Water vapors sorption isotherms of Sonpapdi, an Indian traditional sweet, were studied over a selected temperature range of 25 to 37oC using gravimetric method. Various conventional isotherm models, namely GAB, Oswin, Henderson, Caurie and Halsey, were applied on equilibrium moisture uptake data and it was found that GAB isotherm model described adequately the moisture absorption behavior of Sonpapdi.The monolayer moisture content M0 and GAB constant C showed negative temperature dependence for the increase in temperature from 25 to 300C. For the moisture uptake range of 0.02 to 0.07 kg kg-1db, isosteric heat of sorption, qst and differential entropy of sorption, Sd were evaluated. Finally the uptake data was used to determine isokinetic temperature Tβ (405K) and harmonic mean temperature, Thm. (392K). As Tβ > Thm, the overall sorption was found to be enthalpy driven. Properties of sorbed water were also determined.
Sonpapdi, isotherm, isosteric heat of sorption