The aim of the study was to investigate the metabolism of non-digestible oligo- and
polysaccharides by fecal microbiota, using isothermal microcalorimetry. The five tested substrates were
raffinose,
melibiose, a mixture of oligo- and
polysaccharides produced from
raffinose by
levansucrase,
levan synthesized from
raffinose, and
levan from timothy grass. Two inocula were comprised of pooled fecal samples from
overweight or normal-weight children, from healthy adult volunteers and a pure culture of Bacteroides thetaiotaomicron as a reference bacterium for colon microbiota. The growth was analyzed based on the heat evolution curves, and the production of organic
acids and
gases. Taxonomic profiles of the microbiota were assessed by 16S
rDNA sequencing.
Raffinose and
melibiose promoted the growth of bifidobacteria in all fecal pools. Several pool-specific substrate-related responses to
raffinose and
melibiose were revealed.
Lactate-producing bacteria (Streptococcus and Enterococcus) became enriched in the pool of
overweight children resulting in
lactic acid as the major fermentation product on short saccharides. Acetic and
butyric acids were prevalent at fermentation in the normal-weight pool coinciding with the enrichment of Catenibacterium. In the adult pool, the specific promotion of Bacteroides and Lachnospiraceae by
levans was disclosed. In the fecal pool of normal-weight children,
levans stimulated the growth of Senegalimassilia and Lachnoclostridium and this particular pool also showed the highest maximum heat production rate at
levan fermentation.
Levans and
raffinose-derived
oligosaccharides, but not
raffinose and
melibiose were completely fermented by a pure culture of Bacteroides thetaiotaomicron. The main conclusion from the study is that fecal microbiota of normal and
overweight children have different compositions and they respond in specific manners to non-digestible oligo- and
polysaccharides:
raffinose,
melibiose,
raffinose-derived
oligosaccharides and
levans. The potential of the tested saccharides to support a healthy balance of colon microbiota requires further studies.