Water Uptake in Brown Rice during Soaking for Production of No-cooking Rice

Abstract

Water uptake behavior of brown rice during soaking as a part of the process of producing ‘Komal Chawal’, a kind of no cooking rice tradition to the population in the State of Assam, India, is modelled to Fick’s diffusion equation. Grain swelling resulting from water uptake is accounted by the moving boundary formulation. The model is applied to hydration data of brown rice at soaking temperatures of 40 – 65^oC, with saturation moisture content estimated from experimental hydration data. Dependence of effective diffusivity on temperature and moisture content is expressed as a factor estimated from enthalpy-entropy compensation of moisture sorption behavior. Model fitting yielded values of effective diffusivity in a range 2.48 x 10^-11 – 1.21 x 10^-10 m²/s. Calibrated model could predict the evolution of moisture with soaking time, as validated by comparing with experimental data, enabling the prediction of end of soaking period to reach the desired moisture.