In vitro digestibility of commercial and experimental isomalto-oligosaccharides

Isomalto-oligosaccharides (IMO) significantly contribute to the global oligosaccharide market. IMO are linear alpha-(1 -> 6) linked oligosaccharides with isomaltotriose as the representative trisaccharide. Commercial IMO preparations ypically also contain panose-series oligosaccharides as a major component. In humans, IMO are partially digestible but the digestibility of specific components of commerical IMO preparations remains unknown. This study aimed to compare the in vitro digestibility of reference compounds, experimental alpha-gluco-oligosaccharides and commercial IMO. Experimental alpha-gluco-oligosaccharides were synthesized with the recombinant dextransucrase DsrM. Two in vitro digestion methods were used, a reference method matching the AOAC method for dietary fibre, and a protocol that uses brush border glycosyl hydrolases from the rat intestine. The alpha-gluco-oligosaccharides patterns after hydrolysis remain were analyzed by high performance anion exchange chromatography coupled to pulsed amperometric detection. Panose-series oligosaccharides were hydrolysed more rapidly by amylase and amyloglucosidase when compared to hydrolysis by rat intestinal enzymes. The rate of hydrolysis by rat intestinal enzymes decreased in the order panose > isomaltose, kojibiose or nigerose. Hydrolysis of panose-series oligosaccharides but not the hydrolysis of isomalto-oligosaccharides was dependent on the degree of polymerization. Qualitative analysis of oligosaccharides remaining after hydrolysis indicated that rat small intestinal enzymes hydrolyse their substrates from the non-reducing end. Taken together, results inform on the modification or optimization of current production processes for IMO to obtain tailored oligosaccharide preparations with reduced digestibility and an increased content of dietary fibre.