in productivity in the wild blueberry industry, Small Fruits Rev., 3, 33, 2004. 6. Strik, B.C., Blueberry—an expanding world berry crop, Chron. Hort., 45, 7, 2005. 7. Brennan, R.M., Currants and gooseberries, in Fruit Breeding, Vol. 2, Vine and Small Fruit Crops, Janick, J. and Moore, J.N., Eds., John Wiley & Sons, New York, 1996, p. 191. 8. Barney, D.L. and Hummer, K.E., Currants, Gooseberries, and Jostaberries. A Guide for Growers, Marketers, and Researchers in North America, Haworth Press, Binghamton, NY, 2005. 9. Williams, M.H., Boyd, L.M., McNeilage, M.A., MacRae, E.A., Ferguson, A.R., Beatson, R.A., and Martin, P.J., Development and commercialization of “baby kiwi” (Actinidia arguta Planch.), Acta Hort. (ISHS), 610, 81, 2003. 10. Finn, C.E., Temperate berry crops, in Perspectives on New Crops and New Uses, Janick, J., Ed., ASHS Press, Alexandria, VA, 1999, p. 324. 11. Stang, E.J., Elderberry, highbush cranberry, and juneberry management, in Small Fruit Crop Management, Galletta, G. and Himelrick, D., Eds., Prentice Hall, Englewood Cliffs, NJ, 1990, p. 363. 12. Caruso, F.L. and Ramsdell, D.C., Eds., Compendium of Blueberry and Cranberry Diseases, American Phytopathological Society Press, St. Paul, MN, 1995. 13. Darnell, R.L., Strawberry growth and development, in The Strawberry: Cultivars to Marketing, Childers, N.F., Ed., Horticultural Publications, Gainesville, FL, 2003, p. 3.


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Berry fruit: Value-added products for health promotion 14. Darnell, R.L., Blueberry botany/environmental physiology, in Blueberries: For Growers Gardeners and Promoters, Childers, N.F. and Lyrene, P.M., Eds., Horticultural Publications, Gainesville, FL, 2006, p. 5. 15. Eck, P., Blueberry Science, Rutgers University Press, New Brunswick, NJ, 1988. 16. Eck, P., The American Cranberry, Rutgers University Press, New Brunswick, NJ, 1990. 17. Ellis, M.A., Converse, R.H., Williams, R.N., and Williamson, B., Eds., Compendium of Raspberry and Blackberry Diseases and Insects, American Phytopathological Society Press, St. Paul, MN, 1991. 18. Maas, J.L., Ed., Compendium of Strawberry Diseases, 2nd ed., American Phytopathological Society Press, St. Paul, MN, 1998. 19. Darrow, G.M., The Strawberry, Holt, Rinehart and Winston, New York, 1966. 20. Dana, M.N., The strawberry plant and its environment, in The Strawberry: Cultivars to Marketing, Childers, N.F., Ed., Horticultural Publications, Gainesville, FL, 1980, p. 32. 21. Hancock, J.F., Strawberries, CABI Publishing, New York, 1999. 22. Strik, B.C. and Proctor, J.T.A., The relationship between achene number, achene density and berry fresh weight in strawberry, J. Am. Soc. Hort. Sci., 113, 620, 1988. 23. Jennings, D.L. Raspberries and Blackberries: Their Breeding, Diseases and Growth, Academic Press, San Diego, 1988. 24. DeGomez, T.E., Martin, L.W., and Breen, P.J., Effect of nitrogen and pruning on primocane fruiting red raspberry ‘Amity,’ HortScience, 21, 441, 1986. 25. Lockshin, L.S. and Elfving, D.C., Flowering response of ‘Heritage’ red raspberry to temperature and nitrogen, HortScience, 16, 527, 1981. 26. Carew, J.G., Gillespie, T., White, J., Wainwright, H., Brennan, R., and Battey, N.H., The control of the annual growth cycle in raspberry. J. Hort. Sci. Biotechnol., 75, 495, 2000. 27. Strik, B.C., Blackberry cultivars and production trends in the Pacific Northwest, Fruit Var. J., 46, 202, 1992. 28. Takeda, F., Strik, B.C., Peacock, D., and Clark, J.R., Cultivar differences and the effect of winter temperature on flower bud development in blackberry, J. Am. Soc. Hort. Sci., 127, 495, 2002. 29. Takeda, F., Strik, B.C., Peacock, D., and Clark, J.R., Patterns of floral bud development in canes of erect and trailing blackberry, J. Am. Soc. Hort. Sci., 128, 3, 2002. 30. Strik, B.C, et al., Caneberry research at North Willamette Research and Extension Center—an update, Proc. Oregon Hort. Soc., 141, 1994. 31. Warmund, M.R. and Byers, P.L., Rest completion in seven blackberry (Rubus sp.) cultivars, Acta Hort. (ISHS) 585, 693, 2002. 32. Crandall, P.C., Bramble Production. The Management and Marketing of Raspberries and Blackberries, Food Products Press, Binghamton, NY, 1995. 33. Warmund, M.R. and George, M.F., Freezing survival and super-cooling in primary and secondary buds of Rubus spp., Can. J. Plant Sci., 70, 893, 1990. 34. Camp, W.H., The North American blueberries with notes on other groups of Vacciniaceae, Brittonia, 5, 203, 1945. 35. Eck, P., Botany, in Blueberry Culture, Eck, P. and Childers, N., Eds., Rutgers University Press, New Brunswick, NJ, 1966, p. 14. 36. Aalders, L.E. and Hall, I.V., A comparison of flower bud development in the lowbush blueberry, V. angustifolium Ait. under greenhouse and filed conditions, Proc. Am. Soc. Hort. Sci., 85, 281, 1964.


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37. Gough, R.E., Shutak, V.G., and Hauke, R.L., Growth and development of highbush blueberry. II. Reproductive growth, histological studies, J. Am. Soc. Hort. Sci., 103, 476, 1978. 38. Huang, Y.H., Johnson, C.E., and Sundberg, M.D., Floral morphology and development of ‘Sharpblue’ southern highbush blueberry in Louisiana, J. Am. Soc. Hort. Sci., 122, 630, 1997. 39. Ritzinger, R. and Lyrene, P.M., Flower morphology in blueberry species and hybrids, HortScience, 34, 130, 1999. 40. Darnell, R.L. and Lyrene, P.M., Cross-incompatibility of two related rabbiteye blueberry cultivars, HortScience, 24, 1017, 1989. 41. Davies, F.S., Flower position, growth regulators, and fruit set of rabbiteye blueberries, J. Am. Soc. Hort. Sci., 111, 338, 1986. 42. Morrow, E.B., Some effects of cross-pollination versus self-pollination in the cultivated blueberry, Proc. Am. Soc. Hort. Sci., 42, 469, 1943. 43. Eck, P., Blueberry, in Handbook of Fruit Set and Development, Monselise, S.P., Ed., CRC Press, Boca Raton, FL, 1986, p. 75. 44. Maust, B.E., Williamson, J.G., and Darnell, R.L., Flower bud density affects vegetative and fruit development in field-grown southern highbush blueberry, HortScience, 34, 607, 1999. 45. Forsyth, F.R. and Hall, I.V., Ethylene production with accompanying respiration rates from the time of blossoming to fruit maturity in three Vaccinium species, Nat. Can., 96, 257, 1969. 46. Birkhold, K.T., Koch, K.E., and Darnell, R.L., Carbon and nitrogen economy of developing rabbiteye blueberry fruit, J. Am. Soc. Hort. Sci., 117, 139, 1992. 47. Dana, M.N., Cranberry management, in Small Fruit Crop Management, Galletta, G.J. and Himelrick, D., Eds., Prentice Hall, Englewood Cliffs, NJ, 1990, p. 334. 48. Harmat, L., Porpaczy, A., Himelrick, D.G., and Galletta, G.J., Currant and gooseberry management, in Small Fruit Crop Management, Galletta, G.J. and Himelrick, D.G., Eds., Prentice Hall, Englewood Cliffs, NJ, 1990, p. 245. 49. Strik, B.C., Growing Kiwifruit, Extension Service Publication PNW 507, Oregon State University, Corvallis, OR, 2005. 50. Tiyayon, C. and Strik, B.C., The influence of time of overhead shading on yield, fruit quality, and subsequent flowering of hardy kiwifruit, Actinidia arguta, N. Z. J. Crop Hort. Sci., 32, 235, 2004. 51. Kabaluk, J.T., Kempler, C., and Toivonen, P.M.A, Actinidia arguta—characteristics relevant to commercial production, Fruit Var. J., 51, 117, 1997. 52. Galletta, G.J. and Himelrick, D.G., Eds., Small Fruit Crop Management, Prentice Hall, Englewood Cliffs, NJ, 1990. 53. Childers, N.F. and Lyrene, P.M., Eds., Blueberries. For Growers, Gardeners, Promoters, Dr. Norman F. Childers Publications, Gainesville, FL, 2006. 54. Gough, R.E., The Highbush Blueberry, Food Products Press, Binghamton, NY, 1994. 55. Childers, N.F., Ed., Strawberries. A Book for Growers, Others, Dr. Norman F. Childers Publications, Gainesville, FL, 2003. 56. Davenport, J., DeMoranville, C., Hart, J., Poole, R., Roper, T., Planer, T., Larson, B., and Pozdnyakova, L., Nitrogen for Bearing Cranberries, Hart, J., Ed., Extension Service Publication EM 8741, Oregon State University, Corvallis, OR, 2000, p. 17. 57. Hart, J., Strik, B.C., and Rempel, H., Caneberries. Nutrient Management Guide, Extension Service Publication EM 8903-E, Oregon State University, Corvallis, OR, 2006.


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Berry fruit: Value-added products for health promotion 58. Hart, J., Strik, B.C., Yang, W., and White, L., Nutrient Management Guide for Blueberries in Oregon, Extension Service Publication EM 8918, Oregon State University, Corvallis, OR, 2006. 59. Pritts, M. and Handley, D., Eds., Bramble Production Guide, NRAES 35, Natural Resource, Agriculture, and Engineering Service, Ithaca, NY, 1989. 60. Lieten, P., Strawberry production in central Europe, Int. J. Fruit Sci., 5, 91, 2005. 61. Strik, B. and Cahn, H., Pruning and training affect yield but not machine harvest efficiency of ‘Meeker’ red raspberry, HortScience, 34, 611, 1999. 62. Strik, B.C., A review of nitrogen nutrition of Rubus, Acta Hort., 2007 (in press). 63. Rempel, H., Strik, B.C., and Righetti, T., Uptake, partitioning and storage of fertilizer nitrogen in red raspberry as affected by rate and timing of application, J. Am. Soc. Hort. Sci., 129, 439, 2004. 64. Papp, J., Kobzos-Pápai, I., and Nagy, J., Effect of nitrogen application on yield, leaf nutrient status and fruit chemical composition of raspberry and redcurrant varieties, Acta Agron. Acad. Sci. Hung., 33, 337, 1984. 65. Nelson, E. and Martin, L.W., The relationship of soil-applied N and K to yield and quality of ‘Thornless Evergreen’ blackberry, HortScience, 21, 1153, 1986. 66. Alleyne, V. and Clark, J.R., Fruit composition of ‘Arapaho’ blackberry following nitrogen fertilization, HortScience, 32, 282, 1997. 67. Malik, H., Archbold, D., and MacKown, C.T., Nitrogen partitioning by ‘Chester Thornless’ blackberry in pot culture, HortScience, 26, 1492, 1991. 68. Mohadjer, P., Strik, B.C., Zebarth, B.J., and Righetti, T.L., Nitrogen uptake, partitioning and remobilization in ‘Kotata’ blackberry in alternate-year production, J. Hort. Sci. Biotechnol., 76, 700, 2001. 69. Strik, B.C., Clark, J.R., Finn, C., and Buller, G., Management of primocanefruiting blackberry to maximize yield and extend the fruiting season, Acta Hort., 2007 (in press). 70. Eleveld, B., Strik, Brown, K., and Lisec, B., Marion Blackberry Economics. The Costs of Establishing and Producing ‘Marion’ Blackberries in the Willamette Valley, Extension Service Publication EM 8773, Oregon State University, Corvallis, OR, 2001. 71. Bell, N., Strik, B.C., and Martin, L.W., Effect of date of primocane suppression on ‘Marion’ trailing blackberry. II. Cold hardiness, J. Am. Soc. Hort. Sci., 120, 25, 1995. 72. Cortell, J. and Strik, B.C., Effect of floricane number in ‘Marion’ trailing blackberry. I. Primocane growth and cold hardiness, J. Am. Soc. Hort. Sci., 122, 604, 1997. 73. Strik, B. and Buller, G., Reducing thorn contamination in machine-harvested ‘Marion’ blackberry, Acta Hort., 585, 677, 2002. 74. Strik, B. and Buller, G., Improving yield and machine harvest efficiency of ‘Bluecrop’ through high-density planting and trellising, Acta Hort., 574, 227, 2002. 75. Strik, B. and Buller, G., The impact of early cropping on subsequent growth and yield of highbush blueberry in the establishment years at two planting densities is cultivar dependant, HortScience, 40, 1998, 2005. 76. Bryla, D.R. and Strik, B.C., Variation in plant and soil water relations among irrigated blueberry cultivars planted at two distinct in-row spacings, Acta Hort., 715, 295, 2006. 77. Eleveld, B., Strik, B., DeVries, K., and Yang, W., Blueberry Economics. The Costs of Establishing and Producing Blueberries in the Willamette Valley, Extension Service Publication EM 8526, Oregon State University, Corvallis, OR, 2005.


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78. Strik, B., Buller, G., and Hellman, E., Pruning severity affects yield, berry weight, and picking efficiency of highbush blueberry, HortScience, 38, 196, 2003. 79. Aalders, L.E., Hall, I.V., and Forsyth, F.R., Effects of partial defoliation and light intensity on fruit set and berry development in the lowbush blueberry, Hort. Res., 9, 124, 1969. 80. Patten, K. and Neuendorff, E., Influence of light and other parameters on the development and quality of rabbiteye blueberry fruit, in Proceedings of the Texas Blueberry Growers Association Convention, Texas Blueberry Growers Association, Georgetown, TX, 1989, p. 109. 81. Strik, B.C., Brazelton, D., Penhallegon, R., and Ketchum, L., A Grower’s Guide to Pruning Highbush Blueberries, DVD 2, Oregon State University, Corvallis, OR, 1990. 82. Strik, B.C., Bristow, P., Broaddus, A., Davenport, J., Defrancesco, J.T., English, M., Fisher, G., Fitzpatrick, S., Hart, J., Henderson, D., Larson, B., Patten, K., Pinkerton, J., Poole, A., Pscheidt, J., and Vorsa, N., Cranberry Production in the Pacific Northwest, Extension Service Publication PNW 247, Oregon State University, Corvallis, OR, 2002. 83. Strik, B.C. and Poole, A.P., Alternate year pruning recommended for cranberry, HortScience, 27, 1327, 1992. 84. Strik, B.C. and Poole, A., Does sand application to soil surface benefit cranberry production? HortScience, 30, 47, 1995. 85. Penhallegon, R., Lingonberry Production Guide for the Pacific Northwest, Extension Service Publication PNW 583-E, Oregon State University, Corvallis, OR, 2006. 86. Tiyayon, C. and Strik, B.C., Flowering and fruiting morphology of hardy kiwifruit, Actinidia arguta, Acta Hort., 610, 171, 2003. 87. Strik, B. and Hummer, K., ‘Ananasnaya’ hardy kiwifruit, J. Am. Pomol. Soc., 60, 106, 2006. 88. Fisk, C.L., McDaniel, M.R., Strik, B.C., and Zhao, Y., Physicochemical, sensory, and nutritive qualities of hardy kiwifruit (Actinidia arguta ‘Ananasnaya’) as affected by harvest maturity and storage, J. Food Sci., 74, 210, 2006.


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chapter 2

Chemical components of berry fruits Stephen T. Talcott Contents 2.1 Introduction ................................................................................................. 2.2 Basic chemical compositions of berries................................................... 2.2.1 Carbohydrates................................................................................. 2.2.2 Organic acids .................................................................................. 2.2.3 Enzymes........................................................................................... 2.2.4 Cell wall components .................................................................... 2.2.5 Berry pigments ............................................................................... 2.2.6 Vitamins and minerals .................................................................. 2.3 Chemical content of berries ...................................................................... 2.3.1 Strawberry ....................................................................................... 2.3.2 Blueberry ......................................................................................... 2.3.3 Blackberry........................................................................................ 2.3.4 Raspberry......................................................................................... 2.4 Conclusion.................................................................................................... References..............................................................................................................

51 54 54 55 55 56 57 58 58 63 66 66 67 67 68

2.1 Introduction Berries are universally recognized as having a basic chemical composition that accentuates their sweet taste, fruity aroma, and healthy properties that are enjoyed by societies throughout the world. Berries are soft fruits that range in color from red to blue or black. They a good source of essential vitamins and minerals, and have diverse phytochemical compositions that relate to consumer satisfaction and health. The chemical composition of berry fruits can be highly variable depending on the cultivar, growing location, 51


52


ripeness stage, and harvest and storage conditions because of their generally nonclimacteric nature with respect to their production and response to ethylene. In addition, the environmental conditions of growth can be a major factor impacting overall fruit quality. Although numerous chemical parameters relate to berry quality, identifying specific quality factors beyond simple sugar content is difficult because there are numerous factors that relate to consumer acceptance. However, the overall quality of many berry types is attributable to harvesting at the maximal level of ripeness when fruits have their highest sugar and aroma content. Other factors include a proper sugar/ acid balance, firm texture, volatile aroma profile, and external color derived from anthocyanins, which generally relate to consumers’ perception of quality. Once consumed, the nutritional benefits of berries are realized from their carbohydrate, vitamin, mineral, dietary fiber, and polyphenolic concentrations. Different varieties of berries contain highly variable concentrations of ascorbic acid, folic acid, select minerals, carotenoids, and a diversity of polyphenolics that impact color, taste, and nutrition. Berries are generally low in calories and high in dietary fiber and contain only small amounts of fat and protein (Table 2.1). Fruit and vegetable consumption has been widely associated with decreased incidences of chronic diseases, including coronary heart disease and cancer. With national trends to increase fruit, vegetable, and whole grain consumption, berries provide an important source of chemical compounds essential for human health.1 Understanding those factors that influence consumer perception of berry quality is important for the selection of new or improved breeding lines and in developing new food formulations with berries or berry flavors. Those quality factors within the control of producers include harvesting at optimal ripeness, proper temperature control, and variations in storage environment, such as controlled/modified atmospheres and relative humidity. These conditions can influence numerous biochemical changes that affect overall fruit quality.2,3 The degree of fruit ripeness not only impacts the color and flavor, but also the postharvest keeping quality. Some changes in berries during maturation and ripening are evident, such as the loss of chlorophyll, the development of secondary metabolites that influence color, and the production of aroma volatiles. However, more subtle changes also occur during fruit development and postharvest handling, such as changes in the balance of sugars and acids and altered cell wall chemistry, which influence consumer perception of texture and juiciness. As the fruit reach the point of marketability, careful consideration of harvesting and handling conditions is critical for fruit quality. Initial removal of field heat and storage in a high relative humidity environment will prevent excessive moisture loss, slow microbial decay, and decrease the activity of cell wall active enzymes that cause rapid deterioration. Despite the many beneficial properties of berries based on their concentrations of vitamins, minerals, fiber, and antioxidant polyphenolics, if the quality of the fruit is below consumer acceptance for purchase, such benefits are never realized.

84.2 57 0.74 0.33 0.24 14.5 2.4 9.96 0.11 4.88 4.97 ND ND 0.03 88.2 43 1.39 0.49 0.37 9.61 5.3 4.88 0.07 2.31 2.4 0.07 0.03 ND 85.8 52 1.2 0.65 0.46 11.9 6.5 4.42 0.2 1.86 2.35 ND ND ND 85.9 50 1.1 0.26 0.54 12.2 5.3 6.89 NA NA NA NA NA NA

Carbohydrate calculated by difference from proximate analysis. NA, not available; ND, not detected.

a

Water (g) Energy (kcal) Protein (g) Total lipids (g) Ash (g) Carbohydratea(g) Total fiber (g) Total sugars (g) Sucrose (g) Glucose (g) Fructose (g) Maltose (g) Galactose (g) Starch (g) 90.95 32 0.67 0.3 0.4 7.68 2.0 4.66 0.12 2.04 2.5 ND ND 0.04

81.96 63 1.4 0.41 0.86 15.38 NA NA NA NA NA NA NA NA 87.87 44 0.88 0.58 0.49 10.18 4.3 NA NA NA NA NA NA NA 83.95 56 1.4 0.2 0.66 13.8 4.3 7.37 0.61 3.22 3.53 NA NA NA

90.7 37 0.4 0.1 0.1 8.7 NA NA NA NA NA NA NA NA

79.8 73 0.66 0.5 0.64 18.4 7 NA NA NA NA NA NA NA

Blueberry Blackberry Raspberry Boysenberry Strawberry Black currant Gooseberry Red currant Huckleberry Elderberry

Chapter 2:

Table 2.1 Chemical Content of Proximates and Carbohydrates in Berries From the U.S. Department of Agriculture Nutrient Database2


Chemical components of berry fruits 53


54


2.2 Basic chemical compositions of berries 2.2.1

Carbohydrates

The chemical properties affecting berry flavor are a combination of volatile and nonvolatile compounds that relate to the basic taste, color, texture, and aroma of the fruit. Paramount to overall flavor is the composition and concentration of soluble sugars (sucrose, glucose, and fructose) in relation to organic acids and aroma volatiles (Table 2.1). Fruit harvest must be delayed until the fruit is ripe enough to accumulate sufficient sugars to balance fruit acidity and astringency. Therefore, the timing of the harvest and subsequent postharvest handling conditions are critical because of the relatively short shelf life from harvest to retail distribution. Varying sugar contents in relation to the overall flavor are common factors that relate to cultivar differentiation of strawberries,4 yet sugar content alone is generally a poor index for the table quality of berry fruits. The sugar content of ripe berries is generally an equimolar mixture of glucose and fructose, with sucrose concentrations varying based on the degree of ripeness or duration of postharvest storage. In berry plants, the carbon from photosynthesis is most often directed into sucrose for transport via the phloem into starch and other molecules, but starch is not significantly accumulated in berry fruits.4 Although starch is the primary storage reserve in plants and is formed into starch granules via starch synthesis that polymerizes adenosine diphosphate (ADP)-glucose into higher molecular weight polymers, its storage in berry plants is primarily in the roots, stems, and leaves and it is only present in the early stages of fruit development.5 As a mixture of two-glycan polymers (amylase and amylopectin), starch is critical for plant growth and development as a reserve energy source. During early berry development, sucrose generally dominates as the primary carbohydrate and is converted to glucose and fructose as ripening progresses, and its conversion and formation can continue during postharvest storage. Sucrose is a nonreducing disaccharide composed of α-D-glucopyranoside and β-D-fructofuranoside and is not a respiratory substrate since it cannot be phosphorylated. Sucrose hydrolysis can occur via an acid-catalyzed reaction, but hydrolysis from invertase activity in berry fruit during maturation and ripening is more likely to yield high concentrations of glucose and fructose in the ripe fruit. Since fructose is characteristically sweeter than glucose or sucrose, its concentration in berries is a desirable organoleptic trait, but total sugar content is generally a better marker for consumer acceptability. Among the factors affecting fruit quality, concentrations of soluble sugars are most commonly measured in relation to the organoleptic factors of sweetness, acidity, astringency, and overall flavor perception. For fresh fruits, the majority of consumers prefer sweeter fruit; this is not only a consequence of higher sugar concentration, but also the balance among acids, aroma active volatiles, and other constituents, such as polyphenolics, that can affect sweetness perception.


Chapter 2:

2.2.2

Chemical components of berry fruits

55

Organic acids

The sugar content in berries is counterbalanced by the presence of several predominant organic acids such as citric and malic acid, as well as phenolic acids that can impart bitter or astringent flavors, that are responsible for the basic taste components. The compliment of organic and phenolic acids in berries is responsible for the titratable acidity of the fruit and is commonly measured as an overall index of fruit quality, whereas measurements of pH are often poor indicators of fruit quality characteristics. High concentrations of organic acids in most fruits is also critical for fruit preservation, maintaining a low pH in processed fruit applications such as jams and jellies.6,7 Organic acids also help to stabilize ascorbic acid and are critical in fruit color by serving to stabilize anthocyanins and extend the shelf life of fresh and processed berries.

2.2.3

Enzymes

The presence of various hydrolase and oxidase enzymes in fresh, damaged, and pureed berries can cause significant quality deterioration, including a loss of color and texture, and the formation of undesirable brown pigments. The presence of oxidizing enzymes has been reported in a variety of berries and is detrimental to color, nutritional components, and overall acceptability. The extent of browning from enzymes such as polyphenol oxidase (PPO; EC 1.14.18.1) or peroxidase (POD; EC 1.11.1.7) is often initially masked by the dark red color of the anthocyanins, but eventually secondary oxidation or condensation reactions occur that alter consumer appeal. The activity of PPO (or POD when hydrogen peroxide is present) catalyzes the oxidation of o-diphenolic compounds, which will eventually polymerize into brown pigments. POD was found to increase with fruit development in blueberries8 and was found ionically bound to the cell wall. The type and amount of oxidase enzymes greatly influences overall fruit quality and may be limited by either enzyme or substrate concentrations, yet berries have an abundance of polyphenolic substrates such as phenolic acids and flavan-3-ols. Techniques to reduce the harmful effects of enzymes include proper refrigeration, reduced oxygen, pH modification, the addition of enzyme inhibitors, or the addition of reducing agents to control secondary oxidation products. In many varieties of berries, PPO and POD are the primary enzymes responsible for destruction of phytochemicals and quality characteristics8–10 and their activity is related to fruit ripeness, physical damage, and storage temperature. Cell wall degrading enzymes are also important components affecting overall fruit quality as they relate to ripening and postharvest shelf life. Since berries do not have a protective pericarp and possess only a thin cuticle layer, they are particularly susceptible to wounding and the action of enzymes. Because of the high content of pectic substances in most berries, the action of polygalactouronase (PG; EC 3.2.1.15) to cleave pectin chains is a major


56


factor influencing fruit texture. Pectin modification is further aided by the action of pectin methyl esterase (PME; EC 3.1.1.11), which is a ubiquitous enzyme that serves to cleave methyl esters from methoxylated pectins for subsequent depolymerization by PG. Other components of the cell wall include cellulose and hemicellulose, which are also depolymerized by the action of various glucanases. An endo-1,4-β-D-glucanase (EC 3.2.1.4) was found to act primarily on hemicellulose in strawberries, contributing to their softening during storage.11 The degradation of hemicellulose is often monitored by the loss of five-carbon neutral sugars from the activity of carbohydrate-specific enzymes such as β-galactosidase.

2.2.4

Cell wall components

Fruit softening and enzymatic changes affecting berry texture are important components of fruit quality that are often overlooked as parameters affecting consumer perception. A balance exists from fruit development and ripening to harvest such that the fruit is firm enough for handling but not overly soft as to adversely impact the perception of quality. Berry harvesting is often a highly subjective determination, where underripe fruit is texturally too hard and has consumer appeal, yet excessively soft fruit damages easily and contributes to a loss in farm value. However, quality deterioration of ripe berries is often related to excessive fruit softening and the appearance of mold or bacterial decay. Changes in cell wall solubilization, primarily from pectin degradation of the middle lamella, is the primary means by which berries soften. As berries mature and ripen, major textural changes occur as a result of ripening, overripening, fruit damage, or the action of cell wall degrading enzymes during storage. The adequacy of ripeness based on texture, along with color and flavor, must be subjectively made at the time of harvest. Postharvest changes associated with berry ripening proceed at variable rates and in a manner dependent on storage temperature, microbial load, fruit damage, and composition of the cell wall.12 Changes in berry texture are the result of degradation of cell wall constituents including pectin, cellulose, hemicellulose, glycoproteins, and esterified polyphenolics as components of dietary fiber13 and are important components affecting fruit quality as they relate to ripening and postharvest shelf life. These compounds are continually changing throughout fruit development, ripening, and postharvest storage.14–16 Enzymatic action results in polysaccharide depolymerization and subsequent conversion of high molecular weight, water insoluble polymers to increasingly water soluble components that result in fruit softening, enhanced susceptibility to microbial infection, surface browning, and eventually a decrease in consumer acceptability. Berry cell walls contain a high concentration of pectic substances that are cleaved by the action of PG, influencing fruit texture. The normal progression of fruit ripening leads to an increase in water soluble pectins and a subsequent decrease in higher molecular weight pectic substances. Perkins


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et al.17 observed blackberry softening during maturation and ripening by the formation of water soluble uronic acids that increased as much as 50% as pectin solubility increased. Other cell wall components include cellulose and hemicellulose, which are also depolymerized by the action of various glucanases. Polysaccharide degradation can occur from the activation of cell wall bound enzymes or derived from fungal pathogens, altering fruit texture.15 However, polysaccharide depolymerization reactions are not always detrimental to quality, since fruit softening is critical during fruit ripening and for consumer perception of quality. As dietary fiber, levels of both soluble and insoluble polysaccharides have been suggested to enhance human health by reducing serum cholesterol, low-density lipoprotein (LDL) cholesterol, and the risk of coronary heart disease, enhancing satiety, and slowing the uptake of sugars from the diet, influencing diabetic responses.18

2.2.5

Berry pigments

One of the most distinguishing features of most berries is their deep red, blue, or purple color derived from anthocyanins, which is the subject of Chapters 3, 4, and 5. Visual perception of fresh and processed fruit color is the first factor influencing quality perception, superseding both flavor and textural perceptions. Berry color can be influenced by ripeness at harvesting and by numerous degradative reactions to anthocyanins in fresh and processed products, including microbial load, enzymatic action, pH, the presence of ascorbic acid, and the extent of thermal processing. Other compounds with the potential to contribute to the color of fruit are common carotenoids, such as lutein and β-carotene, which have been reported in concentrations up to 46 µg/g of dry fruit weight in blueberries, black currants, black chokeberries, lingonberries, and raspberries.19 Although these concentrations are low in relation to other carotenoid-rich fruits and vegetables, their presence indicates the phytochemical diversity among the berry fruits, along with the antioxidant vitamins and polyphenolics that contribute to the health benefits of berry fruits. Differences among cultivars, the degree of ripeness, postharvest handling, and the degree of processing are major factors influencing the color of berry fruits. In fresh fruit, color losses can be attributed to oxidative and enzyme-catalyzed reactions. Once fruit is damaged or processed to induce cellular decompartmentalization, free radical-induced or enzyme-catalyzed oxidation reactions contribute to overall color loss in the fruit. Although most oxidase enzymes are unable to act directly on anthocyanins, the formation of o-quinones by PPO and the breakdown of peroxides by POD can induce secondary oxidative reactions or form condensation products that are detrimental to color stability.20 Berries contain a diversity of nonanthocyanin polyphenolics that are substrates for oxidation, including hydroxycinnamic acids and flavan-3-ols that serve as the basis for anthocyanin degradation upon their oxidation. Studies have shown that anthocyanins with an o-diphenolic substitution are more affected by these oxidation and condensation


58


reactions.20,21 The presence of ascorbic acid in berries can also affect color stability in both beneficial and detrimental mechanisms.22–24 As a reducing agent, ascorbic acid can augment the effects of o-quinones before they react with anthocyanins,25 but during long-term storage ascorbic acid can exacerbate anthocyanin color stability in a mutually destructive reaction mechanism.23,26,27 In addition, metal-catalyzed destruction of color components in the presence of ascorbic acid or residual peroxide has long been a recognized mechanism for the destruction of plant pigments.28

2.2.6

Vitamins and minerals

Berries contain a diverse array of nutrients with recognized biological activities that promote or contribute to health. The content and diversity of vitamins (Table 2.2), minerals (Table 2.3), and dietary fiber are often the basis for promoting increased daily intake of fruits and vegetables. Many berries contain large concentrations of food folate, B vitamins such as niacin, tocopherols, and vitamin K, which are important for human health. Major minerals in berries include potassium, phosphorous, calcium, and magnesium. Many berries are known for their high ascorbic acid content, which varies among berry varieties and among genotypes, as well as their diversity of polyphenolics, which are the major contributors to total antioxidant capacity. Some berry cultivars have enough ascorbic acid to provide 100% of the daily value in a single serving. One of the most important roles of ascorbic acid is its ability to act as a reducing agent, augmenting the effects of oxidase enzymes by reducing o-quinones back to their o-diphenolic configuration. Ascorbic acid has many recognized health benefits, including collagen and hormone synthesis, antiscorbutic activity, and a wide range of benefits relating to enhanced immunity.1,29 The stability of ascorbic acid is known to be influenced by numerous factors, including temperature, light exposure, atmosphere, fruit damage, food processing, and ascorbic acid oxidase. Overall, berries provide good concentrations of vitamins and minerals as part of an overall balanced diet.

2.3 Chemical content of berries Although berries experience many common physiological and quality changes throughout ripening, there are unique parameters affecting the quality of each fruit. Common analyses for chemical composition of the fruit include individual sugars, total soluble solids, individual organic acids, total acidity and pH, and ascorbic acid (Table 2.4 and Table 2.5). Despite the numerous studies that have evaluated berries for chemical content among cultivars, growing locations, harvest times, and postharvest handling practices, it is often noted that intrinsic factors in the fruit was a greater distinguishing factor than knowledge of its chemical composition. Although many berry types are marketed, the most popular varieties in the United States are strawberry, blueberry, blackberry, and raspberry.

9.7 0.04 0.04 0.42 0.12 0.05 6 ND 54 0.57 0.01 0.36 0.03 19.3

NA, not available; ND, not detected.

Total ascorbic acid (mg) Thiamin (mg) Riboflavin (mg) Niacin (mg) Pantothenic acid (mg) Vitamin B6 (mg) Total folate (µg) Vitamin B12 (µg) Vitamin A (IU) a-Tocopherol (mg) b-Tocopherol (mg) g-Tocopherol (mg) D-Tocopherol (mg) Vitamin K (µg)

Blueberry 21 0.02 0.03 0.65 0.28 0.03 25 ND 214 1.17 0.04 1.34 0.9 19.8

Blackberry 26.2 0.03 0.04 0.6 0.33 0.06 21 ND 33 0.87 0.06 1.42 1.04 7.8 3.1 0.05 0.04 0.77 0.25 0.06 63 ND 67 0.87 NA NA NA 7.8 58.8 0.024 0.022 0.386 0.125 0.047 24 ND 12 0.29 0.01 0.08 0.01 2.2 181 0.05 0.05 0.3 0.398 0.066 — ND 230 1 NA NA NA NA 27.7 0.04 0.03 0.3 0.286 0.08 6 ND 290 0.37 NA NA NA NA

41 0.04 0.05 0.1 0.064 0.07 8 ND 42 0.1 NA NA NA 11

Black Red Raspberry Boysenberry Strawberry currant Gooseberry currant 2.8 0.01 0.03 0.3 NA NA NA ND 79 NA NA NA NA NA

36 0.07 0.06 0.5 0.14 0.23 6 ND 600 NA NA NA NA NA

Huckleberry Elderberry

Chapter 2:

Table 2.2 Vitamin Content in Berries From the U.S. Department of Agriculture Nutrient Database2



NA, not available.

Calcium (mg) Iron (mg) Magnesium (mg) Phosphorus (mg) Potassium (mg) Sodium (mg) Zinc (mg) Copper (mg) Manganese (mg) Selenium (mg) 6 0.28 6 12 77 1 0.16 0.06 0.34 0.1 29 0.62 20 22 162 1 0.53 0.17 0.65 0.4 25 0.69 22 29 151 1 0.42 0.09 0.67 0.2 27 0.85 16 27 139 1 0.22 0.08 0.55 0.2

16 0.42 13 24 153 1 0.14 0.048 0.386 0.4 55 1.54 24 59 322 2 0.27 0.086 0.256 NA 25 0.31 10 27 198 1 0.12 0.07 0.144 0.6

33 1 13 44 275 1 0.23 0.107 0.186 0.6

15 0.3 NA NA NA 10 NA NA NA NA

38 1.6 5 39 280 6 0.11 0.061 NA 0.6

Black Red Blueberry Blackberry Raspberry Boysenberry Strawberry currant Gooseberry currant Huckleberry Elderberry

60

Table 2.3 Mineral Content in Berries From the U.S. Department of Agriculture Nutrient Database2



Raspberry

Strawberry

— — — — — —

0.06–2.27 — 0.11–1.85 0.66–1.80 — 0.14–1.22 0.78–1.63 0.53–0.74 — — — — — — —

1.33–2.66 — 1.63–2.82 0.71–1.71 — 0.96–2.30 1.50–1.69 3.47–8.64 —

Glucose (%) Sucrose (%)

— — — — — —

2.18–4.18 — 2.05–3.30 1.23–1.93 — 1.46–2.89 1.84–2.05 2.78–6.27 —

Fructose (%) — 3.77–10.5 5.2–8.7 6.9–10.3 — — — 8.79–13.78 7.6–9.7

9.26–10.54 14.69–17.98 14.2–14.8 10.0–13.0 — 10.5–13.0 — 9.26–10.5 15.2–17.9 9.7–10.9 —

7.1–10.8 — — 5.4–9.4 5.8 9.18–13.1 6.0–8.2 — —

°Brix

21.3–31.1 15.4–32.0 16.1–28.9 11.8–28.8 21.3–31.1

37–104 13.6–33.9 — 40.1–85.3 — 42.7–91.8 — 301–313 — 1.27–1.78 0.13–0.18 — — — — — — 1.27–1.78 0.13–0.18

0.09–2.03 0.12–0.54 — — 0.45–1.03 — 0–0.71 — — — — — 0.55–0.72 0.21–0.28 0.44–0.75 0–0.13 — —

Ascorbic Citric Malic acid acid Total solids (%) (mg/100 g) acid (%) (%)

2.65–2.88 2.85–3.06 2.78–3.03 3.20–3.45 2.88–3.87 2.99–3.08

3.29–3.43 — — — 3.28 — 3.57–3.59 3.67–3.70 3.18–3.49

pH

1.67–2.32 1.90–2.52 1.71–2.30 0.16–0.29 — 1.75–2.38

0.60–0.97 — — — 0.53 0.97–1.20 0.72–0.88 0.67–0.72 0.91–1.07

4 5 7 8 4 3

11 22 13 6 1 6 3 2 6

(Continued)

69 70 71 73 69 74

44 21 42 45 72 49 47 48 34

Number of Titratable acidity (%) samples Reference

Chapter 2:

Table 2.4 Chemical Contentsa That Affect Quality Characteristics of Common Berries



a

0.12–1.14 — 3.28–3.87 —

1.58–2.61 — — — — —

3.34–3.88 —

2.11–3.38 — — — — —

— —

— — — — 10.8–11.4 —

— —

— — — 8.20–13.6 — —

— —

— 18.0 12.4–13.1 — 12.7–38.7 —

— —

— — — — — —

— 0.06–1.10

0.06–1.10 — — — — —

— —

— —

— — — — — — — 0.84–2.62 3.06–3.20 0.16–0.30 2.55–4.28 1.02–4.22

pH

2 5

5 1 7 11 5 11

57 63

63 46 75 65 73 64

Number of Titratable acidity (%) samples Reference

Values are for whole fruit at their maximal or optimal stage of ripeness or are starting concentrations if fruit is processed or held in storage.

Blueberry

0.12–0.26 — — — — —

°Brix

Ascorbic Citric Malic acid acid Total (%) solids (%) (mg/100 g) acid (%)

62

Blackberry

Glucose (%) Sucrose (%) Fructose (%)

Table 2.4 (Continued) Chemical Contentsa That Affect Quality Characteristics of Common Berries




Chapter 2:

2.3.1


63

Strawberry

The popularity and worldwide demand for fresh and processed strawberries have made them one of the most extensively researched berries in the world. The quality of fresh strawberries as a function of their chemical composition and organoleptic attributes is an important area of study. Ford et al.30 demonstrated that the quality of strawberries is the most important factor influencing retail sales, and they indicated that simple screening factors for compounds influencing taste and aroma can be critical for consumer acceptance. Considerable research has been dedicated to evaluate breeding lines and commercial cultivars over several seasons and growing locations to establish both intrinsic and extrinsic factors that relate to optimal fruit quality.31,32 Chandler et al.33 noted that strawberries with higher soluble solids are generally preferred over lower soluble solids, thus optimizing fruit quality through selection of those lines with optimal sugar and acid balance, and desirable aroma characteristics are critical for consumer preference.34 Strawberries are widely considered to be a good dietary source of vitamins and minerals, yet concentrations can vary greatly among cultivars and with postharvest handling conditions. High concentrations of ascorbic acid, potassium, magnesium, iron, zinc, and calcium have been reported in six varieties of strawberries.35 Ascorbic acid was found to increase continuously during strawberry maturation7 and its concentrations are highly influenced by postharvest handling practices, the presence of oxidase enzymes, and the conditions of storage. As an antioxidant, ascorbic acid was shown to account for about 15% of the total antioxidant capacity,36 with polyphenolics accounting for the remainder. Environmental conditions during strawberry growth, especially atmospheric temperature, has been identified as among the most critical factors influencing strawberry fruit quality. Since growing conditions continuously change throughout the season, considerable variation can exist in chemical composition in response to temperature and light exposure. Olsson et al.32 reported significant differences in concentrations of polyphenolics, ascorbic acid, and antioxidant capacity among strawberry cultivars, with differences in growing temperature affecting soluble solids content. Atmospheric temperatures and solar radiation were also found to be critical factors affecting chemical composition, with Hellman and Travis37 and Chandler et al.33 observing that as growing temperatures increased, a general decrease in fruit quality was observed. These effects were especially true for winter production strawberries, where Del Pozo-Insfran et al.21 showed the appreciable effects that cultivar, harvest date, and production year had on sugar, polyphenolics, and antioxidant content in 22 strawberry lines. In this study, high soluble solids and low polyphenolic content characterized fruit harvested in early season conditions (11.4°C average temperature), whereas later harvests (15.9°C average temperature) were characterized by appreciably higher polyphenolics, sugar, and ascorbic acid concentrations. Wang and Camp38 showed similar effects, where higher day/night growth temperatures


64


(25°C/12°C) enhanced the development of anthocyanins and decreased soluble solids, organic acids, and ascorbic acid compared to lower temperatures (18°C/12°C). Likewise, Wang and Zheng39 showed that fruits grown in lower temperature environments contained lower concentrations of several classes of polyphenolics that affected antioxidant capacity. The bright red color of strawberries is an initial distinguishing factor for consumers in judging quality and the perception of flavor. Strawberries are considered mature when their red color reaches in excess of two-thirds of the fruit surface, with approximately 7% soluble solids.40 However, it was reported that no single parameter, such as soluble solids or color, relates to overall fruit quality and that even multiple assays for chemical composition are often limited in characterizing the flavor and quality of the fruit.41–43 Berry flavor is a complex interaction among chemical attributes, including sugars, acids, and volatiles,31 yet when quantified, these parameters still may not directly relate to consumers’ perception of fruit quality. Like all berries, strawberries have a limited shelf life, with significant microbial decay, fruit softening, water loss, loss of red color, brown pigment formation, and flavor changes. Therefore, it is critical to evaluate numerous fruits, growing locations, and harvest times for chemical composition, organoleptic attributes, and handling regimes to gain a better understanding of those factors impacting consumer acceptability. Numerous studies have demonstrated the effects of breeding lines and cultural practices on changes in the chemical composition of strawberries. The chemical composition of nine hybrids and two varieties of strawberries were evaluated during ripening (green, pink, and red) and it was found that sugars and ascorbic acid increased, whereas organic acid changes were highly genotype dependent and did not show a clear trend over time.44 Simple sugars such as glucose, fructose, and sucrose account for nearly all of the soluble carbohydrates in strawberries,31 with glucose and fructose the predominate sugars, at approximately the same ratio throughout ripening. Montero et al.7 monitored the sugar and acid content of strawberries throughout development (fruit set through senescence), with a maximum sucrose content found at 21 to 28 days of development with a subsequent increase in glucose, fructose, and ascorbic acid as the fruit matured. However, throughout development only small differences were observed in pH and titratable acidity despite an overall increase in malic, citric, and shikimic acids. Sturm et al.42 found that individual sugars (sucrose, glucose, fructose, and xylose) and organic acids (citric, fumaric, and shikimic acids) in 13 strawberry lines at two ripeness stages were highly variable among varieties, yet it was these parameters in relation to optimal harvest time that had the greatest impact on consumer acceptability. The change in sugars from a preponderance of sucrose in early fruit development through the full ripe stage to an overall predominance of glucose and fructose is a strong indication of sucrose hydrolysis from the activity of invertase as fruit ripens and during postharvest storage. The varying sensory perception of these sugars, along with relatively small changes in organic acids, serves to alter the sugar/acid balance, enhancing the perception of sweetness.


Chapter 2:


65

Postharvest and storage conditions can greatly impact the chemical composition of berries, so storage conditions must be developed and controlled for each berry type. Cordenunsi et al.45 evaluated the chemical parameters of strawberries over 1 week of storage at 6°C. Although storage differences among cultivars were significant, compositional changes affecting pH and titratable acidity were minimal, sucrose was lost after 2 days, and a loss of up to 50% of ascorbic acid was observed. Strawberries held in high concentrations of carbon dioxide (10% to 30%) and variable oxygen concentrations showed losses of ascorbic acid were enhanced by long-term storage compared to a greater retention in black currants and blackberries.46 However, the postharvest quality of strawberries measured for sugars, acids, and aroma active compounds impacting flavor following 9 to 13 days of storage in air or 20 kPa carbon dioxide revealed better overall quality in the high carbon dioxide atmosphere.47 Postharvest practices and minimal processing of strawberries show a variable response depending on the severity of physical wounding and the cultivar. Castro et al.48 demonstrated that whole and capped strawberries held for up to 3 days under refrigerated storage conditions maintained their chemical composition, while cut pieces (3 to 18 mm) experienced a 26% to 50% loss in ascorbic acid within 5 minutes. Likewise, Nunes et al.49 evaluated strawberries 1 week after 0 and 6 hour delays in postharvest cooling and found the delay caused enhanced water loss, reduced texture, and lowered titratable acidity with a subsequent loss of ascorbic acid, total soluble solids, and sugars. Overall, these results demonstrated that improper handling and storage can have adverse effects on the chemical composition, quality, and nutritional content of berries. Changes in cell wall composition and physical characteristics as related to fruit texture and consumer acceptance are important quality factors for strawberries. Beyond simple desiccation of the fruit during prolonged storage, cell wall depolymerization during maturation occurs despite low polygalactouronase content in strawberries.50 As fruit develops and matures, textural changes are influenced by the amount of water uptake,51 expanding cell volume,52 cell wall composition,53,54 the presence of metals such as calcium,55 and the action of cell wall degrading enzymes. Strawberries of optimal quality have a soft texture due to ripening-induced softening, but excessive depolymerization of high molecular weight pectins and the subsequent formation of smaller, water soluble subunits are associated with decreased quality characteristics. Rosli et al.12 compared the polysaccharide content of three strawberry cultivars during ripening and found that water soluble polysaccharides formed continuously until the beginning of color formation, while both cellulose and hemicellulose continuously decreased with ripening. Cell wall polysaccharides were evaluated during strawberry ripening in two tissue types, with increased formation of water soluble pectin formed in cortical tissue compared to pith tissue, with a 94% decrease in firmness from the final stages of fruit development through complete ripening and a 75% average decrease in alcohol insoluble polysaccharides.56 Huber53 suggests that pectin biosynthesis occurs during strawberry ripening, with


66


textural differences being due to loose binding to the cell wall that may result in enhanced solubilization during storage. However, changes in polysaccharide solubility are also attributed to enzyme action that promotes fruit softening. This role was demonstrated by Vicente et al.,11 where strawberries were heated to 45°C for 3 hours and stored at 20°C for 2 days, revealing that heated fruit had a firmer texture than unheated fruit due to the inhibition of βglucanase, β-xylosidase, β-glactosidase, and polygalactouronase, while activated pectin methyl esterase (PME) enhanced metal ion cross-linkages in the pectin.

2.3.2

Blueberry

Blueberries, along with strawberries, are among the most popular berries in retail markets and are sold in numerous fresh, frozen, and processed forms for a variety of food applications. Considerable research has been conducted on the phytochemical content and potential health benefits of blueberries, but the fruit is also distinguished for its sweet, aromatic flavor, high dietary fiber, and low fat. The sugar content of ripe blueberries as evaluated by Kader et al.57 and Ayaz et al.58 was an equal ratio of glucose and fructose, providing an indication of invertase activity as the fruit ripened. The concentrations of organic acids were also found to increase during ripening, where quinic, citric, and malic acids predominate in ripe fruit.58 Blueberries are also susceptible to quality deterioration due to the action of oxidase enzymes, where polyphenol oxidase and peroxidase are reported to increase as the fruit ripens.59,60 The cell wall composition and resulting texture of blueberries is an important quality parameter,61 and their smooth skin surface and waxy cuticle experience less damage during harvest in relation to other berries. However, the increased popularity and market demand for blueberries, coupled with the limited availability of labor, has resulted in more machine-harvested fruit.62 Mechanical harvesters are not selective for unripe or decayed fruit and can damage and bruise the fruit; thus the need for a postharvest sorting step to ensure optimal fruit quality.

2.3.3

Blackberry

Numerous parallels exist among the different berry types with regard to factors influencing composition and quality. The quality and organoleptic characteristics of blackberries are also highly dependent on their content and composition of sugars and acids. Kafkas et al.63 evaluated five blackberry lines for sugar, acid, and ascorbic acid composition and found fructose as the primary sugar and malic acid as the primary organic acid, but little or no ascorbic acid was present. Ethylene was found to be influential in blackberry detachment from the plant, but was not influential in fruit ripening, as soluble solids increase and titratable acidity decreases throughout the ripening process.17 The sucrose present in unripe blackberries is also quickly converted to glucose and fructose as the fruit ripens, with often less than 1% remaining in fully ripe fruit. In 11 blackberry lines harvested over different growing seasons and two geographic locations, Reyes-Carmona et al.64


Chapter 2:


67

found that genotypic differences in fruit composition for total acidity, ascorbic acid, soluble solids, and polyphenolics were greater than the effects of season or climate at the harvest sites. An increase in soluble solids content and a decrease in titratable acidity in two varieties of blackberries was observed during ripening that changed the sugar:acid ratio by 10-fold with an overall increase in antioxidant phytochemical composition.65 Blackberries exhibited a 60% decrease in acidity as they ripened from 50% color development to full ripeness, with a subsequent increase in soluble solids and pH, and did not exhibit major changes in solids, acidity, or texture after being held in storage for 7 days at 2°C.66

2.3.4

Raspberry

The optimum quality characteristics for raspberries are similar to those of blackberries as related to an appropriate harvest time to obtain maximal color and flavor in relation to desired fruit texture. The ripening of raspberries was found to be enhanced by ethylene when exogenously applied, but a classical response exhibiting a rapid increase in respiration was not found.67,68 As in other berries, the cell wall composition of raspberries appreciably changes with ripening, with a decrease in both cellulose and pectin observed from enzyme-induced hydrolytic reactions.16 Anthocyanin development in raspberries is also critical for quality considerations, and fruit color is attributable in part to the content and concentration of organic acids, such as citric and malic acid, that affect the visible color characteristics.69 In five raspberry cultivars held for 1 week under controlled atmosphere conditions (10% oxygen and 15% or 31% carbon dioxide), Haffner et al.70 showed that the total soluble solids were unaffected and titratable acidity decreased, but the response of ascorbic acid varied greatly among the cultivars. However, in processed raspberry pulps, ascorbic acid concentrations decreased steadily over time in a temperature-dependent manner that was consistent with the loss of anthocyanins.71

2.4 Conclusion Numerous factors affect the chemical composition and quality characteristics of berry fruits. Despite the numerous changes that occur in the fruit throughout ripening, consumers generally consume fully ripe fruit that are characterized by their high content of simple sugars, such as sucrose, glucose, and fructose, where the sweetness is most commonly counterbalanced by citric and malic acids. The color of the fruit is critical for initial consumer acceptability, but is quickly replaced by sweetness and a firm texture upon consumption. Although there are obvious color, taste, and textural differences among the various berry types, they follow similar trends in development and ripening to produce high-quality fruits that are good sources of numerous vitamins and minerals important for human health. Among fruit cultivars, it is apparent that there are numerous intrinsic factors affecting quality


68


and consumer acceptance that are not fully defined by the chemical content of the fruit. However, without extensive organoleptic evaluations of berry cultivars over numerous growing locations and harvest seasons, chemical analysis of their color substances, sugars, acids, and textural properties will continue to be used to define the quality of berry fruits.

References 1. Beattie, J., Crozier, A., and Duthie, G.G., Potential health benefits of berries, Curr. Nutr. Food Sci., 1, 71, 2005. 2. U.S. Department of Agriculture, USDA National Nutrient Database for Standard Reference, Release 18, March 27, 2006, available at http://www.ars.usda.gov/. 3. Manning, K., Isolation of a set of ripening-related genes from strawberry: their identification and possible relationship to fruit quality traits, Planta, 205, 622, 1998. 4. Shaw, D.V., Genotypic variation and genotypic correlation for sugars and organic acids of strawberries, J. Am. Soc. Hort. Sci., 113, 770, 1988. 5. Souleyre, E.J.F., Iannetta, P.P.M., Ross, H.A., Hancock, R.D., Shepherd, L.V.T., Viola, R., Taylor, M.A., and Davies, H.V., Starch metabolism in developing strawberry (Fragaria × ananassa) fruits, Physiol. Plant., 21, 369, 2004. 6. Viljakainen, S., Visti, A., and Laakso, S., Concentrations of organic acids and soluble sugars in juices from Nordic berries, Acta Agric. Scand., 52, 101, 2002. 7. Montero, T.M., Molla, E.M., Esteban, R.M., and Lopez-Andreu, F.J., Quality attributes of strawberry during ripening, Sci. Hort., 65, 239, 1996. 8. Miesle, T.J., Proctor, A., and Lagrimini, L.M., Peroxidase activity, isoenzymes, and tissue localization in developing highbush blueberry, J. Am. Soc. Hort. Sci., 116, 827, 1991. 9. Wesche-Ebeling, P. and Montgomery, M.W., Strawberry polyphenoloxidase: purification and characterization, J. Food Sci., 55, 1315, 1990. 10. Cano, M.P., Hernandez, A., and De Ancos B., High pressure and temperature effects on enzyme inactivation in strawberry and orange products, J. Food Sci., 62, 85, 1997. 11. Vicente, A.R., Costa, M.L., Martínez, G.A., Chaves, A.R., and Civello P.M., Effect of heat treatments on cell wall degradation and softening in strawberry fruit, Postharvest Biol. Technol., 38, 213, 2005. 12. Rosli, H.G., Cevello, P.M., and Vartinez, G.A., Changes in cell wall composition of three Fragaria × ananassa cultivars with different softening rate during ripening, Plant Physiol. Biochem., 42, 823, 2004. 13. Carpita, N.C. and Gibeaut, D.M., Structural models of primary cell walls in flowering plants: consistency of molecular structure with the physical properties of the walls during growth, Plant J., 3, 1, 1993. 14. Brady, C.J., Fruit ripening, Annu. Rev. Plant Physiol., 38, 155, 1987. 15. Fischer, R.L. and Bennet, A.B., Role of cell wall hydrolases in fruit ripening, Annu. Rev. Plant Physiol., 42, 675, 1991. 16. Stewart, D.S., Iannetta, P.P.M., and Davies, H.V., Ripening-related changes in raspberry cell wall composition and structure, Phytochemistry, 56, 423, 2001. 17. Perkins-Veazie, P., Clark, J.R., Huber, D.J., and Baldwin, E.A., Ripening physiology in ‘Navaho’ thornless blackberries: color, respiration, ethylene production, softening, and compositional changes, J. Am. Soc. Hort. Sci., 125, 357, 2000.


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18. Behall, K. and Reiser, S., Effects of pectin on human metabolism, chemistry, and function of pectins, in Chemistry and Function of Pectins, Mishman, M.L. and Jen, J.J., Eds., American Chemical Society, Washington, DC, 1986, p. 248. 19. Olsson, M.E., Gustavsson, K.-E., Andersson, S., Nilsson, Å., and Duan, R.-D., Inhibition of cancer cell proliferation in vitro by fruit and berry extracts and correlations with antioxidant levels, J. Agric. Food Chem., 52, 7264, 2004. 20. Kader, F., Nicolas, J.-P., and Metche, M., Degradation of pelargonidin 3glucoside in the presence of chlorogenic acid and blueberry polyphenol oxidase, J. Sci. Food. Agric., 79, 517, 1999. 21. Del Pozo-Insfran, D., Duncan, C.E., Yu, K.C., Talcott, S.T., and Chandler, C.K., Polyphenolics, ascorbic acid, and soluble solids concentrations of strawberry cultivars and selections grown in a winter annual hill production system, J. Am. Soc. Hort. Sci., 131, 89, 2006. 22. Jurd, L. and Asen, S., The formation of metal and co-pigment complexes of cyanidin 3-glucoside, Phytochemistry, 5, 1263, 1966. 23. Garzon, G.A. and Wrolstad, R.E., Comparison of the stability of pelargonidinbased anthocyanins in strawberry juice and concentrate, J. Food Sci., 67, 1288, 2002. 24. Garcia-Viguera, C., Zafrilla, P., Artes, F., Romero, F., Abellan, P., and TomasBarberan, F.A., Color and anthocyanin stability of red raspberry jam, J. Sci. Food Agric., 78, 565, 1998. 25. Talcott, S.T., Brenes, C.H., Pires, D.M., and Del Pozo-Insfran, D., Phytochemical stability and color retention of copigmented and processed muscadine grape juice, J. Agric. Food Chem., 51, 957, 2003. 26. Iacobucci, G.A. and Sweeny, J.G., The chemistry of anthocyanins and related falvylium salts, Tetrahedron, 23, 1057, 1983. 27. Krifi, B. and Metche, M., Degradation of anthocyanins from blood orange juices, Int. J. Food Sci.. Technol., 35, 275, 2000. 28. Timberlake, C., Metallic components of fruit juices: III. Oxidation and stability of ascorbic acid in model systems resembling blackcurrant juice, J. Sci. Food Agric., 11, 258, 1960. 29. Lee, S.K. and Kader, A.A., Preharvest and postharvest factors influencing vitamin C content of horticultural crops, Postharvest Biol. Technol., 20, 207, 2000. 30. Ford, A., Hansen, K., Herrington, M., Moisander, J., Nottingham, S., Prytz, S., and Zorin, M., Subjective and objective determination of strawberry quality, Acta Hort. (ISHS), 439, 319, 1997. 31. Cordenunsi, B.R., Nascimento, J.R.O., Genovese, M.I., and Lajolo, F.M., Influence of cultivar on quality parameters and chemical composition of strawberry fruits grown in Brazil, J. Agric. Food Chem., 50, 2581, 2002. 32. Olsson, M.E., Ekvall, J., Gustavsson, K.-E., Nilsson, J., Pillai, D., Sjöholm, I., Svensson, U., Akesson, B., and Nyman, M.G.L., Antioxidants, low molecular weight carbohydrates, and total antioxidant capacity in strawberries (Fragaria × ananassa): effects of cultivar, ripening, and storage, J. Agric. Food Chem., 52, 2490, 2004. 33. Chandler, C.K., Herrington, M., and Slade, A., Effect of harvest date on soluble solids and titratable acidity in fruit of strawberry grown in a winter, annual hill production system, Acta Hort., 626, 353, 2003. 34. Shamaila, M., Baumann, T.E., Eaton, G.W., Powrie, W.D., and Skura, B.J., Quality attributes of strawberry cultivars grown in British Columbia, J. Food. Sci., 3, 696, 720, 1992.


