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 > 90% at reaction temperatures of 150-160 degrees C for 4-7 min. Starch acetates prepared by reaction at 160 degrees C to DS values of 0.4-0.9 were > 90% soluble in room temperature water. Acetylation rates and water solubilities decreased in the order waxy > normal > high 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 degrees C) 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.