PRODUCTION OF CHEDDAR CHEESE USING A LACTOCOCCUS-LACTIS SSP CREMORIS SK11 DERIVATIVE WITH ENHANCED AMINOPEPTIDASE ACTIVITY

A Lactobacillus helveticus CNRZ32 DNA fragment encoding aminopeptidase N (PepN) was cloned into pIL253 to construct pSUW34. The cell-free extract general aminopeptidase activity of Lactococcus lactis ssp. cremoris SK11 transformed with the pSUW34 construct was increased approximately 100-fold relative to L. lactis ssp. cremoris SK11 wild type and pIL253 transformants. Cheddar cheese was manufactured with L. lactis ssp. cremoris HP in combination with either SK11 (pIL253) or SK11 (pSUW34). A 99% reduction in viable SK11 derivatives occurred within 2 weeks of ripening. The SK11 (pSUW34)/HP cheese had approximately 1000-fold greater aminopeptidase activity and elevated levels of TCA and PTA soluble nitrogen. The increased accumulation of particular ee amino acids in the SK11 (pSUW34)/HP cheese varied between 15% (methionine) and 230% (lysine). Both the SK11 (pSUW34)/HP and SK11 (pIL253)/HP cheeses were non-bitter and had no significant sensory differences. Thus, the increased free amino acid pool in the SK11 (pSUW34)/HP cheese did not result in accelerated flavor development.