Water absorption characteristics of paddy, brown rice and husk during soaking

Water absorption characteristics of paddy, brown rice and husk were measured at three temperatures ranging from 30 to 60 °C. From the water absorption characteristics curve, it was observed that the husk was a significant barrier in the water absorption process by brown rice. Using the measured moisture data, a non-linear regression method was applied to an approximate solution of the diffusion equation MR = A1exp(−kt) for an infinite cylinder shape. The geometrical shape factor was estimated using the value of constant A1 and the characteristics length. The predicted value of moisture content at any time was in good agreement with the observed data. The mean values determined for the diffusion coefficients were 4.91 × 10−11 m2/s for paddy, 9.56 × 10−11 m2/s for brown rice and 1.16 × 10−08 m2/s for husk. Analysis of variance showed that soaking temperatures did not have significant effect on diffusion coefficients. An Arrhenius-type equation was used to relate the diffusion coefficient of paddy, brown rice and husk to absolute temperature (K) and the energy of activation was estimated. The values determined were 31.50 kJ/mole for paddy, 37.32 kJ/mole for brown rice and 19.25 kJ/mole for husk.