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.

The search for new technologies and options of activities to improve agricultural production systems are goals continuously desired by companies. Thus, the objective of this study was to evaluate the performance of soybean grain drying, using a furnace dryer automatically fed with eucalyptus chips, the quality of the grains before and after drying, as well as contamination by polycyclic aromatic hydrocarbons (PAHs). Twenty-seven samples were collected before drying and 27 samples were collected after drying, totaling 54 samples of around 1.0 kg each, at 5-minute intervals. The following experimental evaluations were carried out: dryerperformance, calorific value and fuel consumption; grainsmoisture content, germination, electrical conductivity, apparent specific mass, thousand-grain weight, color, oil acidity index and polycyclic aromatic hydrocarbons. The dryer showed an average efficiency of 75.61% for drying the grains. The average fuel consumption was 21.78 kg of chip per ton of dry grains. The specific energy consumption to remove 1.0 kg of water was 11,871.80 kJ. In general, drying did not compromise the final quality of soybeans. Soybeans showed the presence of two PAHs before drying and three more PAHs appeared after drying. Average concentrations were lower than the maximum values allowed by European Union Law No 835/2011. The drying conditions used for soybean grains influenced the low formation of PAHs.