Contribution of cathepsin B and L to endogenous proteolysis in the course of modern Jinhua ham processing

Although cathepsins have significant effects on protein degradation during the manufacture of Jinhua ham, the influences of cathepsin B and cathepsin L have seldom been assessed. In our research, the cathepsin B and L activities, proteolytic index (PI) values and the changes in microstructure and protein expression levels are investigated. E−64 is further selected as cathepsin inhibitor to verify the effect of cathepsin B and L on proteolysis and set up control groups. The results show a high level of enzymatic residual activity and PI values increase from 2.58% to 22.60% which implies a noticeable proteolysis. Microstructure analysis presents that the muscle fiber is sparse and the distribution is irregular over time. Based on immunohistochemistry analysis, the weak or strong red fluorescent which marks cathepsins can be observed in the ham muscle tissues, which is consistent with the active cathepsins. The increased number of sheet-like blue collagen fibrous proliferation in the interstitial space results in the reduction of enzyme staining sites. The decreased content of 38 and 36 kDa fragments indicates that cathepsins are released from lysosome dramatically, which is liable for proteins degradation and the formation of flavor. These results can highlight the important contribution of cathepsin B and L to protein degradation throughout overall processing, and have a new understanding towards the changes of endogenous protease in Jinhua ham.