Evaluation of new parboiled rice process using humidified hot air fluidized bed drying

Abstract

This study aims to experimentally investigate the drying characteristics and quality of a paddy dried by hot air (HA) and humidified hot air (HHA) fluidization technique. Qualities such as head rice yield (HRY), white belly, degree of gelatinization (DSG), and color of dried paddy were evaluated. A paddy with an initial moisture content of 14% d.b. was soaked in hot water at a temperature of 70 °C for 5 h then dried at a temperature of 130,150, and 170 °C, relative humidity in the range of 0.3–12%, an air velocity of 3.9 m/s, and a bed height of 10 cm. The results showed that the drying time of the paddy in the HHA condition took longer than the HA drying condition. Because HHA provided a higher grain temperature and a slow rate of drying, the degree of starch gelatinization was significantly higher when compared to HA. The subsequent HRY was relatively higher than using HA drying. However, the color of the sample obtained from the HHA condition was relatively browner, but the parboiled rice product still had a light brown color for the drying temperature range used in this study. To produce parboiled rice, HHA could be operated up to the temperature of 170 °C, relative humidity of 6%, and DOM of 10%.

Keywords:

• Degree of milling
• drying
• fluidization
• head rice yield
• parboiling process

Acknowledgments

The authors express their sincere appreciation to Thailand Research Fund (Grant no. DPG5980004) and the Faculty of Engineering at King Mongkut’s University of Technology North Bangkok for supporting the study financially.