Bioavailability of new synthesised glucooligosaccharides in the intestinal tract of gnotobiotic rats

Using germ-free rats and previously germ-free rats inoculated with a complex human flora (heteroxenic rats), the digestibility of new glucooligosaccharides (GOS) and the effect of the digestive flora on their fermentation were studied. The GOS were synthesized using a glucosyltransferase reaction and were composed of a mixture of mono- to heptasaccharides (degree of polymerisation (DP) from 1 to 7), with alpha-1,6 and alpha-1,2 linkages. In germ-free rats, two diets containing GOS (20 g kg-1 diet and 40 g kg-1 diet) were compared to a control diet containing sucrose. The extent of GOS digestion was about 20% and the major component. DP 5, was almost fully resistant to the action of endogenous enzymes. In heteroxenic rats, only GOS (20 g kg-1 diet) was compared to the control diet. Gaseous H2 and CH4 excretions measured in a respiratory chamber significantly increased by GOS fermentation (1.8 and 2.9 times, respectively, P < 0.001). As compared to the control group, there were no modifications of the pH, short-chain fatty acids (SCFA), and lactic acid concentrations in the caecum of rats fed with the GOS diet, but there were changes of the SCFA profile, ie butyric, isobutyric and isovaleric acid proportions significantly decreased (P < 0.01), whereas the caproic acid proportion increased (P < 0.05). GOS appeared to be completely fermented. Changes in the gaseous excretion and in the SCFA profile suggest that the intake of a low amount of this new synthetised GOS led to some decrease in the proteolytic activity and in an enhancement of the glycolytic fermentation.