Important Factors in Microbial Food Spoilage ◾ 249
can cause spoilage in these foods. If the food is stored under aerobic conditions, psychrotrophic
aerobes are the predominant spoilage bacteria. In foods stored under anaerobic conditions (also in
the interior of a prepared food), anaerobic and facultative anaerobic bacteria predominate. If the
food is given low-heat treatment and not exposed to post-heat contamination during storage at low
temperatures, psychrotrophic thermoduric bacteria can cause it to spoil.
Some Important Psychrotrophic Aerobic Spoilage Bacteria
These include Pseudomonas fluorescens, Pse. fragi, other Pseudomonas species, Acinetobacter,
Moraxella, and Flavobacterium. (Some molds and yeasts are included in this group.)
Some Important Psychrotrophic Facultative Anaerobic Spoilage Bacteria
These include Bro. thermosphacta, Lactobacillus viridescens, Lab. sake, Lab. curvatus, unidentified
Lactobacillus spp., Leuconostoc carnosum, Leu. gelidum, Leu. mesenteroides, unidentified Leuconostoc
spp., some Enterococcus spp., Alcaligenes spp., Enterobacter spp., Serratia liquefaciens, some Hafnia
and Proteus spp., and Shewanella (previously Alteromonas) putrefaciens (and some microaerophilic
yeasts).
Some Important Thermoduric Psychrotrophs
These include facultative anaerobes, such as spores of Bacillus coagulans and Bac. megaterium; some
strains of Lab. viridescens; and anaerobes, such as spores of Clostridium laramie, Clo. estertheticum,
Clo. algidicarnis, Clo. putrefaciens, and unidentified Clostridium spp. The spores survive low-heat
treatment. Following germination and outgrowth, the cells grow at low temperatures.
When a food is temperature abused above 5°C (such as during transport or display in stores),
some true mesophiles (growth temperature range 15°C–45°C, optimum 25°C–40°C) can also grow.
However, at 10°C–15°C, psychrotrophs will generally grow much faster than these mesophiles.
Thermophilic Bacteria
By definition, the bacteria in this group grow between 40°C and 90°C with optimum growth at
55°C–65°C. Some high-heat-processed foods are kept warm between 50°C and 60°C for a long
period of time (at delis, fast-food establishments, and restaurants). Spores of some thermophilic
Bacillus and Clostridium spp. can be present in these heat-treated foods, which, at warm temperatures, germinate and multiply to cause spoilage. In addition, some thermoduric vegetative bacteria
surviving low-heat processing (such as pasteurization) or thermophiles getting in food as post-heat
contamination can also multiply in these warm foods, especially if the temperature is close to
50°C. These include some lactic acid bacteria, such as Pediococcus acidilactici and Streptococcus
thermophilus, as well as some Bacillus and Clostridium spp. They can also survive and cause spoilage of foods that are cooked at low heat (60°C–65°C as for some processed meats) or kept warm
for a long time.
Aciduric Bacteria
Bacteria that can grow relatively rapidly in food at pH 4.6 or below are generally regarded as aciduric
(or acidophilic). They are usually associated with spoilage of acidic food products, such as fruit juices,
can cause spoilage in these foods. If the food is stored under aerobic conditions, psychrotrophic
aerobes are the predominant spoilage bacteria. In foods stored under anaerobic conditions (also in
the interior of a prepared food), anaerobic and facultative anaerobic bacteria predominate. If the
food is given low-heat treatment and not exposed to post-heat contamination during storage at low
temperatures, psychrotrophic thermoduric bacteria can cause it to spoil.
Some Important Psychrotrophic Aerobic Spoilage Bacteria
These include Pseudomonas fluorescens, Pse. fragi, other Pseudomonas species, Acinetobacter,
Moraxella, and Flavobacterium. (Some molds and yeasts are included in this group.)
Some Important Psychrotrophic Facultative Anaerobic Spoilage Bacteria
These include Bro. thermosphacta, Lactobacillus viridescens, Lab. sake, Lab. curvatus, unidentified
Lactobacillus spp., Leuconostoc carnosum, Leu. gelidum, Leu. mesenteroides, unidentified Leuconostoc
spp., some Enterococcus spp., Alcaligenes spp., Enterobacter spp., Serratia liquefaciens, some Hafnia
and Proteus spp., and Shewanella (previously Alteromonas) putrefaciens (and some microaerophilic
yeasts).
Some Important Thermoduric Psychrotrophs
These include facultative anaerobes, such as spores of Bacillus coagulans and Bac. megaterium; some
strains of Lab. viridescens; and anaerobes, such as spores of Clostridium laramie, Clo. estertheticum,
Clo. algidicarnis, Clo. putrefaciens, and unidentified Clostridium spp. The spores survive low-heat
treatment. Following germination and outgrowth, the cells grow at low temperatures.
When a food is temperature abused above 5°C (such as during transport or display in stores),
some true mesophiles (growth temperature range 15°C–45°C, optimum 25°C–40°C) can also grow.
However, at 10°C–15°C, psychrotrophs will generally grow much faster than these mesophiles.
Thermophilic Bacteria
By definition, the bacteria in this group grow between 40°C and 90°C with optimum growth at
55°C–65°C. Some high-heat-processed foods are kept warm between 50°C and 60°C for a long
period of time (at delis, fast-food establishments, and restaurants). Spores of some thermophilic
Bacillus and Clostridium spp. can be present in these heat-treated foods, which, at warm temperatures, germinate and multiply to cause spoilage. In addition, some thermoduric vegetative bacteria
surviving low-heat processing (such as pasteurization) or thermophiles getting in food as post-heat
contamination can also multiply in these warm foods, especially if the temperature is close to
50°C. These include some lactic acid bacteria, such as Pediococcus acidilactici and Streptococcus
thermophilus, as well as some Bacillus and Clostridium spp. They can also survive and cause spoilage of foods that are cooked at low heat (60°C–65°C as for some processed meats) or kept warm
for a long time.
Aciduric Bacteria
Bacteria that can grow relatively rapidly in food at pH 4.6 or below are generally regarded as aciduric
(or acidophilic). They are usually associated with spoilage of acidic food products, such as fruit juices,