Preparation of exopolysaccharides by heat-resistant Weizmannia coagulans using anion exchange resins

Abstract

Weizmannia coagulans with high temperature tolerance and stability was selected for the production of exopolysaccharides (EPS) at the fermentation temperature of 52 °C. The weak basic anion exchange resin was employed in the fermentation for the construction of buffer system to neutralize some lactic acid and form intermolecular hydrogen bonds with hydroxyl groups on capsular polysaccharides of bacteria via tertiary amine groups, resulting in the increased growth space for capsular polysaccharides. In addition, the fermentation at relatively high temperature significantly decreased the adsorption of Ca2+ derived from CaO used for pH adjustment to the resin and sustained the ion exchange capability of the resin available for the formation of intermolecular hydrogen bonds with capsular polysaccharides. The concentration of EPS obtained achieved up to 19.8 g/L, which was increased by approximately 20-fold as compared to the concentration of EPS obtained by conventional fermentation. The conversion rate of carbohydrates to EPS reached up to 35.1%. The EPS produced under the optimized fermentation condition included neutral and acidic heteropolysaccharides with a molecular mass of 3.4 × 104–1.5 × 106 Da. The concentration and molecular mass distribution of EPS exhibited good reproducibility. This study provides a novel method for the industrial production of EPS.