Modeling Desorption Isotherms and Thermodynamic Properties 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 30ºC and water activities of 0.07 to 0.97. Data were fitted to five mathematical equations. Using the best-fit mathematical model, thermodynamic properties of fresh tea leaves including net isosteric heat of sorption, differential entropy were estimated. The applicability of enthalpy – entropy compensation theory for fresh tea leaves was also evaluated. Results showed that the modified Oswin model was best fitted with the experimental data. Thermodynamics properties like net isosteric heat of sorption and differential entropy were found to decrease exponentially with the increase in moisture content. Net isosteric heat of sorption and differential entropy increased exponentially with decreasing moisture content of fresh tea leaves. Isosteric heat of sorption of fresh tea leaves was very close to heat of vaporization of pure water when the moisture content of tea leaves exceeded 40% (d.b.). The enthalpy-entropy compensation theory could be successfully applied for the moisture desorption behavior of fresh tea leaf samples and it was enthalpy driven spontaneous process.

Use of Temperature and Humidity Sensors to Determine Moisture Content of Oolong Tea

“…Temperature significantly affected the sorption isotherm. The effect of temperature on EMC was consistent with results with Central African tea [ 23 ], black and green tea [ 1 ], black tea [ 22 ], and fresh tea [ 28 ].…”

“…The Oswin equation was used to express the relationship between EMC and ERH value at a fixed temperature [ 27 ]. This EMC equation was found adequate for tea [ 1 , 2 , 21 , 28 ]. where M is the moisture content in %, ERH is the equilibrium relate humidity in decimal, and A and B are constants.…”

Determinación de la higroscopicidad y comportamiento termodinámico de la madera juvenil y madura a través de sus isotermas de sorción

“…El método de sales saturadas COST Action E8(Jowitt and Wagstaffe 1989) es ampliamente utilizado en la obtención de las curvas de sorción de materiales orgánicos higroscópicos. En la literatura es posible encontrar un gran número de referencias en las cuales esta metodología es utilizada en diversos campos, como por ejemplo: alimentación(Inazu et al 2001;Lahsasni et al 2004;Moreira et al 2005;Peng et al 2007;Botheju et al 2012;Talla 2014), medicina(Kaya and Kahyaoglu 2007;Zhan et al 2010) y materiales ligo-celulósicos…”