Modeling desorption isotherm of fresh tea leaves Camellia sinensis var. Assamica

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