Inulin like fructans are used as prebiotics as they are non digestible. Resistance to digestion in the upper GI tract results from:
Inulin is a dietary fibre, its a fructan with 2-60 fructose units linked a beta (1-2)bond. Due to this beta - configuration of anomeric C2 in their fructose monomers it is resistant to digestion in the GIT. Ref: Food Science and Technology Bulletin : Functional Foods By Glenn R. Gibson, Page 5; Dietary Fibre : New Frontiers for Food and Health By J. W. van der Kamp, Julie Jones, Barry Mccleary, David J. Topping, Page 177; Functional Foods : Concept to Product By Glenn R. Gibson, Christine M. Williams, Page 249.
Absence of digestive enzyme in the upper GIT
Beta configuration of anomeric C2
Low pH of the stomach
Presence of a-osidic linkages