+34-973-702-593 István S. Pretorius (Chapter 25)
Fax: +34-973-702-596 Department of Microbiology
E-mail: olga.martin@ca.udl.es Stellenbosch University
Private Bag X1, Matieland 7602, South Africa
M. I. Mínguez-Mosquera (Chapters 26, 30) Phone: +27-21-808-2861
Group of Chemistry and Biochemistry Fax: +27-21-808-2872
of Pigments. Food Biotechnology Department E-mail: ipretori@sun.ac
3. Handbook of Fruits and
Fruit Processing
Editor
Y. H. Hui
Associate Editors
J´ zsef Barta, M. Pilar Cano, Todd W. Gusek,
o
Jiwan S. Sidhu, and Nirmal K. Sinha
4. C 2006 Blackwell Publishing Danvers, MA 01923. For those organizations that have
All rights reserved been granted a photocopy license by CCC, a sepa-
rate system of payments has been arranged. The fee
Blackwell Publishing Professional codes for users of the Transactional Reporting Service
2121 State Avenue, Ames, Iowa 50014, USA are ISBN-13: 978-0-8138-1981-5; ISBN-10: 0-8138-
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Office: 1-515-292-0140 First edition, 2006
Fax: 1-515-292-3348
Web site: www.blackwellprofessional.com Library of Congress Cataloging-in-Publication Data
Blackwell Publishing Ltd Handbook of fruits and fruit processing / editor, Y.H.
9600 Garsington Road, Oxford OX4 2DQ, UK Hui; associate editors, J´ zsef Barta . . .
o
Tel.: +44 (0)1865 776868 [et al.].— 1st ed.
p. cm.
Blackwell Publishing Asia Includes index.
550 Swanston Street, Carlton, Victoria 3053, Australia ISBN-13: 978-0-8138-1981-5 (alk. paper)
Tel.: +61 (0)3 8359 1011 ISBN-10: 0-8138-1981-4 (alk. paper)
1. Food industry and trade. 2. Fruit—Processing.
Authorization to photocopy items for internal or per- I. Hui, Y. H. (Yiu H.) II. Barta, J´ zsef.
o
sonal use, or the internal or personal use of specific
clients, is granted by Blackwell Publishing, provided TP370.H264 2006
that the base fee of $.10 per copy is paid directly to 664 .8—dc22
the Copyright Clearance Center, 222 Rosewood Drive, 2005013055
The last digit is the print number: 9 8 7 6 5 4 3 2 1
5. Contents
Contributors, vii
Preface, xi
Part I Processing Technology
1. Fruit Microbiology, 3
A. Kalia and R. P. Gupta
2. Nutritional Values of Fruits, 29
C. S´ nchez-Moreno, S. De Pascual-Teresa, B. De Ancos, and M. P. Cano
a
3. Fruit Processing: Principles of Heat Treatment, 45
I. K¨ rmendy
o
4. Fruit Freezing Principles, 59
B. De Ancos, C. S´ nchez-Moreno, S. De Pascual-Teresa, and M. P. Cano
a
5. Fruit Drying Principles, 81
J. Barta
6. Non-Thermal Pasteurization of Fruit Juice Using High Voltage Pulsed Electric Fields, 95
Zs. Cserhalmi
7. Minimally Processed Fruits and Fruit Products and Their Microbiological Safety, 115
Cs. Balla and J. Farkas
8. Fresh-Cut Fruits, 129
O. Mart´n-Belloso, R. Soliva-Fortuny, and G. Oms-Oliu
ı
9. Food Additives in Fruit Processing, 145
P. S. Raju and A. S. Bawa
10. Fruit Processing Waste Management, 171
J. Monspart-S´ nyi
e
Part II Products Manufacturing
11. Manufacturing Jams and Jellies, 189
H. S. Vibhakara and A. S. Bawa
12. Manufacturing Fruit Beverages, 205
E. Horv´ th-Kerkai
a
13. Fruit as an Ingredient in a Fruit Product, 217
Gy. P´ tkai
a
14. Fruit Processing Plant, 231
J. Barta
15. Fruits: Sanitation and Safety, 245
S. Al-Zenki and H. Al-Omariah
v
6. vi Contents
Part III Commodity Processing
16. Apples, 265
N. K. Sinha
17. Apricots, 279
M. Siddiq
18. Horticultural and Quality Aspects of Citrus Fruits, 293
M. J. Rodrigo and L. Zacar´as ı
19. Oranges and Citrus Juices, 309
K. S. Sandhu and K. S. Minhas
20. Sweet Cherries, 359
J. Alonso and R. Alique
21. Cranberry, Blueberry, Currant, and Gooseberry, 369
K. K. Girard and N. K. Sinha
22. Date Fruits Production and Processing, 391
J. S. Sidhu
23. Grape Juice, 421
O. Mart´n-Belloso and A. R. Marsell´ s-Fontanet
ı e
24. Grapes and Raisins, 439
N. R. Bhat, B. B. Desai, and M. K. Suleiman
25. Grape and Wine Biotechnology: Setting New Goals for the Design of
Improved Grapevines, Wine Yeast, and Malolactic Bacteria, 453
I. S. Pretorius
26. Olive Processing, 491
B. Gandul-Rojas and M. I. M´nguez-Mosquera
ı
27. Peach and Nectarine, 519
M. Siddiq
28. Pear Drying, 533
R. de Pinho Ferreira Guin´ e
29. Plums and Prunes, 553
M. Siddiq
30. Processing of Red Pepper Fruits (Capsicum annuum L.) for Production
of Paprika and Paprika Oleoresin, 565
A. P´ rez-G´ lvez, M. Jar´ n-Gal´ n, and M. I. M´nguez-Mosquera
e a e a ı
31. Strawberries and Raspberries, 581
N. K. Sinha
32. Tropical Fruits: Guava, Lychee, Papaya, 597
J. S. Sidhu
33. Banana, Mango, and Passion Fruit, 635
L. G. Occe˜ a-Po
n
34. Nutritional and Medicinal Uses of Prickly Pear Cladodes and Fruits:
Processing Technology Experiences and Constraints, 651
M. Hamdi
35. Speciality Fruits Unique to Hungary, 665
M. St´ ger-M´ t´
e ae
Index, 679
7. Contributors
Rafael Alique (Chapter 20) Csaba Balla (Chapter 7)
Instituto del Frío (CSIC) Corvinus University of Budapest, Faculty of
C/José Antonio Novais n◦ 10 Food Science, Department of Refrigeration
28040 Madrid, Spain and Livestock Products Technology
Phone: +34915492300 Hungary 1118, Budapest, Ménesi út 45
Phone: 36-1-482-6064
Jesús Alonso (Chapter 20) Fax: 36-1-482-6321
Instituto del Frío (CSIC) E-mail: csaba.balla@uni-corvinus.hu
C/José Antonio Novais n◦ 10
28040 Madrid, Spain J´ zsef Barta, Ph.D. (Chapters 5, 14)
o
Phone: +34915492300 Head of the Department
E-mail: jalonso@if.csic.es Corvinus University of Budapest
Faculty of Food Science
Husam Al-Omariah (Chapter 15) Department of Food Preservation
Biotechnology Department Budapest, Ménesi út 45
Kuwait Institute for Scientific Research Hungary 1118
P.O. Box 24885, 13109-Safat, Kuwait Phone: 36-1-482-6212
Fax: 36-1-482-6327
Sameer Al-Zenki (Chapter 15) E-mail: jozsef.barta@uni-corvinus.hu
Biotechnology Department
Kuwait Institute for Scientific Research A.S. Bawa (Chapters 9, 11)
P.O. Box 24885, 13109-Safat, Kuwait Fruits and Vegetables Technology
Phone: (965)-483-6100 Defence Food Research Laboratory
Fax: (965)-483-4670 Siddarthanagar, Mysore-570 011, India
E-mail: szenki@kisr.edu.kw Phone: 0821-247-3783
Fax: 0821-247-3468
Begoña De Ancos (Chapters 2, 4) E-mail: dfoodlab@sancharnet.in
Department of Plant Foods Science
and Technology, Instituto del Frío N. R. Bhat (Chapter 24)
Consejo Superior de Investigaciones Arid Land Agriculture Department
Científicas (CSIC) Ciudad Universitaria Kuwait Institute for Scientific Research
E-28040 Madrid, Spain P.O. Box 24885, 13109-Safat, Kuwait
E-mail: ancos@if.csic.es E-mail: nbhat@safat.kisr.edu.kw
vii
8. viii Contributors
M. Pilar Cano, Ph.D. (Chapters 2, 4) Beatriz Gandul-Rojas (Chapter 26)
Director Group of Chemistry and Biochemistry
Instituto del Frío-CSIC of Pigments. Food Biotechnology Department
C/Jose Antonio Novais, 10 Instituto de la Grasa (CSIC).
