Synthesis of Hydroxypropyl <i>Dioscorea alata</i> Starch Rapidly Prepared with Ultrasonic-Microwave Assistance

Abstract

In this study, ultrasonic-microwave assisted synthesis of the hydroxypropyl Dioscorea alata starch was investigated and optimized. Under the irradiation of ultrasonic-microwave, Dioscorea alata starch was added to the reactor as raw material, and five factors (propylene oxide, sodium hydroxide, anhydrous sodium sulfate, microwave treatment time and microwave power) that influence the preparation of hydroxypropyl Dioscorea alata starch were analyzed using single-factor and orthogonal experiment methodology. Characteristic of products was evaluated by determining their molar substitution (MS). During the experiment , ultrasonication power was fixed at 50 w. The optimum conditions were determined as propylene oxide 12% (w/w), sodium hydroxide 1.0% (w/w), anhydrous sodium sulfate 8% (w/w), microwave irradiation time 110 s and microwave power 80 w. The optimal condition of the product gives a MS value at 0.82. The hydroxypropyl Dioscorea alata starch paste shows higher light transmittance(25.5%) and solubility in cold water, lower gelatinization temperature(59°C) in comparison to native starch. Compared with conventional process, the reaction time was significantly shortened by ultrasonic-microwav