Drying kinetics, milling quality and quantity of 2-acetyl-1-pyrroline of Thai Hom Mali rice dried by heat pump dryer under different drying conditions

Author: Siri Doungporn ^*, Nattapol Poomsa-ad and Lamul Wiset

Received 2 September 2009, accepted 2 April 2010.

Abstract

The effects of drying media and drying temperatures on drying kinetics, concentration of 2-acetyl-1-pyrroline (2AP), milling quality and whiteness of Thai Hom Mali rice cv. Khao Dawk Mali 105 were investigated. Samples were dried in a heat pump dryer and were subjected to different drying media (hot air, carbon dioxide and nitrogen gas) and drying temperatures (40, 50, 60 and 70°C). Paddy samples dried at 40 and 70°C in all media were selected to be analyzed with regard to 2AP concentrations. The results showed that the moisture ratio of paddy dried under carbon dioxide or nitrogen gas at 40°C decreased faster than that of hot air. The effective diffusion coefficient was enhanced by drying temperature. The 2AP content had significantly decreased at 70°C. There was no interaction between drying media and drying temperature on head rice yield. The highest percentage of head rice yield was obtained in samples subjected to carbon dioxide gas and dried at 40°C. In addition, the whiteness of rice obtained from paddy dried at 40°C in all media had significantly the highest values.

Key words: Drying behavior, fragrant rice, inert gas, heat pump dryer, diffusion.