Preparation, structural characterization and rheological properties of a novel fucose-containing exopolysaccharide from Clavibacter michiganensis

Abstract

Bacterial exopolysaccharide (EPS) has excellent application value in the food field owing to thickening, gelling, stabilizing, emulsifying and flocculating properties, among them fucose-containing EPS may serve as functional additive applied in food industry. In the present study, a bacterial strain M1 capable of producing fucose-containing EPS isolated from decaying tomato was identified as Clavibacter michiganensis. Different fermentation media affect the yields, monosaccharide compositions, and molecular weights of EPSs. The yield (6.49 ± 0.162 g/L) and l-fucose content (31.68 ± 1.40 mol%) of the EPS produced from the fermentation medium with sucrose and yeast extract was the highest. After purification by gel chromatography, the structure of purified EPS fraction was analyzed. Monosacchride composition showed that the EPS was composed of l-fucose, d-glucose and d-galactose with a ratio of 2:1:1. Methylation results further proved the composition of EPS was T-Galp-(1→, →3)-α-l-Fucp-(1→, →3,4)-α-l-Fucp-(1→, and →3)-β-d-Glcp-(1→. Nuclear magnetic resonance analysis indicated that the main chain of EPS was →3)-β-d-Glcp-(1→4)-α-l-Fucp-(1→3)-α-l-Fucp, with α-d-Galp linked at the 3-position of the first α-l-Fucp as the branch chain. The apparent viscosity of EPS was consistently higher than that of xanthan gum at different concentrations, and both increased with increasing concentrations. According to the results of oscillation frequency sweep, the rheological property of EPS solution was closer to viscoelastic fluid rather than weak gel like xanthan gum. This study presents a simple and novel strategy to obtain fucose-containing EPS, which could be helpful for developing potential functional additives for food industry.