Comparative moisture sorption isotherms, modelling and isosteric heat of sorption of controlled and irradiated Moroccan rosemary leaves

•The sorption isotherms of controlled and irradiated rosemary have a sigmoid shaped curve, thus reflecting a Type II isotherm according to Brunauer’s classification.•The method of conservation applied to the plant “gamma radiation” change its absorbance and water activity.•Enderby model provided the best fit to experimental data obtained for the controlled and irradiated roemary over a range of water activity from 0.05 to 0.9.•The net isosteric heat of sorption of controlled and irradiated rosemary decreased with increasing of equilibrium moisture content. In this paper, we studied and compared water sorption isotherms of irradiated and non-irradiated (controlled) rosemary leaves at three temperatures: 30, 40 and 50°C, using the standard static gravimetric method. This method consists on the use of different salts solutions, over a range of water activity from 0.05 to 0.9. The sorption isotherms of all samples were conceived to be typical type II sigmoid. These isotherms have been fitted using four different sorption equations (modified Oswin, Enderby, Peleg, and LESPAM), Enderby model was proved to be the most suitable for describing the sorption curves for controlled and irradiated rosemary leaves. The experimental data curves allows us to calculate the value of the optimal water activity as for the conservation of controlled and irradiated rosemary leaves. Respectively, the net isosteric heat of sorption of our samples was computed from the predicted sorption data by applying the integrated form of the Clausius–Clapeyron equation.