Abstract: The present study was designed to evaluate the effect of the chymosin from Bacillus licheniformis on the proteolysis of Cheddar cheese during ripening. The chymosin was used to produce cheddar cheese (CDF) and Cheddar cheese analogue (CD3), and a commercial milk-clotting enzyme preparation was also used to prepare Cheddar cheese (CCF). The variation of proteolysis indexes was analyzed during cheese ripening. The results showed that the contents of casein, soluble nitrogen at pH 4.6 (pH 4.6-SN), 12% trichloroacetic acid-soluble?nitrogen (12% TCA-SN), 5% phosphotungstic acid-soluble?nitrogen (PTA-SN) and total free amino acid in CDF, CD3 and CCF increased significantly with maturation time, and were significantly higher in CDF than in CCF during maturation (P < 0.05). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed that the degree of hydrolysis of α-casein (α-CN) was higher in CDF. The results of pH 4.6-SN analysis showed that the total peptide content increased first and then decreased with ripening time, but the ratio of hydrophobic peptide to hydrophilic peptide showed a continuous downward trend. At the sixth month of ripening, the ratios of hydrophobic peptide to hydrophilic peptide in CDF, CD3 and CCF were 2.668, 2.822 and 3.788, respectively. Principal component analysis (PCA) showed that for all three cheeses, the proteolysis degree was positively correlated with maturity, but negatively correlated with the ratio of hydrophobic peptides to hydrophilic peptides. The above results showed that cheese produced with Bacillus licheniformis chymosin had higher degree of proteolysis, but smaller proportion of hydrophobic peptides. Our findings could provide a theoretical basis for the application of Bacillus licheniformis chymosin in cheese production.

Key words: Bacillus licheniformis; chymosin; Cheddar cheese; proteolysis