Fundamental Food Microbiology, Third Edition - Fuad Fathir

44 FUNDAMENTAL FOOD MICROBIOLOGY
optimum growth condition is present in the food. This aspect is discussed in Chapter
6. The objective of this chapter is to develop an understanding of the microbial types
(and their levels where possible) that can be expected under normal conditions in
different food groups. It has to be recognized that microbial load in a food results
from initial contamination from different sources and growth of the contaminants
before testing; normally, it is difficult to separate the two.
II. RAW AND READY-TO-EAT MEAT PRODUCTS
Following slaughter and dressing, the carcasses of animals and birds contain many
types of microorganisms, predominantly bacteria, coming from the skin, hair, feathers,
gastrointestinal tract, etc.; the environment of the feedlot and pasture (feed,
water, soil, and manure); and the environment at the slaughtering facilities (equipment,
air, water, and humans). Normally, carcasses contain an average of 10 1–3
bacterial cells/in. 2 . Different enteric pathogens, Salmonella serovars, Yersinia enterocolitica,
Campylobacter jejuni, Escherichia coli, Clostridium perfringens, and Staphylococcus
aureus, both from animals or birds and humans, can be present, but
normally at a low level. Carcasses of birds, as compared with those of animals,
generally have a higher incidence of Salmonella contamination coming from fecal
matter. 1–4
Following boning, chilled raw meat and ground meat contain microorganisms
coming from the carcasses as well as from different equipment used during processing,
personnel, air, and water. Some of the equipment used can be important sources
of microorganisms, such as conveyors, grinders, slicers, and similar types that can
be difficult to clean. Chilled meat has mesophiles, such as Micrococcus, Enterococcus,
Staphylococcus, Bacillus, Clostridium, Lactobacillus, coliforms, and other
Enterobacteriaceae, including enteric pathogens. However, because the meats are
stored at low temperature (–1 to 5�C), the psychrotrophs constitute major problems.
The predominant psychrotrophs in raw meats are some lactobacilli and leuconostocs,
Brochothrix thermosphacta, Clo. laramie, some coliforms, Serratia, Pseudomonas,
Alteromonas, Achromobacter, Alcaligenes, Acinetobacter, Morexella, Aeromonas,
and Proteus. Psychrotrophic pathogens include Listeria monocytogenes and Yer.
enterocolitica. The microbial load of fresh meat varies greatly, with bacteria predominating.
Ground meat can have 10 4–5 microorganisms/g; Salmonella can be
present at ca. 1 cell/25 g. As indicated before, the frequency of the presence of
Salmonella is higher in chicken than in red meats. If the products are kept under
aerobic conditions, psychrotrophic aerobes will grow rapidly, especially Gramnegative
rods, such as Pseudomonas, Alteromonas, Proteus, and Alcaligenes, as well
as yeasts. Under anaerobic packaging, growth of psychrotrophic facultative anaerobes
and anaerobes (e.g., Lactobacillus, Leuconostoc, Brochothrix, Serratia, some
coliforms, and Clostridium) predominates. The pH of the meat (which is low in
beef, ca. 5.6, but high in birds, ca. 6.0), high protein content, and low carbohydrate
level, along with the environment, determine which types predominate during storage.