Ciudad Universitaria Av. Padre García Tejero 4, 41012
28040-Madrid, Spain Sevilla, Spain
Phone: 34-91-5492300
Fax: 34-91-5493627 Kristen K. Girard (Chapter 21)
E-mail: pcano@if.csic.es Principal Scientist
Ocean Spray Cranberries, Inc.
Zsuzsanna Cserhalmi (Chapter 6) Ingredients
Central Food Research Institute 1 Ocean Spray Dr.
Hungary 1022 Budapest, Hermann O. u. 15 Middleboro MA 02349, USA
Phone: 36-1-214-1248 E-mail: kgirard@oceanspray.com
Fax: 36-1-355-8928
E-mail: zs.cserhalmi@cfri.hu Rajinder P. Gupta (Chapter 1)
Department of Microbiology,
Sonia De Pascual-Teresa (Chapters 2, 4) College of Basic Sciences and Humanities
Department of Plant Foods Science Punjab Agricultural University
and Technology, Instituto del Frío Ludhiana-141004, India
Consejo Superior de Investigaciones rpguptag@rediffmail.com
Científicas (CSIC) Ciudad Universitaria
E-28040 Madrid, Spain Todd W. Gusek, Ph.D.
E-mail: soniapt@if.csic.es Principal Scientist, Central Research
Cargill, Inc.
B. B. Desai (Chapter 24) PO Box 5699
Arid Land Agriculture Department Minneapolis, MN 55440, USA
Kuwait Institute for Scientific Research Phone: (952)742-6523
P.O. Box 24885, 13109-Safat, Kuwait Fax: (952)742-4925
E-mail: todd gusek@cargill.com
J´ zsef Farkas (Chapter 7)
o
Corvinus University of Budapest M. Hamdi (Chapter 34)
Faculty of Food Science, Department Director, Department of Biochemical and Chemical
of Refrigeration and Livestock Products Engineering Microbial and Food Processes
Technology and Central Food Research Institute Higher School of Food Industries
Hungary 1118, Budapest, Ménesi út 45 National Institute of Applied Sciences
and, 1022, Budapest, Hermann O. u. 15 and Technology. BP: 676. 1080 Tunisia
Phone: 36-1-482-6303 Phone: 216-98-326675
Fax: 36-1-482-6321 Fax: 216-71-704-329
E-mail: j.farkas@cfri.hu E-mail: moktar.hamdi@insat.rnu.tn
Raquel de Pinho Ferreira Guin´ (Chapter 28)
e Emoke Horváth-Kerkai (Chapter 12)
Associate Professor Corvinus University of Budapest, Faculty
Department of Food Engineering of Food Science, Department of
ESAV, Polytechnic Institute of Viseu Food Preservation Hungary 1118
Campus Politécnico, Repeses Budapest, Ménesi út 45.
3504-510 Viseu, Portugal Phone: 36-1-482-6035
E-mail: raquelguine@esav.ipv.pt Fax: 36-1-482-6327
E-mail: emoke.kerkai@uni-corvinus.hu
9. Contributors ix
Y. H. Hui, Ph.D. Av. Padre García Tejero 4, 41012
Senior Scientist Sevilla, Spain
Science Technology System Phone: +34954691054
P.O. Box 1374 Fax: +34954691262
West Sacramento, CA 95691, USA E-mail: minguez@cica.es.
Phone: 916-372-2655
Fax: 916-372-2690 Kuldip Singh Minhas (Chapter 19)
E-mail: yhhui@aol.com Professor
Food Science and Technology
Manuel Jarén-Galán (Chapter 30) Punjab Agricultural University
Group of Chemistry and Biochemistry Ludhiana, Punjab, India
of Pigments. Food Biotechnology Department Phone: 0161-2401960 Extn. 305
Instituto de la Grasa (CSIC)
Av. Padre García Tejero 4, 41012 Judit Monspart-Sényi (Chapter 10)
Sevilla, Spain Corvinus University of Budapest, Faculty
of Food Science, Department of Food Preservation
Anu Kalia (Chapter 1) Hungary 1118, Budapest, Ménesi út 45
Department of Microbiology, Phone: 36-1-482-6037
College of Basic Sciences and Humanities Fax: 36-1-482-6327
Punjab Agricultural University E-mail: judit.senyi@uni-corvinus.hu
Ludhiana-141004, India
kaliaanu@rediffmail.com Lillian G. Occeña-Po (Chapter 33)
Department of Food Science and Human Nutrition
Imre Körmendy (Chapter 3) Michigan State University
Corvinus University of Budapest, East Lansing, MI 48824, USA
Faculty of Food Science, Department Phone: 517-432-7022
of Food Preservation Hungary 1118 Fax: 517-353-8963
Budapest, Ménesi út 45 E-mail: occena@msu.edu
Phone: 36-1-482-6212
Fax: 36-1-482-6327 Gemma Oms-Oliu (Chapter 8)
E-mail: imre.kormendy@uni-corvinus.hu Department of Food Technology, University of
Lleida Av. Alcalde Rovira Roure, 191. 25198
Olga Martín-Belloso (Chapters 8, 23) Lleida, Spain
Department of Food Technology, University Phone: +34-973-702-593
of Lleida Av. Alcalde Rovira Roure, 191. 25198 Fax: +34-973-702-596
Lleida, Spain E-mail: goms@tecal.udl.es
Phone: +34-973-702-593
Fax: +34-973-702-596 Györgyi Pátkai (Chapter 13)
E-mail: omartin@tecal.udl.es Corvinus University of Budapest, Faculty
of Food Science, Department of Food Preservation
Angel Robert Marsellés-Fontanet (Chapter 23) Hungary 1118, Budapest, Ménesi út 45
Department of Food Technology, University Phone: 36-1-482-6212
of Lleida Av. Alcalde Rovira Roure, 191. 25198 Fax: 36-1-482-6327
Lleida, Spain E-mail: gyorgyi.patkai@uni-corvinus.hu
Phone: +34 973 702 593
Fax: +34 973 702 596 Antonio Pérez-Gálvez (Chapter 30)
E-mail: rmarselles@tecal.udl.es Group of Chemistry and Biochemistry
of Pigments, Food Biotechnology Department
M. Isabel Mínguez-Mosquera (Chapters 26, 30) Instituto de la Grasa (CSIC).
Group of Chemistry and Biochemistry Av. Padre García Tejero 4, 41012,
of Pigments. Food Biotechnology Department Sevilla, Spain
Instituto de la Grasa (CSIC)
10. x Contributors
Isak S. Pretorius (Chapter 25) East Lansing, MI 48824, USA
The Australian Wine Research Institute Phone: 517-355-8474
PO Box 197, Glen Osmond Fax: 517-353-8963
Adelaide, SA 5064 E-mail: siddiq@msu.edu
Australia
Phone: +61-8-83036835 Nirmal K. Sinha, Ph.D. (Chapters 16, 21, 31)
Fax: +61-8-83036601 VP, Research and Development
E-mail: Sakkie.Pretorius@awri.com.au Graceland Fruit, Inc.
