Isolation, Purification, and Characterization of Exopolysaccharide Produced by Leuconostoc Citreum N21 from Dried Milk Cake

Abstract

A strain with high production of exopolysaccharide (EPS) was isolated from dried milk cake (a traditional fermented food from Inner Mongolia). The strain was called N21 and later identified as Leuconostoc citreum (Leu. citreum). The strain was cultured in Man-Rogosa-Sharpe medium containing 50 g/L of sucrose for 48 h at 30 °C and the EPS purified, with a yield of 24.5 g/L. An average molecular weight of 6.07 × 10⁶ g/mol was determined by high-performance size-exclusion chromatography. The structure of the purified EPS was investigated through gas chromatography, ¹H and ¹³C nuclear magnetic resonance spectroscopy, and Fourier transform infrared spectroscopy. The results demonstrated a polysaccharide composed of D-glucopyranose units in a linear chain with consecutive α (1 → 6) linkages. No branching was found in the structure of the exopolysaccharide. The purified EPS showed high water solubility and emulsibility. Based on the thermogravimetric curve, the degradation temperature of the EPS was 308.47 °C, which suggested that the dextran in the study exhibited high thermal stability. The results indicated that Leu. citreum N21 could be widely used to produce linear EPS and that the EPS has potential applications in food science and processing as a food additive.

Keywords

Exopolysaccharide / Dextran / Characterization / Leuconostoc citreum / Structure

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