Noni seeds have been used for years as an important medicinal source, with wide use in the pharmaceutical and food industry. Drying is a fundamental process in the post-harvest stages, where it enables the safe storage of the product. Therefore, the present study aimed to fit different mathematical models to experimental data of drying kinetics of noni seeds, determine the effective diffusion coefficient and obtain the activation energy for the process during drying under different conditions of air temperature. The experiment used noni seeds with initial moisture content of 0.46 (decimal, d.b.) and dehydrated up to equilibrium moisture content. Drying was conducted under different controlled conditions of temperature, 40; 50; 60; 70 and 80 ºC and relative humidity, 24.4; 16.0; 9.9; 5.7 and 3.3%, respectively. Eleven mathematical models were fitted to the experimental data. The parameters to evaluate the fitting of the mathematical models were mean relative error (P), mean estimated error (SE), coefficient of determination (R2), Chi-square test (c2), Akaike Information Criterion (AIC) and Schwarz’s Bayesian Information Criterion (BIC). Considering the fitting criteria, the model Two Terms was selected to describe the drying kinetics of noni seeds. Effective diffusion coefficient ranged from 8.70 to 23.71 × 10-10 m2 s-1 and its relationship with drying temperature can be described by the Arrhenius equation. The activation energy for noni seeds drying was 24.20 kJ mol-1 for the studied temperature range.

As well as most agricultural products, some medicinal plants need to go through a drying process to ensure quality maintenance, however each product behaves differently. Therefore, the present study aimed to evaluate the drying kinetics of spiked pepper (Piper aduncum L.) leaves and determine their thermodynamic properties at different drying temperatures in laboratory scale. Leaves with initial moisture content of 78% w.b. (wet basis) were subjected to drying at temperatures of 40, 50, 60 and 70 ºC and air speed of 0.85 m s-1 in an experimental fixed bed dryer. The drying kinetics of the leaves was described by statistical fitting of mathematical models and determination of effective diffusion coefficient and activation energy. Enthalpy, entropy and Gibbs free energy were also evaluated for all drying conditions. It was concluded that, among the models evaluated, only Midilli and Valcam can be used to represent the drying of Piper aduncum leaves; the first for the two highest temperatures (60 and 70 ºC) and the second for 40 and 50 ºC. The activation energy was approximately 55.64 kJ mol-1, and the effective diffusion coefficient increase with the elevation of temperature. The same occurs with the values of Gibbs free energy, whereas the specific enthalpy and entropy decrease.

RESUMO: O feijão (Phaseolus vulgaris L.) é um produto de grande importância na alimentação humana devido as suas excelentes propriedades nutricionais, sendo uma das mais tradicionais fontes de proteína consumida. No entanto, se os processos pós-colheita aplicados a esta cultura forem realizados de forma inadequada podem comprometer essas propriedades. Objetivou-se com o presente trabalho descrever o comportamento da secagem dos grãos de feijão cultivar IPR Tangará, por meio do ajuste de diferentes modelos matemáticos aos dados experimentais de secagem, determinar as propriedades termodinâmicas, bem como o coeficiente de difusão efetivo e a energia de ativação do processo. Os grãos de feijão foram coletados com teor de água inicial de aproximadamente 30% (b.u., base úmida), e submetidos à secagem nas temperaturas de 40, 45, 50, 55 e 60 ºC, em condições controladas. Aos valores de razão de umidade dos grãos de feijão foram ajustados nove modelos matemáticos, utilizados para a representação do fenômeno de secagem de diversos produtos agrícolas. Conclui-se que apenas os modelos de Page, Midilli, Dois Termos, Logarítmico, Thompson, Aproximação da Difusão e Valcam são adequados para a representação da secagem dos grãos de feijão cultivar IPR Tangará; o coeficiente de difusão efetivo aumenta com a elevação da temperatura do ar de secagem; os valores de entalpia e entropia específica são inversamente proporcionais à temperatura do ar de secagem, enquanto que a energia livre de Gibbs aumenta com a elevação da temperatura do ar. PALAVRAS-CHAVE:Modelos matemáticos, propriedades termodinâmicas, coeficiente de difusão efetivo. DRYING KINETICS OF BEANS GRAINS ( IPR TANGARÁ CULTIVAR)ABSTRACT: Bean (Phaseolus vulgaris L.) is a product of great importance in human diet due to its excellent nutritional properties, being one of the most traditional consumed sources of protein. However, if the post-harvest processes applied to this crop are inadequately performed it may compromise these properties. In view of this crop importance and the consequences of poorly conducted postharvest processes, the objective of this study was to describe the behavior of bens from cultivar IPR Tangará drying. Thus, different mathematical models were adjust to experimental drying data as the thermodynamic properties, effective diffusion coefficient, and process activation energy were determine. The beans were collected with an initial water content of approximately 30% (w.b., wet basis), and subjected to drying temperatures of 40, 45, 50, 55 and 60 ºC, under controlled conditions. The moisture ratio values of bean grains were adjusted by nine mathematical models that are used to represent others agricultural products drying phenomenon. ThePage, Midilli, Two Terms, Logarithmic, Thompson, Diffusion Approximation, and Valcam models are suitable to represent the drying process of bean cultivar IPR Tangará. The effective diffusion coefficient increases with increasing drying air temperature. KEYWORDS:Mathematical models, thermodynamic properties, effective d...

