Molecular interactions between cereal soluble dietary fibre polymers and a model bile salt deduced from 13C NMR titration

Soluble dietary fibres (SDF) such as (1,3:1,4)-beta-D-glucan (beta G) and arabinoxylan (AX) have been reported to lower plasma cholesterol levels in the human body, at least in part by preventing bile salts (BS) from being reabsorbed into the enterohepatic circulation. The mechanism(s) by which SDF interact with BS in the digestive tract is not known. This report describes investigations of molecular interactions between a model bile salt (taurochenodeoxycholate - TCDC) micelle with each of beta G and AX using C-13 NMR. In the presence of beta G, chemical shift changes were observed for many bile salt resonances, but not beta G resonances, without any apparent change in line widths. In contrast, in the presence of AX, no consistent chemical shift changes were observed for either TCDC or AX resonances, but TCDC signal intensities were reduced. This was not due to simple viscosity effects as the viscosity of the beta G used was greater than that of the AX. The results suggest two different mechanisms of interaction between cereal non-starch polysaccharides and TCDC micelles: beta G interacts directly on a molecular length scale with the micelles, whilst AX changes the local environment, resulting in reduced micellar mobility without direct molecular interaction. (C) 2010 Elsevier Ltd. All rights reserved.