Effects of pH, temperature and electrical inputs on muscle protein modifications that impact on meat eating quality, Phase 2

Summary

This research characterised the expression and post-translational modifications of proteins in muscle tissue that influence the commercial quality of fresh lamb. Variation in meat eating quality is largely attributed to the organisation of structural proteins within muscle and the activity of endogenous protease systems that remain active after rigor mortis. The addition or removal of functional groups from proteins, including phosphorylation, acylation, glycosylation, nitration, and ubiquitination, may alter the stability of the cell cytoskeleton. The project studied the phosphorylation patterns of proteins that influence cytoskeletal structure and proteolysis. Proteins with altered relative abundance or modification may provide targets for biomarkers of meat tenderness.
Twenty lambs from similar genetic background were ranked for  tenderness according to shear force (an objective measurement of the force required to bite through cooked meat). The four toughest and four most tender lambs were selected for phosphoproteome analysis. Cellular fractions - connective tissue/myofibrillar and cytoskeletal - from muscle tissue were prepared by differential centrifugation and then subjected to affinity chromatography to enrich for phosphoproteins. The proteins are analysed by 2D electrophoresis to determine their relative abundance. Selectivity for phosphoproteins was verified by staining with the phosphoprotein stain Pro Diamond Q. The identity of the proteins and specific modifications of the proteins are subsequently characterised by mass spectrometry analysis including matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry and liquid chromatography ion trap MS/MS. Current progress described in the report below includeds the identification of protein species and patterns of phosphorylation in muscle tissue that correlate with lamb tenderness. The biomarkers for predicting lamb tenderness determined in this experiment were validated with industry partners to maximise the productivity and quality of Australian lamb products.