The dynamics of Leuconostoc mesenteroides bacteria growth and synthesis of exoplysaccharides when cultured on a medium containing whey and sucrose has been investigated. It was shown that exopolysaccharides were produced during the culture growth and the addition of sucrose increased in the productivity of those compounds without affecting their composition. Using the dynamic and static methods of light scattering, it was shown that sucrose as a medium component modified physicochemical properties of exopolysaccharides changing their structural and thermodynamic characteristics in aqueous medium, which affected their functional activity and determined the way of their most efficient use. kefir fungi, lactic acid bacteria, physicochemical properties of exopolysaccharides.

A screening of lactic acid polysaccharide-synthesizing bacteria, components of the kefir grains, has shown that about 60% of isolates are able to synthesize exopolysaccharides (EPS). The most active cultures, Lactococcus lactis and Leuconostoc mesenteroides, that synthesize exopolysaccharides during the development on a medium with lactose or sucrose, respectively, were selected. The results of IR spectroscopy confirmed the identity of the compositions of the synthesized exopolysaccharides with polysaccharides of kefir grains. A culturing regime for L mesenteroides on whey supplemented with sucrose that provides the production level of kefiran up to 3,4 g/l was developed.

The screening of lactic-acid polysaccharide-synthesizing the bacteria, components of kefir grains, has shown that about 60% of isolates can synthesize exopolysaccharides (EPSs). We selected the most actively synthesizing EPSs cultures during development on a medium with lactose or sucrose: Lactococcus lactis and Leuconostoc mesenteroides, respectively. IR-spectroscopy confirmed the identity of the compositions of the synthesized EPSs with polysaccharides of kefir grains. We also determined the parameters for culturing L. mesenteroides on whey with added sucrose that provides a kefiran production level up to 3.4 g/L were developed.

The associated culture of kefir grains was analyzed by molecular methods for determination of the functional activity of microbial isolates and molecular genetic techniques for their identification. A combination of 16S rRNA analysis and denaturing gradient gel electrophoresis was used to determine the microbial profile of kefir grains and to reveal lactic acid bacteria of two physiological groups, differing in their ability to use lactose for lactic acid fermentation. The role of inducible β-galactosidase of lactic acid bacteria for the functional stability of the microbial community was shown in the study of the functional activity and microbial profile of the kefir grains after long-time cultivation (over 4 years) on lactose-free milk. The results obtained improve our understanding of the possible trophic interactions in such microbial communities and may be used to develop the algorithm for experimental production of a stably associated culture of kefir grains.