Cheesemaking with a Lactococcus lactis strain expressing a mutant oligopeptide binding protein as starter results in a different peptide profile

Lactic starters used for cheese manufacture play an important role in the production of bitter peptides and their degradation to non-bitter products. The oligopeptide transport system (Opp) of lactococci is essential for milk peptide utilization. The periplasmic substrate binding protein serves to capture the substrate with high affinity and to deliver it to a membrane-bound complex that translocates it inside the cell. Prt+- and Lac+-derivatives of MG1363 ΔoppA strains expressing a wild-type MG1363 OppA or a mutant OppA with a single point mutation at residue 471 (OppA(D471R)) from a plasmid were constructed. These strains were used as lactic starters in cheese manufacture to improve flavour quality by removing hydrophobic peptides from the cheese matrix, through their preferential transport by OppA(D471R). Cheeses made with these strains were not significantly different from control cheeses after 1 day of ripening with respect to bacterial counts, pH and proteolysis, and only slight differences were recorded after 9 and 20 days of ripening. HPLC chromatograms of the hydrophilic and hydrophobic peptides present in the water-soluble fraction of experimental cheeses showed significant differences in peptide content as well as in peak profiles. These results suggest a different peptide utilization in the strain expressing OppA(D471R) and make it suitable for use as starter to improve cheese quality.