In vitro digestibility of starches with different crystalline polymorphs at low α-amylase activity to substrate ratio

In this study, potato, lotus seed and wheat starch samples with different degree of gelatinization (DG) were prepared and their in vitro digestibility at low α-amylase activity evaluated by measuring the release of reducing sugar. The hydrolysis rate (k) and the final equilibrium concentration (C_∞) of the three starches increased with increasing DG. Kinetic analyses showed that the Michaelis-Menten constant (K_m) and the catalytic efficiency (k_cat/K_m) increased with increasing DG, indicative of the increasing affinity and catalytic efficiency of α-amylase with all three starch samples. Of the three starches, lotus seed starch showed a much greater increase in k and k_cat/K_m than potato and wheat starches as the DG of starch increased. From this study, we concluded that at low activity of α-amylase, DG is a major determinant for the binding affinity and catalytic efficiency of α-amylase to starch and in turn the digestion rate of starch.