Abstract:Isomaltooligosaccharides (IMO) are oligosaccharides mainly composed of α-1,6 glycosidic bonds linked glucoses, which have physiological characteristics of hypoglycemic index and promoting probiotics proliferation. The current commercial IMO production has low yield and high isomaltose content in the product, while the probiotic function of IMO is mainly attributed to the high polymerization fractions like disaccharides and above. In this study, α-glucosidase from Aspergillus niger and cyclodextrin glucosyltransferase (CGTase) from Bacillus stearothermophilus NO2 were combined for synthesis of IMO with improved yield and polymerization (named IMOH). In this study, the effects of reaction pH, temperature, time, substrate type and enzyme addition on the yield were investigated by single-factor experiments, and the effects of compound enzyme amount and reaction time were subsequently explored. The results showed that the yield of IMOH reached 64.27%, and the high polymerization content of trisaccharides and above was 71.57% under pH 5.5 at 50 ℃, using 300 g/L maltodextrin with DE values ranges from 15 to 20 as the substrate, and with α-glucosidase of 5 U/g substrate (calculated by substrate mass) and CGTase of 20 U/g substrate (calculated by substrate mass). The structural analysis of IMOH products showed that the ratio of α-1,6 bond ratio was 70.67%, and the average molecular weight of products was 706, which was higher than that of commercial IMO50. The in vitro fermentation experiments of intestinal microorganisms suggested that compared with commercial IMO50, the IMOH had a better proliferative effect on Bifidobacterium adolescentis, and could further inhibit the growth of opportunistic bacteria Escherichia coli in intestinal tract, showing a certain in vitro probiotic effect. This study proposed a new process of the IMO synthesis by the dual-enzyme compounds, providing a new idea for the industrial synthesis of IMO with high yield and high degree of polymerization.
