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Food Microbiology and Food Safety
Series Editor
Michael P. Doyle
Center of Food Safety, University of Georgia, Griffin, GA, USA
For other titles published in this series, go to
http://www.springer.com/series/7131
FOOD MICROBIOLOGY AND FOOD SAFETY SERIES
Food Microbiology and Food Safety publishes valuable, practical, and timely
resources for professionals and researchers working on microbiological topics
associated with foods, as well as food safety issues and problems.
Series Editor
Michael P. Doyle, Regents Professor and Director of the Center for Food Safety,
University of Georgia, Griffith, GA, USA
Editorial Board
Francis F. Busta, Director, National Center for Food Protection and Defense,
University of Minnesota, Minneapolis, MN, USA
Bruce R. Cords, Vice President, Environment, Food Safety & Public Health,
Ecolab Inc., St. Paul, MN, USA
Catherine W. Donnelly, Professor of Nutrition and Food Science, University of
Vermont, Burlington, VT, USA
Paul A. Hall, President, AIV Microbiology and Food Safety Consultants, LLC,
Hawthorn Woods, IL, USA
Ailsa D. Hocking, Chief Research Scientist, CSIRO—Food Science Australia,
North Ryde, Australia
Thomas J. Montville, Professor of Food Microbiology, Rutgers University, New
Brunswick, NJ, USA
R. Bruce Tompkin, Formerly Vice President-Product Safety, ConAgra Refrigerated
Prepared Foods, Downers Grove, IL, USA
Titles
Compendium of the Microbiological Spoilage of Foods and Beverages, William
Sperber and Michael Doyle (Eds.) (2009)
Effective Risk Communication, Timothy Sellnow, Robert Ulmer, et al. (2009)
Food Safety Culture, Frank Yiannas (2008)
Molecular Techniques in the Microbial Ecology of Fermented Foods, Luca Cocolin
and Danilo Ercolini (Eds.) (2008)
Viruses in Foods, Sagar M. Goyal (Ed.) (2006)
Foodborne Parasites, Ynes R. Ortega (Ed.) (2006)
PCR Methods in Foods, John Maurer (Ed.) (2006)
William H. Sperber · Michael P. Doyle
Editors
Compendium of the
Microbiological Spoilage
of Foods and Beverages
Foreword by R. Bruce Tompkin
1 3
Editors
William H. Sperber
Cargill, Inc.
Corp. Food Safety & Reg. Affairs
5814 Oakview Circle
Minnetonka MN 55345
USA
bill_sperber@cargill.com
Michael P. Doyle
University of Georgia
Center of Food Safety
1109 Experiment Street
Griffin GA 30223
Melton Building
USA
mdoyle@cfs.griffin.peachnet.edu
ISBN 978-1-4419-0825-4 e-ISBN 978-1-4419-0826-1
DOI 10.1007/978-1-4419-0826-1
Springer New York Dordrecht Heidelberg L ondon
Library of Congress Control Number: 2009929307
© Springer Science+Business Media, LLC 2009
All rights reserved. This work may not be translated or copied in whole or in part without the written
permission of the publisher (Springer Science+Business Media, LLC, 233 Spring Street, New York,
NY 10013, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in
connection with any form of information storage and retrieval, electronic adaptation, computer software,
or by similar or dissimilar methodology now known or hereafter developed is forbidden.
The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are
not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject
to proprietary rights.
Printed on acid-free paper
Springer is part of Springer Science+Business Media (www.springer.com)
Foreword
The increased emphasis on food safety during the past two decades has decreased
the emphasis on the loss of food through spoilage, particularly in developed coun-
tries where food is more abundant. In these countries spoilage is a commercial issue
that affects the profit or loss of producers and manufacturers. In lesser developed
countries spoilage continues to be a major concern. The amount of food lost to
spoilage is not known. As will be evident in this text, s tability and the type of
spoilage are influenced by the inherent properties of the food and many other factors.
During the Second World War a major effort was given to developing the tech-
nologies needed to ship foods to different regions of the world without spoilage.
The food was essential to the military and to populations in countries that could not
provide for themselves. Since then, progress has been made in improved product
formulations, processing, packaging, and distribution systems. New products have
continued to evolve, but for many new perishable foods product stability continues
to be a limiting factor. Many new products have failed to reach the marketplace
because of spoilage issues.
