MODELING DESORPTION ISOTHERMS AND THERMODYNAMIC PROPERTIES OF ASSAM CTC MANUFACTURED FROM TEA CULTIVAR T3E3

Abstract

ABSTRACT Moisture sorption isotherms of Assam CTC manufactured from tea cultivar T3E3 were determined at 30, 40 and 50C using the static gravimetric method over a range of relative humidity from 0.1 to 0.9. The equilibrium moisture content of the tea sample decreased with increase in temperature at constant relative humidity. Seven mathematical models (Brunauer–Emmett–Teller, Peleg, Oswin, Henderson, Halsey, modified Chung–Pfost and Guggenheim–Anderson–de Boer [GAB]) were used for fitting experimental data. The Oswin and GAB models were found to have better suitability for describing the sorption curves. The monolayer moisture content values for the sorption at different temperatures were calculated by using the GAB model. The net isosteric heat of sorption was estimated from equilibrium sorption data, using the Clausius–Clapeyron equation. The enthalpy–entropy compensation theory was applied to sorption isotherms, and plots of Δhd versus ΔSd provided the isokinetic temperatures, indicating an enthalpy-controlled sorption process. PRACTICAL APPLICATIONS Assam CTC tea is an important processed food commodity involving substantial commercial activities at national as well as international levels. Appropriate processing and perfect storage of this commercially important commodity are two critical issues to be addressed to fetch higher prices at competitive tea markets. The cultivars available today for tea production are T3E3, S3A1, S3A3, TV1 to TV31, etc. T3E3 is a very popular yield clone for CTC tea production in Assam. There is a considerable variation in the rate of loss of moisture among these cultivars. The knowledge of equilibrium moisture content (EMC) vis-à-vis water activity (Aw), which is the central theme of the present investigation, is one of the important factors to regulate overall manufacturing processes. Moreover, results of the present investigation will also be helpful to ascertain appropriate storage conditions for processed tea. Because biologic activities in tea during storage are highly sensitive to its moisture content due to the presence of several complex enzymes, such as polyphenol oxidase, peroxidase, etc., inactivation of these enzymes requires the knowledge of safe moisture content. Thus, the results of the present investigation would have important practical applications, particularly in tea processing and marketing sectors.