In vitro activity: Inulin causes (20 g/d and 40 g/d) a significant increase in bifidobacterial counts in feces. Inulin exerts a preferential stimulatory effect on numbers of the health-promoting genus Bifidobacterium, whilst maintaining populations of potential pathogens (Escherichia coli, Clostridium) at relatively low levels. Inulin combined with Bifidobacterium results in more potent inhibition of aberrant crypt foci (ACF) than administration of the two separately, achieving 80% inhibition of small ACF. Inulin is made by a set of linear chains of fructose molecules, with a degree of polymerization (DP) ranging between 3 and 65, it can be fractionated into a slowly fermentable long-chain fraction (DP ranging from 10 to 65, average 25) or in a rapidly fermentable fraction made of oligofructose (DP ranging from 3 to 8, average 4). Long-chain inulin combined with short-chain oligofructose results in larger numbers of caecal, colonic and faecal bacteria of the Clostridium coccoides-Eubacterium rectale cluster than Control in rats, whereas OF alone does not affect this bacterial group in caecum, colon or faeces.

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