1123 Main Street
P.S. Raju (Chapter 9) Frankfort, MI 49635, USA
Fruits and Vegetables Technology Phone: 231-352-7181
Defence Food Research Laboratory Fax: 231-352-4711
Siddarthanagar, Mysore-570 011, India E-mail: nsinha@gracelandfruit.com
Phone: 0821-247-3783
Fax: 0821-247-3468 Robert Soliva-Fortuny (Chapter 8)
E-mail: dfoodlab@sancharnet.in Department of Food Technology, University
of Lleida Av. Alcalde Rovira Roure, 191. 25198
María Jesús Rodrigo (Chapter 18) Lleida, Spain
Instituto de Agroquímica y Tecnología Phone: +34-973-702-593
de Alimentos (CSIC). Apartado Postal 73 Fax: +34-973-702-596
46100 Burjasot, Valencia, Spain E-mail: rsoliva@tecal.udl.es
Concepción Sánchez-Moreno (Chapters 2, 4) Mónika Stéger-Máté (Chapter 35)
Department of Plant Foods Science and Corvinus University of Budapest, Faculty
Technology, Instituto del Frío, Consejo Superior of Food Science, Department of Food Preservation
de Investigaciones Científicas (CSIC) Hungary 1118, Budapest, Ménesi út 45
Ciudad Universitaria, E-28040 Madrid, Spain Phone: 36-1-482-6034
E-mail: csanchezm@if.csic.es Fax: 36-1-482-6327
E-mail: monika.stegernemate@uni-corvinus.hu
Kulwant S. Sandhu (Chapter 19)
Sr. Veg. Technologist (KSS) M. K. Suleiman (Chapter 24)
Department of Food Science and Technology Arid Land Agriculture Department
Punjab Agricultural University Kuwait Institute for Scientific Research
Ludhiana - 141 004, Punjab, India P.O. Box 24885, 13109-Safat, Kuwait
Phone: 0161-2405257, 2401960 extn. 8478
(KSS) H.S. Vibhakara (Chapter 11)
E-mail: ptc@satyam.net.in Fruits and Vegetables Technology
Defence Food Research Laboratory
Jiwan S. Sidhu, Ph.D. (Chapters 22, 32) Siddarthanagar, Mysore-570 011, India
Professor, Department of Family Science Phone: 0821-247-3949
College for Women, Kuwait University Fax: 0821-247-3468
P.O. Box 5969, Safat-13060, Kuwait
Phone: (965)-254-0100 extn. 3307 Lorenzo Zacarías (Chapter 18)
Fax: (965)-251-3929 Instituto de Agroquímica y Tecnología
E-mails: jsidhu@cfw.kuniv.edu; de Alimentos (CSIC). Apartado Postal 73
jiwansidhu2001@yahoo.com 46100 Burjasot, Valencia, Spain
Phone: 34 963900022
Muhammad Siddiq (Chapters 17, 27, 29) Fax: 34 963636301
Food Processing Specialist E-mail: lzacarias@iata.csic.es or
Department of Food Science & Human Nutrition cielor@iata.csic.es
Michigan State University
11. Preface
In the past 30 years, several professional reference Part III is from the commodity processing perspec-
books on fruits and fruit processing have been pub- tive, covering important groups of fruits such as:
lished. The senior editor of this volume was part of
r Apples
an editorial team that published a two-volume text on
r Apricots
the subject in the mid-nineties.
r Citrus fruits and juices
It may not be appropriate for us to state the ad-
r Sweet cherries
vantages of our book over the others available in the
r Cranberries, blueberries, currants, and
market, especially in contents; however, each profes-
sional reference treatise has its strengths. The deci- gooseberries
r Date fruits
sion is left to the readers to determine which title best
r Grapes and raisins, including juices and wine
suits their requirement.
r Olives
This book presents the processing of fruits from
r Peaches and nectarines
four perspectives: scientific basis; manufacturing and
r Pears
engineering principles; production techniques; and
r Plums and Prunes
processing of individual fruits.
r Red pepper fruits
Part I presents up-to-date information on the funda-
r Strawberries and raspberries
mental aspects and processing technology for fruits
r Tropical fruits (guava, lychee, papaya, banana,
and fruit products, covering:
mango, and passion fruit)
r Microbiology
r Nutrition Although many topical subjects are included in our
r Heat treatment text, we do not claim that the coverage is comprehen-
r Freezing sive. This work is the result of the combined efforts
r Drying of nearly fifty professionals from industry, govern-
r New technology: pulsed electric fields ment, and academia. They represent eight countries
r Minimal processing with diverse expertise and backgrounds in the disci-
r Fresh-cut fruits pline of fruit science and technology. An international
r Additives editorial team of six members from four countries
r Waste management led these experts. Each contributor or editor was re-
sponsible for researching and reviewing subjects of
Part II covers the manufacturing aspects of processed
immense depth, breadth, and complexity. Care and
fruit products:
attention were paramount to ensure technical accu-
r Jams and jellies racy for each topic. In sum, this volume is unique in
r Fruit beverages many respects. It is our sincere hope and belief that it
r Fruit as an ingredient will serve as an essential reference on fruits and fruit
r A fruit processing plant processing for professionals in government, industry,
r Sanitation and safety in a fruit processing plant and academia.
xi
12. xii Preface
We wish to thank all the contributors for sharing TechBooks, Inc. for their time, effort, advice, and
their expertise throughout our journey. We also thank expertise. You are the best judges of the quality of
the reviewers for giving their valuable comments on this work.
improving the contents of each chapter. All these pro-
fessionals are the ones who made this book possible. Y. H. Hui
We trust that you will benefit from the fruits of their J. Barta
labor. M. P. Cano
We know firsthand the challenges in developing T. W. Gusek
a book of this scope. What follows are the difficul- J. S. Sidhu
ties in producing the book. We thank the editorial N. Sinha
and production teams at Blackwell Publishing and
15. 4 Part I: Processing Technology
unidentified etiological agents. These new outbreaks NORMAL MICROFLORA OF
of fresh-produce-related food poisoning include ma- PROCESSED FRUIT PRODUCTS
jor outbreaks by tiny culprits as Escherichia coli
0157:H7, Salmonella, Shigella, Cyclospora, Hepati- Postharvest processing methods include diverse
tis A virus, Norwalk disease virus, on a variety of range of physical and chemical treatments to enhance
fruits as cantaloupes, apples, raspberries, and other the shelf life of fresh produce. The minimally pro-
fruits. Erickson and Kornacki (2003) have even ad- cessed fresh-cut fruits remain in a raw fresh state
vocated the appearance of Bacillus anthracis as a without freezing or thermal processing, or addition
potential food contaminant. Factors include global- of preservatives or food additives, and may be eaten
ization of the food supply, inadvertent introduction of raw or conveniently cooked and consumed. These
pathogens into new geographical areas (Frost et al., minimally processed fruits are washed, diced, peeled,
1995; Kapperud et al., 1995), the development of trimmed, and packed, which lead to the removal of
new virulence factors by microorganisms, decreases fruit’s natural cuticle, letting easy access by outer
in immunity among certain segments of the popula- true or opportunistic normal microflora to the internal
tion, and changes in eating habits. disrupted tissues abrassed during processing. Gorny
and Kader (1996) observed that pear slices cut with a
freshly sharpened knife retained visual quality longer
than the fruits cut with a dull hand-slicer.
NORMAL MICROFLORA Rinsing of fresh produce with contaminated wa-
OF FRESH FRUITS ter or reusing processed water adds E. coli 0157:H7,
Fresh fruits have an external toughness, may be water Enterobacter, Shigella, Salmonella sp., Vibrio chlo-
proof, wax-coated protective covering, or skin that reae, Cryptosporidium parvum, Giardia lamblia, Cy-
functions as a barrier for entry of most plant clospora caytanensis, Toxiplasma gondii, and other
pathogenic microbes. The skin, however, harbors a causative agents of foodborne illnesses in humans,
variety of microbes and so the normal microflora of thus increasing the microbial load of the fresh pro-
fruits is varied and includes both bacteria and fungi duce that undergo further processing including addi-
(Hanklin and Lacy, 1992). These microbes get tion of undesirable pathogens from the crop.
associated with fruits, since a variety of sources such Fruits processed as fruit concentrates, jellies, jams,
as the blowing air, composted soil, insects as preserves, and syrups have reduced water activ-
Drosophila melanogaster or the fruit fly inoculate ity (aw ) achieved by sufficient sugar addition and
the skin/outer surface with a variety of Gram- heating at 60–82◦ C, that kills most of xerotolerant
negative bacteria (predominantly Pseudomonas, fungi as well as restrains the growth of bacteria.
