Abstract
Water kefir is abeverage fermented by a microbial consortium captured in kefir grains. The kefir grains matrix is composed of polysaccharide, primarily dextran, whichis 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 Lisolates threeproduced slime colonies on modified MRS (mMRS) agar containing sucrose instead of glucoseand were presumed to produce dextran. Three LABwere 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 16h, 20h and 32h for T1, T3 and T5, respectively. Optimal temperature for dextran production was 23oC for two Leuconostoc mesenteroides strains and 30oC for Lactobacillus hilgardii strain. The produced dextrans were identified based on paper chromatography while the main structure characteristics of purified dextranwere observed by FT-IR spectroscopy. Our study shows that water kefir grains are a natural source of potent dextranproducing LAB.
Highlights
Water kefir is a beverage fermented by a microbial consortium captured in kefir grains
12 lactic acid bacteria were isolated from water kefir grains and were denoted as T1 to T12
The present study describes three new lactic acid bacteria (LAB) strains isolated from water kefir grains that are able to produce dextran
Summary
Water kefir is a beverage fermented by a microbial consortium captured in kefir grains. 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 composition of the kefir grains' microbiota has been excessively studied [3,4,5,6,7] It includes yeasts, acetic acid bacteria and lactic acid bacteria (LAB), with the last being the most abundant [6]. The main component of water kefir grain matrix is dextran [9] This exopolysaccharide (EPS) is synthesized by indigenous LAB. Different authors reported different bacterial species as the predominant EPS producers in water kefir grains and these include Lactobacillus casei (two subspecies) [4], Leuconostoc mesenteroides, Lac-. Insoluble dextran could be applied as matrix for immobilization of biomolecules [17]
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