Structural characteristics and biological activity of lactic acid bacteria exopolysaccharides separated by ethanol/(NH4)2SO4 ATPS

Exopolysaccharides (EPS) from lactic acid bacteria (LAB) as edible and safe bioproducts with health benefits have become an interesting topic. In this study, aqueous two-phase system (ATPS) was established using ethanol and (NH4)2SO4 as phase-forming substances to separate and purify LAB EPS from Lactobacillus plantarum 1.0665. The operating conditions were optimized by a single factor and response surface method (RSM). The results indicated that an effectively selective separation of LAB EPS was achieved by the ATPS consisted of 28 % (w/w) ethanol and 18 % (w/w) (NH4)2SO4 at pH 4.0. Under optimized conditions, the partition coefficient (K) and recovery rate (Y) were well matched with the predicted value of 3.83 ± 0.019 and 74.66 ± 1.05 %. The physicochemical properties of purified LAB EPS were characterized by various technologies. According to the results, LAB EPS was a complex polysaccharide with a triple helix structure mainly composed of mannose, glucose and galactose in the molar ratio of 1.00: 0.32: 0.14, and it proved that the ethanol/(NH4)2SO4 system had good selectivity for LAB EPS. In addition, LAB EPS displayed excellent antioxidant activity, antihypertension activity, anti-gout capacity and hypoglycemic activity in vitro analysis. The results suggested that LAB EPS could be a dietary supplement applied in functional foods.