Water Sorption of Coffee Solubles by Frontal Inverse Gas Chromatography: Thermodynamic Considerations

Information on the sorption mechanism was obtained by investigating the thermodynamic relationships of moisture in freeze‐dried coffee by frontal inverse gas chromatography. The thermodynamic parameters ΔG S , ΔH S and ΔS S were calculated. The negative ΔG S values obtained for water sorption of coffee under all conditions indicated the existence of strong hydrophilic sites in the coffee matrix. Also, the enthalpic and entropic changes showed a distinctive moisture content dependence which reflected a shift from surface sorption at restricted heterogeneous active sites to sorption at more homogeneous binding sites in the bulk phase and structural changes induced by swelling from multimolecular water that occupied the hydrophilic sites.