Physicochemical, mechanical and thermal properties of brown rice grain with various moisture contents

Abstract

SummaryThe effects of moisture content on the mechanical and thermal properties of either a short‐grain variety (Akitakomachi) or two long‐grain varieties (Delta and L201) of brown rice were studied. Total starch contents of the three varieties were comparable, but the amylose content of L201 was significantly higher than that of the other two varieties. The maximum compressive strength of brown rice grain was much higher than the maximum tensile strength. L201 showed the highest maximum compressive and tensile strengths. The phase transition temperatures (glass transition temperature Tg and melting temperature Tm) were examined by differential scanning calorimetry. The Tg and Tm for L201 were higher than those for Delta and Akitakomachi. The maximum compressive strength, maximum tensile strength, Tg and Tm for the three varieties of brown rice grains decreased with increasing moisture content. The Tg of individual brown rice kernels decreased from 53 to 22 °C as moisture content increased from 12 to 25% wet basis. A statistical model was calculated by using linear regression to describe the change in Tg in terms of moisture content.