Erwinia, Lactobacillus). Likewise, hand-picking Thus, the normal microflora of such diligently pro-
the fresh produce inoculates the fruit surfaces cessed fruit products may include highly osmophilic
with Staphylococcus. Contact with soil, especially yeasts and certain endospore-forming Clostridium,
partially processed compost or manure, adds di- Bacillus sp. that withstand canning procedures. Sim-
verse human pathogenic microbes generally of the ilar flora may appear for processed and pasteurized
fecal-oral type including the Enterobacter, Shigella, fruit juices and nectars that loose most vegetative bac-
Salmonella, E. coli 0157:H7, Bacillus cereus, as teria, yeasts, and molds while retaining heat-resistant
well as certain viruses such as Hepatitis A Virus, ascospores or sclerotia producing Paecilomyces sp.,
Rotavirus, and Norwalk disease viruses that are Aspergillus sp., and Penicillum sp. (Splittstoesser,
transmitted by consumption of raw fruits. Normal 1991). Recently, Walls and Chuyate (2000) reported
fungal microflora of fruits includes molds such the occurrence of Alicyclobacillus acidoterrestris,
as Rhizopus, Aspergillus, Penicillum, Eurotium, an endospore-forming bacteria in pasteurized orange
Wallemia, while the yeasts such as Saccharomyces, and apple juices.
Zygosaccharomyces, Hanseniaspora, Candida,
Debaryomyces, and Pichia sp. are predominant.
These microbes are restrained to remain outside on
FACTORS AFFECTING
fruit surfaces as long as the skins are healthy and
MICROBIAL GROWTH
intact. Any cuts or bruises that appear during the Fruits are composed of polysaccharides, sugars, or-
postharvest processing operations allow their entry ganic acids, vitamins, minerals which function as em-
to the less protected internal soft tissue. inent food reservoirs or substrates dictating the kind
16. 1 Fruit Microbiology 5
of microorganisms that will flourish and perpetuate as ATP and DNA require neutrality (Brown, 1964).
in the presence of specific microflora and specific The pH changes also affect the morphology of some
environmental prevailing conditions. Hence, one can microbes as Penicillum chrysogenum that show de-
predict the development of microflora on the basis creased length of hyphae at pH above 6.0. Corlett
of substrate characteristics. Fresh fruits exhibit the and Brown (1980) observed varying ability of or-
presence of mixed populations, and growth rate of ganic acids as microbial growth inhibitors in relation
each microbial type depends upon an array of factors to pH changes.
that govern/influence the appearance of dominating
population, which include the following. Water Activity (Moisture Requirement)
Intrinsic Factors Water is a universal constituent required by all the liv-
ing cells, and microbes are no exceptions but the exact
These imply the parameters that are an inherent part amount of water required for growth of microorgan-
of the plant tissues (Mossel and Ingram, 1955) and isms varies. Hence, several preservation methods in-
thus are characteristics of the growth substrates that volve drying or desiccation of the produce (Worbo
include the following. and Padilla-Zakour, 1999). The water requirement of
microbes is defined as water activity (aw ) or ratio of
Hydrogen Ion Concentration (pH) water vapor pressure of food substrate to that of vapor
pressure of pure water at same temperature
Microbial cells lack the ability to adjust their inter-
nal pH, hence are affected by change in pH, so could p
aw = ,
grow best at pH values around neutral. Bacteria ex- po
hibit a narrow pH range with pathogenic bacteria be-
where p is the vapor pressure of the solution and po
ing the most fastidious; however, yeasts and molds
is the vapor pressure of the solvent.
are more acid-tolerant than bacteria. Fruits possess
Christian (1963) related water activity to relative
more acidic pH (<4.4) favoring growth of yeasts and
humidity as (Table 1.2)
molds. Microbes, in general, experience increased
lag and generation times at either extremes of the RH = 100 × aw .
optimum pH range, which is usually quite narrow.
The small fluctuations in pH have elaborate impact Thus, the relative humidity of a food corresponding
on microbial growth rates, and the pH changes be- to a lower aw tends to dry the surface and vice versa.
come more profound if the substrate has low buffer- In general, most fresh produce has aw value above
ing capabilities leading to rapid changes in response 0.99 which is sufficient for the growth of both bacte-
to metabolites produced by microorganisms during ria and molds; however, bacteria, particularly Gram-
fermentation (Table 1.1). negative, are more stringent regarding aw changes,
Adverse pH affects the functioning of respiring while molds could grow at aw as low as 0.80. The
microbial enzymes and the transport of nutrients into lowest range of permeable aw values for halophilic
the cell. The intracellular pH of microbial cytoplasm bacteria, xerophilic fungi, and osmophilic yeasts is
remains reasonably constant due to relative imper- 0.75–0.61. Morris (1962) elaborated the interaction
meability of cell membrane to hydrogen (H+ ) and of aw values with temperature and nutrition and ob-
hydroxyl (OH− ) ions as key cellular compounds such served that at optimum temperature, range of aw val-
ues remain wide, while lowering/narrowing aw values
reduces growth and multiplication of microbes, and
Table 1.1. Approximate pH Values of Some nutritive properties of substrate increase the range of
Fresh Fruits aw over which microorganisms can survive (Fig. 1.1).
Hence, each microbe has its own characteristic aw
Fruits pH Values Fruits pH Values range and optimum for growth and multiplication
Apples 2.9–3.3 Limes 1.8–2.0 which are affected by temperature, pH, oxygen avail-
Bananas 4.5–4.7 Melons 6.3–6.7 ability, and nutritive properties of substrate as well
Grapefruit 3.4–4.5 Figs 4.6 as the presence of organic acids or other secondary
Watermelons 5.2–5.6 Plums 2.8–4.6 metabolites performing inhibitory action, thus nar-
Oranges 3.6–4.3 rowing the aw range that culminates in decreased
Source: Adapted from Jay (1992). yield of cells and increased lag phase for growth,
17. 6 Part I: Processing Technology
Table 1.2. Lower Limit aw Values of Certain Microorganisms
Bacteria Minimum aw Values Fungi Minimum aw Values
Pseudomonas 0.97 Mucor 0.62 (0.94)
E. coli 0.96 Rhizopus 0.62
Staphylococcus aureus 0.86 Botyritis 0.62
Bacillus subtilis 0.95 Aspergillus 0.85
Clostridium botulinum 0.93 Penicillum 0.95
Enterobacter aerogenes 0.94
Source: Adapted from Jay (1992).
Pseudomonas
1
S.aureus
0.9
E.coli
0.8
B.subtilis
0.7
C.botulinum
0.6
0.5 E.aerogenes
0.4 Mucor
0.3 Rhizopus
0.2 Botyritis
0.1 Aspergillus
0 Penicillum
Pseudomonas
S.aureus
E.coli
B.subtilis
Mucor
C.botulinum
E.aerogenes
Rhizopus
Botyritis
Aspergillus
Penicillum
Figure 1.1. Graphical representation of
aW values of various microbes.
and results in decreased growth rate and size of final accumulate polyhydric alcohols (Troller, 1986). Mi-
population (Wodzinsky and Frazier, 1961). Lowering crobes thus attempt to compensate for increased
of water activity builds up stress and exerts adverse stress by accumulating compatible solutes.
influence on all vital metabolic activities that require
aqueous environment. Charlang and Horowitz (1974)
Redox Potential/Redox Poising Capacity
observed the appearance of non-lethal alterations in
cell membrane permeability of Neurospora crassa The type of microbial growth depends upon oxidation
cells resulting in loss of various essential molecules, and reduction power of the substrate. The oxidation–
as the dynamic cell membrane should remain in fluid reduction potential of a substrate may be defined as
state. the ease with which the substrate loses or gains elec-
The exception to normal aw requirements are ba- trons and, in turn, gets oxidized or reduced, respec-
sically the halophilic bacteria that grow under low tively. Aerobic microbes require oxidized (positive
aw values by accumulating potassium ions in the Eh values) substrates for growth and it is reverse for
cell (Csonka, 1989), while osmophilic yeasts concen- the anaerobes (Walden and Hentges, 1975). The fruits
trate polyols as osmoregulators and enzyme protec- contain sugars and ascorbic acid for maintaining the
tors (Sperber, 1983). Brown (1976) reported proline reduced conditions, though plant foods tend to have
accumulation in response to low aw in halotolerant positive values (300–400 mV). Hence, aerobic bac-
Staphylococcus aureus strains. Xerotolerant fungi teria and molds most commonly spoil fruits and fruit
18. 1 Fruit Microbiology 7
products. The O/R potential of food can be deter- be furnished by substrate since microorganisms are
mined by unable to synthesize essential vitamins. In general,
r Characteristic pH of food
Gram-positive bacteria are least synthetic and require
r Poising capacity
supply of certain vitamins before growth, while
r Oxygen tension of the atmosphere
Gram-negative bacteria and molds are relatively in-
r Atmospheric access of food
dependent and could synthesize most of the vitamins.
