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

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