46 ◾ Fundamental Food Microbiology
processed products (such as breakfast cereals and pasta) may contain an aerobic plate count of
10 2–3 /g, coliform of <10 1–2 /g, and yeasts and molds of <10 1–2 /g. They can contain bacterial spores
and psychrotrophs. Some pathogens, such as Salmonella, Sta. aureus, and Clo. perfringens, have
also been isolated. Depending on the product, they can either grow (such as in dough) or be the
source (when used as ingredients) of spoilage and pathogenic microorganisms as well as mycotoxins. Gums also may be the source of yeasts, molds (also mycotoxins), bacterial spores, and lactic
acid bacteria.
Canned Foods
This group of foods includes those packed in hermetically sealed containers and given high heat
treatment. The products with a pH of 4.6 or above are given heat treatments to obtain commercial
sterility, but those with a pH below 4.6 are given heat treatments of approximately 100°C.
Canned foods prepared and processed to obtain commercial sterility can have spores of thermophilic spoilage bacteria, namely Bacillus stearothermophilus, Clo. thermosaccharolyticum, and
Desulfotomaculum nigrificans. Their major sources in the products are soil and blanching water as
well as sugar and starches that are used as ingredients. In canned products stored at 30°C or below,
thermophilic spores do not germinate to cause spoilage. However, if the cans are temperatureabused to 40°C or higher, the spores germinate; subsequently, the cells multiply and spoil the
products.
If the canned products are given a lower heat treatment (approximately 100°C), spores of
mesophilic bacteria that include both spoilage (Bac. coagulans, Bac. licheniformis, Clo. sporogenes,
Clo. butyricum) and pathogenic types (Bac. cereus, Clo. perfringens, Clo. botulinum), along with
the spores of thermophiles, survive. In low-pH products, particularly in tomato products, Bac.
coagulans spores can germinate, and cells can multiply and cause spoilage. Other spore formers
can germinate and grow in high-pH products. Sta. aureus toxins, if present in raw products, are
not destroyed by the heat treatment of the canned products and can thus cause food poisoning
following consumption of the products.
Sugars and Confectioneries
Refined sugar is obtained from sugarcane and beets. Sugar can have thermophilic spores of Bac. stearothermophilus, Bac. coagulans, Clo. thermosaccharolyticum, and Des. nigrificans as well as mesophilic
bacteria (e.g., Lactobacillus and Leuconostoc), yeasts, and molds. 10 When sugars are used as ingredients
in food products, the spores can survive and cause spoilage of products. Pathogens are not present
in refined sugar unless contaminated. In liquid sugar, mesophiles can grow. Refined sugar, used in
canned products or to make liquid sugar, has strict microbiological standards (for spores).
Confectioneries include a large variety of products with a sweet taste. In general, these products have low A W (0.84 or less) and some have low pH. They may contain many types of bacteria,
yeasts, and molds, but their microbiological standards are well regulated. Although they may
harbor Lactobacillus, Leuconostoc, spores of Bacillus and Clostridium, and yeasts and molds, only
a few osmotolerant yeasts and molds can grow. However, when used as additives in other foods,
confectioneries can be a source of these microbes. If ready-to-consume products are contaminated
with pathogens, either from raw materials, the environment, or personnel, they can cause foodborne diseases.
processed products (such as breakfast cereals and pasta) may contain an aerobic plate count of
10 2–3 /g, coliform of <10 1–2 /g, and yeasts and molds of <10 1–2 /g. They can contain bacterial spores
and psychrotrophs. Some pathogens, such as Salmonella, Sta. aureus, and Clo. perfringens, have
also been isolated. Depending on the product, they can either grow (such as in dough) or be the
source (when used as ingredients) of spoilage and pathogenic microorganisms as well as mycotoxins. Gums also may be the source of yeasts, molds (also mycotoxins), bacterial spores, and lactic
acid bacteria.
Canned Foods
This group of foods includes those packed in hermetically sealed containers and given high heat
treatment. The products with a pH of 4.6 or above are given heat treatments to obtain commercial
sterility, but those with a pH below 4.6 are given heat treatments of approximately 100°C.
Canned foods prepared and processed to obtain commercial sterility can have spores of thermophilic spoilage bacteria, namely Bacillus stearothermophilus, Clo. thermosaccharolyticum, and
Desulfotomaculum nigrificans. Their major sources in the products are soil and blanching water as
well as sugar and starches that are used as ingredients. In canned products stored at 30°C or below,
thermophilic spores do not germinate to cause spoilage. However, if the cans are temperatureabused to 40°C or higher, the spores germinate; subsequently, the cells multiply and spoil the
products.
If the canned products are given a lower heat treatment (approximately 100°C), spores of
mesophilic bacteria that include both spoilage (Bac. coagulans, Bac. licheniformis, Clo. sporogenes,
Clo. butyricum) and pathogenic types (Bac. cereus, Clo. perfringens, Clo. botulinum), along with
the spores of thermophiles, survive. In low-pH products, particularly in tomato products, Bac.
coagulans spores can germinate, and cells can multiply and cause spoilage. Other spore formers
can germinate and grow in high-pH products. Sta. aureus toxins, if present in raw products, are
not destroyed by the heat treatment of the canned products and can thus cause food poisoning
following consumption of the products.
Sugars and Confectioneries
Refined sugar is obtained from sugarcane and beets. Sugar can have thermophilic spores of Bac. stearothermophilus, Bac. coagulans, Clo. thermosaccharolyticum, and Des. nigrificans as well as mesophilic
bacteria (e.g., Lactobacillus and Leuconostoc), yeasts, and molds. 10 When sugars are used as ingredients
in food products, the spores can survive and cause spoilage of products. Pathogens are not present
in refined sugar unless contaminated. In liquid sugar, mesophiles can grow. Refined sugar, used in
canned products or to make liquid sugar, has strict microbiological standards (for spores).
Confectioneries include a large variety of products with a sweet taste. In general, these products have low A W (0.84 or less) and some have low pH. They may contain many types of bacteria,
yeasts, and molds, but their microbiological standards are well regulated. Although they may
harbor Lactobacillus, Leuconostoc, spores of Bacillus and Clostridium, and yeasts and molds, only
a few osmotolerant yeasts and molds can grow. However, when used as additives in other foods,
confectioneries can be a source of these microbes. If ready-to-consume products are contaminated
with pathogens, either from raw materials, the environment, or personnel, they can cause foodborne diseases.