Stability of autolytic lactococci during starter production and storage in commercial whey-based media

Lactococcus lactis ssp. cremoris strains with different autolytic activities were grown in milk and in a commercial whey-based medium. Fermentation under pH control substantially improved total and viable counts of strain NM33-7; highest populations were obtained on the commercial whey-based medium and the cultures had the highest content of viable cells (80%). Cultures grown in milk without pH control gave only 46% viable cells. Once fermentation was completed, cooling prevented a significant decrease in viable counts. Losses in viability of NM33-7 upon extended incubation at 30 °C or storage at 4 °C were higher when the cultures were prepared on whey-based medium than when prepared on milk without pH control. In pH-controlled fermentations, the autolytic activity of NM33-7 was higher when grown on whey-based medium than when grown on milk. A negative correlation was obtained between the autolytic activity of the Lc. lactis ssp. cremoris strains and their subsequent stability during storage.