Proteolysis in biceps femoris during Jinhua ham processing

Sixty experimental Jinhua hams were processed by a traditional method. The nitrogen fractions and free amino acids in biceps femoris were analyzed. Intense proteolysis was found in ham muscle and totally more than 10% of muscle proteins were degraded during the course of Jinhua ham processing. The proteolytic index of Jinhua ham was between 14 and 20. Both insoluble and soluble proteins were degraded to some degree and the later showed more intense degradation. In the soluble fraction, the percentage of non-protein nitrogen (NPN) increased gradually whereas that of protein nitrogen decreased during processing (P < 0.05). However, very small amount of peptides larger than 1 kDa was accumulated during the whole course of processing, which proved that intense degradation reactions were also happened to them, especially at the post ripening stage when dramatic decrease of nitrogen fraction from all the peptides larger than 1 kDa was found. As a result, more than 90% of the NPN products from muscle proteolysis were free amino acids and peptides of MW less than 1 kDa that might make important contribution to Jinhua ham taste and provide precursors for the generation of volatile flavor compounds in ham muscle. The pattern of muscle proteolysis coincided with the reported changes of muscle proteolytic enzymes during processing, seemingly indicating that the enzymes could have played important roles in ham muscle proteolysis.