Effect of acetylation and dual modification on physico-chemical, rheological and morphological characteristics of sweet potato (Ipomoea batatas) starch

Chemical modification of sweet potato (Ipomoea batatas) was carried out by acetylation using vinyl acetate ranging from 4% to 10% and dual modification using propylene oxide at specific level of 7% followed by adipic acid anhydride at levels ranging from 0.05% to 0.12%. Degree of substitution ranges between 0.018–0.058% and 0.020–0.034% for acetylated and dual-modified starch samples, respectively. There was significant increase in water binding and oil-binding capacities, solubility, paste clarity, gel strength due to modification, however, rupture strength, gel elasticity and adhesiveness decrease in both modified starches. Analysis of SEM revealed that the modification altered starch morphology. Acetylation brought about slight aggregation or cluster formation of granules with deep groove in the central core region whereas in dual-modified starches there were present a number of aggregates of starch granules with development of few blister like appearances along with protuberances on their surfaces.