Isotermas de dessorção e calor isostérico dos frutos de crambe

Abstract

RESUMONeste trabalho objetivou-se determinar as isotermas de sorção dos frutos de crambe e obter os valores do calor isostérico de dessorção em função do teor de água de equilíbrio. Para obtenção do teor de água de equilíbrio higroscópico utilizaram-se os frutos de crambe com teor de água inicial de 26,0 (% base seca) e o método estático-gravimétrico e, para cada repetição, foram colocados 10 g de frutos envolvidos por um tecido permeável para permitir o contato do ar com o produto e colocados no interior dos dessecadores enquanto para o controle da umidade relativa no interior dos dessecadores foram utilizadas soluções saturadas. Os dessecadores foram colocados em câmara incubadora tipo B.O.D. regulada para as temperaturas de 25, 30, 35 e 40 °C. O teor de água de equilíbrio higroscópico dos frutos de crambe é diretamente proporcional à atividade de água e decresce com o aumento de temperatura, para um mesmo valor de umidade relativa de equilíbrio. Baseando-se em parâmetros estatísticos os modelos de Copace e Oswin Modificado são os que melhor representam a higroscopicidade dos frutos de crambe quando comparados com os demais modelos testados. O calor isostérico aumenta com a diminuição do teor de água de equilíbrio sendo necessária uma quantidade maior de energia para retirar a água dos frutos de crambe. Palavras-chave:Crambe abyssinica, atividade de água, modelagem matemática Desorption isotherms and isosteric heat of the fruits of crambe ABSTRACT This study aimed to adjust different mathematical models to experimental data of hygroscopicity of crambe fruits, selecting one that best represented the phenomenon, and obtain the values of the isosteric heat of desorption as a function of equilibrium moisture content. To obtain an equilibrium moisture content, crambe fruit was used with an initial moisture content of 26.0% (dry basis) and static gravimetric method. For each replicate 10 g of fruit were placed surrounded by a permeable fabric to permit air contact with the product and placed within the desiccators. To control the relative humidity inside the desiccators, saturated solutions were used. The desiccators were placed in incubator B.O.D., adjusted to temperatures of 25, 30, 35 and 40 °C. The equilibrium moisture content of crambe fruits is directly proportional to water activity and decreases with increasing temperature for the same value of equilibrium relative humidity. Based on statistical parameters, the models of Copace and Modified Oswin are those that best represent the hygroscopicity of crambe fruits compared to other tested models. The isosteric heat increases with decrease in equilibrium moisture content and requires a larger amount of energy to remove water from the crambe fruit.

Desorption isotherms and isosteric heat of 'cajuzinho-do-cerrado' achenes

“…For a certain temperature, the equilibrium moisture content increases with the increment in water activity for 'cajuzinho-do-cerrado' achenes. Similar result was observed by Costa et al (2013) in fruits of Crambe abyssinica (crambe), and this species is an oilseed plant, like 'cajuzinho-do-cerrado' . Table 2 shows the parameters of the hygroscopic equilibrium models, the coefficient of determination (R 2 ), values of relative mean error (P), estimated mean error (SE) and the Chi-square test (χ 2 ), for 'cajuzinho-do-cerrado' achenes obtained by desorption, at different temperatures.…”

“…As for 'cajuzinho-do-cerrado' and also for Raphanus sativus L. (forage radish), tested by Sousa et al (2013), and fruits of Crambe abyssinica (crambe), analyzed by Costa et al (2013), the Copace model was the most adequate for the representation of the desorption process of these species. Thus, according to the behavior of the desorption isotherms for 'cajuzinho-docerrado' achenes, in general, the composition of the product (solutes) has little affinity to water molecules.…”

Determination of the hygroscopic equilibrium and isosteric heat of aji chili pepper

“…The equilibrium moisture of a hygroscopic material is relevant in a drying study because it determines the minimum moisture content that the product may reach under the determined drying air conditions (Costa et al, 2013).…”

“…The hygroscopic behavior of diverse agricultural products has been studied by various researchers using various mathematical models, such as Chung-Pfost, Copace, modified GAB, modified Halsey, Henderson, modified Henderson, Oswin, Sabbah, and Sigma-Copace (Brooker et al, 1974;Hubinger et al, 2009;Ferreira et al, 2011;Silva & Rodovalho, 2012;Teixeira et al, 2012;Costa et al, 2013;Santos et al, 2015;Goneli et al, 2016). However, to develop isotherms that represent this equilibrium relationship, empirical mathematical models are used.…”

Bean grain hysteresis with induced mechanical damage

“…According to Figure 1, the hygroscopic equilibrium curves obtained through desorption and adsorption for bean grains showed a sigmoid shape, typical of many agricultural products: Chaves et al (2015); Hassini et al (2015), Oliveira et al (2010;2014a;b); Siqueira et al (2012); Smaniotto et al (2012); Sousa et al (2013) and Costa et al (2013). It is also observed that the increase of temperature promotes reduction in the equilibrium moisture content of the grains, following the same tendency of the other agricultural products.…”