RESUMO No presente estudo, objetivou-se ajustar diferentes modelos aos dados experimentais da secagem das sementes de tamarindo (Tamarindus indica L.) e selecionar o melhor modelo, determinar o coeficiente de difusão efetivo, a energia de ativação e as propriedades termodinâmicas para o processo, durante a secagem em diversas temperaturas. O experimento foi conduzido no Laboratório de Pós-Colheita de Produtos Vegetais do Instituto Federal Goiano - Campus Rio Verde. As sementes com teor de água inicial de 18 ± 0,25% base seca, foram secas em estufa com ventilação de ar forçada, nas temperaturas controladas de 45, 60, 75 e 90 °C, em quatro repetições. Aos dados experimentais foram ajustados a modelos de regressão não linear utilizados para descrição do fenômeno. Para representar a secagem das sementes de tamarindo o modelo de Midilli foi selecionado para a faixa de 45 a 60 ºC, e para 75 a 90 ºC o modelo ajustado foi o de Dois termos. O coeficiente de difusão efetivo aumenta com a elevação da temperatura do ar de secagem, sendo descrito pela equação de Arrhenius, com energia de ativação de 35,16 kJ mol-1. A entalpia e entropia decrescem, enquanto a energia livre de Gibbs aumenta com o incremento da temperatura de secagem.

ABSTRACT In the present study, the objective was to fit different models to the experimental data of drying of tamarind (Tamarindus indica L.) seeds and to select the best model, to determine the effective diffusion coefficient, activation energy and thermodynamic properties for the process during drying at different temperatures. The experiment was carried out at the Laboratory of Post-Harvest of Vegetable Products of the Instituto Federal Goiano (Federal Institute Goiano) - Campus of Rio Verde, GO, Brazil. Seeds with initial moisture content of 18 ± 0.25% dry basis were oven dried with forced air ventilation, at controlled temperatures of 45, 60, 75 and 90 °C in four repetitions. Nonlinear regression models used to describe the phenomenon were fitted to the experimental data. To represent the drying of tamarind seeds, the Midilli model was selected for the range from 45 to 60 ºC and the Two terms model was selected for the range from 75 to 90 ºC. The effective diffusion coefficient increases with the increase of drying air temperature, being described by the Arrhenius equation, with activation energy of 35.16 kJ mol-1. Enthalpy and entropy decreases, while Gibbs free energy increases with increasing drying temperature.

ABSTRACT Tamarind is used in the food and pharmaceutical industry, and its seed is the main means for the reproduction of this species, thus justifying studies that ensure its post-harvest viability. This research aimed to study the thermodynamic properties of tamarind seeds as a function of the equilibrium moisture content. The experimental data of the water activities were obtained by the indirect static method. The Cavalcanti Mata model was used to determine the thermodynamic properties of tamarind seeds, as it was the model that best fitted the experimental data of the desorption isotherms. The results showed that the thermodynamic properties are influenced by the moisture content and temperature, with an increase in the energy required to remove water from the product with a decrease in moisture content. The net isosteric heat of desorption increases with a reduction of moisture content ranging from 2,618.85 to 2,510.25 kJ kg−1 for the moisture content range of 10.52 to 21.10% db. The latent heat of vaporization, the differential enthalpy, and the Gibbs free energy increase with a reduction of the moisture content of tamarind seeds.

ABSTRACT The knowledge of hygroscopicity is essential for the storage of tamarind seeds, but there is a limitation of a judicious statistical parameter to define the best mathematical model to adjust the isotherms of plant products. Therefore, this study aimed to determine the desorption isotherms of tamarind seeds and test the Akaike information criterion (AIC) and Schwarz Bayesian information criterion (BIC) for choosing the best mathematical model. Seeds with an initial moisture content of 21.00 ± 0.10% dry basis (db) were dried at 45 °C until they reached moisture contents of 17.27 ± 0.10, 15.04 ± 0.16, 14.14 ± 0.06, 12.41 ± 0.17, and 10.52 ± 0.12% db. The water activity of the product was determined by the static-indirect method at temperatures of 10, 20, 30, and 40 °C. Mathematical models frequently used to predict the isotherms of plant products were adjusted to the experimental data. The Cavalcanti Mata model is recommended to estimate the desorption isotherms of tamarind seeds because it presents better adjustments. The AIC and BIC criteria contribute to the choice of the model to predict the desorption isotherms of tamarind seeds.

RESUMO O fruto da cajazeira (Spondias mombin L.) apresenta características relevantes para industrialização e possuem aroma agradável e sabor ácido-adocicado, possui quantidades relevantes de vitamina A e carotenoides no epicarpo do cajá. Objetivou-se, ajustar diferentes modelos matemáticos aos dados experimentais, utilizando como critérios para selecionar o melhor modelo - o Critério de Informação de Akaike (AIC) e o Critério de Informação Bayesiano de Schwarz (BIC), bem como avaliar o coeficiente de difusão efetivo e determinar a energia de ativação para o epicarpo de cajá submetido a diferentes condições de secagem. O experimento foi desenvolvido no Instituto Federal de Educação, Ciência e Tecnologia Goiano. O epicarpo dos frutos de cajá com teor de água inicial 2,89 (base seca, b.s.) foram submetidos à secagem em temperaturas de 40, 50, 60 e 70 °C até teor de água final de 0,11, 0,10, 0,09 e 0,08 (b.s.), respectivamente. O modelo de Midilli apresentou o melhor ajuste aos dados experimentais obtidos. A escolha do modelo foi confirmada pelos critérios de AIC e BIC. O aumento da temperatura de secagem promoveu aumento do coeficiente de difusão efetivo, e a energia de ativação do processo foi de 21,50 kJ mol-1.

ABSTRACT Yellow mombin (Spondias mombin L.) fruits have relevant characteristics for industrialization and exhibit a pleasant aroma and sour-sweet taste, with significant amounts of vitamin A and carotenoids in their epicarp. The objective was to fit different mathematical models to the experimental data, using as criteria to select the best model - the Akaike Information Criteria (AIC) and Schwarz’s Bayesian Information Criteria (BIC), as well as to evaluate the effective diffusion coefficient and to determine the activation energy for yellow mombin epicarp submitted to different drying conditions. The experiment was carried out at the Instituto Federal de Educação, Ciência e Tecnologia Goiano, Brazil The epicarp of yellow mombin fruits with initial moisture content of 2.89 (dry basis, d.b.) were submitted to drying at temperatures of 40, 50, 60 and 70 °C until final moisture contents of 0.11, 0.10, 0.09 and 0.08 (d.b.), respectively. The Midilli model showed the best fit to the experimental data obtained. The choice of the model was confirmed by the AIC and BIC criteria. The increase of the drying temperature promoted increase in the effective diffusion coefficient, and the activation energy of the process was 21.50 kJ mol-1.