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Thermomechanical Transitions of Rice Kernels

¹Department of Food Science, University of Arkansas, 2650 N. Young Ave., Fayetteville, AR 72704. ²Corresponding author. E-mail: tsiebenm@uark.edu Phone: 501-575-2841. Fax: 501-575-6936. ³Department of Food Sciences, Wageningen University, The Netherlands.

Thermomechanical analysis (TMA) and differential scanning calorimetry (DSC) were used to investigate the thermal transitions of long-grain rice kernels. Three distinct thermomechanical transitions were identified as rice kernels were heated from 0 to 200°C. The identified transitions were a low temperature transition with onset at ≈45°C, an intermediate temperature transition at ≈80°C, and a high temperature transition at ≈180°C. Low temperature transition with onset from ≈60°C at 5% moisture content (MC) to 30°C at 20% MC was identified as the glass transition of the rice kernels. Intermediate temperature transition from 60 to 100°C, depending on MC, may be caused by rapid evaporation of moisture in the rice kernels. High temperature transition was associated with melting of the crystalline structure of rice starch. The temperatures of all three transitions decreased as MC increased, confirming that moisture acted as a plasticizer in rice kernels.