α‐Amylase adsorption on starch crystallites

The goal of this work was to characterize the adsorption of Bacillus subtills α‐amylase onto crystalline starchy materials of the B‐type polymorph. Monodisperse spherulitic particles ( R ż6; 5.0 μm), essentially resistant to α‐amylolysis at 25°C were prepared from short amylose chains ( DP n ≈ 15). The α‐amylase adsorbed specifically onto the spherulites, and adsorption was found to be a prerequisite step for hydrolysis. Adsorption was inhibited by the presence of maltose and maltotriose in the reaction mixture. Adsorption isotherm of the enzyme on the particles showed a well developed plateau of 1.62 μg/cm 2 at 25°C corresponding to a monolayer adsorption process. The binding free energy calculated from the initial slope of the isotherm was Δ G ≈ −20.7 kJ/mol. This is smaller than published values for the binding of α‐amylase to soluble amylosic chains (Δ G < −30 kJ/mol).