Characteristics of Dynamics Sorption Isotherms of Date Flesh Powder Rich in Fiber

Dynamic vapor sorption equipment (AQUADVS) was used to determine adsorption and desorption isotherms for powder rich in fiber (PRF) produced from Palm Date flesh of Sifri cultivar (Phoenix dactylifera L.) at temperatures 25, 35 and 45 degrees C in a wide range of water activity (0.09-0.87). Equilibrium was achieved within 29 and 25 h for the adsorption and desorption process respectively. The obtained data were fitted to ten models (Peleg, GAB, BET, Halsey, Oswin, Smith, Modified Henderson, Adam and Shove, Modified Oswin and Modified Halsey). The results indicated that the PRF followed type III behavior. The empirical Peleg model was found to be the best to represent the experimental data in the water activity range 0.09-0.87. The isosteric heat of sorption and the differential entropy decreased by increasing the moisture content and can be predicted by polynomial functions. Glass transition temperatures (T-g) of PRF were determined. The T-g decreased as the moisture content increased and can be correlated using the Gordon and Taylor model (R-2 = 0.976). The PRF should be stored at moisture less than 9 d.b.% and temperature less than 35 degrees C.