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.
The objective of this study was to model the water sorption kinetics of damaged beans. Grains with initial moisture content of 53.85%, dry basis (d.b.), were used. One portion of the grains was used to obtain desorption isotherms, while the other was subjected to drying until the moisture content of 5.26% (d.b.), so that it was subjected to the adsorption. For the induction of damage, a Stein Breakage Tester was used. To obtain the equilibrium moisture content, grains were placed in a climatic chamber at 20, 30, 40 and 50 ± 1 °C combined with relative humidity of 30, 40, 50, 70 and 90 ± 3%. The GAB model fitted well to the equilibrium moisture experimental data of damaged grains and control. With increasing temperature, the monolayer moisture contents decreased in adsorption and desorption processes, ranging from 9.84 to 5.10% d.b. The lower moisture content in the monolayer in damaged grains indicates that lower moisture content is necessary to ensure their conservation.
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.
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...
A B S T R A C TThis study aims to determine the thermodynamic properties of damaged beans. Grains with initial moisture content of 53.85% (d.b.) were used. A part of the grains was used to obtain the desorption isotherms, while another part was subjected to drying until a moisture content of 5.26% (d.b.) was achieved; therefore, it was subjected to the adsorption process. To induce damage, a Stein breakage tester was used. To obtain the equilibrium moisture content, grains were placed in a climatic chamber whose temperatures were 20, 30, 40, and 50 ± 1 °C combined with a relative humidity of 30, 40, 50, 70, and 90 ± 3%. Although in the desorption process, damaged grains had a lower differential enthalpy compared with the control, the reverse behavior was observed in the adsorption process. Mechanical damage caused the formation of a greater number of available adsorption sites, resulting in higher differential entropy values in adsorption and lower values in desorption compared with the control. The mechanical damage had no effect on the Gibbs free energy.Cinética de sorção de água de grãos de feijão danificado: Propriedades termodinâmicas R E S U M OObjetivou-se determinar as propriedades termodinâmicas de grãos de feijão danificados. Foram utilizados grãos com teor de água inicial de 53,85% (b.s.); parte dos grãos foi utilizada para se obter as isotermas de dessorção, enquanto que a outra foi submetida a secagem até o teor de água de 5,26% (b.s.), para que a mesma fosse submetida ao processo de adsorção. Para a indução da danificação foi utilizado um Stein Breakage Tester. Para obter o teor de água de equilíbrio, os grãos foram colocados em câmara climática cujas temperaturas foram de 20, 30, 40 e 50 ± 1 ºC combinadas com umidades relativas de 30, 40, 50, 70 e 90 ± 3%. Na dessorção, os grãos danificados apresentaram menor entalpia diferencial quando comparados com a testemunha enquanto o inverso foi observado na adsorção. A danificação mecânica provocou a formação de um número maior de sítios disponíveis de sorção, resultando em maiores valores de entropia diferencial na adsorção e menores valores na dessorção quando comparados com a testemunha. A danificação mecânica não teve efeito sobre a energia livre de Gibbs.
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