A proteomics approach to identify protein biomarkers associated with meat tenderness in Nguni, Bonsmara, Brahman and Charolais breeds

Ph.D. (Biochemistry)Abstract: The imprecise judgement of meat tenderness because of the slaughter age classification of the animal due to the South African Beef Carcass Classification System has initiated debates between feedlot beef producers and pasture beef producers, including commercial and emerging farmers. Other systems, such as that of the United States Department of Agriculture beef quality grading system, also has the dilemma of differentiating carcasses into tenderness grades. The fluctuation of meat tenderness judgement affects consumers trust and affects the meat industry negatively. The objective of this study was to examine the question of whether there are proteins or a group of proteins that are differentially expressed and respond to different ageing periods that can be an indication of extent of meat tenderness in four beef-producing breeds. To investigate this, carcasses were subjected to a stepwise chilling process post mortem to evaluate the natural meat tenderness development. This was employed with the aim of finding and identifying differentially expressed proteins that change with ageing periods in Bonsmara, Brahman, Charolais and Nguni breeds and to associate differentially expressed proteins identified by proteomics methods with tenderisation mechanisms. The evaluation of meat tenderness was performed by monitoring temperature and pH decline, measuring Warner Bratzler shear force, sarcomere length, myofibril fragment length, drip loss, water holding capacity, collagen characteristics and proteolytic enzymes (calpains/calpastatin system). Protein expression evaluation between different ageing periods within each breed and between different breeds was performed by 2D-SDS-PAGE in 12.5%-polyacrylamide vertical slab gels following isoelectric focusing (pI 5-8) and analysed by PD Quest™ Advanced 2D Analysis Software. It was found that pH and temperature decline of all the breeds followed an ideal path without any breed falling into heat shortening or cold shortening windows and breed did not have an effect on ultimate pH and temperature measurements. All breeds yielded meat of acceptable quality after being subjected to the stepwise chilling process. It was shown that the proteolytic action of μ-calpain and m-calpain is not the only mechanisms involved in the meat tenderisation process and that collagen does not always affect meat tenderness of younger animals. The results showed that..