ACIDIFICATION RATES AND POPULATION RATIOS OF LACTIC STARTERS IN CARBONATED MILK

Milk pH was standardized to between 6.62 and 6.40 with CO2 or lactic a cid and then fermented with a mixed mesophilic culture (MI) composed o f Lactococcus lactis ssp. lactis and Lactococcus lactis ssp. cremoris, as well as two mixed thermophilic starters (T1, T3) composed of Lacto bacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus Du ring fermentation, a decrease in pH occurred in the first 30 min of in cubation in milks standardized with lactic acid which was not true wit h CO2-standardized milks. Thus, the lag time was significantly longer in the CO2-treated milks. When cultures were omitted from milks, an in crease in pH occurred in milk in open vessels when the pH had been adj usted with CO2. In addition to differences in lag time, with the therm ophilic cultures, significant differences were noted in the time and t he pH at which the maximum acidification rates occurred. There was no significant effect of initial pH or of acidifying agent on ratios of c occi to rod in T1 and T3 cultures, after 4 h of incubation. Effects of milk acidification on overall populations and ratios of M1 were only minor, but lower total populations were reached in CO2-treated ferment ed milks, and the Lc. cremoris content was higher in CO2-than in lacti c acid-standardized milks. (C) 1998 Academic Press Limited.