Study of Water Desorption Isotherms from Cocoa Beans (Theobroma Cacao L.) of Cameroon

Abstract

The aim of this work was the determination of desorption isotherms from cocoa beans at different temperatures (20°C, 30°C, 35°C, 40°C and 45°C), moisture ratio (10% and 90%). Gravimetric method and different temperatures were used to get the experimental moisture ratio at equilibrium. Experimental data were adjusted to mathematical isotherm models frequently used for the hygroscopic representation of agricultural products. Cocoa beans varied from 0 to 13% moisture ratio equilibrium. Obtained results showed that the moisture ratio at equilibrium decreases as temperature increases for the same relative humidity. Statistical parameters, modified the Oswin model, GAB, Iglesias Chirife Hasley and Chungs Pfost modified model better represented hygroscopic balance for cocoa beans than Henderson modified and Harkings Jura models. Desorption isotherm models are important for the determination of desorption energy and drying models. The desorption isotherms of cocoa beans were satisfactorily modeled by modified Oswin, GAB, Iglesias, Chirife, Halsey, and modified Chungs Pfost, which can be used as tools in the prediction and optimization of storage conditions in a wide range of water activities and temperatures.

Estimation of Thermodynamic Parameters for Better Conservation of Fresh Tomato (<i>Lycopersicum esculentum</i>)

“…The Clausius-Clapeyron equation, due to its theoretical basis, is often used in the determination of the total heat of sorption (Q st ) of agricultural products [22] [23] [24]. This equation is applied to estimate the quantity of heat useful for the evaporation of water (free + bound) in a product.…”

“…With q o, net isosteric heat of desorption of the first water molecules in the product (KJ/mol) and X o , characteristic water content at which the net isosteric heat of desorption was deduced, i.e. 63% [22].…”

“…The values of the characteristic water content of the product at which the net isosteric heat of desorption was deducted, i.e. 63% (X o ) and that of the net isosteric heat of desorption of the first molecules of water in the product (q o ) determined from the linear empirical Equation (22), by the method of least squares are transcribed in Table 5. From the analysis of this table, it is observed that the [32] for the desorption of fig fruit.…”

“…From the analysis of this table, it is observed that the [32] for the desorption of fig fruit. Indeed, the q o parameter provides important information on the physico-chemical interactions of water with the major constituents of the product and the state of the water in it, an essential parameter for estimating energy requirements during drying [22].…”