Specialty coffee is highly differentiated product because of  its sensorial attributes: aroma, body and brand reputation. In specialized markets, these products are highly valued, and sometimes up to six times their commercial value is paid. Thus, it is essential to preserve their freshness. Sorption isotherms are necessary for determining and studying water sorption changes in specialty coffee during storage. This study aimed to determine the adsorption isotherms of specialty ground roasted-coffee at temperatures of 25 °C, 30 °C and 40 °C and water activities between 0.1 and 0.8 using the dynamic dewpoint method (DDI). The experiment sorption data were modeled using 12 different equations with non-linear regression to represent the dependence of the equilibrium moisture content with both water activity and temperature. In addition, the thermodynamic properties were determined with the experiment adsorption data. The results showed that type III isotherms were obtained according to the Brunauer classification, and the Weibull equation satisfactorily modeled the effect of the temperature on the hygroscopic equilibrium in the specialty ground roasted-coffee. The results of thermodynamic analysis showed that the net isosteric heat of adsorption and Gibbs free energy decreased as the equilibrium moisture content increased, indicating the amount of energy released, a strong bond energy between water molecules in the product components and spontaneity in the adsorption process. The entropy of the adsorption increased with the moisture content, leading to product stability conditions during storage. The results were similar to those reported for the roasted and ground coffee of others cultivars.

Water adsorption properties are necessary for determining and analyzing water sorption in dried and roasted cocoa beans during storage. Thus, this study aimed to determine the water adsorption isotherms and thermodynamic properties at temperatures of 25, 30, and 40°C and water activities between 0.10 and 0.85 using dynamic dew point method. Thirteen different models were fitted to experimental data to represent the dependence of the equilibrium moisture content. Additionally, the thermodynamic properties were determined using the best-fit isotherm model. The isotherms of dried and roasted cocoa beans showed typical behavior of products rich in soluble components, according to Brunauer-Emmett-Teller (BET) classification, which was satisfactorily modeled using the Iglesias and Chirife and Kuhn equations, respectively. The thermodynamic properties showed that the net isosteric heat of adsorption and the Gibbs free energy decreased with the equilibrium moisture content, indicating the energy changes and spontaneity during the adsorption process. The integral entropy of adsorption indicated the best conditions for product stability during storage. ARTICLE HISTORY

Sorption isotherms represent an efficient and valuable tool for predicting the equilibrium moisture content of foods under different humidities and temperatures; thus, they are useful for determining shelf-life and safe storage conditions. The aims of this study were to determine the sorption isotherms of parchment specialty coffee at water activity values of 0.1−0.8 and temperatures of 25, 30, and 40 °C using the dynamic dew point method. The experimental sorption data were modeled using 12 different equations to represent the dependence of equilibrium moisture content on water activity and temperature. Thermodynamic properties were also obtained from the experimental data. The results showed a type II sigmoid shape according to Brunauer-Emmett-Teller (BET) classification, and the double log polynomial (DLP) equation successfully modeled the effects of temperature on the sorption isotherms, obtaining a good fit (R 2 adj = 0.99 and RMSE = 0.1 % dry basis). The dynamic dewpoint isotherm (DDI) method was advantageous for modelling due to its high availability of experimental data. Thermodynamic analyses showed that the net isosteric heat of sorption, Gibbs free energy, and sorption entropy decreased as equilibrium moisture content increased, and the compensation theory provided evidence that the sorption process was controlled by enthalpy (T β > T hm ).

This study aimed to evaluate the performance of the infrared spectrum in the range of 4000−650 cm −1 for characterizing and differentiating dried and ground coffee cherry pulp of different varieties. The spectral data were subjected to first and second derivative treatments to perform the statistical analyses. Three varieties of coffee pulp were previously characterized for color, water activity, moisture, chlorogenic acids, and caffeine. The results of principal component analysis (PCA) showed that Fourier transform infrared (FTIR) spectroscopy is a viable technique for characterizing and differentiating dried and ground coffee cherry pulp among different varieties, showing the best differentiation with treatment of data from the first derivative, which was mainly associated with the caffeine content and chlorogenic acids. This study is the first investigation of FTIR spectroscopy with attenuated total reflectance for characterizing dried and ground coffee cherry pulp from coffee varieties grown in Colombia.

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.