Preparation of water-soluble and water-swellable starch acetates using microwave heating

Starch acetates of degree of substitution 0.1–1.5 were prepared by heating corn starch, acetic acid and acetic anhydride in sealed, stirred, teflon vessels in a microwave reactor. Reaction efficiencies were typically O90% at reaction temperatures of 150–160 8C for 4–7 min. Starch acetates prepared by reaction at 160 8C to DS values of 0.4–0.9 wereO90% soluble in room temperature water. Acetylation rates and water solubilities decreased in the order waxyOnormalOhigh amylose starch. Significant reduction in molecular weights of the starches occurred during microwave reactions. Acetylation occurred preferentially at the C6 position (70%) based on 13C NMR results. Acetylation at lower temperatures (120 8C) gave starches of DS 0.2–0.3 which were water insoluble but highly swellable. These starches retained their native crystallinity, implying that acetate substitution was a block pattern. Published by Elsevier Ltd.