Thermodynamic properties of water desorption in Buchenavia capitata (Vahl) Eichler

Hellismar W Da Silva,Osvaldo Resende,Lílian M Costa,Daniel E C De Oliveira

doi:10.1590/1807-1929/agriambi.v22n12p878-883

Abstract

ABSTRACT Thermodynamic properties provide information on energy demand and kinetic parameters in water sorption processes in agricultural products. Such information is essential to analyze and scale drying and storage equipment. The objective of this study was to determine the thermodynamic properties involved in the water desorption process in Buchenavia capitata (Vahl) Eichler seeds with moisture contents ranging from 13.31 to 7.21% dry basis (d.b.), obtained by the indirect static method, at temperatures of 10, 20, 30 and 40 °C. The latent heat of vaporization, differential entropy and Gibbs free energy increase with the reduction of the moisture content of the seeds. The enthalpy-entropy compensation theory is valid for the desorption process, which is controlled by the enthalpy. The desorption of water in the seeds is not a spontaneous process.

Highlights

The species Buchenavia capitata (Vahl.) Eichler, popularly known in Portuguese as a “boca boa”, is an emergent canopy tree with a natural occurrence in Neotropical forests from 23° N to 23° S (Weaver, 1991)
Enthalpy is an indication of the strength of the water vapor molecules interconnection with the active sorption sites (Oliveira et al, 2014b); and entropy is associated with the degree of disorder of water molecules (Goneli et al, 2010; Majd et al, 2013)
The decrease in moisture content and temperature promoted the reduction of water activity (Table 1), showing that the seeds of B. capitata become more stable for low water storage and lower temperature

Summary

Introduction

The species Buchenavia capitata (Vahl.) Eichler (synonym of B. tetraphylla), popularly known in Portuguese as a “boca boa”, is an emergent canopy tree with a natural occurrence in Neotropical forests from 23° N to 23° S (Weaver, 1991). The sorption isotherms, which relate the hygroscopic equilibrium moisture content of a product with the relative humidity of the surrounding air (Costa et al, 2015) at constant temperature and pressure (Majd et al, 2013), are indispensable for defining the temperature and relative humidity of the air most suitable for storage (Chaves et al, 2015), as well as to determine the thermodynamic properties involved in the interaction between water and food components (Goneli et al, 2013), seeds and other agricultural products. Enthalpy is an indication of the strength of the water vapor molecules interconnection with the active sorption sites (Oliveira et al, 2014b); and entropy is associated with the degree of disorder of water molecules (Goneli et al, 2010; Majd et al, 2013)

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Results