Thus, these two groups of microbes grow profusely
Poising capacity could be defined as the extent to on foods relatively low in B-complex vitamins such
which a food resists externally effected changes in as fruits under the influence of usual low pH and pos-
pH that depend on the concentration of oxidizing or itive Eh values.
reducing compounds in the substrate. The capacity Each microbe has a definite range of food require-
alters the ability of the living tissues to metabolize ments, with some species having wide range and abil-
oxygen at specifically low Eh values that exist in ity to grow on a variety of substrates, while others
the vacuum-packed foods. Aerobic microbes include having narrow range and fastidious requirement al-
bacilli, micrococci, pseudomonas, and actinobacters, lowing growth on limited substrates.
and require positive Eh values, while anaerobes such
as clostridia and bacteriodes require negative Eh val-
Antimicrobial Factors
ues. However, most yeast and molds are aerobic and
few tend to be facultative anaerobes. In the presence Certain naturally occurring substances in substrate
of limited amounts of oxygen, aerobic or faculta- (food) work against the microbes, thus maintain-
tive microbes may produce incompletely oxidized or- ing stability of food; however, these are directed to-
ganic acids. Processing procedures such as heating or ward a specific group of microorganism and have
pasteurization, particularly of fruit juices, make mi- weak activity. Song et al. (1996) reported that the
crobes devoid of reducing substances, but favorable presence of aroma precursor Hexal readily gets con-
for the growth of yeasts. verted to aroma volatiles in vivo by fresh-cut apple
slices. Hexal acts as antibrowning agent as well as
inhibits growth of molds, yeasts, mesophilic and psy-
Available Nutrients
chrotropic bacteria (Lanciotti et al., 1999). Hexanal
Fruits as substrate act as a reservoir of sugars (source and (E)-Hexenal in modified atmosphere packaging
of energy), water, minerals, vitamins, and other (MAP) of sliced apples reduce spoilage microbe pop-
growth-promoting factors, while the protein content ulations (Corbo et al., 2000).
or nitrogen source appears to be little less in fruits. Spices contain essential oils such as eugenol
Carbohydrates include sugars or other carbon sources (clove), allicin (garlic), cinnamic aldehyde and
that act as sources of energy because breakage of eugenol (cinnamon), allyl isothiocynate (mustard),
bonds or oxidation of these compounds helps in the eugenol and thymol (sage), thymol and isothymol
formation of energy currency of cell or ATP. (oregano) that have antimicrobial activity (Shelef,
Microorganisms have varied nutrient require- 1983). Buta and Molin (1998) observed reduction
ments, which are influenced by other conditions such in mold growth on fresh-cut peppers by exogenous
as temperature, pH and Eh values. The microbes be- application of methyl jasmonate.
come more demanding at decreased temperatures, The antimicrobial compounds may originally be
while under optimum temperature conditions, nutri- present in food, added purposely or developed by
ents control the microbial growth only when present associated microbial growth, or by processing meth-
in limiting quantities. Thus, microorganisms that ods. Certain antifungal compounds applied to fruits
grow on a product become the best-suited by ex- include benomyl, biphenyl, and other phenylic com-
ploiting the product, as pectinolytic bacteria such as pounds that exist in small quantities as by-product of
Erwinia cartovora, Pseudomonas sp., or pectinolytic phenol synthesis pathways. Beuchat (1976) observed
molds grow best on fruits and vegetables. that essential oils of oregano, thyme, and sassafras
Nitrogen requirement is usually fulfilled by pro- have bacteriocidal activity, at 100 ppm, to V. para-
teolysis of protein present in substrate and the use haemolyticus in broth, while cinnamon and clove oils
of amino acids, nucleotides, certain polysaccharides, at 200–300 ppm inhibit growth and aflatoxin pro-
and fats under usual microbe-specific conditions. duction by Aspergillus parasiticus (Bullerman et al.,
The accessory food substances or vitamins are to 1977). The hydroxy-cinnamic acid derivatives as
19. 8 Part I: Processing Technology
p-coumaric, ferulic, caffeic, and chlorogenic acids Bacillus cereus, Staphylococcus aureus, and
and benzoic acid in cranberries have antibacterial Clostridium perfringens. There exists a relation
and antifungal activities and are present in most plant of temperature to growth rate of microorganisms
products including fruits. between minimum and maximum temperature range
by (Ratowsky et al., 1982)
√
Extrinsic Factor r = b(T − T0 ),
Extrinsic factors include parameters imposed from where r is the growth rate, b is the slope of regres-
the external environment encountered during storage sion line, and T0 is the conceptual temperature of no
that affect food, and the microbes that tend to develop metabolic significance.
on it. These factors include the following.
Relative Humidity of Environment
Temperature of Storage
Success of a storage temperature depends on the rel-
Microbes grow over a wide range of temperature, and ative humidity of the environment surrounding the
change in temperature at both extremes lengthens the food. Thus, relative humidity affects aw within a pro-
generation time and lag periods. The range is quite cessed food and microbial growth at surfaces. A low
wide from −34◦ C to 90◦ C, and according to range aw food kept at high R.H. value tends to pick up mois-
microbes could be grouped as follows. ture until the establishment of equilibrium, and foods
with high aw lose moisture in a low-humidity envi-
Psychrotrophs. These microorganisms grow well
ronment. Fruits and vegetables undergo a variety of
at 7◦ C or below 7◦ C with the optima ranging
surface growth by yeasts and molds as well as bac-
from 20◦ C to 30◦ C. For example, Lactobacillus,
teria, and thus are liable to spoilage during storage
Micrococcus, Pseudomonas, Enterococcus, Psy-
at low R.H. conditions. However, this practice may
chrobacter, Rhodotorula, Candida and Saccha-
cause certain undesirable attributes such as firmness
romyces (yeasts), Mucor, Penicillum, Rhizopus
and texture loss of the climacteric (perishable) fruits
(molds) and Clostridium botulinum, Listeria mono-
calling for the need of altered gas compositions to re-
cytogenes, Yersinia enterocolitica, Bacillus cereus
tard surface spoilage without lowering R.H. values.
(pathogenic psychrotrophs). The group of microbes
that grow from −10◦ C to 20◦ C with the optima of
10–20◦ C are included as Psychrophiles and include Modified Atmosphere Storage
certain overlapping genera mentioned above.
