Growth of Nonproteolytic Lactococcus lactis in Culture Medium Supplemented with Different Casein Hydrolyzates

Abstract

Abstract The growth and lactic acid production of nonproteolytic variants of Lactococcus lactis , three Lactococcus lactis ssp. cremoris strains (E8, Wg2, and HP) and one Lactococcus lactis ssp. lactis strain (1076), were compared with those of their parent strains in Garches medium supplemented with different casein hydrolyzates. Molecular weight distribution and AA composition of casein hydrolyzates were different. Two fractions of alcalase casein hydrolyzates separated and concentrated by a two-step ultrafiltration process were compared with two commercial casein hydrolyzates. Proteinase-negative variants of lactococci exhibited the same specific growth rate and production of lactic acid as proteinase-positive strains in all enriched Garches media. Cell growth was affected by molecular weight distribution of peptides in hydrolyzates, but not by their AA composition. Lactococcus lactis ssp. lactis grew better than L. lactis ssp. cremoris , but its lactic acid production was similar to that of E8 strains. Among L. lactis ssp. cremoris , Wg2 strains grew better in Garches medium supplemented with casein hydrolyzates with molecular weight 2000Da. Different casein hydrolyzate fractions could be used to supplement culture medium and to standardize milk cultures; however, choice of casein hydrolyzates depends on subspecies of lactococci.