A B S T R A C TJabuticaba is a fruit native of Brazil and, besides containing many nutritional qualities, it also has a good field for use in products such as flour for cakes and biscuits, juice, liqueur, jelly and others. This study aimed to model the drying kinetics and determine the thermodynamic properties of jabuticaba peel at different drying air temperatures. Ripe fruits of jabuticaba (Myrciaria jaboticaba) were collected and pulped manually. Drying was carried out in a forced-air circulation oven with a flow of 5.6 m s -1 at temperatures of 40, 50, 60 and 70 °C. Six mathematical models commonly used to represent the drying process of agricultural products were fitted to the experimental data. The Arrhenius model was used to represent the drying constant as a function of temperature. The Midilli model showed the best fit to the experimental data of drying. The drying constant increased with the increment in drying temperature and promoted an activation energy of 37.29 kJ mol -1 . Enthalpy and Gibbs free energy decreased with the increase in drying temperature, while entropy decreased and was negative.Modelagem matemática e propriedades termodinâmicas da casca da jabuticaba durante o processo de secagem R E S U M OA jabuticaba é um fruto nativo do Brasil e além de conter muitas qualidades nutricionais também possui bom campo para a utilização em subprodutos como farinhas para bolos e biscoitos, suco, licor, geleia e outros. Objetivou-se modelar a cinética de secagem e determinar as propriedades termodinâmicas de casca de jabuticaba em diferentes temperaturas do ar de secagem. Foram utilizadas jabuticabas maduras, colhidas e separadas da polpa manualmente, da espécie Myrciaria jaboticaba. A secagem foi realizada em estufa de circulação forçada de ar com velocidade de 5,6 m s -1 nas temperaturas de 40; 50; 60 e 70 °C. Seis modelos matemáticos usualmente utilizados para a representação do processo de secagem de produtos agrícolas foram ajustados aos dados experimentais. A relação do tipo Arrhenius foi utilizada para representar a constante de secagem em função da temperatura. O modelo de Midilli foi o que melhor se ajustou aos dados experimentais da secagem. A constante de secagem aumentou com o incremento da temperatura de secagem e proporcionou energia de ativação de 37,29 kJ mol -1 . A entalpia e a energia livre de Gibbs diminuíram com o aumento da temperatura de secagem; já a entropia diminuiu e foi negativa.
R E S U M OObjetivou-se, com este trabalho, propor e ajustar modelos matemáticos ao processo de secagem de espuma de graviola em diferentes condições de ar, determinar o coeficiente de difusão efetivo e obter a energia de ativação. Para a formação da espuma foi adicionada, à polpa, albumina, na concentração de 7,43% em massa e submetida à agitação em batedeira doméstica, durante 15 min; em seguida, esta foi espalhada sobre bandejas formando uma camada fina de cerca de 5,0 mm de espessura cujas condições de secagem foram: de 40, 50, 60, 70 e 80 °C, 5,6 m s -1 e 60%. O modelo para determinar o binômio teor de água crítico e tempo crítico e o de Midili se ajustaram bem aos dados experimentais da secagem de espuma de graviola e se obteve acréscimo no coeficiente de difusão efetiva com a elevação da temperatura de secagem e energia de ativação de 33,10 kJ mol -1 . Mathematical modeling of drying of soursop foam A B S T R A C TThe aim of this paper was to propose and to adjust mathematical models for drying process of soursop foam in different air conditions, to determine the effective diffusion coefficient and to obtain the activation energy. For foaming, albumin was added to the pulp at concentration of 7.43% and stirred in mixer for 15 min. Then, it was spread onto trays forming a thin layer about 5.0 mm thick, and the drying conditions were: 40, 50, 60, 70 and 80 °C, 5.6 m s -1 and 60%. The model for determining the binomial critical water content and critical time, and the Midili model, adjusted well to the experimental data of soursop foam drying. Furthermore, an increase was obtained in the effective diffusion coefficient with increase in drying temperature and activation energy of 33.10 kJ mol -1 . Palavras-chave:teor de água crítico tempo crítico foam-mat drying
The objective of this study was to model the water sorption kinetics of damaged beans. Grains with initial moisture content of 53.85%, dry basis (d.b.), were used. One portion of the grains was used to obtain desorption isotherms, while the other was subjected to drying until the moisture content of 5.26% (d.b.), so that it was subjected to the adsorption. For the induction of damage, a Stein Breakage Tester was used. To obtain the equilibrium moisture content, grains were placed in a climatic chamber at 20, 30, 40 and 50 ± 1 °C combined with relative humidity of 30, 40, 50, 70 and 90 ± 3%. The GAB model fitted well to the equilibrium moisture experimental data of damaged grains and control. With increasing temperature, the monolayer moisture contents decreased in adsorption and desorption processes, ranging from 9.84 to 5.10% d.b. The lower moisture content in the monolayer in damaged grains indicates that lower moisture content is necessary to ensure their conservation.
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