Altering the gaseous composition of the environ-
Mesophiles. These include microbes growing best ment that retards the surface spoilage without re-
between 20◦ C and 45◦ C with optimum range of ducing humidity includes the general practice of in-
30–40◦ C. For example, Enterococcus faecalis, Strep- creasing CO2 (to 10%) and is referred as “controlled
tococcus, Staphylococcus, and Leuconostoc. or modified atmosphere” (MA). MA retards senes-
cence, lowers respiration rates, and slows the rate of
Thermophiles. Microbes that grow well above tissue softening or texture loss (Rattanapanone and
45◦ C with the optima ranging between 55◦ C and Watada, 2000; Wright and Kader 1997a; Qi et al.,
65◦ C and with maximum of above 60–85◦ C are 1999). MA storage has been employed for fruits
known as thermotolerant thermophiles. For exam- (apples and pears) with CO2 applied mechanically
ple, Thermus sp. (extreme thermophile), Bacillus or as dry ice, and this retards fungal rotting of fruits
sternothermophilus, Bacillus coagulans, Clostrid- probably by acting as competitive inhibitor of ethy-
ium thermosaccharolyticum are endospore-forming lene action (Gil et al., 1998; Wright and Kader
thermotolerants and grow between 40◦ C and 60◦ C 1997b).
and create major problems in the canning industry. The inhibitory effect increases with decrease in
temperature due to increase in solubility of CO2 at
Thermotrophs. This group includes microbes lower temperatures (Bett et al., 2001). Elevated CO2
similar to mesophiles but grows at slightly higher levels are generally more microbiostatic than micro-
temperature optima and includes pathogenic bac- biocidal probably due to the phenomena of catabo-
teria in foods. For example, Salmonella, Shigella, lite repression. However, an alternative to CO2 ap-
enterovirulent E. coli, Campylobacter, toxigenic plication includes the use of ozone gas at a few ppm
20. 1 Fruit Microbiology 9
concentration that acts as ethylene antagonist as well targeted toward inhibition of a narrow spectrum
as a strong oxidizer that retards microbial growth. of microbes. Other bacteriocins produced by lac-
Sarig et al. (1996) and Palou et al. (2002) reported tic acid bacteria include lactococcins, lacticins,
control of postharvest decay of table grapes caused by lactacins, diplococcin, sakacins, acidophilocins, pe-
Rhizopus stolonifera. A similar report on effect of diocins, and leuconosins. As an inhibitor of spore-
ozone and storage temperature on postharvest dis- forming Clostridium spp., which cause cheese blow-
eases of carrots was observed by Liew and Prange ing due to undesirable gas production, nisin was the
(1994). In general, gaseous ozone introduction to first bacteriocin produced by lactic acid bacteria to
postharvest storage facilities or refrigerated shipping be isolated and approved for use in cheese spreads.
and temporary storage containers is reported to be op- Although mostly active against Gram-positive bacte-
timal at cooler temperatures and high relative humid- ria, bacteriocins can be microbiocidal under certain
ity (85–95%) (Graham, 1997). The most reproducible conditions, even toward Gram-negative bacteria and
benefits of such storage are substantial reduction of yeasts, provided that their cell walls have been sen-
spore production on the surface of infected produce sitized to their action. The antimicrobial action of
and the exclusion of secondary spread from infected nisin and of similar bacteriocins is believed to in-
to adjacent produce (Kim et al., 1999; Khadre and volve cell membrane depolarization leading to leak-
Yousef, 2001). age of cellular components and to loss of electrical
Ozone treatment has been reported to induce pro- potential across the membrane. Propioniobacterium
duction of natural plant defense response compounds produces propionic acid that has inhibitory effect
involved in postharvest decay resistance. Ozone de- on other bacteria. Certain microorganisms may pro-
struction of ethylene in air filtration systems has been duce wide spectrum antimicrobial substances or sec-
linked to extended storage life of diverse ethylene- ondary metabolites capable of killing or inhibiting
sensitive commodities. wide range of microbes called “antibiotics.” How-
ever, growth of one kind of microbe could lead to
lowering of pH of substrate, making the environ-
Implicit Factors
ment unsuitable for other microbes to grow, while
Implicit factors include the parameters depending organic acid production or hydrogen peroxide for-
on developing microflora. The microorganisms while mation could also interfere with the growth of back-
growing in food may produce one or more inhibitory ground microbial population (Jay, 1992).
substances such as acids, alcohols, peroxides, and
antibiotics that check the growth of other microor-
Biofilm Formation
ganisms.
Most of the Gram-negative bacteria exhibit quorum
sensing or the cell-to-cell communication phenom-
General Interference
ena that leads to the formation of a multicellular
This phenomena works when competition occurs be- structure in the life of a unicellular prokaryote that
tween one population of microbes and another re- provides protection to bacterial species from the dele-
garding the supply of the same nutrients. Normal terious environment by precipitation. Adoption of
microflora of fresh produce helps prevent the col- biofilm formation involves release of autoinducers,
onization of pathogens and succeeds in overcoming particularly called the N-acyl homoserine lactones
the contaminant number by overgrowth and efficient that either activate or repress the target genes in-
utilization of available resources. volved in biofilm formation (Surette et al., 1999).
Quorum sensing has a profound role in food safety in
association with behavior of bacteria in food matrix
Production of Inhibitory Substances
and regulates prime events such as spore germina-
Some microbes can produce inhibitory substances tion, biofilm formation on surfaces (Frank, 2000b),
and appear as better competitors for nutrient sup- and virulence factor production. Cells in biofilm are
ply. The inhibitory substances may include “bac- more resistant to heat, chemicals, and sanitizers due
teriocins,” the commonest being “nisin” produced to diffusional barrier created by biomatrix as well as
by certain strains of Lactobacillus lactis, which is very slow growth rates of cells in biofilms (Costerton,
heat stable, attached by digestive enzymes, labile 1995). Morris et al. (1997) have reported certain
and non-toxic for human consumption, and is quite methods for observing microbial biofilms directly
21. 10 Part I: Processing Technology
on leaf surfaces and also to recover the constituent the causative agent to other fruits. The postharvest
microbes for isolation of cultivable microorganisms. rots are most prevalent in fruits, particularly the dam-
Thus, biofilm formation has been emerging as a chal- aged or bruised ones (Sanderson and Spotts, 1995;
lenge for the decontamination techniques routinely Bachmann and Earles, 2000). The processing meth-
used in the food and beverage industries, and requires ods involve the use of temperature, moisture content,
the advent of new revolutionary methods for decon- and ethylene control, thus include the extrinsic pa-
tamination or the modification of the older techniques rameters discussed earlier.
in vision of the current scenario (Frank, 2000a).
FRUIT SPOILAGE
FACTORS AFFECTING
The fruit spoilage is manifested as any kind of phys-
MICROBIAL QUALITY
ical change in color or flavor/aroma of the product
AND FRUIT SPOILAGE
that is deteriorated by microflora that affects the cel-
From quality standpoint, the fresh fruits and the pro- lulose or pectin content of cell walls which, in turn,
cessed fruit products should possess certain charac- is the fundamental material to maintain the structural
teristics such as fresh-like appearance, taste, aroma, integrity of any horticultural product. Fresh fruits
and flavor that should be preserved during stor- possess more effective defense tactics including the
age. Thus, if the primary quality attributes of pro- thicker epidermal tissue and relatively higher con-
duce remain unoffended, the shelf-life characteristics centration of antimicrobial organic acids. The higher
lengthen. As discussed before, fruits possess normal water activity, higher sugar content, and more acidic
microflora as well as the microflora that is added dur- pH (<4.4) of fresh fruits favor the growth of xero-
ing the handling and postharvest processing of fruits, tolerant fungi or osmophilic yeasts. Lamikarna et al.
though harsh treatments during processing can kill or (2000) have reported bacterial spoilage in neutral pH
inhibit certain or most of the microflora while letting fruits.
specific types to become predominant and prevail in Normal microflora of fruits is diverse and includes
the finished product. A variety of factors that affect bacteria such as Pseudomonas, Erwinia, Enterobac-
the microbial quality of fruits include the following. ter, and Lactobacillus sp. (Pao and Petracek, 1997),
and a variety of yeasts and molds. These microbes
remain adhered to outer skin of fruits and come from
Preharvest Factors
several sources such as air, soil, compost, and insect
These factors basically involve production practices infestation. Brackett (1987) reported inoculation of
that have tremendous explicit effect on the micro- Rhizopus sp. spores by egg laying in ruptured epi-
bial quality of fruits. Management practices can af- dermal fissures of fruits by Drosophila melanogaster
fect product quality since stressed produce or me- or the common fruit fly. The microbial load of the
chanical injuries permit microbial contamination. fresh produce could be reduced by rinsing with water
Mold growth and decay on winter squash caused by (Splittstoesser, 1987). However, the source and qual-
Rhizoctoina result from fruits lying on the ground. ity of water dictate the potential for human pathogen
Food safety begins in field as a number of food- contamination upon contact with the harvested pro-
borne disease outbreaks have potential sources in duce.
field that contaminate the fresh produce such as Lund and Snowdon (2000) reported certain com-
the use of partially treated manure, irrigation with mon molds to be involved in fruit spoilage such
livestock-used farm pond water, or storage near as Penicillum sp., Aspergillus sp., Eurotium sp.,
roosting birds (Trevor, 1997). Wallace et al. (1997) Alternaria sp., Cladosporium sp., and Botrytis
reported the presence of verocytotoxin producing cinerea of fresh and dried fruits (Fig. 1.2), while
E. coli O157:H7 from wild birds. certain molds producing heat-resistant ascospores
or sclerotia such as Paecilomyces fulvus, P. niveus,
Aspergillus fischeri, Penicillum vermiculatum, and
Postharvest Handling
P. dangeardii were observed to cause spoilage of
and Processing
thermally processed fruits or the fruit products
Improper or harsh handling of produce causes skin exhibiting characteristic production of off-flavors,
breaks, bruises, or lesions leading to increased visible mold growth, starch and pectin solubilization,
chances of microbial damage. Handlers picking fresh and fruit texture breakdown (Beuchat and Pitt, 1992;
produce with skin lesions could potentially transfer Splittstoesser, 1991).
