Rigor Mortis PDF

Rigor-Mortis CONVERSION OF MUSCLE TO MEAT Dr. Waleed R. El-Ghareeb Dr. Waleed R. El-Ghareeb  Events: Muscle to Meat Animal is slaughtered. Metabolism Shifts From Aerobic To Anaerobic State When O2 Is Depleted. Glycogen is converted to lactic acid, lowerin...

Rigor-Mortis CONVERSION OF MUSCLE TO MEAT Dr. Waleed R. El-Ghareeb Dr. Waleed R. El-Ghareeb  Events: Muscle to Meat Animal is slaughtered. Metabolism Shifts From Aerobic To Anaerobic State When O2 Is Depleted. Glycogen is converted to lactic acid, lowering muscle pH from ~7 to 5.6. Creatine Phosphate and ATP decline. Myosin heads form a tight bond with actin(Actomyosin). Muscle goes into rigor mortis (“Stiffness Of Death”). Proteolysis begins, tenderizing muscle. Dr. Waleed R. El-Ghareeb  Post-Mortem changes (Rigor-Mortis) 1-Rigor mortis: When muscle fibers are completely depleted of Adenosine Triphosphate (ATP) and creatine phosphate (CP), they develop a state of extreme rigidity called rigor. When this occurs after slaughter, the condition is called rigor mortis. In rigor, almost all of the myosin heads attach to actin but in abnormal, fixed and resistant way resulting in excessive muscular contraction, exhaustion of oxidative enzymatic system and accumulation of metabolic products (mostly lactic acid), where muscles and joints assume a stiff condition known as post-mortem rigidity or rigor mortis Dr. Waleed R. El-Ghareeb Dr. Waleed R. El-Ghareeb Aerobic glycolysis Dr. Waleed R. El-Ghareeb Anaerobic glycolysis Dr. Waleed R. El-Ghareeb  Rigor has three phases: Delay phase — while there is plenty of ATP in the muscle (with Mg++), the muscle will remain in the relaxed state. Onset phase — As stores of ATP and Creatine Phosphate (CP is used to dephosphorylate ADP to ATP) are used up, rigor bonds between the thick and thin myofilaments are formed. As more bonds are formed, the muscle loses extensibility. Completion — When all of the CP is gone, the muscle has no way of regenerating ATP. Thus, full rigor mortis will set in. Dr. Waleed R. El-Ghareeb Extensibility of Muscle During Rigor Development (Muscle is extensible and elastic) (Muscle begins to lose extensibility) Dr. Waleed R. El-Ghareeb Figure. Rigor Mortis as a Function of Meat Chemistry and Time The timing of the stages of rigor mortis varies between species. Poultry is often in rigor within 1-2 hours, pork within 4 to 6 hours, beef and lamb within 7 to 15 hours after exsanguination. Dr. Waleed R. El-Ghareeb  ATP, CP, pH and Extensibility Postmortem Muscle Muscle pH Extensibility ATP Creatine Phosphate Dr. Waleed R. El-Ghareeb Dr. Waleed R. El-Ghareeb  Calpains and Calpastatins Calpains (Calcium-activated Proteins) degrade proteins during cooler aging. Calpastatins inhibit the action of calpains. Thus, if an animal has a higher calpastatin level, the calpains are less active, and cooler aging has less affect on muscle tenderness. Brahman cattle are naturally tougher because of higher contents of calpastatin. Dr. Waleed R. El-Ghareeb  PSE Muscle Ante mortem stress (short term stress) usually increases the severity of PSE. Muscle pH drops very fast, body temp increases causing the meat to be pale in color, soft in texture with exudation of water. Negative impact on consumer sales appeal and shrinkage is greatly increased. Dr. Waleed R. El-Ghareeb  PSE in Turkey Normal PSE Dr. Waleed R. El-Ghareeb  DFD - “DARK CUTTERS” Caused by a shortage of glycogen at slaughter (long term stress). Without enough glycogen to convert to lactic acid, the muscle pH stays high, closer to 7.0 (living muscle pH) Antemortem stressors cause DFD. Results in muscle too dark in color, firm in texture, and dry on muscle surface (the opposite of PSE muscle); is sweeter. Beef has the most DFD problems. Rare in poultry Solution: Feed and rest for 24 or 48 hr prior to slaughter. Dr. Waleed R. El-Ghareeb Dark Cutter vs Normal Dr. Waleed R. El-Ghareeb  Factors affecting rigor mortis: I-Intrinsic factors II-Extrinsic factors *Animal species. *Stress. *Age of animal. *Pre-slaughter drug admin. *Sex of animal. * Temperature. *Type of muscle. * Method of slaughter. *Pathology. *Genotype. Dr. Waleed R. El-Ghareeb I- Intrinsic factors: 1- Animal species: Faster in the pigs than in cattle or sheep. 2- Age and sex of animal Cattle showed that the ultimate pH value is higher in entire males than in castrated and females. This may be a sequence of the greater stress susceptibility of entire males. Older animals are stated to produce meat of lower ultimate pH value. Dr. Waleed R. El-Ghareeb 3- Type of muscle: The muscle type is of considerable importance in determining the rate of post-mortem glycolysis, which resulting from the different role of "red" and "white" muscles. Red muscles, adapted to carry out slow, prolonged activity (The long muscles of the back are red muscles). White muscle, which adapted to fast intermittent activity are contains a high levels of ATP-ase activity, a high content of creatine phosphate and glycogen. For these reasons, the rate of post- mortem glycolysis can be significantly greater in white than in red muscles. Dr. Waleed R. El-Ghareeb 4- Pathology (health of animals): Post-mortem glycolysis may be entirely absent in diseased or fatigued animal. 5- Genotype: In the pig particularly, the breed and genotype within the breed are important determinants of rate of glycolysis. Certain breeds of pig e.g. large white pigs are liable to PSE. Dr. Waleed R. El-Ghareeb II- Extrinsic factors: 1- Stress: Stress is usually associated with mishandling, but any factors leading to anxiety or anger are stressors. These include fasting, high and low temperatures, anoxia and conditions during transportation and at the slaughterhouse. 2- Pre-slaughter drug administration: Pre-slaughter administration of drugs including hormones, can alter the course of glycolysis. Calcium salts, increase the rate of glycolysis, while magnesium salts have the opposite effect. In addition, adrenaline and noradrenaline will accelerate the rate of glycolysis. Dr. Waleed R. El-Ghareeb 3- Temperature: A high temperature increases the rate of post-mortem glycolysis, whereas low temperature retards it. As a result, the rates of post-mortem glycolysis will tend to be higher in muscles, which are slow to cool, and vice versa. 4-Method of slaughter: Slaughterhouse procedures can affect the rate of glycolysis. The process of pithing, which is used to destroy the central nervous system at slaughter, accelerates post-mortem glycolysis Dr. Waleed R. El-Ghareeb *Significance of rigor-mortis: 1-It plays an important role in the keeping quality of meat as acid reaction retards the putrefaction of meat. 2-Rigor mortis is of importance for one can determine the degree of keeping quality of meat through measuring the reaction of the muscle. 3- Increase of tenderness, which is said to be produced by the softening and swelling of the collagen fibers, which are converted into softer and more digestible gelatin by the action of lactic acid and heat. This process called meat ripening, conditioning, or tenderization Dr. Waleed R. El-Ghareeb