Characterisation and in vitro fermentation of resistant maltodextrins using human faecal inoculum and analysis of bacterial enzymes present

A commercially available resistant maltodextrin (RMD), which is made out of corn starch by chemically and enzymatically modification, consists of atypical starch linkages and a low average molecular mass of 2kDa. These characteristics of RMD make it rather complicated to identify with any chromatographic or masspectrometric method at this moment. A batch fermentation with human inocula over 48h under anaerobic conditions showed that the degradation of the indigestible RMD is slow in comparison to dietary fibres like FOS. The RMD is only fermentable for ca. 60% and no specific oligosaccharide within the RMD population seems to be preferentially utilised by the microbiota present. Short chain fatty acid (SCFA) production, with acetic acid as the main SCFA, started after ca. 5h of fermentation, while the increase of SCFA at 11h was concurrent with the major degradation of the oligosaccharides of RMD. The microbiota composition as analysed by HITchip, revealed that RMD slightly stimulated the growth of bifidobacteria in comparison to the blank. The activity of carbohydrate degrading enzymes, produced by the microbiota during the in vitro fermentation, revealed that potential capacity to degrade typical starch linkages was high, but the RMD was only slowly and partly degradable during the incubation of 20h. HPAEC elution profiles of Resistant Malto Dextrine fermentation digesta at different time points a=0h , b=11h, c=24h and d=48h. [Display omitted] •RMD is a very branched molecule.•RMD is difficult to separate by chromatographic techniques.•RMD is slowly fermented, up to 60%, by human inocula within 48h.•Digesta enzymes are able to degrade various glucans.•Digesta enzyme have also the capability to degrade non-glucan structures.