Meat is an ideal culture medium for many organisms. It is because of the various intrinsic factors like high moisture of around 75%,rich in nitrogenous compounds of sarcoplasmic and myofibrillar proteins and being supplied with minerals and accessory growth factors. It usually contains some fermentable carbohydrates at a favourable pH for most microorganisms. The inner flesh of meat is generally sterile or only a few numbers of microorganisms can survive there. They are found in bone marrow, lymph etc. Normal slaughtering removes the lymph nodes from edible parts. Let’s have a detailed explanation of Microbiology Of Meat.
Microbiology of Meat
Majority of the spoilage microorganisms are contaminants, coming from external sources during unhygienic and improper bleeding, handling and processing. The exterior surface of the animals normally harbours large numbers and many kind of microorganisms from soil, water feed, and manure, as well as natural surface flora, and the intestinal contents contain the intestinal organisms. Knives, cloths, air, other handling equipment, and hands of workers can serve as intermediate sources of contaminants. During handling of the meat and thereafter, contamination can come from carts, boxes, or other containers; other contaminated meat; air; and personnel. Because of the varied sources, the kinds of microorganisms likely to contaminate meats are many.
Moulds of many genera may reach the surface of meats and grow there. The important species are genera:
Yeasts, mostly asporogenous ones, often are present.
Bacteria of many genera are found, among which some of the more important are Pseudomonas, Acinetobacter, Moraxella, Alcaligens, Micrococcus, Streptococcus, Sarcina, Leuconostoc, Lactobacillus, Proteus, Flavobacterium, Bacillus, Clostridium, Escherichia, Campylobacter, Salmonella, and Streptomyces. Many of these bacteria can grow at chilling temperatures. There also is a possibility of the contamination of meat and meat products with human pathogens, especially those of the intestinal type. Further contamination can take place due to unhygienic handling in retail market and in home
Spoilage Of Meat under Aerobic condition :
Surface slime: caused by species of Pseudomonas, Acinetobacter, Alcaligens, Micrococcus, Streptococcus, Leuconostoc, and Bacillus. The spoilage microflora forms a thin film on meat, which enables them to obtain nourishment from the substrate.
Changes in colour of meat pigments : The red colour of meat, called its “bloom,” may be changed to shades of green, brown, or grey. It is due to the production of oxidizing compounds like peroxides, or hydrogen sulfide, by bacteria. Species of Lactobacillus (mostly heterofermentative) and Leuconostoc are reported to cause the greening of sausage.
Changes in fats : Lipolytic bacteria like Pseudomonas and Achromobacter and yeasts may cause some lipolysis and also accelerate the oxidation of the fats.
Surface discoloration : The “red spot” may be caused bySerratia marcescent. Pseudomonas syncyanea can impart a blue colour to the surface. Yellow discolorations are caused by species of Micrococcus or Flavobacterium, Chromobacterium lividum.
Off odours and off tastes – “Taints and souring or undesirable odours and tastes, in meat are the result of the growth of bacteria on the surface.
Aerobic growth of moulds may cause the following :
Stickiness – Incipient growth of moulds makes the surface of the meat sticky to the touch.
Whiskers – When meat is stored at temperatures near freezing, a limited amount of mycelial growth may take place without sporulation, It is caused by Thamnidium chaetocladioides, or T. elegans; Mucor mucedo, M. lusitanicus, or M. racemosus; Rhizopus.
Black spot is usually is caused by Cladosporium herbarum and white spot by Sporotrichum carnis moulds like Geotrichum. Green patches are caused by Penicillium expansum, Penicillium asperulum, and Penicillium oxalicum.
Moulds also cause oxidation of fats and give off odour and off taste.
Spoilage OF meat under Anaerobic Conditions :
Souring : The term implies a sour odour and perhaps taste. This could be caused by formic, acetic, butyric, propionic, and higher fatty acids or other organic acids such as lactic or succinic acid. There is gas formation accompanying the action of the “butyric” Clostridium species and the coliform bacteria on carbohydrates.
Putrefaction : True putrefaction is the anaerobic decomposition of protein with the production of foul-smelling compounds such as hydrogen sulfide, mercaptans, indole, skatole, ammonia, and amines. It is usually caused by species of Clostridium, but can also by Pseudomonas, Proteus, and Alcaligenes.
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