Microbiological and chemical changes during the manufacture of Kefir made from cows' milk, using a commercial starter culture

The counts of total aerobic mesophilic bacteria, lactic acid bacteria (in three different culture media, M17 agar, MSE agar, and Rogosa agar) and yeasts, and some biochemical parameters (levels of lactose, glucose, galactose, L(+)- and D(-)-lactic acids, ethanol, titratable acidity and pH) were determined during 196 h of fermentation in five batches of Kefir made from cows' milk using a commercial starter culture. Lactococcus spp. predominated during the first 48 h of fermentation (similar to 8 log 10 cfu g(-1)); Lactobacillus spp. became the predominant species after 48h (similar to 8.5loglocfug(-1)). During the first 24h of fermentation, the lactose content decreased from a mean value of 4.92% (w/w) to 4.02% (w/w); the concentration of L(+)-lactic acid increased from 0.01% to 0.76% (w/w) and the pH decreased to 4.24 over the same period. After 24 h of fermentation, the changes in the levels of lactose and L(+)-lactic acid, and in pH, occurred more slowly. Neither glucose nor galactose were detected during fermentation. The production of ethanol was limited, reaching a mean final value of 0.018% (w/w). (c) 2005 Elsevier Ltd. All rights reserved.