RESUMO As folhas de amora preta possuem algumas propriedades farmacológicas e um dos usos mais difundidos e estudados é para alivio dos sintomas do climatério e de outros durante o período pré-menstrual. Desta forma, a secagem se torna importante para a conservação e o armazenamento do produto até o seu uso ou processamento. Diante do exposto, objetivou-se com o presente estudo avaliar a cinética de secagem de folhas de amora preta, bem como determinar o coeficiente de difusão efetivo e a energia de ativação durante o processo de secagem. As folhas de amora preta foram submetidas à secagem em um secador experimental de leito fixo, em quatro condições controladas de temperatura (40, 50, 60 e 70 °C) e duas velocidades do ar de secagem (0,4 e 0,8 m s-1). Aos dados experimentais de razão de teor de água foram ajustados oito modelos matemáticos para representarem o processo de secagem em camada delgada de produtos agrícolas. Com base nos resultados obtidos, verificou-se que o modelo de Midilli foi o que melhor representou o fenômeno da secagem de folhas de amora preta. O aumento da temperatura e da velocidade do ar reduziu o tempo de secagem das folhas de amora preta, bem como aumentou os valores do coeficiente de difusão efetivo, sendo que esta relação pode ser descrita pela equação de Arrhenius, que apresenta uma energia de ativação para a difusão líquida durante a secagem de 65,94 e 66,08 kJ mol-1, para as velocidades do ar de secagem de 0,4 e 0,8 m s-1, respectivamente.

ABSTRACT Blackberry leaves have some pharmacological properties and one of the most widespread and studied uses is to relieve symptoms of the climacteric and other symptoms during the premenstrual period. Thus, drying becomes important for the conservation and storage of the product until its use or processing. The present study aimed to evaluate the drying kinetics of blackberry leaves, as well as to determine the effective diffusion coefficient and the activation energy during the drying process. Blackberry leaves were dried in an experimental fixed-bed dryer under four controlled temperature conditions (40, 50, 60 and 70 °C) and two drying air speeds (0.4 and 0.8 m s-1). With the experimental data of moisture ratio, eight mathematical models were fitted to represent the process of thin-layer drying of agricultural products. Based on the obtained results, it was found that the Midilli model represented best the phenomenon of drying of blackberry leaves. The increase in temperature and air speed reduced the drying time of blackberry leaves and increased the values of the effective diffusion coefficient. This relation can be described by the Arrhenius equation, which has an activation energy for the liquid diffusion during drying of 65.94 and 66.08 kJ mol-1, for drying air speeds of 0.4 and 0.8 m s-1, respectively.

ABSTRACT The control of the temperature of the storage air have the ability to improve a better preservation of some types of agricultural products. However, the most effective temperature for storage as well as the duration of storage varies between products. Therefore, special attention should be concentrated on the storage temperature and its effects on the integrity and longevity of the produce. The objective of the present study was to evaluate the effects of storage temperature and storage period on the quality of castor beans. Castor seeds with a water content of approximately 6.1% (w.b.) were stored for 180 days at temperatures of 15, 25 and 35 °C. The quality of the seeds was evaluated every 45 days throughout the study period by measuring dry matter loss, electrical conductivity, color, and the free fatty acid and peroxide content of the crude oil extracted. Our results indicated that: a) higher storage temperature negatively affect the quality of the seeds and the extracted oil; b) the negative effect of temperature increase with longer storage period; c) the storage temperature of 15 °C least affect the quality of castor bean and the extracted oil.

ABSTRACT: The aim of this study was to adjust mathematical models to the experimental data on the peanut kernels drying in thin layer, as well as to determine the effective diffusion coefficient and the main thermodynamic properties involved in drying of the grains under different air conditions. The peanut kernels, with a water content of 0.59 ± 0.002 (dry basis, d.b.), were dried in a forced air ventilation oven with different temperature levels (40, 50, 60 and 70 °C) until reaching a water content of 0.04 ± 0.001 (d.b.). For the experimental data, eight mathematical models traditionally used to represent the drying kinetics of thin layer of agricultural products were adjusted, also being determined the effective diffusion coefficient and the thermodynamic properties, specific enthalpy and entropy and Gibbs free energy. The Diffusion Approximation, Two Terms, Midilli, Page and Thompson models represent the drying kinetics of peanut kernels in thin layers. The effective diffusivity increases with the increase of temperature, being the relation with the drying temperature described by the Arrhenius' equation. The increase in temperature promotes the decrease of the enthalpy and entropy values and the increase of the Gibbs free energy.

RESUMO Normalmente, os produtos agrícolas têm suas dimensões reduzidas durante o processo de secagem. A quantificação da redução dessas dimensões é importante para o desenvolvimento e otimização de equipamentos destinados à pós-colheita do produto. Em virtude disto, objetivou-se, com o presente trabalho, avaliar o efeito da variação do teor de água durante a secagem sobre a contração volumétrica dos grãos de cártamo e de seus respectivos eixos. Foram utilizados grãos de cártamo colhidos com teor de água inicial de aproximadamente 0,445 decimal b.s. (base seca) e submetidos à secagem em estufa com circulação forçada de ar, na temperatura de 40 °C, até os grãos atingirem o teor de água final de 0,073 ± 0,008 decimal b.s. Durante a secagem, os índices de contração dos eixos e contração volumétrica unitária e da massa de grãos de cártamo foram determinados em diferentes teores de água. Com base nos resultados obtidos pode-se concluir que a redução do teor de água causa redução dos eixos dos grãos de cártamo; consequentemente, a redução dos valores do índice de contração volumétrica da massa e unitária de aproximadamente 16 e 13%, respectivamente, em que ambas as variáveis podem ser representadas pelo modelo de contração linear.

ABSTRACT Agricultural products usually have their size reduced during the drying process. The quantification of the reduction in the dimensions is important for the development and optimization of equipment for the post-harvest of the product. The aim of the present study was to evaluate the effect of the variation in the moisture content during drying on the volumetric shrinkage of safflower grains and their respective axes. Safflower grains were harvested with an initial moisture content of approximately 0.445 decimal d.b. (dry basis) and subjected to drying in an oven with forced air circulation at 40 °C, until the grains reached a final moisture content of 0.073 ± 0.008 decimal d.b. During drying, the contraction of the axes, unit volumetric shrinkage and volumetric shrinkage of the mass of safflower grains were determined at different moisture contents. Based on these results, it can be concluded that reducing the moisture content causes a reduction in the axes of safflower grains and, consequently, reductions in the unit volumetric shrinkage and volumetric shrinkage of the mass of approximately 16 and 13%, respectively, and both variables can be represented by the linear shrinkage model.