Influence of dehulling and roasting process on the thermodynamics of moisture adsorption in sesame seed Original Research Article

Sesame seed can be stored and processed within main three forms; whole sesame seed, dehulled sesame seed, and dehulled-roasted sesame seed. In this study, the effects of dehulling and roasting process on the moisture adsorption isotherms and thermodynamic properties of sesame seed were investigated. The moisture adsorption isotherms of sesame seed were determined using gravimetric static method at 15, 25, and 35 °C. The isotherms exhibited Type II behavior. Though the trend of sorption isotherms of the samples were similar, equilibrium moisture content was decreased with dehulling and roasting process at a certain water activity. The Guggenheim–Anderson–de Boer (GAB) and Halsey models were found to adequately describe the sorption characteristics. Thermodynamic properties (net isosteric heat, differential entropy, spreading pressure, net integral enthalpy and net integral entropy) were calculated to determine the properties of water and energy requirements associated with the adsorption data. The net isosteric heat of adsorption and differential entropy decreased with increasing moisture content. The values of the net isosteric heat of adsorption and differential entropy decreased with application of dehulling and roasting process. The changes in the net isosteric heat of adsorption and differential entropy with moisture content were sufficiently described by power-law model. The net integral enthalpy increased with moisture content to a maximum and then decreased, while the integral entropy decreased to a minimum and then increased with increasing moisture content. The order in the magnitude of integral enthalpy was found as whole sesame (WS) > dehulled-roasted sesame (DRS) > dehulled sesame (DS).