Aromatic and medicinal plants are a natural source of pharmaceutical compounds with curative and therapeutic properties. They have been used for centuries to treat various ailments and offer alternative options to conventional treatments. Among these plants, Marrubium vulgare L., which is widely used in traditional medicine for diabetes treatment, has antioxidant potential as well as anti-inflammatory, healing, and soothing properties, attracting increasing medical interest. In this context, the hygroscopic behavior of Marrubium vulgare L. is reported. The adsorption-desorption isotherms of Marrubium vulgare leaves were determined using the standard static gravimetric method at three temperatures (30, 40, and 50 °C) to ensure physicochemical and microbiological stability throughout the storage process. The results showed that the adsorption-desorption isotherms of all samples followed a sigmoidal pattern, consistent with other agricultural products discussed in the literature. The optimal moisture content for conservation was also determined. The GAB (Guggenheim-Anderson-de Boer) and double polynomial models were the most suitable for describing the sorption curves. The adsorption-desorption data were examined to determine the moisture content of the monolayer (3.4-9.7%), properties of sorbed water in porous structures and surfaces, total heat of wetting, net isosteric heat of sorption, spreading pressure, differential entropy, and enthalpy-entropy compensation. It was also observed that the spreading pressure and average pore radius increase with rising relative humidity and temperature, leading to the appearance of defects on the surface of Marrubium vulgare leaves. Compensation theory is essential to consider when evaluating the impact of temperature on the adsorption-desorption properties. The Gibbs free energy was positive for sorption, indicating that the process is non-spontaneous.
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