Disruptions in the food supply are more severely felt by countries that depend
on readily available low-cost food. For example, the increased diversion of corn
to produce fuel, in combination with other factors, led to higher food prices after
2007 and reduced the ability of international agencies with limited budgets, e.g., the
Food and Agriculture Organization, to provide food assistance. In addition, certain
countries limited exports to ensure a stable food supply for their populations. This
experience demonstrates the dependence of many countries on assistance to bolster
their f ood supply and the significance of barriers to international trade.
The world’s population continues to increase. In 1960, 1980, and 2000 the pop-
ulation was estimated to be 3.0, 4.5, and 6.1 billion, respectively. It is projected to
reach 6.9 and 9.5 billion by 2010 an 2050, respectively.
1
To provide for the popula-
tion increase, improvements in food production and protection against spoilage will
be required.
1
U. S. Census Bureau. (2008). International database. Total midyear population for the world:
1950–2050. Accessed on 24 September 2008. http://www.census.gov/ipc/www/idb/worldpop.
html
v
vi Foreword
Food production, processing, and distribution s ystems generally fall into two
categories: large or small scale. Large-scale systems incorporate new technologies
more quickly and can lead to innovations that bring products of greater variety and
convenience to consumers. This segment of the industry is generally more highly
regulated and its suppliers are frequently audited by large corporations. Proper
coding and inventory control is essential to minimize product loss due to spoilage.
Sell-by or use-by dates are commonly applied to indicate the date the food will be
acceptable and to facilitate traceability. Larger companies strive to improve con-
trol of their incoming raw materials and processing and packaging conditions to
ensure compliance with their code-dating procedures and in some cases further
delay spoilage. Products that exceed the sell-by or use-by dates are discarded by
retailers. The amount discarded is documented by the retailer and can influence
future negotiations between supplier and retailer. Continued spoilage problems can
lead retailers and others to discontinue the item.
Manufacturers may apply special procedures that enable them to meet the
expected demand for their perishable products at certain holidays. For example, this
could involve accumulating and holding certain perishable foods at temperatures
closer to freezing. As the holiday approaches, the food is released for shipment to
retailers. Success requires knowledge of the product, the impact of lowering storage
temperature on microbial growth, and validation that the procedure will be success-
ful. Failure to validate the procedures can lead to significant financial losses during
a critical season and temporary loss of consumer confidence.
Another characteristic of large-scale systems is that processing occurs in fewer
facilities and the products are shipped longer distances. While this may be econom-
ically beneficial for the manufacturer, greater control must be exercised to transfer
food from the manufacturer to the ultimate user without spoilage.
Considerable advances have been made in delaying or preventing spoilage. For
example, this writer spent about 40% of his time solving spoilage issues associated
with raw and cooked perishable meat and poultry products from the mid-1960s to
the early 1990s. The collective effect of the improvements, for example, in pro-
cessing conditions, formulation, packaging, control of temperature, and efforts to
control Listeria and Salmonella reduced this time to well below 5%.
It is of interest that as the quantity of foods produced on a larger scale has
increased, there is a desire by some consumers to return to foods produced on a
smaller, more local scale. This desire is based on the perception that the foods are
fresher, less processed, and more wholesome. It has not been documented, how-
ever, whether this approach results in a greater or lesser amount of food lost through
spoilage on a worldwide basis.
Smaller scale systems are slower to accept and may even reject new technologies.
The smaller businesses generally lack the technical knowledge and support available
in larger companies. Thus, it is not surprising that many of the authors are involved
with large companies and have collaborated with other experts in preparing this text.
LaGrange, IL, USA R. Bruce Tompkin
Preface
Protection of foods and beverages from microbiological spoilage is essential to
assure an adequate food supply for the world’s population. Several generations of
food microbiologists have labored to understand food spoilage and to develop con-
trol procedures for its prevention. Because many of these highly experienced food
microbiologists are at or near retirement age, we were motivated to organize this
Compendium in an effort to document and preserve as much of their accumulated
knowledge and wisdom as possible. We are pleased that many expert food micro-
biologists eagerly agreed to contribute to this effort. To our knowledge, this is the
first reference and textbook focused exclusively on t he microbiological spoilage of
foods and beverages.
