Metabolism of isomalto-oligosaccharides by Lactobacillus reuteri and bifidobacteria

Commercial isomalto-oligosaccharides (IMO) are functional food ingredients. They are composed of alpha(1 -> 6)- and alpha(1 -> 4)-linked oligosaccharides. IMO are partially indigestible, and dietary IMO stimulate beneficial members of intestinal microbiota, including lactobacilli and bifidobacteria. However, data on IMO metabolism by lactobacilli are not available. It was the aim of this study to identify metabolic pathways of IMO metabolism in lactobacilli. This study focused on the host-adapted species Lactobacillus reuteri. Metabolism of bifidobacteria was analysed for comparison. Commercial IMO contained IMO with a degree of polymerization (DP) of up to four and panose-series oligosaccharides (POS) with a DP of up to 5. Lactobacilli metabolized isomaltose preferentially over oligosaccharides with higher DP. Bifidobacteria preferentially metabolized oligosaccharides with higher DP and accumulated glucose. Metabolism of IMO and POS by L. reuteri was attributed to a(1? 6)-specific glucanase DexB and maltose phosphorylase. Contribution of maltose phosphorylase was verified by quantification of IMO and POS phosphorolysis in crude cellular extracts of L. reuteri 100-23. In conclusion, metabolism of IMO by lactobacilli is limited to short-chain oligosaccharides, while bifidobacteria preferentially metabolize oligosaccharides with higher DP. The functionality of commercial IMO can thus be modified by degree of polymerization.