Study on preparation and physicochemical properties of hydroxypropylated starch with different degree of substitution under microwave assistance.

Compared with the traditional method, the microwave assisted method can greatly shorten the reaction time of hydroxypropyl starch and improve product quality. The microwave assisted conditions and physicochemical properties of natural corn starch were studied. Response surface methodology was used to optimize the reaction conditions of three-level-three-factorial center composite design. The optimum parameters were as follows: the additive amount of propylene oxide was 8%, the radiation time was 6.08 min, and the microwave power was 303.43 W. The optimal degree of substitution (DS) of hydroxypropyl starch was determined by the optimal conditions predicted by RSM, which was 0.0729 mg/g. The analysis of physicochemical properties showed that with the increase of the DS of starch derivatives, the transparency (4% to 8.81%), the volume ratio of the condensing volume (21.11% to 33.11%), the hydrophilic (0.73 g/g to 2.46 g/g), and the hydrophobicity (0.67 g/g to 1.01 g/g), and the water evolution rate (46.91% to 36.16%) decreased. Fourier transform infrared spectroscopy showed that the enhancement of peak intensity at 1149 cm-1 indicated the successful introduction of hydroxypropyl group. Scanning electron microscopy showed that the surface morphology of corn starch was affected to some extent. The modification did not change the crystalline type of starch, which was still A type.