LPT 321: Meat Science (1+1)

MICROBES INVOLVED IN DECOMPOSITION OF MEAT

• Decomposition is the breaking–up of organic matter, chiefly protein but also fats and carbohydrates, by the action of bacteria, moulds and yeasts, which split the meat up into a number of chemical substances, many of which are gaseous and foul smelling.
• All forms of foods in their state remain in a fresh and edible state for only a comparatively short time.
• Foods rapidly acquire bacteria, moulds or yeasts, which are the main causes of spoilage or decomposition.
• Before terminal decomposition changes occur, however, other factors such as enzyme action (food and bacterial) and oxidation take place in some foods.
• Enzymes or ferments, which are present in all living cells, catalyze the complicated chemical reactions taking place in the cells.
• Enzymes essentially bring about the process of autolysis, self-destruction or self-degradation and at a rate, which varies markedly in the different tissues.
• In general it is highest in those tissues in which protein is synthesized in large amounts and which have high water contents, e.g. gastrointestinal mucosa, testes, pancreas and adrenals.
• Tissues such as the liver, kidneys and endocrine glands have slower autolytic rates and the tissues with lowest metabolic rates such as skin, muscles, bone, heart and blood vessels have the lowest autolytic rates of all tissues.
• The various forms of food preservation are designed to prevent decomposition by limiting the activity of enzymes, the process of oxidation and bacterial spoilage.
• All forms of food are subject to natural deterioration, their shelf life being dependent on their structure, pH, composition, water content, presence or absence of bacteria and /or damage and conditions of storage.
• Foods with high water content (e.g. meat and offal) are liable to spoil rapidly unless steps are taken to counter deterioration.
• In addition to microbial spoilage, physical damage, which occurs during handling, transportation and processing, can be regarded as a form of spoilage as can insects, rodents and other pests.
• Foods damaged in this way are more susceptible to change by microbial action.
• Fresh meats are initially contaminated from many different sources – soil, dust, faeces and water, equipment, hands and clothing of personnel subsequently adding to this pollution.
• Meat can harbour organisms, mostly of the Gram-positive mesophilic type.
• Depending on the types of bacteria present, meat-borne disease or spoilage or both may result, especially if substandard handling methods are adopted.
• The main types of bacteria involved in the spoilage of meat belong to the following genera:
  • Gram-positive organisms
    • Micrococcus,
    • Staphylococcus (Staph. albus & Staph. aureus)
    • Streptococcus (Str. feacalis, Str. faecium, Str. durans)
    • Lactobacillus,
    • Leuconostoc,
    • Bacillus (B. subtilis, B. thermophilus & B. coagulans),
    • Clostridium (Cl. sporogenes, Cl.histolyticum, Cl. perfringens & Cl. butyricum),
    • Corynebacterium and
    • Microbacterium.
  • Gram-negative organisms
    • Pseudomonas
    • Flavobacterium
    • Acinobacter
    • Achromobacter
    • Alcaligenes
    • Halobacterium
    • Moraxella
    • Escherichia and
    • Klebsiella