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Berry fruit: Value-added products for health promotion 35. Hakala, M., Lapvetelainen, A., Huopalahti, R., Kallio, H., and Tahvonen, R., Effects of varieties and cultivation conditions on the composition of strawberries, J. Food Comp. Anal., 16, 67, 2003. 36. Wang, H., Cao, G., and Prior, R.L., Total antioxidant capacity of fruits, J. Agric. Food Chem., 44, 701, 1996. 37. Hellman, E.W. and Travis, J.D., Growth inhibition of strawberry at high temperatures, Adv. Strawberry Prod., 7, 36, 1998. 38. Wang, S.Y. and Camp, M.J., Temperatures after bloom affect plant growth and fruit quality of strawberry, Sci. Hort., 85, 183, 2000. 39. Wang, S.Y. and Zheng, W., Effect of plant growth temperature on antioxidant capacity in strawberry, J. Agric. Food Chem., 49, 4977, 2001. 40. Kader, A.A., Fruit maturity, ripening, and quality relationships, Acta Hort. (ISHS), 485, 203, 1999. 41. Garcia, J.M., Herrera, S., and Morilla, A., Effects of postharvest dips in calcium chloride on strawberry, J. Agric. Food Chem., 44, 30, 1996. 42. Sturm, K., Koron, D., and Stampar, F., The composition of fruit of different strawberry varieties depending on maturity stage, Food Chem., 83, 417, 2003. 43. Perez, A.G., Olias, R., Espada, J., Olias, J.M., and Sanz, C., Rapid determination of sugars, non-volatile acids and ascorbic acids in strawberry and other fruits, J. Agric. Food Chem., 45, 3545, 1997. 44. Kafkas, E., et al., Quality characteristics of strawberry genotypes at different maturation stages, Food Chem., 100, 122, 2007. 45. Cordenunsi, B.R., Nascimento, J.R.O., and Lajolo, F.M., Physico-chemical changes related to quality of five strawberry fruit cultivars during cool-storage, Food Chem., 83, 167, 2003. 46. Agar, I.T., Streif, J., and Bangerth, F., Effect of high CO2 and controlled atmosphere (CA) on the ascorbic and dehydroascorbic acid content of some berry fruits, Postharvest Biol. Technol., 11, 47, 1997. 47. Pelayo, C., Ebeler, S.E., and Kader, A.A., Postharvest life and flavor quality of three strawberry cultivars kept at 5°C in air or air + 20 kPa CO2, Postharvest Biol. Technol., 27, 171, 2003. 48. Castro, I., Gonçalves, O., Teixeira, J.A., and Vicente, A.A., Comparative study of Salva and Camorosa strawberries for the commercial market, J. Food Sci., 67, 2132, 2002. 49. Nunes, M.C.N., Brecht, J.K., Morais, A.M.M.B., and Sargent, S.A., Physical and chemical quality characteristics of strawberries after storage are reduced by a short delay to cooling, Postharvest Biol. Technol., 6, 17, 1995. 50. Nogata, Y., Ohta, H., and Voragen, A.G.J., Polygalactouronase in strawberry fruit, Phytochemistry, 34, 867, 1993. 51. Knee, M., Sargent, J.A., and Osborne, D.J., Cell wall metabolism in developing strawberry fruit, J. Exp. Bot., 28, 377, 1977. 52. Manning, K., Soft fruits, in Biochemistry of Fruit Ripening, Seymour, G.B., Taylor, J.E., and Tucker, G.A., Eds., Chapman & Hall, London, 1993, p. 347. 53. Huber, D.J., Strawberry fruit softening: the potential roles of polyuronides and hemicelluloses, J. Food Sci., 49, 1310, 1984. 54. Schieber, A., Fügel, R., Henke, M., and Carle, R., Determination of the fruit content of strawberry fruit preparations by gravimetric quantification of hemicellulose, Food Chem., 91, 365, 2005. 55. Legentil, A., Guichard, I., Piffaut, B., and Haluk, J., Characterization of strawberry pectin extracted by chemical means, Lebensm. - Wiss. + Technol., 28, 569, 1995.


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56. Koh, T.H. and Melton, L.D., Ripening-related changes in cell wall polysaccharides of strawberry cortical and pith tissues, Postharvest Biol. Technol., 26, 23, 2002. 57. Kader, F., Rovel, B., and Metche, M., Role of invertase in sugar content in highbush blueberries (Vaccinium corymbosum, L.), Lebensm. - Wiss. + Technol., 26, 593, 1993. 58. Ayaz, F.A., Kadioglu, A., Bertoft, E., Acar, C., and Turna, I., Effect of fruit maturation on sugar and organic acid composition in two blueberries (Vaccinium arctostaphylos and V. myrtillus) native to Turkey, N. Z. J. Crop Hort. Sci., 29, 137, 2001. 59. Miesle, T.J., Proctor, A., and Lagrimini, L.M., Peroxidase activity, isoenzymes, and tissue localization in developing highbush blueberry, J. Am. Soc. Hort. Sci., 116, 827, 1991. 60. Kader, F., Rovel, B., Girardin, M., and Metche, M., Mechanism of browning in fresh highbush blueberry fruit (Vaccinium corymbosum L): partial purification and characterisation of blueberry polyphenol oxidase, J. Sci. Food Agric., 73, 513, 1997. 61. Silva, J.L., Marroquin, E., Matta, F.B., Garner, J.O., and Stojanovic, J., Physicochemical, carbohydrate and sensory characteristics of highbush and rabbiteye blueberry cultivars, J. Sci. Food Agric., 85, 1815, 2005. 62. Mainland, C.M., Kushman, L.J., and Ballinger, W.E., The effect of mechanical harvesting on yield, quality of fruit, and bush damage of highbush blueberry, J. Am. Soc. Hort. Sci., 100, 129, 1975. 63. Kafkas, E., Kosar, M., Turemis, N., and Baser, K.H.C., Analysis of sugars, organic acids and vitamin C contents of blackberry genotypes from Turkey, Food Chem., 97, 732, 2006. 64. Reyes-Carmona, J., Yousef, G.G., Martinez-Peniche, R.A., and Lila, M.A., Antioxidant capacity of fruit extracts of blackberry (Rubus sp.) produced in different climatic regions, J. Food Sci., 70, 497, 2005. 65. Siriwoharn, T., Wrolstad, R.E., Finn, C.E., and Pereira, C.B., Influence of cultivar, maturity, and sampling on blackberry (Rubus L. hybrids) anthocyanins, polyphenolics, and antioxidant properties, J. Agric. Food Chem., 52, 8021, 2004. 66. Perkins-Veazie, P., Collins, J.K., and Clark, J.R., Changes in blackberry fruit quality during storage, Acta Hort., 352, 87, 1993. 67. Perkins-Veazie, P. and Nonnecke, G., Physiological changes during ripening of raspberry fruit, HortScience, 27, 331, 1992. 68. Iannetta, P.P.M., van den Berg, J., Wheatley, R.E., McNicol, R.J., and Davies, H.V., The role of ethylene and cell wall modifying enzymes in raspberry (Rubus idaeus) fruit ripening, Physiol. Plant., 105, 338, 1999. 69. Ancos, B., Gonzales, E., and Cano, M.P., Differentiation of raspberry varieties according to anthocyanin composition, Z. Lebensm. Unters. Forsch. A, 208, 33, 1999. 70. Haffner, K., Rosenfeld, H.J., Skrede, G., and Laixin, W., Quality of red raspberry Rubus idaeus L. cultivars after storage in controlled and normal atmospheres, Postharvest Biol. Technol., 24, 279, 2002. 71. Ochoa, M.R., Kesseler, A.G., Vullioud, M.B., and Lozano, J.E., Physical and chemical characteristics of raspberry pulp: storage effect on composition and color, Lebensm. − Wiss. + Technol., 32, 149, 1999. 72. Lara, I., Garcia, P., and Vendrell, M., Modifications in cell wall composition after cold storage of calcium-treated strawberry (Fragaria × ananassa Duch.) fruit, Postharvest Biol. Technol., 24, 331, 2004.


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Berry fruit: Value-added products for health promotion 73. Rotundo, A., Benvenuti, S., Vampa, G., Melegari, M., and Soragni, F., Quality and yield of Ribes and Rubus cultivars grown in southern Italy hilly locations, Phytother. Res., 12(suppl. 1), S135, 1998. 74. Toivanen, P.M.A., Kempler, C., Escobar, S., and Emond, J., Response of three raspberry cultivars to different modified atmosphere conditions, Acta Hort. (ISHS), 505, 33, 1999. 75. Benvenuti, S., Pellati, F., Melegari, M., and Bertelli, D., Polyphenols, anthocyanins, ascorbic acid, and radical scavenging activity of Rubus, Ribes, and Aronia, J. Food Sci., 69, 164, 2004.


chapter 3

Berry fruit phytochemicals Luke R. Howard and Tiffany J. Hager Contents 3.1 Introduction ................................................................................................. 74 3.2 Phenolic composition of berry fruit......................................................... 74 3.2.1 Phenolic acids and their derivatives........................................... 74 3.2.2 Ellagitannins and ellagic acid derivatives ................................. 76 3.2.3 Anthocyanins .................................................................................. 79 3.2.4 Flavonols.......................................................................................... 85 3.2.5 Proanthocyanidins.......................................................................... 87 3.3 Phenolic content of berry fruit ................................................................. 89 3.3.1 Raspberry......................................................................................... 89 3.3.2 Strawberry ....................................................................................... 91 3.3.3 Blackberry........................................................................................ 92 3.3.4 Blueberry ......................................................................................... 92 3.3.5 Antioxidant capacity of berry fruit ............................................. 93 3.3.6 Relationships between phenolic classes and antioxidant capacity............................................................... 96 3.3.7 Contribution of individual flavonoids to antioxidant capacity .................................................................. 96 3.4 Other phytochemicals in common berry fruit ....................................... 97 3.4.1 Lignans............................................................................................. 97 3.4.2 Sterols ............................................................................................... 98 3.4.3 Stilbenes ........................................................................................... 98 3.5 Conclusion.................................................................................................... 98 References .............................................................................................................99

73


74


3.1 Introduction Common berry fruits, including blackberries (Rubus sp.), strawberries (Fragaria × ananassa), and black raspberries (Rubus occidentalis), red raspberries (Rubus idaeus), and blueberries (Vaccinium spp.), have long been appreciated for their dessert-like quality. Berry fruits have appealing colors imparted by anthocyanin pigments that range from red to purple to black, in addition to unique tastes and aromatic notes. They contain important micronutrients such as vitamin C and folic acid are considered excellent sources of dietary fiber. Recently much attention has focused on natural plant compounds with bioactive properties called phytochemicals that may afford protection against chronic diseases. Berry fruits are a rich source of phytochemicals, in particular phenolic compounds, which are reported to have a range of potential anti–cancer and antiheart disease that were reviewed by Beattie et al.1, and are the subject of Chapter 6.

3.2 Phenolic composition of berry fruit Berry fruit are a rich source of polyphenols, especially flavonoids (anthocyanins, flavonols, flavan-3-ols, and proanthocyanidins) and ellagitannins. Many hydroxybenzoic and hydroxycinnamic acid derivatives are also present in the fruit. Due to genetic differences, which are most apparent in variations in fruit color, berry fruit vary significantly in both phenolic composition and content.

3.2.1

Phenolic acids and their derivatives

The predominant phenolic acids in berry fruit are the hydroxybenzoic and hydroxycinnamic acids (Figure 3.1). Although ellagic acid is a hydroxybenzoic acid, most of the ellagic acid in berries is present in forms known as ellagitannins, which constitute a separate class of phenolics. The hydroxybenzoic and hydroxycinnamic acids rarely occur as free acids, but are commonly found in conjugated forms as esters and glycosides. They may be found in the vacuole in soluble form or be insoluble as a result of linkage with cell wall polysaccharides. Phenolic acids are commonly analyzed by high performance liquid chromatography (HPLC) after an acid or alkaline hydrolysis step. Although this technique has allowed researchers to identify the major phenolic acid—aglycones—in berries, limited information is available on the native ester and glycoside forms present in the fruit. In strawberries, p-coumaric,2–5 t-cinnamic,4,6 p-hydroxybenzoic,4,5 caffeic,4 vanillic,4 protocatechuic,4 and 5-caffeoylquinic (chlorogenic acid)4 acids have been identified following acid or base hydrolysis. Specific hydroxybenzoic and hydroxycinnamic acids identified in the fruit include glucose esters of caffeic,7 p-coumaric,7,8 ferulic,7 and gallic acids,7 and the β-D-glucosides of p-coumaric7,8 and p-hydroxybenzoic acids.7 The glucose ester of p-coumaric acid is one of the major phenolic acids present in the fruit,7,9–11 and is uniformly


Chapter 3:

Berry fruit phytochemicals

75

A.

R3 O

R2 OH

R1 Hydroxybenzoic Acids Acids p-Hydroxybenzoic Acid Protocatechuic Acid Vanillic Acid Syringic Acid Gallic Acid

R1 H H CH 3O CH 3O OH

R2 OH OH OH OH OH

R3 H OH H CH 3O OH

B.

R3 O

R2 R1 Hydroxycinnamic Acids Acid m-Coumaric p-Coumaric Caffeic Ferulic Sinapic Caffeoylquinic Coumaroylquinic

R4

R1 OH H H CH 3O CH 3O H OH

R2 H OH OH OH OH OH H

R3 H H OH H CH 3O OH H

R4 OH OH OH OH OH Quinic acid Quinic acid

Figure 3.1 Structures of various (A) hydroxybenzoic and (B) hydroxycinnamic acids.

distributed throughout the skin and flesh.10 Other predominant phenolic acids include 5-caffeoylquinic and p-hydroxybenzoic acids.4 In blackberries, the hydroxybenzoic acids—p-hydroxybenzoic, protocatechuic, gallic, gentisic, salicylic, and vanillic—are present in free, ester, and glycoside forms, with the ester and glycoside forms of salicylic acid predominating.12 The hydroxycinnamic acids—caffeic, m-coumaric, p-coumaric, and ferulic—are also present in free, ester, and glycoside forms, with the ester forms of m-coumaric, 3,4-dimethoxycinnamic, and hydroxycaffeic, and the glycoside forms of 3,4-dimethoxycinnamic and hydroxycaffeic predominating.12 Esters and glycosides account for 53.1% and 43.6%, respectively, of total phenolic acids, while free acids account for only 3.3%.12 Specific hydroxybenzoic and hydroxycinnamic acid derivatives identified in blackberries include chlorogenic acid (5-caffeoylquinic acid), neochlorogenic acid (3caffeoylquinic acid), 3-p-coumaroylquinic acid, 3-feruolylquinic acid, glucose esters of caffeic, p-coumaric, ferulic, and gallic acids, and the β-D-glucosides of p-coumaric, p-hydroxybenzoic, and protocatechuic acids.7 The phenolic acids identified in red raspberries following acid or base hydrolysis include p-coumaric,3,4 caffeic,3,4 ferulic,3 gallic,3 5-caffeoylquinic,4


76


p-hydroxybenzoic,4 vanillic4 and protocatechuic4 acids. Specific phenolic acid derivatives identified in red raspberries include 5-p-coumaroylquinic acid; glucose esters of caffeic, p-coumaric, and ferulic acids; and the β-D-glucosides of caffeic, p-coumaric, ferulic, and p-hydroxybenzoic acids.7 Raspberries are unique compared to other berries because they contain appreciable levels of p-hydroxybenzoic acid glucoside.7 In blueberries, the hydroxybenzoic acids—gentisic, gallic, protocatechuic, salicylic, syringic, and vanillic—are present in free, ester, and glycoside forms, with the ester and glycoside forms of salicylic acid predominating.12 The hydroxycinnamic acids—caffeic, m-coumaric, o-coumaric, p-coumaric, and ferulic—are also present in free, ester, and glycoside forms, with sinapic and 3-4-dimethoxycinnamic acids present in the ester and glycoside forms, and dihydroxycinnamic acid present in the ester form.12 According to Zadernowski et al.,12 p-coumaric acid is the predominant hydroxycinnamic acid derivative in the ester form, excluding chlorogenic acid (5-O-caffeoylquinic acid), which was not identified in the study due to degradation during alkaline hydrolysis, while 3,4-dimethoxycinnamic and hydroxycaffeic acids are the predominant glycosides. Glycosides and esters account for 56.7% and 40.7%, respectively, of total phenolic acids, while free acids account for only 2.6%.12 Chlorogenic acid (5-O-caffeoylquinic acid) is the predominant hydroxycinnamic acid ester found in blueberries and is the single most abundant polyphenolic compound found in the fruit.13,14 Besides chlorogenic acid, specific hydroxybenzoic and hydroxycinnamic acid derivatives identified in blueberries include neochlorogenic acid (3-caffeoylquinic acid), 5-p-coumaroylquinic, 5-feruoylquinic acid, and the β-D-glucosides of caffeic, p-coumaric, ferulic, p-hydroxybenzoic, protocatechuic, and gallic acids.7

3.2.2

Ellagitannins and ellagic acid derivatives

Berries are a rich source of hydrolysable tannins, specifically ellagitannins, which vary significantly in molecular weight (Figure 3.2). Berry ellagitannins consist of a glucose core esterified with hexahydroxydiphenic acid (HHDP). Upon acid or base hydrolysis of ellagitannins, HHDP spontaneously rearranges to a dilactone form known as ellagic acid. In addition to ellagitannins, berry fruit also contain ellagic acid in free, acylated, and glycosylated forms. Because of the diversity of ellagitannins and ellagic acid derivatives in berries, many studies have reported the total ellagic content of berries following acid hydrolysis, with results expressed as ellagic acid equivalents. Recently several ellagitannins and ellagic acid derivatives have been identified in berries using high performance liquid chromatography mass spectrometry (HPLC-MS). In red raspberries, the ellagitannins lambertianin-C and sanguiin H-6 have been identified in several studies,15–17 along with sanguiin H-10.15,17 The ellagic acid derivatives identified include the 4-arabinoside,18 4-acetylxyloside, and 4-acetylarabinoside.15,17,18 Based on peak intensity and mass counts, sanguiin H-6 appears to be the predominant ellagitannin, followed by

O

OH

OH

HO O O

O

(a)

OH

OH

Ellagic acid (MW: 302.20)

HO

O

HO HO

Ellagitannin Casuarictin Potentillin Pedunculagin

HO

HO O

O

OH

O O O

O

R1 -OG -OG OH

HO

Figure 3.2 Structures of gallic acid, ellagic acid, and various ellagitannins.

Gallic acid (MW: 170.12)

HO

OH

HO

OH O

OH

Molecular Weight 934.69 934.69 782.58

O R1

OH

Chapter 3:

HO

HO


Berry fruit phytochemicals 77


78

Berry fruit: Value-added products for health promotion OH HO

OH

OH OH

OH HO

OH

OH

O O O

HO

O

OO O

HO

O

O O

HO HO

HO

OH

OH O O

HO OO O

OH

O OO

OH

HO HO

O O

HO

OH

O

O

OH

O

OH

OH O

HO HO

OH

OH

OH OH

O O

HO O O O

HO

OH

OH O

OH

OO

OH

O

O O

HO HO

Sanguiin H-6 (MW:1871.31)

OH

O O

O O O

HO

OH HO

OH O

HO

O O

OH OH OH

OH

OH

OH

OH O

HO

OH

OH

O

OH O HO

OH

OH

OO

O

HO HO

OH

O

O O O

HO

OH

O

O

HO

OH O

O

O

OH

OH OH

HO

OH

Lambertianin C (MW: 2805.96)

Figure 3.2 (Continued).

lambertianin-C.15–17 Ellagic acid arabinoside is the major ellagic acid derivative in the fruit (2 mg/100 g fresh weight [FW]), with less than 1 mg/100 g FW of 4-acetylxyloside and 4-acetylarabinoside reported.18 Ellagitannins decrease markedly as fruit ripen,16 and different varieties have been shown to vary significantly in concentration.16,19 The ellagitannins identified in strawberries include casuarictin,20 sanguiin H-6, and HHDP.8 Määtä-Riihinen et al.19 tentatively identified three peaks as ellagitannins based upon HPLC-MS data and reported a total concentration of 18 mg/100 g FW. They observed no ellagic acid derivatives in the fruit, but found ellagic acid in free form at a concentration of 4 mg/100 g FW. In contrast, Seeram et al.8 identified two peaks as isomeric forms of methyl ellagic acid pentose conjugates and tentatively identified three additional peaks as ellagic acid-based compounds. Besides sanguiin H-6 and casuarictin, potentillin and pedunculagin have been identified in strawberry leaves,21 suggesting they may be present in the fruit. Although achenes contain higher levels of ellagic acid than pulp,11,22,23 the achenes only account for about 1% to 5% of the fruit mass. Accordingly, 95% of the ellagic acid resides in the pulp, while only 4% is contained in the seeds.24 The ellagitannins identified in blackberry fruit include potentillin and phenolic ester T1, which appears to be sanguiin H-6 based upon its mass spectral data.25 Pedunculagin and casuaricitin have been identified in blackberry


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79

leaves and shoots, suggesting they may be present in the fruit.25 The ellagitannins and ellagic acid derivatives in blackberries are present predominantly in the seeds26 and the fruit contain much higher levels of ellagitannins (51.1 to 68.2 mg/100 g) than ellagic acid derivatives (1.2 to 3.0 mg/100 g).27 The majority of ellagic acid is found in the seeds (88%), while only 12% is found in the pulp.24 Ellagitannins are reported to decrease in concentration during fruit ripening.28 Ellagitannins and ellagic acid derivatives have not been identified in blueberries, which is not surprising considering the low concentrations of total ellagic acid found in the fruit following acid hydrolysis.3 Apparently Vaccinium sp. lack the genetic capacity to synthesize ellagitannins and ellagic acid derivatives.

3.2.3

Anthocyanins

The major anthocyanidins that may be found in berry fruit differ in the number and position of their hydroxyl and methoxyl groups on the B ring (Figure 3.3). Anthocyanidins rarely occur in nature because of their instability. When glycosylated with one or more sugar moieties, they are called anthocyanins, with single sugars attached at the C3 position of the flavan structure. 3'

A.

4'

2' 7

8

O 2

5' 6'

6

3 5

4

R1

B.

R1 OH

HO

O

R2

OH

+

HO

O

OH OH

OH

O

OH

Flavonol Flavonol Kaempferol Quercetin Myricetin Isorhamnetin Larycitrin Syringetin

R2

Anthocyanidin Anthocyanidin Pelargonidin Cyanidin Delphinidin Peonidin Petunidin Malvidin

R1 H OH OH OCH3 OCH3 OCH3

R2 H H OH H OH OCH3

Figure 3.3 Structures of (A) the flavonoid skeleton and (B) various flavonols and anthocyanidins.


80


Glucose, galactose, arabinose, xylose, and rhamnose are the most common sugars attached to berry anthocyanins. Common diglycosides found in various berry fruit that may be attached at the C3 position of the flavan ring or C5 position of the A ring include rutinose (glucose, rhamnose), sambubiose (glucose, xylose), and sophorose (glucose, glucose). The sugar moieties of berry anthocyanins can be acylated with aliphatic (acetic, malonic, succinic, oxalic) acids. The variety of glycosidic and aliphatic substitutions leads to a wide range of colors in the fruit and can be quite useful in taxonomic classification and the detection of adulterations in fruit juices. The anthocyanins in berry fruit have been well characterized by HPLC-MS (Table 3.1). Strawberry anthocyanins are present almost exclusively in nonacylated form (99%).29 Most of the anthocyanins exist as monoglycosides (93%), with the balance (7%) present as diglycosides.29 The anthocyanins identified in strawberries include the 3-glucosides and 3-rutinosides of cyanidin and perlargonidin, and two acylated derivatives of pelargonidin, 3-(malonyl) glucoside and 3-(6-acetyl)-glucoside,30 as well as a minor peak tentatively identified as pelargonidin 3-diglucoside.8 Previously Wang et al.9 identified two additional acylated compounds, cyanidin 3-(succinoyl) glucoside and pelargonidin 3-(succinoyl)glucoside. Strawberries are also reported to contain small quantities of four flavonol-anthocyanin complexes comprised of pelargonidin 3-glucoside connected to catechin, epicatechin, afzelechin, and epiafzelechin via α 4 → 8 linkages.31 The novel aglycone 5-carboxypyranopelargonidin has also been isolated in small amounts from the fruit.32 Pelargonidin 3-glucoside is the predominant anthocyanin in strawberries, accounting for more than 70% of total anthocyanins,9,11,33 and is largely responsible for the red color of the fruit. The strawberry flesh contains higher levels of pelargonidin 3-glucoside and pelargonidin 3-rutinoside than the achenes, while the achenes contain higher levels of cyanidin 3-glucoside and cyanidin 3-(malonyl) glucoside.11 Cyanidin derivatives predominate in blackberries with various sugar (glucose, arabinose, rutinose, and xylose) moieties attached at C3. The anthocyanins are present predominately in nonacylated form (94%).29 The anthocyanins exist mostly as monoglycosides (90%), with the balance (10%) present as diglycosides.29 Three acylated derivatives—cyanidin 3-(3-malonyl) glucoside, cyanidin 3-(6-malonyl) glucoside, and cyanidin 3-dioxaloylglucoside—as well as the 3-glucoside of pelargonidin have also been identified in the fruit.30 Cyanidin 3-dioxaloylglucoside, a novel zwitterion first identified in Evergreen blackberry (Rubus laciniatus), appears to be a unique anthocyanin in blackberry fruit.34 Several studies have reported the anthocyanin distribution in blackberry genotypes.35,36 The distribution of anthocyanins in 51 blackberry samples ranged from 44% to 95% for cyanidin 3-glucoside, trace to 53% for cyanidin 3-rutinoside, not detected to 11% for cyanidin 3-xyloside, trace to 5% for cyanidin 3-(malonyl) glucoside, and not detected to 15% for cyanidin 3-dioxaloylglucoside.35 In the study by Cho et al.,36 the anthocyanin distribution in six blackberry genotypes ranged from 75% to 84% for cyanidin 3-glucoside, 1% to 12% for cyanidin 3-rutinoside, 4% to 8%

[M+] 581 449 727 727 595 433 579 609

449 419 595 433 535 463 419 535 593

611 611 757 449 581

Black raspberry Cyanidin 3-sambubioside Cyanidin 3-glucoside Cyanidin 3-xylosylrutinoside Cyanidin 3-sambubioside-5-rhamnoside Cyanidin 3-rutinoside Pelargonidin 3-glucoside Pelargonidin 3-rutinoside Peonidin 3-rutinoside

Blackberry Cyanidin 3-glucoside Cyanidin 3-arabinoside Cyanidin 3-rutinoside Pelargonidin 3-glucoside Cyanidin 3-(3-malonyl)-glucoside Peonidin 3-glucoside Cyanidin 3-xyloside Cyanidin 3-(6-malonyl) glucoside Cyanidin 3-dioxaloylglucoside

Red raspberry Cyanidin 3,5-diglucoside Cyanidin 3-sophoroside Cyanidin 3-(2,6-glucosylrutinoside) Cyanidin 3-glucoside Cyanidin 3-sambubioside

m/z

449/287 287 611/287 287 449/287

15 √ √ √ √ √

29 √ √ √ √ √ √ √ √ √

√ √ √ √ √

29 √ √

√ √ √

√ √ √

√

√

16 √ √ √ √

√

√

29

26 √

31 √

√

√

30 √ √ √

√ √ √

19

√

√

√

√

32 √

√

√

√

√

33 √

(continued)

Chapter 3:

287 287 449/287 271 287 301 287 449/287 287

Fragments 287 287 581/287 581/433/287 449/287 271 433/271 463/301

Reference

Table 3.1 Composition and Mass Spectral Data of Anthocyanin Glycosides in Common Berry Fruit



595 727 595 741 433 579 757 727

449 595 433 579 519 475 533 * 545 [M+] 465 465 449 435 449 479

Pelargonidin 3-sophoroside Cyanidin 3-xylosylrutinoside Cyanidin 3-rutinoside Pelargonidin 3-(2,6-glucosylrutinoside) Pelargonidin 3-glucoside Pelargonidin 3-rutinoside Cyanidin 3-sophoroside-5-rhamnoside Cyanidin 3-sambubioside-5-rhamnoside

Strawberry Cyanidin 3-glucoside Cyanidin 3-rutinoside Pelargonidin 3-glucoside Pelargonidin 3-rutinoside Pelargonidin 3-(malonyl)glucoside Pelargonidin 3-(6”-acetyl)glucoside Pelargonidin 3-(succinyl)glucoside Cyanidin 3-(succinyl)glucoside Pelargonidin 3-diglucoside

Blueberry Delphinidin 3-galactoside Delphinidin 3-glucoside Cyanidin 3-galactoside Delphinidin 3-arabinoside Cyanidin 3-glucoside Petunidin 3-galactoside

m/z

Fragments 303 303 287 303 287 317 29 √ √ √ √ √ √

35 √ √ √ √ √ √

√ √ √

√ √

√

11 √

√ √ √ √

√

9 √

√ √ √ √ √ √

36 √ √ √ √ √ √

29 √ √ √ √ √ √

√

√ √ √

37 √ √ √ √ √ √

√

√ √

33 √ √ √ √ √ √

√ √ √

19 √

√ √

34 √

√ √

√

38 √ √ √ √ √ √

√

√ √

8 √

39 √ √ √ √ √ √

13 √ √ √ √ √ √

82

287 449/287 271 433/271 433/271 271 271 * 433/271

324/271 581/287 287 595/271 271 271 611/433/287 581/433/287

Reference

Table 3.1 Composition and Mass Spectral Data of Anthocyanin Glycosides in Common Berry Fruit (Continued)



419 479 463 449 463 493 493 463 535 491 535 449 551 579 507 505 491 535 521 505 535 * * 433 * 287 317 301 317 301 331 331 331 287 287 331 317 303 331 303 301 287 331 317 301 331 * * 301 *

√ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √

√ √ √ √ √

√

√

√

√

√

√ √ √ √ √ √ √ √ √

√ √ √

√ √ √

√ √ √ √ √ √ √ √

√ √ √ √ √ √ √ √ √

√

√

√ √ √ √

√

√ √ √ √ √ √ √ √

√

√ √ √ √ √ √ √ √

√

√ √ √

√ √ √ √

√

√ √ √

√ √ √

Chapter 3:

* No mass spectral data reported.

Cyanidin 3-arabinoside Petunidin 3-glucoside Peonidin 3-galactoside Petunidin 3-arabinoside Peonidin 3-glucoside Malvidin 3-galactoside Malvidin 3-glucoside Malvidin 3-arabinoside Cyanidin 3-(malonyl)glucoside Cyanidin 3-(6”-acetyl)galactoside Malvidin acetyl hexoside Petunidin Pentoside Delphinidin 3-(malonyl)glucoside Malvidin 3-(malonyl)glucoside Delphinidin 3-(6”-acetyl)glucoside Peonidin 3-(6”-acetyl)galactoside Cyanidin 3-(6”-acetyl)glucoside Malvidin 3-(6”-acetyl)galactoside Petunidin 3-(6”-acetyl)glucoside Peonidin 3-(6”-acetyl)glucoside Malvidin 3-(6”-acetyl)glucoside Cyanidin 3-(acetyl)arabinoside Petunidin 3-(acetyl)galactoside Peonidin 3-arabinoside Delphinidin 3-(acetyl)galactoside




84


for cyanidin 3-xyloside, 2% to 3% for cyanidin 3-(malonyl) glucoside, and 3% to 8% for cyanidin 3-dioxaloylglucoside. The effect of genetics on anthocyanin composition was also observed in a study by Reyes-Carmona et al.37 They found that a wild cultivar contained a larger peak of cyanidin 3-rutinoside, but a lower peak of cyanidin 3-glucoside than the cultivar Comanche. They also found that Marion and Evergreen berries had lower peaks of cyanidin glycosides, but contained a peak identified as malvidin 3-glucoside that was not present in the wild and Comanche cultivars. Similar to blackberries, cyanidin derivatives also predominate in red and black raspberries,15,19,38 but their profiles are quite distinct due to genetic differences. The anthocyanins in black and red raspberries are present exclusively in nonacylated form.29 In terms of the degree of glycosylation, the percentages of mono-, di-, and triglycosides in black and red raspberries are reported as 13%, 64%, and 23%, and 22%, 52%, and 26%, respectively.29 The seven anthocyanins identified in red raspberries include cyanidin 3-sophoroside, cyanidin 3-glucoside, cyanidin 3-rutinoside, pelargonidin 3-glucoside, pelargonidin 3-rutinoside, cyanidin 3-sophoroside-5-rhamnoside, and cyanidin 3-sambubioside-5-rhamnoside.30 Black raspberries contain all of the anthocyanins found in red raspberries, with the exception that they lack cyanidin 3-sophoroside, but contain cyanidin 3-sambubioside and peonidin 3-rutinoside.30 Raspberries are unique in that both red and black fruit contain the trisaccharide cyanidin 3-sambubioside-5-rhamnoside, while cyanidin 3-sophoroside-5-rhamnoside is present only in red fruit.30 Cyanidin 3-sophoroside is the major anthocyanin found in red raspberries, followed by cyanidin 3-sophoroside-5-rhamnoside and cyanidin 3-glucoside, while cyanidin 3-rutinoside is the predominant anthocyanin found in black raspberries, followed by cyanidin 3-sambubioside-5-rhamnoside and cyanidin 3-glucoside. Blueberries are a unique berry fruit in that they contain the monoglycosides (glucosides, galactosides, and arabinosides) of delphinidin, cyanidin, petunidin, peonidin, and malvidin. Due to the diversity in monoglycosides and acylation with aliphatic acids such as acetic and malonic, more than 25 anthocyanins have been identified in blueberries.30,39,40 The anthocyanin composition and content of blueberries is influenced by genetics. According to Cho et al.,36 the percentage distribution of monomeric anthocyanins in five blueberry genotypes was delphinidin (27% to 40%), malvidin (22% to 33%), petunidin (19% to 26%), cyanidin (6% to 14%), and peonidin (1% to 5%), while the distribution of acylated anthocyanins ranged from nondetectable to 9%. In terms of the percent distribution of anthocyanin glycosides, galactosides accounted for 60% to 67%, arabinosides 26% to 32%, and glucosides 2% to 29%. Interestingly, four Southern highbush genotypes contained high levels of galactosides and arabinosides, and low levels of glucosides, while Bluecrop, a northern highbush genotype, contained similar levels of the three glycosides, indicating that synthesis of transferases involved in the attachment of specific sugar moieties is genetically coordinated. The effect of genetics on the composition of acylated anthocyanins was reported by Gao and Mazza.39 They found that 7 of 10 lowbush blueberry genotypes did not


Chapter 3:


85

vary significantly in anthocyanin composition, but three genotypes had practically no acylated anthocyanins, suggesting that the synthesis of transferases involved in the attachment of acyl groups is also under genetic control. The percent distribution of anthocyanidins was shown to vary among commercially important blueberry species, with cyanidin, delphinidin, malvidin, peonidin, and petunidin accounting for 31%, 43%, 5%, 7%, and 14% of total anthocyanins in bilberry, 14%, 38%, 24%, 7%, and 16% in lowbush blueberry, and 6%, 41%, 32%, 1%, and 19% in highbush blueberry, respectively.40 The anthocyanins in blueberries are present predominantly in the skin, with the exception of bilberry, in which they reside in both the skin and flesh.

3.2.4

Flavonols

The flavonols have a double bond between C2 and C3, a hydroxyl group at C3, and a ketone group at the C4 position of the C ring of the flavan nucleus (Figure 3.3). The most common flavonols in berry fruit—quercetin, myricetin, and kaempferol—differ in the number and position (C3 and C5) of OH groups on the B ring. Flavonols in plants commonly occur as O-glycosides with sugars attached at the C3 position. Glucose and galactose are the most common sugars attached, but rutinose, xylose, arabinose, and rhamnose may also be found. Similar to anthocyanins, sugar moieties of berry flavonols can be acylated with various acids (acetic, glutaric, glucuronic, oxalic, and caffeic). Many flavonols present in common berry fruit have been identified by HPLC-MS (Table 3.2). The glucuronides and glucosides of quercetin and kaempferol, as well as dihydroflavonol, quercetin rutinoside, and kaempferol coumaroylglucoside have been identified in strawberries. Quercetin 3-glucoside and quercetin 3-glucuronide are the major flavonols in the fruit, although one study indicates that quercetin 3-rutinoside is also a major compound.8 The flavonols in strawberries are concentrated in the achenes, which contain four–fold higher levels than the flesh.11 Four quercetin derivatives (rutinoside, glucoside, glucuronide, methylquercetin-pentose) and kaempferol glucuronide have been identified in red raspberries, and similar to strawberries, quercetin 3-glucoside and quercetin 3-glucuronide are the major flavonols in the fruit.15,17,19 The flavonol composition of blackberries is more complex, with nine quercetin and three kaempferol derivatives identified, including two acylated compounds—quercetin 3-[6-(3-hydroxy-3-methylglutaroyl)]-βgalactoside and quercetin 3-oxalylpentoside. In a study involving five genotypes, quercetin 3-galactoside and quercetin 3-glucoside were found to be the major flavonols in the fruit, with two genotypes having appreciable levels of quercetin 3-[6-(3-hydroxy-3-methylglutaroyl)]-β-galactoside.41 Kaempferol derivatives have been identified in several studies,26,42 but not in others,36,41 suggesting that the ability of fruit to synthesize kaempferol is influenced by genetics. Flavonols are located exclusively in the fleshy part of the drupelet.26 Blueberries are unique compared to other berry fruit in that they contain a large number of flavonols. Fourteen quercetin derivatives, including several compounds acylated with caffeic and acetic acids, three myricetin derivatives,


86


Table 3.2 Composition and Mass Spectral Data of Flavonol Glycosides in Common Berry Fruit m/z

Reference

Red raspberry [M−] Quercetin 3-rutinoside 609 Quercetin 3-glucoside 463 Quercetin 3-glucuronide 477 Methylquercetin-pentose conjugate 447 Kaempferol glucuronide 461 Quercetin 3,4’-diglucoside 625 Quercetin-galactosylrhamnoside 609

Fragments 301 301 301 301 285 463/301 301

Strawberry Quercetin 3-glucuronide Kaempferol 3-glucuronide Quercetin 3-glucoside Kaempferol 3-glucoside Dihydroflavonol Kaempferol 3-rutinoside Quercetin 3-rutinoside

477 461 463 * ** 609 593

301 285 301 * ** 301 285

√ √

463 463 609 607 595 * * * * 477 607

301 301 463/301 301 433/301 * * * * 301 463/301

√ √ √ √ √

493 505

463/301 433/301

* 479 463 463 463 609 433 489

* 317 317 301 301 463/301 301 447/301

Blackberry Quercetin 3-galactoside Quercetin 3-glucoside Quercetin 3-rutinoside Quercetin 3-xylosylglucuronide Quercetin 3-glucosylpentoside Kaempferol 3-glucuronide Kaempferol 3-glucoside Kaempferol 3-galactoside Kaempferol 3-xylosylglucuronide Quercetin 3-glucuronide Quercetin 3-O-[6-(3-hydroxy-3methyl-glutaroyl)-B-D-galactoside Quercetin 3-methoxyhexoside Quercetin 3-oxalylpentoside Blueberry Myricetin 3-arabinoside Myricetin 3-hexoside Myricetin 3-rhamnoside Quercetin 3-galactoside Quercetin 3-glucoside Quercetin 3-rutinoside Quercetin 3-pentoside Quercetin 3-acetylrhamnoside

15

√ √ √ √ √

19

33

19

√ √

17

√ √ √ √ √

34

√ √ √ √ √

45

√ √ √ √ √ √ √ √ √

9

√ √ √ √

26

√ √ √

8

√ √ √ √ √ √ 46

47

√ √ √

√ √

√

√ √ √

33

√ √ √ √ √ √ √

48

47

√ √

√ √ √ √ √ √

37

√

√ √ √ (continued)


Chapter 3:


87

Table 3.2 (Continued) Composition and Mass Spectral Data of Flavonol Glycosides in Common Berry Fruit m/z Quercetin 3-rhamnoside Quercetin 3-methoxyhexoside Quercetin 3-glucuronide Quercetin 3-glucosylpentoside Quercetin 3-caffeoylgalactoside Quercetin 3-caffeoylglucoside Quercetin 3-oxalylpentoside Quercetin 3-acetylgalactoside Quercetin 3-acetylglucoside Kaempferol 3-glucoside

[M] 447 493 477 595 623 623 505 505 505 *

Fragments 301 463/301 301 433/301 463/301 463/301 433/301 463/301 463/301 *

Reference 15

19

√

17

√ √ √ √ √ √ √ √ √

√

√

* No mass spectral data reported. ** Unknown compound.

and kaempferol 3-glucoside, have been identified in the fruit. Quercetin 3-galactoside is the predominant flavonol in the fruit, but several genotypes contain appreciable levels of quercetin 3-rhamnoside.41 Blueberry flavonols are located predominantly in the skin, with small amounts found in the seeds and none detected in the flesh.43

3.2.5

Proanthocyanidins

Proanthocyanidins, also known as condensed tannins, are comprised of oligomeric and polymeric flavan-3-ols (Figure 3.4). Linkage of the flavan-3-ol units occurs mainly through the C4→C8 bond, although a C4→C6 bond may also exist (B-type linkages). The proanthocyanidins are classified according to the type of flavan-3-ols present, which vary in their OH patterns at C3 on the B ring. The two major classes of proanthocyanidins found in berry fruit include procyanidins, composed exclusively of epi(catechin) units, and propelargonidins, composed exclusively of (epi)afzelechin units. Berry fruits vary markedly in proanthocyanidin composition and content. Blueberry and blackberry procyanidins consist exclusively of (epi)catechin units (procyanidins), whereas strawberry and raspberry procyanidins are comprised of both (epi)catechin and (epi)afzelechin (propelargonidin) units.44 The total proanthocyanidin content of highbush blueberries, lowbush blueberries, blackberries, Marion berries, raspberries, and strawberries is 180, 332, 27, 9, 30, and 145 mg/100 g FW.45 Polymeric flavan-3-ols (degree of polymerization greater than 10) are the predominant proanthocyanidins in blueberries and strawberries, while blackberries and raspberries contain nondetectable to trace levels of polymers.45 The polymeric procyanidins from lowbush blueberries were characterized by Gu et al.46 and are reported to range in degree of polymerization from 20 to 114, with epicatechin accounting


88


Figure 3.4 Structures of various monomeric and dimeric procyanidins.

for 100% of extension units, and catechin and epicatechin accounting for 67% and 33%, respectively, of terminal units. Catechin is the major flavan-3-ol in strawberries, ranging in concentration from 2 to 9 mg/100 g FW,11,19,47 and is uniformly distributed in the flesh and achenes.11 Epicatechin is the predominant flavan-3-ol in red raspberries, ranging in concentration from 2 to 5 mg/100 g FW,19,47 while yellow fruit contain low levels (less than 1 mg/100 g FW) of both catechin and epicatechin.19 Blackberries contain much higher levels of epicatechin than catechin, with catechin less than 1 mg/100 g FW and epicatechin 1 to 18 mg/100 g FW.26,47 The flavan-3-ols are located predominantly in seeds, which contain four–fold higher levels of epicatechin than whole fruit.26 Epicatechin is the major flavan-3-ol in blueberries, present at a concentration of 1 mg/100 g FW.47


Chapter 3:


89

3.3 Phenolic content of berry fruit The wide range of values reported for various classes of phenolics in berries (Table 3.3 and Table 3.4) reflect differences in genetics, cultural practices, environmental growing conditions, and possibly maturation. In addition, the values are affected by differences in extraction conditions, analytical procedures, and standards used for quantification, making comparisons among studies difficult. The common method for determining the amount of total phenolics in berries is based on the Folin Ciocalteu (FC) reagent,48 with the total amount of phenolics expressed as gallic acid equivalents. Although the method has several limitations, such as differential responses of various groups of phenolics to the FC reagent and interference from nonphenolic compounds with reducing capacity, it is a simple assay to perform and has been widely used.

3.3.1

Raspberry

The levels of total phenolics over all studies range from 428 to 1079 mg/100 g FW for black fruit, 192 to 512 mg/100 g FW for red fruit, 428 to 451 mg/100 g FW for pink/red fruit, and 241 to 359 mg/100 g FW for yellow fruit. Anthocyanins are the major phenolics present in black raspberries, with levels ranging from 464 to 627 mg/100 g FW. Black raspberries also contain appreciable levels of total ellagic acid,49 which most likely is due to high concentrations of ellagitannins in the fruit (Howard, L.R. and Hager, T.J., unpublished data). Red raspberries contain much lower levels of anthocyanins than black raspberries, with values ranging from 19 to 89 mg/100 g FW. Ellagitannins appear to be the major phenolics in both red and yellow raspberries, with the total ellagic acid content ranging from 38 to 270 mg/ 100 g FW in red fruit and 58 to 194 FW mg/100 g in yellow fruit. Red and black raspberry seeds are a rich source of ellagitannins, containing 870 and 670 mg/100 g seeds of total ellagic acid, respectively.50 Red raspberries also contain appreciable levels of total procyanidins (30 mg/100 g FW).45 Flavonols are minor phenolic constituents in raspberries regardless of color, with values ranging from less than 1 to 19 mg/100 g FW. Consistent with the data summarized in Table 3.3, Kahkonen et al.51 measured the amounts of different phenolic classes in red raspberries with data expressed on a dry weight (DW) basis and reported that ellagitannins (1717 mg/100 g DW) and anthocyanins (230 mg/100 g DW) were the predominant phenolics, with much lower levels of flavonols (23 mg/100 g DW), hydroxycinnamic acids (25 mg/100 g DW), and hydroxybenozoic acids (24 mg/100 g DW) present in the fruit. Viljanen et al.52 also reported that ellagitannins and anthocyanins were the major phenolics in red raspberries, accounting for 51% and 31%, respectively, of total phenolics determined by HPLC. Procyanidins and free ellagic acid accounted for 8% and 9%, respectively, of total phenolics, while flavonols accounted for less than 1%.


90


Table 3.3 Total Contents (mg/100 g FW) of Phenolics, Anthocyanins, Flavonols, and Ellagic Acid in Common Berry Fruit Total Total Total phenolicsa anthocyanins flavonols Raspberry 241–265 NA 359 428–451 192–359 211 513 NA 517 237–512 890–1079 980 Strawberry NA NA NA NA NA 43–94 202–273 Blackberry 822–844 248–633 NA NA 682–1056 193–352 114–178 418–555 275–650 NA 292–446 495–583

Total ellagic acidb

Number of genotypes

Color

Reference

ND ND 0°C

Controlled atmospheres High CO2 storage

Superatmospheric O2 Heat

↑

↑ ↑

↑

↑

↑ or [↓] [↓]

↑ or [↓]

↑ or [↓]

↑

[22], [23], [39], [115], [123], (124), (125), [126], [127], [128] 129, 130, 131, [131], 132, [132] [133], [134]

22, 39, 43, 47, 86, 89, [96], 99, 114, 115, 116, (116), 117, 118, 119, 120, [120], 121, [121], 123, [124], [126], 128

[37], [61], 77, [77], 41, [41], [44], [113] 36, 41, [44], 61, 62, 65, 76, 77, 96, 99, 105, (109), 110, 111, 112

105 107, 108

104

103 36, (36), 101 42

94, 95

References

176

↑ ↑ ↑

↑ ↑ ↑

↑ ↑ or (same) ↑

↑

Antioxidant capacity

↑

Anthocyanins

↑

Phenolic compounds

Increasing growth temperature and light intensity Adding compost in soil Organic or sustainable culture Adding mulch (cover with black plastic) Sandy soil supplement with fertilizer: Ca, Mg, N Elevating CO2 in atmosphere Spraying with methyl jasmonate Maturity factors From green stage to pink stage From pink stage to red stage

Preharvest factors

Table 5.1 Summary of the Effect of Preharvest Conditions, Maturity, and Postharvest Handling on Content of Phenolic Compounds, Anthocyanins, and Antioxidant Capacity in Berry Fruitsa



↑ ↑ ↑ ↑ [↓]

↑ ↑ ↑ — [↓] ↑ — [↓]

↑ ↑

↑ ↑ —

147, 150 149 [148]

150

118, 135, 136, 137 138, 139, [139], [140], 141 143, (143), [143], [144] 145, 146, 147

Designation for references: no brackets represents data supporting increased phenolic compounds, anthocyanins, or antioxidant capacity compared to untreated control; ( ) = same as untreated control; [ ] = decreased compared to untreated control.

↑ ↑ or [↓] [↓]

↑ [↓] —

Chapter 5:

a

Light or red light UV irradiation Ozone Natural compounds, such as Methyl jasmonate (MJ) Allyl isothiocyanate (AITC), tea tree oil (TTO) Ethanol Lysophosphatidylethanolamine 1-methylcyclopropene


Antioxidant capacity and phenolic content of berry fruits 177


178


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123. Holcroft, D.M., Gil, M.I., and Kader, A.A., Effect of carbon dioxide on anthocyanins, phenylalanine ammonia lyase and glucosyltransferase in the arils of stored pomegranates, J. Am. Soc. Hort. Sci., 123, 136, 1998. 124. Haffner, K., Rosenfeld, H.J., Skrede, G., and Laixin, W., Quality of red raspberry Rubus idaeus L. cultivars after storage in controlled and normal atmospheres, Postharvest Biol. Technol., 24, 279, 2002. 125. Wright, K.P. and Kader, A.A., Effect of slicing and controlled-atmosphere storage on the ascorbate content and quality of strawberries and persimmons, Postharvest Biol. Technol., 10, 39, 1997. 126. Remberg, S., Haffner, K., and Blomhoff, R., Total antioxidant capacity and other quality criteria in blueberries cvs ‘Bluecrop,’ ‘Hardyblue,’ ‘Patriot,’ ‘Putte’ and ‘Aron’ after storage in cold sore and controlled atmosphere, Acta Hort. (ISHS), 600, 595, 2003. 127. Agar, I.T., Streif, J., and Bangerth, F., Effect of high CO2 and controlled atmosphere on the ascorbic and dehydroascorbic acid content of some berry fruits, Postharvest Biol. Technol., 11, 47, 1997. 128. Gunes, G., Liu, R.H., and Watkins, C.B., Controlled-atmosphere effects on postharvest quality and antioxidant activity of cranberry fruits, J. Agric. Food Chem., 50, 5932, 2002. 129. Zheng, Y., Wang, C.Y., Wang, S.Y., and Zheng, W., Effect of high-oxygen atmospheres on blueberry phenolics, anthocyanins, and antioxidant capacity, J. Agric. Food Chem., 51, 7132, 2003. 130. Bangerth, F., The effect of different partial pressures of CO2, C2H4, and O2 in the storage atmosphere on the ascorbic acid content of fruits and vegetables, Qual. Plant., 27, 125, 1977. 131. Stewart, D., Oparka, J., Johnstone, C., Iannetta, P.P.M., and Davies, H.V., Effect of modified packaging (MAP) on soft fruit quality, in Annual Report of the Scottish Crop Research Institute for 1999, Scottish Crop Research Institute, Dundee, Scotland, 1999, p. 119. 132. Pérez, A.G. and Sanz, C., Effect of high-oxygen and high-carbon-dioxide atmospheres on strawberry flavor and other quality traits, J. Agric. Food Chem., 49, 2370, 2001. 133. Civello, P.M., Martínez, G.A., Chaves, A.R., and Añón, M.C., Heat treatments delay ripening and postharvest decay of strawberry fruit, J. Agric. Food Chem., 45, 4589, 1997. 134. Yoshikawa, F.T., Mitchell, F.G., and Mayer, G., Moist heat treatments of strawberries are studied, Calif. Agric., 46(2), 26, 1992. 135. Grisebach, H., Biosynthesis of anthocyanins, in Anthocyanins as Food Colors, Markakis, P., Ed., Academic Press, New York, 1982, p. 67. 136. Zhou, Y. and Singh, B.R., Effect of light on anthocyanin levels in submerged, harvested cranberry fruit, J. Biomed. Biotechnol., 5, 259, 2004. 137. Arakawa, O., Hori, Y., and Ogata, R., Relative effectiveness and interaction of ultraviolet-B, red and blue light in anthocyanin synthesis of apple fruit, Physiol. Plant., 64, 323, 1985. 138. Baka, M., Mercier, J., Corcuff, F., Castaigne, F., and Arul, J., Photochemical treatment to improve storability of fresh strawberries, J. Food Sci., 64, 1068, 1999. 139. Graham, W.D. and Stevenson, M.H., Effect of irradiation on vitamin C content of strawberries and potatoes in combination with storage and with further cooking in potatoes, J. Sci. Food Agric., 75, 371, 1997.


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140. Pan, J., Vicente, A.R., Martinez, G.A., Chaves, A.R., and Civello, P.M., Combined use of UV-C irradiation and heat treatment to improve postharvest life of strawberry fruit, J. Sci. Food Agr. 84, 1831, 2004. 141. Vicente, A.R., Repice, B., Martinez, G.A., Chaves, A.R., Civello, P.M., and Sozzi, G.O., Maintenance of fresh boysenberry fruit quality with UV-C light and heat treatments combined with low storage temperature, J. Hort. Sci. Biotechnol., 79, 246, 2004. 142. Graham, D.M., Use of ozone for food processing, Food Technol., 51, 72, 1997. 143. Perez A.G., Sanz, C., Rios, J.J., Olias, R., and Olias, J.M.., Effects of ozone treatment on postharvest strawberry quality, J. Agric. Food Chem., 47, 1652, 1999. 144. Barth, M.M., Zhou, M., Mercier, C., and Payne, J., Ozone storage effects on anthocyanin content and fungal growth in blackberries, J. Food Sci., 60, 1286, 1995. 145. Wang, C.Y., Improving storage quality in blueberries with methyl jasmonate, in Improving Postharvest Technologies of Fruits, Vegetables and Ornamentals, 4th International Conference on Postharvest Science, International Institute of Refrigeration, Murcia, Spain, 2001, p. 206. 146. Wang, C.Y., Maintaining postharvest quality of raspberries with natural volatile compounds, Int. J. Food Sci. Technol., 38, 869, 2003. 147. Ayala-Zavala, J.F., Wang, S.Y., Wang, C.Y., and Gonzalez-Aguilar, G., Methyl jasmonate in conjunction with ethanol treatment increases antioxidant capacity, volatile compounds and postharvest life of strawberry fruit, Eur. Food Res. Technol., 221, 731, 2005. 148. Jiang, Y., Joyce, D.C., and Terry, L.A., 1-Methylcyclopropene treatment affects strawberry fruit decay, Postharvest Biol. Technol., 23, 227, 2001. 149. Özgen, M., Farag, K.M., Ozgen, S., and Palta, J.P., Lysophosphatidylethanolamine accelerates color development and promotes shelf life of cranberries, HortScience, 40, 127, 2005.

