Microwave pretreated esterification improved the substitution degree, structural and physicochemical properties of potato starch esters

Potato starches were pretreated with 600 W microwave and then acetylation was carried out with acetic anhydride and glacial acetic acid (1:1 in volume). The microwave-pretreated-acetylation remarkably modified the physicochemical properties of starch compared with the single acetylation method. The starch granules exhibited rough surfaces but maintained integrity and the crystal structure changed to C-type after microwave-pretreated-acetylation. Meanwhile, the microwave-pretreated starch esters exhibited the higher substitution degree, the higher infrared absorption peak intensity and the lower relative crystallinity compared to un-microwave-pretreated ones. The solubility of microwave-pretreated starches was higher at 80-90 °C than un-pretreated samples, while the swelling power of microwave-pretreated starches was lower at 60-90 °C under a same esterification level. Particularly, the solubility of microwave-pretreated samples at 90 °C was 2.11 times higher than un-pretreated ones, while the swelling power of microwave-pretreated starches exhibited 52.8% lower than un-pretreated samples at 90 °C under the 12 mL/100 g esterification level. The peak viscosity and the gelatinization enthalpy of microwave-pretreated starches were lower than un-pretreated ones under the same esterification level. Particularly, these values of microwave-pretreated starches were 2332 mPa s lower and 8.46 J/g lower than un-pretreated ones at the 12 mL/100 g esterification level, respectively.