In vitro binding of bile salt to rhubarb stalk powder

A new fiber source was developed by blanching, drying and grinding the fresh stalks of rhubarb, an underutilized and universal crop. The product was found to contain 74% total dietary fiber (66% insoluble and 8% soluble dietary fiber), on dry weight basis. Preliminary studies involving experimental animals and hypercholesterolemic subjects revealed that this fiber source is potentially hypolipidemic, though the underlying mechanism still remains unknown. To investigate its mechanism of action, this study was undertaken to determine its potential to complex with bile salts in vitro. Comparison of various fiber sources showed that the rhubarb fiber had the maximum ability to bind taurocholate, and bound 11 and 2.5 fold more bile salt than cellulose and wheat bran respectively. The binding increased linearly with increasing rhubarb fiber concentration. Increasing the bile salt concentration also increased the binding in a dose dependent manner and showed a saturation at a concentration greater than 10mM. The rhubarb fiber had a binding capacity of 40 mu mol of taurocholate per gram. Cholate competed taurocholate for binding indicating that conjugation of bile salt was not a mandatory requirement for the binding. Based on the chemical composition of rhubarb stalk powder, the bile salt binding property appears to be due to a combination of factors present in this product such as its high fiber content (insoluble with pectin), hydrophilic nature and high ash content. The ability to bind bile salts might be responsible for its hypocholesterolemic action observed in experimental animals and humans. (C) 1998 Elsevier Science Inc.