The bifidogenic effect of galacto-oligosaccharides in rats is dependent of their structural characteristics

Abstract

A comparative study to evaluate the resistance to gut digestion, fermentability and modulatory effect of gut microbiota in the large intestine of growing rats (5 wk old) fed novel galacto-oligosaccharides (GOS) derived from lactulose (GOS-Lu) or commercially available derived from lactose (GOS-La) was performed. Rats were fed either a control (AIN-93G) or experimental diet containing 1% (wt:wt) of GOS-Lu or GOS-La for 14 d. Quantitative analysis of oligomers from dietary and ileal samples demonstrated that the trisaccharide fraction of GOS-Lu was significantly more resistant to gut digestion than that from GOS-La, whereas the disaccharide fraction of GOS-Lu was fully resistant to the extreme environment of the upper digestive tract. The low ileal digestibility rates of GOS-Lu was attributed to the great resistance of galactosyl-fructoses to mammalian digestive enzymes, highlighting the key role played by monomer composition and linkage type involved in the oligosaccharide chain. Di- and trisaccharides were completely fermented within the large intestine, enabling both GOS to have a potential prebiotic function. Indeed, the novel GOS-Lu exerted a stronger bifidogenic effect in large intestine than GOS-La, with the former having a significant and selective increase of Bifidobacterium animalis. In addition, both GOS types showed a significant increase in Eubacterium rectale/Clostridium coccoides population relative to control. These data support a direct relationship between patterns of resistance to digestion and bifidogenic properties of galacto-oligosaccharides.