Oxidation of myofibrillar protein and crosslinking behavior during processing of traditional air-dried yak (Bos grunniens) meat in relation to digestibility

In this study, the changes in the digestibility of myofibrillar protein were investigated during the processing of traditional air-dried yak meat to reveal the underlying mechanism of cascade induction among lipid oxidation, protein oxidation, and protein digestibility. The results show that, during the processing, its moisture content, water activity, lightness (L*), yellowness (b*), and springiness were dramatically reduced (P < 0.05), while its pH, hardness, cohesiveness, and chewiness increased significantly (P < 0.05); and its redness (a*) experienced an increase first and a decrease later (P < 0.05). With the extension of processing time, its lipid-oxidized products and protein carbonyl compounds significantly increased (P < 0.05), showing a significant correlation between them (P < 0.05). With the increase in protein oxidation, the α-helices was unfolded and transformed into β-sheet and random coil (P < 0.05). Moreover, the disulfide bonds and dityrosine of the protein cross-linking products were significantly increased (P < 0.05). Therefore, the hydrolysis rate of protein by proteases was largely correlated with carbonyl, disulfide bonds, and dityrosine (P < 0.01). In conclusion, during the processing of air-dried yak meat, lipid-oxidized products appeared to have promoted protein oxidation. It was also found that the decrease in protein digestibility was caused by protein carbonylation and crosslinking, which affected the combination of pepsin and protein.