Moisture sorption isotherm of Moringa (Moringa Oleifera Lam.) seed

Abstract

This study was designed to investigate and model the moisture sorption isotherm of moringaseed during storage. An important factor in the quality loss of dried moringa seeds during storage is the water activity (aw) which influences the stability of the product. Knowledge of sorption isotherms is necessary to correctly carry out drying and storage operations. Sorption Isotherms (SI) of moringa seed were obtained by determining the Equilibrium Moisture Content (EMC) at a temperature range of 20-40℃ and nine aw (0.09-0.92) levels using thermostatic water bath and concentrated H2SO4. The sorption data were fitted into four selected models namely: Brunauer- Emmett-Teller (BET), Guggenheim-Anderson-De Boer (GAB), Hailwood-Horrobin (HH) and Modified Henderson (MHM) models. The performance of the models was tested using Root Mean Square Error (RMSE), co-efficient of determination (R2) and Residual Sum of Squares (RSS). The SI curves generated were sigmoidal in shape indicating Type-II isotherm. The GAB was the best-fitted model and predicted the EMC at all temperatures with highest R2 (0.9994) in adsorption and (0.9994) in desorption processes. The BET and HH models did not fit well at all temperatures with R2 (0.6957) and (0.8439), respectively. The GAB gave the least RMSE and RSS and it ranged 0.0775-0.2124 and 0.0060-0.0431, respectively. Experimental isotherm obtained demonstrated Type-II behaviour, which is typical for most agricultural materials.