Economic impact of Meat Spoilage and Preservation
Dr.Kedar Karki.
Veterinary Health Management Specialist.
Ostrich Nepal Pvt.Ltd
INTRODUCTION.
Rich nutrient matrix meat is the first-choice source of animal protein for many people all over the world. Consumption of meat is continuously increasing worldwide. The annual per capita consumption increased from 10 kg in the 1960s to 26 kg in 2000 and will reach 37 kg by the year 2030. On the other hand, a significant portion of meat and meat products are spoiled every year. It is being reported that approximately 3.5 billion kg of poultry and meat were wasted at the consumer, retailer and foodservice levels which have a substantial economic and environmental impact. Significant portion of this loss is due to microbial spoilage.
The transformation of animals into meat involves several operations: (a) handling and loading of animals on the farm, (b) transporting animals to slaughterhouses, (c) off-loading and holding of animals and (d) slaughtering of animals. Poor operational techniques and facilities in any of these operations will result in unnecessary suffering and injuries to animals which can lead to loss of meat, reduced meat quality and spoilage of meat. Therefore, prevention of contamination after slaughtering during meat cutting and processing is essential. Storage time can be extended through hygienic slaughtering and clean handling of the carcass.
Different technical operations are involved in slaughtering: (a) stunning, (b) bleeding, (c) skinning, (d) evisceration and (e) carcass splitting. Inadequacy at one stage will result in a rigorous negative impact on the product and/or process in the following stage. In addition to the hygiene and storage temperature, the acidity of the meat and the structure of the muscular tissue also affect the rate of meat spoilage. For example, liver will spoil faster than the firm muscular tissue of beef. After few hours of slaughtering of animals, muscles becomes firm and rigid, a condition known as rigor mortis. The process of rigor mortis depends on the stress induced on the animals during the slaughtering process. Raw meat quality is reported to be severely affected by the stress conditions during slaughtering process and the slaughtering methods.Fat, protein, minerals, carbohydrate and water are the constituents of meat.
The quality of meat and meat products degrade as a result of digestive enzymes, microbial spoilage and fat oxidation. Lipid oxidation, protein degradation and the loss of other valuable molecules are the consequence of meat spoilage process. Proteins and lipids can break down resulting in the production of new compounds causing changes in meat flavor, tenderness, juiciness, odour and texture. It is therefore, important to understand the causes of spoilage of meat and meat product in order to develop optimum preservation techniques to maintain the freshness of these food products.
CAUSES OF MEAT SPOILAGE.
Pre-slaughter handling of livestock and post-slaughter handling of meat play an important part in deterioration of meat quality. The glycogen content of animal muscles is reduced when the animal is exposed to pre-slaughter stress which changes the pH of the meat, to higher or lower levels, depending on the production level of lactic acid. Lactic acid is produced due to the breakdown of glycogen content of animal muscles via an anaerobic glycolytic pathway. Higher levels of pH (6.4-6.8) result in Dark, Firm and Dry meat. Long term stress causes Dark, Firm and Dry meat which has a shorter shelf life. Sever short term stress results in a Pale, Soft and Exudative meat. Pale, Soft and Exudative meat has a pH lower than normal ultimate value of 6.2 which is responsible for the breakdown of proteins, providing a favorable medium for the growth of bacteria. There are three main mechanisms for meat and meat products spoilage after slaughtering and during processing and storage: (a) microbial spoilage, (b) lipid oxidation and (c) autolytic enzymatic spoilage.
Microbial spoilage:
Meat and meat products provide excellent growth media for a variety of microflora (bacteria, yeasts and molds) some of which are pathogens. The intestinal tract and the skin of the animal are the main sources of these microorganisms. The composition of microflora in meat depends on various factors: (a) pre-slaughter husbandry practices free range Vs intensive rearing, (b) age of the animal at the time of slaughtering, (c) handling during slaughtering, evisceration and processing, (d) temperature controls during slaughtering, processing and distribution (e) preservation methods, (f) type of packaging and (g) handling and storage by consumer. The major genera of bacteria, yeasts and molds found inmeat and poultry products before spoilage. Mold species include Cladosporium, Sporotrichum, Geotrichum, Penicillium and Mucor while yeasts species include Candida spp., Cryptococcus spp. and Rhodotorula spp. Bacteria species include Pseudomonas, Micrococcus, Streptococcus, Sarcina, Lactobacillus, Salmonella, Escherichia, Clostridium and Bacillus.
Lipid oxidation:
Autoxidation of lipids and the production of free radicals are natural processes which affect fatty acids and lead to oxidative deterioration of meat and off-flavours development.After slaughtering of animals, the fatty acids in tissues undergo oxidation when the blood circulation stops and metabolic processes are blocked. Lipid oxidation is the reaction of oxygen with double bonds of fatty acids.
