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.

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 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 .  Loss of 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 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.