Conversion of Muscle to Meat

1. Conversion of Muscle to Meat Dr. Ir. Jamhari, M.Agr.Sc., IPM. Dr. Endy Triyannanto, S.Pt., M.Eng.

2. Introduction • Muscle function and meat quality. • Muscles do not suddenly terminate all their living functions and become meat. • A number physical and chemical change take place over a period of several hours or even days. • It is a gradual degradative process.

3. Homeostatis • In the living state, all organs and systems within the body cooperate to maintain an internal environment under which each can perform its function efficiently. Only within a narrow range of physiological condition (pH, Temperature, O2 , and energy). • Maintenance of the physiologically balance internal environment = Homeostasis.

4. Homeostatis • Can be regulate by the nervous system and the endocrine system. • These two systems serve as communication and starring mechanism and adjust the function of various organs during period of stress.

5. If homeostasis is broken • Many of the reactions and changes that occurred and affected the development of the quality of meat. • Also, preslaughter stress or environment (immobilization and exsanguinations) may alter postmortem changes due to irregulation in living animal bodies.

6. Handling preslaughter • Immobilization: make animal unconscious = the first step. • Make blood pressure elevate or excessive nerve stimulation = cause tissue damage. • Exsanguination = the removal of as much blood as possible. In fact, only about 50% of the total blood volume can be removed from the body.

7. Exsanguination • Marks the beginning of a series of postmortem changes in the muscle. • Since blood is an excellent medium for growth of spoilage organisms and excess blood in meat cuts is unappealing to the consumers, a thorough bleeding is an essential beginning to the slaughter process.

8. What condition will be occurred after bleeding • The circulatory system will be stopped. • Oxygen and nutrient and wastes also will be stopped transportation. • The aerobic pathway through the TCA cycle and the electron transport chain stops function.

9. What condition will be occurred after bleeding • Less energy in the form of ATP is produced through the anaerobic pathway. • Lactic acid will remain in muscle tissue and increase in concentration as metabolism proceeds. • Heat can make body temperature increased.

10. Postmortem pH decline • The lowering of pH in muscle due to the accumulation of lactic acid. • One of the most significant postmortem changes. • Approximately pH 7.4 in living muscle.

11. Normal condition • pH 7.4 6-8 hours pH 5.6-5.7 and the an ultimate pH (24 hrs postmortem) of about 5.3-5.7.

12. Temperature and pH • Temperature plays a key role in denaturation. • High temp can make a fast heat of continuous metabolism ( glycolysis , lactic acid , pH) and also make the pH of the carcass rapidly decline (5.2-5.4).

13. Denaturation • A loss of protein solubility. • Loss of water • Loss of protein bonding capacity • Loss in intensity of muscle pigment coloration.

14. Conversion of muscle into meat • The formation of lactic acid will lead to the decrease in meat pH. • The decrease in meat pH depends on glycogen reserve when animal is slaughtered. • Normal pH of muscle during slaughter (7,0) will decrease to be the ultimate pH (5,4-5,8) after slaughter.

15. Conversion of muscle into meat • The level of pH decrease determines the quality of the resulted meat. • In animals which are stressed or over-fed, the process of pH decrease will occur very quickly, when carcass is still hot, resulting in meat which is pale in color, soft, exudative or PSE.

16. Conversion of muscle into meat • In exhausted animals, the amount of glycogen reserve is very low so that the lactic acid formed is also low, so that meat pH is relatively high, resulting in dark, firm, dry or DFD.

17. Pale Soft Exudative (PSE) • PSE is said to have occurred when the pH of meat is < 6 at 45 minutes after slaughter. • Meats with pH at 45 minutes being lower than 6.0 • Meats with pH ultimate value of 5.3. • PSE is due to acute stress just before slaughtering.

18. Causes of acute stress • The use of electric goads, • Fighting among animal just before sticking, • Beating of animals prior to slaughter • Overcrowding in the lairage, • Acidification in muscles post-mortem due to the breakdown of glycogen to lactic acid.

19. Causes of acute stress • combination of low pH and high temperature meat causes the denaturation of some muscle proteins. • There is light scattering from meat surface.

20. Dark Firm Dry (DFD) • DFD (also known as dark cutting in beef) is when the ultimate pH postmortem measured after 12 – 48 hours is ≥ 6. • Meats with pH at 45 minutes being 6.4 • Meats with pH ultimate value higher than 6.0 • DFD is due to chronic or long term stress before slaughtering.

21. Causes of cronic stress • transportation animals over long distances, long hours of food deprivation, • Overcrowding of animals in the lairage over a long period of time. • Less glycogen is available affecting the normal process of acidification and leaving the pH of meat high.

22. Causes of cronic stress • High pH results in relatively little denaturation of proteins, water is tightly bound and little or no exudates. • Muscles absorbed light making the meat appear darker.

23. How to prevent PSE and DFD • To develop breeds that are resistance to stress. • More males could be bred for meat purposes. • Loading of animals onto trucks for transportation to the abattoir has to be done with minimum stress.

24. How to prevent PSE and DFD • loading should be done in a quiet atmosphere, avoiding the use of sticks and other forms of force. • trained on proper ways of handling animals. • unloaded immediately when they arrive at the slaughter house. • Unloading of animals at the abattoir should also be done in a quiet and gentle manner.

