Meena Goswami Assistant Professor, Livestock Products Technology College of Veterinary Science and Animal Husbandry DUVASU, Mathura (U.P.)-281001 To discuss factors related to the conversion of muscle to meat. To describe the events that occur during the rigor mortis formation. To show what happens when stress -- either long-term or short-term -- depletes glycogen prior to death. Animal tissues which are suitable for use as food or the edible component originating from live animals. Skeletal muscle constitute 35-65% of meat Differs from them because a series of biochemical and biophysical changes are initiated in muscle at the death of the animal conversion a gradual degradative process Changes Loss of Homeostasis Maintenance of physiologically balanced internal environment Presided over by the nervous system and endocrine glands which co-ordinate adjustment in function Immobilization Animal is rendered unconscious prior to bleeding. Exsanguination Removal of blood from the animal. Marks the beginning of PM changes Circulatory Failure to the Muscles loss of oxygen supply to the muscle Energy metabolism is then shifted to the anaerobic pathway Postmortem pH Decline Mainly due to lactic acid accumulation. rate of pH decline is highly variable. Key role in the denaturation of proteins. Loss of protein solubility, loss of water holding capacity(WHC)and a loss in the intensity of pigments‟ coloration. „Pale Soft and Exudative‟(PSE) and „Dry Firm and Dark‟(DFD) conditions. Effect On Meat Quality NORMAL MEAT DFD MEAT PSE MEAT (Dark, Firm & Dry) (Pale, Soft &Exudative) Normal meat • Prior to slaughter, glycogen content is high • Converted to lactic acid • Tasty and tender meat. good quality& color DFD meat • Occur in cattle or sheep • Glycogen used-up prior to slaughter • After slaughter, little lactic acid production • Darker, drier meat with inferior quality • short shelf-life due to high PH(6.4-6.6) PSE meat • Occur in pigs In living muscle- 7.4 • Short term stress just prior to slaughter Within 6-8 hours postmortem- 5.6 to 5.7 • Rapid breakdown of muscle glycogen At 24 hrs postmortem-5.3 to 5.7 • Pale meat with acidic PH(5.4-5.6) Postmortem Heat Production and Dissipation a rise in muscle temperature occurs soon after exsanguination. Rapid glycolysis results in slow carcass chilling. denaturation of muscle proteins become inevitable scalding and singeing process contribute to a delay in heat dissipation. Rigor Mortis stiffening of the muscles after death A latin word meaning- “stiffness of death” occurs immediately after the slaughter formation of lactic acid from muscle glycogen It is a desirable change in the meat Enhance the keeping quality, increases tenderness and render it more palatable. During rigor mortis, muscles may contract in seemingly random and bizarre ways even though the body is dead. Rigor mortis begins to manifest after about 3 hours after death, and lasts about 72 hours. Approximately 6-12 hour postmortem for beef and lamb, 15 minutes to 3 hours for pork and 5 minutes to 1 hour for poultry. Resolution of rigor: proteolytic enzymes from lysosomes break down the cross-bridges Delay phase – immediately following exsanguinations – muscle is quite extensible and elastic – few acto-myosin bridges are present to prevent extension by a force Fast phase – depends most directly on the level of ATP – excess of oxygen, by stimulating respiration, will delay the onset of rigor mortis – accompanied by a lowering in water holding capacity – Physical changes, such as a loss of elasticity and extensibility, shortening and an increase in tension Completion of Rigor Mortis – Gradually becomes less extensible under an extremely applied force – Attainment of ultimate pH marks this phase. Resolution of Rigor mortis – probably due to a physical degradation of the muscle structure Z line area Acid rigor – characterized in immobilized animals by a long delay period and a short „fast phase‟ and in struggling animals by drastic curtailment of the „delay‟ period. At body temperature, stiffening is accompanied by shortening. Alkaline rigor – characterized by a rapid onset of stiffening and by marked shortening at room temperature. Intermediate type – characterized in starved animals by a curtailment of the „delay period‟ but not of the rapid phase. There is some shortening . Abnormal types of rigor mortis – Thaw rigor – Heat rigor Loss of protection from bacterial invasion first line of this is the epidermal tissues membrane properties are altered lowering of muscle pH - an inhibitory effect on some microorganisms Loss of structural integrity begin soon after exsanguinations disintegration of Z line structure Progressive disruption of the myofibrillar structure Enzymatic degradation cathepsins are held in the inactive state in organelles called lysosomes Tenderization- breakdown of some of the collagen connective tissues of the muscle by cathepsins Meat from unbled animal is tastier than bled animal meat In Halal and kosher method, Blood is removed. Changes in the physical characteristics of meat Colour Bright red to dark purple red If subjected to severe denaturation, color intensity reduced and appear pale even when freshly cut. Firmness amount of „tone‟ particularly in the skeleton muscles become very firm and stiff and again becomes less firm Water binding properties Retained water contributes to the juiciness and palatability of meat. Changes depend on the rate and extent of pH drop and on the amount of protein denaturation. May affect tenderness, juiciness, flavor, emulsifying capacity, binding capacity and cooking losses. Circulation ceases the ability to re-synthesize ATP is lost, lack of ATP causes actin and myosin to combine to form acto-myosin which leads to a stiffening of muscles; the oxygen supply falls resulting in a reduction of the oxidation‟/„reduction‟ potential; the supply of vitamins and antioxidants cease resulting in a slow development of rancidity. nervous and hormonal regulations cease; thereby causing the temperature of the animal to fall and fat to solidity; Respiration ceases which stops ATP synthesis. Contd.. respiration ceases which stops ATP synthesis; glycolysis begins resulting in the conversion of most of glycogen to lactic acid which depresses pH from about 7.4 to its ultimate level of about 5.6; pH depression initiates protein denaturation, liberates and activates cathepsins and completes rigor mortis; reticuloendothelial system ceases to scavenge, thus allowing microorganisms to grow unchecked; accumulation of various metabolites denature muscle proteins. .