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 °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 (Tg)
of PRF were determined. The Tg decreased as the moisture
content increased and can be correlated using the
Gordon and Taylor model (R2
= 0.976). The PRF should be
stored at moisture less than 9 d.b.% and temperature less
than 35 °C. |