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The potential health benefits of phytochemicals in berries for protecting against cancer and coronary heart disease Rui Hai Liu Contents 6.1 Introduction ................................................................................................187 6.2 Health benefits of phytochemicals..........................................................189 6.2.1 Role of phytochemicals in the prevention of cancer...............190 6.2.2 Role of phytochemicals in the prevention of CVD .................192 6.3 Additive and synergistic effects of phytochemicals in whole foods............................................................................................195 6.4 Bioavailability and metabolism of phytochemicals .............................196 6.5 Conclusion...................................................................................................199 References.............................................................................................................199

6.1 Introduction Cardiovascular disease (CVD) and cancer are ranked as the top two leading causes of death in the United States and in most industrialized countries. The causes of both diseases have been linked to diet and lifestyle choices. Epidemiological studies have consistently shown that a high dietary intake of fruits and vegetables is strongly associated with reduced risk of developing such chronic diseases.1–4 It is estimated that one-third of all cancer deaths in the United States could be prevented through appropriate dietary modification.2,5,6 In addition, several dietary

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patterns have been found to have significant health benefits. The Mediterranean diet has been linked with a reduction in CVD. The characteristics of the Mediterranean diet are high monounsaturated fat, mainly from olive oil; high consumption of fruits, vegetables, and grains; moderate consumption of alcohol; and low consumption of red meat. Another pattern that has been associated with health benefits is the “prudent pattern.”7 The prudent pattern consists of higher intakes of fruits, vegetables, legumes, whole grains, and fish. This is in contrast to the “Western pattern” which consists of red meat, processed meats, refined grains, desserts, and high fat dairy products. People following the prudent pattern had a decreased risk of CVD.7 The evidence suggests that a change in dietary behavior, such as increasing one’s consumption of fruits and vegetables, and related lifestyle changes is a practical strategy for significantly reducing the incidence of CVD and cancer.8 Plant-based foods, such as fruits and vegetables, which contain significant amounts of bioactive phytochemicals (Figure 6.1) and have potent antioxidant activity (Figure 6.2), may provide desirable health benefits beyond basic nutrition to reduce the risk of chronic diseases.8 The beneficial effects associated with plant-based food consumption are due in part to the existence of phytochemicals. Cranberry Apple Red grape Strawberry Pineapple Banana Peach Lemon Orange Pear Grapefruit Broccoli Spinach Onion Red Pepper Carrot Cabbage Potato Lettuce Celery Cucumber

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Cranberry Apple Red grape Strawberry Peach Lemon Pear Banana Orange Grapefruit Pineapple Red Pepper Broccoli Carrot Spinach Cabbage Onion Celery Potato Lettuce Cucumber 0

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Total antioxidant activity (µ µmol vitamin C eq/g sample) Figure 6.2 Total antioxidant activity of common fruits and vegetables (adapted from Sun et al.14 and Chu et al.15).

6.2 Health benefits of phytochemicals The “phyto” of the word phytochemicals is derived from the Greek word phyto, which means plant. Therefore phytochemicals are plant chemicals. Phytochemicals are defined as bioactive nonnutrient plant compounds in fruits, vegetables, grains, and other plant-based foods that have been linked to reductions in the risk of major chronic diseases. Although thousands of individual phytochemicals have been identified in fruits, vegetables, and grains, a large percentage of phytochemicals still remain unknown and need to be identified before we can fully understand the health benefits of phytochemicals in whole foods.8 Convincing evidence suggests that the benefits of phytochemicals in fruits, vegetables, and whole grains may be even greater than is currently understood because the oxidative stress induced by free radicals is involved in the etiology of a wide range of chronic diseases.9 Because phytochemicals differ widely in composition and ratio in fruits and vegetables (Figure 6.1), and often have complimentary mechanisms to one another, it is suggested that people consume a wide variety of these plant-based foods. Cells in the human body are constantly exposed to a variety of oxidizing agents. These agents may be present in air, food, and water, or they may be produced by metabolic activities within cells, some of which are necessary


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for life. The key factor is to maintain a balance between oxidants and antioxidants to sustain optimal physiological conditions. Overproduction of oxidants can cause an imbalance, leading to oxidative stress, especially in chronic bacterial, viral, and parasitic infections.10 Oxidative stress can cause oxidative damage to large biomolecules such as lipids, proteins, and DNA, resulting in an increased risk for chronic diseases such as cancer and CVD.9–11 To prevent or slow down the oxidative stress induced by free radicals, sufficient amounts of antioxidants need to be consumed. Fruits, vegetables, and grains contain a wide variety of antioxidant compounds (phytochemicals), such as phenolics and carotenoids, that may help protect cellular systems from oxidative damage and also lower the risk of chronic diseases.12–16 Among the 11 common fruits consumed in the United States, cranberry has the highest total phenolic content, followed by apple, red grape, strawberry, pineapple, banana, peach, lemon, orange, pear, and grapefruit14 (Figure 6.1). Among the 10 common vegetables consumed in the United States, broccoli has the highest total phenolic content, followed by spinach, yellow onion, red pepper, carrot, cabbage, potato, lettuce, celery, and cucumber15 (Figure 6.1).

6.2.1

Role of phytochemicals in the prevention of cancer

Strong epidemiological evidence suggests that regular consumption of fruits and vegetables can reduce an individual’s cancer risk.3,4 Block et al.4 reviewed approximately 200 epidemiological studies that examined the relationship between the intake of fruits and vegetables and cancer of the lung, colon, breast, cervix, esophagus, oral cavity, stomach, bladder, pancreas, and ovary. In 128 of 156 dietary studies, the consumption of fruits and vegetables was found to have a significant protective effect. The risk of cancer was two–fold higher in persons with a low intake of fruits and vegetables than in those with a high intake. Significant protection was found in 24 of 25 studies for lung cancer. Fruits were significantly protective in cancer of the esophagus, oral cavity, and larynx. Fruit and vegetable intake was protective for cancer of the pancreas and stomach in 26 of 30 studies and for colorectal and bladder cancer in 23 of 38 studies. A prospective study involving 9959 men and women in Finland showed an inverse association between the intake of flavonoids and the incidence of cancer at all sites combined.17 After a 24-year follow-up, the risk of lung cancer was reduced by 50% in the highest quartile of flavonol intake. Consumption of quercetin from onions and apples was found to be inversely associated with lung cancer risk.18 The effect of onions was particularly strong against squamous cell carcinoma. Boyle et al.19 showed that increased plasma levels of quercetin after a meal of onions was accompanied by increased resistance to strand breakage by lymphocyte DNA and decreased levels of some oxidative metabolites in the urine. Consumption of fruits in Italy was found to have a profound protective effect against cancers of the upper respiratory and digestive tracts.20 In the same study, the relative risks of cancers of the oral cavity, pharynx, esophagus, and larynx were observed to be 0.4 to 0.5, which correlated with higher


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fruit consumption and was found to reduce the relative risk even more in cancers of the gallbladder, pancreas, prostate, and urinary tract. In a large case-control study in San Francisco, vegetable consumption was inversely related to the risk of developing pancreatic cancer.21 It was found that those persons with an intake of more than five servings of vegetables per day had a 50% reduction in risk of developing the disease compared to those in the lowest consumption quantile.21 Carcinogenesis is a multistep process, and oxidative damage is linked to the formation of tumors through several mechanisms.10,11 Oxidative stress induced by free radicals causes DNA damage, which, when left unrepaired, can lead to base mutation, single- and double-strand breaks, DNA cross-linking, and chromosomal breakage and rearrangement.11 This potentially cancer-inducing oxidative damage might be prevented or limited by dietary antioxidants found in fruits and vegetables. Proliferation of normal healthy cells is tightly regulated by a myriad of cell cycle proteins. These proteins work together in complex pathways to ensure that the cell divides only when necessary and without error. Cells may respond to external mitogens, growth factors, or oxidative stress through the mitogen-activated protein (MAP) kinase signaling pathways.22 Oxidative stress on the cell membrane can stimulate signaling pathways that will protect the cell, such as the stress-activated protein kinase/c-Jun NH2-terminal kinase (SAPK/JNK) and p38 kinase pathways.23 For example, oxidative stress activates apoptosis-stimulating kinase 1 (ASK1), which in turn activates the SAPK/JNK kinases MKK4 and MKK7.24 These kinases phosphorylate and activate JNK, which translocates into the nucleus where it can activate other regulatory proteins such as p53 and the transcription factor Elk-1. In the case of the stress response, p53 will respond by either arresting the cell cycle or inducing apoptosis.25 In order to induce a G1-phase cell cycle arrest, p53 stimulates expression of the cyclin-dependent kinase inhibitor (CKI) p21, whose role is to inhibit the cyclin D1/Cdk4 complex. Cells under oxidative stress are susceptible to DNA damage, which may lead to mutations that alter expression or activity of key regulatory proteins.25 Such mutations can result in deregulation of the cell cycle and subsequent uncontrolled cell proliferation, known as cancer. These cells are then unable to properly respond to further oxidative stress and are highly susceptible to additional DNA damage. This cycle contributes to the increasing genetic instability characteristic of tumor cells.25 Phytochemicals appear to reverse the effects of such mutations by halting the uncontrolled proliferation of cancer cells in vitro through induction of cell cycle arrest or apoptosis. For example, the flavonol quercetin has been shown to cause a G2/M arrest and induce apoptosis in a dose-dependent manner in PC-3 androgen-independent human prostate cancer cells.26 The cells were treated with 25 to 100 µM quercetin for 24 to 72 hours and the median effective concentration (EC50) for growth inhibition was determined to be 50 µM at 24 hours. Flow cytometric analysis revealed that quercetin treatment induced a G2/M accumulation. The effects of quercetin on the


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relevant cell cycle proteins were then analyzed. The CKI p21 was dramatically induced despite the absence of p53 (PC-3 cells contain a mutation in the p53 gene that renders it inactive). The quercetin was found to downregulate expression of Cdc2/Cdk1, which accounted for the increase in hypophosphorylated Rb while the amount of total Rb protein remained constant. Cyclin B1 was down-regulated while cyclin A was unaffected. Quercetin has effectively induced G1/S cell cycle arrest in other cell models such as colon and gastric cancers and leukemia, but it has caused G2/M arrest in others, including breast and laryngeal cancers and nononcogenic fibroblasts.27 Recently we showed that cranberry phytochemical extracts significantly inhibited human breast cancer MCF-7 cell proliferation.28 Apoptotic induction in MCF-7 cells was observed in a dose-dependent manner after exposure to cranberry phytochemical extracts for 4 hours. Cranberry phytochemical extracts at a dose of 50 mg/ml resulted in a 25% higher ratio of apoptotic cells to total cells as compared to the control groups (p < .05). Cranberry phytochemical extracts at doses of 10 to 50 mg/ml significantly arrested MCF-7 cells at the G0/G1 phase (p < .05). A constant increasing pattern of the G1/S index was observed in the cranberry extract treatment group, while the G1:S ratio of the control group decreased concomitantly between the 10and 24-hour treatments. After 24 hours exposure to cranberry extracts, the G1/S index of MCF-7 cells was approximately six times greater than that of the control group (p < 0.05). These results suggest that cranberry phytochemical extracts possess the ability to suppress the proliferation of human breast cancer MCF-7 cells, and this suppression is at least partly attributed to both the initiation of apoptosis and the G1 phase arrest.28 Dietary phytochemicals can act to prevent cancer or interfere with its progression at virtually every stage of cancer development. Studies to date have demonstrated that phytochemicals in common fruits and vegetables can have complementary and overlapping mechanisms of action (Table 6.1), including antioxidant activity and scavenging free radicals; regulation of gene expression in cell proliferation, cell differentiation, oncogenes, and tumor suppressor genes; induction of cell cycle arrest and apoptosis; modulation of enzyme activities in detoxification, oxidation, and reduction; stimulation of the immune system; regulation of hormone-dependent carcinogenesis; and antibacterial and antiviral effects.14,15,26–30

6.2.2

Role of phytochemicals in the prevention of CVD

Dietary flavonoid intake was significantly inversely associated with mortality from coronary heart disease.31 Intake of apples and onions, both high in quercetin, was inversely correlated with total and coronary mortality.32 In a recent Japanese study, the total intake of flavonoids (quercetin, myricetin, kaempferol, luteolin, and ficetin) was inversely correlated with the plasma total cholesterol and low-density lipoprotein (LDL) cholesterol concentrations.33 As a single phytochemical, quercetin intake was inversely related to total cholesterol and LDL plasma levels. Joshipura et al.34 reported that total


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Table 6.1 Proposed Mechanisms by Which Dietary Phytochemicals May Prevent Cancer Antioxidant activity Scavenge free radicals and reduce oxidative stress Inhibition of cell proliferation Induction of cell differentiation Inhibition of oncogene expression Induction of tumor suppression gene expression Induction of cell cycle arrest Induction of apoptosis Inhibition of signal transduction pathways Enzyme induction and enhancing detoxification Phase II enzyme Glutathione peroxidase (GPX) Catalase Superoxide dismutase (SOD) Enzyme inhibition Phase I enzyme (block activation of carcinogens) Cyclooxygenase-2 (COX-2) Inducible nitric oxide synthase (iNOS) Xanthine oxide Enhancement of immune functions and surveillance Antiangiogenesis Inhibition of cell adhesion and invasion Inhibition of nitrosation and nitration Prevention of DNA binding Regulation of steroid hormone metabolism Regulation of estrogen metabolism Antibacterial and antiviral effects

fruit intake and total vegetable intake were both individually associated with decreased risk for coronary heart disease. The inverse associations between total consumption of fruits and vegetables and coronary heart disease were observed at intakes of more than four servings per day. Subjects in the Women’s Health Study had a relative risk of 0.68 for CVD when comparing the highest versus the lowest quintiles of fruit and vegetable intake, and the relative risk for myocardial infarction was only 0.47. It was estimated that there was a 20% to 30% reduction in risk of CVD associated with high fruit and vegetable intake.35 Most recently, in a study involving subjects from the National Health and Nutrition Examination Survey Epidemiologic Follow-up Study, there was a 27% lower CVD mortality with consumption of fruits and vegetables at least three times per day compared to one time per day. Fruit and vegetable intake was inversely associated with the incidence of stroke, stroke mortality, ischemic heart disease mortality, CVD mortality, and all-cause mortality.36 Several mechanisms for the prevention of atherosclerosis by dietary antioxidants in fruits and vegetables have been proposed (Table 6.2). In the LDL


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Table 6.2 Proposed Mechanisms of Action by Which Dietary Antioxidants May Prevent CVD Antioxidant activity Scavenge free radicals and reduce oxidative stress Prevent LDL oxidation Induction of expression of hepatic LDL receptors Regulation of sterol regulatory element binding proteins (SREBPs) Modulation of cholesterol synthesis Regulation of lipid profiles Inhibition of cholesterol absorption Regulation of prostanoid synthesis (PGE2) Reduction of platelet aggregation Regulation of nitric oxide (NO•) production Lowering C-reactive protein (CRP) Regulation of blood pressure

oxidation hypothesis (Figure 6.3), oxidized LDL cholesterol has been suggested as the atherogenic factor that contributes to CVD.37,38 When circulating LDLs are present at high levels, they infiltrate the artery wall and increase intimal LDL, which can then be oxidized by free radicals. This oxidized LDL in the intima is more atherogenic than native LDL and serves as a chemotactic

Figure 6.3 Proposed mechanism of LDL oxidation in fatty streak formation and atherosclerotic disease.


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factor in the recruitment of circulating monocytes and macrophages. Oxidized LDL is typically taken up by macrophage scavenger receptors, thus inducing the formation of inflammatory cytokines and promoting cell proliferation, cholesterol ester accumulation, and foam cell formation (Figure 6.3). Gruel-like lipid-laden foam cell accumulation in the blood vessel, forming fatty streaks, causes further endothelial injury and leads to atherosclerotic disease. Since oxidized LDL plays a key role in the initiation and progression of atherosclerosis, giving dietary supplements of antioxidants capable of preventing LDL oxidation has been an important therapeutic approach. Dietary antioxidants that are incorporated into LDL are themselves oxidized when the LDL is exposed to pro-oxidative conditions; this occurs before any extensive oxidation of sterol or polyunsaturated fatty acids can occur.39 Therefore dietary antioxidants might retard the progression of atherosclerotic lesions. Cranberry extracts were found to have potent antioxidant capacity, preventing in vitro LDL oxidation, with increasing delay and suppression of LDL oxidation in a dose-dependent manner.40 The antioxidant activity of 100 g of cranberries against LDL oxidation was equivalent to 1000 mg vitamin C or 3700 mg vitamin E. In addition, phytochemicals have been shown to have roles in the reduction of platelet aggregation, modulation of cholesterol synthesis and absorption, and reduction of blood pressure. It has also been reported that cranberry phytochemical extracts significantly induced expression of hepatic LDL receptors and increased intracellular uptake of cholesterol in HepG2 cells in vitro in a dose-dependent manner.40 This suggests that cranberry phytochemicals could enhance clearance of excessive plasma cholesterol in circulation through the liver. C-reactive protein, a marker of systemic inflammation, has been reported to be a stronger predictor of CVD than is LDL cholesterol,41,42 suggesting that inflammation is a critical factor in CVD. C-reactive protein is an acute phase reactant secreted by the liver in response to inflammatory cytokines.42 Inflammation not only promotes initiation and progression of atherosclerosis, but also causes acute thrombotic complications of atherosclerosis.43 Fruit and vegetable intake was associated with lower plasma C-reactive protein concentrations,44 suggesting dietary phytochemicals can lower C-reactive protein. Therefore, the anti-inflammatory activity of phytochemicals may play an important role in the prevention of CVD. Dietary antioxidants also have complementary and overlapping mechanisms of action in the prevention of CVD (Table 6.2).

6.3 Additive and synergistic effects of phytochemicals in whole foods Phytochemical extracts from fruits and vegetables have been shown to have potent antioxidant activity (Figure 6.2), and the combination of phytochemicals from fruits and vegetables is proposed to be responsible for the potent antioxidant and anticancer activities of these foods.14,15,45 The total antioxidant activity of phytochemicals in 1 g of apples with peel is equivalent to 83.3 µmol vitamin C equivalents; to put it another way, the antioxidant value


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of 100 g of apples is equivalent to 1500 mg of vitamin C.45 This is far greater than the total antioxidant activity of 0.057 mg of vitamin C (the amount of vitamin C in 1 g of apples with peel) or 0.32 µmol vitamin C equivalents. In other words, vitamin C in apples contributes less than 0.4% of its total antioxidant activity. Thus most of the antioxidant activity comes from other phytochemicals, not vitamin C. The natural combination of phytochemicals in fruits, vegetables, and whole grains is responsible for their potent antioxidant activity. Apple extracts also contain bioactive compounds that inhibit tumor cell growth in vitro. Phytochemicals in apples with peel (50 mg/ml on a wet basis) inhibit colon cancer cell proliferation by 43%. However, this was reduced to 29% when apple without peel was tested.45 Recently we reported that whole-apple extracts prevented mammary cancer in a rat model in a dose-dependent manner.46 At the doses comparable to human consumption of one, three, and six apples per day, the tumor incidences were reduced by 17%, 39% (p < .02), and 44% (p < .01), respectively, and the cumulative tumor numbers were reduced by 25%, 25%, and 61% (p < .01), respectively, after 24 weeks.46 This study demonstrated that whole-apple extracts effectively inhibited mammary cancer growth in the rat model, thus consumption of apples may be an effective strategy for cancer protection. Different species and varieties of fruits, vegetables, and grains have different phytochemical profiles.14–16,45–49 Therefore consumers should obtain their phytochemicals from a wide variety of fruits, vegetables, and whole grains for optimal health benefits. Health benefits from the consumption of fruits and vegetables extend beyond lowering the risk of developing cancers and CVD: benefits also include preventive effects for other chronic diseases such as cataracts, age-related macular degeneration, central neurodegenerative diseases, and diabetes.50 The additive and synergistic effects of phytochemicals in fruits and vegetables have been proposed to be responsible for their potent antioxidant and anticancer activities.45,50 The benefits of a diet rich in fruits and vegetables are attributed to the complex mixture of phytochemicals present in these and other whole foods.14,15,46,50 This partially explains why no single antioxidant can replace the combination of natural phytochemicals in fruits and vegetables in achieving the observed health benefits. Thousands of phytochemicals are present in whole foods. These compounds differ in molecular size, polarity, and solubility, which may affect the bioavailability and distribution of each phytochemical in different macromolecules, subcellular organelles, cells, organs, and tissues. This balanced natural combination of phytochemicals present in fruits and vegetables simply cannot be mimicked by pills or tablets.

6.4 Bioavailability and metabolism of phytochemicals Bioavailability and metabolism are two important questions that need to be addressed in studying the biological effects of phytochemicals in foods. The form of antioxidants found in foods is not necessarily the same as the form


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found in the blood or the targeted tissues after digestion, absorption, distribution, and metabolism. In order to study the mechanisms of action of antioxidants in the prevention of chronic disease, two important questions to be asked are: Are these phytochemicals bioavailable? Are these original antioxidants or their metabolites the bioactive compounds? It is crucial to understand the bioavailability and metabolism of these compounds to gain knowledge of what compounds and how much of these compounds actually reach target tissues. In some cases, the original phytochemicals may be excreted or metabolized, never actually reaching target tissue, and the active compounds may not be the original antioxidant compounds found in foods. To date, many studies have not addressed the bioavailability and metabolism of phytochemicals from whole foods. Examining the bioavailability of compounds from food sources can be challenging because there are many factors that can influence bioavailability. Foods contain a wide variety of phytochemicals, and interactions with other chemicals in the food may affect bioavailability. Phytochemicals may be conjugated with different sugar molecules (glucosides, xylosides, rhamnosides, galactosides) and proteins or bound to other cell structures, such as fibers, which may affect the bioavailability of those compounds. Other factors, such as digestion, food processing, storage, and stage of harvest, may also affect phytochemical bioavailability. Although much progress has been made in understanding the bioavailability and further metabolism of pure compounds, more work is needed to further comprehend the bioavailability of phytochemicals from complex food sources. Dupont et al.51 reported the bioavailability of phenolic compounds from apple cider in humans. No quercetin was found in the volunteers’ plasma after drinking 1.1 L of apple cider. Instead, low levels of 3-methyl quercetin and 4-methyl quercetin were observed within 60 minutes following consumption of the cider. Caffeic acid was rapidly absorbed, but within 90 minutes the caffeic acid in the plasma was undetectable. Catechin, epicatechin, and phlorizin were not seen in the plasma. Hippuric acid and phloretin were both increased in the subjects’ urine following consumption of the cider, but there was no evidence of quercetin, catechin, or epicatechin in the urine.51 In another study involving human subjects, quercetin bioavailability from apples was only 30% of the bioavailability of quercetin from onions.52 In this study, quercetin levels reached a peak after 2.5 hours in the plasma. The bioavailability differences between apples and onions most likely are from the differences in quercetin conjugates in the different foods. Onions contain more quercetin aglycone and quercetin glucosides, whereas apples tend to contain more quercetin monoglycosides and quercetin rutinoside, which may be less bioavailable. Our laboratory examined the bioavailability of both quercetin and quercetin-3-glucoside from apple peel extracts and onion extracts in Caco-2 cells.53 Apple peel extracts contained no free quercetin, and no quercetin accumulation was seen in the Caco-2 cells following incubation with apple peel extracts. Small amounts of quercetin-3-glucoside


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were absorbed by the cells (4%). However, onions contain some free quercetin and greater amounts of quercetin glucosides, and the absorption of quercetin into the Caco-2 cells from onion extracts was much greater than from apple extracts.53 The above results can be explained by the research examining quercetin and quercetin glycoside bioavailability. Walle et al.54 found that, in ileostomy fluid, quercetin primarily existed as the aglycone form. They hypothesized that β-glucosidases hydrolyzed quercetin glucosides to quercetin, which could then be passively transported. In support of this theory, Day et al.55 determined that quercetin glycosides were mainly deglycosylated by lactasephlorizin hydrolase (LPH) before the aglycone then passed into the cell. Some intact glycoside transport by SGLT1 occurred and the glucosides were deglycosylated within the cell by cytosolic β-glucosidase. They also found that quercetin-3-glucoside appeared to utilize only the LPH pathway, not the SLGT1 transporter, but quercetin-4-glucoside used both pathways.55 Apples contain a small amount of quercetin-3-glucoside that, following hydrolysis by LPH, would is available for uptake by intestinal cells. However, apples also contain other conjugates such as quercetin rhamnosides, quercetin xylosides, and quercetin galactosides that are not easily hydrolyzed by LPH, and most likely are not readily absorbed by small intestine cells. In comparison, the quercetin in onions is almost all in the form of quercetin glucosides and free quercetin, making it more bioavailable to small intestine cells. Some bacterial degradation of quercetin conjugates most likely occurs in the human intestinal tract. Enterococcus casseliflavis and Eubacterium ramulus, microorganisms isolated from human feces, were both found to degrade quercetin-3-glucoside as a carbon and energy source.56 E. casseliflavis utilized only the sugar moiety of the glucoside, whereas E. ramulus was also capable of degrading the aromatic ring system, with phloroglucinol produced as an intermediate.56 In human ileostomy subjects, chlorogenic acid absorption was approximately 33%, and only traces of chlorogenic acid were found in the urine.57 The majority of chlorogenic acid reaches the large intestine and can be metabolized by gut microflora. Gonthier et al.58 found that rats fed chlorogenic acid excrete very little chlorogenic acid in their urine, but instead they excrete mainly microbially produced metabolites of chlorogenic acid, such as hippuric acid and m-coumaric acid. A study by Olthof et al.59 involving human subjects showed that half of the ingested chlorogenic acid was converted to hippuric acid in the colon, most likely by microbial metabolism. Catechin and epicatechin are both absorbed by small intestine epithelial cells.60 In contrast to quercetin, epicatechin was not glucuronidated by human liver microsomes, nor was it glucuronidated by human small intestine or large intestine tissue.61 Both liver and intestinal tissues contain uridine diphosphate-glucuronosyltransferases (UGTs) that are involved in the glucuronidation of various other flavonoids. Epicatechin was found to be sulfated by the human liver and intestinal cytosols, indicating that sulfation is the major metabolic pathway for epicatechin metabolism.61


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The mechanisms in the bioavailability of specific phytochemicals are becoming clearer as bioavailability research continues. In general, many flavonoid aglycones tend to pass through the intestinal epithelial cells, where they are further conjugated. The flavonoid glycosides may be absorbed in small amounts, but most absorption seems to occur following hydrolysis by intestinal hydrolases, such as LPH. Upon absorption, these compounds are also conjugated. More research is needed to understand the bioavailability of compounds from whole foods. The effects of the food matrix, interactions between compounds, digestion, and processing on the bioavailability of phytochemicals are still unknown. A good in vitro model would be beneficial in evaluating the bioavailability of phytochemicals from foods by offering a simple method to screen for factors that may affect intestinal absorption of phytochemicals, such as the food matrix, food processing, digestion, and interactions with other foods. Human and animal models can be expensive and time consuming, while a cell culture model allows for rapid, inexpensive screening. The Caco-2 cell culture model has the potential to be a good model to measure the bioavailability of antioxidants, such as carotenoids and flavonids, from whole foods.53,62,63

6.5 Conclusion Dietary modification by increasing the consumption of a wide variety of fruits, vegetables, and whole grains daily is a practical strategy for consumers to optimize their health and reduce the risk of chronic diseases. Phytochemical extracts from fruits and vegetables have strong antioxidant and antiproliferative activities, and the majority of total antioxidant activity is from the combination of phytochemicals. The additive and synergistic effects of phytochemicals in fruits and vegetables are responsible for their potent antioxidant and anticancer activities. The benefit of a diet rich in fruits, vegetables, and whole grains is attributed to the complex mixture of phytochemicals present in these foods. This explains why no single antioxidant can replace the combination of natural phytochemicals in fruits and vegetables. Therefore the evidence suggests that antioxidants are best acquired through whole food consumption.

References 1. Willett, W.C., Diet and health: what should we eat?, Science, 254, 532, 1994. 2. Willett, W.C., Balancing life-style and genomics research for disease prevention, Science, 296, 695, 2002. 3. Steinmetz, K.A. and Potter, J.D., Vegetables, fruit, and cancer. I. Epidemiology, Cancer Causes Control, 2, 325, 1991. 4. Block, G., Patterson, B., and Subar, A., Fruit, vegetables, and cancer prevention: a review of the epidemiological evidence, Nutr. Cancer, 18, 1, 1992. 5. Doll, R. and Peto, R., Avoidable risks of cancer in the United States, J. Natl. Cancer Inst., 66, 1197, 1981.


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6. Willett, W.C., Diet, nutrition, and avoidable cancer, Environ. Health Perspect., 103, 165, 1995. 7. Hu, F., Rimm, E.B., Stampfer, M.J., Ascherio, A., Spiegelman, D., and Willett, W.C., Prospective study of major dietary patterns and risk of coronary heart disease in men, Am. J. Clin. Nutr., 72, 912, 2000. 8. Liu, R.H., Health benefits of fruits and vegetables are from additive and synergistic combination of phytochemicals, Am. J. Clin. Nutr., 78, 517S, 2003. 9. Ames, B.N. and Gold, L.S., Endogenous mutagens and the causes of aging and cancer, Mutat. Res., 250, 3, 1991. 10. Liu, R.H. and Hotchkiss, J.H., Potential genotoxicity of chronically elevated nitric oxide: a review, Mutat. Res., 339, 73, 1995. 11. Ames, B.N., Shigenaga, M.K., and Gold, L.S., DNA lesions, inducible DNA repair, and cell division: the three key factors in mutagenesis and carcinogenesis, Environ. Health Perspect., 101(suppl. 5), 35, 1993. 12. Wang, H., Cao, G.H., and Prior, R.L., Total antioxidant capacity of fruits, J. Agric. Food Chem., 44, 701, 1996. 13. Vinson, J.A., Su, X., Zubik, L., and Bose, P., Phenol antioxidant quantity and quality in foods: fruits, J. Agric. Food Chem., 49, 5315, 2001. 14. Sun, J., Chu, Y.F., Wu, X., and Liu, R.H., Antioxidant and antiproliferative activities of fruits, J. Agric. Food Chem., 50, 7449, 2002. 15. Chu, Y.F., Sun, J., Wu, X., and Liu, R.H., Antioxidant and antiproliferative activities of vegetables, J. Agric. Food Chem., 50, 6910, 2002. 16. Adom, K.K. and Liu, R.H., Antioxidant activity of grains, J. Agric. Food Chem., 50, 6182, 2002. 17. Knekt, P., Jarvinen, R., Seppanen, R., Hellovaara, M., Teppo, L., Pukkala, E., and Aromaa, A., Dietary flavonoids and the risk of lung cancer and other malignant neoplasms, Am. J. Epidemiol., 146, 223, 1997. 18. Le Marchand, L., Murphy, S.P., Hankin, J.H., Wilkens, L.R., and Kolonel, L.N., Intake of flavonoids and lung cancer, J. Natl. Cancer Inst., 92, 154, 2000. 19. Boyle, S.P., Dobson, V.L., Duthie, S.J., Kyle, J.A., and Collins, A.R., Absorption and DNA protective effects of flavonoid glycosides from an onion meal, Eur. J. Nutr., 39, 213, 2000. 20. La Vecchia, C., Altieri, A., and Tavani, A., Vegetables, fruit, antioxidants and cancer: a review of Italian studies, Eur. J. Nutr., 40, 261, 2001. 21. Chan, J.M., Wang, F., and Holly, E.A., Vegetable and fruit intake and pancreatic cancer in a population-based case-control study in the San Francisco Bay area, Cancer Epidemiol. Biomarkers Prev., 14, 2093, 2005. 22. Pearson, G.F., Robinson, F., Beers Gibson, T., Xu, B.E., Karandikar, M., Berman, K., and Cobb, M.H., Mitogen-activated protein (MAP) kinase pathways: regulation and physiological functions, Endocrine Rev., 22, 153, 2001. 23. Bode, A.M. and Dong, Z., Targeting signal transduction pathways by chemopreventive agents, Mutat. Res., 555, 33, 2004. 24. Weston, C.R. and Davis, R.J., The JNK signal transduction pathway, Curr. Opin. Genet. Dev., 12, 14, 2002. 25. Bartek, J. and Lukas, J., Pathways governing G1/S transition and their response to DNA damage, FEBS Lett., 490, 117, 2001. 26. Vijayababu, M.R., Kanagaraj, P., Arunkumar, A., Ilangovan, R., Aruldhas, M.M., and Arunakaran, J., Quercetin-induced growth inhibition of cell death in prostatic carcinoma cells (PC-3) are associated with increase in p21 and hypophosphorylated retinoblastoma proteins expression, J. Cancer Res. Clin. Oncol., 131, 765, 2005.


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27. Casagrande, F. and Darbon, J.M., Effects of structurally related flavonoids on cell cycle progression on human melanoma cells: regulation of cyclin-dependent kinases CDK2 and CDK1, Biochem. Pharmacol., 61, 1205, 2001. 28. Sun, J. and Liu, R.H., Cranberry phytochemical extracts induce cell cycle arrest and apoptosis in human MCF-7 breast cancer cells, Cancer Lett., 241, 124, 2006. 29. Dragsted, L.O., Strube, M., and Larsen, J.C., Cancer-protective factors in fruits and vegetables: biochemical and biological background, Pharmacol Toxicol., 72, 116, 1993. 30. Waladkhani, A.R. and Clemens, M.R., Effect of dietary phytochemicals on cancer development, Int. J. Mol. Med., 1, 747, 1998. 31. Hertog, M.G.L., Kromhout, D., Aravanis, C., Blackburn, H., Buzina, R., Fidanza, F., Giampaoli, S., Jansen, A., Menotti, A., Nedeljkovic, S., Pekkarinen, M., Simic, B.S., Toshima, H., Feskens, E.J.M., Hollman, P.C.H., and Katan, M.B., Flavonoid intake and long-term risk of coronary heart disease and cancer in the seven countries study, Arch. Intern. Med., 155, 381, 1995. 32. Knekt, P., Jarvinen, R., Reunanen, A., and Maatela, J., Flavonoid intake and coronary mortality in Finland: a cohort study, BMJ, 312, 478, 1996. 33. Arai, Y., Watanabe, S., Kimira, M., Shimoi, K., Mochizuki, R., and Kinae, N., Dietary intakes of flavonols, flavones and isoflavones by Japanese women and the inverse correlation between quercetin intake and plasma LDL cholesterol concentration, J. Nutr., 131(9), 2243, 2000. 34. Joshipura, K.J., Hu, F.B., Manson, J.E., Stampfer, M.J., Rimm, E.B., Speizer, F.E., Colditz, G., Ascherio, A., Rosner, B., Spiegelman, D., and Willett, W.C., The effect of fruit and vegetable intake on risk for coronary heart disease, Ann. Intern. Med., 134, 1106, 2001. 35. Liu, S., Manson, J.E., Lee, I.M., Cole, S.R., Hennekens, C.H., Willett, W.C., and Buring, J.E., Fruit and vegetable intake and risk of cardiovascular disease: the Women’s Health Study, Am. J. Clin. Nutr., 72, 922, 2000. 36. Bazzano, L.A., He, J., Ogden, L.G., Loria, C.M., Vupputuri, S., Myers, L., and Whelton, P.K., Fruit and vegetable intake and risk of cardiovascular disease in US adults: the first National Health and Nutrition Examination Survey Epidemiologic Follow-up Study, Am. J. Clin. Nutr., 76, 93, 2002. 37. Berliner, J., Leitinger, N., Watson, A., Huber, J., Fogelman, A., and Navab, M., Oxidized lipids in atherogenesis: formation, destruction and action, Thromb. Haemost., 78, 195, 1997. 38. Witztum, J.L. and Berliner, J.A., Oxidized phospholipids and isoprostanes in atherosclerosis, Curr. Opin. Lipidol., 9, 441, 1998. 39. Sanchez-Moreno, C., Jimenez-Escrig, A., and Saura-Calixto, F., Study of low-density lipoprotein oxidizability indexes to measure the antioxidant activity of dietary polyphenols, Nutr. Res., 20, 941, 2000. 40. Chu, Y.F. and Liu, R.H., Cranberries inhibit LDL oxidation and induce LDL receptor expression in hepatocytes, Life Sci., 77, 1892, 2005. 41. Ridker, P.M., Rifai, N., Rose, L., Buring, J.E., and Cook, N.R., Comparison of C-reactive protein and low-density lipoprotein cholesterol levels in the prediction of first cardiovascular events, N. Engl. J. Med., 347, 1557, 2002. 42. Ridker, P.M., Clinical application of C-reactive protein for cardiovascular disease detection and prevention, Circulation, 107, 363, 2003. 43. Libby, P., Ridker, P.M., and Maseri, A., Inflammation and atherosclerosis, Circulation, 105, 1135, 2002.


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44. Gao, X., Bermudez, O.I., and Tucker, K.L., Plasma C-reactive protein and homocysteine concentrations are related to frequent fruit and vegetable intake in Hispanic and non-Hispanic white elders, J. Nutr., 134, 913, 2004. 45. Eberhardt, M.V., Lee, C.Y., and Liu, R.H., Antioxidant activity of fresh apples, Nature, 405, 903, 2000. 46. Liu, R.H., Liu, J., and Chen, B., Apples prevent mammary tumors in rats, J. Agric. Food Chem., 53, 2341, 2005. 47. Adom, K.K., Sorrells, M.E., and Liu, R.H., Phytochemicals and antioxidant activity of wheat varieties, J. Agric. Food Chem., 51, 7825, 2003. 48. Adom, K.K., Sorrells, M.E., and Liu, R.H., Phytochemicals and antioxidant activity of milled fractions of different wheat varieties, J. Agric. Food Chem., 53, 2297, 2005. 49. Adom, K.K. and Liu, R.H., A rapid peroxylradical scavenging capacity (PSC) assay for assessing both hydrophilic and lipophilic antioxidants, J. Agric. Food Chem., 53, 6572, 2005. 50. Liu, R.H., Potential synergy of phytochemicals in cancer prevention: mechanism of action, J. Nutr., 134, 3479S, 2004. 51. Dupont, S., Bennett, R.N., Mellon, F.A., and Williamson, G., Polyphenols from alcoholic apple cider are absorbed, metabolized, and excreted by humans, J. Nutr., 132, 172, 2002. 52. Hollman, P., van Trijp, J.M., Buysman, M.N., van der Gaag, M.S., Mengelers, M.J., de Vries, J.H., and Katan, M.B., Relative bioavailability of the various antioxidant flavonoid quercetin from various foods in man, FEBS Lett., 418, 152, 1997. 53. Boyer, J., Brown, D., and Liu, R.H., Uptake of quercetin and quercetin-3glucoside from whole onions and apple peels by Caco-2 cell monolayers, J. Agric. Food Chem., 52, 7172, 2004. 54. Walle, T., Otake, Y., Walle, U.K., and Wilson, F.A., Quercetin glucosides are completely hydrolyzed in ileostomy patients before absorption, J. Nutr., 130, 2658, 2000. 55. Day, A., Gee, J.M., DuPont, M.S., Johnson, I.T., and Williamson, G., Absorption of quercetin-3-glucoside and quercetin-4-glucoside in the rat small intestine: the role of lactase phlorizin hydrolase and the sodium dependent glucose transporter, Biochem. Pharmacol., 65, 119, 2003. 56. Schneider, H., Schwiertz, A., Collins, M.D., and Blaut, M., Anaerobic transformation of quercetin-3-glucoside by bacteria from the human intestinal tract, Arch. Microbiol., 171, 81, 1999. 57. Olthof, M., Hollman, P., and Katan, M., Chlorogenic acid and caffeic acid are absorbed by humans, J. Nutr., 2001, 66, 2001. 58. Gonthier, M., Verny, M.A., Besson, C., Remesy, C., and Scalbert, A., Chlorogenic acid bioavailability largely depends on its metabolism by the gut microflora in rats, J. Nutr., 133, 1853, 2003. 59. Olthof, M., Hollman, P.C., Buijsman, M.N., van Amelsvoort, J.M., and Katan, M.B., Chlorogenic acid, quercetin-3-rutinoside and black tea polyphenols are extensively metabolized in humans, J. Nutr., 133, 1806, 2003. 60. Spencer, J., Metabolism of tea flavonoids in the gastrointestinal tract, J. Nutr., 133, 3255S, 2003. 61. Vaidyanathan, J. and Walle, T., Glucuronidation and sulfation of the tea flavonoid (−)-epicatechin by the human and rat enzymes, Drug Metab. Dispos., 30, 897, 2002.


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62. Liu, C.-S., Glahn, R.P., and Liu, R.H., Assessment of carotenoid bioavailability of whole foods using a Caco-2 cell culture model coupled with an in vitro digestion, J. Agric. Food Chem., 52, 4330, 2004. 63. Boyer, J., Brown, D., and Liu, R.H., In vitro digestion and lactase treatment influence uptake of quercetin and quercetin glucoside by the Caco-2 cell monolayer, Nutr. J., 4, 1, 2005.


5802_P002.fm Page 205 Monday, January 8, 2007 6:20 PM

Part II

Quality and safety of berry fruit during postharvest handling and storage



chapter 7

Quality of berries associated with preharvest and postharvest conditions Elizabeth Mitcham Contents 7.1 Introduction ............................................................................................... 7.2 Effect of harvest maturity and cultivar on fruit quality .......................................................................................... 7.2.1 Soluble solids, titratable acidity, and flavor ............................ 7.2.2 Pigments ........................................................................................ 7.2.3 Cell wall deterioration and softening....................................... 7.3 Changes after harvest............................................................................... 7.3.1 Changes in anthocyanins ............................................................ 7.3.2 Firmness......................................................................................... 7.3.3 Soluble solids, titratable acidity, and sensory quality ........... 7.3.4 Deterioration by pathogens........................................................ 7.3.5 Nutritional loss during postharvest handling and storage .................................................................................... 7.3.6 Enhancing nutritional content after harvest............................ References ...........................................................................................................

207 208 209 210 211 212 212 213 213 214 215 220 223

7.1 Introduction Berry fruits are among the most perishable of fruit crops and must be handled carefully to ensure the highest postharvest quality when they reach the consumer. Some berries have very high respiration rates and therefore a potentially short postharvest life. Many are fragile and easily bruised, requiring 207


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careful handling during harvest, packaging, and transportation. The fruits known horticulturally as berries are not all true berries, botanically speaking. Blueberry is considered a false berry because it is berry-like, but it is derived from an inferior ovary rather than a superior ovary.1 The button on the end of the fruit is actually the calyx scar. Blackberry, boysenberry, and raspberry are not berries at all, but are aggregate drupes, and strawberry, also an aggregate fruit, is an achene fruit. Blackberry, raspberry, and boysenberry are composed of drupelets with a fleshy mesocarp and a lignified endocarp containing the true seed, all held together by a receptacle. Each drupelet is supplied with assimilate and water by a separate vascular supply and contains a single seed.2 Raspberry druplets have fine hairs on the surface, while those of boysenberry do not. Boysenberry and blackberry retain their receptacle at harvest, while raspberry do not. Raspberries and blackberries are some of the most perishable of the berry fruits, with very high respiration rates. Blueberries, cranberries, currants, and strawberries have lower respiration rates and longer storage life. Ethylene production is generally low for this group of fruit, and many are nonclimacteric.3–5 One exception is blueberries, and there is some question about certain cultivars of blackberries.6 Ease of detachment is often a good guide to proper harvest maturity for blackberries, raspberries, and blueberries. The force required to remove blackberry fruit from the pedicel declines during ripening and varies among cultivars.6 Ethylene accelerates abscission and pigment changes in raspberry7 and blackberry6 fruit. While ethylene does not appear to regulate ripening of the nonclimacteric berry fruits, auxin is proposed to be the primary hormone controlling fruit ripening in strawberries. Auxin is synthesized in the achenes, the true fruits embedded in the fruit surface (commonly considered the seeds), and stimulates initial fruit growth.8 A gradual decline in auxin concentrations in later stages of growth has been proposed to initiate ripening,9 and auxin regulates transcription of many ripening-related genes in strawberry.10,11 It is not known if auxin plays a role in regulating ripening of other berry fruit.

7.2 Effect of harvest maturity and cultivar on fruit quality The characteristics and composition of ripe fruit are the result of biochemical and physiological changes. Harvest of berries should be at near full ripe stage, or the maximum ripeness stage that can be safely distributed to market to maximize sweetness and flavor development, as berries do not accumulate starch during development and therefore do not increase in soluble solids (an estimate of sugar content) after harvest.4 Titratable acidity, largely made up of citric acid in most berries, often decreases as the fruit ripens and after harvest. This decrease can increase the perceived sweetness of berries or result in bland flavor if the final concentrations are too low.


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7.2.1

Berry quality—preharvest and postharvest factors

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Soluble solids, titratable acidity, and flavor

Maturity for strawberries is defined on the basis of skin color, with a requirement for more than one-half or three-fourths of the surface being red or pink, depending on the U.S. grade. In California, fruit must have a minimum of two-thirds red or pink color. Strawberries ripen quickly on the plant.12 There is an increase in soluble solids, total sugars, total ascorbic acid, pH, and water soluble pectins, and decreases in acidity, total phenols, and activities of polyphenol oxidase and peroxidase in strawberries as they ripen.13 When strawberries are harvested with at least three-fourths red color, they continue their development and ripening during storage, developing the same pH, acidity, soluble solids, ascorbic acid, and total phenolics content during storage as the at-harvest levels present in fruit harvested at the full red color stage.14 However, fruit harvested at half-color do not develop like those ripened in the field. Volatile production of strawberries was the highest over a 10-day storage period when fruit were picked with more red color.15 Also, three-fourths red fruit were as firm and red after storage as the full red stage fruit were at harvest, thus strawberries harvested at three-fourths red stage can be stored longer than strawberries harvested full red, while retaining better color and firmness.14 For strawberries, a minimum of 7% soluble solids and a maximum of 0.8% titratable acidity are recommended for best eating quality.16 The harvesting of blueberries, blackberries, and raspberries is determined by color development.17 Fruit should be harvested with full or nearly full color development to maximize eating quality. Berries should also easily detach from the plant when ripe. Because fruit ripens on the plant at different times, plants must be harvested every few days, depending on the weather, to prevent overripening. As blueberries develop and ripen, there is an increase in soluble solids and a decrease in overall titratable acidity. Ripe berries will remain attached for several days to weeks and sugars will continue to accumulate. Blueberries exhibit increases in malic, chlorogenic, and phosphoric acid and decreases in citric and quinic acids during ripening.18 The amount of citric acid in blueberries varies with the variety. Blueberry cultivar soluble solids content ranged from 9% to 11.5% and titratable acidity ranged from 0.54 to 1.13 citric acid equivalents, resulting in a soluble solids:titratable acidity ratio ranging from 10 to 19 among the 10 cultivars tested at harvest.19 Raspberries also increase in soluble solids and decrease in titratable acidity as they develop and ripen.4 Titratable acidity, soluble solids, and pH contribute to fruit flavor, and acidity and soluble solids vary greatly between cultivars. Blackberries increase in soluble solids content and decrease in titratable acidity during ripening on the plant.20,21 The increase in soluble solids occurs particularly between the 50% black and shiny black stage, and increases during storage due to weight loss.22 There are greater changes in titratable acidity than soluble solids content as ripening progresses. Titratable acidity decreases as much as 50% between the 50% black and shiny black stages and 10% to 30% between the shiny black and dull black stages, depending on the cultivar.22 Following storage, titratable acidity decreases 10% to 30%,


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depending on the stage at harvest. Sometimes titratable acidity increases in very ripe fruit due to weight loss in storage. Blackberries can develop a red discoloration after harvest. This is theorized to result from harvesting of less mature fruit, resulting in less total pigment and a lower pH or differences in the relative concentration of various pigments.22 Harvest maturity is one of the main factors that determines nutritional quality.23 Freshly harvested fruit generally has a higher vitamin content than stored products, as nutrients begin to be lost as soon as the fruit is harvested.23 Woods et al.21 found significant variations among blackberry cultivars in their antioxidative properties (Trolox equivalent antioxidant capacity [TEAC] values), and these were also influenced by harvest maturity. However, Perkins-Veazie and Collins22 showed that while anthocyanin content in blackberries differed among color stages, there was no difference among cultivars, indicating other compounds are involved in blackberry antioxidant activity. Antioxidant activity declined between the red and dull black ripening stages of blackberry. Vitamin C content either declined or remained unchanged with ripening. Ascorbic acid content ranged from 15.4 to 32.0 mg/100 g among five cultivars of raspberries.24 In black raspberries, significant changes in the antioxidant capacity occur during the periods surrounding peak ripeness, and this appears to be cultivar dependent.25 Berry fruit is generally rich in phenolic acids.26 The fruit phenolic content can be as high as 0.4% in some berries.27 High sugars and high acids are required for good berry flavor.28 High acid with low sugar results in a tart berry, while high sugar and low acid results in a bland taste. When both are low, the fruit is tasteless. Volatile compounds are also important to aroma and flavor, especially ester compounds. Cultivar selection has a large influence on sensory quality. Good correlations were found between sensory sourness and titratable acidity, total phenolics, astringency, and sensory sweetness in strawberry cultivars.29 Off-flavors were positively correlated with astringency and negatively correlated with strawberry flavor intensity. Blueberry flavor appears to be closely related with acid content, as high acid cultivars were also rated as high in blueberry flavor by sensory panelists and low-acid varieties had low flavor scores.30 Preharvest and postharvest factors can also influence fruit composition and quality, such as genetic and environmental factors (light, temperature, relative humidity, water supply). Sunny days and cool nights produce better flavored berries than cloudy, humid days and warm nights. Inadequate light intensity reduces ascorbic acid, pH, color, and soluble solids. Excess nitrogen decreases firmness, soluble solids, and flavor.

7.2.2

Pigments

Anthocyanins are the main types of pigment responsible for the color of strawberries, blueberries, raspberries, and blackberries. Anthocyanins may be localized in the skin or in the entire fruit and are largely responsible for fruit color, although small amounts of carotenoids are also present. A high


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correlation was found between objective skin color measurements (L*, a*, b* values) and anthocyanin content in red raspberries.31 The anthocyanin content varies between cultivars of raspberries and increases with fruit maturity before harvest and during storage.5 As strawberries ripen, an increase in anthocyanin content is accompanied by decreases in firmness and chlorophyll content. Strawberry fruit color develops quickly from first blush to fully red in only 24 to 36 hours.12 The accumulation of anthocyanins in strawberries coincides with the induction of phenylalanine ammonia lyase and uridine diphosphate glucose:flavonoid O3-glucosyltransferase enzymes.8 The total anthocyanin content of blueberry cultivars ranged from 57 to 208 absorbance units/g fresh weight (FW) at harvest.9

7.2.3

Cell wall deterioration and softening

Berry fruits soften as they ripen. Fruit firmness in raspberries was shown to be influenced by overall fruit size, hairiness, number and size of drupelets, and receptacle cavity size.5 Extensive fruit softening occurred with the transition in blueberry color from red to blue-red. A 50% red strawberry will lose 25% of its firmness in the 24 hours it takes to turn fully red and an additional 15% if it remains on the plant another 24 hours.12 When the strawberry is removed from the plant, color and flavor development continue, but there is little change in acid and sugar content or firmness. There can be considerable differences among cultivars in the firmness of ripe or partially ripe berries.28 Fruit textural changes result, at least in part, from changes in cell wall composition and architecture through the action of hydrolytic enzymes. Both polyuronides and hemicelluloses are important to the texture of strawberries.32 Pectins shift from insoluble to soluble during fruit ripening.32,33 Cellulase activity increased sixfold in maturing and softening strawberries, and ethylene has no influence on cellulose levels.34 Several pectin modifying genes have been cloned in strawberries, including pectatelyase,35 endopolygalacturonase,36 β-galactosidase,37 and pectin esterase.38 In blueberries, there was a 20% to 60% increase in water soluble pectin during ripening, while chelator soluble pectin increased slightly, and the contribution of pectin to the insoluble material in the fruit decreased twofold.33 In highbush blueberries, the activity of pectin methylesterase peaked at the red color stage, before the peak in polygalacturonase activity which occurred at the blue-red stage.39 Vicente40 found that hemicellulose metabolism was important during the softening of blueberries. In the early stages, there were increases in the solubilization of pectin and hemicellulose polymers, but without a decrease in polymer size. At later stages, there was a decrease in the size of hemicellulose polymers, but not those of pectin. Cell wall disassembly occurs in three stages in boysenberries and raspberries.40 In the earliest stage, there were decreases in cellulose and solubilization of cross-linking glycans. In the second stage, there was a large increase in pectin solubilization and loss of arabinose, but the pectin pieces remained large. In the final stage, there was


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a large decrease in the size of the pectin molecules and a loss of galactose. The pectins of boysenberries, raspberries, and blueberries were found to be rich in arabinose relative to galactose, in contrast to results for other fruits such as tomato and melon.40 Cellulase activity, but not polygalacturonase activity, increased during the ripening of blackberries,41 and therefore cellulase is considered the key enzyme responsible for softening in blackberry fruit. Cellulase releases pectins from the cell walls of ripening fruits, and these soluble pectins also bind polyphenols, reducing astringency and making the fruit more palatable.42

7.3 Changes after harvest Fresh fruit is living tissue and continually changes after harvest. Such changes can only be slowed by judicious use of proper postharvest handling procedures, particularly the lowest safe storage temperature. Potential postharvest life varies among berries, but is generally shorter than for many other types of fruit. Respiration and ethylene production rates vary among cultivars of red raspberry.43 However, the higher respiration rates observed with some cultivars of red raspberry were not associated with decreased overall storage life. The respiration rate of red raspberry was negatively correlated with percent changes in firmness during storage at 0°C and confirmed that rapidly respiring cultivars ripen relatively slowly in prolonged storage.

7.3.1

Changes in anthocyanins

Anthocyanin content of blueberries increased by 22% to 55% during 21 days of storage at 5°C.9 Sjulin and Robbins44 observed darkening of red raspberries during storage. Color change occurred faster at higher storage temperatures, especially during the first 4 days of storage.31 Storage of red raspberries for 16 days at 0°C maintained fruit color (higher a* and b* values) better than storage at 5°C.31 During 36 days of storage at 0°C, there was an increase in anthocyanin content and pH in red raspberries43 and fruit became less red and bluer in color due to the increase in pH.31,45 Cultivars generally maintained their at-harvest rankings of quality even after cold storage.43 During storage of raspberries, color darkened and became more blue and less red as anthocyanins developed and pH increased.45 This change occurred more slowly at lower temperatures.31 The rate of pH increase was different among cultivars, while the rate of decrease in titratable acidity was the same among red raspberry cultivars.45 The amount of anthocyanins may be more important in visible color changes than shifts in acidity levels. Robbins and Moore31 reported that cultivars going into storage with lighter, redder fruit, with little blue, resulted in lighter, redder, less blue fruit after storage. Strawberries also exhibited darkening after harvest, regardless of the maturity at harvest.14,15,46 The ability of strawberries to develop full color in storage when harvested partially ripe varies with the cultivar. The development


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of red color after harvest is also influenced by storage temperature.47 At temperatures of 24°C to 29°C, partially ripe strawberries developed full red color in 4 or 2 days, respectively, and at 18°C 90% color developed after 4 days of storage. The after-storage hue of Chandler and Oso Grande strawberries harvested at the three-fourths red stage was similar to that of fruit harvested at full red; however, the hue of Sweet Charlie strawberries harvested at three-fourths red did not change significantly during storage.14 The color of strawberries tends to increase in chroma during fruit development. After storage, higher chroma values were observed in fruit that were harvested with three-fourths red or full red color, indicating that the red color was more pure or vivid. The increase in red color during ripening of strawberries on the plant or after harvest was accompanied by an increase in total anthocyanins; however, total anthocyanin, cyanidin-3-glucoside, and pelargonidin-3-glucoside content were much lower in strawberries ripened in cold storage compared with those ripened in the field.14

7.3.2

Firmness

The firmness of strawberries decreased during ripening, in the field and after harvest.14 In Nunes et al.’s study,14 the firmness of Chandler and Sweet Charlie strawberries harvested full red did not change during storage, although the fruit appeared riper. Strawberries harvested at one-half or three-fourths red color were not firmer than fruit harvested at full color after 8 days of cold storage. During storage, changes in the rate and direction of firmness in red raspberries varied among the cultivars.43,48 Robbins et al.43 observed an increase in firmness of some red raspberry cultivars during storage, which they postulated was due to temporary calcium binding of pectic polymers. Mitcham et al.30 found increases in blueberry firmness during 3 weeks of cold storage in several cultivars, but Forney et al.49 found no change in firmness after 3 weeks of storage at 0°C or 7°C, but did find increases in firmness after 6 and 9 weeks of storage in Burlington blueberries. The increase in firmness was temperature dependent, being greater when fruit was held at 7°C than at 0°C. Associated with fruit firming was a corrugation and thickening of the epidermal and hypodermal cell walls.50 Strawberries also exhibited an increase in fruit firmness as a result of exposure to 15% carbon dioxide (CO2) after harvest.51 This effect was seen in most, but not all cultivars tested.

7.3.3

Soluble solids, titratable acidity, and sensory quality

Changes in the balance between sugar and acid content during storage of red raspberries52,53 affect the sensory quality of the fruit.54 The titratable acidity of red raspberries decreased, while soluble solids increased during storage at 0°C,43 which was likely due to water loss. Burlington blueberries decreased in both soluble solids content and titratable acidity during storage.49 The soluble solids content of several southern highbush blueberries did not


214


show significant changes during 21 days of storage at 5°C, except Climax, which showed a significant increase in soluble solids.9 This increase could not be entirely accounted for by weight loss. Titratable acidity increased in two blueberry cultivars, decreased in a third, and remained unchanged in seven others. The titratable acidity of strawberries decreased as fruit ripened on the plant. This trend generally occurs as fruit continues to ripen during storage.55 However, while Nunes et al.14 observed a decrease in titratable acidity during storage of fruit harvested fully red, they observed an increase in titratable acidity in several cultivars during storage of strawberries harvested at three-fourths red color or less.14 The soluble solids content of strawberries increased as fruit ripened in the field and was correlated with red color development within a planting.14 Strawberries showed increases in soluble solids after harvest as well,14 but soluble solids content was higher in fruit ripened in the field.13,47 Also, postharvest increases in soluble solids are probably not due to conversion of starch to sugars, since strawberries accumulate very little starch. The increase may be due to solubilization of cell wall pectins increases in titratable acidity or increases in anthocyanins, all of which contribute to soluble solids, or due to dehydration. Changes in the surface color of strawberries during ripening coincided with the production of volatiles.15 When strawberries were harvested at red or pink color and stored at 15°C, volatiles production peaked after 4 days and was eightfold higher in red fruit than pink. The postharvest life of strawberries based on sensory quality was shorter than that for appearance quality and varied among varieties.29 The postharvest life based on sensory quality was short in Aromas strawberries stored in air or 20% CO2 at 5°C and for Selva strawberries stored in 20% CO2. However, Selva and Diamonte strawberries retained their flavor quality during storage at 5°C in air and 20% CO2, respectively. The differences in sensory quality were based on the level and proportion of flavor components (sugars, organic acids, and aroma compounds) and fermentative metabolites.

