MOISTURE RETENTION IN CHUFA (CYPERUS-ESCULENTUS, L), EQUILIBRIUM ISOTHERMS AND ISOSTERIC HEATS

Equilibrium isotherms at three different temperatures (25 degrees, 35 degrees and 45 degrees C) were obtained from samples of chufa tuber (C yperus sculentus) with different moisture contents. The data obtained were fitted to Henderson, Gab and Bet models using non linear and line ar regression procedures. The results showed that the Gab model offere d the best fit for the whole range of water activities considered (0.0 2-0.95). Afterwards, the isosteric heat of sorption for the chufa was calculated from the equilibrium isotherms and differential scanning ca lorimetry and thermogravimetry. The Clausius-Clapeyron equation was us ed for calculating the isosteric heats of chufa from the isotherms. Th e enthalpy involved in water vaporization was calculated by thermal an alysis, differential scanning calorimetry (DSC) and thermogravimetry ( TG) and then, the isosteric heats of sorption. Both procedures gave si milar results.