Involvement of protein degradation, calpain autolysis and protein nitrosylation in fresh meat quality during early postmortem refrigerated storage
Fresh meat quality including meat tenderness and water holding capacity are important for consumer acceptance and industry profitability in the US. Exploring the basic mechanism that regulates the development of meat quality attributes is critical for delivering consistently high quality fresh meat to consumers. The overall hypothesis of this study was that biochemical factors that influence proteolysis during the antemortem or the early postmortem period can contribute to variations in fresh meat quality. The objective was to determine the extent to which protein modifications including protein degradation, protein nitrosylation and calpain autolysis affect the development of fresh meat quality.
The first experiment was designed to test the hypothesis that protein degradation and calpain activation could influence water holding capacity of fresh pork. Intensity of intact desmin was positively correlated with moisture loss, while intensity of intact integrin was negatively correlated with moisture loss during postmortem storage. Significant correlations were found between different calpain autolysis products and intensity of intact desmin and moisture loss. These results support the hypothesis that proteolysis of desmin contributes to greater water holding capacity. The second experiment hypothesized that the properties of calpains could be regulated by a nitric oxide donor S-nitrosoglutathione. S-Nitrosoglutathione could further nitrosylate y-calpain in both the absence and the presence of calcium especially at pH 6.5. The combination of S-nitrosoglutathione and calcium affected the activity of m- and y-calpain and regulated the rate of y-calpain autolysis. In the third experiment, the hypothesis that the muscle fiber type could be related to the levels of protein nitrosylation in postmortem beef was tested. Beef longissimus dorsi muscle showed higher percentage of type IIA/X and lower percentage of type I myosin heavy chain isoforms than psoas major muscle. The intensity of protein nitrosylation in longissimus dorsi muscle was greater compared to psoas major muscle in samples prepared 1 d postmortem. In conclusion, biochemical and biophysical reactions during preslaughter and postmortem storage can mediate the development of fresh meat quality during postmortem aging.