Abstract: In this study, 9 strains, KC1, KC2, KC5, KC6, KC7, KC15, KC16, KC17 and KC22 , were isolated and screened out from Tibetan kefir. All of the strains were identified as Streptococcus thermophilus. KC1, KC2, KC6 and KC17 were found to be capable of producing exopolysaccharides, while KC5, KC7, KC15, KC16 and KC22 had no such ability. The exopolysaccharide-producing strains presented better fermentation performance and fermented milks obtained with each of them had higher viscosity and adhesiveness when compared to the non-exopolysaccharide-producing strains, thus further demonstrating that exopolysaccharides from Streptococcus thermophilus can provide fermented milk with excellent texture.

Key words: Tibetan kefir, Streptococcus thermophilus, exopolysaccharide