Physico-chemical characterization of an exopolysaccharide produced by a non-ropy strain of Leuconostoc sp. CFR 2181 isolated from dahi, an Indian traditional lactic fermented milk product

Abstract

Exopolysaccharide (EPS) producing non-ropy strain of lactic acid bacteria (LAB) was isolated from dahi, an Indian traditional fermented milk product, and on the basis of morphology, physiological and biochemical tests it was identified as Leuconostoc sp. CFR 2181. In shake flask fermentation for 72 h at 22 °C, the quantity of EPS produced by the isolate was 13.8 g/L in modified MRS broth and 25.4 g/L in EPS medium (a newly formulated simplified synthetic medium). The EPS was non-gelling and non-film forming. It was completely soluble in water and 1N sodium hydroxide solution. The purified EPS contained 84% of total carbohydrates, 11.2% of reducing sugars, 2% of moisture, 0.8% of proteins and 0.6% uronic acid. The EPS consisted mainly of glucose (91%) with minor quantities of rhamnose and arabinose (1.8% each). Gel permeation chromatography indicated considerable heterogeneity of EPS, having three fractions with molecular weights ranging from 1.0 × 10 4 to 1.5 × 10 6 Da. Enzymatic hydrolysis with pullulanase and α-amylase and NMR analysis of the EPS indicated the presence of α (1 → 6) linkages and the absence of α (1 → 4) linkages.