Abstract
In drying processes and in the storage of agricultural products, the study of thermodynamic properties is indispensable in the search for solutions to issues of stability and optimization of the conditions of agro-industrial processes. The aim of this work was to determine hygroscopic equilibrium isotherms and study the thermodynamic properties of white bean grains submitted to different equilibrium temperatures and relative humidity levels. Phaseolus vulgaris L. grains were used, with an initial water content of 0.142 (dry basis), temperature variations ranging between 18 and 50 °C, and relative humidity between 19% and 78%. Fifteen mathematical models were tested to determine the hygroscopic equilibrium isotherms, and the Sigma model was the one that best suited the experimental data. The thermodynamic properties of the beans were determined from Sigma-Copace model. The integral isosteric heat of desorption and the differential entropy increased with the reduction of the water content, and the phenomenon of water desorption of white bean grains was a non-spontaneous process controlled by enthalpy.
Highlights
Legumes are food items of high nutritional value; among them, the common bean (Phaseolus vulgaris L.) stands out as an excellent source of protein and is an integral part of the diet of a large majority of the Brazilian population (Brigide et al, 2014; Barros & Prudencio, 2016)
Brazil is the third largest producer of beans in the world, with 3.02 million tons produced in the three crops of 2018/19, according to an estimate by Companhia Nacional de Abastecimento (CONAB), the “colors” class being the one with the highest production, followed by the “black” class (CONAB, 2019)
The mathematical model that best suited the experimental data representing the hygroscopic equilibrium curves of white bean grains was that of Sigma-Copace
Summary
Legumes are food items of high nutritional value; among them, the common bean (Phaseolus vulgaris L.) stands out as an excellent source of protein and is an integral part of the diet of a large majority of the Brazilian population (Brigide et al, 2014; Barros & Prudencio, 2016). Brazil is the third largest producer of beans in the world, with 3.02 million tons produced in the three crops of 2018/19, according to an estimate by Companhia Nacional de Abastecimento (CONAB), the “colors” class being the one with the highest production, followed by the “black” class (CONAB, 2019). In order to obtain the best-quality grains in the harvest, that is, to reach the maximum dry matter content and market value, drying should be carried out at the moment of physiological maturity. At this stage, the grains have a high water content, which hinders harvesting and processing operations in addition to causing mechanical damage and accelerated deterioration during storage (Andrade et al, 2010). The equilibrium water content is reached when the partial pressure of water vapor in the Editor: Gizele Ingrid Gadotti Received in: 10-17-2018 Accepted in: 2-12-2021
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