The production of mixed cultures containing strains of Lactacoccus lactis, Leuconostoc cremoris and Lactobacillus rhamnosus, on commercial starter media

Mixed starters containing Lactococcus lactis, Leuconostoc cremoris and Lactobacillus rhamnosus strains were produced on commercial starter media (MB Complete, Thermolac, Marlac), as well as on milk. With the exception of Marlac, the starters were cultured under pH control, The effect of media and incubation temperature (22 or 32 degreesC) on population ratios, on specific acidifying activities (SAA) of the cultures as well as on their ability to produce aroma compounds in milk was studied. The starters had higher contents in lactobacilli when they were produced at 32 degreesC, whereas a tendency to obtain higher Leuconostoc populations was observed at 22 degreesC, With respect to the lactococci, there was a significant interaction between temperature and growth medium for both strains. Thus, Le. cremoris T2 reached higher populations at 32 degreesC if grown in MB complete and Thermolac, whereas in Marlac and skim milk, viable counts were higher at 22 degreesC. The lactococci represented 50% of the total population of the culture at the beginning of the incubation, but they composed between 80% and 99% of the total population following fermentation. The best medium for growth of Leuconostoc was milk, but populations of only 10(8) Cfu/ml were reached. The lactobacilli did not grow well in MB Complete, and their development was best in the low-phosphate Marlac medium. The cultures grown on Marlac had the highest SAA values, whereas those grown on MB complete had the lowest. Overall, more ethanol and diacetyl were detected in the fermented milks when the starters used to inoculate them were produced at 22 degreesC.