Thermal Food Processing

168 Thermal Food Processing: New Technologies and Quality Issues
Gram-negative bacteria constitute the greatest spoilage potential for meat and
meat products. When fresh meat is chill-stored aerobically, members of the genera
Pseudomonas, Acinetobacter, Psychrobacter, and Moraxella display the fastest
growth rates and hence the greatest spoilage potential. 22 On the other hand, species
like Shewanella and Enterobacteriaceae require more favorable conditions than
the organisms mentioned to produce spoilage metabolites.
Gram-positive organisms may constitute predominant microflora of fresh meat
products and will directly influence the shelf life of meat products. The main groups
of Gram-positive organisms include micrococci, followed by lactic acid bacteria
and Brochotrix thermosphacta. 23 Gram-positive microflora include non-spore-forming
pathogens Staphylococcus aureus and L. monocytogenes, as well as the spore
formers Clostridium spp. and Bacillus spp. A comprehensive review of Grampositive
organisms present in meat products is provided by Holzapfel. 23
Typical cooking processes employed for thermally processed meats achieve
internal temperatures of 68°C (154°F), which would destroy the majority of nonspore-forming
pathogens, Salmonella spp., Escherichia coli O157:H7, S. aureus,
and others, including Listeria. 24 Thus, the majority of flora in processed products
would represent microorganisms resulting from recontamination of the products.
In processed meats, growth of microorganisms may result in souring combined
with other off-odors and off-flavors, discoloration, gas production, and the
formation of polysaccharides in the form of slime. A typical example would be
the greening of cured meats, caused by growth of thermotolerant organisms
Weissella viridescens, Enterococcus faecium, or Enterococcus faecalis or contamination
with Carnobacterium viridans, homo- and heterofermentative lactobacilli,
or Leuconostocs subsequent to the heat processing. 25,26
Nonetheless, it is important to recognize that some of the Gram-positive
organisms in meat products are in fact used for meat fermentations to achieve
other desirable changes in processed meat products.
6.5.2 SAFETY: DESTRUCTION OF PATHOGENS
Food-borne illnesses can be classified as infections, where the consumer ingests
foods containing live organisms mostly in large numbers, or intoxications, where
the consumer ingests food containing preformed toxins. However, only food-borne
pathogens of major importance are discussed briefly in this review due to their
higher incidence and importance in meat products. Comprehensive reviews on these
pathogens and their thermal destruction characteristics can be found in a treatise
by the International Commission for Microbiological Specification of Foods
(ICMSF). 20 Similarly, recent incidents of foot-and-mouth disease and bovine spongiform
encephalopathy in cattle indictate that new safety issues will arise in the future.
The focus of this section will be on bacterial pathogens of significance in
meat products and their destruction during thermal processing in combination
with other methodologies. The pathogens of concern in meat products include E.
coli O157:H7, Salmonella spp., L. monocytogenes, S. aureus, and Clostridium
spp. (C. perfringens and C. botulinum).