Moisture Adsorption Isotherms Characteristic of Coffee (Arabusta) Powder at Various Fitting Models

Abstract

Water sorption test of coffee (Arabusta) powder carried out under laboratory conditions are presented together with mathematical analyses of the moisture adsorption isotherms. Coffee powder moisture adsorption isotherms were determined within the range of 0.07-0.97 water activity at 29°C, using saturated salt solutions dynamic method. Sorption isotherms of coffee powder have a sigmoid sharp (type II). The data obtained were fitted to several models of two-parameter (BET, Hasleys, Kuhn, Chung and Pfost, Freundlich and Oswin) and three-parameter (GAB). A non-linear least square regression analysis was used to evaluate the models constants.In relation to the isotherm models the best models were Halsey (in the wide range of water activity) and Kuhn (in the range of water activity 0.07-0.5) obtaining minor values of % mean relative errors and higher correlation coefficient. Critical value of equilibrium moisture content of coffee powder corresponding to the aw equal to 0.6 was 34.6 g water per 100 g dry matter. These values are useful for storing conditions optimisation from the point of view of microorganisms growth and structural changes analyses. The monolayer moisture content values for BET were higher than those for GAB, these values are 22.14 and 2.57 g water per 100 g dry matter, respectively.

Conventional and Advanced Exergy and Exergoeconomic Analysis of a Spray Drying System: A Case Study of an Instant Coffee Factory in Ecuador

“…The concentration of water and coffee in equilibrium with the environment (x e i ) was chosen as the dead state of reference. Those values were obtained from previous studies on Arabica coffee by Yao et al [26]. For the calculation of the chemical exergy of each state point that has soluble coffee solids, water, and air, Equation ( 13) [17] was used, where x i is the mole fraction of the different substances.…”