We also think that this Compendium is necessary now because t he resources of
the food industry and academia have increasingly become focused on food safety
initiatives over the past 30 years. To a significant extent, resources previously avail-
able to develop an understanding and the means to control food spoilage have
been shifted into food safety programs. The emergence of prominent foodborne
pathogens, such as Escherichia coli O157:H7, Listeria monocytogenes, and Campy-
lobacter, combined with increased competition for limited financial resources, has
resulted i n decreased attention being given to food spoilage research. Global public
health issues such as bovine spongiform encephalopathy and avian influenza H5N1,
and their potential impacts on the food supply, have further reinforced the shift
toward “mission-oriented” research. The increased number of potential microbio-
logical food safety issues affecting the food supply also fueled a substantial increase
in the number of food safety regulations and policies, both at the national and the
international levels. Moreover, food regulatory actions are almost always related to
food safety controls and requirements, thereby commanding a larger share of the
food industry’s technical resources to assure regulatory compliance.
The shift in emphasis from food quality research toward various types of food
safety programs is understandable and necessary. This shift, however, is not as coun-
terproductive for food quality and spoilage research as might first be suspected. The
implementation of numerous new food safety control procedures and regulations
can also help to reduce food spoilage and protect product quality through its shelf
life as they also provide greater assurance of food safety. For example, pasteur-
ization treatments intended to eliminate pathogens in raw milk also significantly
vii
viii Preface
enhance the quality and shelf life of fluid milk. In fact, the unanticipated enhance-
ment of product quality was a very strong selling point in gaining the food industry’s
acceptance of the hazard analysis and critical control point (HACCP) system of food
safety management in the 1970s. Because of t he successful development of HACCP,
there remains today a very strong link between food quality and food safety control
measures.
We are further motivated to develop this Compendium because, ultimately, the
control of food spoilage means more than simply providing high quality, convenient,
processed foods for consumption in economically developed regions of the world.
We must think about feeding people in every region of the world. Food spoilage is
a significant threat to food security, our ability to provide an adequate food supply
to a large and increasing global human population. Shrinking fossil fuel and water
reserves, soil erosion, loss of soil fertility, climate change, and political uncertainty
are important factors that collectively threaten food security. If food spoilage and
other factors that contribute to the waste of food could be substantially reduced,
we would be able to feed more people without increasing primary food produc-
tion. In the opinion of a former World Health Organization official, “This large
increasing world population needs food and we have a moral obligation t o utilize
all our skills and technologies to increase not only food production but also to limit
food spoilage (italics added for emphasis).”
1
Together with many of our colleagues,
we share Dr. Käferstein’s sense of professional responsibility. We anticipate that
this Compendium will play a role in the global reduction of food spoilage and the
accompanying enhancement of food security.
In 1958 professor William C. Frazier first published his widely used textbook,
Food Microbiology. His comprehensive yet concise explanations of food spoilage
and food safety were prominent features in the education of several generations of
food microbiologists, including this Compendium’s editors. It is our sincerest hope
that this Compendium will provide similar benefits to future generations of food
microbiologists.
Minnetonka, MN, USA William H. Sperber
Griffin, GA, USA Michael P. Doyle
1
Käferstein, F. K. (1990). Food irradiation and its role in improving food safety and the security
of food. Food Control 1, 211–214.
