Characterisation of a novel water-soluble polysaccharide from Leuconostoc citreum SK24.002

Water-soluble polysaccharides that are produced from sucrose by lactobacillus strains isolated from Chinese traditional pickled vegetables were investigated. Strain SK24.002, which secreted an exopolysaccharide with a high dextranase resistance, was identified as Leuconostoc citreum via 16S rDNA sequence analysis. A polysaccharide yield of 35 g/L was achieved at 20 h in Man-Rogosa-Sharpe medium containing 100 g/L sucrose. The water-soluble polysaccharide consisted exclusively of glucose, and the weight-average molecular weight was 4.62 × 107 Da. Spectroscopy results demonstrated that the water-soluble exopolysaccharide was mainly composed of α-1,3 and α-1,6 linked d-glucopyranose units. Methylation analysis revealed that the ratio of α-1,6 linkages to α-1,3 linkages was 5:4. These results suggested a possible molecular structure for the water-soluble exopolysaccharide that consists of a backbone chain of alternating α-1,3 and α-1,6 linkages with a branched point at the C6 of the 1,3,6-linked d-glucopyranose unit. This novel polysaccharide may have applications as a functional ingredient in processed foods.