Conversion of Muscle to meat Rigor Mortis Dr

Conversion of Muscle to meat, Rigor Mortis Dr. R. K. Jaiswal Asstt. Prof. -cum-Jr. Scientist Dept. of Livestock Products Technology Bihar Veterinary College Bihar Animal Sciences University Patna-800014 (Bihar)

Introduction üMeat – Post rigor aspect of muscle üConversion of Muscle to Meat – a series of biochemical events following sticking, culminating in resolution of rigor. üExsanguination leads to immediate loss of oxygen supply to the muscle, decreasing oxidation reduction potential, resulting in cytochrome system, thus ETC and TCA cycle inhibition. üDepletion of creatinine phosphate soon follows. üHence, ATP re-phosphorylation aerobically ceases.

üHence anaerobic glycolysis commences, lactic acid accumulation follows. Decline in p. H follows suit. üResynthesis of ATP anaerobically inadequate to prevent actin-myosin formation. üOnset of rigor

Cardinal changes in Conversion of Muscle to Meat üLoss of Homeostasis üPost-mortem glycolysis and p. H decline üRigor Mortis üLoss of Protection from Invading Microorganisms üDegradation due to proteolytic enzymes üLoss of Structural Integrity üThus the conversion of muscle to meat is a culmination of the above biochemical changes and ultimately the resolution of rigor mortis.

Loss of Homeostasis üHomeostasis mechanism, a system for the physiologically balanced internal environment which helps the body to cope up with the stresses of oxygen deficiency, extreme variation in temperature, energy supply, etc. , is lost. üThe homeostasis is controlled by nervous system, which ceases to function within 4 -6 minutes after bleeding. üIn the absence of blood supply, there is loss of body heat and temperature starts declining.

Decline in p. H üIn the absence of oxygen, anaerobic glycolysis leads to the formation of lactic acid, and thus decrease in p. H. üRate and extent of p. H decline influenced by species of food animal, various pre-slaughter factors environmental temperature, etc. üp. H drop steady in the first 5 -7 hours, followed by little decrease in the next 15 -20 hours to ultimate ph. ( 5. 5 - 5. 7 from 6. 8 -7. 2) üThe rate of p. H decline is enhanced at high environmental temperature. A low ultimate p. H is desired to have a check on the proliferating microorganisms during storage.

ü A sharp decline in post-mortem p. H even before the dissipation of body heat through carcass chilling – PSE ü Contrary to this, muscles which maintain a consistently high p. H during post-mortem conversion to meat - DFD

Rigor Mortis ü Stiffening of muscles after death ü ATP complexed with Mg++ at certain concentration required for breaking the actomyosin bond for relaxation of muscle ü ATP concentration decreases, permanent actomyosin cross bridges begin to form. ü Muscle gradually becomes less and less extensible under an externally applied force. This is delayed phase of rigor mortis

ü Then actomyosin formation picks up and the muscle begins to loose extensibility rapidly. This phase is called the fast or onset phase of rigor mortis. ü When all the creatine phosphate (CP) is depleted, ADP can no longer be phosphorylated to ATP, muscle becomes quite inextensible and stiff. ü This stage marks the completion of rigor mortis

Loss of Protection against Invading Micro-organisms üDuring post-mortem period, body defense mechanism stops operating and membrane properties are altered. üSo, during conversion to meat, muscle is quite susceptible to invading micro-organisms. üExcept for low p. H, most of the other post-mortem changes favour bacterial growth. üHence, utmost handling precautions are necessary to prevent contamination of meat.

Degradation due to proteolytic enzymes ü Several autolytic lysosomal enzymes called cathepsins, which remain inactive in a living muscle tissue, are activated as the muscle p. H declines. ü These enzymes initiate the degradation of muscle protein structure. ü Catheptic enzymes are capable of breaking down even collagenous connective tissue of the muscle and cause tenderisation of meat during aging.

Loss of Structural Integrity • Post-mortem alteration of membrane properties initiates the degradation of muscular proteins. • There is a progressive disruption of myofibrillar structure. • The resolution of rigor mortis is reported to occur due to disintegration of Z-line structure. • A rapid decline in muscle p. H also causes denaturation of collagenous connective tissue.

Conversion of Muscle to Meat ü Conversion of 'Muscle' to 'Meat‘ : Sequence of Biochemical changes ü Disruption of homeostasis results in decrease in body temperature. ü Decrease in oxidation reduction potential shifts glycolysis to anaerobic glycolysis, resulting in accumulation of lactic acid and inadequate replenishment of ATP leads to irreversible actomyosin bond formation, increase in muscle tension.

ü Decrease in ATP also results in disruption of structural integrity of proteins ü The decrease in p. H ensures that cathepsins become active and thus sarcoplasmic proteins denature. ü Reduction in ATP, formation of actomyosin, approaching of the muscle p. H to isoelectric points of myofibrillar proteins and denaturation of proteins, lead to reduced WHC.

ü Resolution of rigor is the decrease in muscle tension due to proteolytic degradation of specific myofibrillar proteins that lead to dissolution of Z discs, loss of ultra structural integrity. ü Muscle, post the resolution of rigor is referred to as meat

Ageing ü Ageing - the holding of carcasses just above its freezing point so as to obviate microbial spoilage and accompanied by an enhancement in tenderness and flavour of meat. ü The enhancement in flavour is mainly attributed to inosine (inosine monophosphate), a breakdown product of ATP(adenosine monophosphate). ü The breakdown of protein and fat during ageing resulting in formation of hydrogen sulphide, ammonia, acetaldehyde, acetone and diacetyl.

ü An increase in free amino acids also adds to the development of characteristic meat flavour. ü The improvement in tenderness is on account of the subtle proteolysis that take place in the cytoskeletal proteins. ü Ageing period in different species of food animals Cattle : 14 days Sheep and Goats : 7 days Pigs : 5 days Chicken : 2 days

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