Contents
Foreword ................................... v
Preface .................................... vii
Contributors ................................. xi
Introduction to the Microbiological Spoilage of Foods
and Beverages ................................ 1
William H. Sperber
Microbiological Spoilage of Dairy Products ................ 41
Loralyn H. Ledenbach and Robert T. Marshall
Microbiological Spoilage of Meat and Poultry Products ......... 69
John Cerveny, Joseph D. Meyer, and Paul A. Hall
Microbiological Spoilage of Fish and Seafood Products ......... 87
Lone Gram
Microbiological Spoilage of Eggs and Egg Products ........... 121
Joseph R. Shebuski and Timothy A. Freier
Microbiological Spoilage of Fruits and Vegetables ............ 135
Margaret Barth, Thomas R. Hankinson, Hong Zhuang,
and Frederick Breidt
Microbiological Spoilage of Canned Foods ................ 185
George M. Evancho, Suzanne Tortorelli, and Virginia N. Scott
Microbiological Spoilage of Cereal Products ............... 223
Frederick K. Cook and Billie L. Johnson
Microbiological Spoilage of Beverages ................... 245
Kathleen A. Lawlor, James D. Schuman, Peter G. Simpson,
and Peter J. Taormina
Microbiological Spoilage of Acidified Specialty Products ......... 285
William H. Sperber
ix
Contributors
Margaret Barth Responsible Source, 350 Berkshire Drive, Lake Forest, IL
60045, USA, Margaret.barth@sbcglobal.net
Karen Battista Kraft Foods, 200 DeForest Avenue, East Hanover, NJ 07936,
Karen.battista@kraft.com
Frederick Breidt USDA Agricultural Research Service, 322 Shaub Hall, Box
7624, North Carolina State University, Raleigh, NC 27603, USA,
fred.breidt@ars.usda.gov
John Cerveny 17 Ridgeview Court, Apt. 7, Madison, WI 53704, USA,
jcerveny@itis.com
Frederick K. Cook Malt-O-Meal Company, 701 West 5th St, Northfield MN
55057, fred_cook@malt-o-meal.com
George M. Evancho 19693 Marimar Court, Lewes, DE 19958-3500, USA,
george_evancho@verizon.net
Timothy A. Freier Cargill, Inc., 15407 McGinty Road W., Wayzata, MN 55391,
USA, tim_freier@cargill.com
Lone Gram National Institute of Aquatic Resources, Technical University of
Denmark, Soltofts Plads Bldg 221, DK-2800 Kgs Lyngby, gram@aqua.dtu.dk
Paul A. Hall AIV Microbiology and Food Safety Consultants, LLC, 17
Tournament Drive South, Hawthorn Woods, IL 60047, USA,
paul.hall@sbcglobal.net
Thomas R. Hankinson Produce Safety Solutions, Inc., 1120 Newark Road,
Toughkenamon, PA 19374, USA, trhank@aol.com
Billie L. Johnson Menu Foods Midwest, 1400 East Logan Ave., Emporia, KS
66801, USA, bjohnson@menufoods.com
Kathleen A. Lawlor PepsiCo, Inc., 100 Stevens Avenue, Valhalla, NY 10595,
USA, kathy.lawlor@pepsi.com
xi
xii Contributors
Loralyn H. Ledenbach Kraft Foods, Inc., 801 Waukegan Road, Glenview, IL
60025, USA, lharris@kraft.com
Robert T. Marshall University of Missouri, 122 Eckles Hall, Columbia, MO
65211, USA, marshallr@missouri.edu
Joseph D. Meyer Kellogg’s, 919 Aldora Lane, Waunakee, WI 53597-3001, USA,
joseph.meyer@kellogg.com
Theodora Morille-Hinds Kraft Foods, 555 South Broadway, Tarrytown, NY
10591, USA, tmorille-hinds@kraft.com
Joan M. Pinkas McCormick & Co. Inc., 204 Wight Avenue, Hunt Valley, MD
21031, USA, joan_pinkas@mccormick.com
James D. Schuman PepsiCo, Inc., 617 Main Street, Barrington, IL 60010, USA,
jay_schuman@quakeroats.com
Virginia N. Scott U.S. Food and Drug Administration, 5100 Paint Branch
Parkway, College Park, MD. 20740, jennyscott@verizon.net
Joseph R. Shebuski Cargill, Inc., 15407 McGinty Road W., Wayzata, MN 55391,
USA, joe_shebuski@cargill.com
Peter G. Simpson The Coca-Cola Company, P. O. Box 1734, Atlanta, GA 30301,
USA, pesimpson@na.ko.com
William H. Sperber Cargill, Inc., Corp. Food Safety & Reg. Affairs, 5814
Oakview Circle, Minnetonka MN 55345, USA, bill_sperber@cargill.com
Peter J. Taormina John Morrell & Co., 805 E. Kemper Road, Cincinnati, OH
45246, USA, ptaormina@johnmorrell.com
Sterling Thompson The Hershey Company, 1025 Reese Avenue, Hershey, PA
17033, USA, sthompson@hersheys.com
Suzanne Tortorelli Campbell Soup Company, 1 Campbell Place, Camden, NJ
08103, USA, suzanne_tortorelli@campbellsoup.com
Hong Zhuang Agricultural Research Service—USDA, Russell Research Center,
950 College Station Road, Athens, GA 30605, hong.zhuang@ars.usda.gov
Introduction to the Microbiological Spoilage
of Foods and Beverages
William H. Sperber
Introduction
Though direct evidence of ancient food-handling practices is difficult to obtain and
examine, it seems safe to assume that over the span of several million years, pre-
historic humans struggled to maintain an adequate food supply. Their daily food
needed to be hunted or harvested and consumed before it spoiled and became unfit
to eat. Freshly killed animals, for example, could not have been kept for very long
periods of time. Moreover, many early humans were nomadic, continually searching
for food. We can imagine that, with an unreliable food supply, their lives must have
often been literally “feast or famine.” Yet, our ancestors gradually learned by acci-
dent, or by trial and error, simple techniques that could extend the storage time of
their food (Block, 1991). Their brain capacity was similar to that of modern humans;
therefore, some of them were likely early scientists and technologists. They would
have learned that primitive cereal grains, nuts and berries, etc. could be stored in
covered vessels to keep them dry and safer from mold spoilage. Animal products
could be kept in cool places or dried and smoked over a fire, as the controlled use
of fire by humans is thought to have begun about 400,000 years ago. Quite likely,
naturally desiccated or fermented foods were also noticed and produced routinely to
provide a more stable supply of edible food. Along with the development of agricul-
tural practices for crop and animal production, the “simple” food-handling practices
developed during the relatively countless millennia of prehistory paved the way for
human civilizations.