22. 1 Fruit Microbiology 11
tive external protective system, thus causing active
invasion and active spoilage in fruits. The degrada-
tive enzyme brigade includes the following.
Pectinases
These enzymes depolymerize the pectin, which is a
polymer of ␣-1, 4-linked d-galactopyranosyluronic
acid units interspersed with 1, 2-linked rhamnopy-
ranose units. On the basis of site and type of reac-
tion on the pectin polymer, pectinases are of three
main types, i.e., pectin methyl esterases produced
by Botrytis cinerea, Monilinia fructicola, Penicillum
citrinum, and Erwinia cartovora (Cheeson, 1980),
polygalacturonase, and pectin lyase.
Figure 1.2. Degradation of fruit texture due to growth
of cellulase/pectinase-producing bacteria followed by
fungal growth. Cellulases
Several types of cellulase enzymes attack the na-
tive cellulose and cleave the cross-linkage between
-d-glucose into shorter chains. Cellulases con-
Fruit safety risks could be increased by certain tribute toward tissue softening and maceration as well
spoilage types that create microenvironments suit- as yield glucose, making it available to opportunistic
able for the growth of human pathogens as the pri- microflora.
mary spoilage by one group of phytopathogens pro-
duces substances required for nurturing growth and Proteases
development of human pathogens. Wade and Beuchat
(2003) have well documented the crucial role of pro- These enzymes degrade the protein content of fresh
teolytic fungi and the associated implications on the produce giving simpler units of polypeptides, i.e.,
changes in pH of the pericarp of the decayed and amino acids. The action of proteases is limiting in
damaged raw fruits in survival and growth of various fruit spoilage as fruits are not rich in proteins.
foodborne pathogens. Botrytis or Rhizopus spoilage
of fruits could help create environment for the prolif- Phosphatidases
eration of Salmonella enterica serovar typhimurium
These enzymes cleave the phosphorylated com-
(Wells and Butterfield, 1997), while Dingman (2000)
pounds present in cell cytoplasm and the energy re-
observed the growth of E. coli 0157:H7 in bruised
leased is utilized to cope with the increased respira-
apple tissues. Similar reports of Riordan et al. (2000)
tion rates.
and Conway et al. (2000) depicted the impact of prior
mold contamination of wounded apples by Penicil-
lum expansum and Glomerella cingulata on survival Dehydrogenases
of E. coli 0157:H7 and Listeria monocytogenes. These enzymes dehydrogenate the compounds, thus
Technically, the fresh produce deteriorating mi- increasing the amount of reduced products that may
croflora is diverse and remains on surface skin of lead to increased fermentation reaction under mi-
fruits, and the basis of invasion process could be of croaerobic/anaerobic conditions.
two types.
Opportunistic Pathogens
True Pathogens
These microorganisms lack the degradative enzyme
These microbes possess ability to actively infect plant brigade and thus gain access only when the normal
tissues as they produce one or several kinds of cellu- plant product defense system weakens, which is the
lytic or pectinolytic and other degradative enzymes situation of mechanical injury or cuticular damage
to overcome tough and impervious outer covering of caused by the insect infestation or by natural openings
fruits which acts as the first and the foremost effec- present on the surface of the fresh produce. Thus,
23. 12 Part I: Processing Technology
MODES OF FRUIT SPOILAGE
Fruit spoilage occurs as a result of relatively strong
interdependent abiotic and biotic stresses posed par-
ticularly during the postharvest handling of produce
(Fig. 1.5). Harvested fruits continue to respire by uti-
lizing the stored available sugars and adjunct organic
acids culminating to significant increase in stress-
related/stress-induced carbon dioxide and ethylene
production that leads to rapid senescence (Brecht,
1995). Moreover, postharvest processing that in-
volves washing, rinsing, peeling, and other treat-
ments result in major protective epidermal tissue
damage and disruption which in turn leads to un-
Figure 1.3. Growth of Aspergillus on surface of apple sheathing of the vacuole-sequestered enzymes and
fruits visible due to formation of spores. related substrates and their amalgamation with the cy-
toplasmic contents. Cutting/dicing increases the aw
and surface area as well as stress-induced ethylene
an opportunistic pathogen slips in through the dam- production which accelerates the water loss, while the
age caused by biotic and abiotic stresses on the pro- sugar availability promptly invites enhanced micro-
duce and generally involves movement via natural bial invasion and rapid growth (Wiley, 1994; Watada
gateways as the lenticels, stomata, hydathodes, or and Qi, 1999). The physiological state of fruit also
the other pores/lesions caused by insect infestation determines the pattern of spoilage to be followed as
or invasion by true pathogens. Damage of the prod- with increase in age/maturity, the normal defense
uct during harvesting or by postharvest processing tactics of the plant produce deteriorates. Harvested
techniques and equipments enables opportunistic mi- produce loses water by transpiration, thus gets de-
croflora to invade the internal unarmed tissue and hydrated, followed by climacteric ripening, enzy-
causes spoilage (Fig. 1.3). matic discoloration of cut surfaces to senescence,
Hence, spoilage connotes any physical change in thus increasing possibilities of damage by microflora
color, taste, flavor, texture, or aroma caused by micro- (Fig. 1.6). Harsh handling and ill-maintained equip-
bial growth in fruit/fruit product, thereby resulting in ment during processing lead to increased damage or
product that becomes unacceptable for human con-
sumption (Fig. 1.4).
Figure 1.4. Fungal hyphae and spores of Aspergillus Figure 1.5. White hyphal mass of Aspergillus
niger on guava fruits. fumigatus on surface of orange fruit.
24. 1 Fruit Microbiology 13
Abiotic forces Biotic forces
Damage by Damage by external Preharvest Postharvest
State of sources insect damage by
produce infestation microbes
damage
pH wind blown sand lesions invasion
water activity rubbing egg-laying fermentation
transpiration harvesting degradative
ethylene processing enzymes
production procedures damage of
and outer
senescence equipments layer
INTERNAL TISSUE INVASION
PHYSICAL CHANGES IN PRODUCE
RAPID SOFTENING OF PRODUCE
SHRINKAGE OF PRODUCE
DECAY
DECREASED SHELF LIFE OF PRODUCE
Figure 1.6. Modes of fruit spoilage and factors responsible for spoilage.
removal of the outer cuticle leading to tissue disrup- grow faster than the molds and this usually includes
tion that provokes stress-induced increased respira- the genera such as Cryptococcus, Rhodotorula, and
tion and microbial decay (Gorny and Kader, 1996). Saccharomyces sp. in fresh fruits, and Zygosaccha-
Spanier et al. (1998) reported the development of romyces rouxii, Hanseniaspora, Candida, Debary-
off-flavors in fresh-cut pineapple that appeared un- omyces, and Pichia sp. in dried fruits.
