Abstract
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.
Highlights
Specialty coffee is highly differentiated product because of its sensorial attributes: aroma, body and brand reputation
0.975 and of the root mean square error (RMSE) higher than 0.389 % d.b., with respect to those obtained by the Weibull model the models showed a well goodness of fit and parameters statistically significant (95%), these models have been used in others food product and they have obtained an excellent goodness of fit: YOGENDRARAJAH et al (2015) in adsorption isotherms of whole black peppercorns (Peleg, Oswin, and DLP), OLIVEIRA et al (2016) in roasted coffee
The adsorption isotherms were modeled with the Weibull model, which proved to be satisfactory for the prediction of the experiment data and can be used to describe the behavior of specialty, ground roasted-coffee during storage conditions with a water activity interval between 0.1 and 0.8 and temperatures between 25 °C and 40 °C
Summary
Specialty coffee is highly differentiated product because of its sensorial attributes: aroma, body and brand reputation. O objetivo deste trabalho foi determinar as isotermas de adsorção de café especial torrado e moído para temperaturas de 25 °C, 30 °C e 40 °C e atividades de água entre 0.1 e 0.8 usando o método dinâmico de ponto de orvalho (DDI). Os resultados mostraram que foram obtidas isotermas tipo III, de acordo com a classificação Brunauer e a equação Weibull modelou satisfatoriamente o efeito da temperatura sobre o equilíbrio higroscópico em café especial torrado e moído. A entropia de adsorção aumentou com o teor de água, levando a condições de estabilidade do produto durante o armazenamento; foi possível concluir que para garantir a estabilidade do café torrado e moído de alta qualidade deve-se armazenar em ambientes onde a atividade de água não exceda de 0.5 para temperaturas entre 25 °C e 40 °C. This product is generally destined to specialized markets where the prices reached can be up to six times the value of a traditional coffee (TAPIERO et al, 2017)
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