Study on Hot-Air Fluidization for the Production and Quality of Parboiled Aromatic Rice

This research investigates the production of parboiled fragrant rice using a hot-air fluidized bed drying technique, aiming to determine the optimal drying conditions for achieving complete starch gelatinization and high head rice yield (HRY) while retaining the key volatile compound, 2-acetyl-1-pyrroline (2-AP), in Khao Dawk Mali 105 (KDML105) rice. Paddy was soaked at 50°C until reaching a moisture content of 50% dry basis (d.b.), followed by drying in a fluidized bed dryer at temperatures of 130, 150, and 170°C with varying bed heights of 5, 7.5, and 10 cm. During the drying process, changes in grain moisture content and temperature, degree of starch gelatinization (DSG), head rice yield (HRY), and 2-AP content were continuously monitored.

The results revealed that a rapid increase in grain temperature at high drying temperatures accelerated starch gelatinization, resulting in an initially higher HRY and also promoting the formation of 2-AP. At a drying temperature of 150°C, complete gelatinization of the parboiled rice was achieved only at a bed height of 5 cm. As the bed height increased, a higher drying temperature of 170°C was required to attain complete gelatinization. Experimental findings indicated that the drying condition of 170°C at a bed height of 5 cm optimally produced completely gelatinized parboiled rice with a high HRY (approximately 67%). Furthermore, after drying to a moisture content of no less than 25% d.b., the 2-AP content was approximately 14.5 µg/kg, which was notably higher than the initial value prior to drying. In conclusion, hot-air fluidized bed drying is an effective method for producing parboiled fragrant rice with high HRY while successfully retaining the 2-AP aroma. This technique presents a viable approach for value addition and upgrading the quality of Thai parboiled rice in the global market.