Water dynamics adsorption properties of dried and roasted cocoa beans (theobroma cacao L.)

Abstract

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.

Keywords

• spontaneous process
• energy released
• water activity
• equilibrium moisture content
• dynamic dew point isotherm