Thermodynamic Behavior of Green Whole and Decaffeinated Coffee Beans During Adsorption

Differential and integral thermodynamic parameters were estimated for whole green coffee beans decaffeinated with either ethyl acetate (EADB) and methylene chloride (MCDB). Adsorption isotherms were prepared at 25, 35, and 45°C. Changes in thermodynamic properties were estimated by the method of Othmer. Variations in the integral enthalpy with respect to moisture indicated that MCDB have a heterogeneous distribution of binding forces at the active sites. EADB showed smaller enthalpy values at lower moisture contents as compared to MCDB, and maintained a distribution of binding energy at the active sites similar to that of whole beans. We suggest storing MCDB at 25°C with a moisture content of 0.9 g H2O/100 g d.m., and of 2.3-4.0 g H2O/100 g d.m. for EADB and whole beans, to obtain maximum stability.