Power Ultrasound Enhanced One-Step Soaking and Gelatinization for Rough Rice Parboiling

The conventional parboiling of rough rice is a lengthy process that takes 24-28 h to complete. It would be beneficial to the industry if the processing time could be reduced. The objective of this study was to develop an ultrasound based one-step protocol for soaking and gelatinization during rice parboiling. The gelatinization temperature was measured by alkali (KOH) degradation and found to be 72◦C. The combined soaking and gelatinization was conducted at 75◦C with or without sonication (control). The moisture content during soaking was measured following the AOAC oven method. Starch gelatinization was evaluated by differential scanning calorimetry (DSC). Moisture content after 3 h of ultrasonic soaking (48.6% w.b.) was equivalent to 10 h conventional soaking (44.0% w.b.), indicating that ultrasound reduced some 70% of soaking time. DSC showed that the retrogradation peaks (Tr) values for 80◦C soaking and ultrasonic horn (US.horn) soaking, which were accomplished during 4 h, was 53.8◦C and 53.5◦C, respectively. This showed that US.horn soaked samples at 75◦C partially gelatinized at the same time frame (4 h) with the samples soaked at 80◦C. This study showed the feasibility of ultrasound to enhance the rice parboiling by reducing processing time.