Moisture Sorption Properties of Castor Seeds

Equilibrium moisture contents were determined for Gray Small Size (GSS) and White Big Size (WBS) castor seeds at 30, 40, 50, 60 and 70°C and water activities in the range of 0.07 to 0.98. Four sorption models namely modified Henderson, Halsey, Oswin, and Guggenheim Anderson de Boer (GAB) were applied for analyzing the experimental data. The curve-fitting of the sorption data was evaluated using non-linear regression analysis and compared using the standard error of estimate, mean relative percent deviation, fraction explained variation and residual plots. The sorption capacity of the seeds decreased with increase in temperature at constant water activity and increased with increase in water activity at constant temperature. The isotherms curves were sigmoidal in shape and of type II behavior according to BET classification. The modified Oswin model was the most suitable for describing the relationships between equilibrium moisture content, relative humidity and temperature at desorption while at adsorption. The Modified GAB predicted a type I sorption curve for a type II BET classification obtained experimentally. Sorption hysteresis occurred with higher values as the temperature increased. These are useful information for this less researched drought resistant oil crop whose processing is still at traditional manual level.