Post-mortem Handling of Carcasses and Meat Quality PDF

**Meat Hygiene \| Part I \| 5^th^ year** Post-mortem Handling of Carcasses and Meat Quality ================================================== Cold shortening is the result of the rapid chilling of carcasses immediately after slaughter, before the glycogen in the muscle has been converted to lacti...

**Meat Hygiene \| Part I \| 5^th^ year** Post-mortem Handling of Carcasses and Meat Quality ================================================== Cold shortening is the result of the rapid chilling of carcasses immediately after slaughter, before the glycogen in the muscle has been converted to lactic acid. Due to muscle is cooled below about 10°C before the onset of rigor the meat will be tough after cooking.. Beef carcasses tend to cool slowly because of their bulk and are again less prone. Lamb carcasses are small enough to cool rapidly and generally do not enter rigor quickly. They are therefore most prone to shortening. Different muscles in the carcass will also be differently predisposed to cold shortening because of inherent metabolic differences. So, while the m. longissimus dorsi is very prone to cold shortening, Variation in antemortem handling may also deplete glycogen stores.The mechanism of cold shortening is thought to be stimulation, by the low temperature, of massive release of calcium ions from the sarcoplasmic reticulum without subsequent sequestration. in cold-shortened meat ,tenderization decreases as muscles shorten more Therefore, meat with shorter sarcomeres tends to tenderize least. In normal beef, cold shortening can be prevented by ensuring that muscle temperature does not fall below 10°C until the muscle pH has reached 6.1, which would normally take about 10 h. By this time, the progress of rigor will be sufficiently advanced to prevent cold contraction.. Heat ring ========= When beef is subjected to rapid cooling. In particular, the region of the m. longissimus dorsi closest to the exterior of the carcass cools faster than the inside, slowing the pace of pH drop. This causes a darker band of muscle to show up. This has an unpleasant look.. Very fast chilling ================== very fast chilling (VFC) expected cold shortening did not occur of meat has been investigated more fully In this procedure the rate of chilling is extreme, with the carcasses held in intensely cold air (-70 to -20°C) moving at high speeds. this can lead to tender meat in some circumstances, rather than the toughening associated with cold shortening. The reasons may be that A hard crust formed by the frozen surface of the meat could prevent shortening of the underlying muscle by virtue of the physical restraint. The differential freezing might cause breaks in the meat structure, so tenderizing the meat might promote proteolysis by stimulating the calpain system. Thaw rigor ========== If the rate of cooling of the carcass is sufficiently high and the meat freezes before the onset of rigor then, on thawing, the muscle shortens severely (to up to 50% of its length) and becomes very tough after cooking. Additionally, very large amounts of drip or exudate (30% of muscle weight) are lost during thawing. This is known as thaw rigor. It is thought that, on thawing, glycolysis is completed very rapidly and ATP breakdown is extremely rapid. This rapid metabolism is accompanied by a very strong contract Heat shortening =============== If muscles are stimulated, and allowed to contract and shorten, at high temperatures, without subsequent relaxation, then they may subsequently become tough. Carcass Handling Procedures to Improve Quality 1- Electrical stimulation ======================================================================== Electrical stimulation of carcasses at various times after slaughter speeds up the normal post-mortem processes by causing intense muscle contractions. In beef carcasses, the fall in pH to about 6.0 could take 10--12 h under normal conditions. Electrical stimulation may improve flavour by affecting the concentrations of flavour precursors and enhancers, such as nucleotides, in the muscles. electrical stimulation of beef leads to the accumulation of peptides and glutamic acid which are thought to contribute to better flavour. 2- Hot processing ================= Conventional systems chill the whole carcass to a temperature of 7°C or less before subsequent cutting into smaller parts and further processing. This can be wasteful of chiller capacity, and energy consumption. A solution is to process the carcass when it is still hot, before chilling. Because the processing largely involves removal of muscles from the skeleton it is often referred to as hot boning, hot deboning or hot cutting. As well as saving refrigeration space and energy, the system may require less labour and reduce the time needed to produce marketable meat. Meat yield can be improved by up to about 2% because of the reduction in evaporative and drying losses. The meat also tends to have better WHC, so loses less drip during storage and colour is more uniform. Both these effects can be attributed to faster, more uniform cooling of the smaller meat pieces, compared with whole carcasses. Because the muscles are removed before they have gone into rigor, Hot processing is especially suitable for beef forequarter meat. Hot processing could influence the microbiological characteristics of the meat. Exposure of a large surface area allows the potential for the contamination by bacteria from the operative's hands and tools, and contamination at a time when the meat temperature is high and the meat surface is wet or sticky. This might predispose hot processed meat to faster spoilage or the growth of pathogenic bacteria associated with food poisoning. Novel carcass suspension methods ================================ The conventional way to suspend carcasses during chilling is by the hind legs using a hook passed behind the Achilles tendon. The weight of the carcass puts many muscles into tension so stretching them as they pass into rigor. This stretching may increase sarcomere lengths and produce more tender meat. 4- Meat Packaging ================= This has three main functions: - It protects the meat from contamination and inhibits microbial growth, - it reduces or eliminates evaporative weight loss and surface drying - it may enhance the appearance of the product. Consumers like meat such as beef and lamb to appear bright red because they associate the color with freshness. The red is produced by reaction of the muscle haem pigments with oxygen. Covering meat with plastic films of different gas permeability can affect this reaction and so alter the color of the meat surface.