Influence of acetylation on the physicochemical properties of composited starches from sweet potato (<i>Ipomoea batatas</i> L.) and water yam (<i>Dioscorea alata</i> L.)

Abstract

The study investigates the effect of acetylation on the physicochemical properties of composited starches from sweet potato and water yam. Starch was respectively isolated from both sources, dried and subjected to acetylation at different combination. The result shows that the modified starches were of low percentage of acetylation and low degree of substitution. Acetylation increased the water absorption capacity of the starch while compositing itself seemed to have a counteracting influence on the parameter. The oil absorption capacity generally got reduced with acetylation while synergistic role of acetylation and compositing was observed in the swelling capacity of a composited starch (SP/WY-20/80) and counteracting influence in others. The solubility indices of starches were greatly enhanced by acetylation and compositing at all temperatures of evaluation (50-90°C). Acetylation improved the colour lightness (L*-value) of the starches (93.05-94.02) while that of the native starches ranged between 92.18 and 92.31. Most pasting variables (peak, breakdown, final and setback viscosities) were lower in acetylated composite starches than that of the unmodified counterparts. Freeze-thaw stability of gels from composited starches was greatly enhanced as lower volume of exudate was generated from the acetylated starches in all the freeze-thaw cycles. The findings in this study have the potential of creating awareness among the food industry with respect to acetylated starch production from both sweet potato and water yam.

Key words:Acetylation, starch, sweet potato, water yam, physicochemical properties.