Diffusion and rheology characteristics of barley mixed linkage β-glucan and possible implications for digestion

beta-Glucan is one of the most studied soluble dietary fibres, and is known for its positive effects on human health such as lowering glycemic responses and reducing serum cholesterol levels. Viscosity and diffusion phenomena are thought to play an important role in imparting these beneficial effects through interactions with digestive enzymes and bile salt micelles in the digestive tract. Correlations between viscosity, probe diffusivity, and molecular structure for three barley beta-glucans are studied here to enhance understanding of the molecular basis for these nutritional effects. Fluorescence recovery after photobleaching (FRAP) is used to measure the diffusion coefficients of a dextran probe similar in size to both digestive enzymes and bile salt micelles in beta-glucan solutions. Diffusion coefficients are found to decrease with an increase in the viscosity, but showed systematic deviations from Stokes-Einstein behaviour, similar to those found for cereal arabinoxylans, and thus indicating that bulk viscosity measurements cannot be reliably used as sole indicator of diffusion processes, due to local aggregation and microviscosity effects. The diffusion coefficient values are 10-100 times slower than predicted for diffusion in the absence of beta-glucan, consistent with a functional role in retarding digestion and absorption processes in the small intestine. (C) 2011 Elsevier Ltd. All rights reserved.