Synthesis and in-vitro fecal fermentation of potential prebiotic -glucooligosaccharides using microbial glucansucrase
Novel -glucooligosaccharides were synthesized by the acceptor reaction of Leuconostoc citreum SK24.002 glucansucrase with maltose and sucrose. The impact of synthesis conditions, including the ratio of sucrose to maltose and the substrate concentration, on formation of -glucooligosaccharide was evaluated. At the optimized experimental conditions, the yield of a mixture of -glucooligosaccharides with DP 3-5 reached approximately 56.4% with the concentration of 170.7 mg/mL. Each of these -glucooligosaccharides was purified, and the structures were assigned as follows: α-D-Glcp-(1,6)-α-D-Glcp-(1,4)-D-Glcp (DP3), α-D-Glcp-(1,3)-α-D-Glcp-(1,6)-α-D-Glcp-(1,4)-D-Glcp (DP4), and α-D-Glcp-(1,6)-α-D-Glcp-(1,3)-α-D-Glcp-(1,6)-α-D-Glcp-(1,4)-D-Glcp (DP5), respectively. Of three structurally different oligosaccharides, the fermentation selectivity by fecal bacteria was determined in anaerobic batch culture. Fructooligosaccharide (FOS) was used as a positive prebiotic control. Similar to FOS, all three -glucooligosaccharides selectively stimulated the proliferation of Bifidobacteria and Lactobacilli compared with the control. DP3 exerted the strongest prebiotic ability for increasing the Bifidobacteria and Lactobacilli population, whereas DP5 produced the most short-chain fatty acids. In addition, DP4 produced the highest butyrate concentration and resulted in the lowest acetate: propionate ratio. These results suggested that the enzymatically-synthesized -glucooligosaccharides were potential prebiotics, underlining correlations between structural features of oligosaccharides and their impact on the metabolism of fecal microbiota.