Fundamental Food Microbiology, Third Edition - Fuad Fathir

292 FUNDAMENTAL FOOD MICROBIOLOGY
III. 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 to 74�C (140 to 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 postheat contaminants. Thus, these products have the potential of harboring
pathogens and spoilage bacteria that can multiply under vacuum or MA
at refrigerated temperature. As these products are expected to have a long shelf
life, some up to 100 d, 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
homes of consumers. Depending on the time and temperature of abuse, the product
temperature can go to 10 to 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 to 6 h) at 12 to 15�C can reduce the
shelf life of such products by 8 to 10 d.
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 32),
applying the highest permissible heat treatment to a product at the final step and