Determination of desorption isotherms, latent heat and isosteric heat of pequi diaspore

Abstract

A B S T R A C TThe objective was to determine water sorption isotherms of diaspores of pequi fruits in order to obtain information on the amount of water that this product desorbs at the temperatures of 10, 20, 30 and 40 °C and water activities from 0.20 to 0.89, adjusting different mathematical models to experimental data, and to determine its latent heat and isosteric heat. The equilibrium moisture content was obtained through the indirect static method, using the device Hygropalm Model Aw 1. The Modified Henderson model was the one that best fitted the data and was selected to predict the equilibrium moisture content of pequi diaspore. It was observed that the higher the temperature for the same equilibrium moisture content (% d.b.), the higher the water activity values . As temperature values increased, there was a reduction in the vaporization latent heat of the product. Determinação das isotermas de dessorção, calor latente e calor isostérico de diásporos de pequi R E S U M O Objetivou-se, com este trabalho, determinar as isotermas de dessorção de água de diásporos de pequi a fim de obter informações da quantidade de água que este produto dessorve nas temperaturas de 10, 20, 30, 40 °C e atividades de água entre 0,20 e 0,89, ajustar diferentes modelos matemáticos aos dados experimentais e determinar o calor latente e o calor isostérico. Para obtenção do equilíbrio higroscópico foi utilizado o método estático indireto com uso do equipamento Hygropalm Model Aw 1. O modelo Henderson Modificado foi o que melhor se ajustou aos dados sendo selecionado para predição do equilíbrio higroscópico dos diásporos de pequi. Verificou-se que quanto maior a temperatura para um mesmo teor de água de equilíbrio (% b.s.) maiores são os valores de atividade de água. Com o aumento da temperatura ocorre redução da magnitude do calor latente de vaporização do produto. Os valores de calor isostérico para os diásporos de pequi na faixa de teor de água de 4,02 a 16,63 (% b.s.) variaram de 2.776,49 a 2.558,39 kJ kg -1 .

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

“…), is higher than 1 ( Figure 1A). These results indicate that the energy required to evaporate the water bound to the active sites of the product is always greater than the energy required to evaporate the pure water, as was also observed for seeds of 'tucumã-de-Goiás' (Oliveira et al, 2014a), jatropha (Chaves et al, 2015), pequi diaspores (Sousa et al, 2016) and baru fruits (Resende et al, 2017).…”

“…The decrease in moisture content and temperature promoted the reduction of water activity ( The latent heat of vaporization increases with the reduction of the moisture content of B. capitata seeds and reduces with increasing temperature (Figure 1B), following the trend of most agricultural products (Corrêa et al, 1998;Oliveira et al, 2014a;Chaves et al, 2015;Sousa et al, 2016).…”

“…The heat of vaporization is defined as the minimum amount of energy required to evaporate a unit of mass of water bound to the biological structure of agricultural products (Corrêa et al, 1998;Sousa et al, 2016). The latent heat of vaporization is influenced by temperature and, mainly, by the moisture content of the product (Brooker et al, 1992).…”

Hygroscopicity of ‘sucupira-branca’ (Pterodon emarginatus Vogel) fruits

“…Temperature influences the hygroscopicity of 'sucupirabranca' fruits and this behavior has been observed for most agricultural products (Goneli et al, 2013;Corrêa et al, 2014;Silva et al, 2015;Barbosa et al, 2016;Sousa et al, 2016). To obtain the same water activity, the equilibrium moisture content decreases with the increment in temperature or, similarly, for a same equilibrium moisture content, the increase of temperature requires an increase in water activity (Figure 1), i.e., for a safe storage in environments with high temperatures and water activity, it is necessary to reduce the water content of the 'sucupira-branca' fruits.…”

“…The degree of fit of each model was evaluated based on the significance of the regression coefficient by t-test, at 0.05 significance level, the magnitude of the determination coefficient (R 2 ), estimated mean error (SE), relative mean error (P) and chi-square test (χ 2 ), according to Sousa et al (2016). The values of net isosteric heat of sorption (or differential enthalpy), for each equilibrium moisture content, were…”