7.3.4

Deterioration by pathogens

Postharvest decay is a common cause of deterioration in berry fruit. Botrytis cinerea is one of the most common pathogens observed after harvest.5 In many fruit, such postharvest decay results in large part from preharvest quiescent infections.56 Other infections occurred as a result of nesting; spreading of infections from fruit to fruit. All berry fruit have tender skins and raspberry has a very fragile structure because of the open receptacle cavity that is easily injured, allowing invasion by pathogens. Blueberry cultivars vary in their susceptibility to postharvest decay.57 Colletotrichum acutatum, Colletotrichum gloeosporioides, and B. cinerea were the main rots observed. In general, late-season berries were more susceptible to decay than fruit from earlier harvests. To control decay, prompt and thorough cooling after harvest is critical, followed by storage at the lowest safe temperature to prevent deterioration


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215

of the fruit. Rhizopus rot spores are present in the air and easily spread. The fungus will not grow at temperatures lower than 5°C, and temperature management is the simplest method of control. However, the common pathogen B. cinerea continues to grow slowly at 0°C. Modified atmosphere packaging for shipment with 15% to 20% CO2 and 5% to 10% oxygen (O2) reduces the growth of B. cinerea and other pathogens (such as Rhizopus stolonifer) and reduces the respiration and softening rates of strawberries, blueberries, raspberries, and blackberries, thereby extending postharvest life.58,59 Blueberries maintained acceptable firmness and decay levels after 60 days of storage in 15% CO2.59 It is unknown what effect this storage regime had on fruit flavor. Storage of strawberries in elevated CO2 atmospheres reduced respiration rates during treatment and for a period of time after treatment. The higher the CO2 concentration, the more pronounced the residual effects.60 Blueberries also showed a decrease in respiration rate with higher CO2 concentrations.61 Whole-pallet covers and consumer packages for containment of the modified atmosphere are commonly used for berries. Prompt cooling must be done before applying atmosphere modification.58 Off-flavors can result from high CO2 treatment, depending on the cultivar, temperature, and exposure time. A modified atmosphere containing 20% CO2 was effective in suppressing the growth of B. cinerea on strawberries and reducing nesting of infection from diseased to healthy berries.62 High CO2 has also been shown to control decay on blueberries49,63 and raspberries.5 Storage of strawberries in 20% CO2 resulted in off-flavor development after 3 days.64 Off-flavors were due to increases in ethyl acetate and ethanol, but not acetaldehyde. Off-flavors were also noted when blueberries were stored in CO2 greater than 10% for several weeks.49 After 6 weeks in 25% CO2, stress-induced volatiles, ethanol, and ethyl acetate accumulated. It was recommended that blueberries be stored at 0°C with 10% CO2.49 Low-dose irradiation has been demonstrated to be effective for the control of decay in strawberries, used either alone or in combination with elevated CO2 atmospheres,65 and is used commercially to a limited extent. Blackberries stored in up to 0.3 ppm ozone for 12 days at 2°C showed suppressed fungal growth and better retention of fruit surface color.66 Continuous ozone exposure at 0.1 ppm during storage at 2°C completely controlled decay by B. cinerea, while 20% of untreated blackberries decayed.66 Irradiation of blueberries with ultraviolet C (UV-C) light (up to 4000 J; 354 nm) provided a slight reduction in decay by Colletotrichum gloeosporioides.67

7.3.5

Nutritional loss during postharvest handling and storage

Water-soluble vitamins are more susceptible to postharvest losses than fat-soluble vitamins, and vitamin C (ascorbic acid) is especially susceptible to postharvest losses. Losses after harvest are promoted by longer storage times, higher temperatures, low relative humidity, and physical damage. Harvesting methods can cause physical injury and therefore can affect the


216


nutritional quality of the fruit. Delays from harvest to cooling or processing increase the loss of nutrients. Strawberries lose vitamin C rapidly during postharvest handling if the fruit is capped (calyx removed) and all fruit loses vitamin C if bruised during harvest.68 The ascorbic acid content is relatively high in strawberries (about 60 mg/100 g FW), depending on the cultivar, but water stress can induce ascorbic acid loss in strawberries.69 Wrapping the fruit with plastic film reduced water loss and reduced ascorbic acid loss in strawberries.69,70 The effect was not due to modification of the atmosphere, as this was minimal. The total ascorbic acid content of the wrapped strawberries changed little during 8 days of storage at 1°C or 10°C, while the unwrapped strawberries lost 20% to 30% of their ascorbic acid content over the 8 days. The ascorbic acid content increases in strawberries as they ripen, particularly at the later stages of color development. Nunes et al.14 observed increases in total ascorbic acid of as much as 21% in two strawberry cultivars. The increases were larger in fruit harvested less ripe, as the fruit continued to ripen and synthesize ascorbic acid during storage. Nunes et al.14 proposed that ascorbic acid might be synthesized from D-glucose during storage of strawberries. As much as 100% of a nutrient can be lost between harvest and consumption without detectable changes in flavor or texture.71 Losses vary by nutrient type, type of fruit, physical damage, temperature, and storage environment.72 The ascorbic acid content in raspberries was unchanged or slightly higher after storage in air, 15% CO2, or 31% CO2 for 7 days at 1.7°C.24 Postharvest handling and storage operations that maintain the quality characteristics of color, flavor, and texture, and control decay also reduce micronutrient losses.73 However, large losses can occur in fruit stored for a long time. For fresh-cut strawberries, the postcutting life based on visual quality ended before there was a significant loss of vitamin C.74 Nutrients in frozen, pasteurized, and sterilized products are relatively stable; however, large losses may occur before processing and during preparation for consumption. Vitamins in fruits are primarily destroyed by oxidation catalyzed by enzymes, light, prooxidant metals, active O2 species or other chemical oxidants.75 Most studies of vitamin loss in fruits and vegetables have focused on ascorbic acid. In addition to being an essential nutrient, ascorbic acid has reducing and antioxidant properties. Both ascorbic acid and its oxidized product, dehydroascorbic acid (DHA), have similar vitamin C activity, but only ascorbic acid has reducing properties, which are important for inhibiting browning reactions. Vitamin C activity is irreversibly destroyed when DHA is hydrolyzed. During storage, DHA increases at the expense of ascorbic acid76 and may be responsible for more than 50% of the vitamin C activity in some fresh fruits and vegetables. Storage in controlled or modified atmospheres can affect the loss of nutrients such as ascorbic acid. Bangerth77 found reduced losses of ascorbic acid in apples and red currents stored in reduced O2 atmospheres and accelerated ascorbic acid losses during storage in elevated CO2 atmospheres. In general, the lower the O2 concentration, the slower the loss of ascorbic acid;


Chapter 7:


217

however, the effect of elevated CO2 was variable, depending on the concentration, the storage temperature, and the type of fruit. Oxidation of ascorbic acid to DHA was reduced by modified atmosphere packaging in fresh-cut peppers (Capsicum annum L.).78 The total ascorbate content in fresh-cut strawberries was unaffected after storage for 7 days at 5°C under controlled atmospheres.74 Storage of strawberries in modified atmospheres using package liners reduced the loss of ascorbic acid during 12 days of cold storage.79 Strawberries stored in controlled atmospheres with 5% O2 and 0.5% CO2 maintained higher levels of ascorbic acid than fruit stored in air; however, when the fruit was stored in controlled atmospheres with 15% CO2, there was no difference in ascorbic acid content between the controlled atmosphere and air-stored fruit.79 Vitamin C content was reduced by high CO2 (10% to 30%) storage, particularly in strawberries. In this study, reducing the O2 concentration in the storage atmosphere in the presence of high CO2 had little effect on the vitamin C content. Ascorbic acid was decreased more by high CO2 than DHA.80 High CO2 may stimulate the oxidation of ascorbic acid by inducing injury and ethylene production, which increases ascorbate peroxidase activity.81 Loss of ascorbic acid was accelerated when fruit was transferred from a controlled atmosphere in cold storage to retail storage conditions at 18°C. Washing intact or sliced strawberries in 100 ppm sodium hypochlorite can induce significant oxidation of reduced ascorbic acid, but it did not affect total ascorbic acid content and therefore may not be nutritionally significant (Figure 7.1).74 Irradiation treatment results in negligible losses in niacin, thiamin, riboflavin, and β-carotene. Ascorbic acid is more radiosensitive and its losses range from 0 to 90%, depending on the commodity, cultivar, irradiation dose and duration, and storage temperature.82 Irradiation of strawberries with 1 to 3 kGy combined with refrigeration resulted in reduced levels of total ascorbic acid and increased levels of DHA immediately after treatment and after 5 days of storage (Figure 7.2).83 After 10 days of storage, the levels of DHA were also decreased. At present, there are very few data available describing the extent to which postharvest practices and storage affect phytonutrient content.84 The phenolic content of strawberries has shown inconsistent trends, in some cases increasing14,27 and in other cases decreasing or remaining unchanged.14 The anthocyanin content increased with time in storage for red raspberries45 and the rate of increase was similar among cultivars. There is a positive correlation between antioxidant activity and total phenolic or anthocyanin content.85,86 The anthocyanin content in dull black blackberries decreased after 7 days of storage, but that in shiny black and 50% black fruit did not change during storage.22 Anthocyanin synthesis continues in harvested strawberries and blueberries, even at low storage temperatures. However, the content of total anthocyanins, cyanidin-3-glucoside, and pelargonidin3-glucoside was much lower in strawberries that ripened in cold storage instead of in the field.14 The anthocyanin concentration in strawberries increased in both external and internal tissues during postharvest storage in



% of L-absorbate present as L-dehydroascorbat

218 8

7.4%c 7

6.5%bc

6 5.1%b

5 4 3 2.3%a 2 1 0 0

1

2

3

4

5

Treatment

Figure 7.1 Effect of different washing treatments on the percentage of total ascorbate oxidized to dehydroascorbate in strawberries. Values followed by different letters are significantly different, p < .05. Treatments: 1 = control, sliced without washing; 2 = sliced, washed in water; 3 = sliced, washed in water with 100 ppm sodium hypochlorite; 4 = washed in water with 100 ppm sodium hypochlorite, then sliced. (From Wright, K.P. and Kader, A.A., Effect of slicing and controlled-atmosphere storage on the ascorbate content and quality of strawberries and persimmons, Postharvest Biol. Technol., 10, 39, 1997, with permission.)

air at 5°C for 10 days, but the increase was lower in fruit stored in air enriched with 10% or 20% CO2.27 Anthocyanin levels in Aromas and Diamante strawberries were not affected by storage duration or atmosphere, but in Selva, the accumulation of anthocyanins observed in air-stored fruit was inhibited by CO2 (Figure 7.3). CO2 promotes anthocyanin loss in stored strawberries.87 Gil et al.87 found that controlled atmosphere storage decreased the anthocyanin content of internal strawberry tissues, but did not affect the anthocyanin content in external tissues. Storage of red raspberries in CO2 atmospheres (15% or 30% CO2) inhibited the increase in anthocyanin levels that occurred in air storage (Table 7.1).24 Heat treatments may reduce phenylalanine ammonia lyase activity and anthocyanin accumulation in strawberries during storage.88 The total antioxidant capacity of blueberries (as measured using the ferric reducing antioxidant capacity [FRAP]) method) was measured at harvest and after storage. The total antioxidant capacity varied among the varieties and decreased considerably during 1 month of storage.89 The fruit maturity of blueberries had a significant effect on antioxidant activity, total phenolic content, and anthocyanin content.90 During storage at 5°C, none of nine blueberry cultivars tested showed a significant decrease from the antioxidant


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219

90 Total L-Ascorbic Acid

80 70 60 50 40 30 20 10 0 0 kGy 1 kGy 2 kGy 3 kGy

L-dehydroascorbic Acid

12 10 8 6 4 2 0 0

5

10

Storage Days

Figure 7.2 Effect of irradiation dose and storage time on the total L-ascorbic acid and L-dehydroascorbic acid content of strawberry fruit. (Adapted from Graham, W.D. and Stevenson, M.H., Effect of irradiation on vitamin C content of strawberries and potatoes in combination with storage and with further cooking in potatoes, J. Sci. Food Agric., 75, 371, 1997.)

values at harvest until the end of the marketable life was reached for that cultivar (3 to 7 weeks). One cultivar demonstrated a 29% increase in antioxidant activity. Antioxidant activity, total phenolic content, and anthocyanin content were strongly correlated with each other and moderately correlated with soluble solids content. The three factors showed no correlation with firmness, percent severely bruised berries, or weight loss. Vaccinium corymbosum cv. Bluecrop also showed a 1.2-fold increase in anthocyanin content during 8 days of storage at 20°C, which was accompanied by a 1.2-fold increase in oxygen radical absorption capacity (ORAC), while storage at 0°C, 10°C, or 30°C did not result in significant changes.91 Lowbush blueberry clones did not show a change in ORAC during 8 days of storage at 0°C, 10°C, 20°C, or 30°C, despite a 27% loss in ascorbate at 20°C and 30°C.91 Kalt and McDonald92 reported a mean 18% increase in anthocyanin content in three lowbush blueberry (Vaccinium angustifolium) cultivars, each harvested at three different maturities, when stored at 1°C for 2 weeks. These results


Pelargonidin-3-glucoside (mg L−1)

220

Berry fruit: Value-added products for health promotion A,Air A, Air+20kPaCO2 S,Air S,Air+20kPaCO2 D,Air D,Air+20kPaCO2

200

150

100

50 0

2

4

6

8

10

Days at 5°C

Figure 7.3 Total anthocyanin content (mean ± SD) of three strawberry cultivars stored at 5°C in air or air + 20% CO2. A = Aromas; D = Diamonte; S = Selva. (From Pelayo, C., Ebeler, S.E., and Kader, A.A., Postharvest life and flavor quality of three strawberry cultivars kept at 5°C in air or air + 20 kPa CO2, Postharvest Biol. Technol., 27, 171, 2003, with permission.)

indicate that the antioxidant health benefits of blueberries can be retained for several weeks after harvest, as the antioxidant activity appears to be stable in blueberries. When blueberries are harvested immature (50% to 75% blue), the antioxidant activity increased during cold storage to significant levels, although it did not reach the level found in fruit harvested mature.90

7.3.6

Enhancing nutritional content after harvest

Controlled stresses may be used as a tool to enhance the health benefits of fruits after harvest.93 These stresses might include wounding, phytohormone treatments, UV light exposure, other radiation treatments, controlled or modified atmosphere exposure, and water stress. Kalt et al.91 showed that storing different types of berries at temperatures greater than 0°C induced phenolic synthesis and increased the fruit total antioxidant capacity. Studies with black raspberries showed that storage of fruit at higher temperatures (up to 28°C) increased the level of bioactive compounds (such as anthocyanins) and antioxidant capacity, but the increase may have been due to moisture loss and metabolism of sugars.94 Tissue deterioration, fungal decay, and moisture loss were promoted by higher temperatures, while storage at 4°C maintained

22.5a 21.0b 21.6ab 20.8b *** NS 40.1bc 48.5a 41.7b 37.0c *** *

56.6a 40.7b 33.0c 41.5b 37.4bc *** 2.4b 6.3s 6.7a 6.6a *** **

6.3a 6.9a 6.5a 3.7b 4.1b *** 0.00b 5.18a 1.18b 1.04b *** NS

1.04c 1.02c 2.01ab 1.92ab 3.26a *

Rotting weight (%)

10.14 9.91 9.85 9.79 NS NS

9.26c 9.79b 10.50a 9.87b 10.20ab ***

Soluble solids (%)

2.32a 2.11c 2.16bc 2.29b *** *

2.24b 1.90c 1.96c 2.52a 2.29b ***

Titratable acidity (% citric acid)

23.2b 23.0b 24.7a 23.2b ** NS

15.4d 16.4d 25.3c 28.6b 32.0a ***

Ascorbic acid (mg/100 g)

Source: Modified from Haffner, K., Rosenfeld, H.J., Skrede, G., and Wang, L., Quality of red raspberry, Rubus idaeus L. cultivars after storage in controlled and normal atmospheres, Postharvest Biol. Technol., 24, 279, 2002.

NA = air; CA1 = 10% O2 + 15% CO2; CA2 = 10% O2 + 30% CO2. NS = not significant; *p < .05; **p < .01; ***p < .001.

Interactions A×B

Treatment (B) Start Air CA1 CA2

20.8bc 22.5a 22.1a 21.9ab 20.0c ***

Firmness (cm)

Chapter 7:

Cultivar (A) Veten Malling Admiral Malling Orion Glen Lyon Glen Ample

Hue°

Anthocyanin (mg/100 g)

Table 7.1 Effects of Cultivar and Storage Conditions on Chemical and Physical Variables of Raspberries


Berry quality—preharvest and postharvest factors 221


222


Phenolic compounds (mg/100 g F.W.)

160

Control MJ10−4 M Ethanol MJ+ETOH

150 140 130 120 110

ORAC TE (µmol/g F.W.)

100

9.0

8.5

8.0

0

5

7

11

Figure 7.4 Effect of ethanol, methyl jasmonate and their combination on (a) total antioxidant capacity and (b) total phenolic compounds in Allstar strawberries after 12 days storage at 7.5°C. (Adapted from Ayala-Zavala, J.F., Wang, S.Y., Wang, C.Y., and Gonzalez-Aguilar, G.A., Methyl jasmonate in conjunction with ethanol treatment increases antioxidant capacity, volatile compounds and postharvest life of strawberry fruit, Eur. Food Res. Technol., 221, 731, 2005.)

the levels of bioactive compounds and antioxidant capacity present at harvest and prolonged the shelf life of the fruit. Treatment of strawberries after harvest with methyl jasmonate (22.4 mg/l) or ethanol vapors (400 µl/l) increased the antioxidant capacity of the fruit during storage at 7.5°C, and the combination treatment had the highest antioxidant capacity, total phenolics (Figure 7.4), and anthocyanins.95 These treatments also maintained fruit quality and reduced fungal decay during storage.


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Not all of the health-promoting properties of berries are best maintained or maximized under optimal conditions during storage. It appears that a balance must be maintained between optimizing storage life and quality after storage and maintaining or inducing maximum nutritional quality. Postharvest treatments and storage regimes must be reevaluated if the goal is to maximize nutritional quality.

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19. Perkins-Veazie, P., Clark, J.R., Collins, J.K., and Magee, J., Southern highbush blueberry clones differ in postharvest fruit quality, Fruit Varieties J., 49, 46, 1995. 20. Walsh, C.S., Popenoe, J., and Solomos, T., Thornless blackberry is a climacteric fruit, HortScience, 18, 482, 1983. 21. Woods, F.M., Dozier, W.A., Ebel, R.C., Thomas, R., Nesbitt, M., Wilkins, B.S. and Himelrick, D.G., Cultivar and maturity effects on fruit quality and antioxidant properties in blackberry, HortScience, 41, 1043, 2006. 22. Perkins-Veazie, P. and Collins, J.K., Cultivar and maturity affect postharvest quality of fruit from erect blackberries, HortScience, 31, 258, 1996. 23. Kader, A.A., Influence of preharvest and postharvest environment on nutritional composition of fruits and vegetables, in Horticulture and Human Health: Contributions of Fruits and Vegetables, Quebedeaux, B. and Bliss, F.A. (Eds.), Prentice-Hall, Englewood Cliffs, NJ, 1988, p. 18. 24. Haffner, K., Rosenfeld, H.J., Skrede, G., and Laixin, W., Quality of red raspberry, Rubus idaeus L. cultivars after storage in controlled and normal atmospheres, Postharvest Biol. Technol., 24, 279, 2002. 25. Ozgen, M., Tulio, Jr., A.Z., Chanon, A.M., Janakiraman, N., Reese, R.N. and Miller, A.R., Phytonutrient accumulation and antioxidant capacity of eight developmental stages of black raspberry fruit, HortScience, 41, 1082, 2006. 26. Zadernowski, R., Naczk, M., and Nesterowicz, J., Phenolic acid profiles in some small berries, J. Agric. Food Chem., 53, 2118, 2005. 27. Holcroft, D.M. and Kader, A.A., Carbon dioxide-induced changes in color and anthocyanin synthesis of stored strawberry fruit, HortScience, 34, 1244, 1999. 28. Kader, A.A., Quality and its maintenance in relation to the postharvest physiology of strawberry, in Dale, A. and Luby, J.J., Eds., The Strawberry into the Twenty-First Century, Timber Press, Portland, OR, 1991, p. 145. 29. Pelayo, C., Ebeler, S.E., and Kader, A.A., Postharvest life and flavor quality of three strawberry cultivars kept at 5°C in air or air + 20 kPa CO2, Postharvest Biol. Technol., 27, 171, 2003. 30. Mitcham, E., Biasi, W., Gaskell, M., Faber, B., and Lobo, R., Sensory quality and postharvest performance of southern highbush blueberry cultivars grown in southern California, HortScience, 41, 1043, 2006. 31. Robbins, J.A. and Moore, P.P., Color change in fresh red raspberry fruit stored at 0, 4.5, or 20°C, HortScience, 25, 1623, 1990. 32. Huber, D.J., Strawberry fruit softening: the potential roles of polyuronides and hemicelluloses, J. Food Sci., 49, 1310, 1984. 33. Proctor, A. and Peng, L.C., Pectin transitions during blueberry fruit development and ripening, J. Food Sci., 54, 385, 1989. 34. Abeles, F.B. and Takeda, F., Cellulase activity and ethylene in ripening strawberry and apple fruits, Sci. Hort., 42, 269, 1990. 35. Medina-Escobar, N., Cardenas, J., Moyano, E., Caballero, J.L., and MunozBlanco, J., Cloning, molecular characterization and expression pattern of a strawberry-specific cDNA with sequence homology to pectate lyase from higher plants, Plant Mol. Biol., 34, 867, 1997. 36. Redondo-Nevado, J., Moyano, E., Medina-Escobar, N., Caballero, J.L., and Munoz-Blanco, J., A fruit-specific and developmentally regulated endopolygalacturonase gene from strawberry (Frageria × annanassa cv. Chandler), J. Exp. Bot., 52, 1941, 2001.


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37. Trainotti, L., Spinello, R., Piovan, A., Spolaore, S., and Casadoro, G., β-galactosidases with a lectin-like domain are expressed in strawberry, J. Exp. Bot., 52, 1635, 2001. 38. Castillejo, C., de la Fuente, J.I., Iannetta, P., Botella, M.A., and Valpuesta, V., Pectin esterase gene family in strawberry fruit: study of FaPE1, a ripeningspecific isoform, J. Exp. Bot., 55, 909, 2004. 39. Proctor, A. and Miesle, T.J., Polygalacturonase and pectinmethylesterase activities in developing highbush blueberries, HortScience, 26, 579, 1991. 40. Vicente, A.R., The temporal sequence of cell wall disassembly events in developing boysenberry, raspberry and blueberry fruits, Masters thesis, University of California–Davis, Davis, CA, 2006. 41. Abeles, F.B. and Takeda, F., Increased cellulose activity during blackberry fruit ripening, HortScience, 24, 851, 1989. 42. Ozawa, T., Lilley, T.H., and Haslam, E., Polyphenol interactions: astringency and the loss of astringency in ripening fruit, Phytochemistry, 26, 2937, 1987. 43. Robbins, J., Sjulin, T.M., and Patterson, M., Postharvest storage characteristics and respiration rates in five cultivars of red raspberries, HortScience, 24, 980, 1989. 44. Sjulin, T.M. and Robbins, J.A., Shelf life studies of red raspberry varieties, in Proceedings of the 73rd Annual Meeting of the Western Washington Horticultural Association, Western Washington Horticultural Association, Mount Vernon, WA, 1983, p. 96. 45. Robbins, J. and Sjulin, T.M., Postharvest storage characteristics and respiration rates in five cultivars of red raspberry, HortScience, 24, 980, 1989. 46. Sacks, E.J. and Shaw, D.V., Color change in fresh strawberry fruit of seven genotypes stored at 0°C, HortScience, 28, 209, 1993. 47. Austin, M.E., Shutak, V.G., and Christopher, E.P., Color changes in harvested strawberry fruit, J. Am. Soc. Hort. Sci., 75, 382, 1960. 48. Sjulin, T.M. and Robbins, J., Progress in extending raspberry shelf life: fresh market studies of red raspberries, in Proceedings of the 74th Annual Meeting of the Western Washington Horticultural Association, Western Washington Horticultural Association, Mount Vernon, WA, 1984, p. 96. 49. Forney, C.F., Jordan, M.A. and Nicholas, K.U.K.G., Effect of CO2 on physical, chemical and quality changes in ‘Burlington’ blueberries, Acta Hort. (ISHS), 600, 587, 2003. 50. Allan-Wojtas, P.M., Forney, C.F., Carbyn, S.E., and Nicholas, K.U.K.G., Microstructural indicators of quality-related characteristics of blueberries—an integrated approach, Lebensm. - Wiss. Technol., 34, 23, 2001. 51. Smith, R.B. and Skog, L.J., Postharvest carbon dioxide treatment enhances firmness of several cultivars of strawberry, HortScience, 27, 420, 1992. 52. Sjulin, T.M. and Robbins, J.A., Effects of maturity, harvest date and storage time of postharvest quality of red raspberry fruit, J. Am. Soc. Hort. Sci., 112, 481, 1987. 53. Varseveld, G.W. and Richardson, D.G. 1980. Evaluation of storage and processing quality of mechanically and hand-harvested Rubus spp. fruit, Acta Hort. (ISHS), 112, 265, 1980. 54. Nestby, R., Soluble solids and titratable acid in berries of cultivars and cross populations of raspberries, Meld. Norg. LandbrHøgsk., 57, 1, 1978. 55. Woodward, J.R., Physical and chemical changes in developing strawberry fruits, J. Sci. Food Agric., 23, 465, 1972.


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56. Sommer, N.F., Fortlage, R.F., Mitchell, F.G., and Maxie, E.C., Reduction of postharvest losses of strawberry fruits from gray mold, J. Am. Soc. Hort. Sci., 98, 285, 1973. 57. Smith, B.J., Magee, J.B., and Gupton, C.L., Susceptibility of rabbiteye blueberry cultivars to postharvest diseases, Plant Dis., 80, 215, 1996. 58. Mitchell, F.G., Mitcham, E., Thompson, J.F., and Welch, N., Handling strawberries for fresh market, Publication 2442, Postharvest Technology Research and Information Center, University of California–Davis, Davis, CA, 1996. 59. Luchsinger, L., Villalobos, A., and Lizana, A., Effect of controlled atmosphere in postharvest life of ‘Elliot’ blueberry, HortScience, 41, 1044, 2006. 60. Li, C. and Kader, A.A., Residual effects of controlled atmospheres on postharvest physiology and quality of strawberries, J. Am. Soc. Hort. Sci., 114, 629, 1989. 61. Song, Y., Ki, H.K., and Yam, K.L., Respiration rate of blueberry in modified atmosphere at various temperatures, J. Am. Soc. Hort. Sci., 117, 925, 1992. 62. El-Kazzaz, M.K., Sommer, N.F., and Fortlage, R.J., Effect of different atmospheres on postharvest decay and quality of fresh strawberries, Phytopathology, 73, 282, 1983. 63. Ceponis, M.J. and Cappellini, R.A., Reducing decay in fresh blueberries with controlled atmospheres, HortScience, 20, 228, 1985. 64. Larsen, M. and Watkins, C.B. Firmness and concentrations of acetaldehyde, ethyl acetate and ethanol in strawberries stored in controlled and modified atmospheres, Postharvest Biol. Technol., 5, 39, 1995. 65. Brecht, J.K., Sargent, S.A., Bartz, J.A., Chau, K.V., and Emond, J.P., Irradiation plus modified atmosphere for storage of strawberries, Proc. Fla. State Hort. Soc., 105, 97, 1992. 66. Barth, M.M., Zhou, C., Mercier, J., and Payne, F.A., Ozone storage effects on anthocyanin content and fungal growth in blackberries, J. Food Sci., 60, 1286, 1995. 67. Perkins-Veazie, P. and Collins, J., UVC light treatment reduces decay of blueberries, HortScience, 41, 1043, 2006. 68. Ezell, B.D., Darrow, G.M., Wilcox, M.S., and Scott, D.H., Ascorbic acid content of strawberries, Food Res., 12, 510, 1947. 69. Nunes, M.C.N., Brecht, J.K., Morais, A.M., and Sargent, S.A., Controlling temperature and water loss to maintain ascorbic acid in strawberries during postharvest handling, J. Food Sci., 63, 1033, 1998. 70. Lee, S.K. and Kader, A.A., Preharvest and postharvest factors influencing vitamin C content of horticultural crops, Postharvest Biol. Technol., 20, 207, 2000. 71. Buescher, R., Howard, L., and Dexter, P., Postharvest enhancement of fruits and vegetables for improved human health, HortScience, 34, 1167, 1999. 72. Shewfelt, R., Sources of variation in the nutrient content of agricultural commodities from the farm to the consumer, J. Food Qual., 13, 37, 1990. 73. Clydesdale, F.M., Minerals: Their chemistry and fate in food, in Trace Minerals in Food, Smith, K., Ed., Marcel Dekker, New York, 1988, p. 57. 74. Wright, K.P. and Kader, A.A., Effect of slicing and controlled-atmosphere storage on the ascorbate content and quality of strawberries and persimmons, Postharvest Biol. Technol., 10, 39, 1997. 75. Gregory, J., Vitamins, in Food Chemistry, Fennema, O., Ed., Marcel Dekker, New York, 1996, p. 531.


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76. Wills, R., Wimalasiri, P., and Greenfield, H., Dehydroascorbic acid levels in fresh fruit and vegetables in relation to total vitamin C activity, J. Agric. Food Chem., 32, 836, 1984. 77. Bangerth, F., The effect of different partial pressures of CO2, C2H4, and O2 in the storage atmosphere on the ascorbic acid content of fruits and vegetables, Qual. Plant., 27, 125, 1977 [in German with English summary]. 78. Howard, L.R. and Hernandez-Brenes, C., Antioxidant content and market quality of jalapeno pepper rings as affected by minimal processing and modified atmosphere packaging, J. Food Qual., 21, 317, 1998. 79. Vinokur, Y., Rodov, V., and Horev, B., Effect of postharvest factors on the content of ascorbic acid in Israeli varieties of strawberry, Acta Hort. (ISHS), 567, 763, 2002. 80. Agar, I.T., Streif, J., and Bangerth, F., Effect of high CO2 and controlled atmosphere on the ascorbic and dehydroascorbic acid content of some berry fruits, Postharvest Biol. Technol., 11, 47, 1997. 81. Mehlhorn, H., Ethylene-promoted ascorbate peroxidase activity protects plants against hydrogen peroxide, ozone and paraquat, Plant Cell Environ., 13, 971, 1990. 82. Maxie, E.C. and Abdel-Kader, A.S., Food irradiation—physiology of fruits as related to feasibility of the technology, Adv. Food Res., 15, 105, 1966. 83. Graham, W.D. and Stevenson, M.H., Effect of irradiation on vitamin C content of strawberries and potatoes in combination with storage and with further cooking in potatoes, J. Sci. Food Agric., 75, 371, 1997. 84. Goldman, I.L., Kader, A.A., and Heintz, M.S., Influence of production, handling and storage on phytonutrient content of foods, Nutr. Rev., 57, S46, 1999. 85. Wang, H., Cao, G., and Prior, R.L., Total antioxidant capacity of fruits, J. Agric. Food Chem., 44, 701, 1996. 86. Wang, S.Y., and Lin, H.S., Antioxidant activity in fruits and leaves of blackberry, raspberry, and strawberry varies with cultivar and developmental stages, J. Agric. Food Chem., 48, 140, 2000. 87. Gil, M.I., Holcroft, D.M., and Kader, A.A., Changes in strawberry anthocyanins and other polyphenols in response to carbon dioxide treatments, J. Agric. Food Chem., 45, 1662, 1997. 88. Civello, P., Martinez, G., Chaves, A., Anon, M., Heat treatments delay ripening and postharvest decay of strawberry fruit, J. Agric. Food Chem., 45, 4589, 1997. 89. Remberg, S.F., Haffner, K., and Blomhoff, R., Total antioxidant capacity and other quality criteria in blueberries cvs ‘Bluecrop,’ ‘Hardyblue,’ ‘Patriot,’ ‘Putte,’ and ‘Aron’ after storage in cold store and controlled atmosphere, Acta Hort. (ISHS), 600, 595, 2003. 90. Conner, A.M., Luby, J.J., Hancock, J.F., Berkheimer, S., and Hanson, E.J., Changes in fruit antioxidant activity among blueberry cultivars during cold-temperature storage, J. Agric. Food Chem., 50, 893, 2002. 91. Kalt, W., Forney, C.F., Martin, A., and Prior, R.L., Antioxidant capacity, vitamin C, phenolics and anthocyanins after fresh storage of small fruits, J. Agric. Food Chem., 47, 4638, 1999. 92. Kalt, W. and McDonald, J.E., Chemical composition of lowbush blueberry cultivars, J. Am. Soc. Hort. Sci., 121, 142, 1996.


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93. Cisneros-Zevallos, L., The use of controlled postharvest abiotic stresses as a tool for enhancing the nutraceutrical content and adding-value of fresh fruits and vegetables, J. Food Sci., 68, 1560, 2003. 94. Tulio, A.Z., Jr., Channon, A.M., Janakiramam, N., Ozgen, M., Stone, G.D., and Reese, R.N., Effects of storage temperatures on the antioxidant capacity and anthocyanin contents of black raspberries, HortScience, 41, 1043, 2006. 95. Ayala-Zavala, J.F., Wang, C.Y., Wang, S.Y., and Gonzalez-Aguilar, G.A., Methyl jasmonate in conjunction with ethanol treatment increases antioxidant capacity, volatile compounds and postharvest life of strawberry fruit, Eur. Food Res. Technol., 221, 731, 2005.


chapter 8

Microbial safety concerns of berry fruit Mark A. Daeschel and Pathima Udompijitkul Contents 8.1 Introduction ................................................................................................230 8.1.1 Historical safety record and potential safety concerns...........230 8.1.2 Microbial safety concerns of berries ..........................................232 8.1.3 Potential sources of contamination of berries ..........................239 8.2 Food safety strategies and programs .....................................................240 8.3 Specific strategies for ensuring microbial safety of berries ................242 8.3.1 Preharvest strategies .....................................................................242 8.3.2 The safe harvesting of berries.....................................................243 8.3.3 Processing safe berry products ...................................................246 8.4 Ensuring microbial safety of berries after production and processing............................................................................................246 8.4.1 Transportation and distribution..................................................246 8.4.2 Direct sales .....................................................................................248 8.4.3 Retail handling ..............................................................................248 8.4.4 The role of consumers in ensuring safety.................................249 8.5 Intervention technologies for ensuring microbial safety of berries......................................................................................................250 8.5.1 Temperature control......................................................................251 8.5.2 Surface disinfectants .....................................................................251 8.5.3 Low-dose irradiation ....................................................................252 8.5.4 Biocontrol........................................................................................253 8.6 Conclusion...................................................................................................254 References.............................................................................................................255

229


230


8.1 Introduction 8.1.1

Historical safety record and potential safety concerns

The per capita consumption of fresh fruits and vegetables continues to increase as a result of unprecedented availability and irrefutable evidence that fresh produce is a primary component in maintaining a healthy lifestyle. Furthermore, the rich diversity of fresh plant foods in terms of flavors, textures, and colors provides satisfaction on many levels. Produce, while on its journey from the farm production site to its final consumer destination, will encounter a variety of environments and thus potential impacts on quality and safety. It is a paramount responsibility of all those involved in the fresh produce business to protect these foods from processes and situations that may compromise safety. We are all custodians of our produce and must be vigilant in preventing contamination with physical, chemical, and biological hazards. In our quest for novel, exciting, more nutritious, and more convenient fresh foods, we must be on guard that we are not compromising heretofore impassable hurdles to contamination. It is only through effective collaborative efforts of industry, government, academia, and consumer education that we will minimize the threat of contamination of fresh produce. These foods are perhaps the most worrisome in terms of food safety because of the minimal processing they receive. In fact, it is their most desirable consumer characteristics of being fresh and unprocessed that provides the greatest opportunity for contamination to persist through the chain of distribution. Not all fresh plant foods are equal in terms of their ability to serve as sources of contamination. Certainly plant foods harvested directly from the ground may be more prone to physical, chemical, and microbial hazards, while those that have a natural protective barrier such as a peel or skin (oranges, bananas) that is removed just prior to consumption present fewer safety problems. During the writing of this chapter, a nationwide outbreak occurred of Escherichia coli associated with bagged spinach. The U.S. Food and Drug Administration (FDA) issued a warning to consumers not to buy bagged spinach. Sales and distribution of all bagged salad-type produce plummeted overnight. Leafy vegetables such as spinach and lettuce have been involved in several microbial contamination problems. The relatively high surface area of these vegetables, coupled with intensive agricultural practices, the dislocation and cutting of the leaves from the plant, and sorting, cleaning, and washing procedures have been suggested as opportunities for microbial contamination. Some fruits and vegetables have very hydrophobic smooth surfaces that tend to limit microbial adhesion while others have acidic interiors that limit the growth of potential pathogens. In this chapter, we will focus on reviewing the microbial safety history of berry fruits, the potential safety issues with these foods, and how producers, processors, distributors, and consumers can all help in preventing these desirable products from becoming a liability to human safety. Berry fruits and products derived from them have in general enjoyed a safe record of consumption and have not been implicated as a significant source of microbial


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pathogen contamination. Nonetheless, the record is not spotless and microorganisms have a way of appearing where we least expect them. Where appropriate, we will discuss the scientific literature that has addressed microbial contamination of other fruits and vegetables and point out observations that are relevant to safe berry fruit production and processing. Fresh fruits and vegetables are important for the health and well-being of the American consumer. In recent years, several outbreaks of foodborne illness have been associated with the consumption of both domestic and imported fresh fruits and vegetables.1–3 It has also been recognized that nonpasteurized fresh fruit juice can act as a vector for infectious disease.4 Most troublesome is the observation that serious foodborne pathogens, such as E. coli and Salmonella sp. are able to persist in the acidic environment of fruit juices such as apple and orange.5 Until recently, it was widely accepted that most low pH, high acid foods such as fruit were of minimal concern for food poisoning outbreaks. However, the appearance of acid-resistant strains of pathogens in our food supply has prompted a reexamination of how fresh fruits are grown, harvested, stored, and processed. The FDA has taken a leadership role and has provided a guidance document for industry entitled “Guide to Minimize Microbial Food Safety Hazards for Fresh Fruits and Vegetables.”6 A warning label is now required for nonpasteurized fruit juices.6 Recently the FDA issued its request on the application of its Hazard Analysis and Critical Control Point (HACCP) program for juice products to ensure safety and sanitary processing of fruit and vegetable juices. Deadlines for compliance are January 22, 2002, for large businesses; January 21, 2003, for small businesses; and January 20, 2004, for very small businesses. Microbial contamination of food is a serious problem that has come to the forefront of the American consciousness with respect to purchases of fresh and processed food. A complex array of factors, including emerging pathogen detection, centralization of food processing operations, and consumer demand for fresh and minimally processed products, now interact, thereby potentially compromising the safety of our food supply. Research and reported foodborne outbreaks have indicated that fresh produce and juices can serve as vectors for infectious diseases.5,7–9 Table 8.1 lists the reported foodborne outbreaks linked to unpasteurized juices and ciders since 1990. Table 8.2 gives examples of reported outbreaks of foodborne parasitic disease associated with raw berries. Table 8.3 provides recall data on contaminated berry juices.10 Since 1997, the federal response has been guided by what is known as the President’s Food Safety Initiative. Accordingly, Congress has allocated resources to the U.S. Department of Agriculture (USDA) and FDA to develop programs to enhance food safety. A subpart of the program, entitled “The Produce Safety Initiative,” focuses on the safety of imported and domestic fruits and vegetables. It has become apparent that on the one hand, American consumers demand safe food, while on the other, they want products that are fresh, nutritious, and devoid of chemical preservatives. Thus the challenge is to provide safe foods that are attractive to the consumer. This is an achievable goal, but only if there exists an understanding


232


Table 8.1 Reported Foodborne Outbreaks Linked to Unpasteurized Juice/Cider Since 1990 Year

Product

Pathogen

Location

1991 1993 1995 1996 1996a

Apple cider Apple cider Orange juice Apple cider Apple cider

Escherichia coli O157:H7 Cryptosporidium parvum Salmonella sp. E. coli O157:H7 E. coli O157:H7

1996 1996 1998b 1999 1999 1999

Apple cider Apple cider Apple cider Orange juice Apple cider Orange juice

E. coli O157:H7 C. parvum E. coli O157:H7 Salmonella anatum E. coli O157:H7 Salmonella muenchen

2000

Orange juice

Salmonella enteritidis

Massachusetts Maine Florida Connecticut Western United States and Canada Washington New York Ontario Florida Oklahoma 20 states and 3 Canadian provinces Six western states

Number of cases 23 160 63 10 66

2 31 14 4 7 423

88

a

Unpasteurized juice from California was involved. Fourteen of the 66 people affected were from British Columbia. One child died in the USA.

b

Local health officials identified one batch of noncommercial, custom-pressed apple cider as the most likely source (Health Canada70).

of how foodborne pathogens enter the production/processing stream and what parameters dictate their survival. Oregon, Washington, and Idaho are the nation’s major producers of berry crops, including blueberries, boysenberries, blackberries, red raspberries, and strawberries. Major berry products include fresh fruit, frozen fruit, juice, concentrate, and puree. Berries are a significant agricultural commodity in the Northwest. In Oregon,11 the production values of strawberries, raspberries (including red and black raspberries), blueberries, and blackberries (including Evergreen and Marion blackberries) in 2005 were $15.68, $17.62, $30.43, and $22.69 million, respectively. The total caneberry production value in 2005 was $53.62 million. In the United States, the total utilized production value of berries (including blackberries, blueberries, raspberries, boysenberries, loganberries, and strawberries) was about $0.1 billion.12

8.1.2

Microbial safety concerns of berries

Berries are densely cultivated and are constantly exposed to soils, irrigation water, and human contact. Current production practices were not designed to curtail potential pathogen contamination. Most disturbing is the observation that E. coli O157:H7 can survive in cow manure-amended soil for more than 6 months under dry conditions.13 A review of the literature pertaining

0 0

315 104

Guatemala Various Raspberries Guatemala Banquet Blackberries suspected likely hall

Source: Adapted from FDA.20 NR, not reported.

C. cayetanensis

C. cayetanensis

1012

Guatemala Various Raspberries

1997 Multistate U.S., and Ontario, Canada 1998 Ontario, Canada 1999 Ontario, Canada

C. cayetanensis

0

0

1465

1996 20 U.S. states Guatemala Various Raspberries and 2 Canadian provinces

C. cayetanensis

0

87

Venue

Raspberries Guatemala Two likely likely social events

Location

No. of deaths

1995 Florida

Year

No. of cases

Cyclospora cayetanensis

Pathogen

Type of berry

NR

No

No

No

No

Isolated from produce

Source of contamination unknown. Source of contamination unknown.

Raspberries from both events were purchased from separate sources. Two clusters reported. Possible contamination due to fruit spraying with insecticides and fungicides mixed with contaminated water. Source of contamination unknown.

Comments

Chapter 8:

Produce source

Table 8.2 Examples of Reported Outbreaks of Foodborne Parasitic Disease Associated With Raw Berries


Microbial safety concerns of berry fruit 233


234


Table 8.3 Recall Data on Contaminated Berry Juices Year 1999 1998

Food product Cranberry-raspberry drink Raspberry drink Kiwi, lime, and grapefruit-flavored fruit juice beverage

Hazards

Location

Mold contamination Southeast United States Mold contamination Ten states Glass Multiple states

Source: Anderson.10

to microbial hazards associated with fresh fruits and vegetables implicated E. coli O157:H7, Salmonella sp., and Listeria monocytogenes as bacterial pathogens of significant concern in fresh produce safety.14–16 Thus effective technologies are needed to remove pathogens from fruits. Fungal spoilage organisms can also compromise berry crops by decreasing the fruit yield and quality. Botrytis cinerea has been isolated from the soils of berry fields and is responsible for “gray mold” and postharvest damage in a wide range of fruits.17,18 In addition, Botrytis has been classified as a human allergen, since patients with sensitivities to mold display a high occurrence of specific IgE antibodies to Botrytis.19 Raw raspberries and possibly blackberries imported from Guatemala have been associated with several large Cyclospora cayetanensis outbreaks (Table 8.2). The natural host for this parasite has not been identified; however, contaminated water used for pesticide application and poor harvester hygiene have been suggested as the most likely routes of contamination. Frozen raspberries and frozen strawberries have been linked to several outbreaks of hepatitis A (Table 8.4). Hepatitis A, a virus spread by human feces, is thought to have contaminated the berries by contact with infected harvesters or contaminated irrigation water. Frozen raspberries have also been associated with illness due to calicivirus, which is also spread through human feces (Table 8.4). Raw berries destined for the fresh market are harvested by hand and field packed into retail containers without being washed. Strawberries destined for freezing are destemmed in the field, either using a metal device or a thumbnail. Berries that are to be processed are transported, usually at ambient temperature, to a processing facility, where they are washed with potable water or water containing an antimicrobial (e.g., chlorine), sometimes sliced, and often mixed with up to 30% sucrose before freezing. The extra human handling during harvesting and comingling in the processing facility may explain the greater association of outbreaks with frozen berries. Also, viruses and parasites may actually be preserved by the freezing step. To date, bacterial foodborne illnesses have not been directly linked to the consumption of berries. However, reservoirs for enteric organisms such as Salmonella and E. coli O157:H7 are similar to those of hepatitis A virus, suggesting that bacterial pathogens may also be occasional contaminants of berries.


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235

8 7

Log CFU/ml

6 5 4 3 2 1 0 0

1

2

3

4

5

Time (days)

Figure 8.1 Survival of E. coli O157:H7 in fruit juice and puree: Chardonnay grape juice (♦); Pinot Noir grape juice (■); raspberry juice (∆); strawberry juice (x); raspberry puree (∗); strawberry puree (•).

An FDA survey of imported produce found Salmonella in 1 of 143 samples of strawberries.20 Recently we conducted preliminary experiments to assess the ability of E. coli O157:H7 and Salmonella sp. to persist in the acid environment of berry juice and puree. As shown in Figure 8.1 and Figure 8.2, these pathogens were able to survive in juice and puree at room temperature within the 5-day 8 7

Log CFU/ml

6 5 4 3 2 1 0 0

1

2

3

4

5

Time (days)

Figure 8.2 Survival of Salmonella sp. in fruit juice and puree: Chardonnay grape juice (♦); Pinot Noir grape juice (■); raspberry juice (∆); strawberry juice (x); raspberry puree (∗); strawberry puree (•).

Year

1997

1998

1983

1988

1990

Pathogen

Calicivirus

Calicivirus

Hepatitis A

Hepatitis A

Hepatitis A Georgia, Montana

Scotland

California (1988)

Scotland

Scotland

Imported

Bosnia

Raspberries (frozen)




Type of berry

Strawberries School, institution (frozen) for the disabled

Home

Hotel

Two separate events Unknown

Venue

15 (Georgia), 13 (Missouri) + 29 secondary

5

24

>500

>200

No. of cases

No

No

0

No

0

0

NR

NR

0

0

Isolated from produce

No. of deaths

Likely contamination occurred before shipping from Bosnia. Source of contamination unknown. Suspected raspberry mousse prepared from frozen raspberries. Suggested contamination by infected picker(s). Raspberries from a small farm were frozen at home. Several pickers at the farm had symptoms of hepatitis A. Frozen strawberries used to make dessert. Empty strawberry containers with same lot number obtained from both locations

Comments

236

Scotland

Finland

Quebec, Canada

Location

Produce source

Table 8.4 Examples of Reported Outbreaks of Foodborne Viral Disease Associated With Contaminated Frozen Berries



Multistate U.S.

NR, not reported. Source: Adapted from FDA.11

1997 Mexico Schools Strawberries (frozen)

242 + 14 suspect 0 No

Chapter 8:

Hepatitis A

implicated same source. Suspected contamination by infected picker(s). Strawberries picked and stems removed in field. Fruits washed in 3 ppm chlorine prior to slicing and freezing. Frozen strawberries and strawberry shortcake were implicated in the outbreak. Possible contamination during harvesting. Hand washing in the field limited. Stems removed with fingernails. Evidence suggested low levels of nonuniform contamination.


Microbial safety concerns of berry fruit 237


238


experimental time frame. More long-term studies are currently in progress, including survival under refrigeration conditions. Berry juice and puree are the traditional value-added products in the Northwest and are defined as acid foods because their natural pH values are less than 4.6 (Table 8.5). Thus berry products are usually not regarded as potentially hazardous. However, it is observed that serious foodborne pathogens such as E. coli and Salmonella sp. are able to persist in the acidic environment of fruit juices such as apple and orange.2,5 The appearance of acid-resistant strains of pathogens in acid and acidified foods has prompted a reexamination of how fresh berries are grown, harvested, stored, and processed. Considering the frequency of foodborne outbreaks associated with contaminated apple ciders and the severity of the illnesses they caused, the FDA has recently concluded that there is a risk of serious illness from consuming juice products that have not been processed in a manner to produce at least a 5 log10 unit reduction in the pertinent target microorganism for a period of at least as long as the shelf life of the products when stored under normal and moderate abuse conditions. Such juices must bear the following statement: WARNING: This product has not been pasteurized and, therefore, may contain harmful bacteria which can cause serious illness in children, the elderly, and persons with weakened immune systems. This requirement has prompted the development and validation of efficacious technologies that meet the FDA requirement, while having minimal impact on the nutritional and sensory qualities of juice products.21

Table 8.5 pH Values of Different Berries and Their Products Type of berries Blackberries, Washington Blueberries, Maine Blueberries, frozen Blueberries, Maine Blueberries, frozen Grapes, Oregon Raspberries Raspberries, New Jersey Raspberries, frozen Strawberries Strawberries, California Strawberries, frozen Strawberry jam

pH range 3.85–4.50 3.12–3.33 3.11–3.22 3.12–3.33 3.11–3.22 2.95–3.60 3.22–3.95 3.50–3.82 3.18–3.26 3.00–3.90 3.32–3.50 3.21–3.32 3.00–3.40


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8.1.3


239

Potential sources of contaminations of berries

Food contamination may occur from microbiological, chemical, and physical sources. Potential microbiological hazards are the primary safety issue of concern with fresh fruits. Contamination of fresh fruits by human pathogens may occur at any stage during production, harvesting, handling, processing, storage, distribution, and consumer purchase. Poor agronomic practices, use of contaminated water for crop irrigation, application of improperly composted animal manure as fertilizer, and lack of training of field workers on good personal hygiene can contribute significantly to the contamination. Poor sanitation control during postharvest handling activities is another mechanism for pathogen contamination of fresh fruits, including improperly cleaned bins, buckets, and trucks used for transportation from the field to packinghouse, cross-contamination of dump tank water, poor personal hygiene among employees, and improperly cleaned equipment. Microbiological, physical, and chemical hazards may occur during processing of fruits; for example, the microbiological risks of fresh-cut fruits in cutting or slicing operation. The internal tissue of fresh fruits is normally protected from microbiological invasion by waxy outer skins or peels. However, cutting circumvents this physical barrier, allowing juices to leak from the inner tissues onto the surface of fruits. These juices contain all the nutrients necessary to support and accelerate microbiological growth. These factors, plus an increase in the exposed surface area of cut fruit, can all contribute to greater microbiological populations, including a potential increase in human pathogens levels. Hurst22 summarized key microbiological risks of fresh-cut produce, including a lack of a kill step in the process to eliminate potential human pathogens; some pathogens, such as L. monocytogenes are psychotrophic and can grow at refrigeration temperatures. Longer shelf life (10 to 14 days) may provide sufficient time for pathogen growth, whereas a modified atmosphere may suppress the growth of spoilage organisms, and certain pathogens (L. monocytogenes) survive and may actually thrive under these conditions. Moreover, fresh-cut fruits are consumed raw with few or no antimicrobial barriers in place. Chemical and physical hazards may also become significant in addition to microbiological hazards. Chemical contaminants can be naturally present in foods or can be introduced during processing when compounds generally recognized as safe (e.g., antioxidants, sulfiting agents, preservatives) are not used according to government regulatory guidelines. It is incumbent upon the processor to ensure that chemical compounds such as sanitizers and lubricants are used with strict adherence to existing regulations and product specifications. The good manufacturing practices (GMPs) mandate that potential contaminating chemicals be physically segregated from foods or food ingredients. Physical contaminants can be defined as any material not normally found in food that can produce an injury or illness in the consumer. They can enter the


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food supply through contaminated raw materials, faulty processing equipment, improper packaging, and poor employee hygiene practices. Examples of physical hazards that can compromise food safety include metal fragments, gravel, plastic, glass particles, and jewelry; these hazards affect product safety. Prevention methods can rely on visual examination, frequent inspections of equipment, and the use of metal and glass detectors.

8.2 Food safety strategies and programs A strategy that prevents the initial microbial contamination of berries is safer than relying on corrective actions after contamination has occurred. Because it is not practical to eliminate all potential hazards associated with fresh produce, berry producers and processors must rely on risk reduction rather than total risk elimination. To minimize microbiological safety hazards during agricultural operations, the FDA Center for Food Safety and Applied Nutrition (CFSAN) developed in 1998 the “Guide to Minimize Microbial Food Safety Hazards for Fresh Fruits and Vegetables.”6 This publication addresses potential food safety issues associated with farmland, irrigation water, fertilizer usage and pesticide monitoring, harvest practices, field sanitation, and worker hygiene, and sets forth good agricultural practices (GAPs) for producers to ensure food safety. It stresses prevention of contamination over corrective actions once contamination has occurred and establishes a format for developing a system of accountability of sanitary practices at all levels of the agricultural and packinghouse environment. The GAPs can serve as guidance for farmers throughout the growth, harvesting, packing, and transportation phases of each berry crop. However, once the fruit has been transported from the field, other food safety protocols must be followed. The GMPs are described in the Code of Federal Regulations (CFR) section 21, part 110, and are required by law in the United States for all food manufacturing companies. The GMPs address four main areas of food processing, including the design of buildings and facilities to protect against product contamination, sanitation of equipment and utensils to prevent contaminants from being introduced into the food, personnel hygiene to protect adulteration of foods by food handlers, and process controls that ensure adequate food processing during production. The most important issues that are addressed in the GAPs include • • • • • • • •

Water Manure and municipal biosolids Worker health and hygiene Sanitary facilities Field/packing facility sanitation Transportation/distribution Consumer packaging Traceback.


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The GAPs focus on microbial hazards for fresh produce, on risk reduction, not risk elimination, and provide broad, scientifically based principles. The guide is one of the first steps to improve the safety of fresh produce as it moves from farm to the table. At this point, they are guidelines that will eventually become enforceable regulations. However, the GMPs are required by law (21 CFR 110) and apply to all food manufacturing companies to ensure good food plant sanitation. Further processing and manufacturing into finished products in no way exempts raw materials from the requirements of cleanliness and freedom from deleterious impurities. GMPs are prescribed for four main areas of food processing: 1. 2. 3. 4.

Personnel hygiene to prevent the spread of illness. Adequate buildings and facilities. Sanitary food contact surfaces (e.g., equipment and utensils). Process controls to prevent cross-contamination.

Sanitation standard operating procedures (SSOPs) focus more narrowly on specific procedures that allow a fruit-processing plant to achieve sanitary process control in its daily operations. SSOPs are mandatory for all foodprocessing plants (21 CFR 120.6) subject to the HACCP program. Although specific protocols may vary from facility to facility, SSOPs provide specific step-by-step procedures to ensure sanitary handling of foods. These documents describe procedures for eight sanitation conditions: 1. 2. 3. 4. 5. 6. 7. 8.

Safety of water. Cleanliness of utensils and equipment. Prevention of cross-contamination. Hand washing and toilet facilities. Protection of food from contaminants. Labeling and storage of toxic compounds. Monitoring employee health. Pest control.

Specific sanitation procedures recommended for fresh-cut fruit and vegetable processing have been discussed by Hurst.22 A more focused approach toward controlling food safety—HACCP— was developed by the FDA to establish safety standards throughout the food industry. The HACCP program is a structured approach to the identification, assessment of risk, and control of hazards associated with a food production process or practice. It aims to identify possible problems before they occur and establish control measures at production stages that are critical to product safety. Design and implementation of the HACCP system involves seven basic principles or steps: 1. 2. 3. 4.

Identify possible food safety hazards. Determine critical control points. Establish preventive measures. Monitor the manufacturing process to detect hazards.


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Berry fruit: Value-added products for health promotion 5. Plan corrective actions. 6. Prepare a method to verify that the HACCP plan is working. 7. Document the HACCP system by maintaining records.

The HACCP program is a proven, cost-effective method of maximizing food safety because it focuses on hazard control at its source. It offers systematic control by covering all aspects of production and handling from raw materials to consumer preparation. In the Federal Register of January 19, 2001, the FDA published final regulations to ensure the safe and sanitary processing of fruit and vegetable juices. These regulations mandate the application of HACCP principles to the processing of juices, including berry juice products. Although HACCP is not mandatory for all food industries, it has been embraced by the fresh-cut processing industry as a useful tool for implementing food safety practices in the production environment. The HACCP program is well suited to identify hazards, monitor production for adherence to operational standards, and develop an effective record-keeping system in a fresh-cut produce facility. With close attention to prerequisite programs, a processor can implement HACCP to round out their food safety program. In summary, utilizing the principles of GAPs and GMPs during growing, harvesting, washing, sorting, packing, and transporting of fresh fruits will minimize microbial food safety hazards. Developing specific step-by-step SSOP protocols and implementing a HACCP program will further ensure the safety of fresh and processed products from farm to market to consumer.

