ABSTRACT The use of residues resulting from the processing of agricultural products is an widely studied topic, which is justified by the need to reduce costs and by the search for productive sustainability, which has as one of its principles the full use production, reducing waste and therefore increasing the amount of products extracted per unit of area. Residual seeds, resulting from the production of fruit pulps, are rich in nutrients and with the potential to be further improved by the application of germination, increasing the protein content and the content of bioactive compounds. However, in the germination process, the product acquires a high water content, requiring immediate drying and control of the water adsorption kinetics after dehydration. Therefore, the objective of this study was to determine the water adsorption isotherms of germinated seeds flours from pumpkins of three varieties at temperatures of 15, 25 and 35 °C, to obtain the most appropriate mathematical model to describe the hygroscopic behavior and to determine the thermodynamic properties of water adsorption, through the values of the integral isosteric heat, differential entropy, differential enthalpy and Gibbs free energy for the studied conditions. The GAB and Peleg models fit the experimental data well. With increasing water activity, there was a reduction in isosteric heat and entropy. The enthalpy-entropy compensation theory was confirmed. Gibbs free energy was negative for all temperatures, increasing with increasing equilibrium water content, demonstrating that it is a spontaneous process.

Resumo O acuri é uma fruta pouco explorada industrialmente, mas com grandes perspectivas e possibilidades de uso. Para tanto, torna-se necessário reduzir o seu teor de água, aumentando então a sua vida útil, o que possibilitará sua utilização em mercados distantes dos locais de produção. Nesse sentido, objetivou-se secar fatias de acuri, com espessura de aproximadamente 4,07 mm, nas temperaturas de 60, 70, 80 e 90 °C, ajustar diferentes modelos matemáticos aos dados experimentais e determinar os coeficientes de difusão, a energia de ativação e as propriedades termodinâmicas. Observou-se que o aumento de temperatura de 30°C reduziu em 36% o tempo total de processo, sendo obtidas taxas de secagem máximas de 1,22; 1,88; 2,16, e 2,45 kg de água kg de matéria seca min-1 nas temperaturas de 60, 70, 80 e 90 °C, respectivamente. Dentre os modelos matemáticos testados, o modelo logarítmico apresentou os melhores parâmetros de ajustes aos dados experimentais e foi selecionado como o mais adequado para representar o fenômeno investigado. Os coeficientes de difusão efetivos aumentaram com o incremento de temperatura, apresentando-se na ordem de 10-10 m2 s-1 , e sua dependência com a temperatura foi descrita pela Equação de Arrhenius, que apresentou energia de ativação de 17,66 kJ mol-1 . Os valores de entalpia e entropia reduziram com a elevação da temperatura de secagem, enquanto que a energia livre de Gibbs foi ampliada na faixa de temperatura avaliada.

Abstract Acuri is a fruit little explored industrially with great perspectives and possibilities for use, but for this to occur the moisture content must be reduced, thus increasing its shelf life and enabling it to be used in markets far from its place of production. Hence the objective here was to dry acuri slices with a thickness of approximately 4.07 mm at temperatures of 60, 70, 80 and 90 °C, adjust different mathematical models to the experimental data and determine the diffusion coefficients, the activation energy and the thermodynamic properties. It was observed that a temperature increase of 30 °C reduced the total process time by 36%, with maximum drying rates of 1.22; 1.88; 2.16 and 2.45 kg of water kg of dry matter min -1 at the temperatures of 60, 70, 80 and 90 °C, respectively. Of the mathematical models tested, the Logarithmic model presented the best fit to the experimental data and was selected as the most adequate model to represent the phenomenon investigated. The effective diffusion coefficients increased with increase in temperature to the order of 10-10 m2 s-1 and the temperature dependence was described by the Arrhenius equation which presented an activation energy of 17.66 kJ mol-1. The enthalpy and entropy values decreased with increase in drying temperature, while Gibbs free energy increased in the temperature range evaluated.