Physical properties of acetylated sweet potato starches as affected by degree of substitution

This study examined the flow properties, paste clarity, freeze-thaw stability and gel strength of acetylated sweet potato starch (ASPS) pastes and gels as a function of degree of substitution (DS). ASPS showed high shear-thinning flow behaviors with high Casson yield stress Σoc. Consistency index (K), apparent viscosity (Η _a,100) and Σoc values of ASPS increased with an increase in DS. In the temperature range of 25∼70 ^oC, ASPS followed an Arrhenius temperature relationship. The activation energies (Ea=13.2∼14.3 kJ/mol) of the ASPS samples were much lower than that (18.1 kJ/mol) of the native sweet potato starch (SPS). ASPS gels showed better freeze-thaw stability with a significant decrease in syneresis (%) compared to SPS gel. The gel strength values of ASPS were much lower than that of SPS, and significantly decreased with an increase in DS. The clarity of native SPS paste increased after acetylation.