Characteristics of lactococci cultures produced in commercial media

Strains of Lactococcus lactis ssp lactis and L. lactis ssp cremoris were propagated on milk, three commercial highly buffered media (HE media), and four commercial media designed for external pH control (EC media). With milk and HE media, fermentation was allowed to proceed until a pH of 4.9 was reached. With EC media, pH was maintained at 6.0 with 5 N NH4OH. The cultures were analyzed for chain length, viable population, specific acidifying activity (SAA) and specific proteolytic activity (SPA). The starters were stored at 4 degrees C for 3 days, and analyses for chain length, viable population and SAA were repeated. It was more difficult to standardize medium composition with the rehydrated commercial blends, as their titratable acidities had greater proportional variations than milk. As a rule, chain length was longer in fresh cultures than in the stored starters, and L. lactis spp cremoris cultures had longer chains than L. lactis ssp lactis. All commercial media produced starters with total populations at least as high as that obtained in milk. With the EC media, populations could be five times greater than with milk; increases were less important in HE media, The increase in population in EC and HE media was more marked with L. lactis ssp lactis than for L. lactis ssp cremoris strains. Storage at 4 degrees C for 3 days did not significantly reduce L. lactis populations, but mortality (up to 70%) was observed with L. lactis ssp cremoris. The overall SAA of L. lactis ssp lactis cultures in EC media was 35% lower than milk- or HE media-grown starters, but the greater populations reached in EC media enabled a significant reduction in inoculation rate, Some statistically significant correlations were obtained between SAA and SPA (positive) as well as with chain length (negative), but the coefficients of determination were generally very low, The drop in pH during storage at 4 degrees C was less with HE media than in milk, and was in relation to their buffering capacity.