Superiority of 1-kestose, the Smallest Fructo-oligosaccharide, to a Synthetic Mixture of Fructo-oligosaccharides in the Selective Stimulating Activity on Bifidobacteria

A synthetic mixture of fructo-oligosaccharides (mFOS), consisting largely of nystose (GF 3 ) and a lesser amount of 1-kestose (GF 2 ) has been reported to be selectively utilized by bifidobacteria. In the present study, we tried to identify which fructo-oligosaccharide molecule in mFOS is really involved in the stimulation of bifidobacteria in the gut, using both the gnotobiotic murine model and in vitro culture. 1-Kestose administration to gnotobiotic mice that were associated with human fecal microbiota significantly increased the number of bifidobacteria while mFOS administration was unable to sustain bifidobacteria in these hosts. Moreover a simultaneous decrease in the number of clostridia was found in host mice administered 1-kestose but not in those administered mFOS. The acetate/ propionate ratio in the feces was far higher in host mice administered 1-kestose than in those administered mFOS, suggesting the selective growth activation of bifidobacteria by 1-kestose. The culture study demonstrated that 1-kestose exerts a strong growth-stimulating activity on bifidobacteria but a negligible one on clostridia. On the other hand, nystose was able to stimulate clostridia if the clostridia were exposed to nystose for some time. These results suggest the superiority of 1-kestose to mFOS, which consists largely of nystose, in the selective stimulating activity on bifidobacteria.