ABSTRACT
Rice starch is gradually used as a food ingredient. The characteristics of native starch are limited for using in some products. Therefore, microwave heating which is a non-chemically method was used for modify rice starch in this study. Changing of rice starch properties during microwave heating was investigated aimed for improving food product quality. Pasting properties of native starch (NS) showed the highest value for pasting temperature (66.8°C) and pasting viscosity (peak=3,583 cP, trough=1,542 cP, final=2,805 cP and setback=956 cP) than microwave treated rice starch (MRS) at 4 different time periods (10 s, 20 s, 30 s and 40 s). The results of pasting viscosity among MRS at 4 different time periods showed the lower values when increasing heating time. MRS at 40 s (MRS_40S) gave the lowest pasting temperature (52.9°C) which was needed lower temperature to gelatinize starch. NS had significant lower To (60.0°C), Tp (68.8°C), and Tc (75.5°C), and higher enthalpy (12.22 J/g) than the MRS. To, Tp and Tc of MRS was increased when treated time increasing, while enthalpy was decreased due to starch was gradually gelatinized and loss of crystallinity. XRD patterns of NS were found to be A-type because it showed peak of 2θ at 15°, 17°, 18° and 23° while XRD pattern of MRS_40S was changed and displayed peak only at 2θ (V-type). These changing of XRD patterns may due to loss of crystallinity during heating. The results indicated that microwave heating could change rice starch properties, especially MRS_40S displayed complete gelatinization. In addition, MRS_40S could be applied for using as texture improver for some food products which needs low viscosity e.g. soup, curry sauces and some beverages.