8.3 Specific strategies for ensuring microbial safety of berries 8.3.1

Preharvest strategies

Bower et al.23 discussed in a great detail the potential risks of contamination of berries during production and suggested strategies to reduce the risks. To prevent preharvest contamination of berries, a specific set of GAPs have to be developed. As described in Table 8.6, the GAPs begin by reviewing the history of the farmland to ensure that no prior land use has compromised the microbial or chemical safety of the site. The adjacent land is also evaluated to verify that no contamination is being carried to produce fields by water, wind, or vehicles. The purity of the water source is also important, since streams, reservoirs, and wells can spread microbial contaminants. Fertilizer use and pesticide monitoring are also important components of GAPs. Improperly composted manure can become a direct source of pathogens for a berry crop. Contamination can also occur when crops are irrigated with equipment that was used to apply liquid manure. GAPs encourage rigorous management techniques to ensure the proper application of organic fertilizers. Careful records must be maintained for all fertilizer applications, and only authorized pesticides and herbicides should be applied.


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Table 8.6 Preharvest Good Agricultural Practices for Berries 1. Site selection and adjacent land use Test for microbial/chemical hazards from prior use of farmland. Ensure that no contamination is carried by water, wind, or vehicles from adjacent land. Avoid fields that are susceptible to flooding. Use mulch to reduce contact between the soil and berries. 2. Purity of the water source Evaluate water for irrigation (since streams, reservoirs, wells, and public water systems can potentially spread contaminants). Periodically test water sources for microbes. Do not irrigate crops with equipment that has been used to apply liquid manure. 3. Fertilizer use and pesticide monitoring Be aware of the proper application of organic fertilizers. Follow rigorous management techniques for treating manure. Maintain careful records of all fertilizer applications. Use only authorized pesticides and herbicides. Apply all chemicals appropriately. 4. Wildlife, pest, and vermin control Maintain an effective pest control program Exclude wildlife and domestic animals from fields. Periodically verify that the pest control plan is working. 5. Worker hygiene and field sanitation Do not allow ill workers to contact raw produce. Supply potable water for drinking and hand washing. Provide toilet facilities with hand-washing stations. Follow local, state, and federal regulations for worker health. Establish a training program that covers worker sanitation. Protect harvest containers from contacting soil. Source: Adapted from Bower et al.23

Good agricultural practices also stress field sanitation, including an effective pest control program. Wildlife and domestic animals should always be excluded from produce fields, and worker health should be monitored to prevent ill workers from contacting raw produce. To maintain worker hygiene, toilet facilities with hand-washing stations must be provided, as well as potable water for drinking and hand washing.

8.3.2

The safe harvesting of berries

Bower et al.23 note that the three key parts of a safe harvest system are sanitary harvest conditions, cooling berries right after harvest, and safe handling and storage practices.


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Most microbial contamination is on the surface of fresh produce, necessitating a washing step to reduce the possibility of foodborne illness before sale. Washing also helps to prevent the spread of microorganisms from one berry to the next. To decrease the possibility of waterborne contaminants compromising the quality of the berries, it is essential to use potable water whenever there is water-produce contact. Approved sanitizers such as liquid chlorine, sodium hypochlorite, or calcium hypochlorite can help control contamination when produce is immersed in wash water. If a sanitizer such as chlorine is added to the wash water (pH 6.0 to 7.0) to control bacteria, the concentration of free (unreacted) chlorine (100 to 150 ppm) should be tested frequently. Berries in the field can come in contact with soil, domestic and wild animal feces, and poor quality water during harvest. Not all berries are cooled and washed after harvest (e.g., strawberries), thus increasing the possibility of microbial contamination. To minimize this risk, clean pallets and sanitized containers should be available for freshly harvested berries, and care should be taken to ensure that the containers do not become exposed to soil and manure when produce is packed in the field. Employees should stand on any container where contaminated shoes can become a vector. Good worker hygiene and field sanitation practices are also essential. All workers who handle fresh produce should receive training on the importance of good hygiene, including the necessity for effective hand washing. When possible, harvesting of berries should be carried out at night or during the early morning hours to minimize exposure to high daytime temperatures. Freshly harvested berries should be held in the shade with adequate ventilation whenever possible. If berries are temporarily stored beneath a tree for shade, the containers should be covered with clean, sanitized tarps to protect the berries from contamination by birds. Water, ice, and forced air are among the methods devised to remove field heat from produce after harvesting, thereby slowing or inhibiting microorganism growth and extending the shelf life of the produce. Systems that utilize air cooling have the lowest risk of contamination during the cooling process; however, they can potentially transfer microorganism-containing dust particles and water droplets onto fresh produce. Cooling systems based on water and ice have the greatest potential for contamination, even when potable water is used. The addition of chlorine (50 to 200 ppm) can help control bacteria; however, chlorine reacts with organic compounds and can rapidly lose its effectiveness. If water is used for cooling, the temperature should be greater than that of the produce to prevent the temperature difference from pulling microorganisms from the surface of the fruit inward where they cannot be easily removed.23 Bacteria can rapidly multiply in areas where poor sanitation is practiced. Harvest storage areas should be maintained in a clean, sanitary condition and containers should be cleaned and sanitized prior to the arrival of fresh produce. Fresh berries should not be transported in trucks recently


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Receiving Washing Inspection Roll – milling Heating Cooling

Enzymes

Treatment with enzymes Pressing Centrifuging Clarifying

Pectolytic enzymes

Filtration Sugar, Water, Acids

Blending correction

Concentrated flavor

Deaeration CCP 2

Pasteurization

CCP 3

Aseptic filling Clear juice

Figure 8.3 Flow diagram for berry juice production (adapted from Nagy et al.71).

used to haul animals or animal products without extensive cleaning and sanitation before loading. Harvesting and packing operations should effectively clean and sanitize all food-contact surfaces. This includes washing, grading, sorting, and packing lines, as well as equipment, floors, and drains, to prevent fresh produce from becoming contaminated with pathogenic microorganisms. Cross-contamination between raw and washed berries from sources such as wash water, rinse water, ice, dust, equipment, utensils, and vehicles must be prevented. The presence of fecal coliforms can serve as an indicator if contaminants are suspected.


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8.3.3


Processing safe berry products

The GAPs serve as guidance for fruit producers throughout the growth, harvesting, packing, and transportation of each berry crop. However, once the fruit has been transported from the field, other food safety protocols, including GMPs, SSOPs, and HACCP, must be followed. Bower et al.23 provide detailed guidelines for implementing GMPs and SSOPs during various berry processes. It is important to emphasize the HACCP program for berry juice production. Processing of all juice products, including juice, concentrate, and puree sold in the United States is subject to HACCP requirements. The HACCP system is structured to address food safety issues by monitoring critical points in the manufacturing process to ensure that the final product is safe. Juice processors must operate under an approved HACCP plan to prevent their finished juice products from being labeled “adulterated.” Good manufacturing practices and SSOPs are prerequisite programs for HACCP and should be documented and regularly audited along with the HACCP plan. Consequently it is not necessary to include specific sanitation protocols in the HACCP plan. Factors that lead to spoilage or quality loss of the fruit, but do not affect the product’s safety, should be addressed in the GMPs or SSOPs, and not in the HACCP plan. The HACCP plan for fruit juice manufacturers contains a 5 log pathogen reduction step that is capable of preventing, reducing, or eliminating pathogenic microorganisms by 100,000-fold. This step must be implemented prior to the final fill and must be validated (21 CFR 120.24). Potential technologies for achieving a 5 log reduction include thermal processing, high hydrostatic processing, dense phase carbon dioxide pressure processing, and ultraviolet (UV) processing. Mandatory warning labels are required for juices (and beverages that contain fruit juice) that do not contain a 5 log pathogen reduction step (21 CFR 101.17). The guideline for preparing an HACCP plan for berry juice was developed by Bower et al.23 Figure 8.3 shows an example of a berry juice processing flow diagram and three critical control points (CCPs) determined during the process.

8.4 Ensuring microbial safety of berries after production and processing 8.4.1

Transportation and distribution

Transportation systems for fresh produce can be classified into different levels, including transportation from the field to the cooler, packing facility, distribution and wholesale terminal markets, or retail centers. Microbial cross contamination may occur from other foods and nonfood sources and contaminated surfaces during loading, unloading, storage, and transportation operations. Therefore, the distribution and transportation conditions can have profound effects on microbial safety. If these procedures are managed properly, the risk of illness associated with microbial contamination in fresh


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produce can be effectively reduced.24,25 Food safety during transportation and distribution can be enhanced by applying preventive methods such as good sanitation practices and the HACCP program.26 This will ensure that food products that reach consumers are high quality and safe to eat.27 During distribution and transportation of fresh produce, loading dock workers, truck drivers, and retail workers all share the responsibility in preventing cross contamination and maintaining appropriate temperatures.25 Thus, an effective way to ensure safety from microbial food hazards during transportation can be achieved by an active and ongoing dialogue with responsible personnel so that an effective management program designed to deliver safe foods to consumer can be fully implemented.24,27 However, additional microbiological and other safety assurance tests on products after transportation may be necessary to compare obtained data with the results from preshipment to determine whether corrections are needed.26 Although recognizing that the transportation system is one of the important factors contributing to the safety of fresh produce and that effective, safe transport is an important part of the chain of custody, it is often overlooked.25 The following basic considerations should be applied in order to prevent microbial cross contamination and maintain the safety of berries during transportation and distribution: • The sanitation condition of trucks and other carriers, loading equipment, cargo pallets, and load securing devices. This equipment should be evaluated for cleanliness, odors, and obvious dirt or debris before the loading process and should be regularly washed and sanitized. The shipping record needs to be monitored periodically to prevent cross contamination from other food and nonfood products. Vehicles that have recently been used for transporting live animals, animal products, or other sources of pathogenic bacteria have to be sanitized properly prior to loading fresh berries.24–26 • Proper air circulation. As fresh berries are regularly shipped in refrigerated trailers, proper air circulation is critical to maintain the temperature throughout the vehicle. With improper cooling, heat generated by product respiration, and heat absorbed from outside the vehicle results in an increase in product temperature to undesirable levels, thus increasing the risk of foodborne illness and the chance of economic losses. To ensure adequate airflow, appropriate shipping containers, vehicles, loading patterns, and alignment of vent holes in the containers are required.25,27,28 In addition, different types and varieties of berries may require different optimum temperatures during transportation; delivery of mixed loads with incompatible refrigeration requirements should be avoided.24 • Education of employers and employees on food safety. Despite the fact that many sources contribute to contamination of fresh berries, workers seem to be the most likely cause.29 Therefore, suitable personal hygienic practice is essential among all personnel who are responsible for every step in the transportation and distribution system.


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Berry fruit: Value-added products for health promotion • Physical damage of fresh berries. Physical damage encourages microorganisms to invade fresh produce tissue, leading to accelerated deterioration and an increased risk of illness from consumption of infectious produce. Hence, efforts to minimize physical damage during distribution and transportation are needed.

8.4.2

Direct sales

Direct farm sales and farmer’s markets have been a traditional way to link local food producers with consumers, while at the same time creating a sense of community and place. The U-pick farm operation is another avenue for marketing produce directly. The latter is especially popular for people interested in obtaining fresh berry fruits such as blueberries, strawberries, and raspberries. For most U-pick consumers, it is viewed as a family outing, with several family members participating. Even though the chain of custody is shorter in this type of sale, common sense food safety measures should be in place to limit the possibility of pathogen contamination. Most, if not all, farmer’s markets are subject to inspection and licensing by local agencies to ensure food safety. At the U-pick farms, the owner/ operator should follow these guidelines: • Provide convenient, clean, well-maintained, and serviced toilet facilities in the fields. • Encourage hand washing before picking. Supply liquid soap in dispensers, potable water, and single-use paper towels for hand washing. • Fruit picked but left behind by customers should be discarded. • Prohibit customers from bringing pets into the fields.

8.4.3

Retail handling

Factors that contribute to the presence of pathogenic microorganisms on fresh produce during retail handling include cross contamination from other foods in the store, contamination from preparation and display areas, and improper display temperature.30 Retail display cases must be clean and the proper refrigeration temperature must be maintained.25 The existence of pathogenic microorganisms on retail food products was reported by Thunberg et al.,31 who observed that several Listeria sp., including L. monocytogenes, an enterotoxigenic isolate of Staphylococcus sp., and a toxigenic species of Bacillus sp. were isolated from fresh produce displayed in a retail market. The postharvest quality and microbial quality of fresh produce are strongly influenced by temperature, relative humidity, and the composition of the storage atmosphere.32 Temperature and relative humidity are set as a critical limit during transportation and storage for monitoring programs involved in the HACCP system. Fresh produce is perhaps exposed to the greatest temperature abuse during retail handling. The combination of time and temperature during holding and the relative perishability of each type of produce can contribute to temperature abuse at the retail level. The average


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display temperatures of fresh produce are 7.6°C and 8.4°C in winter and summer, respectively.33 While 4°C is the recommended temperature for storing some retail produce commodities, there is the report that as much as 90% of those products are stored above this temperature. The recommended optimum relative humidity for the storage of fresh strawberries, raspberries, blackberries, Logan blackberries, and dewberries is 85% to 90%. However, it is difficult to maintain such high relative humidity in a large storage room.34,35 Beuchat36 estimated that the postharvest losses of fresh produce can be 30% or more due to microbial spoilage. While the growth of saprophytic fungi, yeast, and bacteria contribute to spoilage of fresh produce,32 the control of microbial proliferate during storage is essential. In order to prolong shelf life, promote a fresher appearance, and reduce the weight loss of fresh produce through evaporation of water; humidification technology (misting) may be used on fresh produce during retail display. This method raises the moisture content of the air in a refrigerated open cabinet to the optimum level and lowers the vapor pressure difference between water at the surface of produce and in the air, resulting in a lower rate of dehydration. A washing effect can also occur during humidification.32,37 However, it has been reported that a mist machine used to spray water aerosol over produce bins was believed to be the cause of an outbreak of Legionnaire’s disease in Louisiana, an infection caused by the bacterium Legionella pneumophilia. Water in the reservoir of a mist machine was contaminated with this pathogenic bacterium. The illness develops when people inhale small droplets that contain this bacterium. The FDA recommended that cleaning and maintenance of mist machines should be performed weekly in order to ensure the safety of consumers and reduce the possibility of a foodborne outbreak.38,39

8.4.4

The role of consumers in ensuring safety

Most fresh berries such as strawberries and raspberries are not washed during the entire production process, including harvesting, packing, and transportation. They are also regularly consumed fresh without further processing.29,40 Recognizing this has led to the recommendation of the most appropriate and practical method for reducing naturally occurring microorganisms on fresh berries in the home. Washing with cold running tap water is recommended for reducing indigenous microflora on fresh produce before eating or preparation.41 Washing lettuce and broccoli with tap water can reduce the natural microflora by 92.4% and 1 log10 colony-forming units (CFU)/g, respectively,32,42 while dipping strawberries in water reduces the population of E. coli O157:H7 only 0.8 log10 units.40 Besides water, diluted vinegar, chlorine solution, and commercial cleaning solutions specified for fresh fruits and vegetables are also used for washing fresh produce.43 Consumers usually believe that the incidence of foodborne illness is less frequently due to mishandling in the home. This misconception can lead to


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inappropriate and unsafe food handling practices at the consumer level.43,44 Bryan45 reported that the improper handling and treatment of foods in the home was the dominant factor leading to reported foodborne outbreaks in the United States between 1961 and 1982. Potential sources of pathogenic microorganisms in fresh produce can be cross contamination from hands, food preparation surfaces, kitchen cutting boards, and knives during food preparation in the kitchen.46–48 Transmission of foodborne pathogens such as Campylobacter jejuni and Salmonella sp. has occurred because of inadequate cleaning of kitchen cutting boards after use in preparing raw meat.49,50 According to Zhao et al.,47 large populations of Enterobacter aerogenes were transferred to fresh produce cut on the same cutting board as contaminated meat. Moreover, these bacteria survived on the board for at least 4 hours. Ak et al.46 suggest that an effective method for disinfecting a contaminated cutting board is to rinse it with hot water and a detergent. Microwave irradiation was successful in eliminating bacteria from the surface and the interior of wooden cutting boards, whereas its lethal effect on bacteria on the surfaces of plastic cutting boards was limited.51 The best approach to reduce the problem of foodborne illness resulting from improper food handling practices at the consumer level is to engage in educational campaigns aimed at providing practical information about the appropriate way to handle fresh produce prior to consumption. These educational materials should be simple to read and easy to follow. They should be accessed conveniently from multiple sources, such as supermarket brochures, magazines and newspapers, produce containers, television programs, websites, and refrigerator magnets.43

8.5 Intervention technologies for ensuring microbial safety of berries Intervention technologies for inactivating or eliminating pathogens in food can utilize many well-recognized approaches, including heat preservation, chemical preservation using acidulants, antimicrobials, modified and controlled atmosphere storage or packaging, food irradiation, high hydrostatic pressure, etc. However, it is complex and a challenge for fresh produce, as some of the intervention technologies mentioned above will damage or kill living plant cells, leading to the loss of produce “freshness.” This section focuses on specific intervention methods that can be integrated into a safe food production and processing system to control pathogens and ensure microbiological safety of fresh fruits, including berries. These include temperature control, use of surface disinfectants, low-dose irradiation, and biocontrol. Each method has distinct advantages and disadvantages depending upon the type of fruit, mitigation protocol, and other variables. As discussed in previous sections, the best method for eliminating pathogens from fresh fruits is to prevent contamination in the first place. However, this is not always possible and the need to wash and sanitize many types of produce


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remains of paramount importance to prevent disease outbreaks. It is important to point out that washing and sanitizing are unlikely to totally eliminate all pathogens after the produce is contaminated. Some berries cannot be washed because of their delicate structure and problems with mold proliferation, and thus are often packaged in the field with minimal postharvest handling or washing. The efficacy of the method used to reduce microbial populations usually depends upon the type of treatment, the type and physiology of the target microorganisms, characteristics of the produce surface (cracks, crevices, hydrophobic tendency, and texture), exposure time and concentration of the cleaner/sanitizer, pH, and temperature. The concentration/level of sanitizers or other intervention methods may be limited by unacceptable sensory impact on the produce. Infiltration of microorganisms into points below the surface of produce is problematic. While it is known that microorganisms can enter produce under certain handling conditions, the significance of any such contamination to public health requires further study.

8.5.1

Temperature control

While refrigeration is critical for the quality and shelf life of fruits, it cannot be relied on to prevent the growth of pathogenic microorganisms on produce. Populations of L. monocytogenes remained constant or grew on a variety of whole and cut produce stored at refrigeration temperatures.52 Under certain chilled storage conditions, spoilage of the product by the native microflora might not occur until after pathogen populations reach levels capable of causing disease. While the growth of some pathogens may be inhibited by refrigeration temperatures, survival can be enhanced under certain conditions. For example, salmonellae and E. coli O157:H7 survive for a longer period of time in fruit juices under refrigeration than at room temperature.4,53

8.5.2

Surface disinfectants

The simple practice of washing raw fruits in hot water or water containing detergent removes a portion of the pathogenic and spoilage microorganisms that may be present, but studies showing the efficacy of these treatments are few. Even washing fruits in potable water, then washing again or rinsing in potable water aids in removing microorganisms. Additional 10-fold to 100-fold reductions can sometimes be achieved by treatment with disinfectants. The resistance of microorganisms to disinfectants varies greatly with the type and pH of the disinfectant, contact time, temperature, and the chemical and physical properties of the fruit surface. Each type of disinfectant has its own efficacy in killing microbial cells. Effectiveness depends on the nature of the cells, as well as the characteristics of the fruit tissues and juices. Some types of disinfectants are appropriate for use in direct contact washes, while others are suitable only for equipment and containers used


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to process, store, or transport fruits. The mechanism of action of many disinfectants on microbial cells and the influence of factors associated with plant materials are poorly understood. The legal use of various treatments also differs from country to country. The most commonly studied and used surface disinfectants for whole and fresh-cut fruits include chlorine, chlorine dioxide, bromine, iodine, quaternary ammonium compounds, acidic compounds with or without fatty acid surfactants, alkaline compounds, hydrogen peroxide, and ozone. Their application depends on the type and nature of the fruits, application temperature, dosage, etc. Rodgers et al.54 compared different chemical sanitizers for inactivating E. coli O157:H7 and L. monocytogenes on strawberries. Ozone (3 ppm), chlorine dioxide (3 and 5 ppm), chlorinated trisodium phosphate (100 and 200 ppm chlorine), and peroxyacetic acid (80 ppm) were assessed for the reduction of these two pathogens inoculated on fresh strawberries at a level of 106. Ozone and chlorine dioxide (5 ppm) were the most effective treatments, reducing populations about 5.6 log, with chlorine dioxide (3 ppm) and chlorinated trisodium phosphate (200 ppm chlorine) resulting in maximum reductions of about 4.9 log. Peroxyacetic acid was the least effective sanitizer (about 4.4 log reduction). During storage at 4°C for 9 days after treatment, populations of both pathogens remained relatively unchanged. The functionality, examples of application, and conditions in the use of surface disinfectants in fruit and vegetable sanitation have been discussed in great detail by Beuchat55 and Heard.56

8.5.3

Low-dose irradiation

Ionizing radiation from 60Co, 137Cs, or machine-generated electron beams, alone or in combination with other treatments such as hot water, may be used as a means of extending the shelf life of fresh produce.57 The lethality of irradiation is determined by the targeted microorganisms (types of bacteria, molds, or yeast), the condition of the treated item, and environmental factors. Low-dose treatments (less than 1 kGy) inhibit sprouting of tubers, bulbs, and roots, delay produce maturation, eliminate insects in grains, fruits, and nuts, and kill parasites in meats. Medium-dose treatments (1 to 10 kGy) reduce microbial populations, including pathogens, on or in foods. However, produce treated with doses greater than 1 kGy cannot use the term “fresh” (21 CFR 101.95). Several studies have investigated the use of irradiation in combination with other treatments on prolonging the postharvest life of fresh strawberries. For example, O’Connor and Mitchell58 analyzed 17 samples of strawberries from seven different growers for total counts, Enterobacteriaceae, fluorescent pseudomonads, and yeast and mold counts before and after irradiation at 1.2 or 2 kGy. Enterobacteriaceae were absent (less than 5 CFU/g) from all irradiated strawberries (fresh and stored for 5 days at 8°C), but were always detected at counts of greater than 30 CFU/g in untreated samples. Ouattara et al.59 determined the effectiveness of low-dose irradiation (0 and


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3 kGy) combined with protein-based edible coatings on extending the shelf life of fresh strawberries. Results showed that coating with irradiated protein solutions resulted in significant reductions in the percentage of mold contamination. Pan et al.60 investigated the effects of ultraviolet C (UV-C) (4.1 kJ/m2) and heat treatment (45°C, 3 hours in air) either separately or combined on fruit quality and the development of surface fungal infections in in vitro germination assays on conidia of B. cinerea and Rhizopus stolonifer. The combined treatment reduced fungal infections and delayed in vitro germination of B. cinerea conidia. It was concluded that the combination of UV-C and heat treatment enhanced the benefits of applying each treatment separately and could be useful for improving and extending the postharvest life of strawberries.

8.5.4

Biocontrol

The application of biocontrol concepts may be useful for creating additional microbial hurdles in fruits, especially fresh-cut fruits, to enhance product safety. Biocontrol methods include the use of56 • Antagonistic organisms to control the growth of either spoilage or pathogenic species, most often called biopreservation. • Natural antimicrobial compounds to control microbial growth. • Natural plant defenses to reduce microbial attack-induced resistance. There are few published reports on the use of biocontrol agents to prevent the growth of human pathogens on fruits. Janisiewicz et al.61 reported that Pseudomonas syringiae prevented the growth of E. coli O157:H7 in wounds of apples. Populations of the pathogen increased 2 log in wounds that were not treated with the antagonist, but they did not increase in wounds treated with P. syringiae. The application of microorganisms to prevent the proliferation of postharvest spoilage organisms has been studied extensively.62–66 Studies suggest that nonpathogenic microorganisms applied to produce surfaces might outcompete pathogens for physical space and nutrients and may produce antagonistic compounds that negatively affect the viability of pathogens. Additional research on biocontrol of human pathogens on produce is warranted to fully evaluate this approach as being practical and efficacious. Microorganisms such as lactic acid bacteria are used as biopreservative agents in foods to inhibit the growth of other undesirable species.56 Mechanisms of antagonism include competition for nutrients, binding of nutrients, and production of metabolic products with antimicrobial activity. Fermentation with lactic acid bacteria is a traditional biopreservation method employed to increase the safety and quality of foods, including fruit. In recent years, lactic acid bacteria have been used as competitive biocontrol agents and antagonists in nonfermented foods.67 These organisms are often present on the surface of fruits and vegetables and, if encouraged, may reduce the growth of


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other indigenous spoilage organisms or foodborne pathogens. Lactic acid bacteria are known to produce antimicrobial metabolites, such as lactic and acetic acid, hydrogen peroxide, and enzymes including lactoperoxidase. The use of natural antimicrobials from plants and their possible application in minimally processed fruits and vegetables was reviewed by Lopez-Malo.68 Plants, herbs, and spices, as well as their derived essential oils and isolated compounds contain a large number of substances that are known to inhibit various metabolic activities of bacteria, yeast, and molds, although many of them are yet incompletely exploited. Major components with antimicrobial activity found in these resources are phenolic compounds, terpenes, aliphatic alcohol, aldehydes, ketones, acids, and isoflavonoids. Their effectiveness in inhibiting spoilage and pathogenic microorganisms depends on many factors, including the composition of the food (pH, water activity, presence of other inhibitors, interaction with the food matrix, etc.), initial contamination level, handling and distribution (length, temperature, and packaging in storage), and possible synergistic or additive interaction effects with other antimicrobial factors. The application of natural antimicrobials in fruits requires a better understanding of the modes of action and their interactions with other preservation factors, as well as knowledge of the interactions between the stress factors applied and the fruit matrix. Several studies have demonstrated that berry phenolic compounds inhibit the growth of human pathogens such as Salmonella, Staphylococcus, and E. coli O157:H7. Utilization of the antimicrobial activity of berry phenolic compounds as stand-alone natural antimicrobial agents or in concert with other antimicrobial systems may offer many new applications for the produce industry. The concept of “induced resistance” in plants to microorganisms that cause pathologies in plant systems has also attracted attention.69 In recent years, researchers have begun to focus efforts on the mechanisms and signaling pathways plants use to resist disease. In addition, biotechnology companies are engineering plants to resist pests. While speculative, it is conceivable that research on biocontrol efforts through induced resistance or genetic engineering could lead to plants that resist human pathogens in addition to plant pathogens.

8.6 Conclusion Fresh berries are an important component of our diet and as such must be provided to the consumer free of any contaminating pathogenic microorganisms. The historical record of berry safety clearly indicates that berry fruit is not significant source of microorganisms that cause foodborne illness. However, that is not to say that we in the berry industry can afford to be lax or take shortcuts that may compromise safety. Food safety is a complex dynamic interplay between very adaptable and opportunistic microorganisms, an ever evolving and changing agricultural production landscape, and a human population whose food choices demand fresher and less processed products.


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In this chapter we examined the potential food safety concerns that may exist with berry fruits and the ecological, environmental, and production practices that may be important in pathogen contamination. The inherent acidic composition of berries is likely a primary barrier to long-term pathogen survival and growth. However, transient contamination of berries with pathogens can present a potential food safety threat. Therefore it is prudent that producers, transporters, and retailers of fresh berry fruits provide the same safety oversight and procedures as would be required for potentially more hazardous produce such as leafy vegetables and melons. Good agricultural practices are the cornerstone of ensuring the safety of fresh berries; however, it does not end there. In our discussion, we have stressed that ensuring safety is the responsibility of all parties involved in the production, transportation, handling, display, and sale of berries and berry products. The consuming public also has a responsibility and should be involved in practicing safe procedures when storing, handling, and serving food. Keep it safe!

References 1. Armstrong, G.L., Hollingsworth, J., and Morris, J.G., Emerging foodborne pathogens: Escherichia coli O157:H7 as a model of entry of a new pathogen into the food supply of the developed world, Epidemiol. Rev., 18, 29, 1996. 2. Cody, S,H., Glynn, M.K., Farrar, J.A., Cairns, K.L., Griffin, P.M., Kobayashi, J., Fyfe, M., Hoffman, R., King, A.S., Lewis, J.H., Swaminathan, B., Bryant, R.G., and Vugia, D.J., An outbreak of Escherichia coli O157:H7 infection from unpasteurized commercial apple juice, Ann. Intern. Med., 130, 202, 1999. 3. Cook, K.A., Dobbs, T.E., Hlady, W.G., Wells, J.G., Barrett, T.J., Puhr, N.D., Lancette, G.A., Bodager, D.W., Toth, B.L., Genese, C.A., Highsmith, A.K., Pilot, K.E., Finelli, L., and Swerdlow, D.L., Outbreak of Salmonella serotype Hartford infections associated with unpasteurized orange juice, JAMA, 208, 1504, 1998. 4. Parish, M.E., Narisco, J.A., and Freidrich, L.M., Survival of Salmonella in orange juice, J. Food Safety, 17, 273, 1997. 5. Centers for Disease Control and Prevention, Salmonella typhimurium outbreak traced to a commercial apple cider, MMWR Morb. Mortal. Wkly. Rep., 24, 87, 1975. 6. Guide to minimize microbial food safety hazards for fresh fruits and vegetables, U.S. Food and Drug Administration, Washington, DC, http:// www.food safety.gov/~dms/prodguid.html, 1998. 7. Golden, D.A., Rhodehamel, E.J., and Donald A.K., Growth of Salmonella spp. on cantaloupe, watermelon and honeydew melons, J. Food Prot., 56, 194, 1992. 8. Osteram, M.T., Cyclosporiasis and raspberries—lessons for the future, N. Engl. J. Med., 336, 1548, 1997. 9. Richert, K.J., Albrecht, J.A., Bullerman, L.B., and Sumner, S.S., Survival and growth of Escherichia coli O157:H7 on broccoli, cucumber and green pepper, Dairy Food Environ. Sanit., 20, 24, 2000. 10. Anderson, S., Recent FDA juice HACCP regulations, Food Safety, 7, 18, 2001. 11. Oregon berry production, National Agricultural Statistics Service, USDA, Washington, DC, http://www.nass.usda.gov/Statistics_by_State/Oregon/ Publications/Fruits_Nuts_and_Berries/01_27be.pdf, 2005.


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12. Noncitrus fruits and nuts 2005 summary, National Agricultural Statistics Service, USDA, Washington, DC, http://usda.mannlib.cornell.edu/usda/nass/ NoncFruiNu//2000s/2006/NoncFruiNu-07-06-2006_final.pdf, 2006. 13. Jiang, X.P., Morgan, J.M., and Doyle, M.P., Survival of Escherichia coli O157:H7 in cow manure-amended soil, Poster abstract P081, J. Food Prot., 64(suppl. A), 45, 2001. 14. Beuchat, L.R., Listeria monocytogenes: incidence on vegetables, Food Control, 7, 223, 1996. 15. Ryu, J.H. and Beuchat, L.R., Influence of acid tolerance responses on survival, growth, and thermal cross-protection of Escherichia coli O157:H7 in acidified media and fruit juices, Int. J Food Microbiol., 45, 185, 1998. 16. Nguyen, C. and Carlin, F., The microbiology of minimally processed fresh fruits and vegetables, Crit. Rev. Food Sci. Nutr., 34, 371, 1994. 17. Samson, R.A. and van Reenen-Hoekstra, E.S., Introduction to Food-Borne Fungi. Centraalbureau voor Schimmelcultures, Baarn, The Netherlands, 1988, p. 178. 18. Williamson, B., Goodman, B.A., Chudek, J.A., and Johnston, D.J., Nuclear magnetic resonance (NMR) microimaging of soft fruits infected by Botrytis cinerea, in Recent Advances in Botrytis Research: Proceedings of the 10th International Botrytis Symposium, Verhoeff, K., Malathrakis, N.E., and Williamson, B., Eds., Pudoc Scientific Publishers, Wageningen, The Netherlands, 1992, p. 140. 19. Karlsson-Borga, A., Jonsson, P., and Rolfsen, W., Specific IgE antibodies to widespread mold genera in patients with suspected mold allergy, Ann. Allergy, 63, 521, 1989. 20. Analysis and evaluation of preventive control measures for the control and reduction/elimination of microbial hazards on fresh and fresh-cut produce, Center for Food Safety and Applied Nutrition, USDA, Washington, DC, http://www.cfsan.fda.gov/~comm/ift3-toc.html, 2001. 21. Food labeling: warning and notice statements; labeling of juice products, Fed. Reg., 63, 20449, 2000. 22. Hurst, W.C., Safety aspects of fresh-cut fruits and vegetables, in Fresh-Cut Fruits and Vegetables: Science, Technology, and Market, Lamikanra, O., Ed., CRC Press, New York, 2002, p. 45. 23. Bower, C.K., Stan, S., Daeschel, M., and Zhao, Y., Promoting the safety of Northwest fresh and processed berries, Publication EM 8838, Oregon State University Extension Service, Corvallis, OR, 2003. 24. Guide to minimize microbial food safety hazards for fresh fruits and vegetables, U.S. Food and Drug Administration, Washington, DC, 1998. 25. Brackett, R.E., Incidence, contributing factors, and control of bacterial pathogens in produce, Postharvest Biol. Technol., 15, 305, 1999. 26. FSIS safety and security guidelines for the transportation and distribution of meat, poultry, and egg products, Food Safety and Inspection Service, Washington, DC, 2003. 27. Good transportation practices code, Canadian Food Inspection System, Ottawa, Ontario, Canada, http://www.cfis.agr.ca/english/cnsltdoc/transport/ transporte.html, 2001. 28. Shewfelt, R.L. and Prussia, S.E., Postharvest Handling: A Systems Approach, Academic Press, San Diego, CA, 1993. 29. Notermans, S., van Zandvoort-Roelofsen, J.S., Barendsz, A.W., and Beczner, J., Risk profile for strawberries, Food Prot. Trends, 24, 730, 2004.


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30. Beuchat, L.R. and Ryu, J.H., Produce handling and processing practices, Emerg. Infect. Dis., 3, 459, 1997. 31. Thunberg, R.L., Tran, T.T., Bennett, R.W., Matthews, R.N., and Belay, N., Microbial evaluation of selected fresh produce obtained at retail markets, J. Food Prot., 65, 677, 2002. 32. Mohd-Som, F., Spomer, L.A., Martin, S.E., and Schmidt, S.J., Microflora changes in misted and non-misted broccoli at refrigerated storage temperatures, J. Food Qual., 18, 279, 1995. 33. LeBlanc, D.I., Stark, R., Goguen, B., and Beaulieu, C., Perishable food temperature in retail stores, in New Developments in Refrigeration for Food Safety and Quality, Refrigeration Science and Technology Proceedings of the Meeting of Commission C2, with Commissions B2, D1, and D2-3, Oct. 2–4, 1996, Lexington, KY, International Institute of Refrigeration, Paris, 1996, p. 42. 34. Paull, R.E., Effect of temperature and relative humidity on fresh commodity quality, Postharvest Biol. Technol., 15, 263, 1999. 35. Wright, R.C., Dean, H.R., and Whiteman, T.M., The commercial storage of fruits, vegetables, and florist and nursery stocks, Agriculture Handbook 66, U.S. Department of Agriculture, Beltsville, MD, 1954. 36. Beuchat, L.R., Surface disinfection of raw produce, Dairy Food Environ. Sanit., 12, 6, 1992. 37. Brown, T., Corry, J.E.L., and James, S.J., Humidification of chilled fruit and vegetables on retail display using an ultrasonic fogging system with water/ air ozonation, Int. J. Food Refrig., 27, 862, 2004. 38. Legionnaires’s disease outbreak associated with grocery store mist machine— Louisiana, Dairy Food Environ. Sanit., 10, 508, 1990. 39. Sharifzadeh, K., Legionnaire’s disease outbreak due to produce mist machines, Dairy Food Environ. Sanit., 10, 550, 1990. 40. Yu, K., Newman, M.C., Archbold, D.D., and Hamilton-Kemp, T.R., Survival of Escherichia coli O157:H7 on strawberry fruit and reduction of the pathogen population by chemical agents, J. Food Prot., 64, 1334, 2001. 41. Washing food: does it promote food safety, Food Safety and Inspection Service, Washington, DC, http://www.fsis.usda.gov/Fact_Sheets/Does_Washing_ Food_Promote_Food_Safety/index.asp, 2006. 42. Adams, M.R., Hartley, A.D., and Cox, L.J., Factors affecting the efficacy of washing procedures used in the production of prepared salads, Food Microbiol., 6, 69, 1989. 43. Li-Cohen, A.E. and Bruhn, C.M., Safety of consumer handling of fresh produce from the time of purchase to the plate: a comprehensive consumer survey, J. Food Prot., 65, 1287, 2002. 44. Healthy marketplace: working towards ensuring the supply of safer food, WHO-EM/FCS/005/E/G/11.03/1000, World Health Organization, Cairo, 2003. 45. Bryan, F.L., Risks of practices, procedures and processes that lead to outbreaks of foodborne diseases, J. Food Prot., 51, 663, 1988. 46 Ak, N.O., Cliver, D.O., and Kaspar, C.W., Decontamination of plastic and wooden cutting boards for kitchen use, J. Food Prot., 57, 23, 1994. 47. Zhao, P., Zhoa, T., Doyle, M.P., Rubino, J.R., and Meng, J., Development of a model for evaluation of microbial cross-contamination in the kitchen, J. Food Prot., 61, 960, 1998.


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48. Venkitanarayanan, K.S., Ezeike, G.O., Hung, Y.C., and Doyle, M.P., Inactivation of Escherichia coli O157:H7 and Listeria monocytogenes on plastic kitchen cutting boards by electrolyzed oxidizing water, J. Food Prot., 62, 857, 1999. 49. Boer, E.D. and Hahne, M., Cross-contamination with Campylobacter jejuni and Salmonella spp. from raw chicken products during food preparation, J. Food Prot., 53, 1067, 1990. 50. Klontz, K.C., Timbo, B., Fein, S., and Levy, A., Prevalence of selected food consumption and preparation behaviors associated with increased risks of food-borne disease, J. Food Prot., 58, 927, 1995. 51. Park, P.K. and Cliver, D.O., Disinfection of household cutting boards with microwave oven, J. Food Prot., 59, 1049, 1996. 52. Farber, J.M., Wang, S.L., Cai, Y., and Zhang, S., Changes in populations of Listeria monocytogenes inoculated on packaged fresh-cut vegetables, J Food Prot., 61, 192, 1998. 53. Zhao, T., Doyle, M.P., and Besser, R.E., Fate of enterohemorrhagic Escherichia coli O157:H7 in apple cider with and without preservatives, Appl. Environ. Microbiol., 59, 2526, 1993. 54. Rodgers, S.L., Cash, J.N., Siddiq, M., and Ryser, E.T., A comparison of different chemical sanitizers for inactivating Escherichia coli O157:H7 and Listeria monocytogenes in solution and on apples, lettuce, strawberries, and cantaloupe, J. Food Prot., 67, 721, 2004. 55. Beuchat, L.P., Use of sanitizers in raw fruit and vegetable processing, in Minimally Processed Fruits and Vegetables. Fundamental Aspects and Applications, Alzamora, S.M., Tapia, M.L., and Lopex-Malo, A., Eds., Aspen, Gaithersburg, MD, 2000, p. 63. 56. Heard, G.M., Microbiology of fresh-cut produce, in Fresh-Cut Fruits and Vegetables: Science, Technology, and Market, Lamikanra, O., Ed., CRC Press, New York, 2002, p. 187. 57. Thayer, D.W., Josephson, E.S., Brynjolfsson, A., and Giddings, G.G., Radiation pasteurization of food, Issue Paper No. 7, Council for Agricultural Science and Technology, Ames, IA, 1996, p. 1. 58. O’Connor, R.E. and Mitchell, G.E., Effect of irradiation on microorganisms in strawberries, Int. J. Food Microbiol., 12, 247, 1991. 59. Ouattaraa, B., Sabatoc, S.F., and Lacroix, M., Use of gamma-irradiation technology in combination with edible coating to produce shelf-stable foods, Radiat. Phys. Chem., 63, 305, 2002. 60. Pan, J., Vicente, A.R., Mart’nez, G.A., Chaves, A.R., and Civello, P.M., Combined use of UV-C irradiation and heat treatment to improve postharvest life of strawberry fruit, J. Sci. Food Agric., 84, 1831, 2004. 61. Janisiewicz, W.J., Conway, W.S., and Leverentz, B., Biological control of postharvest decays of apple can prevent growth of Escherichia coli O157:H7 in apple wounds, J Food Prot., 62, 1372, 1999. 62. Smilanick, J.L. and Denis-Arrue, R., Control of green mold of lemons with Pseudomonas species, Plant Dis., 76, 481, 1992. 63. Janisiewicz, W.J. and Bors, B., Development of a microbial community of bacterial and yeast antagonists to control wound-invading postharvest pathogens of fruit, Appl. Environ. Microbiol., 61, 3261, 1995. 64. Leibinger, W., Breuker, B., Hahn, M., and Mendgen, K., Control of postharvest pathogens and colonization of the apple surface by antagonistic microorganisms in the field, Phytopathology, 87, 1103, 1997.


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65. El-Ghaouth, A., Smilanick, J.L., Brown, G.E., Ippolito, A., Wisniewski, M., and Wilson, C.L., Application of Candida saitoana and glycochitosan for the control of postharvest diseases of apple and citrus fruit under semi-commercial conditions, Plant Dis., 84, 243, 2000. 66. Usall, J., Teixido, N., Fons, E., and Vinas, I., Biological control of blue mould on apple by a strain of Candida sake under several controlled atmosphere conditions, Int. J. Food Microbiol., 58, 83, 2000. 67. Breidt, F. and Fleming, H.P., Using lactic acid bacteria to improve the safety of minimally processed fruits and vegetables, Food Technol., 51, 44, 1997. 68. Lopez-Malo, A., Alzamora, S.M., and Guerrero, S., Natural antimicrobial from plants, in Minimally Processed Fruits and Vegetables. Fundamental Aspects and Applications, Alzamora, S.M., Tapia, M.L., and Lopex-Malo, A., Eds., Aspen, Gaithersburg, MD, 2000, p. 237. 69. Hammerschmidt, R., Induced disease resistance: how do induced plants stop pathogens, Physiol. Mol. Plant Pathol., 55, 77, 1999. 70. Health Canada, Qualitative risk assessment: unpasteurized fruit juice/cider, in Health Risk Assessment, Food Directorate, Health Products and Food Branch, Ottawa, Ontario, Canada, 2000. 71. Nagy S., Chen, C.S., and Shaw, P.E., Fruit Juice Processing Technology, Agscience, Auburndale, FL, 1993.


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chapter 9

Postharvest handling, storage, and treatment of fresh market berries Cynthia Bower Contents 9.1 Introduction ............................................................................................... 262 9.1.1 From field to market ...................................................................262 9.1.2 The importance of shelf life extension ..................................... 264 9.2 Decay and disease control....................................................................... 265 9.2.1 Postharvest diseases in berries .................................................. 265 9.2.2 Chemical control of postharvest decay .................................... 268 9.2.3 Sanitation ....................................................................................... 269 9.3 Cold storage for extending shelf life ..................................................... 269 9.3.1 Postharvest cooling requirements ............................................. 270 9.3.2 Additional methods for quality retention................................ 271 9.4 Controlled atmosphere for storage and packaging ............................ 273 9.4.1 Controlled atmosphere storage.................................................. 273 9.4.2 Modified atmosphere packaging ............................................... 276 9.4.3 Effects of CA and MAP............................................................... 278 9.5 Edible coatings for extending the shelf life of berries........................ 278 9.5.1 Developing coatings and films .................................................. 279 9.5.2 Incorporating antimicrobial agents ........................................... 279 9.5.3 Other novel coatings.................................................................... 280 9.6 Other technologies or treatments for shelf life extension.................. 280 9.6.1 Irradiation...................................................................................... 281 9.6.2 Biocontrol agents .......................................................................... 281

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9.6.3 Other treatments........................................................................... 281 9.7 Conclusion.................................................................................................. 282 References ........................................................................................................... 284

9.1 Introduction A perfect berry growing in the field may not reach the consumer in the same flawless condition. Producing high-quality berry fruit is only the first step. Delivering them to market in premium condition is also essential to command the buyer’s attention. The handling of berries during harvesting, sorting, packing, storage, and transport determines whether the crop will be suitable for fresh market sales. Postharvest handling and storage techniques have been designed to maintain the maximum quality, prolong shelf life, and retain consumer appeal so that the grower will receive the highest market price at the time of sale. The goal of this chapter is to provide information on quality retention in fresh berry fruits through proper postharvest handling and storage.

9.1.1

From field to market

Production of consistently high-quality berries must be combined with careful harvesting, immediate cooling, appropriate packaging, rapid transport, and effective marketing to compete in the fresh market sector. This begins with finding and training the seasonal labor needed to harvest, sort, and pack the crop, since producing berry fruit for fresh market sales is very labor intensive. Mechanical harvesting is a less expensive method than employing manual labor, but the savings are diminished if the harvested berries are not acceptable as a fresh market commodity. Berries harvested by machines can be easily bruised, significantly decreasing their shelf life. For blueberries, the firmness of those harvested by machine was decreased by 36% when compared to berries harvested by hand.1 Mechanical harvesters cannot distinguish between good and unacceptable quality fruit, necessitating extra postharvest handling to separate berries from foreign matter and sort them according to quality. This additional step is time consuming, further decreasing the quality of the berries, resulting in a shorter shelf life, and a berry crop that is less competitive in the fresh market and more suited for frozen or processed products. Although new prototypes show promise, mechanical harvesting methods are currently not recommended for most cultivars of berry intended for fresh market sales. Instead, experienced pickers should be instructed to select only perfectly ripe berries for harvest. Visible defects such as broken skin, decay, mold, and insect damage should be manually sorted out while picking to minimize handling, thereby increasing the shelf life of the crop. It is recommended that high-value fresh market berries be harvested directly into retail containers to further decrease the possibility of bruising.2 After harvesting, rapid cooling of the berries is required to remove field heat. Postharvest cooling slows the berry’s respiration and decreases


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the enzyme activity that leads to softening. Cooling also delays the growth of spoilage microorganisms (bacteria and mold), which cause decay and premature loss of quality. Recommended temperatures for cooling and storage vary according to different chilling susceptibilities among berries. For example, strawberries must be quickly cooled to slow the decay of berries at the center of the pallet, as they continue to produce heat from their natural respiration. However, blueberries do not benefit from immediate cooling due to condensation that forms on the cooled berries when moved to ambient temperatures for packaging.3 Packaging is another important consideration for retaining postharvest quality and extending the shelf life of perishable fruit. The container must enclose and protect the berries from mechanical damage, yet still be convenient for transport. Packaging can be made from a variety materials to fill specific needs. Containers made from pulp absorb unwanted surface moisture, protecting the berries from water damage and extending their shelf life. Clamshell containers provide a more rigid packaging system that offers added protection for high value products such as fresh berries. Cushioned packaging materials may be required during harvest to prevent bruising when berries are dropped from a height greater than 15 cm.4 Air-freighted berries require a sturdier, better insulated package than berries destined for the local market. Controlled atmosphere (CA) requirements (temperature, humidity, oxygen/carbon dioxide [O2/CO2] mix) also influence the packaging type. Vented packaging, allowing refrigerated air to circulate while the berries are being cooled, is essential when berries are harvested directly into their final containers. For example, strawberries, which are usually packaged in the field before precooling, used to be packaged in open-top pint baskets. They are now packaged in the more protective clamshell packaging with hinged lids.5 There is a decrease in the vent area associated with the new containers; however, it is still sufficient to allow forced-air precooling before the berries are transferred into refrigerated storage. After cooling, a layer of plastic wrap may be added to minimize moisture loss during storage. Optimum storage conditions vary among different berries.6,7 CA storage accounts for these differences by adjusting the normal atmospheric composition of air around the fruit to one that will slow the respiration rate. Generally O2 levels are lowered and the amount of CO2 is increased. In addition to extending the shelf life, proper storage conditions also slow enzyme degradation and retain concentrations of easily lost vitamins such as ascorbic acid. Modified atmosphere packaging (MAP) may be employed to maintain the favorable environment within a sealed package until the product is sold. The modified atmosphere extends the shelf life of the berries, while the sealed container protects them from exposure to disease and other environmental contaminants. Rapid transport is also necessary for providing high-quality fresh market berries. Bruising can occur in transit from the vibrations common during normal shipping procedures.8 Poor-quality berries cannot be sold in the fresh market, which results in a direct dollar loss to the grower. Ideally berry fruit


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Harvest U-Pick Cool

Roadside Stands

Package Farmer’s Market

Transport

Grocery Stores Interstate Sales

Overseas Restaurants

Figure 9.1 Destination of berry fruit intended for fresh market sales.

would be picked often so that harvesting would occur at the appropriate ripeness for each berry. The crop would be handled carefully during sorting and packaging, and then cooled immediately to retain flavor and extend shelf life. The berries would be rapidly shipped under refrigeration for fresh market sales (Figure 9.1). Berries for sale in retail outlets should be displayed under refrigeration without mist to extend shelf life and inhibit the growth of mold. These conditions, together with effective marketing, will ensure that the berries garner their maximum value.

9.1.2

The importance of shelf life extension

Fresh market berry fruit offers convenience, since little or no preparation time is needed to add strawberries to short cake or stir blueberries into yogurt. Consumers are also becoming more aware of the health benefits associated with fresh berries. Antioxidants, compounds that protect against cancer-causing free radicals in our tissues, have been found in berry fruit.9 Berries also contain phytochemicals that inhibit mutagenesis caused by carcinogenic compounds.10 Certain fresh berries have demonstrated antibacterial activity and may even enhance shelf life when added to foods.11 However, these health benefits diminish in the berries over time. For example, the folate concentration in strawberries decreased after 9 days when stored at 4°C.12 This highlights the importance of proper handling and storage protocols for fresh market berries to prolong shelf life, preserve maximum quality, and retain the health benefits of the fruit. When considering berry quality, there is more to the evaluation process than meets the eye. The purchase of fresh berries is generally based on perceived quality attributes such as freshness, plumpness, color, and overall appearance. A uniform blue color with a dusty appearance (“bloom”) is highly desirable for blueberries; however, bloom can be easily lost through excessive handling. Because berries are so easily damaged between field and market, a strict regimen of proper postharvest handling is essential to maintain the quality necessary for fresh market sales. Table 9.1 lists postharvest techniques commonly used for preserving the quality of berry fruit.


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Table 9.1 Factors Affecting Postharvest Quality of Fresh Market Berry Fruit Postharvest techniques

Method for preserving quality

Rationale

Harvesting

Pick directly into retail containers Store berries away from heat and sunlight

To reduce handling of berries To prevent additional heating

Cooling

Cool berries immediately (generally using a forced-air system)

To remove field heat

Refrigerated storage

Store in a cold room (equipped with refrigeration unit)

To slow ripening and decrease microbial growth

Controlled atmosphere storage

Decrease oxygen levels during storage and increase concentration of carbon dioxide

To reduce the respiration rate of the berries and slow the ripening process

Packaging

Use rigid containers Provide a plastic overwrap

To protect berries from damage To resist environmental contaminants

Modified atmosphere packaging

Seal packaged berries in an environment favorable to decreased ripening

To extend shelf life and protect the berries from external contaminants

Transport to market

Hire refrigerated trucks

To decrease respiration of berries and inhibit the growth of mold

9.2 Decay and disease control Berries are a highly perishable commodity by design. They are the reproductive component of the plant, consisting of soft, edible tissue specifically designed to attract animals to assist in the dispersal of seeds. Unfortunately the evolutionary characteristics, which are so valuable for the plants, make it difficult for humans to prolong the storage time of fresh market berries.

9.2.1

Postharvest diseases in berries

Berries are subject to postharvest losses from a variety of sources. Physical injuries, such as bruising and abrasions, may occur during handling as warm berries are transported from the field. When damage results in leakage of juice, the berries become more susceptible to postharvest decay, rendering them unsuitable for fresh market sales. Egg-laying insects, attracted to the warm berry juices, may also transfer contaminants from infected to healthy fruit. Even the environment may expose berries to disease organisms through farm equipment, pallets, and other difficult-to-sanitize items. Once the


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berries have been damaged, regardless of the initial cause, the exposed tissue becomes vulnerable to secondary invasions by common saprophytes. Diseases are the greatest cause of postharvest losses in berries. The high humidity in cold storage, which is necessary to preserve freshness, can actually promote microbial spoilage unless there is adequate air flow to prevent moisture condensation on the berry surface. Fungi thrive on the carbohydrate substrate provided by fruit juice and are much more prevalent than bacterial or viral spoilage organisms on postharvest berries. Common pathogens of berry fruits are listed in Table 9.2. Removal of visibly decayed berries can sometimes prevent the spread of diseases to healthy berries (nesting). However, fungal diseases are difficult to control since some, such as Rhizopus sp., have spores that can be easily spread through the air, and others, such as Botrytis cinerea, can grow at refrigerated temperatures. Storage and shipment under CA conditions may be required to suppress the growth of fungal contaminants on berries if immediate sale is not possible. Botrytis cinerea (gray mold) is an important cause of decay in berry fruit. However, controlling it is not as easy as simply reducing the number of contaminating fungal spores. The incidence of B. cinerea infection on fresh grapes after prolonged cold storage was not influenced by conidial density on the grape surfaces, but by the resistance level of the host.13 Initial infection can occur during postharvest handling or even earlier, while the fruit is still maturing in the field. Fungal spores are able to survive in a dormant state within the berry until the sugar concentration is sufficient to support their growth. Postharvest handling can spread the fungus, which may continue to grow even at cold storage temperatures. Not all infected berries show evidence of disease. Bacterial pathogens can contaminate berries, leading to serious illness in humans. Listeria monocytogenes, Salmonella sp., and Escherichia coli O157:H7 were each capable of survival, but not growth, on the surfaces of fresh strawberries.2,14 Viral outbreaks, such as hepatitis, have been transmitted through berries by workers during handling.15 Protozoan parasites are also a concern. A cyclosporiasis outbreak in 1996 was associated with fresh raspberries imported from Guatemala;16 another outbreak occurred in 1997.17 Many bacteria, viruses, and protozoa can survive on fruit long enough to infect consumers. Since fresh market berries are generally not washed before sale, there is no chance for the producer to disinfect them, leaving the ultimate responsibility for food safety in the hands of the consumer. Berries can also be infested with insect pests and spiders. These pose little damage to stored fruits, but may require treatment before export. For example, blueberry maggots (Rhagoletis mendax) can create quarantine issues during shipment, as can the discovery of black widow spiders. Methyl bromide and sulfur dioxide (SO2) are both effective against insect pests such as mealybugs;18 however, the U.S. Environmental Protection Agency (EPA) will limit the use of methyl bromide starting in 2006.

76 77 77 77

Important cause of fruit rot on strawberries, blueberries, cranberries, and grapes Principal storage rot of cranberries; can also affect grapes Affects grapes Occasionally occurs on strawberries Occasionally occurs on berries and grapes Occasionally occurs on berries and grapes Occasionally occurs on berries and grapes Occasionally occurs on berries and grapes

Colletotrichum acutatum and Colletotrichum gloesosporiodes Botryosphaeria dothidea Penicillium sp. Phytophthora cactorum Cladosporium sp. Fusarium sp. Alternaria sp. Mucor sp.

Anthracnose fruit rot (black spot)

Botryosphaeria fruit rot

Blue mold

Leather rot

Cladosporium rot

Fusarium rot

Alternaria rot

Leak

78

75

73, 74

72

70, 71

Common postharvest rot in overripe berries, but cannot grow below 5°C

Rhizopus stolonifer

70, 71

References

Rhizopus rot

Important cause of fruit rot on strawberries, blackberries, blueberries, raspberries, and grapes

Remarks

Botrytis cinerea

Causative agent

Gray mold

Disease

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Table 9.2 Common Fungal Diseases of Berry Fruit During Postharvest Storage


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268

9.2.2


Chemical control of postharvest decay

Latent damage (injuries that occur at one point during postharvest handling, but don’t appear until later) can also increase the risk of contamination. If a berry experiences rough handling during harvest, signs of bruising may not be visible immediately; however, increased susceptibility to infection may occur, leading to a lower quality fruit that may eventually be discarded. Latent damage also arises from quiescent infections, which were acquired in the field, but were inhibited by the host’s natural defenses until after harvest. Since berries that suffer tissue injuries require the same cost inputs as undamaged berries for packing, cooling, transporting, and marketing, it is economically beneficial to find and remove damaged fruit as early in the process as possible. Postharvest chemical treatments are generally not necessary for fresh market berry fruits. Careful harvesting, followed by prompt cooling and rapid sale should be sufficient to control most diseases. When chemical agents are needed to control decay, the choice of treatment can be guided by the susceptibility of the infecting organism, its depth of penetration into the host tissue, and the characteristics of the compound being applied. Sometimes pathogens are resistant to chemical treatments except at very high doses or the infecting organisms are inaccessible within the berry. Chemical agents, when applied after harvest, must be at a safe dose so as to leave no toxic residues on the berries. To control decay organisms during long-term storage (such as grapes being prepared for export), fumigation with SO2 has proven effective in blocking the cellular metabolism of microorganisms. Postharvest decay of table grapes infected by Penicillium expansum and B. cinerea can be reduced by SO2-generating pads during long-term cold storage.19 Table grapes in gas-tight containers can be fumigated by slow-release SO2-generating pads without noticeably injuring the fruit.20 There are two common varieties of SO2-generating units for storage and transportation of grapes. The first is a slow-release method designed for grapes that have received a preliminary fumigation with SO2. The second “two-stage” method involves an initial rapid release of SO2, followed by a slower release to maintain an effective concentration of the fumigant. The SO2 gas can be retained by using plastic liners within the shipping containers to control postharvest decay for at least 1 month. The amount of SO2 required for long-term control (6 weeks, 0°C) of B. cinerea on grapes was found to be more than 5.5 µmol/kg-hr (3.00 µl/l inlet concentration), although nesting was effectively controlled at concentrations of 3.6 µmol/kg-hr.20 Grapes should receive regular fumigation during transport to suppress the growth of B. cinerea; however, exposure to SO2 can injure some cultivars.21,22 Injuries associated with the use of SO2 include bleaching and accumulation of sulfite residues. Damaged berries accumulated up to seven times more sulfite residue than their undamaged counterparts.23 Careful handling of grape clusters is also required because SO2 can cause berries to loosen from their pedicels. To minimize the amount of SO2 required for fumigation, only sound berries that are free from decay should be treated.


