Postmortem changes in meat quality and myofibrillar protein degradation in turkey breast muscle
Rathgeber, Bruce Mitchell
The purpose of this research was to evaluate the effect of elevated carcass temperature in combination with rapidly declining pH or with postrigor muscle on turkey breast meat quality. Two groups of twelve turkey carcasses with similar ultimate pH values were selected based on 15 min postmortem (PM) breast muscle pH (rapid-glycolyzing (RG), pH 6.0). One side of each carcass was held near 40°C and immersion chilling was delayed until 110 min PM (DC), while the other side was chilled at 20 min PM (IC). Raw breast meat quality was assessed using measurements of colour and protein extractability, while quality characteristics of cooked product were assessed using cook yield and torsion gelometry. The extractability and degradation of 10 specific proteins was monitored using SDS-PAGE and Western blotting. Additionally, holding postrigor turkey breast meat at 40°C was evaluated as a model for mimicking changes due to rapid PM glycolysis. Sarcoplasmic and myofibrillar protein extractability was reduced for breast samples from RG and DC carcasses as well as for postrigor meat held at 40°C (P < 0.05). All colour values ('L*a*b*') increased for DC ground breast meat. Strain at fracture for breast meat gels was lower for RG samples. Both stress and strain at fracture and cook yield were reduced for DC breast meat gels. The reduction in meat quality measurements was additive for RG samples that were delay-chilled. Densitometry of Western blot analyses revealed that the extractability of glycogen phosphorylase, creatine kinase, and M-protein was reduced for RG or DC samples. Increased myosin degradation was observed for samples from either RG or DC carcasses with up to 20% of myosin degraded in RG/DC samples. Nebulin degradation was also more extensive in RG samples than for controls. Heating postrigor breast increased myosin degradation, however, differences in the banding pattern of myosin fragments compared to samples from RG carcasses were observed. These results provide conclusive evidence that rapid PM glycolysis and delayed chilling have detrimental effects on turkey breast meat quality. The association of postmortem protein degradation with meat of reduced quality merits further investigations into the relationship between postmortem proteolytic activity and meat quality.