Equilibrium sorption isotherms of Moringa oleifera leaves at different temperatures

Abstract

Adsorption and desorption isotherms for Moringa oleifera leaves were investigated using concentrated H₂SO₄ solutions to vary the micro-climate over different temperatures (27, 32, 37°C) and water activity (a_w) (0.1–0.8). Plots of equilibrium moisture content (EMC) against a_w were used to generate isotherm curves, local isotherm (L_i) concept and stability. The experimental data obtained were compared with four widely recommended models in the literature for food sorption isotherms [GAB, modified GAB (MGAB), modified Oswin (MOE) and OSWIN models]. Results obtained showed that the moisture sorption isotherms were sigmoidal in shape and were influenced by temperature. The four sorption models adequately predicted the adsorption and desorption isotherms for Moringa oleifera leaves at the evaluated temperatures, with R² values between 0.980 and 0.998. The sequence in which the evaluated models effectively fitted the moisture sorption, were GAB, MGAB, MOE and OSWIN models, with GAB being the best. While the GAB model was most suitable for fitting the adsorption [Mean square error (MSE = 183.08), standard error of estimate (SEE = 549.24), R² = 0.980)], MGAB was better for desorption isotherm [(MSE = 141.950), SSE = 425.86), R² = 0.998] of Moringa oleifera leaves under practical storage temperature and water activity used in this study.