Enzymatic actions are natural process in the muscle cells of the animals after they have been slaughtered and are the leading cause of meat deterioration. The enzymes have the ability to combine chemically with other organic compounds and work as catalysts for chemical reactions that finally end up in meat self deterioration. In the autolysis process, the complex compounds carbohydrates, fats and protein of the tissues are broken down into simpler ones resulting in softening and greenish discoloration of the meat. These autolysis changes include proteolysis and fat hydrolysis which are prerequisite for microbial decomposition. Excessive autolysis is termed “souring”. Postmortem breakdown of polypeptides are the result of tissue proteases and is responsible for flavor and is textural changes in meat. Post mortem aging of red meat results in the tenderization process. Post-mortem autolysis takes place in all animal tissues but at different rates in different organs, quicker in glandular tissue such as the liver and slower in striated muscle. The enzymes calpains, cathepsins and aminopeptidases are found to be responsible for the post mortem autolysis of meat through digestion of the z- line proteins of the myofibril . Among these enzymes, calpains has been described as a preliminary contributor to the proteolytic tenderization process of meat. Cathepsins were, also, found to contribute to tenderization at low pH. Proteolytic enzymes are active at low temperatures (5°C) which lead to deterioration of meat quality due to growth of microbes and biogenic amines production.
Meat preservation became necessary for transporting meat for long distances without spoiling of texture, color and nutritional value after the development and rapid growth of super markets. The aims of preservation methods are: (a) to inhibit the microbial spoilage and (b) to minimize the oxidation and enzymatic spoilage. Traditional methods of meat preservation such as drying, smoking, brining, fermentation, refrigeration and canning have been replaced by new preservation techniques such as chemical, bio-preservative and non-thermal techniques. Current meat preservation methods are broadly categorized into three methods (a) controlling temperature (b) controlling water activity (c) use of chemical or bio-preservatives. A combination of these preservation techniques can be used to diminish the process of spoilage.
Low temperature methods:
The basic aim of cooling techniques is to slow or limit the spoilage rate as temperature below the optimal range can inhibit the microbial growth. Low temperature methods of storage are used in three levels: (a) chilling (b) freezing and (c) super-chilling. All these levels help to inhibit or completely stop bacterial growth. However, the growth of psychrophilic group of bacteria, yeasts and molds is not prevented by all levels of refrigeration and both enzymatic and non enzymatic changes will continue at a much slower rate.
Chilling:
Chilling is employed at slaughtering plants immediately after slaughtering and during transport and storage. It is necessary to reduce the temperature of carcass immediately after evisceration to 4°C within 4 h of slaughtering. Chilling is critical formeat hygiene, safety, shelf life, appearance and nutritional quality. It is employed by two methods: (a) immersion chilling, in which the product is immersed in chilled (0- 4°C) water and (b) air chilling, in which the carcasses are misted with water in a room with circulating. Carcass surface temperature is reduced at faster rate by air chilling which improves carcass drying and minimizes microbial spoilage. The microbial quality of the air-chilled product is better than that of a water-chilled product.
Freezing:
Freezing is an excellent method of keeping the original characteristics of fresh meat. Meat contains about 50-75% by weight water, depending on the species, and the process of freezing converts most of water into ice. Meat freezing phenomenon is fast and almost 75% of tissue fluid freezes at -5°C. The freezing rate is increased with decreases in temperature, almost 98% of water freezes at -20°C and complete crystal formation occurs at – 65°C. However, more than 10% of muscle bound water chemically bound to specific sites such as carbonyl and amino group of proteins and hydrogen bonding will not freeze. Freezing rate slow and fast affects the quality of frozen meat significantly. Fast freezing produce better quality meat than slow freezing. During slow freezing formation of large ice crystals damages the cell and results in protein denaturation. Concentration of enzymes and presence of other compounds govern the process of protein denaturation.
Super chilling:
Super chilling is a different concept than refrigeration and freezing and it has the potential to reduce storage and transport costs. Super-chilling refers to the temperature zone below its initial freezing point (1-2°C) but where ice crystals are not generated. In this process, instead of adding external ice to the food product, part of the internal water is frozen and works as a refrigeration reservoir, ensuring its refrigeration during distribution and transportation. Respiratory metabolism and aging process are repressed but cell activity is maintained during the storage period of super chilling
CONCLUSION:
Because worldwide population growth and globalization of the food supply, the control of meat spoilage becomes essential in order to increase its shelf life and maintain its nutritional value, texture and flavor. Meat is the first-choice of animal protein for human and consumption of meat is continuously increasing worldwide. The annual per capita consumption increased by 2.6 fold in 2000 and will increase by 3.7 fold by 2030 compared to that of 1960s. On the other hand, the rich nutrient matrix meat is subject to various types of spoilage depending on handling and storage conditions. Significant portions 3.5 billion kg of meat and meat products are spoiled every year at the consumer, retailer and foodservice levels which have a substantial economic and environmental impact. It is stated that if 5% of this meat loss is preserved it could satisfy the daily needs of approximately 320,000 people for meat and poultry. Meat spoilage leads to the development of off-flavors, off-odors and often slimes formation due to the breakdown of valuable contents fat, protein and carbohydrates which make the product undesirable for human consumption. Proper handling, pretreatment and preservation techniques can improve the quality of meat and meat products and increase their shelf life. For controlling enzymatic, oxidative and microbial spoilage, low temperature storage and chemical techniques are the most common in the industry today. It is essential to store the meat at lower than 4°C immediately after slaughtering and during transport and storage as it is critical for meat hygiene, safety, shelf life, appearance and eating quality. Although, microbial and enzymatic spoilage can be stopped or minimized at lower temperature. However, oxidative spoilage cannot be prevented by freezing. However, more efforts are required to understand the role of animal age, animal type, stress level before and during the slaughtering process, initial microbial load, type and nature of bacteria and their interactions in order to optimize the shelf-life of meat.
SAFETY AND QUALITY OF POULTRY & GOAT MEAT IN INDIA: A KEY NOTE
