MUSCLE PROTEIN-CHANGES POST-MORTEM IN RELATION TO PORK QUALITY TRAITS

The relationship between post-mortem traits of muscle proteins and wat er loss traits was investigated using 84 pork loins representing the f our quality traits of PSE, RSE (reddish-pink, soft, exudative), RFN (r eddish-pink,firm, non-exudative) and DFD, Protein solubility measureme nts (sarcoplasmic, myofibrillar and total) were lower and myosin denat uration (quantified by myofibrillar ATPase activity) was higher for PS E samples compared with samples from the other quality classes. RSE sa mples were similar to RFN samples in protein solubility and myosin den aturation, although RSE had lower values then DFD samples for protein solubility measurements. RFN samples had lower drip, thaw, cook and to tal water loss than RSE samples and all water loss traits were lowest for DFD samples and highest for PSE samples, Insoluble phosphorylase w as the only characteristic that differentiated among PSE, RSE and RFN samples. SDS-PAGE and Western blots indicated that in PSE and RSE samp les, the myofibrillar protein titin was less degraded and nebulin was more degraded compared with RFN and DFD samples. SDS-PAGE of extracted and unextracted myofibrils showed that the reduced myofibrillar solub ility of PSE samples was caused by decreased extractability of the myo sin heavy chain in these samples. In conclusion, although RSE samples have unacceptably high water loss, muscle protein denaturation was min imal and did not explain the low water-holding capacity. (C) 1997 Else vier Science Ltd.