Enthalpic and entropic mechanisms related to water sorption of yogurt

Moisture sorption isotherms of plain, concentrated, freeze-dried, and freeze-dried concentrated yogurts at 20, 35, and 50 degrees C were used to calculate integral properties. Enthalpy-entropy compensation for all yogurt preparations showed two isokinetic temperatures. The first isokinetic temperature was observed at low moisture contents and was controlled by changes in the entropy of water, whereas the second isokinetic temperature was considered to be enthalpy-driven and was of the same magnitude for all yogurt products (T-B2=327.4 +/- 0.7 K). Application of the Dubinin-Radushkevich equation suggested that the moisture zone controlled by entropy was produced when adsorption ocurred in the micropore range.