Modeling sorption isotherms and isosteric heat of sorption of roasted coffee beans

[EN] The aim of this work was determine the sorption isotherms in roasted beans of specialty coffee at temperatures of 25, 30 and 40 °C and water activities between 0.1 and 0.8 using the dynamic dew point method. The experimental sorption data were modeled using 12 different equations to represent the dependence of equilibrium moisture content with aw and temperature. The net isosteric heat of sorption was determined from the experimental sorption data using the Clausius-Clapeyron equation. The Weibull model satisfactorily modeled the effect of the temperature on the hygroscopic equilibrium in roasted coffee beans (R2adj =0.902 and RMSE = 0.00550 kg·kg-1d.b.). The net isosteric heat of sorption increase with increased moisture content.Collazos-Escobar, G.; Gutiérrez-Guzmán, N.; Vaquiro-Herrera, H.; Cortes-Macias, E. (2018). Modeling sorption isotherms and isosteric heat of sorption of roasted coffee beans. En IDS 2018. 21st International Drying Symposium Proceedings. Editorial Universitat Politècnica de València. 427-434. https://doi.org/10.4995/IDS2018.2018.7668OCS42743

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

Modelado de las isotermas de desorción y calor isosterico de sorción en granos de café pergamino húmedo (Coffee arabica L.)

Drying is one of the essential operations to guarantee the stability and quality of parchment coffee beans. The objective of the present work was to model the desorption isotherms of the wet parchment coffee beans by means of a prototype of convective drying at laboratory scale and the estimation of the energy requirement of the process. The experimental data were modeled with three empirical expressions that link the dependence of equilibrium moisture content and water activity with temperature. The net isosteric heat of sorption was estimated by the Clausius-Clapeyron equation. The Iglesias and Chirife model satisfactorily modeled representing the effect of temperature on the isotherms of the wet parchment coffee beans; presented a determination coefficient higher than 0.97 and a root mean square error lower than 0.1 kg kg−1 dry basis, all of which indicate a good fit for practical purposes. The net isothermal heat of sorption decreased with increases in moisture content indicating the net energy expenditure of the drying process.El secado es una de las operaciones imprescindibles para garantizar la estabilidad y calidad de los granos de café pergamino. El objetivo del presente trabajo fue modelizar las isotermas de desorción de los granos de café pergamino húmedo mediante un prototipo de secado convectivo a escala de laboratorio y la estimación del requerimiento de energía del proceso. Los datos experimentales fueron modelizados con tres expresiones empíricas que vinculan la dependencia del contenido de humedad de equilibrio y la actividad de agua con la temperatura. El calor isosterico neto de sorción fue estimado mediante la ecuación de Clausius-Clapeyron. El modelo de Iglesias y Chirife logro representar satisfactoriamente el efecto de la temperatura en las isotermas de los granos de café pergamino húmedo; presento un coeficiente de determinación ajustado mayor a 0.97 y un error cuadrático medio menor a 0.1 kg kg−1, base seca, indicando buen ajuste para fines prácticos. El calor isosterico neto de sorción disminuyo con incrementos del contenido de humedad indicando el gasto energético neto del proceso de secado

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

Modelado de las isotermas de desorción y calor isosterico de sorción en granos de café pergamino húmedo (Coffee arabica L.)

Drying is one of the essential operations to guarantee the stability and quality of parchment coffee beans. The objective of the present work was to model the desorption isotherms of the wet parchment coffee beans by means of a prototype of convective drying at laboratory scale and the estimation of the energy requirement of the process. The experimental data were modeled with three empirical expressions that link the dependence of equilibrium moisturecontent and water activity with temperature. The net isosteric heat of sorption was estimated by the Clausius-Clapeyron equation. The Iglesias and Chirife model satisfactorily modeled representing the effect of temperature on the isotherms of the wet parchment coffee beans; presented a determination coefficient higher than 0.97 and a root mean square error lower than 0.1 kg kg−1 dry basis, all of which indicate a good fit for practical purposes. The netisothermal heat of sorption decreased with increases in moisture content indicating the net energy expenditure of the drying process.El secado es una de las operaciones imprescindibles para garantizar la estabilidad y calidad de los granos de café pergamino. El objetivo del presente trabajo fue modelizar las isotermas de desorción de los granos de café pergamino húmedo mediante un prototipo de secado convectivo a escala de laboratorio y la estimación del requerimiento de energía del proceso. Los datos experimentales fueron modelizados con tres expresiones empíricas que vinculan ladependencia del contenido de humedad de equilibrio y la actividad de agua con la temperatura. El calor isosterico neto de sorción fue estimado mediante la ecuación de Clausius-Clapeyron. El modelo de Iglesias y Chirife logro representar satisfactoriamente el efecto de la temperatura en las isotermas de los granos de café pergamino húmedo; presento un coeficiente de determinación ajustado mayor a 0.97 y un error cuadrático medio menor a 0.1 kg kg−1,base seca, indicando buen ajuste para fines prácticos. El calor isosterico neto de sorción disminuyo con incrementos del contenido de humedad indicando el gasto energético neto del proceso de secado

Non-invasive monitoring of potato drying by means of air-coupled ultrasound

10 páginas, 8 figuras, 2 tablasAir-coupled ultrasound could be considered a suitable on-line technique for the non-invasive industrial testing of potato products manufactured in slices such as dried, fried or baked potato chips. Thus, the aim of the present study is to test the feasibility of air-coupled ultrasound to monitor the modifications in the physicochemical parameters of potato slices caused by drying. For that purpose, the potato slices (6 mm) were air dried (60 °C) for different drying times (15, 90, 180, 300 and 420 min). Air-coupled ultrasonic measurements were taken using through-transmission mode (250 kHz) and different compositional and textural parameters were measured. During drying, the ultrasonic velocity and the impedance increased significantly (p < 0.05) from 509 m/s (raw) to 673 m/s (dried for 420 min) and from 0.544 MRayl (raw) to 0.844 MRayl (dried for 420 min), respectively. Furthermore, a reduction was observed in the material attenuation, which was computed by the increase in the variation of the transmission coefficient with frequency (ΔTC). A principal component regression (PCR) model was successfully trained and validated and it demonstrated the potential capacity of the computed ultrasonic parameters to predict the apparent elastic modulus (E) (R = 0.96) and the Total Relaxation Capacity (TRC) (R = 0.99) during the drying of potato slices. The ultrasonic analysis and experimental set-up proposed in this study may be easily implemented and tested with other products, such as dried, fried or extruded snacks based on fruits or vegetables, for industrial quality control purposes.The authors acknowledge the financial support of the Universitat Politécnica de Valencia (Project 20200421