Effect of alkali treatment on structure and function of pea starch granules

The effect of alkaline treatment on the structural and functional properties of pea starch granules was studied using a range of characterization methods including amylose content, scanning electron microscopy (SEM), X-ray diffraction (XRD), 13C nuclear magnetic resonance (NMR), swelling power, differential scanning calorimetry (DSC), the Rapid Visco Analyser (RVA) and in vitro digestibility. The amylose content decreased by about 20–25% after 15 days of alkaline treatment and there were small decreases in relative crystallinity and double helix content. Deformations were observed on the surface of alkali-treated granules, and there was evidence of adhesion between some of the granules. There was a 25–30% reduction in peak and final RVA pasting viscosities, but only a small reduction in swelling power. The endothermic transition of alkali-treated starch was broadened with a shift of the endothermic peak to higher temperature. However, the endothermic enthalpy remained largely unaffected. Alkali-treatment greatly increased the rate of in vitro enzymatic breakdown of the pea starch. More prolonged alkaline treatment for 30 days did not cause further significant changes to the structural and functional properties of the starch granules. The effects of alkali on structure and function of pea starch are explained on the basis of limited gelatinization of the granules.