248 ◾ Fundamental Food Microbiology
been, with most probability, facultative anaerobic Lactobacillus or Leuconostoc, or both, because of
their growth advantages. 1
In this context, it is important to recognize that the generation time of a microbial species,
even under optimum conditions of growth, is much longer in a food than in a microbiological
broth. Also, under the same storage conditions, the growth behavior of a microbial mixed population can be quite different in a food as compared to a broth. Because of this, the predominant
types obtained following growing an initial mixed microbial population from a food in a broth
and in the same food under identical conditions could be different. Although growing in a broth
is convenient and, if properly designed, can provide valuable initial information, it is always better
to have studies with specific foods.
Food Spoilage Molds
Many species of molds are involved in food spoilage primarily on solid foods with very low water
activity levels (0.7–0.8). They grow in a wide pH range of 3–8. The most common spoilage species
are Mucor, Rhizopus, Botrytis, Penicillium, and Aspergillus. Some of these spoilage molds produce
mycotoxins (toxigenic), such as Penicillium and Aspergillus. Fruits and vegetables are highly susceptible to mold spoilage. For example, Botrytis sp. is known to cause spoilage of fruits, such as raspberries,
grapes, strawberries, kiwi fruit, pears, peaches, plums, and cherries, and vegetables, such as carrots,
lettuce, peas, and beans, while Mucor and Rhizopus spp. affect apples, strawberries, etc. 6
Food Spoilage Yeasts
Yeasts generally cause spoilage in foods containing high sugar or salt content, such as maple syrup,
fermented foods (pickles, sauerkrauts), and alcoholic beverages. In addition, they also grow in
fruits and juices with a low pH and on the surface of meat and cheese. The major spoilage yeasts
include Saccharomyces spp., Zygosaccharomyces, Candida, and Dekkera/Brettanomyces. 7
Some important Food Spoilage Bacteria
Theoretically, any microorganism (including microorganisms used in food fermentation and
pathogens) that can multiply in a food to reach a high level (spoilage detection level) is capable of
causing it to spoil. Yet, in reality, bacterial species from only several genera have been implicated
more with spoilage of most foods. This is dictated by the bacterial characteristics, food characteristics, and the storage conditions (Chapter 2). The influence of some of these factors in determining
predominant spoilage bacteria in foods is briefly discussed. 2,3 Pathogens are not included here.
Psychrotrophic Bacteria
As indicated before, psychrotrophic bacteria constitute the bacterial species capable of growing at
5°C and below but multiply quite rapidly at 10°C–25°C and even at higher temperatures. 5 Many
foods are stored on ice (chilling) and in refrigerators, and some are expected to have a long shelf
life (50 days or more). Between processing and consumption, they can be temperature abused to
10°C and higher. Psychrotrophic bacteria (also many yeasts and molds that are psychrotrophic)
been, with most probability, facultative anaerobic Lactobacillus or Leuconostoc, or both, because of
their growth advantages. 1
In this context, it is important to recognize that the generation time of a microbial species,
even under optimum conditions of growth, is much longer in a food than in a microbiological
broth. Also, under the same storage conditions, the growth behavior of a microbial mixed population can be quite different in a food as compared to a broth. Because of this, the predominant
types obtained following growing an initial mixed microbial population from a food in a broth
and in the same food under identical conditions could be different. Although growing in a broth
is convenient and, if properly designed, can provide valuable initial information, it is always better
to have studies with specific foods.
Food Spoilage Molds
Many species of molds are involved in food spoilage primarily on solid foods with very low water
activity levels (0.7–0.8). They grow in a wide pH range of 3–8. The most common spoilage species
are Mucor, Rhizopus, Botrytis, Penicillium, and Aspergillus. Some of these spoilage molds produce
mycotoxins (toxigenic), such as Penicillium and Aspergillus. Fruits and vegetables are highly susceptible to mold spoilage. For example, Botrytis sp. is known to cause spoilage of fruits, such as raspberries,
grapes, strawberries, kiwi fruit, pears, peaches, plums, and cherries, and vegetables, such as carrots,
lettuce, peas, and beans, while Mucor and Rhizopus spp. affect apples, strawberries, etc. 6
Food Spoilage Yeasts
Yeasts generally cause spoilage in foods containing high sugar or salt content, such as maple syrup,
fermented foods (pickles, sauerkrauts), and alcoholic beverages. In addition, they also grow in
fruits and juices with a low pH and on the surface of meat and cheese. The major spoilage yeasts
include Saccharomyces spp., Zygosaccharomyces, Candida, and Dekkera/Brettanomyces. 7
Some important Food Spoilage Bacteria
Theoretically, any microorganism (including microorganisms used in food fermentation and
pathogens) that can multiply in a food to reach a high level (spoilage detection level) is capable of
causing it to spoil. Yet, in reality, bacterial species from only several genera have been implicated
more with spoilage of most foods. This is dictated by the bacterial characteristics, food characteristics, and the storage conditions (Chapter 2). The influence of some of these factors in determining
predominant spoilage bacteria in foods is briefly discussed. 2,3 Pathogens are not included here.
Psychrotrophic Bacteria
As indicated before, psychrotrophic bacteria constitute the bacterial species capable of growing at
5°C and below but multiply quite rapidly at 10°C–25°C and even at higher temperatures. 5 Many
foods are stored on ice (chilling) and in refrigerators, and some are expected to have a long shelf
life (50 days or more). Between processing and consumption, they can be temperature abused to
10°C and higher. Psychrotrophic bacteria (also many yeasts and molds that are psychrotrophic)