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Other chemical methods to control postharvest decay of berry fruit have been evaluated. Fumigation with acetic acid controlled decay of table grapes as well as SO2 for 6 weeks at 5°C, with no significant differences in °Brix, titratable acidity, pH, and color of the fruit.24 Fungal pathogens of strawberry fruits were controlled using a dimethoxybenzoic acid dip to inhibit in vitro spore germination and mycelial growth of B. cinerea and Rhizopus stolonifer.25 Exposure to a solution of 30% ethanol (24°C) completely inhibited the germination of B. cinerea spores in freshly harvested table grapes and reduced decay by 50% after 35 days of storage at 1°C.26 Chlorination has been used as a preventive rinse for blueberries; however, it removes the bloom and bleaches the fruit, making the berries unacceptable for fresh market sales. Exposure to ozone gas (0.3 ppm) successfully controlled B. cinerea on grapes stored for 7 weeks at 5°C; however, ozone was significantly less effective when sprayed onto the fruit.27 In addition, at sporicidal concentrations, ozone gas is toxic to humans.

9.2.3

Sanitation

Extending the shelf life of berries requires an effective method to inhibit microbial growth, together with a storage environment that is unfavorable to the progression of disease. Berries require high humidity during refrigerated storage to maintain their shape and volume. Wet berries are more susceptible to decay, necessitating rigorous sanitation practices in cold rooms to inhibit microbial growth. Damaged berries may leak juice, which can carry contaminants from one surface to another. Decayed fruit are at risk when they come into contact with any type of contaminated equipment during packing and storage. Wooden baskets and bins are difficult to clean and may support fungal growth when wet. Berry handlers can also act as vectors to spread contamination. Chlorine (sodium hypochlorite) solution is a common disinfectant for sanitizing food handling areas, although microorganisms sometimes demonstrate resistance. Ozone gas can also be used as a disinfectant when applied to surfaces that may come in contact with berries, as it inhibits sporulation of fungi and alters normal mycelial growth. Hydrogen peroxide can also inhibit fungi associated with postharvest decay. Keeping berries under constant refrigeration and maintaining clean work surfaces are two control measures recommended for inhibiting decay-causing microorganisms that can lead to loss of marketable berries. Ultimately, adhering to good agricultural practices (GAPs) and having a well-designed hazard analysis critical control points (HACCP) plan are the best strategies for protecting fresh berry fruit after harvest.

9.3 Cold storage for extending shelf life Rapid postharvest cooling is the most important step for maintaining the quality of freshly picked berry fruit. Immediate refrigeration decreases the respiration rate of the berries and slows their ripening process. It reduces textural and color changes and slows the loss of flavor and salable weight.


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Cooling also inhibits the growth of microorganisms that cause decay. Strawberries held at 5°C developed more decay and had a shorter shelf life than those held at 0°C.28 However, cooled air holds less water than the warm field air surrounding the berries at harvest, so humidity during refrigerated storage must be maintained to prevent moisture loss, which will cause the berries to shrivel. Rapid cooling with proper humidity enhances the marketing possibilities for growers by allowing a longer storage time of the crop before sale.

9.3.1

Postharvest cooling requirements

Refrigeration must be applied immediately after harvest to maximize the shelf life of perishable fruits such as berries. Precooling refers to the practice of reducing the product’s temperature before subsequent operations such as sorting and packaging are carried out at ambient temperatures. However, these temperature fluctuations can have a detrimental effect on berry quality. Although the term precooling is falling out of favor, the goal remains the same: to provide continuous refrigeration from shortly after harvest until the consumer selects the product for purchase, without allowing the temperature of the berries to rise at any time in between. Several refrigeration methods are available for reducing the temperature of freshly picked berry fruit. Forced-air ventilation is most commonly used to rapidly remove field heat. This technology consists of a refrigerated room equipped with fans capable of pulling large volumes of cold air through and around pallets filled with vented containers of produce. The use of forced-air cooling reduces berry deterioration, prolongs shelf life, and decreases the energy-intensive interval required for cooling, resulting in more efficient use of farm resources. In addition to removing field heat, the cold moving air evaporates excess moisture from the surface of the berries, making them less susceptible to postharvest decay. Blueberries are often harvested during hours when morning or evening dew is present. Removal of field moisture by forced-air ventilation retains the quality of the berries without causing weight loss or processing damage.29 Another technology is “room cooling,” where the fruit is placed in a refrigerated space that does not contain a source of moving air. This method is less effective than forced-air cooling for rapidly decreasing the temperature of a perishable product since, in still air, berries cool slowly, with heat lost only through conduction. This process is further slowed because the berries are typically surrounded by insulators such as cellophane, paperboard, and air. Room cooling is an uneven and extremely slow method of refrigeration that has proven unsatisfactory for perishable fruits such as berries. It is especially inadequate for large containers or pallets, where the berries at the center continue to respire and produce heat long after the more exposed berries near the outside have cooled. A refrigerated room is more efficiently used as a storage space for a previously cooled product, and when serving in that capacity, it requires only a small refrigeration unit. In addition to energy savings, an advantage of moving cooled berries from a forced-air


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environment to a refrigerated room is that less humidity control is required, since less moisture is lost through convection in the absence of moving air. Rates for cooling a product depend on the temperature and velocity of the air flow during the initial refrigeration phase. When cooling berries directly from the field, all containers should be positioned to allow maximum air circulation throughout the room. If forced-air cooling is used, the fans should be shut off as soon as the desired temperature is reached to prevent moisture loss from the berries. The choice of cooling method and rate of refrigeration will depend on the characteristics of each variety of berry fruit. For example, blueberries are generally not refrigerated immediately after harvest since severe condensation problems can occur when the temperature is allowed to rise again during subsequent packing steps.3 Many processes have been developed for cooling produce fresh from the field; however, not all methods are appropriate for berries. Crushed ice has been used to cover the top of harvested products (top icing), and ice water slurries have been injected into packages already stacked on pallets (liquid icing). However, icing is not recommended for cooling berry fruit because of the increased risk of freezing. Hydrocooling is also regarded as inappropriate for removing field heat from freshly harvested berries. Chilled water flowing over fresh fruit removes heat 15 times faster than air at the same temperature. However, most berries cannot tolerate wetting and become more susceptible to the growth of decay-causing organisms when moisture is present. Postharvest hydrocooling of strawberries was compared with conventional forced-air cooling to evaluate the subsequent risk of decay during storage. No differences were found for short-term storage (7 days at 1°C) unless berries were exposed to fungal spores in the water during hydrocooling.30 However, hydrocooling and evaporative cooling, a process which mists the product under low humidity conditions, are technologies not generally used to cool berries intended for fresh market sales.

9.3.2

Additional methods for quality retention

Berry fruit should be picked during the coolest part of the day, if possible, and should be held in a shaded area for the shortest time possible before applying continuous refrigeration. During the initial cooling process, lowering the temperature of the berry fruit is the primary goal; however, loss of moisture is also an important consideration. Humidity must be maintained during storage to prevent the berries from losing moisture. Water loss directly translates into a lower salable weight and a reduced profit. The water within a berry is in equilibrium with the water vapor in the air. If the relative humidity is lower than 95%, moisture will move from inside the fruit to the outside air. Grapes subjected to low moisture conditions may experience drying of their stems, causing individual berries to shatter loose from the cluster. Damaged berries are even more susceptible to shrinkage, since injuries to the skin increase the rate of water loss. Forced-air ventilation, which is valuable for rapidly lowering the temperature of warm berries, can


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accelerate the loss of moisture from cooling fruit unless adequate humidity is supplied. After cooling, a relative humidity of 95% can be maintained by wrapping the packaged berries with plastic film or packing them in containers with plastic liners; however, corrugated boxes may weaken in the presence of high humidity, allowing the berries to become bruised during transport. Although high humidity is essential for stored berries, moisture promotes the growth of disease-causing organisms. This can be offset to some degree by maintaining adequate air circulation and applying the coldest storage temperatures allowable for each fruit without permitting freezing. Berries are mostly water, but they contain sugars and other soluble compounds that depress the freezing point below 0°C. The choice of cooling method and temperature of storage depend upon the type of berry fruit being cooled. For example, strawberries benefit from near-freezing temperatures (0.6°C) that would damage a crop such as cranberries, which prefer temperatures closer to 4°C. Recommended storage conditions with estimated postharvest shelf lives are shown in Table 9.3. Most berry fruit (such as blackberries, blueberries, raspberries, strawberries, and grapes) are not sensitive to chilling injuries, despite the near-freezing temperatures recommended for cold storage. However, all berries can suffer tissue damage after direct, prolonged contact with ice. The injuries may not be visible for several days, but they can render the berry more susceptible to decay. Cranberries are sensitive to chilling injuries,31 resulting in a dull appearance and rubbery texture. Warming the cold berries to 21°C for 1 day each month was found to reduce the damage.32 Transporting cooled berries in a refrigerated vehicle will also preserve quality and extend shelf life for the fresh market. Although refrigerated trucks are not designed to cool warm berries loaded directly from the field, they can maintain the temperature of a previously cooled container. Loading the pallets to ensure maximum air circulation will also delay quality loss Table 9.3 Recommended Cold Storage Conditions for Fresh Berry Fruit Common name

Scientific name

Storage temperature (°C)

Rubus sp.

Blueberries

Vaccinium sp.

0.5 to 0

90–95

2–3 weeks

Cranberries

Vaccinium macrocarpon

2.0 to 4.0

90–95

2–4 months

Grapes

Vitis sp.

0.5 to 0

85

Raspberries

Rubus ideaus

0.5 to 0

90–95

5–7 days

Strawberries

Fragaria × ananassa

0.5 to 0

90–95

5–7 days

Storage time will vary depending on cultivars. Source: Adapted from Salunkhe and Desai.79

90–95

Postharvest shelf lifea

Blackberries and their hybrids

a

0.5 to 0

Optimum humidity (%)

2–3 days

2–6 weeks


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during transport of fresh berry fruit. Maintaining a humidified environment may be difficult; however, short transit times combined with plastic-lined containers can be effective in preventing excessive moisture loss.

9.4 Controlled atmosphere for storage and packaging Senescence of highly perishable foods, such as fresh berry fruit, results from the cellular metabolism of the food itself through the process of respiration. Berries, like all fresh produce, are still alive after harvest. They continue to respire by taking up O2 and releasing CO2 as a waste product. Generally, the shelf life of a fruit varies inversely with its respiration rate, allowing cultivars with lower respiratory rates to be stored longer than those with higher rates. The goal of CA storage is to slow the rate of respiration by continuously adjusting the ratio of gases that blanket the fruit. MAP is a self-contained form of CA, designed to maintain a CA for produce during transportation and storage.

9.4.1

Controlled atmosphere storage

Controlled atmosphere technologies were developed to preserve the quality of postharvest fruits and vegetables. Air normally contains about 21% O2 and 0.03% CO2. Since the shelf life of a fruit is inversely related to its rate of respiration, adjusting the levels of O2 and CO2 to a ratio that decreases the fruit’s respiration rate will slow the ripening process and extend the storage time. Low O2 levels can be used to delay ripening by inhibiting enzymes in the ethylene production pathway. High CO2 concentrations can also disrupt enzyme systems, such as the lipoxygenase pathway, which is involved in the formation of aroma volatile compounds. Maintaining optimal CA conditions is especially important for strawberries, blackberries, and raspberries, which all have high rates of respiration. Figure 9.2 compares the percentages of gases found in air versus those that might be used for CA storage. Controlled atmosphere storage also decreases the decay rate of fresh fruit by inhibiting aerobic bacteria and fungi. Low O2 levels and high CO2 concentrations demonstrated fungistatic effects on molds and produced less softening and a longer shelf life when used to store strawberries.33 The most common gases used for CA storage are O2, CO2, and nitrogen (N2). In the proper proportions, these gases exert an inhibitory effect on many microorganisms. High CO2 levels interfere with normal cellular metabolism and can inhibit molds and aerobic gram-negative bacteria; however, facultative and anaerobic bacteria are resistant, as are most fermentative yeasts.34 Treatments involving high concentrations of CO2 did not cause permanent injury during short-term storage.35 Other gases (such as chlorine, ethylene, nitrous oxide, ozone, and sulfur dioxide) have been evaluated as antimicrobial agents for use in CA systems, but safety, regulatory, and monetary issues have made them less attractive for commercial use. Postharvest control of insects is an important issue when berry fruit must meet quarantine requirements before export. Low O2 levels can be effective


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Berry fruit: Value-added products for health promotion Nitrogen 78%

Other Gases (apprx 1% )

Oxygen 21%

Carbon Dioxide 0.035%

Nitrogen 78%

An example of controlled atmosphere storage gases

Oxygen 2%

Carbon Dioxide 20%

Figure 9.2 Normal percentage of atmospheric gases.

in controlling postharvest insect infestations.36 Thrips (Frankliniella occidentalis) were completely eradicated on strawberries stored in a low O2 (less than 1%) environment or with high levels of CO2 (50% to 90%) without any damage to the berries.37 In addition to inhibiting microorganisms and insects, CAs with O2 levels less than 1% can also protect against infestations by birds and rodents. However, the fruit must be able to withstand the stress of a low O2 environment for a sufficient length of time to completely control pests. Mild stress from adjusting the O2/CO2 concentrations usually results in no decrease in fruit quality. However, severe stress decreases oxidative phosphorylation, which prevents glycolysis and allows undesirable compounds to be formed as pyruvate is directed through the anaerobic pathway.38 Low O2 (less than 1%) did not significantly affect the soluble solids content, pH, or titratable acidity of strawberries after 10 days of storage. However, when O2 levels were too low (0% to 0.25%), strong off-flavors were detectable, corresponding with volatiles produced during the fermentation that occurs under anaerobic conditions.36 Combining low O2 levels with refrigerated storage reduces the stress on berry fruits stored under CA conditions. Generally the negative effects caused by low O2 levels are reversible when more favorable conditions are restored. Although low O2 levels are


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typically associated with preservative effects in fruit, CA storage using high O2 concentrations has also proven beneficial. Grapes preserved with 80% O2 (10°C, 95% relative humidity) were able to retain their quality for 60 days.39 Elevated CO2 concentrations (greater than 50%) resulted in less decay of strawberries stored at 5°C and shielded the fruit from chilling injuries.38 However, the resulting disturbance in the respiratory enzyme system led to increased deterioration after 8 days of storage. CO2 levels greater than 20% caused discoloration, softening, and off-flavor of raspberries.40 The ethanol and acetaldehyde concentrations were even higher in strawberries when CO2 levels were greater than 50% compared to those stored in 20% CO2. High concentrations of CO2 (greater than 50%) decreased the reddish color of strawberries, causing their skins to acquire a blue-red cast, although low O2 levels (less than 1%) had no effect on skin color.28 Taste panels rated strawberries stored in high CO2 environments as having off-flavors; however, sequential storage with 50% CO2 followed by storage in air for several days before retail sale can eliminate this problem. When correctly applied, CA conditions decrease the respiration rate and delay ripening, thereby increasing the shelf life of some berry fruit by up to 6 weeks. The benefits of using CA storage are listed in Figure 9.3. However, CA storage is not without disadvantages. The technology is expensive, all containers must be airtight, and the gas exchange process can be slow. In addition, MAP may render products more vulnerable to the growth of foodborne pathogens if temperature abuse occurs during transport and storage, raising the concern that L. monocytogenes, Yersinia enterocolitica, Clostridium botulinum, and other pathogens will be able to grow. Systems designed for CA storage can maintain the correct environment by pumping in N2 gas to reduce O2 levels to the desired level. Berries within the storage unit continue to respire, further depleting O2 and elevating CO2. The quantity of CO2 is carefully monitored and when it exceeds a preset level, it can be removed by circulating the storage gases through a scrubber. Ethylene gas can also be removed at this time, although it generally does not pose a problem for berries. Humidity must be monitored and carefully regulated. Introducing 1.5% O2 to rapidly establish low O2 conditions, followed by an optimum mix of O2 and CO2 has proven effective for extending the shelf Decreases rate of ripening

• lowers respiration rate • regulates ethylene production • decreases sensitivity to ethylene gas

Reduces postharvest chemicals

• inhibits microorganisms (bacteria, mold) • controls insects • kills birds and rodents

Increases marketability

• allows fully ripe fruit to be harvested • reduces exposure to chilling temperatures • permits transport to distant markets • extends quality and safety of fruits

Figure 9.3 Benefits of controlled atmosphere storage for berry fruit.


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Table 9.4 Controlled Atmosphere Requirements for Berries Berry fruit

Temperature (°C)

Percent O2

Percent CO2

Commercial use

Blackberry

0.5 to 0

5–10

10–20

Gases are sealed within pallet covers during transport

Blueberry

0.5 to 0

1–10

10–15

Sometimes used during transport

Cranberry (Vaccinium sp.)

2.0 to 4.0

1–2

0–5

Grapes

0.5 to 0

5–10

15–20

Sometimes used during transport to replace sulfur dioxide for decay control

Raspberry

0.5 to 0

5–10

15–20


Strawberry

0.5 to 0

5–10

15–20


Not used commercially

Source: Adapted from Salunkhe and Desai, 1984,79 Kader,80 and Haffner et al.81

life of fresh fruits.38 No loss of quality was visible when strawberries were treated with 0% O2 or up to 80% CO2 for 6 days. When O2 levels were too low (less than 0.25%) or CO2 levels were too high (greater than 50%), strong off-flavors were detectable, corresponding with volatiles (e.g., ethanol, acetaldehyde) produced during the fermentative process that occurs under anaerobic conditions.28 However, sensory impacts can be ameliorated by transferring the berries to air (0°C) before sale to reduce ethanol and acetaldehyde levels. Conditions for storing berry fruits under CAs are listed in Table 9.4.

9.4.2

Modified atmosphere packaging

Modified atmosphere packaging is a packaging technology developed to extend shelf life by blanketing a product with a specialized atmosphere to maintain freshness within the package. Generally CO2 is increased and O2 levels are decreased to slow the metabolic activity of the fruit. Berries preserved by this technology retain their quality and nutritional value longer than those stored in air. MAP inhibits the growth of many pathogens and expands marketing options by increasing the time that fresh berries can spend in transit and retail outlets awaiting purchase. Whereas CAs involve


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continuous infusion of carefully controlled gases, MAP is generally a one-time adjustment of the atmosphere combined with a packaging material that prevents the newly introduced gases from being lost. Modified atmospheres can also be created passively by a fruit’s own respiration as it consumes O2 and gives off CO2 within a permeable packaging material. Berries tend to lose moisture when the relative humidity decreases during storage; however, most MAP films are designed to be impermeable to water. This increases the possibility that condensation will form on the inside of the package during temperature fluctuations, allowing decay-causing microorganisms to grow. Methods for dispersing condensed water have been developed, such as using surface treatments to spread the liquid into a uniformly thin film, or adding a natural adsorbent such as clay to retain excess moisture.41 A variety of MAP designs are being developed in response to the growing demand for fresh market fruit. Selecting favorable conditions for MAP depends on the characteristics of the produce (e.g., respiration rate, mass, temperature requirements), as well as properties of the packaging (e.g., surface area, film thickness, perforation size). For MAP technologies to be effective, the packaging must be able to contain the desired atmosphere for the duration of transport and storage. A popular system available commercially for strawberries is a pallet box bulk unit wrapped with a barrier plastic film to hold the selected gases (Figure 9.4). Cartons that contain liners can

Figure 9.4 Pallet box wrapped with plastic film to contain the modified atmosphere during transport of strawberries. (Photo provided by Elizabeth Mitcham, University of California–Davis.)


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also retain MAP gases. Packaging materials that control the oxygen transmission rate (OTR) permit commodities with high respiration rates to receive enough O2 to prevent fermentation from occurring. Microperforated films provide a high OTR by allowing a more rapid exchange of gas than traditional plastic films. Grapes packaged with 15 kPa O2 and 10 kPa CO2 in a microperforated polypropylene film (35 µm) were found to have a lower incidence of B. cinerea infection than the control clusters (60 days at 0°C).42

9.4.3

Effects of CA and MAP

The primary use of CA storage and packaging for berry fruit is to lower the respiration rate until the product can be sold. By slowing biochemical changes that occur during postharvest handling and storage, the shelf life of the berries can be significantly extended. CA and MAP technologies reduce the need for postharvest fungicides and insecticides, and allow fully ripe fruit to be harvested. After transport, when the berry fruits are removed from CA conditions and exposed to air for marketing, residual effects may persist. Reduced respiration rates, decreased ethylene production, and delayed incidence of decay were still present 1 week after strawberries were removed from reduced O2 storage.43 However, there is a critical point beyond which the fruit is damaged by the low O2 conditions. Thresholds for each product must be determined individually to ensure quality while being stored under CA conditions. Controlled atmosphere storage can offset the effects of ethylene production, which naturally occurs in fruits. Ethylene is a colorless gas that triggers ripening of fruit. Its presence allows some produce to be harvested before it is fully ripe, since the ripening process will occur during storage and transit. Fruits that are sensitive to ethylene are called climacteric. Strawberries are nonclimacteric fruits and must be harvested with at least 75% of their surface already red, since the color intensity will not continue to increase after harvest.28 Most berry fruits are nonclimacteric, and neither produce nor respond to ethylene in any significant way. Blueberries are an exception, since they can continue to ripen in the presence of ethylene; however, blueberries must be harvested almost fully ripe to attain acceptable flavor for fresh market sales. Oxygen concentrations of less than 5% are associated with decreased ethylene production, while CO2 concentrations of less than 1% result in elevated ethylene levels.38

9.5 Edible coatings for extending the shelf life of berries Edible coatings can be applied as a barrier to extend the shelf life of fresh market berries. Although waxes have been used for centuries to prevent moisture loss and protect perishable fruits from damage and contamination, new coatings with superior properties are continually being developed. Edible films can be fortified with vitamins, probiotics, and antioxidants to improve the nutritional value of the food. They can also be formulated with antimicrobial agents to protect against foodborne pathogens. Coatings and


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films are biodegradable and may even lead to the decreased use of packaging materials. In some respects, edible coatings can be considered to be similar to MAP, since they both create a micro-controlled atmosphere around the berries, thereby modifying gas exchange with the surrounding air.

9.5.1

Developing coatings and films

An edible coating can be described as a food-safe solution that is directly applied to the surface of a product. Edible films are prepared separately as thin layers and then applied to the outside of a food as a barrier. A variety of different films and coatings have been developed for protecting fruits, including polysaccharides such as starch, seaweed extracts, chitinous material, and cellulose derivatives.44 Protein and lipid coatings have also been produced. However, these are generally not used for berries. Ideally these edible films should be transparent and should not interfere with the aroma and flavor of the food they protect. They should be easy to apply in a uniform layer and they should adhere tightly to the food without transferring to surrounding materials. Edible films composed of polysaccharide compounds are usually hydrophilic, providing a barrier against oxygen and hydrophobic compounds such as lipids. Unfortunately polysaccharides do not prevent the migration of water from fruit to the coating. To design a film with water-barrier properties capable of reducing moisture loss, it would be necessary to incorporate hydrophobic compounds such as oils or waxes. Fatty substances tightly align at the molecular level to effectively repel water, but are sometimes difficult to stabilize when forming film barriers. Bilayer coatings can contribute valuable characteristics from both hydrophilic and hydrophobic moieties. Coatings are capable of extending the shelf life of fresh fruit by reducing moisture loss and slowing the ripening process. However, to protect against the development of off-flavors, coatings should not be applied at a thickness that prevents aerobic respiration from occurring within the encased cells.

9.5.2

Incorporating antimicrobial agents

Edible coatings can seal the surface of a fruit, sometimes creating a low O2 environment that is favorable for anaerobic pathogens such as C. botulinum. Incorporating antimicrobial compounds into coatings can inhibit unwanted microbial growth. Chitosan is derived from the shells of shrimp and crabs, and is known to exhibit antifungal activity in strawberries and raspberries.45 Fresh strawberries coated with a 2% chitosan-based solution demonstrated activity against the fungi Cladosporium sp. and Rhizopus sp. (5°C, 50% relative humidity). Coated strawberries experienced less weight loss and had lower aerobic microorganism counts than untreated controls.46 Edible films should not be detectable on the surface of a berry. Acid-dissolved chitosan coatings have been perceived as bitter and astringent when applied to fresh strawberries (Fragaria ananassa). Sensory testing performed on chitosan solutions dissolved in acetic acid (0.6%) or lactic acid (0.6%)


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indicated that chitosan coatings improved the appearance of the strawberries without affecting their flavor, sweetness, or firmness.47 Chitosan solutions were also evaluated for antifungal activity as preharvest sprays rather than postharvest coatings. Strawberry plants received chitosan treatments 5 days before harvest, when the fruit was not yet fully red. After harvest, the berries were challenged with B. cinerea. Chitosan-sprayed berries experienced significantly less postharvest decay than the controls and their texture remained firmer throughout storage (4 weeks at 3°C).48 Chitosan coatings containing essential oils can also be inhibitory to fungi.49 When anise was combined with chitosan, the resulting coating was able to inhibit the growth of B. cinerea on strawberries.50 Antibacterial activity can also be incorporated into chitosan films by adding an antimicrobial enzyme such as lysozyme. A film matrix prepared with chitosan and lysozyme retained activity against E. coli and Streptococcus faecalis without affecting water vapor permeability, although the tensile strength and percent elongation values were found to decrease with increasing lysozyme concentrations.51

9.5.3

Other novel coatings

New films and coatings for preserving berry fruit are always being studied. An edible coating based on aloe vera gel was evaluated for its ability to extend the shelf life of grapes during storage. Grape clusters coated with aloe vera gel experienced less softening, rachis browning, and color changes than untreated controls (35 days at 1°C).52 Microbial decay caused by yeast and molds was also significantly decreased in aloe vera-coated berries without negatively impacting taste, aroma, or flavor characteristics. Calcium has been added to edible coatings to control postharvest decay in raspberries, strawberries,53 and blueberries.54 Wheat gluten coatings and films were evaluated for their ability to extend the postharvest life of fresh strawberries, with promising antimicrobial results and consumer acceptance.55 Currently there is little demand for coatings designed to extend the shelf life of fresh market berry fruit. Berries are frequently packed right in the field with as little handling as possible. This process does not encourage the development of edible coatings. Additional issues surrounding the production of edible films for berries involve manufacturing as well as formulation problems. It is thought that coatings and films might not adhere to the food and other film components might migrate inside. There is also a negative public perception concerning chemical additives on fresh fruit. These are just a few of the concerns that keep this technology from becoming more common in fresh market sales.

9.6 Other technologies or treatments for shelf life extension Consumers desire safe, healthy foods that are minimally processed and ready to eat. Fresh berry fruits fall into this category as a highly nutritious choice. Controlling postharvest diseases generally requires fungicides.


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However, the current trend toward using fewer chemicals in food, together with growers’ concerns over fungicide-resistant pathogens, have led to the search for alternative treatments. To maintain the quality of freshly harvested fruits such as berries, a variety of technologies are being evaluated. Low-dose irradiation has been successful in inhibiting the postharvest growth of gray mold on strawberries. Control of fungi has also been accomplished by harnessing other organisms and employing them as biocontrol agents.

9.6.1

Irradiation

The use of ionizing radiation for extending the shelf life of fruits and vegetables has received considerable attention. Gamma irradiation (2 kGy) inhibited Rhizopus sp. and Botrytis sp. decay in grapes during shipping and storage56 and may offer an alternative to sulfur dioxide fumigation. Berry firmness and other sensory qualities were not affected by the process. Gamma irradiation of fresh strawberries also significantly delayed the growth of molds.57 However, consumer acceptance of irradiated food remains low. A study conducted in 2000 determined that only 50% of the people polled would purchase an irradiated food product.58

9.6.2

Biocontrol agents

The current trend to reduce the quantity of chemicals applied postharvest to berry fruit is being driven by environmental and health concerns. The concept of applying environmentally friendly biocontrol agents is often more appealing to consumers than treating fresh produce with chemicals. Aureobasidium pullulans, a yeast-like fungus, was found to suppress the growth of B. cinerea and R. stolonifer on strawberries and grapes.59,60 Aureobasidium outcompetes other fungi for nutrients, thereby preventing the growth of decay-causing fungi, even at refrigerator temperatures. Trichoderma isolates were able to control anthracnose (Colletotrichum acutatum) and gray mold (B. cinerea) on strawberries with the same effectiveness as the chemical fungicide fenhexamid.61 Metschnikowia fructicola also inhibited postharvest rots in strawberries more effectively than fenhexamid.62 Bacillus pumilus and Pseudomonas fluorescens were also able to suppress B. cinerea on strawberries.63 However, biological controls have not achieved widespread use in the fresh market berry sector.

9.6.3

Other treatments

Researchers continue to search for new methods to extend the shelf life of fresh berry fruit. For highbush blueberries (Vaccinium corymbosum L.), the ethylene inhibitor 1-methylcyclopropene (400 nl/l) was effective in slowing postharvest ripening when used in combination with CA storage (10 to 15 kPa


282


O2 and 10 kPa CO2) at 0°C for 12 weeks.64 Another form of storage that alters the atmosphere surrounding the fruit is hypobaric storage. Reduced pressures (0.50 atm) were effective against postharvest rots such as B. cinerea and Rhizopus in strawberries and grapes.65 Low levels of ultraviolet C (UV-C) light (1.0 kJ/m2) was also able to reduce the incidence of postharvest Botrytis decay on strawberries significantly better than in nonirradiated controls.66 Jasmonates are naturally occurring compounds that activate antifungal genes in plants. When methyl jasmonate was applied as a postharvest treatment on strawberries and raspberries, B. cinerea was significantly decreased.67,68 Eugenol, thymol, and menthol (0.5 ml) were individually tested for their ability to preserve grapes for 35 days when used in combination with MAP (1.4 to 2.0 kPa CO2 and 10.0 to 14.5 kPa O2). Each treatment was found to be effective in inhibiting fungal decay caused by B. cinerea. In addition, weight loss and color changes were slowed and firmness was retained; however, there were noticeable changes in aroma.69

9.7 Conclusion The quality of fresh market berries after harvest depends to a large extent on postharvest care. The cumulative effects from handling, storing, and transporting to market are critical in delivering a product that appeals to consumers. Mechanized harvesting, sorting, and packaging technologies must continue to improve if damage to fruit is to be minimized. Until then, the longest shelf life will be achieved when berries are harvested by hand directly into retail containers. Each berry fruit has different postharvest storage and transport requirements. These are summarized in Table 9.5. The short shelf life makes shipping perishable fruits long distances for fresh market sale difficult. Spoilage of fresh berry fruit is sometimes difficult to measure. Defects can include immature berries, which are less sweet at the time of harvest, splitting of berries (from overripening), and shriveling (from age and water loss). Overripe blueberries may appear uninjured when picked, but they do not transport well, arriving in an unacceptable condition for the consumer. In a hungry and increasingly competitive world, reducing postharvest food losses is a worthy agricultural goal. Even a partial reduction could significantly reduce the overall cost of food production and lessen our dependence on marginal land and other scarce resources. With improvements in storage technologies and the increase in global trade, today’s consumer expects to find fresh berries available for purchase outside of the local harvest season. Proper postharvest handling, storage, and treatment of fresh market berry fruit will ensure that this commodity remains available worldwide throughout the year.

Not used commercially O2: 5–10% CO2: 15–20% O2: 5–10% CO2: 15–20%

O2: 5–10% CO2: 15–20%

2°C to 4°C 90–95% RH 0.5°C to 0°C 90–95% RH 0.5°C to 0°C 90–95% RH

0.5°C to 0°C 85% RH

Forced-air cooled (10°C) Forced-air cooling (5°C) Forced-air cooling (1°C)

Forced-air cooling (less than 2°C) within 12 hours of harvest

Packed in polybags, commonly 12 oz. bags, 24 per carton Harvest directly into open-mesh baskets or clear clamshell containers Commonly packaged in small containers, vented clamshells, and sold in units of 12 per carton Grapes are generally packaged as single or small clusters of berries in plastic, vented clamshells

Maximize red color without allowing fruit to overripen Uniform red surface color

Firm, fully colored berries, and easily detached

Turgid berries, fully colored, and easily detached from stems; soluble solids concentration between 14% and 18%

Cranberries (Vaccinium macrocarpon)

Strawberries (Fragaria × ananassa)

Raspberries (Rubus ideaus)

Grapes (Vitis sp.)


Depends on the cultivar. RH, relative humidity.

Chapter 9:

a

O2: 1–10% CO2: 10–15%

0.5°C to 0°C 90–95% RH

Forced-air cooling (10°C)

Packaged in small vented clamshell containers and sold in units of 12 per carton

O2: 5–10% CO2: 10–20%

Controlled atmosphere

Firm, fully blue fruit

0.5°C to 0°C 90–95% RH

Cold storagea

Blueberries (Vaccinium sp.)

Forced-air cooling (5°C)

Cooling method

Harvest directly into containers (e.g., a vented “clamshell” box), pack in units of 12 per carton

Sorting and packaging

Firm berries should be uniform in color and easily detached

Maturity at harvest

Blackberries and hybrids (Rubus sp.)

Berry fruit

Table 9.5 Postharvest Handling of Fresh Market Berry Fruit


283


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35. Mathooko, F.M., Regulation of respiratory metabolism in fruits and vegetables by carbon dioxide, Postharvest Biol. Technol., 9, 247, 1996. 36. Ke, D. and Kader, A.A., External and internal factors influence fruit tolerance to low-oxygen atmospheres, J. Am. Soc. Hort. Sci., 117, 913, 1992. 37. Aharoni, Y., Stewart, J.K., and Guadagni, D.G., Modified atmospheres to control western flower thrips on harvested strawberries, J. Econ. Entomol., 74, 338, 1981. 38. Kader, A.A., Regulation of fruit physiology by controlled/modified atmospheres, Acta Hort. (ISHS), 398, 59, 1995. 39. Deng, Y., Wu, Y., and Li, Y., Effects of high O2 levels on post-harvest quality and shelf life of table grapes during long-term storage, Eur. Food Res. Technol., 221, 392, 2005. 40. Agar, I.T. and Streif, J., Effect of high CO2 and controlled atmosphere (CA) storage on the fruit quality of raspberry, Gartenbauwwissenschaft, 61, 261, 1996. 41. Toivonen, P.M.A., Kempler, C., and Stan, S., The use of a natural clay adsorbent improves quality retention in three cultivars of raspberries stored in modified atmosphere packages, J. Food Qual., 25, 385, 2002. 42. Artes-Hernandez, F., Aguayo, E., and Artes, F., Alternative atmosphere treatments for keeping quality of ‘Autumn seedless’ table grapes during long-term cold storage, Postharvest Biol. Technol., 31, 59, 2004. 43. Li, C. and Kader, A.A., Residual effects of controlled atmospheres on postharvest physiology and quality of strawberries, J. Am. Soc. Hort. Sci., 114, 629, 1989. 44. Lowings, P.H. and Curts, D.F., The preservation of fresh fruits and vegetables, Inst. Food Sci. Technol. Proc., 15, 52, 1982. 45. Zhang, D. and Quantick, P.C., Antifungal effects of chitosan coating on fresh strawberries and raspberries during storage, J. Hort. Sci. Biotechnol., 73, 763, 1998. 46. Park, S.I., Stan, S.D., Daeschel, M.A., and Zhao, Y., Antifungal coatings on fresh strawberries (Fragaria ∞ ananassa) to control mold growth during cold storage, J. Food Sci., 70, M202, 2005. 47. Han, C., Lederer, C., McDaniel, M., and Zhao, Y., Sensory evaluation of fresh strawberries (Fragaria ananassa) coated with chitosan-based edible coatings, J Food Sci., 70, S172, 2005. 48. Bhaskara-Reddy, M.V., Belkacemi, K., Corcuff, R., Castaigne, F., and Arul, J., Effect of pre-harvest chitosan sprays on post-harvest infection by Botrytis cinerea and quality of strawberry fruit, Postharvest Biol. Technol., 20, 39, 2000. 49. El Ghaouth, A., Arul, J., Ponnampalam, R., and Boulet, M., Chitosan coating effect on storability and quality of fresh strawberries, J. Food Sci., 56, 1618, 1991. 50. Zivanovic, S., Chi, S., and Draughon, A.F., Antimicrobial activity of chitosan films enriched with essential oils, J. Food Sci., 70, M45, 2005. 51. Park, S.I., Daeschel, M.A., and Zhao, Y., Functional properties of antimicrobial lysozyme-chitosan composite films, J. Food Sci., 69, M215, 2004. 52. Valverde, J.M., Valero, D., Martinez-Romero, D., Guillen, F., Castillo, S., and Serrano, M., Novel edible coating based on Aloe vera gel to maintain table grape quality and safety, J. Agric. Food Chem., 53, 7807, 2005. 53. Garcia, J.M., Herrera, S., and Morilla, A., Effects of postharvest dips in calcium chloride on strawberry, J. Agric. Food Chem., 44, 30, 1996. 54. Hanson, E.J., Beggs, J.L., and Beaudry, R.M., Applying calcium chloride postharvest to improve highbush blueberry firmness, HortScience, 28, 1033, 1993.


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Part III

Processing technologies for developing value-added berry fruit products



chapter 10

Freezing process of berries Yanyun Zhao Contents 10.1 Introduction ............................................................................................... 10.2 Principles of the freezing process .......................................................... 10.2.1 Freezing steps and freezing rate................................................ 10.2.2 Chemical changes......................................................................... 10.2.3 Volume and texture changes ...................................................... 10.2.4 Microbial changes ........................................................................ 10.2.5 Nutrients of frozen berries ......................................................... 10.3 Methods for freezing berries................................................................... 10.3.1 Preparation of berries for freezing ............................................ 10.3.2 Air-blast freezer ............................................................................ 10.3.3 Spiral belt freezer ......................................................................... 10.3.4 Fluidized bed freezer................................................................... 10.3.5 Liquid immersion and cryogenic freezer................................. 10.4 Innovation in the freezing process of berries....................................... 10.4.1 Vacuum impregnation pretreatment using cryoprotectants or cryostabilizers .................................. 10.4.2 Edible coatings to improve integrity and control drip loss of frozen berries ..................................... 10.5 Ensuring the quality of frozen berries .................................................. 10.5.1 Quality standards of frozen berries .......................................... 10.5.2 Rapid freezing to obtain small regular ice crystal formation .................................................................... 10.5.3 Prevention of quality deterioration during frozen storage ............................................................................... 10.5.3.1 Ice crystal size and shape............................................. 10.5.3.2 Moisture migration........................................................ 10.5.3.3 Sublimation.....................................................................

292 293 293 294 294 295 295 296 296 298 298 301 301 303 303 303 304 304 305 305 305 307 307

291


292


10.5.3.4 Solute crystallization and pH change ........................ 307 10.5.3.5 Freeze/thaw cycles........................................................ 307 10.5.4 Packages for limiting moisture loss and gas transfer ............308 10.6 Applications of frozen berries ................................................................ 308 10.7 Conclusion.................................................................................................. 310 References ........................................................................................................... 310

10.1 Introduction The market of frozen berries is huge. In the United States, the volume of frozen berries, including blackberries, blueberries, boysenberries, red and black raspberries, and strawberries, was about 478, 415, 434, 391, and 698 million pounds in 2000, 2001, 2002, 2003, and 2004, respectively (Table 10.1). Freezing is the most traditional method of preserving berries. Most berries can be frozen satisfactorily, with long shelf life and minimal impacts on quality and nutritional loss. However, the quality of the frozen berries will vary with the nature of the fruit, stage of maturity, and the type of freezing method and packaging. Selecting fruit with a firm texture and well-developed flavor, and freezing and storing following appropriate practices are critical to the final product quality. In addition to serving as a food preservation method, the freezing process is also a commonly recommended pretreatment procedure prior to other berry processes. Freezing is recommended prior to juice processing because it disrupts tissue cell structure for easy juice extraction, thus increasing the yield. Frozen berries are used for making dehydrated product because of the enhanced removal of moisture during drying. Moreover, frozen berries are used to make berry jams and preserves because freezing facilitates easy cooking. Hence, understanding the principles of the berry freezing process, the critical quality controls, and selection of appropriate freezing methods and storage conditions is critical for achieving high quality product and improving economic efficiency. This chapter covers the basic principles of Table 10.1 Stocks of Frozen Berries in Cold Storage (all warehouses) Type of berry Blackberries Blueberries Boysenberries Black raspberries Red raspberries Total strawberries Total frozen berries

2000

2001

2002

2003

2004

23,470 85,383 4,537 1,559 53,824 309,551 478,324

22,171 100,526 3,152 2,840 42,162 243,716 414,567

22,796 88,705 3,171 2,612 50,660 266,376 434,320

23,395 76,834 1,502 1,058 40,887 247,173 390,849

42,032 77,331 3,674 1,814 89,527 483,466 697,844

All data shown in thousands of pounds. Source: Data are from the National Agricultural Statistics Service (NASS), Agricultural Statistics Board, U.S. Department of Agriculture, Washington, D.C.


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Freezing process of berries

293

the freezing process, freezing methods applicable for berries, critical quality and safety control procedures, and common food applications of frozen berries.

10.2 Principles of the freezing process The principles of the freezing process are based on (1) low temperature, (2) reduced water activity due to ice formation and high concentrations of solutes, and (3) blanching of some fruits and vegetables prior to freezing. Several reactions take place during the freezing process, including (1) chemical reactions, (2) effects on the tissue structures of plant products, and (3) biological reactions, typically microbial reactions. These reactions are closely associated with various properties of the food, such as its chemical composition and maturity, and are directly affected by conditions of the freezing process, such as freezing rate and method, packaging, and storage conditions.

10.2.1 Freezing steps and freezing rate Freezing consists of lowering the temperature of a food to −18°C or less, which crystallizes some of the water and solutes. There are two steps in freezing process:1 • Supercooling. When the water temperature is below the freezing point and crystallization does not occur, the water is “supercooled.” Supercooling can occur when ice nucleation is not present and no ice crystals form. • Crystallization of water. Formation of a systematically organized solid phase from a solution and solute. The freezing rate is defined as the degree of temperature reduction in a food per minute (°C/min). It directly determines the quality of the frozen product and is affected by many product and processing factors. For fruits, the extent of cell wall rupture can be controlled by the freezing rate. For rapid freezing, with a freezing rate greater than 4°C/min, a large number of small ice crystals form. These small ice crystals produce less cell wall rupture than slow freezing (freezing rate less than 4°C/min), in which large ice crystals form, producing more cell wall ruptures. Factors affecting the freezing rate include • Temperature difference between the food product and the cooling medium. • Air velocity when cold air is used as a cooling agent. • Product characteristics, such as composition, structure, size, and shape. • Contact between the product and cooling medium. • Initial product temperature. • Type of freezing equipment used.


294


10.2.2 Chemical changes After harvesting, berries continue to undergo chemical changes that can cause spoilage and quality deterioration. Fresh fruits should be frozen as soon after harvest as possible and at their peak of ripeness in order to produce high-quality frozen products. When berries are frozen, chemical changes can occur, including concentration of solutes and chemicals in the liquid phase, enzyme activity, and oxidative reactions. During freezing, as water migrates to ice crystals, the nonaqueous materials (solutes) become concentrated in the residual unfrozen water. The residual unfrozen water undergoes changes in pH, titratable acidity, ionic strength, viscosity, freezing point, surface and interfacial tensions, and oxidation-reduction potential. In addition, carbon dioxide and oxygen are expelled from the solution/water structure and water/solute interactions are altered, macromolecules are forced closer together, and eutectic formation occurs. As water molecules are removed from solution and deposited onto ice crystals, various solutes increase in concentration, eventually reaching their saturation point, then simultaneous ice crystallization and solute crystallization becomes possible.1–3 Enzymes present in berries can cause the loss of color, nutrients, and flavor in frozen products. Enzymes must be inactivated to prevent such reactions from occurring. “Blanching,” a process in which fruits and vegetables are subjected to hot water or steam for a short time and then cooled before freezing, is usually used to inactivate enzymes in vegetables and some fruits. The major problem associated with enzymes in berries is the development of browning discoloration and the loss of vitamin C. Since frozen berries are sometimes consumed raw, instead of blanching, enzymes in frozen berries can be controlled by using chemical compounds that interfere with deteriorative chemical reactions. Ascorbic acid is the most common control chemical used for this purpose, and it may be used in its pure form or in commercial mixtures with sugars. Other methods that may be utilized include soaking the fruit in a dilute vinegar solution or coating the fruit with sugar and lemon juice. However, these latter methods do not prevent browning as effectively as treatment with ascorbic acid. Another group of chemical changes that can take place in frozen products is the development of rancid oxidative flavors due to reaction of the frozen product with air (oxygen). When berries are frozen, the solutes are more concentrated, and thus can be more easily oxidated. This reaction can be controlled by using packaging materials that are oxygen barriers, to limit the oxygen passing into the product. Vacuum packaging is another approach to reduce oxidative changes.

10.2.3 Volume and texture changes Fresh berries contain about 85% to 90% water. Water and other chemical substances are held within the fairly rigid cell walls, which give structure and texture to the fruit. When water forms ice during freezing, it expands.


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Pure water expands about 9% when freezing at 0°C. Most foods expand, but to a lesser extent than pure water, because other components are contracting. The overall extent of volume expansion for a given frozen fruit depends on many factors, including fruit composition, the fraction of unfrozen water, the temperature at which the fruit is frozen and stored, the size of the ice crystals, and cooling prior to and after freezing. The volume changes in frozen berries in turn affect the texture of the thawed product. Freezing damage in plant tissue systems includes disruption of metabolic systems, dislocation of enzyme systems, loss of turgor due to cell wall and cell membrane damage, and permanent transfer of intracellular water to the extracellular fluid through osmosis.2 These cannot be reversed upon thawing. If the ice crystals rupture the cell wall, the texture of the fruit, when thawed, will be much softer than when it was raw. The larger the ice crystals formed, that is, the more the volume changes, the more the texture changes in thawed fruit. Drip loss, defined as the amount of liquid collected when frozen food is thawed, has been used as a indicator of the quality of frozen food. Drip loss is a direct measure of volume changes in frozen food and thus the texture of thawed product.

10.2.4 Microbial changes The freezing process does not actually destroy the microorganisms that may be present on berries. Instead, during freezing and frozen storage, some microorganisms are killed, some are injured, and others survive. The growth of microorganisms is dependent on temperature. Pathogenic microorganisms usually do not grow at temperatures below 5°C, and most other microorganisms do not grow at temperatures less than −5°C. Thus there is a gradual decline in the number of microorganisms during freezing. However, sufficient populations are still present to multiply. Hence food preservation by freezing relies on inhibition of the growth of any surviving microorganisms. Controlling the temperature during freezing and storage is critical to prevent the growth of existing microorganisms. In addition, when blanching is applied prior to freezing, it can also destroy some microorganisms.

10.2.5 Nutrients of frozen berries When properly done, freezing may potentially preserve the greatest quantity of nutrients. To maintain the nutritional quality of frozen berries, it is essential to freeze the fruit fast by using appropriate freezing methods, store the frozen product at −18°C, and use it within suggested storage times. The U.S. Food and Drug Administration (FDA) published its final rule about the nutrition profiles of frozen fruits and vegetables in the Federal Register on March 25, 1998.4 In an effort to evaluate the nutrient content of frozen fruits and vegetables compared to raw fruits and vegetables, the agency reviewed both the American Frozen Food Institute’s (AFFI) supplemental data5 and similar data from the U.S. Department of Agriculture (USDA). The nutrient profiles of selected raw fruits and vegetables and


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frozen, single-ingredient versions of the same fruits and vegetables revealed relatively equivalent nutrient profiles. In fact, some data show that the nutrient content for certain nutrients was higher in the frozen version of the food than in the raw version of the food. This is probably due to the fact that unprocessed (i.e., raw) fruits and vegetables may lose some of their nutrients over time under certain storage conditions.4

10.3 Methods for freezing berries Berries may be frozen individually, packed in dry sugar or syrup (block frozen berries), or crushed into purees before freezing, depending on the final application of the finished product. Different types of freezers, including air-blast, spiral, fluidized bed, liquid immersion, spray, plate, and cryogenic, are available for specific applications. The type of freezer selected should be based on freezing rate, cost, function, and feasibility. The freezing rate directly determines final product quality. Financial considerations should take into account both the capital and running costs of the equipment and also projected losses from product damage and dehydration. Functional considerations include whether the freezer is required for continuous or batch operation and whether the freezer is physically able to freeze the product. The feasibility of operating the freezer in a specific plant location should also be considered. For processing individual quick frozen (IQF) berries, air-blast, spiral, and fluidized bed freezers can be utilized. Air-blast freezers are also the most common type used for freezing packed berries. The following sections discuss preparation procedures for freezing berries and the major types of freezers used.

10.3.1 Preparation of berries for freezing Depending on the varieties and harvest times, berries vary significantly in flavor, color, and firmness. Only the berries harvested at peak quality should be used for freezing to ensure final product quality and safety. Full-flavored, ripe berries of about the same size and with tender skins should be selected. After berries are harvested either by hand or machine, field debris should be removed, usually using a blower. The berries are then sorted, washed, and drained. For strawberries, stems need to be removed before sorting and washing. For some other berries, such as blueberries, steam blanching for 1 minute and cooling immediately may be applied if desired, since preheating in steam tenderizes the skin and makes a better flavored product. Figure 10.1 is a general flow diagram of the freezing process for berries. Berries may be individually quick frozen, packed in sugar syrup or dry sugar, or dry packed without sugar before freezing.6,7 In syrup packing, berries are well covered with syrup or juice during freezing and thawing to prevent darkening of the berries at the top. Crumpled freezer paper can be placed under the lid of a rigid container to hold fruit under the syrup or juice.


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Raw fruits (choice of cultivars and crop production)

Maturity assessment

Picking and transportation

Inspection

Preparation before freezing (cleaning/washing, sorting, size grading, slicing, etc.)

Inspection again

Pack in sugar, syrup, or dried pack as needed

Freezing

Frozen storage at −23oC

Transportation

Marketing

Figure 10.1 A general flow diagram for the freezing process of berries.

When plastic bags are used, air has to be removed to prevent oxidation. In sugar syrup packing, sugar is first dissolved in water. If hot water is used, cool the syrup to about 21°C before using. The syrup can be made ahead of time and kept in the refrigerator. For sugar packing, one part sugar by weight is added to four parts fruit by weight, making the fruit sweet enough and preserving its quality. The sugar and fruit are gently mixed until juice is drawn out and the sugar is dissolved. The fruit and juice are then packed in pails or drums. The drums are usually lined with plastic bags or a piece of crumpled moisture and vapor resistance paper is placed on top to hold the fruit in juice. In unsweetened packing, the fruit is placed in containers without liquid or sweetening, or may be covered with water containing ascorbic acid to prevent browning discoloration. Some berries, such as strawberries, may be


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more mushy when packed without sugar. It is best to cover light-colored berries with water containing ascorbic acid. Berries may be crushed or sliced in their own juice without sweetening and then pressed into the juice or water with a small piece of crumpled paper, similar to syrup or sugar packing. The selection of a packing method is based on market demand, profitability, and the quality of the fruit. Generally syrup packing is best for dessert use, and dry sugar and unsweetened packing are best for most cooking purposes. Details on the specific applications of different types of packed frozen berries are discussed in Section 10.6. Table 10.2 describes suggested packing methods for different varieties of berries. When berries are packed, the pallets of pails or drums are taken into a freezer at −28°C under forced-air circulation. It takes about 5 days to freeze the packed berries, depending on the type of freezer used.

10.3.2 Air-blast freezer In air-blast freezers, cold air vigorously circulates, enabling freezing to proceed at a moderately rapid rate. There are batch-type and continuous systems. In the batch-type system, fruit is loosely placed on trays that are placed on carts or freezing coils in a low temperature room with cold air blowing over the product.8 In some systems, the cold air is circulated by means of large fans, while in other systems the air is blown through refrigerated coils located either inside the room or in an adjoining blower room. The continuous system, such as tunnel freezing, is possibly the most commonly used freezing system. In tunnel freezing, a long, slow-moving mesh belt passes through a tunnel or enclosure containing very cold moving air. The speed of the belt varies according to the time necessary to freeze the product. Usually the cold air is introduced into the tunnel at the opposite end from where the product to be frozen enters, that is, the air flow is usually counter to the direction of product flow. The temperature of the air is usually between −18°C and −34°C. The air velocity varies from 30 m/min to 1067 m/min; 762 m/min is considered a practical and economical air velocity at −29°C.8 To achieve rapid freezing, it is necessary to recirculate a rather large volume of the air in order to obtain a relatively small increase in the temperature of the air as it touches and leaves the product. Air has a very low specific heat, thus a large volume must be carefully distributed through the system. Air-blast freezer is economical and capable of accommodating foods in a variety of sizes and shapes, and it can be used by berry processors for processing both IQF and pack-frozen berries. However, it can result in product with excessive dehydration if conditions are not carefully controlled.8

10.3.3 Spiral belt freezer Spiral belt freezers use a belt that can be bent laterally. The original spiral belt design uses a spiraling rail system to carry the belt, with a central drum that drives the belt through friction at the belt edge.

Select fully ripe, juicy berries; sort, wash carefully in cold water, and drain thoroughly.

Raspberries

(Continued)

Syrup pack: Pack berries into containers and cover with cold 40% syrup. Leave headspace, seal, and freeze. Unsweetened pack: Tray pack or pack berries into containers. Leave headspace, seal, and freeze. Crushed or puree: Crush or press berries through a fine sieve for puree. To 2 lb. crushed berries or puree, add 1 to 11/2 cups of sugar, depending on tartness of the fruit. Stir until sugar is dissolved. Pack into containers. Leave headspace, seal, and freeze. Syrup pack: Pack berries into containers and cover with cold 40% or 50% syrup, depending on the sweetness of the fruit. Leave headspace, seal, and freeze. Sugar pack: To 1 lb. of berries, add 3/4 cup of sugar. Turn berries over until most of the sugar is dissolved. Fill containers. Leave headspace, seal, and freeze. Unsweetened pack: Pack berries into containers. Leave headspace, seal, and freeze. Crushed or puree: Crush or press through a sieve for puree. To each 2 lb. of crushed berries or puree, add 1 cup sugar. Stir until sugar is dissolved. Pack into containers. Leave headspace, seal, and freeze. Sugar pack: To 1 lb. of berries add 3/4 cup of sugar and mix carefully to avoid crushing. Put into containers. Leave headspace, seal, and freeze. Syrup pack: Put berries into containers and cover with cold 40% syrup. Leave headspace, seal, and freeze.

Select full-flavored, ripe berries with uniform size and tender skins; sort, wash, and drain berries; if desired, steam blanching for 1 minute and cool immediately to tenderize skin and make better flavored product. Select firm, plump, and fully ripe berries with glossy skins, since green berries may cause off-flavor; sort berries into uniform sizes, avoiding infected and injured fruit; remove any leaves; wash and drain berries.

Among most firm berries: blueberries, elderberries, huckleberries

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Among the most soft berries: blackberries, boysenberries, dewberries, loganberries, youngberries

Type of packs

Sample preparation

Variety of berry

Table 10.2 Types of Packs Commonly Used for Freezing Berries


Freezing process of berries 299

Whole fruit or sliced; crushed fruit may be used, thus different handling may be applied. Whole berries: Select firm, ripe, red berries with a slightly tart flavor. Sliced berries: Slice large berries into 3/4 inch or other thickness based on needs or crush for fast freezing. Berries should be sorted, washed in cold water, and well drained, and hulls removed.

Sample preparation

Unsweetened pack: Put berries into containers. Leave headspace, seal, and freeze. Crushed or puree: Crush or press through a sieve for puree. To 2 lb. of crushed berries or puree, add 3/4 to 1 cup of sugar, depending on the sweetness of the fruit. Mix until the sugar is dissolved. Put into containers. Leave headspace, seal, and freeze. Syrup pack: Put berries into containers and cover with cold 50% syrup. Leave headspace, seal, and freeze. Sugar pack: Add 3/4 cup of sugar to 1 lb. of strawberries. Stir until most of the sugar is dissolved or let stand for 15 minutes. Put into containers. Leave headspace, seal, and freeze. Unsweetened pack: Tray pack or pack into containers. Leave headspace. For better color, cover with water containing ascorbic acid. Seal and freeze. Sliced or crushed: Slice or crush partially or completely. To 1 lb. of berries add 3/4 cup of sugar and mix well. Pack into containers. Leave headspace, seal, and freeze. Puree: Press berries through a sieve. To 2 lb. of puree, add 2/3 cup of sugar and mix well. Put into containers. Leave headspace, seal, and freeze.

Type of packs

300

Source: Modified from Mixon.7

Strawberries

Variety of berry

Table 10.2 (Continued) Types of Packs Commonly Used for Freezing Berries




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The latest spiral belt design uses a self-stacking, self-enclosing stainless steel belt for compactness, greater reliability, and improved airflow. This design eliminates the traditional rail system and friction drive. The number of tiers in the belt stack can be varied to accommodate different capacities. In-feeds and out-feeds can be located to suit most line layouts. This type of freezer is available in a range of models with different belt widths and may be completely factory assembled or partially assembled in modules for quick installation and future portability.8 Spiral freezers are good systems for products requiring a long freezing time (generally 10 minutes to 2 hours) and for products that require careful handling. Berries can be frozen using this system for IQF products with high quality and efficiency.

