C-13 CP/MAS NMR study of the interaction of bile acids with barley beta-D-glucan

Dietary beta-D-glucan is associated with low blood cholesterol levels due to increased excretion of bile acids, but there is little evidence for the mechanism involved in enhanced bile acid clearance. Solid-state C-13 NMR spectroscopy has now been used to investigate the possibility of specific binding between a representative bile acid salt, glycocholic acid, and barley beta-glucan. From the similarity in chemical shift values for beta-D-glucan in the solid and solution states, it is concluded that the beta-D-glucan adopts the same conformation in both states. The dye Congo red is known to form a complex with beta-D-glucan that can precipitate from aqueous solution. In this case, the formation of a complex involving specific binding was evidenced by the appearance in the solid-state spectrum of resonances characteristic of the dye molecule, that otherwise would not be present. In contrast, no resonances characteristic of the bile acid were observed in the solid-state NMR spectrum of the mixture of beta-D-glucan and the bile acid salt. These results suggest that the hypocholesterolemic property of beta-D-glucan does not involve a simple binding of bile acid salt molecules to specific sites on the beta-D-glucan polymer. Copyright (C) 1996 Elsevier Science Ltd