Physicochemical Properties of Kefir Manufactured by a Two-Step Fermentation

The objective of this study was to assess the physicochemical and sensory changes of a kefir manufactured by a two-step fer-mentation (MTY, 1st step: 37oC for 9 h; 2nd step: 24oC for 15 h) and compare it with kefirs produced by two conventional meth-ods (GTY, fermentation at 37oC for 24 h; KEY, 22oC for 24 h). Rapid changes in pH and titratable acidity (TA) were observed in samples from all three manufacturing methods during fermentation process and storage period. Lactic acid bacteria (LAB) counts of MTY increased gradually up to 12 h of fermentation, reaching 9.28 Log CFU/mL, with maximum value observed in this experiment of 9.48 Log CFU/mL. The LAB counts of all samples decreased significantly during storage. The highest vis-cosity was observed for MTY (1750-1771 cPs), compared with the lowest viscosity observed for KEY (1250-1277 cPs). The viscosity of all samples increased slightly during storage (1250-1805 cPs, p<0.05), as well as carbon dioxide content (0.01-1.36%, p<0.05), except for GTY. The most significant increase in alcohol concentration during storage period was seen in MTY from 0.01 % to 1.36 % (p<0.05). MTY scored significantly higher in most items of the sensory analysis, indicating that the prod-uct manufactured by the two-step fermentation method is more acceptable compared with conventionally produced kefirs