AN APPLICATION OF GLASS TRANSITION TEMPERATURE TO EXPLAIN RICE KERNEL FISSURE OCCURRENCE DURING THE DRYING PROCESS*

Abstract

Fissure formation during rice drying is a major cause of rice milling quality reduction. This work has applied principles of polymer science in studying thermal and hygroscopic properties of rice kernels, particularly the glass transition temperature (T_g ). This data was used to develop a hypothesis that explains the occurrence of rice kernel fissuring as a result of drying. The drying process was mapped onto a state diagram to illustrate the changes in state that a kernel could incur through drying and tempering operations. An experiment was designed to validate the hypothesis in which the effect of the T_g on rice drying and tempering in terms of milling quality was determined. Results showed that drying air temperatures up to 60°C and high moisture removal rates could be used without reducing the milling quality, as long as sufficient tempering was allowed at a temperature above the T_g of the rice.

*Published with the approval of the Director, Agricultural Experiment Station, University of Arkansas. Mention of a commercial name does not imply endorsement by the University of Arkansas.

Keywords:

• Drying
• Fissuring
• Glass transition temperature
• Rice
• Tempering

ACKNOWLEDGMENTS

We wish to acknowledge the financial support of the Arkansas Rice Research and Promotion Board and the corporate sponsors of the University of Arkansas Rice Processing Program.

Notes

*Published with the approval of the Director, Agricultural Experiment Station, University of Arkansas. Mention of a commercial name does not imply endorsement by the University of Arkansas.

*All moisture contents are expressed on a wet basis.