Thermodynamic properties of water desorption in lettuce seeds

Semina: Ciências Agrárias

Gabriel Henrique Horta de Oliveira¹  Juliana Soares Zeymer²  Paulo Cesar Corrêa²  Fernanda Machado Baptestini³ 

[1] Instituto Federal de Educação, Ciência e Tecnologia Sudeste de Minas Gerais;Universidade Federal de Viçosa;Universidade Federal do Espírito Santo;

关键词: Differential enthalpy;    Differential entropy;    Enthalpy-entropy compensation theory;    Equilibrium moisture content;    Gibbs free energy;    Isosteric heat.;   

DOI  :  10.5433/1679-0359.2018v39n3p921

来源: DOAJ

【 摘 要 】

Knowledge of the movement of water molecules inside material is important for the study of interactions between water and chemical components of agricultural products. The thermodynamic properties calculation reports this need, being the source of information to design drying equipment, calculate the energy required in this process and evaluate the physical phenomena that occur on the food surface. Given the importance of the subject, the objective of this study was to determine the thermodynamic properties of the water desorption process in lettuce seeds. Lettuce seeds had an initial moisture content of 9.3% (d.b.). The equilibrium moisture content of seeds was determined by static gravimetric method at different temperatures (10, 20, 30, 40 and 50 ± 1 °C) and relative humidity values (between 11 and 96%). Experiments were conducted in triplicate. It was observed that, with increasing equilibrium moisture content, there was a reduction in the energy required for evaporation of water in lettuce seeds, with values of integral isosteric heat of desorption in the water content range 2.1 to 21.2% (d.b.) which varied from ‘4164.89 to 2477.43’ kJ kg-1. With increasing equilibrium moisture content there was a decrease in differential entropy, resulting in lower demand for mobility of water molecules. The Gibbs free energy also decreased with increasing equilibrium moisture content and was positive for all temperatures studied, showing non-spontaneity of water desorption in the seeds. The enthalpy-entropy compensation theory was has been satisfactorily applied to the sorption phenomenon and the water desorption process in lettuce seeds was controlled by enthalpy.

【 授权许可】

Unknown