The effect of in vitro digestive processes on the viscosity of dietary fibres and their influence on glucose diffusion

The consumption of soluble dietary fibres is associated with a variety of physiological responses, one of which is their ability to modulate postprandial glycaemic response due to increasing digesta viscosity. The effects that the different digestive processes in the stomach and small intestine have on the thickening ability of six soluble fibres were investigated in this study. Moreover, the ability of these fibres to resist loss of viscosity following two-stage in vitro digestion, simulating gastric and small intestinal phases, was analyzed. In a second set of experiments, protein and starch were included to simulate a food model, which allowed for glucose release. The second stage was carried out inside a dialysis system. The primary determinant of starch digestibility was the concentration of glucose in the dialysate over a 3 h period. Irrespective of the concentration level or simulated condition, xanthan gum (XG) retained viscosity more than all other fibre types (p < 0.05). XG reduced glucose concentrations in the dialysate in comparison to the control and the others fibres employed in this study (p < 0.05). The ability of XG to attenuate glucose diffusion means that it may be a target for future studies, both in vitro and in vivo, which seek to analyze food ingredients as aids in effectively mediating the postprandial glycaemic response in humans.