Preservation of Meat

Preservation of Meat

	Preservation of Meat - Meat and meat products, serve as excellent growth media for a variety of bacteria. Although the outer surface of meat in generally covered by microorganisms, the inner part of the meat contains few organisms. The contamination in meat comes mostly from external sources during bleeding, handling and processing. The main sources of microorganisms in meat are the' exterior of the animal and the intestinal tract. Microorganisms that contaminate meat vary widely but include both molds and bacteria. Molds such as Cladosporium, Sporotrichum, Geotrichum, Penicillium, Mucor etc., grow on the meat surfaces.
Bacteria such as species of: Pseudomonas, Micrococcus, Streptococcus, Sarcina, Lactobacillus, Salmonella, Escherichia, Clostridium; and Bacillus, are most common. Meat preservation is usually accomplished by a combination of methods. Unless cooling is rapid and prompt soon after slaughter, meat may undergo considerable changes in. quality and' appearance. Prevention of contamination during slaughter and processing is the best way to keep the microbial load down to a minimum.
Once the meat is contaminated, complete removal becomes difficult. Washing the animal before the slaughter may reduce the initial load and covering of meat immediately after slaughter may prevent further contamination. Unless cooled immediately, it will allow the multiplication of microorganisms already present. Today, meat is generally preserved by the use of low temperature. Modern packing houses chill the meat promptly to freezing temperature and store it at slightly above the freezing temperature.
Freezing however, does not eliminate physchrophilic microorganisms. The use of radiation in combination with chilling storage has also been used to lengthen the keeping time. Drying of meat as a method of preservation is an age old practice. A combination of smoking and drying, or salting, and smoking before drying, are common methods used to reduce the microbial load. Freeze drying of meat is also possible. Chemicals such as salt, sugar, sodium nitrate and sodium nitrite are used both as curing agents and as preservatives in meat processing. The primary purpose of sodium chloride is to reduce the aw while nitrate and nitrite serve both in fixing the colour as well as in being bacteriostatic. A variety of, antibiotics have been used in meat preservation but their use is prohibited.Raw meat is subject to spoilage by its own enzymes as well as by microbial action. Autolytic changes include proteolysis and fat hydrolysis. Excessive autolysis is called "souring".
	Types of spoilage under aerobic conditions include: (i) "surface slime" production caused by species of Pseudomonas, Streptococcus, Leuconostoc, Bacillus and Micrococcus, (ii) changes in meat colour as a result of H2S or peroxides produced by the bacteria, (iii) changes in lipids caused by lipolytic organisms or chemical rancidity, (iv) production of fluorescence caused by the growth of Photobacterium, (v) pigmentation due to growth of different bacteria, and (vi) off odour and off tastes production. Under aerobic conditions, yeasts and molds may grow and make the meat sticky, rancid, and spotty due to growth. Under anaerobic conditions, facultative and anaerobic bacteria grow within the meat and cause spoilage such as souring and putrefaction.

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