Water Kefir grain as a source of potent dextran producing lactic acid bacteria

Water kefir is a beverage fermented by a microbial consortium captured in kefir grains. The kefir grains matrix is composed of polysaccharide, primarily dextran, which is produced by members of the microbial consortium. In this study, we have isolated lactic acid bacteria (LAB) from non-commercial water kefir grains (from Belgrade, Serbia) and screened for dextran production. Among twelve LAB isolates three produced slime colonies on modified MRS (mMRS) agar containing sucrose instead of glucose and were presumed to produce dextran. Three LAB were identified, based on morphological, physiological and biochemical characteristics and 16S rRNA sequencing, as Leuconostoc mesenteroides (strains T1 and T3) and Lactobacillus hilgardii (strain T5). The isolated strains were able to synthesize a substantial amount of dextran in mMRS broth containing 5% sucrose. Maximal yields (11.56, 18.00 and 18.46 g/l) were obtained after 16, 20 and 32 h for T1, T3 and T5, respectively. Optimal temperature for dextran production was 23 degrees C for two Leuconostoc mesenteroides strains and 30 degrees C for Lactobacilus hilgardii strain. The produced dextrans were identified based on paper chromatography, while the main structure characteristics of purified dextran were observed by FT-IR spectroscopy. Our study shows that water kefir grains are a natural source of potent dextran producing LAB.