Less than 10,000 years of recorded history describes the civilizations that pro-
vided the numerous advances leading to our modern civilization. Chief among these
advances were the development of agricultural and food preservation technologies
that permitted large human populations to live permanently in one place and use
their surplus time to develop the other technologies we enjoy today, such as writing
W.H. Sperber (B)
Cargill, Inc., Food Safety & Reg. Affairs, 5814 Oakview Circle, Minnetonka, MN 55345, USA
e-mail: bill_sperber@cargill.com
1
W.H. Sperber, M.P. Doyle (eds.), Compendium of the Microbiological Spoilage
of Foods and Beverages, Food Microbiology and Food Safety,
DOI 10.1007/978-1-4419-0826-1_1,
C
Springer Science+Business Media, LLC 2009
2 W.H. Sperber
this chapter on a laptop computer while sitting in a heated office on a Minnesota
winter evening.
Yet, for most of this 10,000-year period, food preservation was accomplished by
quite simple, but not completely effective, technologies. These typically involved
the use of the techniques that had been put into practice countless years earlier –
drying, salting, smoking, fermentation, and cool storage when possible. Only in
the past 200 years of our long existence have we humans developed more advanced
technologies for advanced food production, preservation, and distribution. Preserva-
tion of some foods by canning began in the early nineteenth century. In the middle
of that century, Louis Pasteur and the first microbiologists began to understand and
control the microbiological causes of disease, foodborne illness, and food spoilage.
Another century elapsed before the emergence of major advances leading to the
widespread availability of fresh and processed foods. The most significant advances,
after 1945, were the development of reliable mechanical refrigeration systems,
logistical systems for the refrigerated transportation and distribution of food, and
widely available home refrigerators and freezers. Numerous refinements continue
to improve the microbiological quality of our food supply today. Additional refine-
ments will certainly be made in the future.
In the past several decades, we have also made substantial improvements i n food
production and management systems. National governments and the f ood industry
promulgated and implemented Good Manufacturing Practices (GMPs) in the United
States, which are called Good Hygienic Practices (GHPs) in the rest of the world.
In particular, those GMPs related to employee practices, sanitary design of food
production facilities and equipment, and cleaning and sanitation procedures have
improved food quality. Similarly, the HACCP (hazard analysis and critical control
point) system, while developed to assure food safety, has also improved food qual-
ity. The HACCP system entails three broad and essential functions – product design,
process control, and management accountability (Troller, 1993; Mortimore &
Wallace, 1998). These topics will be handled in greater detail later in this chapter
and in several of the following chapters.
Additional food regulations and industry practices have been implemented to
reduce the public health threat posed by particular foodborne pathogens. While this
compendium is focused solely on the microbiological spoilage of foods, regulations
and practices that are used to improve public health protection against foodborne
pathogens will also improve the microbiological quality of food, thereby reducing
the i ncidence of microbiological spoilage and extending the shelf life of foods.
