Moisture sorption isotherms, isosteric heat, and Gibbs free energy of stevia leaves

Abstract

There is scientific evidence that Stevia leaves, commonly used as a sugar substitute, can reduce the risk of obesity, diabetes, hypertension, or cardiovascular diseases. In this study, the moisture sorption isotherms of stevia leaves at 35°C, 45°C, and 55°C were analyzed by the static gravimetric method within a relative humidity range between 0.06 and 0.92. The experimental data obtained exhibits a J‐shaped Type II sorption isotherms. The data were fitted to six mathematical models: Iglesias & Chirife, Lewicki, Oswin, Hasley, GAB, and Khun. GAB model was the one best‐fitted to the isotherms obtained. The monolayer value was between 0.0479 and 0.0589 g water/g dry matter. The isosteric heat of adsorption and Gibbs free energy were obtained at different temperatures using the Clausius–Clapeyron equation. The isosteric heat of adsorption exponentially decreased from 2850 J/g to 2480 J/g as the equilibrium moisture content increased from 0.062 to 0.522 g water/g dry matter. The chemical potential of adsorption increased at high moisture content values. These results suggest an exothermic, spontaneous process. Novelty Impact Statement The importance of studying adsorption isotherms, and its fitting to a mathematical model, allows us to know the potential of the water that influences on the reactions of physical‐chemical deterioration correlated with the stevia leaves stability and quality. The thermodynamic properties derived from moisture adsorption isotherms provide relevant information about the water chemical potential and the energy amount required in moisture adsorption processes, and its relationship with stevia stability in different storage conditions.

Isotermas dinámicas de sorción de humedad y propiedades termodinámicas de café soluble

“…Las propiedades termodinámicas que describen la relación entre agua y matriz alimentaria son útiles para evaluar los requisitos energéticos en los procesos de concentración y secado, el diseño y la optimización de los secadores industriales y determinar mejores condiciones de almacenamiento (López-Vidaña et al, 2021). Los fenómenos de sorción en términos de calor isostérico neto de sorción, energía libre de Gibbs y entropía de sorción se evaluaron en la matriz alimentaria de café soluble en polvo, haciendo uso de las isotermas de adsorción de humedad halladas en las distintas temperaturas.…”

“…El análisis termodinámico de los datos de sorción de humedad puede proponer un criterio científico confiable para la predicción de estabilidad de alimentos deshidratados (Arslan-Tontul, 2020b;López-Vidaña et al, 2021). Algunos parámetros termodinámicos como calor isostérico neto, la entalpia y la entropía se pueden estimar basándose en la isoterma de sorción a diferentes temperaturas, generando información útil para comprender la conexión fisicoquímica del agua cuando un alimento está sujeto a diferentes temperaturas y niveles de humedad relativa (Arslan-Tontul, 2020a;Zungur-Bastıoğlu et al, 2017).…”

Indirect and mixed‐mode solar drying and its effect on physicochemical properties of raw and cooked chicken breast meat

“…A prototype of the mixed solar dryer described by López-Vidaña et al (2021) with some modifications was utilized (Figure 1). First, the absorber plate in the solar collector was replaced, changing steel for aluminum covered with high absorption black paint selective surface.…”

“…On the other hand, industrial dryers eliminate these inconveniences, allowing efficiency through suitable designs, and improving food's nutritional and organoleptic properties (Téllez et al, 2021, López‐Vidaña et al, 2021). Unfortunately, industrial drying is an energy‐intensive process (López‐Vidaña et al, 2020), generally supported by polluting energies, increasing the carbon footprint. Therefore, the development of energy‐efficient methods is essential to solving this problem (Castillo‐Téllez et al, 2020).…”

Improvements and Evaluation on Bitter Orange Leaves (Citrus aurantium L.) Solar Drying in Humid Climates

“…On the other hand, drying operation food behavior can be predicted during drying by applying mathematical modeling [33][34][35]. Moreover, mathematical modeling is a proper tool for optimizing the drying process, although thin layer models are the most used for dryer designs [36].…”