faty
Get Complete Project Material File(s) Now! »
Energy restriction and glycogen depletion in muscle of living animals
Numerous studies have investigated pH changes and other biochemical parameters in post mortem mammalian muscle (Bate-Smith & Bendall, 1949; Lawrie, 1953; Howard & Lawrie, 1956; Tarrant et al., 1972; Hamm 1974). Although glucose homeostasis is essential in order for a live animal to cope with its environment, researchers concluded that ante mortem glycogen depletion in muscle resulted in meat with higher pHu values which is detrimental for the conversion of muscle to good quality meat (Purchas et al., 1999). Beef with pHu values higher than 6.0 was undesirable because of its dark colour (Bartoš et al., 1993; Mounier et al., 2006), high variation in tenderness (Silva et al., 1999) and increased water binding capacity (Apple et al., 2005). Ante mortem stressors and factors (i.e. breed type and feed withdrawal) as well as the control and standardization of the post mortem environment (e.g. rigor temperature) that influence key traits like tenderness have also been extensively researched (Bendall, 1973; Bendall, 1979). Immonen & Puolanne (2000) stated that the determination of factors that result in a low pHu and to establishing the limits for residual glycogen levels obtained under various conditions are central to stress and meat quality research. Stressors encountered by livestock cause catecholamine release in the immediate preslaughter period (Lacourt & Tarrant, 1985). Epinephrine activates muscle adenylate cyclase which stimulates glycogen breakdown (Voet & Voet, 1990). Lowered glycogen prevents an accepTable decrease in pH and attainment of pHu for optimal conversion of muscle to meat (Purchas et al., 1999; Warriss, 1990). This statement should rather be viewed within breed types as metabolic rate (Frisch & Vercoe, 1977) and stress responsiveness (Muchenje et al., 2009) vary between breeds.
Influence of carbohydrate metabolism on meat colour
Post mortem glycolysis decreases pH, making the muscle appear brighter and superficially more wet. If the ultimate meat pH is high, the physical state of proteins will be above their isoelectric point. Proteins will associate with more water in muscle and therefore fibers will be tightly packed. This meat is dark because its surface does not scatter light to the same extent as the more open surface of meat with a lower ultimate pH (Seideman et al., 1984). Low temperatures delay metmyoglobin formation both directly and indirectly by suppressing the residual activity of oxygen utilizing enzymes (Lawrie, 1998). Prolongation of high muscle temperature at lower pH causes proteins to denature and the precipitation of sarcoplasmic proteins is associated with a decrease in myofibrillar solubility, water is liberated and superficially wet meat reflects more light. The characteristic colour of meat is a function of its pigment content and light scattering properties. On exposure of meat surface to oxygen, the purple ferrous haem pigment, myoglobin, forms a bright red covalent complex, oxymyoglobin. Formation of desirable oxymyoglobin is enhanced by conditions that increase oxygen solubility such as low temperature, low pH (glycolytic potential), high oxygen tension and low enzyme activity (MacDougall, 1982). Meat pH has a great influence on meat colour development (Abril et al., 2001) through its effects on the physical state of proteins. At a high pHu (>6.0) myofibers hold a lot of water (Offer & Trinick, 1983). At a higher myofibrillar volume, light is able to penetrate to a deeper depth and be absorbed by myoglobin before it is scattered back to the eye (MacDougall, 1982). Meat appears translucent and dark. At normal pHu values (5.5) myofibers hold less water and meat appears brighter and glossier (Ledward, 1992).
CHAPTER 1 INTRODUCTION
1.1 Project theme
1.2 Project title
1.3 Hypothesis and justification
CHAPTER 2 LITERATURE REVIEW
2.1 Biochemistry and physiology of catecholamines
2.2 Catecholamines and animal temperament
2.3 The role of catecholamines in energy metabolism of living animals
2.4 Glucose homeostasis in a living animal and its effect on meat quality
2.5 Post mortem carbohydrate metabolism in the conversion of muscle to meat
2.6 Toughening and tenderising phases in the conversion of muscle to meat
2.7 Beef breed types
CHAPTER 3 MATERIALS AND METHODS
3.1 Experimental animals
3.2 Slaughter process and physical carcass and meat properties
3.3 Urinary catecholamines and energy metabolites
3.4 Toughening phase
3.5 Tenderising phase
3.6 Statistical analyses
CHAPTER 4 RESULTS
4.1 Carcass characteristics
4.2 pH and temperature (ºC) in m. longissimus from 1 to 24 hours post mortem
4.3 Biochemical observations: urinary catecholamines, catecholamines turnover rates and muscle energy metabolites
4.4 Physical meat properties: Meat colour, water binding capacity, muscle fiber typing and Warner-Bratzler shear force
4.5 The toughening phase of the conversion of muscle to meat: sarcomere lengths
4.6 The tenderising phase of the conversion of muscle to meat: calcium activated proteolytic enzyme activity and myofibrillar fragmentation lengths
CHAPTER 5 DISCUSSION
5.1 Warm carcass weight, cold carcass weight, dressing percentage, pH and temperature profiles between Brahman, Nguni and Simmental type cattle subject to 24 or 3 hours feed withdrawal
5.2 Differences in urinary catecholamines and catecholamine turnover rates between Brahman, Nguni and Simmental type cattle subjected to 24 or 3 hours feed withdrawal
5.3 Differences in post mortem energy metabolites from m. longissimus between Brahman, Nguni and Simmental type cattle subjected to 24 or 3 hours feed withdrawal
5.4 The toughening phase of the conversion of muscle to meat
5.5 The tenderising phase of the conversion of muscle to meat
5.6 Physical properties of meat
CHAPTER 6 CONCLUSION AND RECOMMENDATIONS