Buckwheat has become important in the food sector as its flour does not contain gluten. Since buckwheat is a relatively new crop in the agricultural environment, there is little information available regarding its processing. Drying is one of the most important post-harvest stages of buckwheat. The aim of the present study was to describe the drying process of buckwheat grains. Buckwheat grains with a moisture content of 0.41 ± 0.01 (dry basis, d.b.) were harvested, followed by drying in an experimental dryer at the temperatures of 40, 50, 60, 70, and 80 °C, at an air speed of 0.8 m s-1. The drying rate was determined, and the mathematical models generally employed to describe the drying process of several agricultural products were fitted to the experimentally obtained data. Model selection was based on the Gauss-Newton non-linear regression method and was complemented by Akaike Information Criterion and Schwarz’s Bayesian Information Criterion. It was concluded that the drying rate increased with an increase in temperature and decreased with an increase in drying time. It is recommended to use the Midilli model to represent the drying kinetics of buckwheat grains at the temperatures of 40, 60, and 70 °C, while the Approximation of diffusion model is recommended for the temperatures of 50 and 80 °C. The magnitudes of effective diffusion coefficients ranged from 1.8990 × 10-11 m2 s-1 to 17.8831 × 10-11 m2 s-1. The activation energy required to initiate the drying process was determined to be 49.75 kJ mol-1.

Buckwheat is a prominent crop in present-day agriculture due to its nutraceutical properties; however, information on this crop regarding the post-harvest process is scarce, as well as the characterization of its physical properties and such information is essential for the development and improvement of machinery used in post-harvest processes. Thus, the objective of this study was to determine the volumetric shrinkage, porosity, bulk density and true density of buckwheat grains throughout the drying process, as well as to fit mathematical models to the experimental values of true and bulk volumetric shrinkages. Buckwheat grains of the cultivar IPR 91 - Baili with an initial moisture content of 0.250 (decimal, dry basis.) were used. The samples used to determine the physical properties were subjected to oven drying with forced air circulation stabilized at 40 ± 1 °C. The mass of the samples was periodically weighed, so that when the product reached predetermined values of moisture content, the samples were removed and their physical properties were determined. It is concluded that the reduction in moisture content during drying causes increase in bulk density, true density and porosity. The reduction of the moisture content influences bulk volumetric shrinkage and true volumetric shrinkage of the grains, causing reductions in their values of approximately 14.47 and 14.70%, respectively, and a linear model can represent both variables satisfactorily.

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Araticum (Annona crassiflora) fruits have relevant characteristics for industrialization, a characteristic aroma and a slightly acidic flavor, with relevant amounts of vitamins A, C, B1 and B2. The objective of this study was to fit different mathematical models to the experimental data, evaluate the effective diffusion coefficient and determine the activation energy for the araticum epicarp subjected to different drying conditions. The epicarps of araticum fruits were dried at temperatures of 40, 50, 60 and 70 °C. Midilli, Logarithmic and Two Terms models can be used to represent the drying of araticum epicarp, and the Two Terms model was selected according to the Akaike Information Criterion (AIC) and Schwarz's Bayesian Information Criterion (BIC). The linear model satisfactorily represented the effective diffusion coefficient as a function of drying temperature. In the evaluation of enthalpy, entropy and Gibbs free energy, both enthalpy and entropy tend to decrease when temperature increases. The higher the temperature used for drying of araticum epicarp, the lower the value of diffusivity, i.e., the lower the resistance to water removal.

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