42 ◾ Fundamental Food Microbiology
Carcasses of birds, as compared with those of animals, generally have a higher incidence of
Salmonella contamination coming from fecal matter. 1–3
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 temperatures (–1°C 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, Moraxella, 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
approximately 1 cell/25 g. As indicated previously, 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 Gram-negative 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) predominate. The pH of the meat (which is low in beef, approximately
5.6, but high in birds, approximately 6.0), high protein content, and low carbohydrate level, along
with the environment, determine the types that predominate during storage.
Low-heat-processed red meat and poultry products include perishable cured or uncured products that have been subjected to heat treatment to approximately 160°F (71°C), packaged aerobically or anaerobically, and stored at refrigerated temperature. They include products such as
franks, bologna, lunchmeats, and hams. The products, especially those packaged anaerobically
and cured, are expected to have a long storage life (50 days or more). The microbial sources before
heat treatment include the raw meat, ingredients used in formulation, processing equipment, air,
and personnel. Heat treatment, especially at an internal temperature of 160°F or higher, kills most
microorganisms except for some thermodurics, which include Micrococcus; some Enterococcus;
and maybe some Lactobacillus and spores of Bacillus and Clostridium. The microbial level can be
10 1–2 /g. Following heating, the products, some of which are further processed (such as removing
casings or slicing), come in contact with equipment, personnel, air, and water before final packaging. Different types of bacteria, yeasts, and molds, including pathogens, can enter these products,
depending on the conditions of the processing plants. Although the initial bacterial level normally
does not exceed 10 2 /g, some of them can be psychrotrophic facultative anaerobic and anaerobic
bacteria (Lactobacillus, Leuconostoc, some coliforms, Serratia, Listeria, Clostridium spp.). During
extended storage in vacuum or modified-air packages, even from a low initial level, the bacterial
population can rise and adversely affect the safety and shelf life of products. This is aggravated by
fluctuation in storage temperature and in products having low fat, high pH, and high A W .
Raw and Pasteurized Milk
Raw milk comes from cows, buffalo, sheep, and goats although the largest volume comes from
cows. Pasteurized or market milk includes whole, skim, low-fat, and flavored milks, as well as
cream, which are heat treated (pasteurized) according to regulatory specifications. 4,5 Milk is high
Carcasses of birds, as compared with those of animals, generally have a higher incidence of
Salmonella contamination coming from fecal matter. 1–3
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 temperatures (–1°C 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, Moraxella, 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
approximately 1 cell/25 g. As indicated previously, 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 Gram-negative 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) predominate. The pH of the meat (which is low in beef, approximately
5.6, but high in birds, approximately 6.0), high protein content, and low carbohydrate level, along
with the environment, determine the types that predominate during storage.
Low-heat-processed red meat and poultry products include perishable cured or uncured products that have been subjected to heat treatment to approximately 160°F (71°C), packaged aerobically or anaerobically, and stored at refrigerated temperature. They include products such as
franks, bologna, lunchmeats, and hams. The products, especially those packaged anaerobically
and cured, are expected to have a long storage life (50 days or more). The microbial sources before
heat treatment include the raw meat, ingredients used in formulation, processing equipment, air,
and personnel. Heat treatment, especially at an internal temperature of 160°F or higher, kills most
microorganisms except for some thermodurics, which include Micrococcus; some Enterococcus;
and maybe some Lactobacillus and spores of Bacillus and Clostridium. The microbial level can be
10 1–2 /g. Following heating, the products, some of which are further processed (such as removing
casings or slicing), come in contact with equipment, personnel, air, and water before final packaging. Different types of bacteria, yeasts, and molds, including pathogens, can enter these products,
depending on the conditions of the processing plants. Although the initial bacterial level normally
does not exceed 10 2 /g, some of them can be psychrotrophic facultative anaerobic and anaerobic
bacteria (Lactobacillus, Leuconostoc, some coliforms, Serratia, Listeria, Clostridium spp.). During
extended storage in vacuum or modified-air packages, even from a low initial level, the bacterial
population can rise and adversely affect the safety and shelf life of products. This is aggravated by
fluctuation in storage temperature and in products having low fat, high pH, and high A W .
Raw and Pasteurized Milk
Raw milk comes from cows, buffalo, sheep, and goats although the largest volume comes from
cows. Pasteurized or market milk includes whole, skim, low-fat, and flavored milks, as well as
cream, which are heat treated (pasteurized) according to regulatory specifications. 4,5 Milk is high