Abstract
Water absorption in dried beans has been investigated. Diffusion equations based on wetting theory are proposed and an analytical solution was obtained using Duhamel's theorem. The green bean, red bean, California small white bean and soybean are considered. Some green beans and red beans were irradiated by gamma-rays. The theoretical predictions are in excellent agreement with the experimental data. The diffusion coefficients of water in green bean and red bean satisfy the Arrhenius equation. The testa wetting was analyzed on a thermodynamic basis. The wetting time of water molecules from water reservoir to embryo of green bean and red bean via testa was found to satisfy a modified Arrhenius equation. The activation energy of diffusion is greater for non-irradiated red bean than for irradiated red bean, but the energy barrier of wetting is smaller for non-irradiated red bean than for irradiated red bean. However, the effects of gamma-rays on diffusion and wetting in green bean are not pronounced. The time to cook the green bean until well done was analyzed and the effect of water uptake on cooking time is discussed. The water transport in hulled green bean was also investigated. The wetting behavior was not observed in the hulled green bean. This is direct evidence of the wetting behavior of the testa. The water uptake in the hulled green bean is greater than that in the coated green bean. © 2005 Society of Chemical Industry.