Fundamental Food Microbiology, Third Edition - Fuad Fathir

NEW FOOD SPOILAGE BACTERIA IN REFRIGERATED FOODS 293
eliminating or minimizing postheat treatment contamination. Other recommendations
are to incorporate multiple barriers or hurdles (Chapter 40) along with
refrigeration and vacuum or MA packaging. Some of these can be incorporated
into the product formulation to reduce the pH and A w. In addition, acceptable and
suitable preservatives (e.g., biopreservatives; see Chapter 16) can be included to
combat microbial survival and growth. Some packaged products, such as processed
meats, can also be given a hydrostatic pressure processing treatment
(Chapter 39).
Many of the food processors are following one or more of these recommendations,
especially good sanitation. This helps reduce the initial microbial population
of the products considerably. Yet incidences of spoilage of (and foodborne
diseases from) vacuum- or MA-packaged refrigerated products are not infrequent
and, at times with some processors, spoilage occurs at epidemic proportion both
in raw and low-heat-processed products. Many of the bacteria frequently isolated
from such spoiled products are being recognized either as new species or species
that were not of major concern before. Some of these are Clo. laramie, Clo.
estertheticum, Clo. algidicarnis, Carnobacterium spp., Leuconostoc carnosum,
Leu. gelidum, Lactobacillus sake, Lab. curvatus, atypical or unidentifiable lactobacilli
and leuconostocs, Brochothrix thermosphacta, Enterococcus spp., Serratia
liquifaciens, Hafnia spp., Proteus spp., and some other Enterobacteriaceae. Except
for spores of Clostridium spp., and some thermodurics (some lactobacilli and
enterococci), cells of the others are sensitive to heat treatment (pasteurization)
given to the processed products. Thus, they are getting in heated products as
postheat contaminants on the product surfaces (so are some pathogens). There is
a growing speculation and belief among scientists that although these bacterial
species have become major causes of spoilage of vacuum- or MA-packaged
refrigerated foods, most are neither new nor variants of the existing species. They
are present in the environment but probably as minor flora. Three reasons could
have helped them become major spoilage organisms. The first could be the changes
in the environment of food, such as efficient vacuum (or compositions used in
MA) packaging and oxygen barrier systems, higher pH in some meat products
(low fat, high phosphate), and long storage time at low temperature; these might
have controlled the growth of traditional bacteria associated with food spoilage
before but are not efficient for these nontraditional bacteria. A second reason could
be that in order to produce a safer food with long shelf life, food processors are
using "super sanitation," which has efficiently eliminated the traditional microorganisms
associated with spoilage before, but at the same time has enabled the
minor flora to establish in the environment to contaminate the products. Finally,
processors might be introducing equipment that are highly efficient in producing
large volume of products, but may also be the microbiologist’s nightmare for
efficient cleaning and sanitation. As a result, the equipment harboring the microorganisms
in dead spots remain unaffected by sanitation and serve as a source of
inoculation to the products. Some of the examples used here may justify these
assumptions. 5
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