Thermodynamic analysis and modeling of water vapor adsorption isotherms of roasted specialty coffee (Coffee arabica L. cv. Colombia)

[EN] The experimental assessment and computer modeling of the water vapor adsorption isotherms of roasted specialty coffee is addressed in this study. Thus, both coffee beans and ground coffee of medium (850 mu m) and fine (600 mu m) particle sizes were analyzed over a range of water activities of between 0.1 and 0.9 and at temperatures of 25, 35, and 45 C. The adsorption isotherms were determined using the dynamic dew point (DDI) method. The computer modeling of adsorption isotherms was addressed in order to describe the influence of the water activity and temperature on the equilibrium moisture content. Furthermore, the hygroscopic capacity of roasted coffee was analyzed by differential thermodynamic analysis. Experimental results and modeling showed that the high level of moisture adsorption found in the ground coffee was related to a large adsorption area, suggesting that specialty coffee should preferably be stored as beans. The Peleg empirical model was the most suitable at representing both type III upward concave adsorption behavior and the effect of temperature on the adsorption isotherms. Differential thermodynamic analysis revealed an increase in the water adsorption energy at low equilibrium moisture content, while negative Gibbs free energy values revealed the spontaneity of the adsorption process.The authors thank the Centro Surcolombiano de Investigacion en Cafe (CESURCAFE) of the Universidad Surcolombiana Neiva-Huila of Colombia and the Grupo de Analisis y Simulacion de Procesos Agroalimentarios (ASPA) of the Universitat Politecnica de Valencia-Espana, for their support which was indispensable for this study.Collazos-Escobar, GA.; Gutiérrez-Guzmán, N.; Garcia-Perez, J.; Bon Corbín, J.; Váquiro-Herrera, HA. (2022). Thermodynamic analysis and modeling of water vapor adsorption isotherms of roasted specialty coffee (Coffee arabica L. cv. Colombia). LWT - Food Science and Technology. 160:1-10. https://doi.org/10.1016/j.lwt.2022.11333511016

Análisis termodinámico y modelización de isotérmas de adsorción de vapor de agua del café especial tostado (Coffee arabica L. cv. Colombia)

[EN] Water vapor adsorption isotherms represent an effective and valuable tool for predicting the hygroscopic behavior of foods under different humidities and temperatures. Besides, isotherms can be used to determine the effective thermodynamic properties and thus, establish the shelf life and the most suitable storage conditions for food materials. The aims of this work were to determine and model the water vapor adsorption isotherms and to assess the thermodynamic properties of roasted specialty coffee. Thus, both coffee beans and ground coffee at medium and fine particle sizes were analyzed in a range of water activities between 0.1¿0.9 and temperatures of 25, 35, and 45 °C. The adsorption isotherms were determined using the dynamic dew point (DDI) method. Modeling of the adsorption isotherms was carried out using 10 different models to represent the influence of the water activity and the temperature on the equilibrium moisture content. Furthermore, the hygroscopic capacity of roasted coffee was analyzed by differential thermodynamic analysis. Experimental results and modeling showed that the higher moisture adsorption found in the ground coffee was related to a larger adsorption area, suggesting that specialty coffee could be stored more safely as beans. The Peleg empirical model was the most suitable to represent the type III upward concave adsorption behavior and the effect of temperature on adsorption isotherms. Differential thermodynamic analysis indicated an increase in water adsorption energy with decreasing equilibrium moisture content, while negative Gibbs free energy values revealed the spontaneity of the adsorption process.[ES] Las isotermas de adsorción de vapor de agua representan una herramienta eficaz y valiosa para predecir el comportamiento higroscópico de los alimentos bajo diferentes humedades y temperaturas. Además, se pueden utilizar para determinar las propiedades termodinámicas efectivas y así, establecer la vida útil y las condiciones de almacenamiento más adecuadas de los alimentos. Los objetivos de este trabajo fueron determinar y modelizar las isotermas de adsorción de vapor de agua y cuantificar las propiedades termodinámicas del café especial tostado. Así, se analizó tanto el café engrano como el molido a tamaños de partícula medio y fino en un rango de actividades de agua entre 0.1-0.9 y temperaturas de 25, 35 y 45 °C. Las isotermas de adsorción se determinaron utilizando el método del punto de rocío dinámico (DDI). La modelización de las isotermas de adsorción se realizó utilizando 10 modelos diferentes para representar la influencia de la actividad del agua y la temperatura en el contenido de humedad de equilibrio. Además, se estudió la capacidad higroscópica del café tostado mediante análisis termodinámico diferencial. Los resultados experimentales y la modelización mostraron que la mayor adsorción de humedad en el café molido se relacionó con una mayor área de adsorción, lo que sugiere que el café especial podría almacenarse de manera más segura en la etapa de grano. El modelo empírico de Peleg fue el más adecuado para representar el comportamiento de adsorción cóncavo ascendente de tipo III y el infecto inverso de la temperatura a altas actividades de agua en las isotermas de adsorción. El análisis termodinámico diferencial indicó un aumento en la energía de adsorción de agua con el descenso del contenido de humedad de equilibrio, mientras que los valores negativos de la energía libre de Gibbs revelaron la espontaneidad del proceso deCollazos Escobar, GA. (2020). Thermodynamic analysis and modeling of water vapor adsorption isotherms of roasted specialty coffee (Coffee arabica L. cv. Colombia). http://hdl.handle.net/10251/151534TFG