258 ◾ Fundamental Food Microbiology
low-fat products, have pH values as high as 6.8 (compared to pH < 6.0 in other products) because
of the addition of phosphate and other ingredients and higher moisture. They are cooked at an
internal temperature of 150°F–160°F (65°C–71°C). Depending on the size of the products, the
surface can be exposed to the final temperature for a longer time than the center. As the products are made from ground or chopped meats, microorganisms are distributed throughout the
products (as compared with mainly on the surfaces of a roast or retail cuts, but preformed roasts,
steaks, etc. made from chopped meat have microorganisms throughout the products). Thus, the
thermodurics surviving cooking are present throughout the products. The products, following
cooking, are extensively handled before they are again vacuum packaged or packed with modified
atmospheres of CO 2 or CO 2 + N 2 or sold unpackaged. Depending on the post-heat treatment processing steps (slicing, portioning, and skinning) involved, the products can be contaminated with
microorganisms from equipment, personnel, air, and water. Some of the microorganisms establish
themselves in the processing environment, especially in places difficult to sanitize (or dead spots).
In products such as franks, they contaminate only the surface; but in sliced products, they are
distributed over the slices following cutting.
Vacuum-packaged and gas-packaged products, during storage, can be spoiled by psychrotrophic Lactobacillus spp. (such as homofermentative Lab. sake, Lab. curvatus, heterofermentative
Lab. viridescens) and Leuconostoc spp. (such as Leu. carnosum, Leu. gelidum, and Leu. mesenteroides). In vacuum-packaged products, the package becomes loose because of growth. The products,
depending on bacterial types, show a cloudy appearance, a large accumulation of gas (CO 2 ) and
liquid, slime formation resulting from bacterial cells, and dextran production by Leuconostoc spp.
in products containing sucrose (or honey) and a slight acidic odor. In some products, growth of
Serratia spp. (Serratia liquefaciens) causes amino acid breakdown, which then causes an ammonialike odor (diaper smell). Low-fat-containing, vacuum-packaged turkey rolls (portions or sliced)
develop a pink color after approximately five weeks, probably because of growth of some lactic
acid bacteria. Under aerobic conditions of storage (unpackaged or permeable-film wrapped), some
Lactobacillus spp. rapidly produce H 2 O 2 , which can oxidize nitrosohemochrome (formed by heating nitrosomyoglobin) to brown metmyoglobin or to oxidized porphyrins, some of which are
green in color. Refrigerated luncheon meat can develop brown to yellow spots with fluorescence
from the growth of Enterococcus casseliflavus (Chapter 21). Yeasts and molds can grow inside if a
package, because of even undetectable damage, allows air to leak in.
Unpackaged cooked products that do not have carbohydrates can become putrid from the
growth of and protein degradation by proteolytic Gram-negative bacteria. If the products are
stored for long times, yeasts and molds can also grow, causing off-flavor, discoloration, and sliminess. Because of growth of H 2 O 2 -producing lactic acid bacteria, they can have green to gray
discolorations.
eggs and egg Products
Shell Eggs
The pores in the eggshell and inner membrane do not prevent entrance of bacteria and hyphae of
molds, especially when the pore size increases during storage. The presence of moisture enhances
the entrance of motile bacteria. The albumen (egg white) and yolk have approximately 0.5%–1.0%
carbohydrate and are high in proteins but low in nonprotein nitrogen. During storage, the pH
can shift to the alkaline side (pH 9–10). In addition, lysozyme (causes lysis of bacterial cell wall
low-fat products, have pH values as high as 6.8 (compared to pH < 6.0 in other products) because
of the addition of phosphate and other ingredients and higher moisture. They are cooked at an
internal temperature of 150°F–160°F (65°C–71°C). Depending on the size of the products, the
surface can be exposed to the final temperature for a longer time than the center. As the products are made from ground or chopped meats, microorganisms are distributed throughout the
products (as compared with mainly on the surfaces of a roast or retail cuts, but preformed roasts,
steaks, etc. made from chopped meat have microorganisms throughout the products). Thus, the
thermodurics surviving cooking are present throughout the products. The products, following
cooking, are extensively handled before they are again vacuum packaged or packed with modified
atmospheres of CO 2 or CO 2 + N 2 or sold unpackaged. Depending on the post-heat treatment processing steps (slicing, portioning, and skinning) involved, the products can be contaminated with
microorganisms from equipment, personnel, air, and water. Some of the microorganisms establish
themselves in the processing environment, especially in places difficult to sanitize (or dead spots).
In products such as franks, they contaminate only the surface; but in sliced products, they are
distributed over the slices following cutting.
Vacuum-packaged and gas-packaged products, during storage, can be spoiled by psychrotrophic Lactobacillus spp. (such as homofermentative Lab. sake, Lab. curvatus, heterofermentative
Lab. viridescens) and Leuconostoc spp. (such as Leu. carnosum, Leu. gelidum, and Leu. mesenteroides). In vacuum-packaged products, the package becomes loose because of growth. The products,
depending on bacterial types, show a cloudy appearance, a large accumulation of gas (CO 2 ) and
liquid, slime formation resulting from bacterial cells, and dextran production by Leuconostoc spp.
in products containing sucrose (or honey) and a slight acidic odor. In some products, growth of
Serratia spp. (Serratia liquefaciens) causes amino acid breakdown, which then causes an ammonialike odor (diaper smell). Low-fat-containing, vacuum-packaged turkey rolls (portions or sliced)
develop a pink color after approximately five weeks, probably because of growth of some lactic
acid bacteria. Under aerobic conditions of storage (unpackaged or permeable-film wrapped), some
Lactobacillus spp. rapidly produce H 2 O 2 , which can oxidize nitrosohemochrome (formed by heating nitrosomyoglobin) to brown metmyoglobin or to oxidized porphyrins, some of which are
green in color. Refrigerated luncheon meat can develop brown to yellow spots with fluorescence
from the growth of Enterococcus casseliflavus (Chapter 21). Yeasts and molds can grow inside if a
package, because of even undetectable damage, allows air to leak in.
Unpackaged cooked products that do not have carbohydrates can become putrid from the
growth of and protein degradation by proteolytic Gram-negative bacteria. If the products are
stored for long times, yeasts and molds can also grow, causing off-flavor, discoloration, and sliminess. Because of growth of H 2 O 2 -producing lactic acid bacteria, they can have green to gray
discolorations.
eggs and egg Products
Shell Eggs
The pores in the eggshell and inner membrane do not prevent entrance of bacteria and hyphae of
molds, especially when the pore size increases during storage. The presence of moisture enhances
the entrance of motile bacteria. The albumen (egg white) and yolk have approximately 0.5%–1.0%
carbohydrate and are high in proteins but low in nonprotein nitrogen. During storage, the pH
can shift to the alkaline side (pH 9–10). In addition, lysozyme (causes lysis of bacterial cell wall