Abstract:
Desorption isotherm of fresh tea leaves was studied using static gravimetric method of
saturated salt solutions at temperatures of 15, 20, 25 and 30 C and water activities of
0.07 to 0.97. Results indicated that the equilibrium moisture content of fresh tea leaves
decreased with increasing temperature at any given water activity. All sorption
isotherm curves obtained were Type II sigmoidal, according to BET classification. The
experimental data were fitted to five different sorption isotherm models. Modified
Oswin model fitted well with the experimental data. Isosteric heat of sorption of fresh
tea leaves was calculated using Clausius-Clapeyron equation and it was very close to
heat of vaporization of pure water when the moisture content of tea leaves exceeded
40% (d.b.). There was a rapid increase of isosteric heat when the moisture content
reached below 20% d.b
