Molecular interactions of a model bile salt and porcine bile with (1,3:1,4)-β-glucans and arabinoxylans probed by 13C NMR and SAXS

•NMR shows dynamic molecular interactions between bile salts and cereal soluble fibres.•Chemical shift changes due to concentration or dilution of bile in presence of fibres.•Line broadening of bile resonances in presence of some fibres suggesting entrapment.•Bile salt induced conformation changes for β-glucan but not arabinoxylan from SAXS.

Two main classes of interaction between soluble dietary fibres (SDFs), such as (1,3:1,4)-β-d-glucan (βG) and arabinoxylan (AX) and bile salt (BS) or diluted porcine bile, were identified by 13C NMR and small angle X-ray scattering (SAXS). Small chemical shift differences of BS NMR resonances were consistent with effective local concentration or dilution of BS micelles mostly by βG, suggesting dynamic interactions; whilst the reduced line widths/intensities observed were mostly caused by wheat AX and the highest molecular size and concentrations of βG. SAXS showed evidence of changes in βG but not AX in the presence of BS micelles, at >13 nm length scale consistent with molecular level interactions. Thus intermolecular interactions between SDF and BS depend on both SDF source and its molecular weight and may occur alone or in combination.