Peptidomic insights on structural protein hydrolysis by exopeptidase activities and its effects on bitterness defects of dry-cured ham

Excessive bitterness is a common problem and is related to the hydrolysis of structural proteins degradation in the dry-cured ham industry. To better understand the effect of structural proteins (myosin, titin, troponin) degradation on sensory development of Jinhua ham, sensory attributes, exopeptidase activities, peptide fragments and cleavage sites of structural proteins were investigated in both premium and defective hams. The results of sensory evaluation and electronic tongue revealed that more than 1.5-fold values in bitterness intensities and less than 0.67-fold values in richness intensities were observed in defective ham, compared with premium ham. The activities of exopeptidase were determined, and the results indicated that the residual activities of TPP I in defective ham were higher, while the residual activities of LAP and AAP were lower, compared with premium ham. The large numbers of unique peptide fragments derived from myosin, titin and troponin were identified in defective ham. Several unique cleavage sites including L-399, L-1047 and K-1053 for MYH 1 and MYH 4, K-257, R-694, K-1374 and K-1651 for MYH 7, and K-92 and K-103 for TNN C1 and TNN C2 were only presented in defective ham, which were intensely response to the excessive accumulation of peptides and the development of excessive bitterness in defective ham. This study could provide a theoretical basis for the regulation of bitterness defects in dry-cured ham in the future.