Fructans

Oligosaccharides and polysaccharides composed of fructose residues joined to a single glucose molecule. Chain lengths run from 3 to 50 residues depending on source: in cereals shorter chains predominate, while Jerusalem artichokes are rich in inulin — a fructan of roughly 35 residues — while onions, garlic and asparagus provide more dietary fructans. The stomach and small intestine barely hydrolyse them, so most reach the large intestine intact, where colonic fermentation produces short-chain fatty acids — the basis of their prebiotic effect — though excess intake can cause flatulence.