Food Loss Data
Despite the advanced technologies that support our modern civilization, a large pro-
portion of our food supply is nevertheless lost to spoilage or otherwise wasted. The
Economic Research Service (ERS) of the United States Department of Agriculture
(USDA) has extensively documented the percentage of food losses in the food chain
from primary production through consumption (ERS, 2005). This research was done
Introduction to the Microbiological Spoilage of Foods and Beverages 3
Table 1 Percent loss of the United States’ food supply from primary production through con-
sumption (abstracted from ERS/USDA, Feb. 1, 2005)
Data for 2003 based on pounds per capita/year
Primary
weight
Retail
weight
Consumer
weight
Consumed
weight
Percent total
lossCommodity
Meat, poultry, and
fish
Red meat 161 112 104 68 58
Poultry 113 71 66 41 64
Fish,shellfish 16161111 31
Grain and cereal
products
194 194 171 136 30
Sweeteners 142 142 126 101 29
Eggs and egg
products
253 250 232 197 22
Dairy products
Fluid milk, yogurt 194 194 171 137 30
Cheese 28.3 28.3 26 22.1 22
Frozen 26.7 26.7 23.5 18.8 30
Dried 3.8 3.8 3.3 2.6 30
Fats and oils 102 102 82 68 33
Fruits
Fresh 127 121 106 53 58
Dried 10 2.4 2.2 2 80
Canned 17 13.4 12.6 11.3 33
Frozen 3.9 3.5 3.3 3 24
Vegetables
Fresh 196 181 160 86 56
Frozen 79 39 37 26 67
Canned 101 47 44 40 60
Dried 16.9 2.3 2.2 2 88
Potato chips 17.2 4.3 4.1 3.7 79
Peanuts and tree nuts 9.3 9.3 8.8 7.9 15
Pounds/year 1811 1597 1396 1037
Pounds/day 4.96 4.38 3.82 2.84
to support the development of the Food Guide Pyramid (MyPyramid) serving sizes.
The percent losses for all food categories during 2003 in the United States are sum-
marized in Table 1. All data are presented as pounds per capita/year. The Primary
Weight column refers to the product weight as it leaves the processing plant, for
example, boned meat products, trimmed vegetables, etc. The retail weight is the
amount of food purchased at retail, the consumer weight is the amount of food avail-
able for consumption at home or at food service establishments, and the consumed
4 W.H. Sperber
weight is the amount of food actually eaten. Food losses can occur from insect or
rodent damage, microbiological spoilage, chemical and physical spoilage, losses in
transportation, further processing, product discarded at the end of shelf life, and
plate waste. According to these data, about five pounds of food are processed each
day for each person in the United States. Only about three pounds are consumed,
indicating an average food loss for all categories of about 40%. ERS economists
feel that the reported data tend to underestimate the actual amount of food losses.
It is not possible to tell from the current data what proportion of the food losses
could be attributed to microbiological spoilage. According to ERS economists, this
capability may be developed in the near future. Under any circumstances, it would
be difficult to know the proportion of microbiological food spoilage with a high
degree of precision. The World Health Organization estimated that in developing
countries the loss caused by spoilage microorganisms ranges from >10% for cereal
grains and legumes to as much as 50% for vegetables and fruits (Käferstein, 1990).
The other food commodities fall within this range. Todd (1987) points out that
worldwide postharvest food losses are caused more by insects and rodents than by
microorganisms. Of course, microorganisms are still important in food losses, with
fungi representing the most important group of spoilage microorganisms responsi-
ble f or food losses.
Microorganisms and Mechanisms Involved in Spoilage
Sources of Contamination
Preharvest Contamination
The sources of microbiological contamination are practically everywhere in the
earth’s biosphere, in or on plants, animals, soil, and water. Many types of bacteria,
such as pseudomonads, lactics, micrococci, and coliforms, grow readily on agricul-
tural and horticultural plants. Many of these and other types of bacteria, particularly
the enterics, also colonize animals, both on the skin or hide and in the gastrointesti-
nal tract. The resident bacteria on both plants and animals can be carried along with
the raw materials during harvest, slaughter, and processing and remain in the food
products derived from these sources (Frazier, 1958).
Soil is an obvious source of contamination, as a diverse community of microor-
ganisms – bacteria, yeasts, molds, actinomycetes, etc. – thrive in most soils and can
grow to very large numbers. Direct contamination with soil microorganisms occurs
during production and harvesting. Indirect contamination with soil occurs through
the deposition of wind-borne dust particles. Wind-borne mold spores, for example,
are a very common cause of mold spoilage of foods, as well as human allergies.
Water can serve as a source and a vector of contamination. Pseudomonads, in
particular, grow well in surface waters, whereas the enteric bacteria are present in
sewage and waters polluted with sewage. Water can serve as a vector of contami-
nation, especially if polluted surface waters are sprayed onto crops for irrigation or
used in primary produce processing.