10.3.4 Fluidized bed freezer The fluidized bed freezer is a modification of the air-blast freezer and is used for processing small IQF products. Solid food particles ranging in size from peas to strawberries can be fluidized by forming a bed of particles 25 to 120 mm deep on a mesh belt (or mesh tray) and then forcing air upward through the bed at a rate sufficient to partially lift or suspend the particles in a manner somewhat reminiscent of a boiling liquid. If the air used for fluidization is appropriately cooled, freezing can be accomplished at a rapid rate. An air velocity of at least 114 m/min is necessary to fluidize the particles, and an air temperature of about −34°C is common.8 Bed depth depends on the ease with which fluidization can be accomplished, and this in turn depends on the size, shape, and uniformity of the particles. Freezing time varies with conditions. For strawberries, it takes 9 to 13 minutes to reduce the temperature from 21°C to −18°C.9 The primary product parameter influencing the energy required for fluidization is the size or mass of the product. The limits of use for the process are based on the energy requirements necessary to maintain the fluidized condition. Fluidized bed freezing has proven successful for berries because of their small sizes. The advantages of fluidized bed freezing compared to conventional air-blast freezing are8 • More efficient heat transfer and more rapid freezing rate. • Less product dehydration and less frequent defrosting of equipment. • Short freezing time, which is responsible for the small loss of moisture. A major disadvantage of fluidized bed freezing is that large or nonuniform products cannot be fluidized at reasonable air velocities.

10.3.5 Liquid immersion and cryogenic freezer In liquid immersion (usually referred to as direct immersion freezing), the product, either packaged or unpackaged, is frozen by immersion in or by spraying with a refrigerant that remains liquid throughout the process.


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The common refrigerants used for immersion freezers are liquid nitrogen and carbon dioxide; Freon must be approved for food product contact. Very rapid freezing is achieved, resulting in superior product quality when the rate of ice crystal formation influences quality. The overall process efficiency is influenced by recovery of expensive refrigerant when the freezing process is complete. Cryogenic freezing refers to very rapid freezing achieved by exposing food items, unpackaged or thinly packaged, to an extremely cold freezant undergoing a change of state. Heat removal is accomplished during a change of state by the freezant, distinguishing this method from liquid immersion freezing. The most common food-grade cryogenic freezants are boiling nitrogen and boiling or subliming carbon dioxide.8 The rate of freezing obtained with cryogenic methods is much faster than that obtained with air-blast freezing, but it is only moderately greater than that obtained with fluidized bed or liquid immersion freezing. Liquid nitrogen is used in many cryogenic freezers. The product is placed on a conveyor belt and moved into the insulated chamber, where it is cooled with moderately cold gaseous nitrogen moving countercurrent to the product. Liquid nitrogen is then sprayed or dribbled on the product. After the desired exposure time, the product passes to an area where it is allowed to equilibrate to the desired final temperature (−18°C to −30°C) before it is discharged. The final product temperature is usually no different than that obtained during conventional methods of freezing. The advantages of liquid nitrogen freezing are8 • Dehydration loss from the product is usually much less than 1%. • Oxygen is excluded during freezing. • Individually frozen pieces of product undergo minimal freezing damage. • The equipment is simple, suitable for continuous flow operations, adaptable to various production rates and product sizes, of relatively low initial cost, and capable of high production rates in a minimal space. The disadvantage of liquid nitrogen freezing is its high operating cost, and this is attributable almost entirely to the cost of liquid nitrogen. In summary, the differences in the costs of forced cold air freezing (air-blast, spiral, and fluidized bed freezing) are likely to be minor. However, when considering the use of cryogenic materials versus cold air, cost differences become significant. The profit motive requires that the least costly method of doing a satisfactory job be used. But what is satisfactory or best varies by product. For some products, the freezing rate is not critical, such as sliced strawberries mixed with sugar. Other products may have significant quality loss when slow freezing is applied. For example, whole strawberries suffer texture damage with excessively slow freezing since they have a high moisture content and lack the physical structure to withstand freezing damage.


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10.4 Innovation in the freezing process of berries Several procedures and methods have been evaluated for improving the quality of frozen berries by focusing on reducing drip loss, improving firmness, and enriching nutrients. For example, calcium was used to improve the firmness of frozen berries, and stabilizers, such as starches and gums, have been used to promote freeze/thaw stability.3 Recently vacuum impregnation with cryoprotectants or cryostabilizers and the use of edible coatings on the surface of berries have been investigated as pretreatments for freezing; these are discussed in the following sections.

10.4.1 Vacuum impregnation pretreatment using cryoprotectants or cryostabilizers Vacuum impregnation is a technology that immerses high porosity foods, such as some types of fruits and vegetables, in a sugar or salt aqueous solution, applying a vacuum, and then restoring the system to atmospheric pressure. The cortex, or the surface of the fruit or vegetable, acts as a semipermeable membrane, allowing solutes from the solution into the food and moisture from the food into the solution. In this multiphase food system, both solutes and water seek equilibrium. When the water activity and concentrations of all components equalize, the movement toward equilibrium stops. Vacuum impregnation has been used as a pretreatment step before many complementary processing stages, such as drying, freezing, and canning, to improve quality and save energy during further processing.10,11 Cryoprotectant is impregnated into fruit before freezing to decrease the amount of freezable water, thus reducing textural changes and drip loss during thawing.12–16 Vacuum impregnation was also applied to impregnate both cryoprotectants (high fructose corn syrup [HFCS] or high methoxyl pectin [HMP]) and minerals (calcium gluconal [CG] and zinc lactate [ZL]) into marionberry15 and strawberries16 before freezing to improve quality and enrich the nutrient content in the berries. The vacuum impregnation process consisted of 15 minutes in a vacuum at 50 mmHg, followed by atmospheric pressure restoration for 30 min. The vacuum impregnation pretreatment increased the maximum compression force of frozen marionberries 45% to 137% and strawberries 50% to 100%, and reduced drip loss 28% to 48% for marionberries and 20% to 50% for strawberries, depending on the specific vacuum impregnation conditions. Calcium provided additional benefits to the texture quality, and zinc improved color stability of frozen berries. It was suggested that vacuum impregnation pretreatment might be applied for commercial freezing of IQF berries when high quality and enhanced nutritional value are required.

10.4.2 Edible coatings to improve integrity and control drip loss of frozen berries Edible coatings is a technology of applying a thin layer of edible material to the surface of a food to protect the food from deterioration or to add other functionalities. This technology has been commercially applied to fresh fruits and


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vegetables, as well as other types of food for the purpose of food processing and preservation. For fresh fruits and vegetables, edible coatings are used to protect the produce from deterioration by retarding dehydration, suppressing respiration, improving textural quality, helping retain volatile flavor compounds, and reducing microbial growth.17 Over the last decade, interest has been rapidly growing in the development and use of edible coatings to prolong shelf life and improve the quality of fresh, frozen, and formulated food products.18 Han et al.19 investigated the use of edible coatings to reduce drip loss and protect the texture of frozen berries by controlling the migration of water from the fruit. A 1% chitosan-based edible coating was applied to the surface of strawberries (Totem) and red raspberries (Tullmeen) before freezing. The berries were then frozen inside an air-blast freezer at −23°C for 5 hours, packaged in zip-sealed polyethylene bags, and stored in the same freezer up to 6 months. The coating reduced the drip loss to 25% and helped maintain the textural quality of frozen berries after thawing.

10.5 Ensuring the quality of frozen berries The chief function of freezing is to preserve food while maintaining its high quality. This is accomplished by reducing product temperature, thereby slowing quality deterioration processes. For frozen berries, the major qualities taken into consideration are flavor, color, nutrients, texture and drip loss after thawing, the loss of surface moisture (dehydration), and potential microbial growth. The following sections cover suggested procedures for ensuring high quality in the final product. It is important to note that quality control should start at the beginning of the process and with raw fruit quality itself.

10.5.1 Quality standards of frozen berries The U.S. Department of Agriculture’s (USDA) Agricultural Marketing Service has established grade standards as a measure of quality for frozen berries. The USDA provides an inspection service that certifies the quality of frozen berries on the basis of these U.S. grade standards. The inspection service is voluntary and paid for by the users. Many processors, wholesalers, and buyers for food retailers use the USDA grade standards to establish values for their products described by grades. Under the program, frozen berries are inspected by highly trained specialists during all phases of preparation, processing, and packaging. Frozen berries are generally ranked in four grades: U.S. Grade A (U.S. Fancy), U.S. Grade B (U.S. Choice), U.S. Grade C (U.S. Standard), and U.S. Grade D (U.S. Substandard).20–23 U.S. Grade A are berries of similar varietal characteristics that possess a practically uniform typical color, a reasonably good character, and a normal flavor and odor. This highest grade of fruits is the most flavorful and attractive, and therefore is usually the most expensive. U.S. Grade B berries are the predominant fruits that are frozen and are of very good quality. They are berries of similar varietal characteristics that


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possess a reasonably uniform typical color; may possess a fairly good character typical of fairly well-ripened to very ripe berries with not more than 30%, by weight, for blackberries and not more than 40%, by weight, for boysenberries, dewberries, loganberries, youngberries, and other similar types that may be crushed; and possess a normal flavor and odor. These berries are only slightly less perfect than Grade A in color, uniformity, and texture. U.S. Grade C frozen berries may contain some broken and uneven pieces. While flavor may not be as sweet as in higher grades, these fruits are still good and wholesome. They are useful where color and texture are not of great importance, such as in puddings, jams, and frozen desserts. Grade C fruits vary more in taste and appearance than the higher grades and they cost less. U.S. Grade D frozen berries are berries that fail to meet the requirements of U.S. Grade C. Table 10.3 is a summary of the U.S. standard grades of frozen berries.

10.5.2 Rapid freezing to obtain small regular ice crystal formation The freezing rate has a significant impact on the quality of frozen berries. Rapid freezing results in a large number of small ice crystals, while slow freezing allows initially formed ice crystals to grow in size. Rapid freezing allows the product to get through the zone of solute concentration more quickly, thus minimizing concentration effects by decreasing the time concentrated solutes are in contact with food tissues, colloids, and individual constituents. Increasing the concentrations of dissolved solids lowers the freezing point of a solution. As the water freezes, it concentrates the dissolved solids and reduces the freezing point of the unfrozen liquid. Lowering the freezing temperature helps maintain desirable sensory properties by lessening the types of damage that occur during frozen storage. Solute concentration damage can be avoided during the freezing process if the freezing point is depressed so that no ice is formed. Lowering the freezing point can also make the product easier to thaw and prepare, and can create softer textures directly out of the freezer.3

10.5.3 Prevention of quality deterioration during frozen storage At subfreezing temperatures, foods are not completely frozen and will continue to deteriorate. Freezing is very destructive to tissue cells or anything else containing water because water expands when it freezes. If the storage temperature is incorrect or there is a temperature fluctuation, physical and chemical reactions can occur to reduce the quality and shorten the shelf life of frozen berries.3

10.5.3.1 Ice crystal size and shape During frozen storage, ice crystals undergo metamorphic changes. The number of ice crystals is reduced and their average size increases as a result of the surface energy between the ice and the unfrozen matrix. Temperature

Source: Adapted from USDA.20–23

Other berries

Strawberries

Frozen blueberries are prepared from sound, properly ripened fresh fruit of the blueberry bush (genus Vaccinium), including species or varieties often called huckleberries, but not of the genus Gaylussacia. They are cleaned and stemmed, properly washed, and packed with or without packing media and are frozen and maintained at temperatures necessary for preservation of the product. Frozen raspberries are prepared from properly ripened fresh fruit (genus Rubus). They are stemmed and cleaned, may be packed with or without packing media, and are frozen and stored at temperatures necessary for preservation of the product. Frozen strawberries are prepared from sound, properly ripened fresh fruit of the strawberry plant. They are stemmed, properly washed, sorted, and drained. They may be packed with or without packing medium, and are then frozen in accordance with good commercial practices and maintained at temperatures necessary for preservation of the product. Frozen berries are prepared from properly ripened fresh fruit. They are stemmed and cleaned. They may be packed with or without packing media, and are frozen and stored at temperatures necessary for preservation of the product.

Description

Red raspberries are red or reddish purple in color. Black raspberries are black in color. Whole: retain approximately their original conformation Sliced: produced by slicing whole strawberries into two or more pieces Blackberries, boysenberries, dewberries, loganberries, youngberries, other similar types, such as nectarberries

Native or wild type, cultivated type

Style/type

U.S. Grade A (Fancy), U.S. Grade B (U.S. Choice), U.S. Grade D (U.S. Substandard)

Grade A (Fancy), Grade B (U.S. Choice), Grade C (U.S. Standard), Grade D (U.S. Substandard)

Grade A (Fancy), Grade B (U.S. Choice), Grade D (U.S. Substandard)

Grade A (Fancy), Grade B (U.S. Choice), Grade C (U.S. Standard), Grade D (U.S. Substandard)

Grade

23

22

21

20

References

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Raspberries

Blueberries

Variety of berry

Table 10.3 U.S. Standards for Grades of Frozen Berries




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fluctuations reduce the size of small crystals more than that of large crystals. During cooling cycles, crystals with larger cross sections are more likely to capture water molecules that are transferring back to the solid phase. The combined effect of product structure, interfaces, and the different moisture concentrations work together to move water toward the surface of the product.

10.5.3.2 Moisture migration Temperature gradients within a product during frozen storage may result in moisture migration. Water will migrate down a temperature gradient because of the temperature dependence of water vapor pressure. When there is a void space around a product in a package, moisture transfers into this space and accumulates on the product surface and on the internal package surface.

10.5.3.3 Sublimation Sublimation occurs as water passes directly from the solid state to the vapor state, or from frozen food into the atmosphere around the product. Moisture vapor in the atmosphere attempts to reach equilibrium with the foods within a room, as well as with the room itself. The temperature of the freezing coil is always lower than the air in the storage room, thus ice will form and accumulate on the coil. Sublimation is a principal contributor to the formation of freezer burn on food products. It increases the oxygen contact with the food surface area, and in turn irreversibly alters color, texture, and flavor.

10.5.3.4 Solute crystallization and pH change After freezing, solutes may be supersaturated in the unfrozen phase. In time, these solutes may crystallize or precipitate and change the relative amounts of solutes and the actual concentration of solutes. Therefore the ionic strength and pH can change due to changing ratios of buffer components. These factors also affect the stability of other molecules, causing changes in the characteristics of molecules in solution.3

10.5.3.5 Freeze/thaw cycles Repeated freezing and thawing is very damaging to tissue structure (i.e., the texture of food). Most frozen food distribution systems have measurable temperature cycles, but there is great variability in the temperatures of consumers’ freezers. Whatever the fluctuation in storage temperature, there will be a lag effect on the food because heat transfer has a finite rate. However, large temperature variations over long storage times can cause noticeable damage. It is generally considered that below −12°C, microbial growth stops or is extremely slow. During frozen storage, the product must not be allowed to thaw, as this will allow any surviving microorganisms to grow. Thawing followed by refreezing causes ice crystals to grow larger, causing rupture of the cell structure and a product with poor texture. To maintain top quality, it is recommended that frozen berries be stored in commercial freezers at −23° or lower immediately after freezing. During transportation and distribution,


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berries should be maintained in insulated packages/containers that are equipped with their own refrigeration units. Upon arrival at the retailer, the fruit should be stored and maintained at −18°C. Storing frozen berries at temperatures higher than −18°C increases the deterioration rate and can shorten shelf life. Frozen berries should be packed in tight-fitting, waterand vapor-proof material so that evaporation and sublimation cannot occur.3

10.5.4 Packages for limiting moisture loss and gas transfer Frozen berries must be packaged properly to protect their flavor, color, moisture content, and nutritive value from the dry environment inside the freezer. In general, packaging materials used for frozen berries should meet the following requirements: • Moisture and vapor resistant to prevent the transfer of moisture and air in and out of the package. • Durable and leak-proof at low temperatures; also, it should not become brittle and crack at low temperatures. • Prevent absorption of off-flavors or odors from the freezer. • Easy to seal and label. The permeability characteristics of packaging materials govern the rate of weight loss during frozen storage. Suggested packaging materials for frozen berries include rigid containers made of plastics, and flexible packaging materials, including plastic bags, heavy aluminum foil, plastic film, polyethylene, and laminated paper. Moisture barrier polymer wraps and bags, waxed cartons, or overwrapped trays are commonly used for packaging frozen berries. Polyethylene is widely used for most IQF berries because it has high abuse resistance at temperatures down to −50°C and gives the best moisture barrier properties of the readily available packaging materials. Polyethylene-coated chipboard is used where delicate berries are block frozen in their containers. Polyethylene-lined multilayer paper bags may be used as larger containers. Waxed cartons are suitable for fragile fruit such as raspberries, and bags can be used for more robust fruit such as blueberries. Paper boxes can be used with plastic bags as liners, as they are easy to stack and help save space.

10.6 Applications of frozen berries The market for frozen berries is huge and growing because of increased consumer awareness of the health benefits of berries and their unique colors, flavors, and tastes. Frozen berries are utilized in many different ways. Some examples of their applications include • End products for direct consumer use. • Beverages, such as smoothies, milk shakes, malted drinks, and yogurt drinks. • Jams, jellies, preserves, and dried fruits.


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• Dairy products such as ice cream, yogurt, frozen novelties, sherbets, fruit bars, and puddings. • Bakery goods, including berry bread, cakes, tarts, muffins, and pie fillings. Table 10.4 provides examples of applications of some frozen berries based on packing types. In the past 10 years, studies have identified an array of components in berries as nutraceutical ingredients. It has been noted that the combination of phytochemicals (naturally occurring chemicals from plants) in berries makes them especially nutritious, with benefits that no individual phytochemical dietary supplement can even come close to providing.24 The use of berries in dairy products is increasing. One example is a new generation of flavored cottage cheeses.24 With cottage cheese, which inherently has texture due to the curd particles, fruit is desirable in both blended and fruit-on-the-bottom varieties. Fruit integrity is most important in side-by-side fruited cottage cheese, as in yogurts. The fruit form used in various dairy products varies based on the manufacturer’s goal for the product. For smoothies and gelato, low particulate fruit varieties are usually used. However, for ice creams, fruit with particulates along with identifiable berries is added. For premium dairy products such as refrigerated desserts, or wherever fruit identity is of utmost importance, IQF berries are appropriate. These fruits typically contain no sugar or preservatives, but some processors offer IQF fruits infused with a sugar solution to prevent them from freezing solid in frozen applications. Either form separates easily when added to a mix, enabling even dispersion. Frozen sweetened and unsweetened berries are also available; however, as the product thaws, traditionally frozen fruit loses its integrity, often breaking up. Table 10.4 Examples of Applications of Some Frozen Berries Based on Packing Types Type of frozen berry Individually quick frozen

Sugar packed (sliced or whole) Puree

Other

Example of applications Ice cream, yogurt, and toppings, cereals, juice, freeze-dried products, jams, preserves, and smoothies Food service and bars mixes Retail grocery chains Dairy products, mainly ice cream Jams and preserves Food service Production of jams, jellies, ice cream, and yogurt Juice manufacturing and brewery specialty products Juice stock, juice stock used for bar mixes, juice stock used for smoothies, and canned strawberries sold in retail grocery chains Drum packs used for syrups and jams


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Frozen berries packed in thick and sweetened syrup are best used as pie fillings. Many consumers perceive pie filling as highly processed, and as a result, it is not typically used in dairy products, except in sundae-type novelty cups.

10.7 Conclusion Freezing is the most common processing and preservation technology applied to berries because of its power to reduce chemical and biological reactions in foods, preservation of nutrients and important quality attributes, and relatively low operating costs. Different freezing equipment—air-blast, spiral belt, fluidized bed, and liquid immersion—and packing methods—liquid or dried, sweetened or unsweetened, or IQF—may be applied based on the requirements of final product quality, end application, and operating costs. The important quality controls in the freezing process include initial product condition (maturity, sanitation condition, etc.), freezing rate (rapid or slow freezing), packing methods before freezing (with or without sugar, dry or liquid sweetener), packaging materials, and storage conditions. When applied appropriately, high quality and longer shelf life of frozen berries can be obtained. Frozen berries have wide applications as end-use products or as ingredients in other manufactured products because of their important nutritive and health benefits, as well as their colors, flavors, and tastes. In addition, the freezing process is a significant step in other food processes, such as dehydration and juice manufacture.

References 1. Desrosier, N. and Tressler, D., Fundamentals of Food Freezing, Avi Publishing, Westport, CT, 1977. 2. Mogons, J., The Quality of Frozen Foods, Academic Press, London, 1984. 3. Kobs, L., Designing frozen foods, Food Product Design, January, 27, 1997. 4. Krese, C. and Jacobs, M., FDA rules frozen fruits and vegetables have equivalent, if not better, nutrient profile than fresh product, American Frozen Foods Institute, http://www.healthyfood.org/sub/news_03.25.98.html, 1998. 5. American Frozen Food Institute, 2003 Frozen Food Pack Statistics Book, American Frozen Food Institute, McLean, VA, 2004. 6. Brief instructions for freezing fruit, Electronic Publication HE-246, North Carolina Cooperative Extension Service, North Carolina State University, Raleigh, NC, http://www.ces.ncsu.edu/depts/fcs/food/pubs/fcs246.pdf, 1993. 7. Mixon, M.J., Freezing fruits and berries, Publication 1430, Mississippi State University Extension Service, Mississippi State, MS, 2002. 8. Freezing methods and quality loss at freezing temperatures, III UNISWORK Food Safety Programme, United Nations Industrial Development Organization (UNIDO), Vienna International Centre, Vienna, Austria, http://www.unido. org/file-storage/download/?file_id=32111, 2004. 9. Fennema, O., Karel, M., and Lund, D., Principles of Food Science, Part 2: Physical Principles of Food Preservation, Marcel Dekker, New York, 1975. 10. Torreggiani, D., Osmotic dehydration in fruit and vegetable processing, Food Res. Int., 26, 59, 1993.


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11. Torreggiani, D., Forni, E., Maestrelli, A., Bertolo, G., and Genna A., Modification of glass transition temperature by osmotic dehydration and color stability of strawberry during frozen storage, in Proceedings of the 19th Congress of Refrigeration, Vol. 1, IIF-IIR, The Hague, 1995, p. 315. 12. Martinez-Monzo, J., Martinez-Navarrete, N., Chiralt, A., and Fito, P., Mechanical and structural change in apple (var. Granny Smith) due to vacuum impregnation with cryoprotectants, J. Food Sci., 63, 499, 1998. 13. Sormani, A., Maffi, D., Bertolo, G., and Torreggiani, D., Textural and structural changes of dehydrofreeze-thawed strawberry slices: effects of different dehydration pretreatments, Int. J. Food Sci. Technol., 5, 479, 1999. 14. Torreggiani, D. and Bertolo, G., Osmotic pretreatments in fruit processing: chemical, physical and structural effects, J. Food Eng., 49, 247, 2001. 15. Xie, J. and Zhao, Y., Improvement of quality and nutritional value in frozen marionberry by vacuum impregnation, J. Hort. Sci. Biotechnol., 78, 248, 2003. 16. Xie, J. and Zhao, Y., Vacuum impregnation with cryoprotectants and nutraceuticals to improve quality and enhance nutritional value of frozen strawberries (Totem), J. Food Prot. Preserv., 28, 117, 2004. 17. Debeaufort, F., Quezada-Gallo, J.A., and Voilley, A., Edible films and coatings: tomorrow’s packagings: a review, Crit. Rev. Food Sci., 38, 299, 1998. 18. Diab, T., Biliaderis, C.G., Gerasopoulos, D., and Sfakiotakis, E., Physicochemical properties and application of pullulan edible films and coatings in fruits preservation, J. Sci. Food Agric., 81, 988, 2001. 19. Han, C., Zhao, Y., Leonard, S.W., and Traber, M.G., Edible coatings to improve storability and enhance nutritional value of fresh and frozen berries, Postharvest Biol. Technol., 33, 67, 2004. 20. USDA, United States standards for grades of frozen blueberries, U.S. Department of Agriculture, Washington, DC, http://www.ams.usda.gov/standards/ fzblberr.pdf, 1957. 21. USDA, United States standards for grades of frozen raspberries, U.S. Department of Agriculture, Washington, DC, http://www.ams.usda.gov/standards/ fzraspbe.pdf, 1957. 22. USDA, United States standards for grades of frozen strawberries, U.S. Department of Agriculture, Washington, DC, http://www.ams.usda.gov/ standards/fzstrawb.pdf, 1958. 23. USDA, United States standards for grades of frozen berries, U.S. Department of Agriculture, Washington, DC, http://www.ams.usda.gov/standards/ berries.pdf, 1967. 24. Berry, D., The latest and greatest on cherries and berries—the use of fruit in dairy products, Dairy Foods, November, 2001.



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Dehydration of berries Fernando E. Figuerola Contents 11.1 Introduction ............................................................................................... 11.2 High-temperature dehydration .............................................................. 11.2.1 Water activity ................................................................................ 11.2.2 Heat transfer ................................................................................. 11.2.3 Mass transfer................................................................................. 11.2.4 Drying phenomena ...................................................................... 11.3 Conventional methods for dehydrating berries .................................. 11.3.1 Drying methods and equipment ............................................... 11.3.1.1 Sun drying ...................................................................... 11.3.1.2 Hot air drying ................................................................ 11.3.1.3 Drum and spray drying ............................................... 11.3.1.4 Vacuum drying .............................................................. 11.3.1.5 Freeze-drying ................................................................. 11.3.2 The drying line ............................................................................. 11.3.3 Further processing of dried berries........................................... 11.4 Innovation in fruit dehydration ............................................................. 11.4.1 Osmotic dehydration ................................................................... 11.4.2 Microwave and combined microwave/vacuum processes .................................................. 11.4.3 Vacuum infusion or impregnation process.............................. 11.5 Critical quality and safety factors: Control of quality and nutritional losses during drying .................................................... 11.5.1 Quality factors .............................................................................. 11.5.2 Nutritional and safety factors .................................................... 11.5.3 Packaging.......................................................................................

314 315 315 317 317 318 319 319 319 320 321 321 322 322 326 327 328 329 329 330 330 331 331

313


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11.6 Applications of dried berry fruit............................................................ 11.6.1 Snack foods ................................................................................... 11.6.2 Breakfast cereals ........................................................................... 11.6.3 Formulated foods ......................................................................... 11.7 Conclusion.................................................................................................. References ...........................................................................................................

332 332 332 332 333 333

11.1 Introduction Dehydration is an ancient food preservation method. The principle of food dehydration is based on the removal of water from food materials, using the driving force of heat transfer for water evaporation or sublimation. In all cases, water is removed with the purpose of decreasing the water activity of food to produce a longer shelf life.1–3 High-temperature dehydration includes two different unit operations: heat transfer from a heat source to the food material, and mass transfer from the food material to the surrounding media. When high temperature is involved, evaporation of water occurs at normal pressure, while in freeze-drying, temperature and pressure are low and sublimation of water is the result of the process.3 Dehydration of berries must consider the effect of temperature on all factors that determine the nature of the fruit, such as phenol content, soluble fiber content, vitamins, etc. The use of high temperatures can produce a deleterious effect in the product instead of maintaining the qualities for which these products are especially appreciated. Dehydration is not the principal preservation or processing method used in berries, but it is one of the more suitable alternatives to maintain specific functional components such as dietary fiber, pigment, and low molecular weight carbohydrates. Dehydration should be used with special care in berries with high phenolics and sugar content in order to avoid chemical changes that may lead to the loss of these important functional components. Dehydration should be carried out at low temperatures to produce a low-rate water removal, thus avoiding hardening and sugar crystallization. One alternative to high-temperature air dehydration is the use of osmotic dehydration or sugar infusion to produce the same reduction in water activity. Another dehydration method normally used for berries is spray drying, which applies a berry powder starting with a concentrated berry juice of about 50°Brix. The dried products are suitable for extracting pigments and other functional compounds. When the term berry fruit is used, a large number of different botanical fruits are included, but there are a few that have real economic importance, including grapes, blueberries, raspberries, strawberries, boysenberries, and cranberries. Most of these species have shown relevant functional activities related to scavenging free radicals, antioxidation, and antiseptic behavior to several microorganisms.


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The value of these species in health enhancement has been noted in the last 10 years and preservation of these qualities is necessary in any processing method. The natural fresh condition represents the baseline to which any processed material should be compared, but concentration of the functional compounds present in the fruit is a requirement for the industrial production of high-value functional foods. Today, dehydration is a common method used to preserve berries. This chapter discusses important dehydration processes used for berries, as well as control of product quality and safety.

11.2 High-temperature dehydration High-temperature dehydration is a combination of two unit operations acting simultaneously: heat transfer and water mass transfer. Heat is normally produced by a combustion source; an indirect heat exchanger transferring energy to an air stream that conducts it to water in the product. Water evaporates and the water vapor produced is then removed from the product surface and out of the drier by the air stream. The heat transferred to the product and the water transferred from the product to the air stream are affected by the air, water content, relative humidity, and dry bulb and wet bulb temperatures.1,3,4 The dehydration process, in fact, is very complex.

11.2.1 Water activity Water activity (aw), not the total amount of water in the product, determines the available water for microbial growth, enzymatic activity, and chemical reactions that change product quality and affect the nutritional value, appearance, and global acceptance of food products. Most bacteria will not grow at water activity levels less than 0.80, while most molds and yeasts will not grow at water activity levels of less than 0.70. If water activity is controlled, it is possible to control the potential sources of spoilage. Dehydration is an effective way to reduce water activity, thus it is an effective way to control microorganisms that can cause damage to food products. Figure 11.1 shows the effect of water activity reduction on fruit leather. If fruit leather is in the presence of a saturated water media, such as a potato-dextrose agar, water activity increases to greater than 0.75, a condition in which molds will develop. If fruit leather is placed in an empty Petri dish at normal relative humidity, the product does not show any mold development for up to 6 months. This shows that at normal environment humidity levels, reduced water activity in the product permits its preservation. All food products have water in the form of bound water. While the amount of water is decreasing in the product matrix, the bound water energy is increasing, thus the amount of free water is reduced. Free water is the active water available for microorganism growth and reactions, while bound water strongly links to hydroxyl groups of polysaccharides, carbonyl and amino groups in proteins, and other polar groups in food product components.


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a

b

Figure 11.1 Effect of water activity of fruit leather pieces in the presence of (a) excess water and at (b) environmental humidity.

Control of nonenzymatic reactions, such as Maillard reactions, could be effective when water activity is reduced to less than 0.4, since most chemical reactions develop with water activity levels of 0.6 to 0.7. Enzymatic reactions normally occur when water activity is 0.6 or greater, but they slow down when water activity is less than 0.6. In berries, enzymatic and oxidative reactions related to phenolic compounds should be controlled, since those compounds determine the antioxidant activity of fruits, one of the most interesting functional properties of berries. Water activity is defined as aw = lwxw = p/p0

(11.1)

where lw is the activity coefficient of water, xw is the mole fraction of water in the aqueous fraction, p is the partial pressure of water in the material, and p0 is the partial pressure of pure water at the same temperature. Defined in this way, water activity is equal to the equilibrium relative humidity (ERH) divided by 100, expressed as a fraction. This relation permits control of the storing process for low-moisture products, which has to be done with use of special packaging materials that permit control of the exchange of moisture between the environment and the product. The idea is to maintain the inside environment at the ERH equivalent to the product’s water activity. Today, a number of materials have been developed to maintain conditions for low-moisture food materials. Most raw berries have water activity levels greater than 0.95, with moisture contents of greater than 88%. A water activity level less than 0.70 for dehydrated berries permits their preservation. However, texture is modified


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by the dehydration process and the reduction of water activity, thus dehydrated berries have a different character compared to the original raw material, including structural transformations, enzymatic changes, nonenzymatic browning, and oxidation. All these deleterious changes depend on the water activity, temperature, and extent of water plasticization.5 The quality of dehydrated berries depends on the process, the rate of water removal, the pretreatments applied, the condition of the fruit (whole, cut, mashed), and the packaging material used. Storage conditions of dried fruits can also have an impact on final product quality.

11.2.2 Heat transfer Heat transfer is produced as a result of a temperature gradient between the air stream and the product surface. The evaporation rate of water is proportionally related to the heat transfer to the product surface. Water evaporation may occur on the surface or in the interior tissues, depending on the amount of free water present in the tissue and the heat transfer rate occurring in the process. Conditions in the air stream are very important for the drying rate. Energy can be supplied by the sun or mechanically produced from a combustion source or from a wave emission unit. Heat provides energy to water for evaporation. The water vapor pressure is increased by one of the heating mechanisms and water is then vaporized or sublimated from the surface of the fruit or from the internal tissues. This water movement occurs based on mass transfer phenomena.3 Heat transfer to the drying material in hot air dehydration occurs by two mechanisms: convection, in which heat is transported from an air stream flowing over or through the material, and conduction, in which heat is moving inside the product. Heat transfer from the air stream to the product surface occurs because of the temperature gradient and is controlled by a heat transfer coefficient that depends mainly on air speed and flow, while heat transfer inside the product depends on the fruit type, water content, and temperature gradient inside the fruit.4 The best way to optimize the heat transfer is to control the airflow; the more turbulent the airflow, the higher the heat transfer coefficient, and thus the faster the heat transfer. Normally heat transfer is controlled by fruit internal resistance, but in a laminar airflow, heat transfer can be lower due to a lower heat transfer coefficient of the product surface. Therefore the heat transfer process can be controlled in a well-designed drier by controlling the air temperature, the airflow speed and the nature of the flow, the way the air contacts the product, and the residence time of the product in the drier, since the temperature on the product surface is part of the driving force in the heating process.

11.2.3 Mass transfer Mass transfer in dehydration occurs by two phenomena: capillary flow due to gradients of capillary suction pressure and diffusion in the liquid or vapor phase. Convection occurs principally between the product surface and air


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with a different partial vapor pressure than the product. During the drying process, water moves from the center of the product to the surface based on diffusion. When water activity is high, that is, the amount of free water is large, water moves inside the product by capillarity. During dehydration, the amount of free water is lower, the capillaries close because of tissue shrinkage, and thus diffusion occurs in the liquid phase. When there is no more free water in the tissue, the dehydration plane is inside the tissue, but not on the surface; hence, water diffusion through the tissue to the surface is in the vapor phase. Mass transfer is one of the important factors in dehydration efficiency, directly impacting the texture and structure of the product to be dried.1,2 The nature of fruit tissue is determined by fruit ripeness, size, the wax content of the cuticle, and the amount of water and soluble solids. These are all important factors influencing water mass transfer from internal tissue to the surface and from the surface to the air stream surrounding the fruit. Berries to be processed or preserved by dehydration normally present an open structure, but the cuticle is a very strong barrier to water removal, especially when a thick layer of wax covers it. This is especially true for blueberries and black currants. Epicuticular wax can be treated with a dye solution, but cracks in the wax permit water transfer to the surface and evaporation from there.6 To summarize, there are several water-movement mechanisms in structured materials. These include liquid water moving by capillary flow, liquid diffusion, diffusion at the surface water layer adsorbed in solid tissue, water vapor diffusion, and water vapor flow caused by pressure differences in vacuum drying.1,4

11.2.4 Drying phenomena When berries are placed in a drier, the process does not follow a lineal behavior. Water is removed in different stages depending on the variety of the fruit, its structure, the presence of seeds, and the nature of the skin and epicuticular waxes. In a homogeneous material model with no volume change during drying, three stages are recognized. When the surface contains a significant amount of free water, after a very short period in which the tissue is warmed, the drying rate is constant. This stage remains until the water content reaches a point called the critical moisture content of the material. After this point, the drying rate decreases following a logarithmic function, becoming virtually zero after several hours. The initial drying process is externally controlled, as mentioned by Crapiste and Rotstein.4 The rate-controlling step for evaporation is the diffusion of water vapor through the thin layer of the air-surface interface. It is assumed that at the beginning, the free water permits the process to be conducted at the wet bulb temperature on the surface. However, berries suffer permanent deformation or shrinkage during the drying process, thus there is no free water on the product surface controlling the drying rate.


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This produces only one stage after the warm-up period. With the exception of freeze-drying, where the total volume of cells and tissue remains almost constant throughout the drying process, all other drying methods involving heat treatments have a very heterogeneous drying process, where the control of water removal is very important to control shrinkage and other damage produced by the process. Drying conditions and fruit transformation greatly affect product quality. Berries have very variable conditions in sugar and acid content, skin or cuticle thickness, seed presence, and water content. These variables determine the drying behavior of the fruit and thus the quality of the dried product. For the dehydration of berries, some pretreatments are used to enhance the drying rate, thus allowing shorter processing times for better product quality, including texture and color, and less damage to valued compounds (vitamins, phenols, etc.). Some of these pretreatments include mechanical or chemical skin perforation and partial water removal with osmotic solutions. All these pretreatments produce a shorter drying time with a higher drying rate.5,7

11.3 Conventional methods for dehydrating berries Conventional methods for the dehydration of berries include sun drying and mechanical dehydrators that use a heated air stream. The fruit is placed on different still or moving devices, where hot air passes over the surface of the fruit or through the fruit in a concurrent or countercurrent direction, depending on the structure and nature of the fruit to be dried. Conventional methods remove moisture from the product to the air driven by the moisture difference between the product surface and the air, and the temperature difference between the surface and the inner tissue of the product.

11.3.1 Drying methods and equipment In addition to classic sun drying, there are several different types of equipment used for fruit dehydration, including hot air drying, drum or spray drying to obtain fruit powders, microwave and vacuum drying, and freeze-drying. In this section, some of the general principles of these methods and equipment are discussed.

11.3.1.1 Sun drying Sun drying is the classic method used in drying fruits, including grapes, prunes, apricots, peaches, and some berries. However, most industrial dehydration occurs under controlled conditions in mechanical driers. In sun drying, the amount of sunlight, the humidity, and movement of the air mass around the product determine the drying rate. Sun drying can take many days. During the drying period, changes in fruit color and flavor can occur due to chemical and biochemical reactions, especially in the first 2 or 3 days. Since water moves very slowly inside fruit tissues, one of the


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advantages of sun drying is that it produces a uniform texture and flavor from the inner tissue to the surface of the fruit. After sun drying, the fruit has to be further processed, including increasing the water content and cleaning the fruit to eliminate all dust materials and other biological contaminants. Sun drying is a process that cannot be well controlled with respect to water removal efficiency, temperature, air relative humidity, and convection coefficients, since all these factors are dependent on the geographic location where the drying occurs. Berries normally grow in temperate or cold weather zones, which makes the sun drying process difficult. Sun drying requires a low relative humidity, low dew point, and long sunny days. Another problem in sun drying of berries is the nature of the cuticle covering the fruit, especially in cranberries, blueberries, and currants, where a thick wax layer exists as a barrier to water evaporation.

11.3.1.2 Hot air drying Hot air drying is one of the most common drying methods for food products, including fruits, vegetables, pasta, coffee, and aromatic and medicinal herbs. Dehydration is carried out in a mechanical device where food materials may be either static or moving and hot air is conducted in different directions depending on the product nature. This is the most used system for dehydration of berries because the process can be well controlled, producing high quality products. Variables to be controlled include the feeding rate, air velocity, air humidity inside the apparatus, air recirculation conditions, and final moisture content in the product. According to Crapiste and Rotstein,4 the selection of a drier for a given food depends on the heat source, the type of drying equipment, transportation of the product, the feed nature and state, operating conditions, and product residence time. Some of the suitable driers for berries include tray cabinet, tunnel type, belt conveyor, and fluidized bed driers. Small whole berries or cut berries can be processed in any of these types of driers. Most of hot air driers use product movement to some extent; however, the product can also be completely still during the drying process. Batch-type driers require some homogenization process, since not all the areas inside the drier have the same efficiency, thus the final moisture content of the product can vary greatly from one area of the dryer to another. Therefore, at the end of process all the products are mixed together and homogenized in a bin cabinet drier with a high-volume, low-speed hot air current. This produces a product with a uniform moisture content. This procedure is sometimes is applied to products dried in a continuous drier to ensure product uniformity. In continuous driers, there are many different ways to move the product for continuity of the process. For example, trays may enter in the lower part of the drier and exit in the upper part. After a certain period of time, each tray moves up one level in the dryer. Other driers have a continuous belt that transports the product from a lower temperature, higher humidity zone to a higher temperature, lower humidity zone. Wet product with a low


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temperature and high humidity will have a low dehydration rate, while the withdrawing (dried) product will have a high temperature and low humidity; thus the drying rate can be controlled. Air movement in these driers may flow parallel to the product flow or countercurrent to it. The direction of airflow can also be horizontal or vertical to the direction of product flow. Airflow is a very important factor in the dehydration rate, not only the air speed, but also the way the air contacts the product. One very important variable in hot air dehydration is the loading of the trays or feeding in a continuous system. The relationship between weight and surface area is an important factor in the efficiency of the drying process. This relationship depends on the nature of the fruit to be processed, its size and form, potential drying rate, and the geometry of the system.

11.3.1.3 Drum and spray drying All the systems discussed previously consider the use of whole or cut fruit; however, fruit powders have become important products. Dried fruit powders are usually produced using drum or spray driers, where the materials to be dried are a concentrated fruit pulp or concentrated fruit juice. Drum driers are heated internally by steam and the fruit pulp or slurry is fed evenly into the drum. The critical factor in this process is the feeding rate, since contact between the pulp or slurry and the hot drum surface has to be as short as possible to avoid heat damage, especially chemical and bioactive degradation. Spray drying, on other hand, usually uses clarified concentrated juice, although cloudy juice can also be used. Spray drying consists of atomization of fruit juice into small drops that are conducted against a hot air current inside of a conical drum, where water is evaporated and dried powder falls to the bottom and is collected. For products containing large amounts of sugar, spray drying has to be carried out with the help of coadjuvants in order to avoid problems with stickiness and to improve the drying rate. This system uses very high temperatures and has high drying rates. Control of the air temperature and the speed of juice feeding are very critical in this system. Also, the amount of coadjuvant should be carefully determined for each product. Berries such as raspberries, blackberries, and strawberries are suitable for this process, producing high-quality dried powders that can be used in the manufacture of different formulated products as natural functional ingredients.

11.3.1.4 Vacuum drying All the methods presented include the physical transportation of heat by one of two mechanisms: convection, a transport method that applies to gases or liquids, and conduction, molecular transport that applies to liquids, gases, and mainly solids. Convection requires mass to permit heat transfer and cannot operate under vacuum conditions. There are only two ways to produce heat transfer in a vacuum: (1) by conduction, which has the problem that the transference inside of fruit will be too small compared to that


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occurring from the heat source to the fruit; and (2) by radiation. Because of this, vacuum drying has been developed mainly after the use of microwave drying. In the last 10 to 15 years, microwave/vacuum dehydration has developed very quickly. Today there are several companies manufacturing driers using this technology at a very affordable cost. Although this system is more expensive that other drying methods, the quality of the products is high enough to compensate for the cost. In this system, products are dried under low temperature with very little damage to their chemical and bioactive constituents. Berries are very well processed by this method, preserving all the principal quality attributes that make the product highly desirable.

11.3.1.5 Freeze-drying One unique method of drying is freeze-drying, a combined method that uses freezing and then sublimation of water at very low pressures and temperatures. A comparison of freeze-drying with other drying methods is shown in Table 11.1. In freeze-drying, fruit—whole, cut, or pulp—is frozen at less than 35°C and then heated at low temperature to produce ice sublimation at a very low pressure, around 0.25 inch of mercury. This low pressure permits sublimation of ice at a very low temperature, a condition where fruit quality is well maintained. The cost of this drying system is higher than other dehydration methods and thus it is mainly used for products with high quality standards, including berries. Table 11.2 compares the different drying methods.

11.3.2 The drying line Figure 11.2 shows a general flow diagram for berry dehydration. Not all the unit operations that appear in the diagram are included in the processing of all types of berries, but most of them are.2 As in all food processing, the most important control for product quality is the raw material itself: its quality, ripeness, variety, agricultural and postharvest management, etc. Today, most of the raw materials come from agricultural production, but there are several types of fruits that come from natural production and collection. The latter, called forest fruits, are very important because of their organic nature, and thus are usually marketed as fresh fruits, but they are also important as high-quality processed ingredients for some formulated foods, including yogurt, ice cream, and breakfast cereal. Raw materials used in the dehydration process can be fresh or frozen. Normally the water content of raw berries is about 90%, with a water activity greater than 0.95%. Hot air dehydration can reduce the moisture level to 12% to 18%, with a water activity of about 0.5 to 0.6. This type of product can used directly as a snack or as an ingredient in other processed foods.

Thiessen Smoky Thiessen Smoky Thiessen Smoky Thiessen Smoky Thiessen Smoky

Variety

Adapted from Kwok et al.20

Vacuum microwave Combination drying Air drying

Freeze-drying

Frozen fruit

Drying method 100 100 67 90 48 64 44 57 34 43

Phenolics (%) 100 100 68 77 50 47 38 37 17 12

Anthocyanin (%) 100 100 50 73 34 45 32 46 31 37

Reducing power (%) 100 100 59 91 36 46 30 38 26 26

DPPH (1,1-diphenyl-2picrylhydrazyl) radical scavenging (%)

100 100 57 79 35 43 29 30 24 25

ABTS (2,2 azinobis (3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging (%)

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Table 11.1 Quality Losses Produced by Different Drying Methods in Saskatoon Berries (Amelanchier alnifolia Nutt.)


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Simple/complex Complex Simple

Spray drying

Vacuum drying Freeze-drying

High High

Medium/high

Low/medium

All berries All berries

Berry fruit powder

Berry fruit powder

Limited to firm fruit like blueberry All berries Firmer berries

Applications

Simple: easy to achieve, easy to learn the technology, easy to manage the process; Simple/complex: requires some expertise, technology knowledge; Complex: requires technology knowledge to operate the equipment, some basics in thermodynamics.

a

Good for nonsensitive powder Good for sensitive powder For sensitive products For very sensitive products

Simple

Low/medium Medium

Low

Investment

324

Cost Cost

Medium microbiological quality High operating costs

Well known Well known

Simple Simple/complex

Hot air, batch Hot air, continuous Drum drying

Disadvantages Dependent on zones and weather Non-high-quality products Non-high-quality products

Advantages General application

Very simple

Complexitya

Sun drying

Drying method

Table 11.2 Comparison of Different Drying Methods




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Warehousing and shipping

Feeding to processing line

Carton filling

Stemming when is necessary Inspecting

Grading

Bin homogenizing

Washing

Dewatering

Drying

Inspecting

Slicing, perforating or skin alcali treatment

Figure 11.2 General flow diagram for dehydration of berries using hot air.

After grading, washing, and inspecting, raw materials may be subjected to some pretreatment for the purpose of enhancing the drying rate or final product quality. The pretreatment step can be done by using mechanical (physical), chemical, or thermal methods. Mechanical treatments include cutting the fruits into small pieces or perforating the skin of the fruit over 20% to 30% of the surface area.5 Chemical treatments include dipping fruits in a high-temperature chemical solution, such as sodium hydroxide or ethyl oleate in boiling water. Most of these treatments significantly affect the acceptability of the product. It has been demonstrated that a high-temperature treatment at 100°C for a short time is more acceptable than a lower temperature of 20°C for a longer time, since the shorter the treatment time, the better the quality of the final product.5 Low-temperature thermal treatment has been used in blueberries. Fruits are individually quick frozen and stored at 40°C until use. Fruits are then thawed at 4°C for at least 5 hours; it is during this time that some damage can occur. This damage increases the drying rate due to enhanced mass transfer. Since there


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is no further treatment after thawing, the qualities of the blueberries are mostly preserved. However, this method may add extra costs to the processing. After pretreatment, the fruit is placed on trays, on a belt conveyor, or in a fluidized bed system for processing in a tunnel or cabinet drier. Because of the resistance of the waxy skin to mass transfer in some berries, the amount of fruit material in a given surface area (mass density of fruit materials) inside the drier has to be well controlled to ensure short processing times. Because of the relatively slow removal of water from berries, the air stream is normally countercurrent to the product or through the product bed. The heating process should be carefully controlled to avoid hardening as the result of sugar migration from the inner tissue to the surface. If case hardening occurs, the drying process becomes very slow. The size of the fruit pieces and the density of the fruit material inside the drier are also very important to obtain uniformly dried material. However, since the geometry of the drier is not always perfect for homogeneous drying, there are always some variations in the moisture content of the final product.2 By cutting fruits into small pieces, this variation can be controlled more easily. Also, products can be homogenized after the primary drying process. After the first drying step, the moisture content is usually lowered to about 12% to 18%; after the homogenizing step, the moisture content can be lowered up to 5%. After the product has been homogenized it should be inspected to remove any defective product. Inspected products are then sent to a packaging line or are kept in bins for further processing. If the products are immediately delivered to other processors, they are dried to a moisture content not less than 10%, while products that are kept for storage in the plant should be processed to a moisture content of about 5%. The dried products are then stored in bulk in a low-humidity environment.

11.3.3 Further processing of dried berries Most dried fruits are processed according to the uses and quality specifications of clients. Processing consists of several potential operations, including further cleaning, grading, washing, and moisture adjustment. Figure 11.3 shows a flow diagram of further processing for dried fruits. The process starts with dried material at a low-moisture level of about 5% to 6%. This product has to be inspected, classified by size, and graded. In the case of cut fruits, the size of the pieces or a size range is stated. After grading, washing is the second most important operation because of the necessity to increase the moisture level up to the clients requirements. This operation has to be carried out with high-quality water that has no chemical residues, is low in metal contamination, and is low in chlorine. Materials with the correct moisture content are sometimes treated with an antimycotic compound such as sorbate, but this operation depends on the moisture content of product and client specifications. Not all clients will accept preservatives added to their products. All products with more than 15%


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Warehousing and shipping

Feeding to processing line

Carton filling

Dry screening

Inspection including magnetic

Grading Sorting

Holding to accumulate fruit graded

Dewatering by centrifuge

Blending to accomplish number/mass

Control of moisture to required values

Washing

Figure 11.3 Flow diagram for processing of dried fruits.

moisture content need some type of food preservative for longer shelf life.2 This processing step has a high correlation with the quality of products. Since the cost of this type of product is fairly high, the process has to be rigorously controlled in all aspects of general quality, safety, and presentation.

11.4 Innovation in fruit dehydration Major technical innovations in berry dehydration include sugar infusion and impregnation under high or low pressure, microwave dehydration under vacuum, and pulsed-mode microwave applications. There are several advantages to the use of sugar infusion and impregnation, most related to improved flavor, texture, and color. These quality factors are very important for commercial acceptance, especially when products are used as industrial ingredients. Sugar infusion is usually applied as a pretreatment before the final drying process because the moisture reduction is not always enough to reduce water activity to levels that will ensure preservation. Water activity reduction by this method is normally in the range of 0.70 to 0.75.


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Infused products need to be further dehydrated using hot air or microwave/ vacuum technology as a complementary process.

11.4.1 Osmotic dehydration Osmotic dehydration process can be done using simple osmosis, osmotic drying, or forced infusion using pressure changes. High pressure or vacuum infusion produces more effective reductions in water activity to levels that permit fruit preservation. Osmotic dehydration consists of diffusion of sugar in a countercurrent mass transfer against water movement. As water is flowing out of the fruit due to the osmotic pressure difference, sugar solution is flowing into the fruit. This process occurs as a result of chemical potential gradients that affect the product-osmotic medium interface.8 In the osmotic dehydration process, tissue maintains its condition, cells are not disrupted, and cell membrane integrity remains intact. Sugar solutions are confined to intercellular spaces; they do not penetrate the cells due to the cell membrane barrier. Most recent studies have been oriented toward defining the kinetic models to apply osmotic drying to biological tissues.8,9 For some berries, osmotic dehydration can be a problem due to their skin structure, which can effect mass transfer, especially when the process is carried out at a low temperature range of 45°C to 55°C. It is well known that temperature has an important impact on diffusion. It has been reported that high temperatures significantly effect water diffusion from fruit tissues, due mainly to swelling and plasticizing of membranes at high temperature. The faster the diffusion of water inside the fruit tissue, the higher the mass transfer on the product surface because of the lower viscosity of the medium.8 Lazarides et al.8 reported that different tissues in the same product have different behaviors in the diffusion of osmotic solutions. Different tissues show different porosities and pore connectivities—factors that greatly influence transport phenomena—especially when the membranes maintain their integrity. This observation has been confirmed by several authors in the temperature range of 5°C to 40°C. In near room temperature osmosis, transport is related to the depth (location) of the tissues. Surface tissues suffer some changes, cells plasmolyze quickly, but inner tissues show fully turgid cells for a longer time, especially when tissues are still alive.9 This heterogeneity in tissue properties makes it difficult to develop practical models to characterize the process. Berries are especially heterogeneous, and thus require new technologies in order to minimize the effects of these tissue characteristics on the process. This has been the goal of many researchers when developing different technologies to enhance mass transfer in osmotic dehydration. Several factors are responsible for osmotic process efficiency, including the type and concentration of osmotic solution, temperature, size and shape of the fruit, osmotic solution:fruit ratio, and the movement of solution by agitation. Improvement of the dehydration rate is very important, since osmotic drying is a rather slow process.10,11 In order to improve the efficiency of mass transfer in osmotic dehydration, several studies have been carried out using vacuum, high pressure, and


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high-intensity electric field pulses to enhance the process.10,11 High pressure in the range of 100 to 700 MPa for 5 minutes and a temperature of about 35°C during pressurization and about 15°C during decompression have been applied to enhance mass transfer during osmotic drying. The temperature of the osmotic solution was in the range of 40°C to 50°C and the fruit:osmotic solution ratio was 1:25 in order to avoiding dilution of the latter. It was found that the diffusivity of water and solution in high-pressure materials was significantly higher than that of normal osmotic dehydration. This is evident up to a pressure of 400 MPa, above which diffusivity does not change significantly.10 Another example of a coadjuvant technique is the use of a high-intensity electrical field pulse (HELP). A HELP applied in carrots by Rastogi et al.11 had five pulses, with an electric field strength of 0.22 to 1.60 kV/cm and a pulse duration of 378 to 405 µsec and a cell disintegration index (Zp) of 0.09 to 0.84 (with 0.0 for intact cell wall permeability and 1 for total cell disintegration). Therefore HELP was responsible for increasing cell wall permeability, thus improving the mass transfer in osmotic dehydration with sucrose as the osmotic agent. Ade-Omowaye et al.12 demonstrated the positive effect of using a combination of different solutes on the sensory quality of red paprika. Sucrose and sodium chloride were used, showing improved water and solid diffusion coefficients and equilibrium moisture and solid contents.

11.4.2 Microwave and combined microwave/vacuum processes Several combinations of osmotic and other types of drying methods have been developed in last decade. A vacuum drying/microwave system using continuous or pulsed energy was used to produce dehydration.13 This method is faster and produces more uniform heating than conventional air dehydration. In addition, quality and energy efficiency are improved. Yongsawatdigul and Gunasekaran13 studied the behavior of microwave/ vacuum technology in producing high-quality dried cranberries. Even though microwave technology is recognized as a better process than air drying, there are a few quality problems, such as texture and surface drying related to temperature control in the process and the drying rate of the surface tissues of the fruit.14 Sunjka et al.15 carried out a comparative study of microwave/vacuum and microwave/convective drying and concluded that there were no major differences in fruit color between these two methods. The power level of the microwave is more important than the vacuum or hot air convective factor. The texture of dried fruit depends on the drying method; microwave/vacuum-dried products are softer than microwave/ convective-dried products. Organoleptic analysis shows that ordinary hot air convective drying is better than both microwave methods.

11.4.3 Vacuum infusion or impregnation process This is a minimal process consisting of forced mass transfer to plant tissues that have been air evacuated by applying a vacuum. Plant tissues are first treated under a vacuum of 0.1 to 0.2 bar for several minutes and then infused


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(or impregnated) with a solution containing different solutes, including calcium and hydrocolloids. To avoid potential impacts of pressure changes on the product and to obtain the maximum mass rate during infusion or impregnation, an isotonic solution should be used in the process.16 Several products have been tested with this technology, and the results have been very promising in whole and sliced apples, peaches, strawberries, pears, mushrooms, cucumbers, and peppers. Infusion solutions that have been used include pectin, alginate, gums, ascorbic acid, malic acid, calcium, sugars, and sodium chloride. In most cases, the sensory characteristics and physical properties of the product are improved. This technique has been used as a pretreatment for both drying and freezing processes, and has been demonstrated to be very useful for retaining firm texture, desirable color, and aroma. Moreno et al.17 reported that some quality attributes of Chilean papaya, including firmness and color, are different from those treated with osmotic dehydration when vacuum impregnation is applied, but the differences were not significant and the product quality from both methods is similar. Mass transfer is slightly enhanced with the use of vacuum impregnation. Changes in pH were different: while the pH decreased with osmotic dehydration, probably due to enzymatic action, the pH increased with vacuum impregnation, probably due to acid lixiviation during the application of the pulsed vacuum at the beginning of the process. Both methods showed improved quality of papaya tissues. Roa et al.18 proposed a mathematical model based on mass transfer equations to predict final mass transfer and composition changes of products that have been vacuum impregnated. Pulsed vacuum impregnation was tested on several fruits, including papaya, pineapple, melon, apricot, and banana (pineo gigante type). It was concluded that simple equations based on the volumetric fraction and a measure of liquid adherence can be used to produce a model that permits prediction of the final mass to an error of less than 2.5% and composition to an error of less than 6%.

11.5 Critical quality and safety factors: Control of quality and nutritional losses during drying Process conditions need to be controlled for two principal reasons: to ensure the process is economically efficient and to obtain a safe and high-quality product. Dehydration is a process with a huge impact on the quality of the final product.

11.5.1 Quality factors The quality of dried fruits is affected by processing and storage conditions, including temperature, relative humidity, and other environmental conditions. Potential changes in texture, transformations of chemical compounds, and losses of color, flavor, and aroma can occur during processing and storage. Thus drying conditions have to be carefully controlled to ensure a minimum impact on product quality. Hot air drying, in general, has a large


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impact on quality, but even innovative drying techniques such as microwave/vacuum drying have some effect on product quality. The color of berries is especially sensitive to the drying process, and strongly depends on process intensity, process length, temperature, and pretreatments applied. Fruit texture can also change, becoming firmer or softer, based on the nature of the fruit and the process applied. Talens et al.19 showed the effect of osmodehydration in preserving volatile compounds responsible for the aroma in strawberries. Osmotic pretreatment before freezing promoted formation of key compounds in the fruit aroma, preventing the loss of volatiles during freezing.

