Abstract: Native corn starch containing 30% moisture and octenyl succinate modified starch were treated by microwave for different periods of time to investigate the effect of microwave radiation on their physico-chemical properties. The moisture content of native starch and modified starch showed a downward trend with increasing microwave radiation time and reached normal levels after 4 min. Partial or even complete rupture on the surface of both starch granules was observed by SEM after microwave radiation. Moreover, their crystallinity basically remained stable before and after microwave radiation. Both starches and their gelatinization products were found to be pseudoplastic non-Newton fluids. Power law model could well fit shear force as a function of shear rate. The viscosity of native corn starch decreased, but octenyl succinate modified starch showed a trend to initially increase and then decrease with increasing microwave radiation time. The storage modulus of native corn starch initially increased and then decreased, and the loss modulus exhibited only minor changes, whereas an opposite changing trend to storage modulus was observed for loss factor. Octenyl succinate modified starch revealed only minor changes in viscoelasticity. For octenyl succinate modified starch, microwave radiation for a period of lower than 6 min resulted in only very minor changes in viscoelasticity when compared to control group (not receiving microwave radiation) and a decrease in storage and loss moduli but a significant increase in loss factor when compared to 6 min microwave radiation.

Key words: microwave radiation, octenyl succinate modified starch, power law equation, SEM, X-ray, rheological properties