Lowering hydrophobic peptides and increasing free amino acids in cheese made with a Lactococcus lactis strain expressing a mutant oligopeptide binding protein

Lactococcus lactis strain AMP2I expresses OppA(D471R), a mutant oligopeptide binding OppA protein in which the aspartyl residue at position 471 was replaced by arginine. This strain was used as starter culture to investigate its ability to lower the levels of hydrophobic peptides in cheese. A 5-fold increased level of chymosin was used to obtain a high initial level of hydrophobic peptides. Cheese made with L. lactis AMP2I contained lower levels of hydrophobic peptides and showed lower ratios of hydrophobic peptides to hydrophilic peptides than control cheese made with L. lactis NCDO712. Both parameters have been correlated with cheese bitterness, which suggests that bitterness in cheese made with the former strain must be lower than in control cheese. Content of total free amino acids was 1.3-fold higher in cheese made with L. lactis AMP2I than in control cheese, an increase that can be attributed to the expression of the mutant oligopeptide binding OppA protein.