Effect of extrusion on morphology, structural, functional properties and in vitro digestibility of corn, field pea and kidney bean starches

Native and extruded corn, field pea (FP), and kidney bean (KB) starches were evaluated for structure, in vitro digestibility and functional properties. Starches were extruded at 20 and 24% feed moisture (FM) using a twin screw extruder. Starches extruded at higher FM showed higher L-* (luminosity) values while lower a(*) and b(*) values. Extrusion led to complete structure destruction, reduced crystallinity and formation of V type polymorph in starches. Extruded starches showed lower water absorption index (WAI), retrogradation (syneresis) and paste viscosities but higher water solubility index (WSI) as compared to native starches. CS showed lower retrogradation tendency than KB and FP starches. WAI, WSI, and retrogradation were higher at lower FM than those at higher FM. Extruded starches showed higher rapidly digestible starch (RDS) and lower resistant starch (RS) content. All starches extruded at higher FM showed significantly lower RDS content as compared to those extruded at lower FM. KB showed the highest RS content followed by FP and CS. Starches extruded at higher FM showed higher RS content as compared to those extruded at lower FM.