SPOILAGE OF MEAT

CONTENTInfection 1.Endogenous 2. Exogenous infection

Factors affecting the growth of Meat Spoilage 1.Tempearture 2.Moisture and Osmotic Pressure 3.pH 4.Oxidation reduction potential 5.Atmospehere 6.High pressure

Prophylaxis

InfectionThe organisms which spoil meat may gain access through infection of the living animal (endogenous disease) or by contamination of the meat post-mortem (exogenous disease).Endogenous (Before death)Consumption of meat from infected animal Example: Anthrax, bovine tuberculosis and brucellosis.Causal agents: Bacillus anthracis, Mycobacterium tuberculosis and Brucella spp20–30 per cent of all cattle in Britain were affected by tuberculosis towards the end of 19th century.

Exogenous infection

ExogenousInfection of meat after processing (After death of animal)

Parasitic worms, bacteria, fungi infects the meat after death and it leads to spoilage of meat. Where there is proper meat inspection to eliminate infected carcasses from distribution, the predominant mode of meat deterioration by invading organisms will be by exogenous infection.

1. Bacteraemia 2. Sources and nature of external contamination

Bacteraemia

There is an equilibrium between invasion of the tissues and removal of the invading organisms such that the tissues of healthy animals are normally free from bacteria.

If an infected knife is used, or organisms are inadvertently introduced from the skin whilst the main blood vessels are being severed, bleeding can itself lead to bacteraemia and to the infection of the animal’s tissues.

Meat can be contaminated by bacteria that persist on powered tools (e.g. air-driven knives) used in carcass dressing

Sources and nature of external contamination

External contamination of the meat is a continuing possibility from the moment of bleeding until consumption.In the abattoir itself there are a large number of potential sources of infection by micro-organisms.These include The hide, Soil adhering The contents of the gastrointestinal tract (if inadvertently released

during dressing operations) Airborne contamination Aqueous sources (the water used for washing the carcass, or for

cleaning the floors) The instruments used in dressing(knives, saws, cleavers and hooks), Various vessels and receptacles, Personnel

Typical microbial counts in sources of microbial contamination in an abattoir

Some characteristics of bacterial meat poisoning

Symptom of Spoilage

Factors affecting the growth of Meat Spoilage

Temperature Moisture pH Oxidation-reduction potential Atmosphere High Pressure

Temperature

The most important single factor governing microbial growth is temperature.Broadly, the higher the temperature the greater is the rate of growth. Many meat micro-organisms will grow to some extent at all temperatures from below 0 °C to above 65°C, but, for a given organism, vigorous growth occurs in a more limited temperature range.Spoilage organisms in three categoriesPsychrophiles : temperature between –2 °C and 7 °C,Mesophiles : 10 °C - 40°C Thermophiles : 43 to 66 °C

The effect of temperature on the rate of growth of various bacteria

Moisture and osmotic pressureAfter temperature, the availability of moisture is perhaps the most important requirement for microbial growth on meat, although some types of bacteria may remain dormant for lengthy periods at low moisture levels, and spores resist destruction by dry heat more than by moist heat. The availability of moisture is complementary to that of osmotic pressure, which is a function of the concentration of soluble, dialyzable substances (salts, carbohydrates, etc.) in the aqueous medium. High solute concentrations tend to inhibit growthMolds and yeasts tolerate higher osmotic pressures than bacteria Bacteria growing from an aw : 1.0 -0.75Yeasts and molds growing slowly at an aw of 0.62

The effect of surface moisture and temperatureon microbial growth on lamb cuts

pHpH of meat will be determined by the amount of lactic acid produced from glycogen during anaerobic glycolysis and this will be curtailed if glycogen is depleted by fatigue, inanition or fear in the animal before slaughter.

Most bacteria grow optimally at about pH 7 Not well below pH 4 or above pH 9

Optimal pH values and salt concentration for ham spoilage organisms

Oxidation–reduction potentialImmediately after death, whilst temperature and pH are still high, it would be expected that the dangers of proliferation of, and spoilage by, anaerobes would be great. That such does not generally occur appears to be due to the level of the oxidation–reduction potential which usually does not fall for some time.

The presence of nitrate in cured meats probably exerts an indirect antibacterial effect through raising the Eh of the system.

Atmosphere

A major grouping of micro-organisms can be made on the basis of the oxygen tension which they need or can be made to tolerate – aerobes, anaerobes and facultative.

The exposed surfaces of fresh meat at chill temperatures would normally support the growth of aerobes such as members of the genera Achromobacter and Pseudomonas.

High Pressure

The degree of pressure inactivation is affected by the type of micro-organism, the pressure applied, the duration and temperature of the applied process and the pH of the medium. The inactivation of micro-organisms by high pressure appears to be due to intracellular damage.There is considerable variation in susceptibility to pressure between the types of micro-organism found in meat.

Prophylaxis

1. Hygiene2. Biological Control3. Antibiotics4. Ionising radiation