Effect of Cooking on Moisture Sorption Isotherms of Shea Nut (Vitellaria paradoxa Gaertn.) Kernels Part II: Modelling and Properties of Sorbed Water

An investigation was undertaken in this work to model the sorption isotherms of cooked and raw shea nut kernels determined by the standard static gravimetric method. The GAB, Halsey and Caurie models were validated and used in describing the sorption behaviour of the kernels. The monolayer moisture contents derived from Caurie’s equation for the desorption of cooked and raw kernels at 40, 50 and 60 °C were 5.49, 4.40 and 2.65 % and 5.22, 3.68 and 2.47 %, respectively. Monolayer moisture contents obtained from the GAB model showed a similar variation. As the temperature of sorption increased from 40 to 60 °C, the number of adsorbed monolayers (N), the surface area of adsorbent (A) and the percent bound water decreased significantly (p < 0.05). It is suggested that the sorption process at all temperatures is multilayered. Desorption isosteric heats were lower for cooked kernels than the raw ones, while the reverse phenomenon was obtained for the adsorption process. It was established that, during storage, cooked kernels adsorbed moisture more slowly, suggesting that they could be stored for a longer period compared to the raw ones.