Study on the factors affecting exopolysaccharide production by fermentation with Tibetan Kefir and its application

Exopolysaccharides(EPSs) production by 15 Tibetan Kefir samples collected from different regions were measured by phenol-sulfuric acid method,and three of them(K4,K7 and K12) with high EPS yields were selected. By single factor test,the fermentation conditions were obtained as follows:inoculation rate of 7% for K7 and K12,9% for K4,fermentation time of 12 h for K12,18 h for K4 and K7,fermentation temperature of37 ℃,skim milk concentration of 11%. The use of the Kefir samples K4 or K12 together with a commercial starter as a mixed starter in fermentation of whole milk showed that the combination of K12 and commercial starter gave the shortest coagulating time(4.52 h). During the 21 d of storage at 4 ℃,the fermented milk produced from this starter combination contained EPS of about 50 mg/L and viable bacterial counts of over8.20 log cfu/m L,maintaining higher water holding capacity and viscosity.