The effect of fibre and gelatinised starch type on amylolysis and apparent viscosity during in vitro digestion at a physiological shear rate

An in vitro system was used to determine if the addition of insoluble or soluble fibre to aqueous suspensions of gelatinised starch affected the rate at which the starch was digested. Pre-gelatinised potato or corn starch suspensions were digested with porcine pancreatic amylase in the presence of either finely milled insoluble fibres from various sources or with guar gum. In vitro digestion was conducted at 37 °C in a rheometer at a low and constant shear rate of 10 s−1 and the quantity of glucose released measured. The rates of starch digestion and suspension viscosity declined asymptotically and were unaffected by the addition of wheat fibre, but were considerably reduced by the addition of wood and AllBran® fibre and to a much greater extent (60%) by the addition of guar. The latter effect may be due to inhibition of amylase activity by non starch polysaccharide sequences.