295
Chapter 23
indicators of Microbial
Food Spoilage
introduction
Microorganisms cause food spoilage in two ways. The first, and the more important one, is through
the growth and active metabolism of food components by live cells. The second is produced, even
in the absence of live cells, by extracellular and intracellular enzymes that react with food components and change their functional properties, leading to spoilage. The loss of food by microbial
spoilage has economic consequences for producers, processors, and consumers. With the increase
in world population, loss of food by microbial (and nonmicrobial) spoilage means that less food is
available for the hungry mouth. World population in 2011 was about 7 billion, and it is expected
to reach 8 billion in 2025 and 9.1 billion in 2050. To fight world hunger, efforts should be directed
not only toward increasing food production, but also to minimizing spoilage so that enough food
is available for consumption. 1 Many preservation methods have been devised to reduce microbial
spoilage and are discussed in Part VI. Under certain methods of preservation, both raw and partially processed (semipreserved, perishable, nonsterile) foods are susceptible to microbial spoilage.
This is more evident in foods that are expected to have a long shelf life. To reduce loss of raw and
partially processed foods by microbial spoilage, two points are important. One is to predict how
long a food, following production, will stay acceptable under the conditions of storage normally
used for that food; that is, what will be the expected shelf life under normal conditions of handling
and storage. The other is to determine the current status, with respect to spoilage, of a food that
has been stored for some time. This information needs to be available well before a food develops
obvious detectable spoilage and therefore becomes unacceptable.
Many criteria have been evaluated for their efficiency as indicators predicting expected shelf
life as well as to estimating stages of microbial food spoilage. These criteria or indicators can be
grouped as sensory, microbiological, and chemical (specific microbial metabolites). Sensory tests
(e.g., changes in color, odor, flavor, texture, and general appearance), although easy and quick to
perform, have several drawbacks as indicators, especially if used alone. Changes in texture and flavor generally appear at the advanced stages of spoilage. Odor changes can be masked by the spices
Chapter 23
indicators of Microbial
Food Spoilage
introduction
Microorganisms cause food spoilage in two ways. The first, and the more important one, is through
the growth and active metabolism of food components by live cells. The second is produced, even
in the absence of live cells, by extracellular and intracellular enzymes that react with food components and change their functional properties, leading to spoilage. The loss of food by microbial
spoilage has economic consequences for producers, processors, and consumers. With the increase
in world population, loss of food by microbial (and nonmicrobial) spoilage means that less food is
available for the hungry mouth. World population in 2011 was about 7 billion, and it is expected
to reach 8 billion in 2025 and 9.1 billion in 2050. To fight world hunger, efforts should be directed
not only toward increasing food production, but also to minimizing spoilage so that enough food
is available for consumption. 1 Many preservation methods have been devised to reduce microbial
spoilage and are discussed in Part VI. Under certain methods of preservation, both raw and partially processed (semipreserved, perishable, nonsterile) foods are susceptible to microbial spoilage.
This is more evident in foods that are expected to have a long shelf life. To reduce loss of raw and
partially processed foods by microbial spoilage, two points are important. One is to predict how
long a food, following production, will stay acceptable under the conditions of storage normally
used for that food; that is, what will be the expected shelf life under normal conditions of handling
and storage. The other is to determine the current status, with respect to spoilage, of a food that
has been stored for some time. This information needs to be available well before a food develops
obvious detectable spoilage and therefore becomes unacceptable.
Many criteria have been evaluated for their efficiency as indicators predicting expected shelf
life as well as to estimating stages of microbial food spoilage. These criteria or indicators can be
grouped as sensory, microbiological, and chemical (specific microbial metabolites). Sensory tests
(e.g., changes in color, odor, flavor, texture, and general appearance), although easy and quick to
perform, have several drawbacks as indicators, especially if used alone. Changes in texture and flavor generally appear at the advanced stages of spoilage. Odor changes can be masked by the spices