The utilization of ultrasound and chilling treatment to reduce GI in Thai glutinous rice (RD6)

Abstract

The source of carbohydrate in the North and North-Eastern areas in Thailand are predominantly based on glutinous rice which high glycemic index (GI75-92). Lower GI glutinous rice was interesting prospect to develop diabetics. There are modified methods to reduce GI by limit the accessibility of the digestive enzymes on starch molecule. The most common physical modification method used for reducing GI on starch are hydrothermal and gelatinization-retrogradation methods. Ultrasound is the sound wave at frequency exceeding audible threshold of the human hearing rang. It is studied on starch to change the molecular structure for improving some physicochemical properties. Therefore, this resecrch focused on the utilization of ultrasound and chilling treatment to reduce GI in Thai glutinousonrice (RD6). The glutinous rice was treated with ultrasound for 15 and 30 min and amplitude at 40, 70, and 100%. All of the ultrasound-treated rice was stored at 4 o Cfor 24 h. Then, thery were analyzed on the ratio crystalline to amorphous by FTIR, thermal properties by DSC, RVA pasting properties, and GI. With increasing time and amplitude of ultrasound, the ratio of crystalline to amorphous decreased from 0.779 to 0.662. The onset temperatureand enthalpy (∆H) decreased from 62.38 to 58.10 o C, and 1.81 to 0.70 J/g, respectively. The peak viscosity, and final viscosity from RVA increased from 3079 to 3838.67 cP and 2407.33 to 2922 cP, respectively. When increasing time and amplitude of ultrasound, the hydrolysis index (HI) and eGI slightly increased with longer time and higher amplitude than the others. The chilled samplesafter ultrasound treatment showed that the ratio of crystalline to amorphous, and ∆H increased while HI and eGI decreased when compared to unchilled ultrasound treated rice.