Effects of crude enzyme of Lactobacillus casei LLG on water-soluble peptides of enzyme-modified cheese

The effects of crude enzyme extract of Lactobacillus casei ssp. casei LLG on the water-soluble peptides of enzyme-modified cheese (EMC) were studied by reverse phase HPLC and amino acid analysis. A wide range of peptidolytic activities (aminopeptidase 1615.44 unit/ml; x-prolyldipeptidyl peptidase 66.73 unit/ml; proline-iminopeptidase 38.63 unit/ml) were detected in the crude enzyme extract. Bitter enzyme-modified cheese (EMC N24) was prepared with Neutrase® 0.5L for 24 h at 45°C and treated with (EMC NL72) and without (EMC N96) the crude enzyme for 72 h at 35°C. The percent peak areas of two hydrophobic peptides (peak I and peak II) in EMC N24 were increased from 1.63% to 3.65% and from 0.88% to 3.23% in EMC N96, respectively, but decreased to below the detectable range in EMC NL72. The bitterness of EMC N96 may have been related to the increase in areas of these two peaks. Based on the amino acid compositions, peak I was identified as the αs1-casein fraction 26-31 (Ala-Pro-Phe-Pro-Glu-Val), and peak II as the β-casein fraction 190-192 (Phe-Leu-Leu), respectively. The results suggest that both aminopeptidase and proline-specific peptidases present in the crude extracts are responsible for degrading the hydrophobic peptides in bitter EMC.