Publication no. C-2000-1010-03R |  VIEW ARTICLE

Glassy State Transition and Rice Drying: Development of a Brown Rice State Diagram (1).

A. Perdon (2), T. J. Siebenmorgen (2,3), and A. Mauromoustakos (2). (1) Published with the approval of the director, University of Arkansas Agricultural Experimental Station. (2) Former research assistant; professor and head, Food Science Department; and associate professor, respectively, Agricultural Statistics Laboratory, University of Arkansas, Fayetteville, AR. (3) Corresponding author. E-mail: <tsiebenm@comp.uark.edu> Cereal Chem. 77(6):708-713. Accepted June 14, 2000. Copyright 2000 American Association of Cereal Chemists, Inc.

The effect of moisture content (MC) on the glass transition temperature (T(g)) of individual brown rice kernels of Bengal, a medium-grain cultivar, and Cypress, a long-grain cultivar, was studied. Three methods were investigated for measuring T(g): differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and dynamic mechanical analysis (DMA). Among these methods, TMA was chosen, because it can also measure changes in the thermal volumetric coefficient (beta) of the kernel during glass transition. TMA-measured T(g) at similar MC levels for both cultivars were not significantly different and were combined to generate a brown rice state diagram. Individual kernel T(g) for both cultivars increased from 22 to 58°C as MC decreased from 27 to 3% wb. Linear and sigmoid models were derived to relate T(g) to MC. The linear model was sufficient to describe the property changes in the MC range encountered during rice drying. Mean beta values across both cultivars in the rubbery state was 4.62 × 10(^-4)/°C and was higher than the mean beta value of 0.87 × 10(^-4)/°C in the glassy state. A hypothetical rice drying process was mapped onto the combined state diagram generated for Bengal and Cypress.