Exchanging lactocepin plasmids in lactococcal starters to study bitterness development in Gouda cheese: a preliminary investigation

Most fast-milk-coagulating Lactococcus lactis starter strains contain a plasmid-encoded cell envelope proteinase (lactocepin; EC 3.4.21.96) having P I-type (lactocepin I) or P I/III intermediate-type (lactocepin I/III) specificity (those with P III-type specificity are rare). We assessed the effect of lactocepin I and lactocepin I/III on peptide accumulation and bitterness development in dry-salted Gouda cheese by exchanging lactocepin plasmids between two L. lactis starter strains low in autolysis, thus eliminating the effects of other starter variables. Gouda was made using starter strains, either L. lactis subsp. cremoris HP (lactocepin I) or L. lactis subsp. lactis U (lactocepin I/III), or using constructs of these two strains with exchanged lactocepin plasmids. Bitterness in Gouda was consistently greater when the starter strains contained lactocepin I. Following ripening, cheese peptide profiles (determined by high-performance liquid chromatography) were found to vary more in relation to starter lactocepin specificity than in relation to starter strain background or sub-species ( lactis or cremoris).