Resistance to gut digestion and bifidogenic effect of galacto-oligosaccharides in rats is dependent of linkage type and monomer composition

Resumen del trabajo presentado al Workshop Current Trends in Biomedicine: The microbiome: role in health and disease, celebrado en Baeza (España) del 8 al 10 de octubre de 2012.A comparative study regarding the resistance to gut digestion, fermentability and selective growth of beneficia! bacteria in the large intestine of growing rats (5 wk old) fed novel galactooligosaccharides (GOS) derived from lactulose (GOS-Lu) or commercially available derived from lactase (GOS-La) was carried out. Animals were fed either a control diet or diets containing 1% (w/w) of GOS-Lu [degree of polymerization(DP) >= 2] or GOS-La (DP >= 3)] for 14 d; chromium oxide was included in diets as an indigestible marker. Quantitative analysis of carbohydrates from di.etary and ileal samples demonstrated that the trisaccharide fraction of GOS-Lu was significantly more resistant to gut digestion than that from GOS-La, according to their ileal digestibility rates (12.5 and 52.9%, respectively), whilst the disaccharide fraction of GOS-Lu was fully resistant to the extreme environment of the upper digestive tract. The low ileal digestibility of GOS-Lu was attributed to the great resistance of galactosyl-fructoses to mainmalian digestive enzymes, highlighting the key role played by monomer composition and linkage type involved in the oligosaccharide chain. The partial digestion of GOS-La trisaccharides showed that glycosidic linkages β(l-6) and β(1-2) between galactose and glucose monomers were significantly more resistant to gastrointestinal digestion than the linkage β(l-4) between galactose units. The absence of GOS-La and GOS-Lu digestion-resistant oligosaccharides in fecal samples indicated that they were readily fermented within the large intestine, enabling both GOS to have a potential prebiotic function. A significant increase in the growth of both Bifidobacteria and Eubacterium rectale/Clostridium coccoides groups was observed in response to GOS-Lu treatment in large intestine; at specie level, a significant and selective increase of Bifidobacterium anima lis was revealed. These novel data support a direct relationship between pattems of resistance to digestion and bifidogenic properties of galactooligosaccharides.Peer Reviewe