New Food Spoilage Bacteria in Refrigerated Foods ◾ 275
Consumers prefer refrigerated foods because of their better taste, texture, quality, and convenience. They also perceive these foods to be relatively fresh, nutritious, and close to natural as compared with frozen, canned, or dried foods and fast foods. The popularity of these refrigerated or
chilled foods has convinced food experts that this is not a fad—it is here to stay, and the demand
will continue to increase in the future. 3,4
Microbiological Problems
Vacuum- or MA-packaged refrigerated (≤5°C) foods are expected to inhibit the growth of aerobic,
most mesophilic, and thermophilic microorganisms. However, if the product contains dissolved
or trapped oxygen and the modified air contains oxygen, aerobic and microaerophilic microorganisms capable of growing at refrigerated temperatures can also grow as long as the oxygen is available. Similar possibilities also exist if the packaging material is relatively permeable to atmospheric
oxygen. 5
Even under ideal conditions (no oxygen and refrigeration at ≤5°C), the vacuum-packaged
unheated foods normally harbor both anaerobic and facultative anaerobic spoilage and pathogenic
bacteria that can multiply during refrigerated storage. Heat-processed products are usually given
a low-heat treatment that, depending on a product, varies from 60°C to 74°C (140°F–170°F)
for a specified time. At this temperature, pathogenic and spoilage bacterial spores and cells of
some thermoduric bacteria can survive. Some of these survivors can be anaerobic and facultative
anaerobic and can multiply at refrigerated temperatures. Many of these heat-processed products
are, however, handled extensively following heating and before final repackaging under vacuum or
MA. Pathogenic and spoilage bacteria that can grow during storage can also get into the products
during this time as post-heat contaminants. Thus, these products have the potential of harboring
pathogens and spoilage bacteria that can multiply under vacuum or MA at refrigerated temperatures. As these products are expected to have a long shelf life, some up to 100 days, even a very low
population (≤10 1 /g) of psychrotrophic anaerobic and facultative anaerobic bacteria can multiply
and reach a level that causes spoilage of the food or makes it unsafe. These products are often
temperature abused during transportation, in display cases at the retail store, and at the homes
of consumers. Depending on the time and temperature of abuse, the product temperature can go
to 10°C–15°C for a considerable period. The shelf life and safety of the products can be drastically reduced because of accelerated growth rates of psychrotrophs as well as by some mesophiles
(anaerobic and facultative anaerobic) that do not grow at ≤5°C but can at the abusive temperature.
It has been suspected that even a few hours (4–6 h) at 12°C–15°C can reduce the shelf life of such
products by 8–10 days.
There is concern among regulatory agencies regarding the safety of these products because the
incidences of foodborne diseases following consumption of pasteurized refrigerated foods have
been recorded (e.g., Lis. monocytogenes in ready-to-eat processed meat products). Food processors
are also encountering spoilage of these products in higher frequencies (see examples later). To
overcome the microbiological problems in these foods, the National Food Processors Association
has recommended several guidelines. These include selecting good-quality raw materials, installing good sanitary procedures, incorporating hazard analysis critical control points (HACCP) at
all phases between production and consumption of these foods (from field to table), and, where
possible (Chapter 33), applying the highest permissible heat treatment to a product at the final step
and eliminating or minimizing post-heat treatment contamination. Other recommendations are
to incorporate multiple barriers or hurdles (Chapter 41) along with refrigeration and vacuum or
Consumers prefer refrigerated foods because of their better taste, texture, quality, and convenience. They also perceive these foods to be relatively fresh, nutritious, and close to natural as compared with frozen, canned, or dried foods and fast foods. The popularity of these refrigerated or
chilled foods has convinced food experts that this is not a fad—it is here to stay, and the demand
will continue to increase in the future. 3,4
Microbiological Problems
Vacuum- or MA-packaged refrigerated (≤5°C) foods are expected to inhibit the growth of aerobic,
most mesophilic, and thermophilic microorganisms. However, if the product contains dissolved
or trapped oxygen and the modified air contains oxygen, aerobic and microaerophilic microorganisms capable of growing at refrigerated temperatures can also grow as long as the oxygen is available. Similar possibilities also exist if the packaging material is relatively permeable to atmospheric
oxygen. 5
Even under ideal conditions (no oxygen and refrigeration at ≤5°C), the vacuum-packaged
unheated foods normally harbor both anaerobic and facultative anaerobic spoilage and pathogenic
bacteria that can multiply during refrigerated storage. Heat-processed products are usually given
a low-heat treatment that, depending on a product, varies from 60°C to 74°C (140°F–170°F)
for a specified time. At this temperature, pathogenic and spoilage bacterial spores and cells of
some thermoduric bacteria can survive. Some of these survivors can be anaerobic and facultative
anaerobic and can multiply at refrigerated temperatures. Many of these heat-processed products
are, however, handled extensively following heating and before final repackaging under vacuum or
MA. Pathogenic and spoilage bacteria that can grow during storage can also get into the products
during this time as post-heat contaminants. Thus, these products have the potential of harboring
pathogens and spoilage bacteria that can multiply under vacuum or MA at refrigerated temperatures. As these products are expected to have a long shelf life, some up to 100 days, even a very low
population (≤10 1 /g) of psychrotrophic anaerobic and facultative anaerobic bacteria can multiply
and reach a level that causes spoilage of the food or makes it unsafe. These products are often
temperature abused during transportation, in display cases at the retail store, and at the homes
of consumers. Depending on the time and temperature of abuse, the product temperature can go
to 10°C–15°C for a considerable period. The shelf life and safety of the products can be drastically reduced because of accelerated growth rates of psychrotrophs as well as by some mesophiles
(anaerobic and facultative anaerobic) that do not grow at ≤5°C but can at the abusive temperature.
It has been suspected that even a few hours (4–6 h) at 12°C–15°C can reduce the shelf life of such
products by 8–10 days.
There is concern among regulatory agencies regarding the safety of these products because the
incidences of foodborne diseases following consumption of pasteurized refrigerated foods have
been recorded (e.g., Lis. monocytogenes in ready-to-eat processed meat products). Food processors
are also encountering spoilage of these products in higher frequencies (see examples later). To
overcome the microbiological problems in these foods, the National Food Processors Association
has recommended several guidelines. These include selecting good-quality raw materials, installing good sanitary procedures, incorporating hazard analysis critical control points (HACCP) at
all phases between production and consumption of these foods (from field to table), and, where
possible (Chapter 33), applying the highest permissible heat treatment to a product at the final step
and eliminating or minimizing post-heat treatment contamination. Other recommendations are
to incorporate multiple barriers or hurdles (Chapter 41) along with refrigeration and vacuum or