Introduction to the Microbiological Spoilage of Foods and Beverages 5
Postharvest Contamination
Many raw materials and foods have a structural integrity that protects most of their
mass from microbial contamination (Frazier, 1958). The endosperm of cereal grains
is protected from contamination by a tough bran layer. The shells of eggs and nuts
protect the interior of these foods. When intact, the skin or the rind t hat covers fruits
and vegetables keeps the interior of the produce largely free from external contam-
ination. Similarly, most animal flesh i s sterile in its natural state, being protected
by skin or hide. Therefore, most of the microorganisms in the raw materials of our
food supply are present only on the exterior of the food or in the gastrointestinal
tract in the case of animals. When you think about it, even the gastrointestinal tract
is essentially outside of the animal as well. Therefore, living muscle tissues and
other interior structures are usually sterile.
The first steps of primary processing violate the natural sterility of the inte-
rior parts of our raw food materials. The milling of cereal grains removes most
of the exterior microorganisms with the bran, but some of these microbes will
be relocated into the otherwise nearly microbe-free endosperm. Trimming, chop-
ping, or crushing of fruits and vegetables will similarly contaminate the interior
portions with those microorganisms existing on the exterior. The most prolific pos-
sibility of interior contamination exists in animal slaughter operations. The feces
of animals contain exceedingly high numbers of microorganisms, >10
11
cells/g
feces. If the gastrointestinal tract is not carefully removed during slaughter, very
high contamination of the muscle tissue could occur. In the case of meat produc-
tion, the first slaughter operations contaminate the surface of the exposed mus-
cles to some extent. Further fabrication (cutting) of the carcass into prime cuts
can spread the initial contamination across larger product areas. The grinding of
meat will spread exterior contamination essentially throughout the entire muscle
mass.
During further processing, additional contamination can occur when workers
handle the food. Contamination can occur from unclean hands or gloves and uni-
forms. Human contamination of foods can also occur when talking, coughing,
or sneezing creates aerosols. In-process foods can be further contaminated by
cross-contamination with raw materials and by contact with unclean food-handling
utensils and processing equipment. There are also several points of waterborne
contamination in food-processing plants. The most direct means of potential con-
tamination is the use of water as a food ingredient. If the food plant’s water sup-
ply i s not potable, significant contamination with spoilage microorganisms could
occur. A major indirect source of waterborne contamination may exist during clean-
ing and sanitation operations, since the use of water is essential for most of these
operations. The use of high-pressure hoses to clean floors creates aerosols con-
taining bacteria that were present, and likely growing, on the floor or the process
equipment. The bacteria-containing aerosols can drift through the air and directly
contaminate r aw materials and in-process foods if these are not removed or ade-
quately protected before cleaning commences, or they can indirectly contaminate
food after they are deposited on the food-processing equipment. Another inadver-
tent source of water contamination may be presented by condensate that is formed
6 W.H. Sperber
in refrigeration units and can be spread by the ventilation systems in the food-
processing plants.
Ecology of Microbiological Spoilage
The many kinds of microorganisms that can grow on food have evolved biochemical
mechanisms to digest components of the food, thereby providing energy sources for
their own growth. However, in a given type of food, usually only one or a few types
of microorganisms will grow sufficiently well to become the predominant spoilage
organisms (Mossel & Ingram, 1955). Parameters, such as pH, water activity, and
storage temperature to name a few, exert intensive selective pressures on the orig-
inal food microflora. The driving forces that guide the selection of predominant
spoilage microorganisms will be detailed later in this chapter in sections “Intrin-
sic Factors to Control Microbiological Spoilage” and “Extrinsic Factors to Control
Microbiological Spoilage.”
Microorganisms Involved in Spoilage
It is useful to consider the types of microorganisms involved in food spoilage in two
ways. The first way is a consideration of laboratory tests and biochemical features
that are used to broadly characterize and differentiate microorganisms. The second
way is to describe the groups of similar microorganisms that are involved in food
spoilage.
Means to Characterize and Differentiate Microorganisms
Morphology. A microscope was the first tool with which early microbiologists could
begin to understand microorganisms. The microscope enabled the observation of the
size and shape, or morphology, of microbial cells. Bacterial cells usually appear as
cylindrical rods or spheres. The