25. How to prevent PSE and DFD • Keep transportation and marketing times short. • Keep animals in their rearing at the same group. • Animals should be rested enough to recover from stress before slaughtering. • Provide animals with food and water if they will spend more time in the lairage.

26. How to prevent PSE and DFD • Provide beddings or straw on the floor if the animals will keep longer. • resting period of between 2 – 4 hour in the lairage prior to stunning and/or sticking. • Abattoirs must be well designed. • Stunning methods render animals unconscious prior to sticking. • Carcasses are normally chilled after dressing.

27. PSE and DFD

28. PSE and DFD

29. In living muscle

30. In dying muscle, lactic acid accumulates and lowers pH. • glycogen ——-> lactic acid • muscle pH: 7.0 ——-> 5.6 (because of lactic acid) • muscle color: purple changes to bright red or pink (pH 7.0 ——-> 5.6)

31.  Water found in meat • Bound (charged hydrophilic groups on the muscle proteins attract water, forming a tightly bound layer). • Immobilized (has less orderly molecular orientation toward the charged group). • Free (held only by capillary forces, and their orientation is independent of the charged group).

32. Relationships between pH and WHC of meat

33. Relationships between pH and WHC of meat • pH also is important in determining the water-holding capacity of meat, the ability of meat to retain its water during application of external forces such as cutting, heating, grinding, or pressing. • Where water-holding capacity is the lowest is the isoelectric point, where the number of positively and negatively charged groups of the myofibrillar proteins is equal. 

34. Methods of tenderizing meat • Chilling is the process of carcass chilling at the temperature of 0-5oC for 24 hours. • Aging is the process of hanging the carcass/meat at the chilling temperature for certain duration of time. • Enzyme application, is addition of external protease enzyme to tenderize meat, such as bromelain or papain.

35. Postmortem Changes • Change in the structure of protein due to the process of denaturation. • Meat is more easily broken up by proteolytic enzyme, so that it becomes more tender. • Occurrence of meat pigment oxidation, so that change in the meat color occurs. • Occurrence of fat oxidation, resulting in flavor.

36. Rigormortis • Rigormortis as a phenomenon is the stiffness of the muscles of an animal following the death • After the death of an animal, the oxygen supply ceases. However, glycogen reserve in the muscle before death is converted ‐through enzymatic activity‐ into lactic acid accompanied by a fall in the pH. The amount of lactic acid depends on the glycogen reserves.

37. Rigormortis • The stiffening of muscles is attributed to the dynamics of adenosine triphosphate (ATP) and adenosine diphosphate (ADP) within the muscles accompanied lactic acid accumulation and the fall of pH • Immediately after death in the pre‐rigor phase, the muscles of an animal are soft. After several hours (p g de ending on several factors), muscles begin to stiffen and harden.

38. Rigormortis • Stiffness continues reaching its maximum and last for hours or days before muscles start to relax again

39. Rigormortis • One of the most dramatic postmortem change. • The formation of permanent crossbridges in muscle. • That forms actomyosin. • Can be relax in living animal but be broken by enzymes in carcass.

40. The onset of rigormortis • Lss of elasticity. • Loss of extensibility, shortening and tension development. • The time required for muscle of different animal species to enter the onset of rigor mortis will be showed in Table.

41. Resolution or softening of rigormortis • Alteration in ultra-structure of myofilaments • Changes in other protein of the cytoskeleton • Action of neutral protease enzymes • Relate directly to tenderization in meat aging.

42. Cathepsins • Proteolytic enzymes • Hold in lysosomes. • As the pH of the muscle drop(pH<5.6), these enzymes are released and probably begin to degrade protein structure of the muscle.

43. Calpains • Calcium activated muscle protease • pH optima at 6.6-6.8 • Are found in sarcoplasm in myofibers

44. Factors affecting postmortem changes and meat quality • Meat quality: tenderness, juiciness, color and flavor. • Processing properties: emulsifying capacity, binding ability, cooking loss, cooked meat color. • Some ante- or post mortem’s factors will affect above conditions.

45. Antemortem • The new environment or stress –heat or cold • Are aided by the release of certain hormones- epinephrine and nor-epinephrine –respond • Sex - odor (boar)

46. Antemortem • Diet- fasting 12-24 hrs for animal before slaughter • Pre-slaughter handling : transportation, loading. • Stunning:should be followed as quickly as possible by rapid bleeding

47. Postmortem • Temperature : chilled quickly as possible. • To minimize protein denaturation. • To inhibit growth of microorganisms.

48. Thaw rigor • Resulting from low temperature in muscle before onset of rigor mortis. • Is a severe type of rigor mortis that develops when muscle that was frozen pre-rigor is thawed. • By sudden release of Ca+2 into the sarcoplasm and cause a physical shortening of 60-80% of original length. • Meat quality-dry and severe toughening.

49. Cold shrortening • Resulting from low temperature in muscle before onset of rigor mortis • Chilled temperature above 0oC but below 15-16oC. • Shortening is less severe than that of thaw rigor. • The problem may becomes more serious as efforts are made to produce animals with less fat- Beef and Lamb.

50. Heat rigor • Severe shortening may be induced by maintaining muscle at relatively high temperature (up to 50oC). • Is the result of a rapid depletion of ATP stores.