Meat and Meat Products.

Contamination and Spoilage of Meat and Meat Products.

Meat is an ideal culture medium for many organisms because it is high in moisture; rich in nitrogenous food and various degrees of complexity and plentifully supplied with minerals and accessory growth factors. It usually contains some fermentable carbohydrates at a favorable 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 will remove the lymph nodes form edible parts. Majority of the spoilage microorganisms are contaminants, comes from external sources during unhygienic bleeding, handling and processing. The exterior of the animals normally harbors 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, and hands of workers can serve as intermediate sources of contaminants. During handling of the meat 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. Molds of many genera may reach the surface of meats and grow there. Especially important are species of genera Cladosporium, Sporotrichum, Geotrichum, Thamnidium, Mucor, Penicilium, Alternaria, and Monilia. Yeasts, mostly asporogenous ones, often are present. Bacteria of many genera are found, among which some of the more importanat 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.

Upon death of animals microorganisms gain access to the flesh of the animal. Factors influencing this invasion include:

The load of the gut of the animal: The greater the load, the greater the invasion of tissues. For that reason starvation of 24hr before slaughter has been practiced.

The physiological condition of the animal before slaughtering: If the animal is excited, or fatigued, bacteria are more likely to enter the tissues. The earlier release of juices from tissues and rapid denaturation of proteins favors growth of microbe within the tissue.

The method of killing and bleeding play an important role in the rate of spoilage of the meat.

The rate of cooling: rapid cooling soon after dressing will result the extension of lag phase of microbial growth there by decreases the rate of spoilage.

Upon gaining entry to the flesh the growth of the contaminant microbes are affected by a wealth of factors such as

The kind and amount of contamination with microorganisms and the spread of these organisms in the meat.

The physical properties of the meat.

Chemical properties of the meat. (Presence of inhibitory substances)

Availability of oxygen.

Temperature.

pH

Moisture content

Osmotic pressure etc.

General type of Spoilage of meats and meat Products.

Spoilage under Aerobic condition:

Surface slime: caused by species of Pseudomonas, Acinetobacter, Moraxella, Alcaligens, Micrococcus, Streptococcus, Leuconostoc, and Bacillus. Some species of lactobacillus can also produce slime. The spoilage microflora form a thin film on meat, which enable them to obtain nourishment from the substrate. The temperature and the availability of moisture influence the kind of microorganisms causes surface slime. At chilling temperature high moisture will favor the growth of Pseudomonas while at low moisture those organisms with low a_w, such as micrococci and yeasts dominates and with still less moisture only molds can grow.

Changes in colour of meat pigments : The red colour of meat, called its "bloom," may be changed to shades of green, brown, or grey as a result of the production of oxidizing compounds, e.g., peroxides, or of hydrogen sulfide, by bacteria. Species of Lactobacillus (mostly heterofer?mentative) and Leuconostoc are reported to cause the greening of sausage.

Changes in fats. The oxidation of unsaturated fats in meats takes place chemically in air and may be catalyzed by light and copper. Lipolytic bacteria may cause some lipolysis and also may accelerate the oxidation of the fats. Rancidity of fats may be caused by lipolytic species of Pseudomonas and Achromobacter or by yeasts.

Phosphorescence: This rather uncommon defect is caused by phospho?rescent or luminous bacteria, e.g., Photobacterium spp., growing on the sur?face of the meat.

Moreover, various surface colors due to pigmented bacteria has been reported in spoiled meat. The "red spot" may be caused by Serratia marcescens or other bacteria with red pigments. Pseudo?monas syncyanea can impart a blue color to the surface. Yellow discolora?tions are caused by bacteria with yellow pigments, usually species of Micro?coccus or Flavobacterium. Chromobacterium lividum and other bacteria give greenish-blue to brownish-black spots on stored beef. The purple "stamping?ink" discoloration of surface fat is caused by yellow-pigmented cocci and rods. When the fat becomes rancid and peroxides appear, the yellow color changes to a greenish shade and later becomes purplish to blue.

Off odours and off tastes. "Taints," or undesirable odours and tastes, which appear in meat as a result of the growth of bacteria on the surface often, are evident before other signs of spoilage. "Souring" is the term applied to almost any defect that gives a sour odour that may be due to volatile acids, e.g., for?mic, acetic, butyric, and propionic, or even to growth of yeasts. "Cold-storage flavour" or taint is an indefinite term for a stale flavour. Actinomycetes may be responsible for a musty or earthy flavour.

Under aerobic conditions yeasts may grow on the surface of meats, causing sliminess, lipolysis, off odours and tastes, and discolorations-white, cream, pink, or brown-due to pigments in the yeasts.

Aerobic growth of molds may cause the following:

Stickiness. Incipient growth of molds 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. Such white, fuzzy growth can be caused by a number of molds, including Thamnidium chae?tocladioides, or T. elegans; Mucor mucedo, M. lusitanicus, or M. racemosus; Rhizopus and others. Controlled growth of a special strain of Thamnidium has been recommended for improvement in flavor during aging of beef.

Black spot. This usually is caused by Cladosporium herbarum, but other molds with dark pigments may be responsible.

White spot. Sporotrichum carnis is the most common cause of white spot, although any mold with wet, yeastlike colonies, e.g., Geotrichum, can cause white spot.

Green patches. These are caused for the most part by the green spores of species of Penicillium such as P. expansum, P. asperulum, and P. oxalicum.

Decomposition of fats. Many molds have lipases and hence cause hydrol?ysis of fats. Molds also aid in the oxidation of fats.

Off odours and off tastes. Molds give a musty flavor to meat in the vicinity of their growth. Sometimes the defect is given a name indicating the cause, e.g., "thamnidium taint."

Spots of surface spoilage by yeasts and molds usually are localized to a great extent and can be trimmed off without harm to the rest of the meat. The time that has been allowed for diffusion of the products of decomposition into the meat and the rate of that diffusion will determine the depth to which the defect will appear. Extensive bacterial growth over the surface may bring fairly deep penetration. Then, too, facultative bacteria may grow inward slowly.

Spoilage under Anaerobic Conditions:

Facultative and anaerobic bacteria are able to grow within the meat under anaerobic conditions and cause spoilage.

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. Souring can result from (a) action of the meat's own enzymes during aging or ripening, (b) anaerobic production of fatty acids or lactic acid by bacterial action, or (c) proteolysis without putrefaction, caused by facultative or anaerobic bacteria and sometimes called `stink?ing sour fermentation." Acid and gas formation accompany the action of the "butyric" Clostridium species and the coliform bacteria on carbohydrates. Vacuum-packed meats, especially those in gastight wrappers, commonly support the growth of lactic acid bacteria.

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 usually is caused by spe?cies of Clostridium, but facultative bacteria may cause putrefaction or assist in its production, Generally members of the genera Pseudomonas, Proteus, Clostridium and Alcaligenes cause putrefaction in meat and meat products. . The putrefaction caused by clostridia is usually accompanies by gas formation.

Taint. "Taint" is a still more inexact word applied to any off taste or off odor. The term "bone taint" of meats refers to either souring or putrefaction next to the bones, especially i