Compared effects of three oligosaccharides on metabolism of intestinal microflora in rats inoculated with a human faecal flora

Abstract

Using germ-free rats inoculated with a human faecal flora (gnotobiotic rats), the effects of three oligosaccharides (β-fructo-oligosaccharides (FOS), β-galacto-oligosaccharides (TOS) and α-gluco-oligosaccharides (GOS)) on intestinal bacterial metabolism were compared. The animals were fed on either a control diet or diets containing 4Og/kg of GOS, FOS or TOS. FOS and TOS were the preferred growth substrates for Bifidobacteria which increased in number by 2 log values in faeces of rats when compared with rats fed on GOS or control diets. Ingestion of TOS specifically induced hydrolysis of the substrate, and did not modify the activity of any other enzymes measured in the caecum. GOS led to a non-specific enzymic induction of β-galactosidase (EC 3.2.1.23), β-glucosidase (EC 3.2.1.21) and α-glucosidase (EC 3.2.1.20) activities whereas β-glucuronidase (EC 3.2.1.31) was lowered. Compared with the control group, FOS and TOS diets led to a significant increase in H2and CH4excretion; the GOS diet increased only CH4. Analysis of caecal contents revealed a decrease in pH for all diets compared with controls. Total short-chain fatty acid (SCFA) concentration increased significantly in all groups, but the SCFA profile differed between treatment groups. It was concluded that the three oligosaccharides studied had different effects which may be linked to their chemical structure. Some of these effects may be beneficial to human health