11.5.2 Nutritional and safety factors Normally the effect of the drying process on the nutritional value of foods is caused by the processing time instead of temperature: the longer the processing time, the larger the effect. Kwok et al.20 studied the effects of different drying methods on quality in Saskatoon berries (Amelanchier alnifolia Nutt.). Hot air, freeze-drying, vacuum/microwave drying, and a combination of hot air and vacuum/microwave methods effected several quality parameters, including total phenolics and anthocyanin content and antioxidant activity. The best results were obtained by freeze-drying followed by vacuum/microwave drying. The worst results were obtained in berries dried using hot air, and the second worst results were obtained for the combination of hot air and vacuum/microwave drying. In this study, freeze-dried berries were first frozen at 35°C for 3 days. After 1 day of drying, the water activity was 0.33 to 0.42. In spite of the long freezing period, this freezing method resulted in better product quality. Table 11.1 shows the effect of different dehydration methods on the quality of the berries, including color, antioxidant capacity, flavor, and taste. Almost all the drying methods had some effect on final product quality. As discussed previously, water activity is a major factor in the preservation of dried products. This has to do with microbiological stability as well as chemical and biochemical stability. Chemical and enzymatic reactions require water, as the diffusion of chemical compounds or substrates and enzymes does not take place under low-moisture conditions. A low-water activity generally produces lower reaction rates.6 Thus maintaining a low-moisture content keeps the product chemically and microbiologically stable.

11.5.3 Packaging Packaging plays a very important role in preserving the quality of dried products. Dried berries are very hygroscopic and absorb moisture present in the environment. The shelf life of dried berries depends on packaging and storage conditions. Flexible materials are commonly used for dried foods. Cellophane, polypropylene, polyvinyl chloride (PVC), and other polymers have been the basis for better preservation of dried foods. New materials


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not only have to have high gas and water vapor barrier properties, but also ultraviolet (UV) light protection in order to control deterioration caused by light. This function of packaging materials is critical for providing a barrier between the product and the environment, a barrier to microorganisms, transit protection, and protection from physical, chemical, and sensory changes. In order to maintain good barrier properties, containers have to be hermetically sealed to avoid oxygen, vapor, and volatiles transfer. Moisture can cause significant losses in product quality. Since oxygen contributes to a number of deteriorative reactions, this gas has to be removed from the container. Berries are characterized by their unique colors, flavors, and aromas, and should be maintained in hermetically sealed containers to avoid pigment oxidation, chemical transformation of sugars, changes in texture by crystallization, and loss of texture by humectation.

11.6 Applications of dried berry fruit There are many uses for dried berries. Most are classified as ingredients in other foods. In some of these products, food preservatives may be added to extend shelf life.

11.6.1 Snack foods One of the most popular products in recent years has been the fruit snack. It is an intermediate moisture product that includes a mixture of cereals and dried fruit stabilized with some permitted food preservative. These products contain wild or cultivated berries and are popular because of the recognized health benefits of berries associated with their antioxidant activity, scavenging of free radicals, and high content on soluble dietary fiber. These snacks may also include other ingredients besides dried fruit and cereals, including dried yogurt or honey.

11.6.2 Breakfast cereals The addition of berries to breakfast cereals has become very popular because of the healthy attributes of berries. The benefits of soluble dietary fiber from berries complement very well the insoluble fiber of cereals. Fruit added to breakfast cereals are medium moisture, and coatings are sometimes applied to the surface of the fruit to prevent cereal humectation by fruit moisture. When low-moisture fruit is used, the texture of the fruit may not be acceptable at the moment the cereal is mixed with milk or juice. In some cases, berries are laminated after drying so they will have a better texture, but normally they are softened by the addition of water vapor or some type of oil.

11.6.3 Formulated foods Dried berries can be used as food ingredients in a wide variety of different products, including ice cream, toppings, fruit pieces in pastries and cookies, yogurt, snacks, and pressed for fruit leathers. In some of these products, a


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second heat treatment could be deleterious to the chemical quality of the dried fruit. In this case, it is better to use dried fruits that are protected against deterioration of these compounds.

11.7 Conclusion Dehydration is a valuable solution for the preservation of berries. Different dehydration methods are available to process this high-value product, but some methods may be more suitable than the others depending on the requirements of the final product, available facilities, investment costs, and technical capacity. Sun drying is a low-cost method, but care is needed in order to ensure product quality and microbial safety. Other methods, such as freeze-drying and microwave/vacuum drying, that provide high quality products with high values are more expensive. In the middle, there are several conventional methods that use water removal and water activity depression to preserve the product. Dehydration, when starting with high-quality raw materials, applying appropriate drying methods, and using proper packaging, can preserve berries for a long time with high quality. Dried berries have broad applications as snacks or as functional food ingredients in many different types of manufactured foods.

References 1. Van Arsdel, W.B., Copley, M.J., and Morgan, A.I., Food Dehydration, 2nd ed., Vol. 1, Avi Publishing, Westport, CT, 1973, p. 347. 2. Van Arsdel, W.B., Copley, M.J., and Morgan, A.I., Food Dehydration, Vol. 2, Avi Publishing, Westport, CT, 1973, p. 529. 3. Fellows, P., Food Processing Technology, CRC Press, Boca Raton, FL, 2000, p. 591. 4. Crapiste, G.H. and Rotstein, E., Design and performance evaluation of dryers, in Handbook of Food Engineering Practice, Valentas, K.J., Rotstein, E., and Singh, R.P., Eds., CRC Press, Boca Raton, FL, 1997, chap. 4. 5. Roos, Y.H., Water activity and plasticization, in Food Shelf Life Stability: Chemical, Biochemical, and Microbiological Changes, Eskin, N.A.M. and Robinson, D.S., Eds., CRC Press, Boca Raton, FL, 2001, chap. 1. 6. St. George, S.D., Cenkowski, S., and Muir, W.E., A review of drying technologies for the preservation of nutritional compounds in waxy skinned fruit, Paper no. 04-104, 2004 North Central ASAE/CSAE Conference, September 24–25, 2004, Winnipeg, Manitoba, Canada. 7. Grabowski, S., Marcotte, M., Poirier, M., and Kudra, T., Drying characteristics of osmotically pretreated cranberries—energy and quality aspects, Drying Technol., 20, 1989, 2002. 8. Lazarides, H.N., Fito, P., Chiralt, A., Gekas, V., and Lenar, A., Advances in osmotic dehydration, in Processing of Foods: Quality Optimization and Process Assessment in Conventional and Emerging Technologies, Oliveira, F.A.R. and Oliveira, J.C., Eds., CRC Press, Boca Raton, FL, 1999, chap. 11. 9. Salvatori, D., Andres, A., Albors, A., Chiralt, A., and Fito, P., Structural and compositional profiles in osmotically dehydrated apple, J. Food Sci., 63, 606, 1998.


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10. Rastogi, N. and Niranjan, K., Enhanced mass transfer during osmotic dehydration of high pressure treated pineapple, J. Food Sci., 63, 508, 1998. 11. Rastogi, N., Eshtiaghi, M., and Knorr, D., Accelerated mass transfer during osmotic dehydration of intensity electrical field pulse pretreated carrots, J. Food Sci., 64, 1020, 1999. 12. Ade-Omowaye, B.I.O., Rastogi, N.K., Angersbach, A., and Knorr, D., Osmotic dehydration behavior of red paprika (Capsicum annum L.), J. Food Sci., 67, 1790, 2002. 13. Yongsawatdigul, J. and Gunasekaran, S., Microwave-vacuum drying of cranberries: part II. Quality evaluation, J. Food Proc. Preserv., 20, 145, 1996. 14. Jolly, P.G., Temperature controlled combined microwave-convection drying, J. Microwave Power, 22, 65, 1986. 15. Sunjka, P.S., Rennie, T.J., Beaudry, C., and Raghavan, G.S.V., Microwaveconvective and microwave-vacuum drying of cranberries: a comparative study, Drying Technol., 22, 1217, 2004. 16. Martinez-Monteagudo, S.I., Salais-Fierro, F., Perez-Carrillo, J.R., ValdezFragoso, A., Welti-Chanes, J., and Müjica-Paz, H., Impregnation and infiltration kinetics of isotonic solution in whole jalapeño pepper using a vacuum pulse, J. Food Sci., 71, E125, 2006. 17. Moreno, J., Bugueno, G., Velasco, V., Petzold, G., and Tabilo-Munizaga, G., Osmotic dehydration and vacuum impregnation on physicochemical properties of Chilean papaya (Carica candamarcensis), J. Food Sci., 69, E102, 2004. 18. Roa, V., Tapia, M.S., and Millan, F., Mass balances in porous food impregnation, J. Food Sci., 66, 1332, 2001. 19. Talens, P., Escriche, I., Martinez-Navarrete, N., and Chiralt, A., Study of the influence of osmotic dehydration and freezing on the volatile profile of strawberries, J. Food Sci., 67, 1648, 2002. 20. Kwok, B.H.L., Hu, C., Durance, T., and Kitts, D.D., Dehydration techniques affect phytochemical contents and free radical scavenging activities of Saskatoon berries (Amelanchier alnifolia Nutt.), J. Food Sci., 69, S122, 2004.

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chapter 12

Commercial canning of berries Hosahalli S. Ramaswamy and Yang Meng Contents 12.1 Introduction ............................................................................................... 336 12.2 Canning principles.................................................................................... 337 12.2.1 Target microorganisms or enzymes .......................................... 338 12.2.2 Microflora in canned berry fruits .............................................. 339 12.2.3 Composition of berry fruits........................................................ 339 12.2.4 Microbial destruction kinetics.................................................... 340 12.2.4.1 Survivor curve and D value ........................................ 340 12.2.4.2 Thermal inactivation time of enzymes ...................... 341 12.2.4.3 Temperature dependence and z value ....................... 342 12.2.4.4 Lethality .......................................................................... 342 12.2.5 Heat penetration test ................................................................... 343 12.2.6 Thermal process calculations ..................................................... 345 12.2.6.1 General methods............................................................ 345 12.2.6.2 Formula methods........................................................... 346 12.3 Process calculations .................................................................................. 347 12.4 Canning operations .................................................................................. 349 12.4.1 Raw material selection ................................................................ 351 12.4.2 Washing.......................................................................................... 351 12.4.3 Sorting/grading............................................................................ 352 12.4.4 Filling ............................................................................................. 352 12.4.4.1 Type of pack ...................................................................352 12.4.4.2 Type of covering liquid ................................................ 352 12.4.4.3 Container specifications and types ............................353 12.4.4.4 Container sizes ............................................................... 353 12.4.4.5 Can lacquer..................................................................... 354

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12.4.5 Exhausting and vacuum ............................................................. 354 12.4.6 Seaming/closing........................................................................... 355 12.4.7 Container coding.......................................................................... 355 12.4.8 Retort operations .......................................................................... 355 12.4.9 Cooling........................................................................................... 356 12.4.10 Labeling and storage ...................................................................357 12.5 Grades of canned berries......................................................................... 357 12.6 Canning of berry fruit.............................................................................. 358 12.6.1 Blackberry...................................................................................... 358 12.6.2 Blueberry ....................................................................................... 359 12.6.3 Black currant ................................................................................. 359 12.6.4 Cranberry....................................................................................... 360 12.6.5 Gooseberry .................................................................................... 360 12.6.6 Loganberry .................................................................................... 361 12.6.7 Raspberry....................................................................................... 361 12.6.8 Strawberry ..................................................................................... 361 Nomenclature ......................................................................................................363 References ........................................................................................................... 364

12.1 Introduction Since ancient times, several techniques have been used for the preservation of berry fruits and their products: drying, concentration, freezing, fermentation, and chemical preservation by use of vinegar, wine, sugar, and spices. Since Nicholas Appert proposed the processing method of canning foods in 1809, canning has proven to be one of the most effective techniques used for fruit preservation.1 In the early stages of this method, food was placed into wide-mouthed glass bottles or jars and carefully corked, after which they were heated in boiling water. It was believed that if food is sufficiently heated and sealed in an airtight container, it will not spoil. Louis Pasteur, in 1864, demonstrated that food spoilage is caused by the growth of microorganisms and heat can kill microorganisms. The basic principles of canning have not changed dramatically since Nicholas Appert developed the process: provide enough heat to destroy the microorganisms in foods enclosed in a hermetically sealed container. By the turn of the century, significant progress in microbiology and the heating behavior of packaged foods led to scientific approaches in thermal process calculation. In the 1910s and 1920s, the basic biological and toxicological characteristics of Clostridium botulinum were first determined by several researchers. The importance of controlling C. botulinum in canned foods became clear and the basis for its control was established. A detailed historical perspective of the developments in thermal processing is provided by Lopez.2 In 1920, Bigelow et al. developed the “general method,” which is the first scientifically based process calculation method. Ball3 developed the “Ball formula method.” In 1950, Stumbo revised the Ball formula method and made the process calculation more versatile and accurate. The general


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method and formula method are still the basic procedures used for process calculations in canning industry. In the last few decades, Pflug,4 Hayakawa,5,6 Teixeira et al.,7 Griffin et al.,8,9 Manson et al.,10 Tung and Garland,11 Ramaswamy et al.,12 Pham,13 and many others have further refined mathematical heat process determination concepts and applications. The intervening period also saw significant developments in the manufacturing of thermal processing equipment in the form of improved versions of the retort system. Next in the line of process equipment were continuous systems for thermal sterilization of food cans and glass jars and systems for handling high-temperature, short-time (HTST) processes in batch or continuous modes in still or rotary autoclaves. Developments such as aseptic processing and packaging, thin profile processing, fully automated agitating retorts, and retort systems based on different media have revolutionized the food industry.14 New processes such as combined methods technology15 are continually being introduced, especially for heat-sensitive products such as berry fruits, to preserve overall color, flavor, and other quality attributes. Berry fruits, in general, are commodities with special organoleptic properties that must be carefully preserved when establishing operating conditions for a thermal process.

12.2 Canning principles Canning is the most commonly used technique to heat sterilize foods in order to prevent microbiological and enzymatic spoilage. A variety of foods are canned, including meat, fish, poultry, fruit, dairy, and vegetable products. Heat processes used for these foods are dependent on the type of the food, its chemical composition, and the types of microorganisms that cause spoilage or public health concerns, in addition to properties related to container material, shape, and size, as well as properties related to the heating medium. Any thermal process for a food should be designed to achieve three basic objectives, the most important being to reduce the number of microorganisms to statistically small levels, whether they are of public health concern or of the spoilage type, which cause off-flavors and odors. The second objective is to create an environment in the container that will suppress the growth or activity of spoilage-type microorganisms by utilizing one or more of the following methods: (1) oxygen removal, (2) pH control, and (3) control of storage temperature. The third objective is to ensure an adequate or hermetic seal of the container to prevent recontamination following processing and during storage. Thermal processing is not intended to completely sterilize the packaged food. Such an approach might produce a stable product, but it will be at the expense of severe destruction of product quality. The success of thermal processing depends on selectively destroying the microorganisms of spoilage and public health concern while creating an environment around the product to minimize the growth and activity of other microorganisms. In order to determine the extent of heat treatment, several factors must be known:16 (1) The type and the heat resistance of the target microorganism, spore, or enzyme present in the food; (2) the pH of the food; (3) the storage


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conditions following the process; (4) heating conditions; and (5) thermophysical properties of the food, and container shape and size.

12.2.1 Target microorganisms or enzymes The first step in designing a thermal process is to verify the target microorganisms or enzymes upon which the process should be based. Several factors should be considered. For example, in foods that are packaged under vacuum in hermetically sealed containers, low oxygen levels are achieved. The aerobic microorganisms that require oxygen thus have no supporting environment to exist. In addition, spores of the aerobic microorganisms are less heat resistant than anaerobic microorganisms. Therefore the target microorganisms should be anaerobic microorganisms. Considering that the growth and activity of most anaerobic microorganisms are pH dependent, foods are generally classified based on their pH values. From a thermal processing point of view, foods are divided into three pH groups: high-acid foods (pH < 3.7), acid or medium-acid foods (3.7 < pH < 4.5), and low-acid foods (pH > 4.5). Examples of foods in each group are as follows: high-acid foods include apple, apple juice, apple cider, applesauce, berries, cherry (red sour), cranberry juice, cranberry sauce, fruit jellies, grapefruit juice, grape fruit pulp, lemon juice, lime juice, orange juice, plum, pineapple juice, sour pickles, sauerkraut, and vinegar; medium acid foods include fruit jams, fruit cocktail, grapes, tomato, tomato juice, peaches, pineapple slices, potato salad, prune juice, and vegetable juice; and low-acid foods include meat, fish, vegetables, mixed entrees (beans and pork, chicken with noodles, etc.), and most soups.17 For low-acid foods (pH > 4.5), the target microorganism is C. botulinum. It is a highly heat-resistant, rod-shaped, spore-forming, anaerobic pathogen, and if it is not destroyed by the heat treatment, it can thrive and produce a deadly botulism toxin when stored under anaerobic conditions at ambient temperatures. It has been generally recognized that C. botulinum does not grow and produce toxin at a pH of less than 4.6. Hence the dividing pH between the low-acid and acid groups is set at 4.5 such that in medium- and high-acid foods (pH < 4.5) it is not necessary to worry about C. botulinum. Berry fruits and their products are mostly considered as high-acid foods (pH < 3.7). Other anaerobic microorganisms that are more heat resistant than C. botulinum, such as Bacillus stearothermophilus, Bacillus thermoacidurans, and Clostridium thermosaccolyticum, although highly heat resistant, low-acid, and spore forming, are of little concern if the processed cans are stored at temperatures below 30°C, because they are generally thermophilic in nature (optimal growth temperature approximately 50°C to 55°C). Anaerobic, spore-forming microorganisms are so heat resistant that normally severe heat treatment (sterilization at temperatures greater than 110°C) is used for long-term storage under elevated storage temperature conditions. For acid and medium-acid foods (pH < 4.5), C. botulinum and most spore formers will not grow and the target of the thermal process is usually the heat resistant, spoilage-type vegetative bacteria or enzymes, which are easily destroyed, even by a mild heat treatment (pasteurization in boiling water).18


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If not inactivated following thermal processing, several heat-resistant enzymes in fruits (including peroxidase, pectin esterase, lipoxygenase, catalase, and polyphenol oxidase) may cause undesirable quality changes in the final canned product during storage, especially related to color, texture, and flavor. For thermal processing of acid foods, such as berry fruits, inactivation of these enzyme systems is often used as a basis because they usually possess a higher thermal resistance than the microorganisms present in the food. As peroxidase is known to have a very high heat resistance, its destruction is often used as an adequate marker for the destruction of all heatresistant enzymes present in the food. Nevertheless, the heat resistance of enzymes varies with the fruit, its variety, pH, and total soluble solids.19

12.2.2 Microflora in canned berry fruits Of the three groups of microorganisms, yeasts are heat sensitive; a 5-minute exposure to 66°C destroys living forms and the same exposure time at about 80°C destroys spores. Non-spore-forming bacteria are also very heat sensitive. Obviously the heat process for the preservation of berry fruits will not necessarily kill spore-forming bacteria such as C. botulinum; however, they are unlikely to cause problems even if they are present. Molds in canned berry fruits are quite insignificant because some are destroyed with spores in 30 minutes at about 66°C, the effect being greater in anaerobic conditions. Some molds possess an extremely high resistance to heat in canned acid foods, including the species Byssochlamys, Paecilomyces, and Phialophora. Byssochlamys fulva is exceptionally heat resistant as it breaks down pectinous materials, disintegrating fruit and sometimes producing gas. Its limited ability to grow in the presence of air permits its growth in products such as sterilized compotes and jams. It has been found that B. fulva is more heat resistant in foods containing citric acid,20 which is the most important organic acid in berry fruits. The thermal resistance of microorganisms in fruits depends upon various factors, such as the amount and type of sugar present, the pH, and the type of acid.21 Organic acids have a detrimental effect on microorganisms due to the toxicity of the hydrogen ion and the undissociated molecule. Lower pH levels are more toxic to bacteria, which explains the addition of an acidulant to adjust the pH to a standard value, often allowing for a shorter sterilization time. In some instances, however, decreasing the temperature is also possible. Different acids possess various levels of effectiveness in lowering the heat resistance of microorganisms. This order is lactic acid > citric acid > acetic acid. Based on the pH of the product, the order is acetic acid > citric acid > lactic acid.19

12.2.3 Composition of berry fruits The acids present in berries are advantageous for preservation, especially because they have a bacteriostatic effect. In good-quality berry fruits ready for processing, the organic acid most frequently encountered is citric acid.20 In blueberries,


340


40% of the organic acids present is quinic acid. Organic acids reach peak levels in fruits just as they reach the ripeness stage. The organic acids content tends to decrease in several types of fruit at the end of the ripening period through conversion to sugars. Thus the acid content decreases while the sugar content increases. During storage, the acid is consumed through respiration. Berry fruits are rich in sugars; however, their levels depend on a variety of factors, such as species, soil, location, and the ripening stage. Sugar levels generally range between 0.5% and 25%. When the fruit is detached from the mother plant, sugar levels decrease due to the increase in respiration rate (cells consume sugar). In maturing fruit, the total sugar content rises for two main reasons: (1) hydrolysis of polysaccharides and (2) formation of sugars as secondary products following acid conversion.

12.2.4 Microbial destruction kinetics Target microorganisms for thermal destruction in a food vary according to the type of food and the composition. Thus these target components and their respective thermal resistances determine the thermal process itself. To establish a thermal processing schedule, the thermal destruction rates of the target microorganisms must be determined under the conditions that normally prevail in the container so that an appropriate heating time can be determined at a given temperature. Furthermore, because packaged foods cannot be heated to process temperatures instantaneously, data on the temperature dependence of the microbial destruction rate are also needed to integrate the destruction effect through the temperature profile under processing conditions.

12.2.4.1 Survivor curve and D value Normally the thermal destruction of microorganisms is traditionally assumed to follow first-order inactivation kinetics, with their destruction being a semilogarithmic function of time at a constant temperature, which ignores any lag or tailing phenomena that could be important. In other words, the logarithm of the surviving number of microorganisms in a heat treatment at a particular temperature plotted against the heating time will give a straight-line curve known as the survivor curve (Figure 12.1). The microbial destruction rate at a given temperature is defined as the decimal reduction time (D value), which is the heating time in minutes at a given temperature required to cause a one decimal reduction in the surviving microbial population. Graphically this represents the time range between which the survival curve passes through one logarithmic cycle (Figure 12.1). Mathematically it can be written as D=

t2 − t1 , N log ⎡⎢ N1 ⎤⎥ ⎣ 2⎦

(12.1)

where N1 and N2 represent the microbial population at time t1 and t2, respectively.


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341

Number of survivors

100000 10000 1000 100

D

10 0

5

10

15

20

Heating time (min)

Figure 12.1 A typical survivor curve.

The logarithmic nature of the survivor curve indicates that the complete destruction of a microbial population is not theoretically possible because a decimal fraction of the population should remain even after an infinite number of D values. In food microbiology, another term that generally contradicts this logarithmic destruction approach is often employed: thermal death time (TDT), which is the heating time required to cause complete microbial destruction. Such data are obtained by subjecting a microbial population to a series of heat treatments at a given temperature and testing for survivors. The death in this instance generally indicates the failure of a given microbial population after the heat treatment to show a positive growth in the subculture media. Comparing the TDT approach with the decimal reduction approach, it can easily be seen that the TDT value depends on the initial microbial load (while the D value does not). Furthermore, the TDT represents a multiple of the D value. For example, if the TDT represents the time to reduce a population from 1012 to 100, then the TDT is a measure of 12 D values, or TDT = nD,

(12.2)

where n is the number of decimal reductions.

12.2.4.2 Thermal inactivation time of enzymes The thermal inactivation curve for enzymes is established in a manner similar to that of the TDT curve for bacteria. This is done by subjecting the food sample to a series of heat treatments at a specific temperature and testing for residual enzyme concentrations. When there is no measurable residual activity, the enzyme is considered inactivated and the corresponding heating time is called the thermal inactivation time (TIT). Since most enzyme systems in berry fruits (peroxidase, pectinesterase, and polyphenol oxidase) generally possess a higher thermal resistance than


342


D value (min)

1000

100

10 Z 1 90

95

100

105

110

Temperature (°C)

Figure 12.2 A typical thermal resistance curve.

microorganisms, the calculation of the process time for canned berry fruits is based on the TIT of the most heat-resistant enzyme present in the product.

12.2.4.3 Temperature dependence and z value The temperature sensitivity of D values at various temperatures is normally expressed as a thermal resistance curve with log D values plotted against temperature (Figure 12.2). The temperature sensitivity indicator is called the z value, which represents a temperature range that results in a 10-fold change in D values, or graphically it represents the temperature range through which the D value curve passes through one logarithmic cycle. Mathematically it can be written as

z=

T2 − T1 , D log ⎡⎢ D1 ⎤⎥ ⎣ 2⎦

(12.3)

where D1 and D2 are D values at temperature T1 and T2 (in °C), respectively.

12.2.4.4 Lethality The effectiveness of a thermal process in killing microorganisms or inactivating enzymes in a food product may be denoted by the lethality; in other words, the lethality is a measure of the effectiveness of the heat treatment. To compare the relative sterilizing capacities of different heat processes, lethality (F0 value) is defined as an equivalent heating time at a reference temperature, which is usually taken to be 121°C for sterilization or 82°C for pasteurization. The F0 value can be expressed as

Lethality

or

F0 = F × 10

T − T0 z

,

(12.4)


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where T0 is the reference temperature and F is the heating time at temperature T. Thus an F value of 2 minutes at 88°C is equivalent to an F0 value of 20 minutes at 82°C, while the same F value at 85°C is equivalent to an F0 value of 6.3 minutes at 82°F when z = 6°C. For real thermal processes, heating to the appropriate temperature and the subsequent cooling are not instantaneous, where the food passes through a time-temperature profile. It is possible to use this concept to integrate the lethal effects through the various time-temperature combinations. The combined lethality thus obtained for a process is called the process lethality and is also represented by the symbol F0. The term always applies to a specific location in the product container or the slowest heating point (cold spot). For conduction heating, the cold spot is the thermal center, whereas for convection heating, it is located approximately one-tenth of the length of the can from the bottom. Generally it is assumed that if the cold spot receives an adequate process lethality, then all other points within the container will receive an equal or greater process lethality. The criterion for the adequacy of a thermal process is normally based on microbiological consideration, especially for low-acid foods for which the minimal criterion is the destruction of C. botulinum spores. It has been arbitrarily established that the minimum process should be severe enough to reduce the population of C. botulinum through 12 decimal reductions (the “bot cook”). Based on published information, a decimal reduction time of 0.21 minutes at 121°C is normally assumed for C. botulinum.22 A 12-decimal reduction would thus be equivalent to an F0 value of 12 × 0.21 = 2.52 minutes. The minimal process lethality (F0) required is therefore 2.52 minutes. In practice, an F0 value of 5 minutes is perhaps more common for low-acid foods. The reason is the occurrence of more heat-resistant spoilage-type microorganisms that are not a public health concern. The average D value for these spoilage microorganisms is about 1 minute. An F0 value of 5 minutes would only be adequate to achieve a 5D process with reference to these spoilage microorganisms. Thus it is essential to control the raw material quality to keep the initial count of these organisms below 100 per container on average if the spoilage rate is to be kept below 1 can in 1000 (102 to 10−3 = 5D). In the case of acid foods, such as berry fruits, the criterion for the adequacy of the process is based more specifically on the reduction in the amount of spoilage-causing bacteria and inactivation of the most heat-resistant enzymes present. The two objectives of thermal process calculations are (1) to estimate how much destruction a given process will accomplish and (2) to arrive at an appropriate process time required to accomplish the desired level of destruction or inactivation (in the case of enzymes). In order to attain these two objectives, thermal destruction kinetics and the product heating profile must be obtained.

12.2.5 Heat penetration test In order to establish thermal process schedules, information on the temperature history of the product going through the process is needed in addition


344


Temperature (°C)

120

100

80 Convection heating Conduction heating Retort temperature 60 0

20

40

60

80

Process time (min)

Figure 12.3 Typical heat penetration curves.

Log (TR–T)

to thermal resistance characteristics of the target microorganisms or enzymes. A heat penetration test is carried out to gather the time-temperature data, normally with a thermocouple measuring the product temperatures. Simple time-temperature curves during heating and cooling of conduction and convection heating are shown in Figure 12.3. Heat penetration parameters are obtained from a plot of the logarithm of the temperature difference between the retort and the product center, known as the temperature deficit (TR − T during heating and T − Tw during cooling), against time on a linear scale. For the heating process, as shown in Figure 12.4, a straight line is obtained after the initial lag. By extending the 2 1.8

log(TR−Tpih)

1.6

log(TR–Tih)

1.4 1.2 1

jch=(TR–Tpih)/(TR–Tih)

0.8 0.6 0.4 fh

0.2 0 0

10

20

30

40

Heating time (min)

Figure 12.4 Heat penetration parameters.

50

60


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345

straight line portion of the curve to the y axis representing Tpih, the heating lag factor (jch) is obtained (see Equation 12.5). jch is a measure of the thermal lag (or delay) in heating the product. Part of the lag is due to the come-up time of the retort, and this can be accounted for by determining the new zero time for the process. Ball and Olson23 used 58% of the come-up time as a useful contribution to the process, and this is widely accepted.24 This implies that 42% of the come-up time should be added to the process time at retort temperature. jch =

TR − Tpih TR − T0

(12.5)

The slope of the line (Figure 12.4) represents the time for the curve to traverse one log cycle. The negative reciprocal of this slope is referred to as the heating rate index (fh). fh is an indicator of the heating rate. The higher the value, the longer it takes for the log to traverse one cycle, indicating a slow rate of heat penetration. For the cooling process, a similar approach can be used to get the cooling parameters: the cooling rate index (fc) and the cooling lag factor (jcc).22

12.2.6 Thermal process calculations Thermal process calculations are carried out using thermal destruction kinetics of target microorganisms or enzymes and heat penetration parameters. The purpose of thermal process calculations is to determine the required process time under a given set of heating conditions that results in the required process lethality, or alternatively, to estimate the achieved lethality of a process. The process calculation methods are broadly divided into two classes: (1) general methods and (2) formula methods. The general methods integrate the lethal effects by a graphical or numerical integration procedure based on the time-temperature profiles obtained from the test containers processed under actual commercial processing conditions. Formula methods, on the other hand, make use of the heat penetration parameters together with several mathematical procedures to integrate the lethal effects.14

12.2.6.1 General methods In the original general method, the reciprocal of the TDT is defined as the lethal rate at the corresponding temperature. A lethal rate curve is drawn by plotting the lethal rate against the heating time; the area under this curve yields the sterilization value of the process. A sterilization value of unity is the minimal requirement with respect to the target microorganism or enzyme. If the resulting sterilization value is greater than or less than the desired value, the cooling curve is shifted manually to the left or right and the procedure is repeated to get the new sterilization value. This whole


346


process is repeated until the desired sterilization value is obtained and the corresponding process time is noted. The improved general method, devised by Ball,3 calculates the process lethality F0 value at the reference temperature T0 with graphical or numerical integration of Equation 12.6: F0 =

∫

t

10

T −T0 z

dt ,

(12.6)

0

(T −T )/z

where 10 0 is the lethal rate (L value) at any temperature T. The general method is the most accurate method for determining the sterilization value of a heat process. It is used as a basic method for calculating the F0 value used to compare the performance of the formula methods. While the results of the general method are very specific to the product under the conditions employed for testing, extrapolation and generalization should be avoided.

12.2.6.2 Formula methods The formula methods are based on characterizing heat penetration data and combining kinetic data with heat penetration parameters. Ball’s method3 is the simplest and most widely used technique for process calculations. It is based on the following equations derived from the heat penetration curve to estimate the process time, B (in minutes): ⎛j I ⎞ B = fh log ⎜ ch h ⎟ , ⎜⎝ g ⎟⎠ c Ih = TR − Ti, gc = TR − Tic,

(12.7) (12.8) (12.9)

where B is the process time (in minutes), fh is the heating rate index (in minutes), jch is the heating lag factor, Ih is the initial temperature difference at the start of heating process, TR is the retort temperature, Ti is the initial product temperature, and gc is the temperature difference at the end of heating or beginning of cooling, respectively. The determination of gc is the key to estimating the process time. Ball provided the relationship between fh/U and gc in the form of a table as well as in figure format. U is numerically equivalent to U = F0Fi Fi = 10

(12.10)

T0 −TR z

,

(12.11)

where F0 is the desired process lethality and Fi is the number of minutes at the retort temperature (TR) equivalent to 1 minute at the reference temperature, T0.


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347

In deriving these relationships, Ball assumed (1) the cooling rate index (fc) is equal to the heating rate index (fh); (2) the cooling lag factor jcc is 1.41; (3) the z value is 10°C; and (4) the effectiveness of the come-up time is 42%. These assumptions give some limitations to the use of Ball’s method. In order to overcome the limitations of Ball’s method, Stumbo and Longley25 published revised tables for process calculations, taking into account the variability of jcc and z values. Stumbo’s method is very flexible; it can accommodate the destruction of bacteria spores, vegetative cells, or nutrients, all of which possess different thermal resistances (D and z values). All types of thermal processes can be calculated; for example, the z value of a typical pasteurization process is 5.6°C (vegetative bacteria), that of a sterilization process is 10°C (C. botulinum), and that of nutrients is typically 22°C to 28°C. Table 12.1 shows the fh/U versus gc relationships (z = 5.6°C) necessary for typical pasteurization processes.22 Formula methods can be used to determine the process time if the target process lethality F0 value is known and it can also be used to calculate the delivered lethality of a given process. Since it uses heat penetration data in the form of parameters (fh, jch, and jcc) for the same product in many different containers, different retort temperatures (TR), or different initial product temperatures (Ti), new processes can be calculated directly using available parameter conversion procedures.

12.3 Process calculations Heat processing is quite clearly the most destructive method of berry fruit processing. Since berry fruits are high in organic acids, such as citric and quinic acid, their overall pH is quite low and they require much less rigorous heat treatment as compared to low-acid foods such as meats. In order to establish a processing schedule for canned berry fruits subjected to pasteurization, the most heat-resistant microorganism of public health concern in the container must be identified and evaluated for its thermal destruction rate. In most cases, however, it is the most heat-resistant enzyme system and vegetative bacteria that are used as the basis for establishing the thermal process. The thermal inactivation time for the particular enzyme, which is usually peroxidase, should be adequate to provide a microbiologically safe berry fruit product. In contrast to the destruction of spores during the sterilization process, the pasteurization process targets vegetative cells only. The D and z values of these vegetative cells are much smaller than those of spores. This decreased thermal resistance permits the use of lower processing temperatures. With reference to berry fruit pasteurization, first, the reference temperature is changed from 121°C to a lower value, typically 85°C. In addition, the reference z value is changed from 10°C to 5.6°C. Process calculations can then be performed by either the general or formula method. A typical process calculation using the improved general method (numerical integration technique) is shown in Table 12.2.

0.4

2.68E-0.5 2.10E-0.2 0.282 1.14 1.83 2.33 2.71 3.01 3.25 3.47 3.67 3.84 5.22 6.27 7.14 7.87 8.51 9.07 9.56 10.0 10.4 13.0 14.3 15.2 15.8 16.3 16.8 17.1 17.4

fh/U

0.2 0.5 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 100.00 200.00 300.00 400.00 500.00 600.00 700.00 800.00 900.00 2.88E-0.5 2.40E-0.2 0.305 1.19 1.92 2.48 2.92 3.29 3.61 3.89 4.14 4.38 6.12 7.34 8.31 9.10 9.78 10.4 10.9 11.4 11.8 14.5 16.0 17.0 17.8 18.4 18.9 19.3 19.7

2.98E-0.5 2.60E-0.2 0.317 1.21 1.97 2.55 3.03 3.43 3.78 4.10 4.38 4.64 6.57 7.88 8.89 9.72 10.4 11.0 11.6 12.0 12.5 15.2 16.8 17.9 18.7 19.4 19.9 20.4 20.8 3.07E-0.5 2.79E-0.2 0.329 1.29 2.01 2.63 3.14 3.57 3.96 4.30 4.62 4.91 7.01 8.41 9.48 10.3 11.1 11.7 12.2 12.7 13.1 16.0 17.7 18.8 19.7 20.4 21.0 21.5 22.0 3.17E-0.5 2.99E-0.2 0.340 1.26 2.05 2.70 3.24 3.72 4.13 4.51 4.85 5.17 7.46 8.95 10.1 11.0 11.7 12.3 12.9 13.4 13.8 16.8 18.5 19.7 20.6 21.4 22.1 22.6 23.1

Values of gc (°F) when j of cooling curve is 1.40 0.8 1.00 1.20 3.27E-0.5 3.18E-0.2 0.352 1.29 2.10 2.77 3.35 3.86 4.31 4.72 5.09 5.44 7.91 9.48 10.7 11.6 12.3 13.0 13.6 14.1 14.5 17.5 19.3 20.6 21.6 22.4 23.1 23.7 24.3

1.60 3.36E-0.5 3.38E-0.2 0.364 1.31 2.14 2.85 3.46 4.00 4.49 4.93 5.33 5.70 8.35 10.0 11.2 12.2 13.0 13.6 14.2 14.7 15.2 18.3 20.1 21.5 22.6 23.4 24.2 24.8 25.4

1.80 3.46E-0.5 3.57E-0.2 0.376 1.33 2.19 2.92 3.57 4.14 4.66 5.14 5.57 5.97 8.80 10.6 11.8 12.8 13.6 14.3 14.9 15.4 15.9 19.0 21.0 22.4 23.5 24.5 25.3 25.9 26.6

2.00

348

2.78E-0.5 2.21E-0.2 0.294 1.17 1.88 2.41 2.81 3.15 3.43 3.68 3.90 4.11 5.67 6.81 7.72 8.49 9.15 9.72 10.2 10.7 11.1 13.7 15.2 16.1 16.8 17.4 17.8 18.2 18.5

0.6

Table 12.1 fh/U Relationships When z = 5.6°C (10°F)




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349

Table 12.2 Process Calculation by the Improved General Method (Numerical Integration Technique) Time (minutes)

Temperature (°C)

Lethal rate (L = 10(T−85)/5.6)

L × time interval

0 2 4 6 8 10 12

54 71 82 91 85 71 54

0.000 0.003 0.291 11.79 1.000 0.003 0.000 F0 = Σ (L × Δt)

0.000 0.006 0.582 23.58 2.000 0.006 0.000 26 minutes

The formula method may also be employed using one of two approaches. The first approach is based on the criterion of achieving a certain minimal center point temperature in the product, for example, 85°C. In this scenario, the process time can easily be calculated using Equation 12.7. The parameters fh and jch are obtained from the heat penetration data, and Ti and TR are known. The value for gc is also known because gc = TR − 85°C (using the above criterion). A sample calculation to determine the process time to achieve a final temperature (Tc) of 85°C is shown in Table 12.3. The other approach using the formula method is based on Stumbo’s method to calculate process time when the required process lethality (with any selected reference temperature, e.g., 85°C, and z value, e.g., 5.6°C) is known or to calculate process lethality when the process time is given. Calculation examples are shown in Table 12.4 and Table 12.5.

12.4 Canning operations Considering variations in the canning process for different types of berry fruits, the following operations are described in general, with reference to specific fruits whenever appropriate. The flow chart of a typical berry fruit canning process is shown in Figure 12.5. Table 12.3 Process Time Calculation Using Ball’s Formula Method 1. fh 2. jch 3. Retort temperature (TR) 4. Initial temperature (Ti) 5. Ih = TR − Ti 6. jchIh 7. log(jchIh) 8. Final temperature (Tc) 9. gc = TR − Tc 10. log (gc) 11. B = fh[log(jchIh) − log(gc)]

16.2 minutes 1.2 100°C 15°C 85°C 102 2.01 85°C 15°C 1.18 13.4 minutes


350


Table 12.4 Calculation of Process Time Using Stumbo’s Formula Method 1. fh 2. jch 3. Retort temperature (TR) 4. Initial temperature (Ti) 5. Ih = TR − Ti 6. jchIh 7. log(jchIh) 8. Required process lethality (F0) 9. z 10. Fi = 10[(85−TR)/z] 11. U = F0Fi 12. fh/U 13. jcc 14. From Stumbo’s table, for z = 5.6°C, jcc = 1.6, obtain gc value by interpolation fh/U gc (°F) 10 5.44 20 7.91 Interpolate 10.3 5.51 5.51°F temperature difference corresponds to 3.06°C temperature difference 15. log(gc) 16. B = fh[log(jchIh) − log(gc)]

12.3 minutes 1.12 93°C 15°C 78°C 87.4 1.94 30 minutes 5.6°C 0.04 1.2 minutes 10.3 1.6

0.49 17.8 minutes

Table 12.5 Calculation of Process Lethality Using Stumbo’s Formula Method 1. fh 2. jch 3. Retort temperature (TR) 4. Initial temperature (Ti) 5. Ih = TR − Ti 6. jchIh 7. log(jchIh) 8. Process time (B) 9. z 10. Fi = 10[(85−TR)/z] 11. B/fh 12. log(gc) = log(jchIh) − B/fh 13. gc 14. jcc 15. From Stumbo’s table, for z = 5.6°C, jcc = 1.8, obtain fh/U by interpolation 5.62°C temperature difference corresponds to 10.1°F temperature difference gc fh/U 10 30 11.2 40 Interpolate 10.1 30.8 16. U = fh/(fh/U) 17. F0 = U/Fi

16 minutes 1.36 93°C 20°C 73°C 99.3 2.00 20 minutes 5.6°C 0.04 1.25 0.75 5.62°C 1.8

0.52 13 minutes


Chapter 12:


Raw material

Thermal processing

Cooling

Washing

Sealing

351

Sorting/grading

Exhausting

Labeling

Filling

Storage

Figure 12.5 Typical berry fruit canning operations.

12.4.1 Raw material selection The quality of processed fruit depends largely on the quality of the raw fruit, and this in turn depends on how the fruit is harvested, handled, and stored.26 Harvesting at the proper maturity is an important step in the thermal processing of berry fruits. Practically all berry fruits are harvested in the “firm-ripe” stage, when they have attained the desired shape and size, and are still firm enough to withstand reasonable handling without bruising. In the “mellow-ripe” stage, most berries are in prime condition for consuming. Therefore most berry fruits are canned in the “mellow-ripe” stage to capture maximum natural nutrients, flavor, aroma, and color. A few berry fruits, such as black currants and gooseberries, are canned in the “firm-ripe” stage. In such cases, different ingredients may be added, such as spices, salt, sugar, calcium, colors, flavors, and nutrients (e.g., vitamin C), to compensate for the underdeveloped full natural flavor and aroma. Berries that are used to produce juices, purees, preserves, marmalades, and sauces are processed in the “soft-ripe” stage because flavor and aroma are more important than texture.26

12.4.2 Washing Berries are washed with water to remove dust, dirt, insect frass, mold spores, and plant parts that will affect their color, aroma, and flavor. This process should be carried out thoroughly to ensure the removal of the heat-resistant micromycete Neosartorya fischeri, which has been linked to mold formation in canned fruits.27 In addition, the water is also used to cool the produce by removing field heat following harvesting. The volume of water required varies with the method of preparation for canning and the kind of the berry fruit.2 Detergents are frequently used in the wash or rinse water. The water temperature should be kept low because it will keep the fruit firm and reduce leaching. The effectiveness of the washing operation depends on the amount, temperature, acidity, hardness, and mineral content of the water and the force at which it is applied.26


352


12.4.3 Sorting/grading This operation ensures the removal of inferior and damaged produce. An inspection belt may be used in addition to trained personnel who detect poor-quality produce unsuitable for canning. Sorting labor costs may be reduced by new technologies that are noninvasive, such as magnetic resonance imaging.28 Considerable recent research has been focused on using optical techniques to measure the internal quality of fruit. Near-infrared spectroscopy (NIRS), which measures diffusely reflected or transmitted light over a range of invisible wavelengths longer than visible light, has been used for predicting the sweetness of fresh fruits. Commercial application of NIRS for sorting apples and other fruits for sweetness has started recently. However, there are still considerable technological challenges for measuring firmness and other quality attributes of fresh fruit.29 Acceptable fruits are then size sorted, where they are mechanically passed over a screen with different size holes or slits. Undersized fruit is sorted out and used as concentrate or for jam manufacture.28 Fruits with aesthetic defects may be used for juices and concentrates.

12.4.4 Filling Can filling is usually done by automatic machines, although it may be done by hand for very soft fruits that have a tendency to bruise easily. Mechanical fillers are adjusted to dispense each can a predetermined volume of fruit from a chamber and add a given amount of syrup or water. These quantities must be uniform in order to ensure accurate and constant fill weights, which is desirable not only for economic reasons, but is also technically important. Most berry fruit products require a headspace in the can, especially those that are processed in an agitating retort. The headspace bubble in the can is crucial for movement of the contents during agitation. The amount of headspace in a can is important; insufficient space may cause the can ends to bulge, whereas excessive space can cause under processing and even collapse of cans during processing, as well as lead to can corrosion during storage due to insufficient vacuum.

12.4.4.1 Type of pack Berry fruits are available for canning mostly in the form of whole fruit as well as in other forms such as sauce, puree, juice, or in mixed fruit packs such as fruit cocktail.

12.4.4.2 Type of covering liquid During thermal processing of canned berries, heat is first transferred from the heating medium (steam or water) to the container surface and then to the covering liquid. The covering liquid may include syrup, water, mixtures of fruit juices and water, or fruit juices alone. Heat from the covering liquid is then transferred to the fruit itself. Besides facilitating heat transfer to the


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fruit, the covering media also serves to sweeten the product and improve the quality characteristics (aroma and color), as well as to fortify the nutrients. The most common syrups in canned berry products are sucrose syrup (cane or beet sugar), corn syrup, invert sugar syrup, dextrose, and high fructose corn syrup.2 The different designations for syrups range from light fruit juice syrups to extra heavy syrups. Their designations followed by their °Brix measurement are extra heavy syrup (E), 22° to 35°; heavy syrup (H), 18° to 22°; light syrup (L), 14° to 18°; and light fruit juice syrup or water (W), less than 14°.2 Another option is canning in natural fruit juices.30 Syrup strengths can be verified using a refractometer or a Brix hydrometer. Recent market trends, however, have found a growing popularity toward packing in concentrated juice of the same fruit with no sugar added.28 According to Canadian labeling standards, when fruits are packed without sugar the label may indicate “no sugar added” or “unsweetened.”

12.4.4.3 Container specifications and types In the United States, Canada, and a majority of other countries, can dimensions are expressed using two numbers, each number consisting of three digits. The first of both numbers refers to whole inches, and the second and third digits together refer to the additional fraction of the dimension expressed in sixteenths of an inch. The first three-digit number refers to the can diameter and the second three-digit number refers to the can height. For example, a can with the dimensions 401 × 411 would be 4 1/16 inches in diameter (from the outside edge of both double seams) and 4 11/16 inches in height (the outside edge of both terminal seams). Specifications for dimensions of glass containers are similar to cans, except that specific numbers for jars are assigned to the equivalent can dimensions. Glass containers are frequently used for products such as berry fruits. Three numbers are used for rectangular cans to denote the dimensions of length, width, and height, respectively. In addition to the traditional can, which is recyclable, but costly with respect to its requirements for tin, steel, and aluminum, other types of containers are competing for an advantage in the processed fruit industry. Plasticring six-pack carriers for beverages, thinner wall metal cans, and paper-based composites (e.g., paper, plastic, and metal foil laminates) have been and will undoubtedly be used on a larger scale in the future due to current concerns for convenience, cost, and environmental issues.28

12.4.4.4 Container sizes In the California canned fruit industry, the most popular consumer sizes are the buffet (8 oz.), the no. 303 (16 oz.), and the no. 2 1/2 (l lb. 13 oz.). Canned fruits in Canada are usually packed in standard sizes of 5 fl. oz. (142 ml), 10 fl. oz. (284 ml), 14 fl. oz. (398 ml), 19 fl. oz. (540 ml), 28 fl oz. (796 ml), 48 fl oz. (1.36 l), and 100 fl. oz. (2.84 l). For information on “Suggested New Quantity Statements for Fruits,” refer to the Almanac of the Canning, Freezing, Preserving Industries.31 Suggested container


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sizes are listed for a variety of canned fruits with different levels of syrup (from light to extra heavy), along with the imperial and metric measures for net capacity. A table with label measurements for various can sizes is also included, with the common name of the can, the can size from 202 × 204 to 603 × 700, and label sizes.

12.4.4.5 Can lacquer As high-acid and highly colored fruits, most berries require an acid-resistant lacquer. Cans for jams made from these fruits also require a lacquer. Gooseberry fruit is an exception, which can be packed in plain-bodied cans. Two kinds of lacquered cans are available: an acid-resisting (AR) lacquer (for acid foods, mostly fruits) and a sulfur-resisting (SR) lacquer (for low-acid foods such as vegetables, beans, and meat). The “R” enamel protects the natural pigment of highly colored fruits such as dark-colored berries.2

12.4.5 Exhausting and vacuum The primary reason for exhausting and vacuum is to create an anaerobic environment in the can that inhibits microbial spoilage. Vacuum treatment also removes occluded gases from fruit tissue, which is necessary in order to increase its specific gravity. Generally three methods of can exhausting are used in order to remove headspace gas and produce a vacuum. The conventional technique is thermal exhausting, which involves the passage of cans through a steam chamber or exhaust box. The steam replaces the air inside the can and it is sealed while still hot. The vacuum is created in the can following condensation of the steam. This process is very energy intensive because of the excessive steam requirements. Another available method is “steam-flow” or “steam-vac” closing, where high-pressure steam is injected into the can headspace just prior to closing (approximately 5 to 8 minutes at 100°C).28 Thus all of the air is quickly replaced with steam, which will condense and form a vacuum following seaming. Steam-flow closing is relatively efficient, less energy intensive, and less expensive than thermal exhausting. High-speed mechanical vacuum sealing is also commonly used. In this method, cans filled cold with fruit and syrup are passed into a clincher that clinches the cans (first operation roll seam) but does not form an airtight seal. The cans are then subjected to a vacuum for only a short period of time. This practice removes the free headspace air, but not all dissolved gases within the product. An advantage of this method is that it eliminates the need for exhausting of cans as a separate unit operation and saves processing space. Vacuum can-closing machines may pose potential problems for fruits packed in syrup. Because of the excess liquid in the can, the vacuum applied may draw some of the liquid out of the can. In order to prevent such loss of liquid, a prevacuum step before vacuum closing is employed, where a vacuum is drawn first on fruit alone in the can, and then, while still under vacuum, the syrup is added.2 The filled cans are then subjected to the vacuum sealer with practically no dissolved air in the can and no subsequent loss of syrup.


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12.4.6 Seaming/closing The can should be closed immediately after filling and exhausting to prevent excessive cooling of the surface of the product. Modern can seaming machines operate at speeds as high as 300 cans/min. Liquid products may be sealed in cans at speeds of up to 1600 cans/min.2 The double-seaming operation is critical to ensure a hermetic seal and good quality of the final product during storage. Faulty seaming can result in deformations in the can during processing and eventually recontamination. Glass jars are closed with a screw cap.

12.4.7 Container coding All containers should be coded for recall purposes in case of problems in the stored product, such as spoilage, contamination, or consumer complaints. The code should provide necessary information such as the canning plant where packed; the day, year, and hour packed; the packing period; and the line on which the product was packed.2 This practice should be carefully followed, along with the filing of adequate production and shipping records.

12.4.8 Retort operations The simplest pasteurization equipment is a water bath maintained at an appropriately high temperature.32 Full crates containing berries packed in syrup or water are placed in steam-heated water in large steel tanks. After the required processing time, cold water is added to the tank for cooling or the crates are lifted out and immersed in a cold water tank for cooling. Continuous water bath pasteurizers consist of a long tank through which cans move along on a belt. Alternately, the containers can travel through a tunnel along a conveyor belt and are subjected to continuous water sprays. As they travel, the cans pass through several temperature zones from preheating and pasteurization to the final cool. In the pasteurization section, steam (100°C) at atmospheric pressure is sometimes injected for quicker heating. The moderated temperatures that are possible in these systems make them ideal pasteurizers for berry products in glass jars that are sensitive to thermal shocks. Another type of unit that is used for pasteurization of berry products is the continuous agitating atmospheric cooker.32 Its operation is similar to that of more conventional high-pressure continuous cookers, but the operation is limited to atmospheric pressure to accomplish pasteurization. These agitation processes are used to uniformly cook products throughout the container. Product agitation is also possible in batch-type rotary retorts, in which cans are often subjected to end-over-end agitation. Aseptic or ultra-high temperature (UHT) processing has become a success story for fruit beverages, purees, and juices containing small particles. In this process, the food and the packaging material are sterilized separately and then assembled under sterile conditions. The product is first subjected


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to heat by passing the liquid product through a shell and tube or plate heat exchanger and held for sufficient time in holding tubes to complete the required pasteurization treatment. Following the required treatment, the product is then passed through another heat exchanger where it is cooled. The filling and sealing operations are then performed in presterilized containers (laminated cartons) under aseptic conditions. Plate-type indirect heat exchangers are extensively used for such purposes. The juice flows through one side of a wall while the heating medium (steam or hot water) flows on the other side. The plate is designed in such a way that it yields extremely high rates of heat transfer. Tubular heat exchangers are also available for pasteurization purposes. For more viscous products such as cream, yogurt, and salad dressing, and for products containing small particulate matter, scraped surface heat exchangers are used to prevent surface fouling problems and promote rapid heat transfer. Because the packaging material must be sterilized prior to filling, the material should possess physical properties that permit this application as well as that of hermetic sealing. One type of composite package that is extensively used as a packaging material for aseptic processing is a paperboardfoil-plastic laminate known as “Tetra-Pak.” This type of package consists of a series of six layers of materials, with polypropylene as the outermost layer, followed by “Surlyn” aluminum foil, polyethylene, paperboard, and polyethylene again as the innermost layer. Polypropylene and polyethylene act as heat-sealing surfaces, whereas aluminum foil acts as a barrier material that is protected from mechanical damage by the paperboard. This composite package acts as a barrier to oxygen, light, moisture, and microorganisms, and it meets all of the requirements necessary for successful application of the aseptic process, including heat sealability and strength. Prior to filling, a common sterilization method for this packaging material is the use of hydrogen peroxide in combination with heat or ultraviolet radiation treatment. For maximum nutrient retention, HTST pasteurization methods are often recommended if heat resistant enzymes such as peroxidase or pectin esterase are not present in the product. This is because increases in processing temperatures will cause faster destruction rates for microbial population as compared to nutrients. The presence of heat resistant enzymes, which have a higher heat tolerance than microorganisms, do not always permit fruits, for example, to be subjected to such a process.

12.4.9 Cooling After thermal processing, the contents of the can should be cooled to an average temperature of about 35°C to 40°C.33 Storage at higher temperatures will cause loss of color and darkening or pink discoloration (stack burn). If cans are cooled too far below the average temperature, they will remain wet and rusting may result due to insufficient surface drying. Water used for cooling should be noncorrosive, low in bacterial and yeast content, and chlorinated for measurable free-chlorine residual detected at the discharge


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end of the cooler. The cooling water should also be chlorinated with 2 ppm of available chlorine to prevent infection of the can contents with spoilage microorganisms.

12.4.10 Labeling and storage Following cooling, cans are labeled for identification purposes. Adequately processed cans usually ensure acceptable canned fruit quality on the retail market for at least 1 year. Storage temperature has been found to be the most important variable in the maintenance of an acceptable product with minimal flavor, color, texture, and nutritive changes. Common storage temperatures for canned berries seldom average above 21°C.1 Above 27°C, gradual softening occurs. Freezing causes greater changes and canned berries should not be allowed to freeze. Freezing can cause distortion of the can seams and may eventually lead to microbial spoilage. The most important cause of quality deterioration in canned fruit is very slow chemical changes that take place during storage, resulting in changes in nutritive value, flavor, color, and texture. However, based on estimated kinetic parameters for modeling quality changes, it may be possible to predict color degradation of juices or other liquid foods during processing.34

12.5 Grades of canned berries Most heat-processed fruits in Canada are sold by grade. The standards are established by the Processed Fruit and Vegetable Regulations of the Canada Agricultural Products Standards Act. The products are graded on a variety of quality factors such as flavor and aroma, tenderness and maturity, color, consistency of texture, appearance of the packing media, uniformity of size and shape, and freedom from defects and foreign matter.35 There are three general grades: Canada Fancy, Canada Choice, and Canada Standard. Canada Fancy fruits are free from blemishes, clean, and of good color and uniform size. Canada Choice fruits have slight variations in size, color, and maturity, but are almost completely free of blemishes. Canada Standard fruits are mainly used for sauces and puddings because they may be broken and more or less ripe. The appropriate grade must appear on the main part of the label. The U.S. grade standards for fresh and processed fruits are under the jurisdiction of the U.S. Department of Agriculture (USDA) Food Safety and Quality Service (FSQS). The USDA provides an inspection service to certify the quality of processed fruits based on U.S. grade standards. The inspection service is voluntary and paid for by the user. Under the program, processed fruits are inspected by highly trained specialists during all phases of preparation, processing, and packaging. Many processors and wholesalers use the USDA grade standards to establish the value of their product described by the grades. Manufacturers and packers frequently employ them in quality control work.


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Berry fruit: Value-added products for health promotion Table 12.6 Score Points of Factors for Different Grades of Canned Blackberries and Other Similar Berries Factors

Points

Grade A

Grade B

Grade C

Grade D

Color Uniformity of size Absence of defects Character of fruits Total score

20 20 30 30 100

18–20 18–20 27–30 27–30 ≥90

16–17 16–17 24–26 24–26 ≥80

14–15 14–15 21–23 21–23 ≥70

≤13 ≤13 ≤20 ≤20

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Food Plant Sanitation (Food Science and Technology)

Food Process Design (Food Science and Technology)

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Phase Transitions in Foods (Food Science and Technology) (Food Science and Technology)

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