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Abstract
The relationship between post-mortem traits of muscle proteins and water loss traits
was investigated using 84 pork loins representing the four quality traits of PSE,
RSE (reddishpink, soft, exudative), RFN (reddish-pink, firm, non-exudative) and DFD.
Protein solubility measurements (sarcoplasmic, myofibrillar and total) were lower
and myosin denaturation (quantified by myofibrillar ATPase activity) was higher for
PSE samples compared with samples from the other quality classes. RSE samples were
similar to RFN samples in protein solubility and myosin denaturation, although RSE
had lower values then DFD samples for protein solubility measurements. RFN samples
had lower drip, thaw, cook and total water loss than RSE samples and all water loss
traits were lowest for DFD samples and highest for PSE samples. Insoluble phosphorylase
was the only characteristic that differentiated among PSE, RSE and RFN samples. SDS-PAGE
and Western blots indicated that in PSE and RSE samples, 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
solubility of PSE samples was caused by decreased extractability of the myosin heavy
chain in these samples. In conclusion, although RSE samples have unacceptably high
water loss, muscle protein denaturation was minimal and did not explain the low water-holding
capacity.