The Effects of Soluble Dietary Fibres on Starch Hydrolysis and Sugar Release During Simulated Human Digestion

One of the health benefits of dietary fibre consumption is attenuation in postprandial glycemia, which is usually attributed to digesta viscosity. In our earlier work we were able to demonstrate that digestive secretions have a profound influence on viscosity of DF-containing solutions and that their ability to retain viscosity is dependent on the type of fibre present in the system. In the present study, the ability of various fibres to reduce starch hydrolysis and subsequent glucose diffusion was examined within a 3-stage simulated digestion. All initial treatments were formulated to have the same apparent viscosity. Soluble flaxseed gum and soluble soybean polysaccharide showed substantial reductions in viscosity and behaved as dilute solutions after simulated small intestinal digestion. On the other hand, xanthan and guar gum had measurably higher viscosities and much lower tan δ. Reducing sugars were released more gradually for xanthan and guar gum. This was also observed using microscopy, where the surface of starch granules extracted from the digesta of the control, soluble soybean polysaccharide and soluble flaxseed gum treatments showed substantial hydrolysis, through the manifestation of both exo- and endo-corrosion during simulated small intestinal digestion. The progression of these changes was delayed for the granules extracted from the more viscous treatments. Also, the dietary fibres with a measurable elastic component were able to reduce the rate of diffusion of glucose into the dialysate. These observations lead to a better understanding of the physiological mechanisms by which dietary fibres help to control postprandial glycemia, and also help to predict which fibres may best impart these effects.