Changes of arginyl and leucyl aminopeptidase activities in biceps femoris along Jinhua ham processing

Sixty experimental Jinhua hams were processed by a traditional method. The potential arginyl (RAP) and leucyl (LAP) aminopeptidase activities in biceps femoris were determined. The effects of temperature, salt content, sodium nitrate content and pH value on muscle RAP and LAP activities were evaluated using response surface methodology. Porcine muscle was found to possess very strong potential RAP and LAP activities that decreased gradually during processing from 165,980.97 U g−1 and 89,201.52 U g−1 before salting to 3164.70 U g−1 and 5373.66 U g−1 after aging, respectively. Temperature, pH value and salt content had significant effects on RAP and LAP activities (P < 0.0001). They interacted with each other in their effects on RAP activity (P < 0.0001) and influenced LAP activity in exponential way (P < 0.05). However, 0-50 mg L−1 sodium nitrate had no detectable effect on either RAP or LAP activity (P > 0.05). The regression models showed that muscle RAP and LAP maintained their activities all through Jinhua ham processing. LAP could display very strong actual activity during aging and post-aging, indicating that muscle LAP may play the most important role in generating free amino acids during the processing of Jinhua ham.