Spoilage of Specific Food Groups ◾ 257
bacteria predominates. In vacuum-packaged products, growth of lactic acid bacteria predominates
in the initial stage. Heterofermentative lactic acid bacteria can cause accumulation of gas in the
package. Some lactic acid bacteria also grow by utilizing amino acids. When the glucose is used
up, Gram-negative facultative anaerobes grow and degrade amino acids to produce a putrid odor.
To reduce spoilage of fresh meats, the initial microbial level should be reduced. In addition,
storage at low temperatures (close to 0°C to –1°C), modified atmosphere packaging, and vacuum
packaging should be done. Several other methods to reduce initial microbial load and slow the
growth rate of Gram-negative rods are being either used or tested. These include the addition of
small amounts of organic acids to lower the pH of meat (slightly above pH 5.0), drying of meat
surfaces (to reduce A W ), and a combination of the factors given previously, including lower storage
temperature.
Ready-to-Eat Meat Products
This group includes high-heat-processed and low-heat-processed uncured and cured meat products. High-heat-processed cured and uncured meats are given heat treatment to make them commercially sterile. Thus, they may only have some thermophilic spores surviving, which will not
germinate unless the products are temperature abused. This aspect has been explained along with
microbial growth in the canned products and canning (see Chapters 4 and 33).
Low-heat-processed uncured meats, such as roasts, are given heat treatment at an internal temperature of 140°F–160°F (60°C–71°C). Generally, the surface of the meats (and thus most of the
microorganisms) is exposed to the final temperature for one hour or more, depending on the size
of the meat (which could be more than 10 lb [4.6 kg]). Under this condition, only the spores of
Bacillus and Clostridium spp. and some extremely thermoduric vegetative species (Lab. viridescens,
some Enterococcus, Micrococcus inside the product) can survive. However, the products, even when
cooked in bags and not cut into portions, are opened and handled before final vacuum packaging
and refrigerated storage. 1,3 Many types of microorganisms can enter as post-heat contaminants
into the products from equipment, personnel, water, and air. In some situations, spices and other
ingredients are added to the products after heating, which, in turn, can be the source of microbial contamination of the products. Some products are sliced before vacuum packaging, which
increases the chances of contamination on the surface area of the product from the equipment
and environment. Psychrotrophic facultative anaerobic and anaerobic bacteria have been implicated in the spoilage of these products. In vacuum-packaged roast beef, roast turkey, and roast
chicken, heterofermentative Lactobacillus spp. and Leuconostoc spp., as post-heat contaminants,
have been involved in spoilage with the accumulation of large quantities of gas (CO 2 ) and liquid
(resulting from acid production) inside the bag without causing much flavor, color, or texture
change. 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
four weeks), have been detected. In spoiled sliced roast beef, the brown color of roast beef changes
to pink (in one week), and the beef has a putrid odor (after six weeks). Proteus and Hafnia spp. are
involved in spoilage of this product (Chapter 21).
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
bacteria predominates. In vacuum-packaged products, growth of lactic acid bacteria predominates
in the initial stage. Heterofermentative lactic acid bacteria can cause accumulation of gas in the
package. Some lactic acid bacteria also grow by utilizing amino acids. When the glucose is used
up, Gram-negative facultative anaerobes grow and degrade amino acids to produce a putrid odor.
To reduce spoilage of fresh meats, the initial microbial level should be reduced. In addition,
storage at low temperatures (close to 0°C to –1°C), modified atmosphere packaging, and vacuum
packaging should be done. Several other methods to reduce initial microbial load and slow the
growth rate of Gram-negative rods are being either used or tested. These include the addition of
small amounts of organic acids to lower the pH of meat (slightly above pH 5.0), drying of meat
surfaces (to reduce A W ), and a combination of the factors given previously, including lower storage
temperature.
Ready-to-Eat Meat Products
This group includes high-heat-processed and low-heat-processed uncured and cured meat products. High-heat-processed cured and uncured meats are given heat treatment to make them commercially sterile. Thus, they may only have some thermophilic spores surviving, which will not
germinate unless the products are temperature abused. This aspect has been explained along with
microbial growth in the canned products and canning (see Chapters 4 and 33).
Low-heat-processed uncured meats, such as roasts, are given heat treatment at an internal temperature of 140°F–160°F (60°C–71°C). Generally, the surface of the meats (and thus most of the
microorganisms) is exposed to the final temperature for one hour or more, depending on the size
of the meat (which could be more than 10 lb [4.6 kg]). Under this condition, only the spores of
Bacillus and Clostridium spp. and some extremely thermoduric vegetative species (Lab. viridescens,
some Enterococcus, Micrococcus inside the product) can survive. However, the products, even when
cooked in bags and not cut into portions, are opened and handled before final vacuum packaging
and refrigerated storage. 1,3 Many types of microorganisms can enter as post-heat contaminants
into the products from equipment, personnel, water, and air. In some situations, spices and other
ingredients are added to the products after heating, which, in turn, can be the source of microbial contamination of the products. Some products are sliced before vacuum packaging, which
increases the chances of contamination on the surface area of the product from the equipment
and environment. Psychrotrophic facultative anaerobic and anaerobic bacteria have been implicated in the spoilage of these products. In vacuum-packaged roast beef, roast turkey, and roast
chicken, heterofermentative Lactobacillus spp. and Leuconostoc spp., as post-heat contaminants,
have been involved in spoilage with the accumulation of large quantities of gas (CO 2 ) and liquid
(resulting from acid production) inside the bag without causing much flavor, color, or texture
change. 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
four weeks), have been detected. In spoiled sliced roast beef, the brown color of roast beef changes
to pink (in one week), and the beef has a putrid odor (after six weeks). Proteus and Hafnia spp. are
involved in spoilage of this product (Chapter 21).
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