Structural elucidation and physicochemical properties of litchi polysaccharide with the promoting effect on exopolysaccharide production by Weissella confusa

Exopolysaccharide (EPS), as a secondary metabolite of microorganisms, has been commonly used in the dairy industry to replace the traditional stabilizers. However, the EPS production by microorganism is generally low, which limits its application. A litchi polysaccharide (Lzp2-2) with the promoting effect on EPS production by Weissella confusa was purified. The SEM and FT-IR analysis indicated that Lzp2-2 displayed a compact netlike structure and typical bands of carbohydrates. The structure of Lzp2-2 was further elucidated, which was comprised of a major backbone structure [-> 3)-beta-D-Galp-(1 -> 6)-beta-D-Galp-(1 -> 6)-beta-D-Galp-(1 -> 3)-beta-D-Glcp-(1 -> 6)-alpha-D-Glcp-(1 -> 3)-alpha-D-Glcp-(1 ->] linked with two side chains [alpha-L-Araf-(1 -> 5)-alpha-L-Araf-(1 ->, and beta-D-Glcp- (1 -> or alpha-L-Araf-(1 ->] at the O-3 and O-6) of beta-D-Galp-(1 ->, respectively. Finally, Lzp2-2 was applied as an additive to the medium of yoghurt fermented by W. confusa. The results indicated Lzp2-2 not only promoted the EPS production to improve the viscosity, texture and mouthfeel of yoghurt, but also facilitated the generation of other secondary metabolites (volatile organic compounds), thus elevating the flavor of yoghurt.