Effect of Feed Moisture During Extrusion Processing on the Instant, Pasting, and Rheological Properties of Potato Starch

ABSTRACT

Starch is widely used in many food applications. However, the poor dispersibility of native potato starch (PS) in water poses some challenges. In this study, PS was extruded at different feed moisture contents (20%, 30%, 40%, and 50%) using a twin‐screw extruder to improve the dispersibility and instant properties. The hydration properties, such as water solubility index (WSI) and water absorption index (WAI), were used to compare the instant properties of PS. Pasting analysis was performed to understand the difference in PS behavior after extrusion. Furthermore, the pastes were characterized using rotational and oscillatory rheological measurements. Results reported that extrusion treatment at 20% moisture content increased the PS WSI from 3.5% to 86%. Fourier transformation infra‐red (FTIR) spectroscopy revealed that extrusion treatment destroyed the short‐order crystalline structure of PS granules, thereby increasing WSI and WAI. The PS melt viscosity and the specific mechanical energy during extrusion increased as the feed moisture content reduced. Extruded PS showed reduced peak viscosity and even exhibited cold‐water swelling in samples extruded at 20% and 30% moisture. PS pastes showed shear‐thinning behavior. Strain sweep analysis confirms a viscoelastic solid‐like structure in extruded PS pastes, with deviations toward a liquid‐like structure at higher strain% for the extruded sample with 20% moisture. Moreover, extrusion has reduced the gel strength of the PS pastes and increased frequency dependency. Overall, this study showed that extrusion treatment at lower feed moisture content was beneficial for improving the PS instant properties, at the expense of some loss in viscoelastic characteristics.