damaged physically, in lower portion of container Thus, senescence and spoilage depend on prod-
kept at 4◦ C for 7–10 days. Walls and Chuyate (2000) uct type, abiotic factors, and microbes involved in
reported survival of acid- and heat-tolerant Alicy- deterioration process, and it is convenient to de-
clobacillus acidoterrestris that produces 2-methoxy scribe spoilage on the basis of visible symptoms.
phenol or guaiacol imparting phenolic off-flavor in Thus, a customary approach is to name the spoilage
pasteurized orange and apple juices. Jay (1992) re- type by symptomatological appearance such as soft
ported osmophilic yeasts to be associated primarily rot or black rot. However, this definitely results in
with the spoilage of cut fruits due to their ability to discrepancy in ascertaining the causal pathogen of
25. 14 Part I: Processing Technology
spoilage and this ambiguity could be overruled by present in a given sample. This method ushers little
classifying on the basis of causal microbe such as value for the determination of microbiological status
Rhizopus rot, Cladosporium rot, etc. of a food sample as usually total cell counts exceed
105 cfu per g or ml of the sample. New variations
METHODS TO EVALUATE of microscopes render researchers the capability to
MICROBIAL QUALITY predict the presence of pathogens on the surfaces of
fruits clinging or attached to internal surfaces. Con-
Food quality and safety are ensured by analysis of focal scanning laser microscopy has been reported to
food for the presence of microbes, and such mi- show the presence of E. coli 0157:H7 on surfaces
crobial analyses are routinely performed as quaran- and internal structures of apple (Burnett et al.,
tine/regulatory procedures. The methods employed 2000).
for adjudging the quality of food include an array of Drawbacks: This technique suffers from a ma-
microbiological to biochemical assays to ascertain jor drawback of not providing the types of bacteria
the acceptability or unacceptability of a food prod- present in the sample as well as it does not differenti-
uct for human consumption or a processing/handling ate between the normal microflora and the pathogen-
practice that needs to be followed. Thus, enumerating causing spoilage.
the microbial load of the produce could help in de-
termining the quality as well as the related safety as-
pects of product and effectiveness of the processing
technique employed to kill spoilage microbes. Aerobic Plate Counts (APC) or Total Plate
Microbiological methods for pathogen identifica- Counts (TPC)
tion primarily involve conventional cultural tech- It is the most practical approach to determine the
niques of growing microbes on culture media and ob- presence of cultivatable microbes in a sampled food
serving the ability to form viable countable colonies product having ability to spoil food. This technique,
showing characteristic growth on such media as well thus, reveals the total number of microbes in a food
as the direct microscopic methods for various groups product under a particular set of incubation temper-
of microbes. ature, time, or culture media and can be used to pref-
Hence, microbiological criteria are specifically erentially screen out a specific group of microbes,
employed to assess: thereby, helping in determining the utility of food
r Safety of food or food ingredient added for specific purpose. How-
r Shelf life of perishable products ever, the APC of the refrigerated fruits/fruit products
r Suitability of food or ingredient for specific indicate utensil or equipment conditions prevailing
purpose during storage and distribution of the product.
r Adherence to general manufacturing practices Drawbacks: Though APC bacterial count is the
most practical and easy technique, it suffers from
The routine culturing techniques require longer certain inherent drawbacks as listed below:
time to obtain results. To overcome this hurdle, r It provides the viable cell count that does not
nowadays, use of indicator organisms that provide
rapid, simple, and reliable information without the reflect the quality of raw material used for
requirement of isolation and identification of specific processing.
r It is unable to record the extent of quality loss at
pathogens is performed. However, such tests could be
used as the presumptive ones with the confirmation low count levels.
r It provides negligible information regarding
provided by a battery of biochemical tests, and may
include specialized serological typing also (Swami- organoleptic quality that is degraded at low
nathan and Feng, 1994). The microbiological tech- counts.
r It requires scrupulous researcher to interpret APC
niques could be summarized as follows.
results.
Conventional Techniques Certain variations to APC method are now available
to classify according to the types of microbes as
Direct Microscopic Count
molds, yeasts, or thermophilic spore counts. These
This method involves the microscopic examination counts are basically used for microbiological analy-
for evaluating the viable or non-viable microbes sis of the canned fruits/fruit products.
26. 1 Fruit Microbiology 15
1. Howard Mold Count. This technique involves the formats and diverse technologies that are quite spe-
enumeration of molds in products such as the cific and more sensitive (Mermelstein et al., 2002).
canned fruits and provides the inclusion of the Some of the assays involved in the rapid enumeration
moldy material. of pathogens in food samples are as follows.
2. Yeasts and Mold Counts. The high sugar prod-
ucts such as fruit drinks or fruit beverages are
Modification of Conventional Techniques
prone to contamination and overgrowth by yeasts
and molds more than the bacterial counterparts r Miniaturized Biochemical Assays: The use of
and thus enumeration of these microbes gives the certain biochemical test kits for identification of
presumptive glimpse of the microbiological status pure cultures of bacterial isolates delivers results
of the product. A similar kind of count involves in less than 1 day with high accuracy of 90–99%
the heat-resistant mold count providing the pres- comparable to conventional techniques making
ence of molds such as Aspergillus fischeri and the procedure simpler, cost- and
Byssochlamys fulva in heat-processed fruit prod- performance-effective (Hartman et al., 1992).
ucts such as the fruit concentrates. r Modified Process/Specialized Media: Use of
3. Thermophilic Spore Count. The technique again petrifilms (Curiale et al., 1991) and hydrophobic
advocates the presence of spore-forming bacteria grid membrane filters eliminates the need for
as the major contaminants of canned fruits, fruit media preparation, thus economizes storage and
beverages, and fruit juices that are being thermally incubation space as well as simplifies disposal
processed by pasteurization and thus specifically after analysis while the use of chromogenic
enriches the spore-forming genera. (ONPG/X-gal) or fluorogenic (MUG/GUD)
substances provides quick measure of specific
enzyme activities to quickly ascertain the
New Methods for Rapid Analysis presence of a specific microbe, and the
The physical characteristics of food result in non- bioluminescence assays provide quick assessment
uniform distribution of microbes and thus such a non- of direct live cell counts with sensitivity to provide
uniform homogenate results in inconsistent presence results with low counts within few minutes.
of specific pathogen providing non-reproducible re-
sults following the analysis of the same sample. Thus,
DNA-Based Assays
the drawbacks of the conventional microbiological
analysis criteria are: Use of DNA probes technically fishes out the tar-
r Requirement of the selective or enrichment media get gene sequence specific to a particular pathogenic
microbe in the concoction of sample DNA obtained
for isolation of foodborne pathogen suffers from
from the food sample with unique sensitivity and
involvement of several days to provide results.
r Normal microflora interferes with the isolation reproducibility, and has been developed for detec-
tion of most of the foodborne pathogens (Guo et al.,
and identification protocols of low infectious dose
2000; Feng et al., 1996; Lampel et al., 1992; Saiki
and low number pathogens that may be
et al., 1988; Schaad et al., 1995). However, if the
sub-lethally injured during the accomplishment of
target DNA contains several targets, then PCR as-
a variety of processing procedures employed.
says can be used in a multiplex format that ensures
These microorganisms that exist in state of shock
the elimination of culturing steps prior to produc-
after vigorous heat/chemical/radiation treatments
ing the results (Chen and Griffith, 2000; Hill, 1996;
need specific enriched culture media to overcome
Jones and Bej, 1994). PCR protocols can detect very
the shock (Jiang and Doyle, 2003). Thus, unless
small number/few cells of particular pathogens and
the injured cells could resuscitate, they could be
have been successfully developed for various fas-
easily outgrown by other bacteria in the sample.
tidious/uncultivatable pathogens (Guo et al., 2000,
Zhao and Doyle (2001) have reported the use of a
2002). DNA fingerprinting methods are the most re-
universal pre-enrichment broth for growth of
cent ones for the detection of pathogens in fresh pro-
heat-injured pathogens in food.
duce and a semi-automated fluorescent AFLP tech-
Hence, these rapid methods shorten the assay time nique for genomic typing of E. coli 0157:H7 has
by a simple modification of conventional methods been developed (Zhao et al., 2000). Another report of
or may also involve an array of molecular assay occurrence of Acidovorax avenae subsp. citrulli in