Sorption behavior and thermodynamic characteristics of stevia leaves as affected by freeze drying and gamma irradiation technologies

• Published in: Euro-Mediterranean journal for environmental integration 2023-03, Vol.8 (1), p.179-189
• Main Authors: Hidar, Nadia, Noufid, Abdelhamid, El Adnany, El Mustapha, Lahnine, Lamyae, Idlimam, Ali, Mouhib, Mohammed, Jaouad, Abderrahim, Mahrouz, Mostafa
• Format: Article
• Language: English
• Subjects: Adsorption; Aquatic Pollution; Atmospheric Protection/Air Quality Control/Air Pollution; Earth and Environmental Science; Earth Sciences; Entropy; Environmental Chemistry; Environmental Management; Environmental Science and Engineering; Equilibrium; Food; Freeze drying; Gamma irradiation; Humidity; Irradiation; Leaves; Methods; Microorganisms; Moisture content; Original Paper; Sorption; Storage conditions; Sucrose; Sweeteners; Thermodynamics; Waste Management/Waste Technology; Waste Water Technology; Water conservation; Water content; Water Management; Water Pollution Control; Water vapor; γ Radiation
• ISSN: 2365-6433; 2365-7448
• DOI: 10.1007/s41207-023-00346-6

As a result of the growing demand for low-calorie sweeteners, interest in stevia plant has increased. Two methods are applied for the preservation of stevia leaves: freeze drying and gamma irradiation at 1 kGy. Because most studies have focused on sorption characteristics of plants, the present work aims to evaluate the effect of these two technologies on moisture sorption and thermodynamics properties of stevia leaves at 30 °C, 40 °C, and 50 °C using the static gravimetric method. The obtained results indicated that freeze-dried stevia adsorbed more water vapor. According to the adsorption results and for ensuring microbial stability during storage, the moisture content should not be higher than 10.10%, 11.58%, and 13.79% dry weight basis (d.b.) for commercial, irradiated, and freeze-dried stevia leaves, respectively. Guggenheim–Anderson–de Boer (GAB) model was fitted to the experimental data. The monolayer moisture content and the surface area of sorption were shown to decrease with increasing temperature. The isosteric heat and differential entropy of sorption were found to decrease with increasing moisture content. The optimal water activities for conservation values were determined and reported as being 0.35, 0.32, and 0.35 for commercial, freeze-dried, and irradiated stevia, respectively. Thus, this study could be used as a reference to specify the adequate storage conditions of stevia leaves.