Fundamental Food Microbiology, Third Edition - Fuad Fathir

SPOILAGE OF SPECIFIC FOOD GROUPS 273
roast turkey, and roast chicken, heterofermentative Lactobacillus spp. and Leuconostoc
spp., as postheat contaminants, have been involved in spoilage, with the accumulation
of large quantities of gas (CO 2) and liquid (due to acid production) inside
the bag, without causing much flavor, color, or texture changes. Gas production and
purge accumulation in vacuum-packaged roast beef by psychrotrophic Clostridium
spp., along with off-flavor and color changing from brown to pink to red (after 4
weeks), have been detected. In spoiled sliced roast beef, the brown color of roast
beef changes to pink (in 1 week) and the beef has a putrid odor (after 6 weeks).
Proteus and Hafnia spp. are involved in spoilage of this product (Chapter 20).
Low-heat-processed cured meats include a wide variety of products such as
franks, bologna, ham, and luncheon meats made from beef, pork, and poultry. Meats
are mixed with different types of additives to improve color, texture, flavor, shelf
life, and safety. Some of these additives are nitrite, salt, dextrose, phosphate, sorbate,
erythorbate, nonfat dry milk, soy proteins, carrageenan, and different types of spices.
Some of the reduced-fat products have very low fat (£ 2%) as compared to products
normally with �30% fat (some regular franks). Some of the products, especially
low-fat products, have pH values as high as 6.8 (compared to pH < 6.0 in other
products) due to addition of phosphate and other ingredients and higher moisture.
They are cooked at an internal temperature of 150 to 160�F (65 to 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 atmosphere of CO 2 or CO 2 + N 2 or sold unpackaged.
Depending on the postheat 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 cloudy appearance, large accumulation of gas (CO 2) and liquid, slime
formation due to bacterial cells and dextran production by Leuconostoc spp. in
products containing sucrose (or honey), and slight acidic odor. In some products,
growth of Serratia spp. (Serratia liquifacience) causes amino acid breakdown, which
then causes an ammonia-like odor (diaper smell). Low-fat-containing, vacuumpackaged
turkey rolls (portions or sliced) develop a pink color after ca. 5 weeks,
probably because of growth of some lactic acid bacteria. Under aerobic conditions
of storage (unpackaged or permeable-film wrapped), some Lactobacillus spp. rapidly
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