Impact of Feed Moisture on Microstructure, Crystallinity, Pasting, Physico-Functional Properties and In Vitro Digestibility of Twin-Screw Extruded Corn and Potato Starches

The effect of extrusion feed moisture (FM) on the microstructure, pasting, physico-functional properties and in vitro starch digestibility (IVSD) of corn and potato starches was investigated using scanning electron microscopy (SEM), X-ray diffractometry and a rapid visco-analyser. Starches were extruded at 14, 18 and 22% FM with an extrusion temperature of 100 degrees C and a screw speed of 100 rpm. Extruded starches showed lower L* (lightness) values and higher a* and b* values than native starches. An increase in FM increased the L* values and decreased the a* and b* values of extruded starches. Extrusion resulted in complete destruction and reduced crystallinity of the starch structure. Extruded starches showed a lower water absorption index (WAI), peak viscosity (PV), final viscosity (FV), breakdown viscosity (BDV) and setback viscosity (SBV) with a higher water solubility index (WSI) and IVSD than native starches. FM showed a negative correlation with the WSI and IVSD and a positive correlation with the WAI, PV, FV, BDV and SBV of extruded starches.