April 27, 2003

Meat can be a potential source of food infection and food poisoning, as it is exposed to several undesirable conditions before it reaches the consumers

As meat constitutes a main portion of the diet of most people in Pakistan, millions of animals are slaughtered and thousands of tons of meat are supplied daily to the market. Meat is a highly nutritious edible portion of animals, and has a very high percentage of proteins (about 20%), fats (about 10%) and has very low concentrations of carbohydrates. Meat also has a high percentage of water content, about 75%.

All these factors make it very susceptible for microbial attack. It provides an ideal environment for the growth of a wide range of microorganisms that include pathogenic bacteria such as Listeria monocytgenes, Clostridium perfrinenes, C. botulinum, E. coli and also Salmonella, Yersinia, Campylobacter and Pseudomonas, etc. These organisms can cause listeriosis, botulism, severe diarrhoea, vomiting, abdominal pain, fever, nausea and much more.

Infected animal meat may also be a potential source of infectious, tumour and haemorrhagic viruses that may become active in non-permissive and common hosts. Cryptosporadium parasites that cause diarrhoea and nausea, and prions may also be present in the meat of the infected animals. Prions are small proteinaceous infectious particles that can transmit infectious diseases such as Mad Cow disease. Although the risk of transmission of Mad Cow disease through the food chain is considered to be low, it is not zero. The transmission of this disease by the ingestion of contaminated meat has been documented.

Meat spoilage organisms include bacteria such as Acinetobacter, Moraxella, Alcaligenes, Micrococci, and moulds and yeast, etc. Cooking of meat can destroy these spoilage and pathogenic organisms but the occurrence of heat-resistant spores and the heat-resistant toxins of these organisms cannot be ruled out. The chance of survival of these organisms are particularly high in some partially cooked items, such as steaks and barbecue, in which the interior of the meat remains uncooked.

Although the interior of the meat from a healthy animal is sterile, it can get contaminated due to the way it is handled from the slaughterhouses to the kitchen. These pathogenic and spoilage organisms enter the meat through the dung of the slaughtered animal and soil in which the carcasses are placed. As many organisms such as Listeria monocytgenes, Clostradium perfrinenes, C. botulirum, Acinetobacter and Pseudomonas, etc., are found in the soil, while E. coli, Salmonella, Yersinia, Campylobacter and Cryptosporadium parasites are found in faeces, thus all of these organisms can easily reach the meat and finally the consumers. During the course of a research on meat, carried out by the Department of Microbiology, University of Karachi, eight meat spoilage organisms were identified, out of which three were found to belong to the pathogenic group of microorganisms.

Before reaching the consumers, meat is exposed to several undesirable conditions. In Pakistan, the condition of the slaughter houses of the big cities are deplorable, whereas villages and small cities have no slaughterhouses available. It is commonly seen that the carcasses are placed on the floor in blood, dirt and dung for several hours before being transported. The time of the transportation of meat is also very long due to mismanagement and old means of transportation. The meat is transported in open vehicles in which it is exposed to dust, dirt, smoke and personally acquired infectious agents. Therefore, meat can be a potential source of food infection and food poisoning.

A research was conducted on the spoilage organisms that cause the degradation of the basic structural components of meat, such as proteins, lipids and phospholipids, by their enzymes proteases, lipases and phospholipases.

The composition of beef, mutton and chicken are different — chicken is low in fats and has more protein than beef and mutton, and it was found that most of the spoilage organisms have broad spectrum activity and can cause the spoilage of beef, mutton and chicken. Decomposition occurs with the passage of time under high temperature, humidity and moisture content of the meat. It is noteworthy that meat also has its endogenous degradation system based on its proteolytic system and causes decomposition of the meat, although slower as compared to the microorganisms that grow rapidly and cause the spoilage.

The study ruled out the conventional concept that preservation of meat through refrigeration is completely effective. The reason is the existence of psychrophilic bacteria that are able to proliferate even at low temperatures in refrigerators. Thus the degradation of meat can go on in the refrigerator, but it can be delayed. However, rancidity can occur as fat is prone to oxidation that can adversely affect the flavour, odour and colouration.

Garlic juice and salt were found to have inhibitory effect against spoilage as well as the pathogenic organisms of meat. So, if garlic juice in combination with salt and vinegar is used on the meat and stored in the refrigerator, the meat can be preserved from bacterial spoilage for a relatively long period of time.

At the occasion of Eid-ul-Azha, almost every Muslim family follows the religious ritual of offering the sacrifice of animals. By the time the animal is sacrificed, it has gone through immense amount of stress. It is necessary for animals to be stress- and injury-free during operations prior to slaughter so as not to exhaust muscle glycogen reserves. If the glycogen in the tissues is exhausted and rigor mortise sets in, the whole carcass becomes stiff due to the contraction of the muscle fibres. If the meat is cooked when the muscles are still in rigor, it is extremely tough and tasteless. This condition is prevented by ‘aging’ or ‘ripening’ the meat after slaughtering it, which is achieved by storing the meat at room temperature until the muscles gradually recover their extensibility and become more tender through partial enzymatic breakdown of muscle fibres. At this stage, rigor mortis is said to be resolved. Rigor is completed in cattle after 12-24 hours and is resolved by the time periods that depend on the temperature — 10-11 hours at 30 C. ‘Aging’ also leads to improvement of flavour. If lamb and, to a lesser extent, beef are chilled too rapidly after slaughter of the animal, the muscles may undergo extreme contraction or ‘cold shortening’ which results in the meat being very tough when cooked.

Cold shortening does not take place when the carcass is cooled more slowly, and the temperature must not fall rapidly below 10 C. To achieve this, the carcass is placed at room temperature for some hours to accelerate rigor and then it is rapidly chilled or frozen. This process is called ‘conditioning’.

The long distance that the animals are transported to, poor transport facilities, poor hygiene, high surrounding temperature and lack of refrigeration after slaughter, lead to heavy contamination, growth of microorganism, considerable losses from spoilage and chances of food-borne illnesses. All this can be aggravated by inadequate care of the meat during transportation and in the market. Particularly in case of shipment of the meat to great distances, it is essential to adopt sophisticated techniques and methods of refrigeration. The meat should be transported in closed containers and vehicles, properly wrapped in polythene and hanged instead of being placed on the floor of the vehicle with people sitting on it.

Beside these, a board having highly qualified professionals and microbiologists should be established to look after equality control, conditions and health of animals and the conditions of the slaughterhouses.

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