Studies on the preliminary characterization of a novel exopolysaccharide produced by Streptococcus thermophilus strain from Tibetan kefir grain

摘要

The novel exopolysaccharide (EPS) was produced by a streptococcus thermophilus strain isolated from Tibetan kefir grain, and it was purified using DEAE cellulose 52 and DEAE Sepharose CL-6B column chromatography. Then it was eluted as a single symmetrical narrow peak on high-performance gel-permeation chromatography (HPGPC) and the average molecular mass was estimated to be 30,092Da. Infrared spectrum analysis indicated it had characteristic glycosidic structures. Gas chromatography showed that the EPS is composed of mannose and glucose in a molar ratio of 2.6:1 with trace galactose. The structural features of EPS were investigated by partial hydrolysis with acid, methylation analysis and NMR spectroscopy analysis. The results revealed that the main backbone chain of EPS was (2→3)-β-D-Manp, (3→4)-β-D-Manp, (2→3,6)-α-D-Glcp and trace amounts of galactose.