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

The 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 T_g and melting temperature T_m) were examined by differential scanning calorimetry. The T_g and T_m for L201 were higher than those for Delta and Akitakomachi. The maximum compressive strength, maximum tensile strength, T_g and T_m for the three varieties of brown rice grains decreased with increasing moisture content. The T_g 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 T_g in terms of moisture content.