Effect of Enzyme Extrusion on Structure and Physicochemical Properties of Wheat Starch

This study aimed to investigate the effects of enzyme extrusion on the structural and physicochemical properties of wheat starch. The mixture of α-amylase (0%, 0.1%, 0.2%, 0.5%, 1% and 2%) and wheat starch were prepared and then extruded. After extrusion, the structural and physiochemical properties of wheat starch were analyzed by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray diffractometer (XRD), and rapid viscosity analyzer (RVA). The results showed that no significant difference in bulk density were observed among all treatments (P>0.05). With the increase of enzyme concentration, the water absorption index was decreased, and the hydration index was gradually increased. The gelatinization degree of starch was largely increased after extrusion, which indicated that the starch was almost completely gelatinized. SEM images suggested that the structure of starch granules was completely destroyed and the more extensive destruction was observed with the addition of enzyme. XRD patterns indicated that the relative crystallinity decreased from 17.52% of the native starch to 10.29% of the extruded sample with 2% enzyme. DSC results showed that the gelatinization enthalpy of wheat starch decreased significantly after extrusion (P<0.05). The lowest enthalpy was 0.24 J/g for extruded sample without α-amylase, while the enthalpy increased to about 2.5 J/g with the addition of α-amylase to 2%. This study explored the mechanism underlying the effect of enzyme extrusion on the structural and physicochemical properties of starch, which contributes to providing theoretical guides for the applications of enzyme extrusion in starch-based foods.