RESUMO
BACKGROUND: Calcium alginate gels are widely used to encapsulate active compounds. Some characteristic parameters of these gels are necessary to describe the release of active compounds through mechanistic mathematical models. In this work, transport and kinetics properties of calcium alginate gels were determined through simple experimental techniques. RESULTS: The weight-average molecular weight ( M ¯ w = 192 × 103 Da) and the fraction of residues of α-l-guluronic acid ( F G = 0.356) of sodium alginate were determined by capillary viscometry and 1 H-nuclear magnetic resonance at 25 °C, respectively. Considering the half egg-box model, both values were used to estimate the molecular weight of calcium alginate as M g = 2.02 × 105 Da. An effective diffusion coefficient of water ( D eff , w = 2.256 × 10-9 m2 s-1 ) in calcium alginate was determined using a diffusion cell at 37 °C. Finally, a kinetics constant of depolymerization ( k m = 9.72 × 10-9 m3 mol-1 s-1 ) of calcium alginate was obtained considering dissolution of calcium to a medium under intestinal conditions. CONCLUSION: The experimental techniques used are simple and easily reproducible. The obtained values may be useful in the design, production, and optimization of the alginate-based delivery systems that require specific release kinetics of the encapsulated active compounds. © 2023 Society of Chemical Industry.
Assuntos
Alginatos , Imageamento por Ressonância Magnética , Alginatos/química , Géis/química , Espectroscopia de Ressonância Magnética , Modelos Teóricos , Cálcio/química , Ácidos Hexurônicos/química , Ácido Glucurônico/químicaRESUMO
The diffusion phenomena of sucrose and lactitol in cherries using different proportions during osmotic dehydration was quantified by means of a mathematical model based on Fick's second law. The average effective diffusion coefficient for soluble solids in skin and flesh are 5.37 10-11 m2∕s and 1.24 10-10 m2∕s. Whereas, for water in skin and flesh are 9.27 10-09 m2∕s and 5.48 10-08 m2∕s. A significant difference for water diffusion coefficients (p < 0.05) was observed between the treatments. This could indicate that the diffusion between species and treatments is differential. Effective diffusion coefficients for water in skin and flesh are 2 orders of magnitude greater than effective diffusion coefficients for soluble solids. This is probably due to its lesser molecular weight. Furthermore, the effective diffusion coefficients for water and soluble solids in cherry skin are between 1 and 2 orders of magnitude lower than effective diffusion coefficients for both in cherry flesh, possibly due to the barrier effect exerted by the cherry skin.
RESUMO
This study aimed to assess the influence of volumetric shrinkage in determining the effective diffusion coefficient, and obtain the activation energy of jatropha grains and fruits subjected to drying under varying air conditions. Jatropha grains and fruits were used with moisture content of 0.50 and decimal dry basis 4.40 (db), respectively, dried temperatures of 45, 60, 75, 90, and 105C, and drying air relative humidity of 14.5, 7.4, 3.8, 2.2, and 1.4% for fruits and 15.6, 7.4, 4.0, 1.8, and 1.2 % for grains. The volume of jatropha grains and fruits, considered spheroids, was obtained by measuring the three orthogonal axes during moisture content reduction, and volumetric shrinkage was assessed by reducing the equivalent radius with the drying process. It is concluded that the effective diffusion coefficient of jatropha grains and fruits increases with increasing air temperature; the inclusion of volumetric shrinkage promotes a better fit of the liquid diffusion model; and activation energy of Jatropha grains and fruits is similar but the inclusion of volumetric shrinkage practically did not change this parameter.
Objetivou-se com o presente trabalho verificar a influência da contração volumétrica na determinação do coeficiente de difusão efetivo, bem como obter a energia de ativação dos grãos e dos frutos de pinhão-manso submetidos à secagem em diversas condições de ar. Foram utilizados grãos e frutos de pinhão-manso, com teor de água de 0,50 e 4,40 decimal base seca (b.s), respectivamente, e submetidos à secagem nas temperaturas de 45, 60, 75, 90 e 105 C e umidade relativa do ar de secagem de 14,5; 7,4; 3,8; 2,2 e 1,4% para os frutos e 15,6; 7,4; 4,0; 1,8 e 1,2%, para os grãos. O volume dos grãos e dos frutos de pinhão-manso, considerados esferoides, foi obtido por meio da medição dos três eixos ortogonais ao longo da redução do teor de água e a contração volumétrica avaliada por meio da redução do raio equivalente com o processo de secagem. Conclui-se que, o coeficiente de difusão efetivo dos grãos e dos frutos de pinhão-manso aumenta com a elevação da temperatura do ar, a inclusão da contração volumétrica promove um melhor ajuste do modelo da difusão líquida e a energia de ativação dos grãos e dos frutos de pinhão-manso são similares sendo que a inclusão da contração volumétrica praticamente não altera este parâmetro.
RESUMO
This study aimed to assess the influence of volumetric shrinkage in determining the effective diffusion coefficient, and obtain the activation energy of jatropha grains and fruits subjected to drying under varying air conditions. Jatropha grains and fruits were used with moisture content of 0.50 and decimal dry basis 4.40 (db), respectively, dried temperatures of 45, 60, 75, 90, and 105C, and drying air relative humidity of 14.5, 7.4, 3.8, 2.2, and 1.4% for fruits and 15.6, 7.4, 4.0, 1.8, and 1.2 % for grains. The volume of jatropha grains and fruits, considered spheroids, was obtained by measuring the three orthogonal axes during moisture content reduction, and volumetric shrinkage was assessed by reducing the equivalent radius with the drying process. It is concluded that the effective diffusion coefficient of jatropha grains and fruits increases with increasing air temperature; the inclusion of volumetric shrinkage promotes a better fit of the liquid diffusion model; and activation energy of Jatropha grains and fruits is similar but the inclusion of volumetric shrinkage practically did not change this parameter.
Objetivou-se com o presente trabalho verificar a influência da contração volumétrica na determinação do coeficiente de difusão efetivo, bem como obter a energia de ativação dos grãos e dos frutos de pinhão-manso submetidos à secagem em diversas condições de ar. Foram utilizados grãos e frutos de pinhão-manso, com teor de água de 0,50 e 4,40 decimal base seca (b.s), respectivamente, e submetidos à secagem nas temperaturas de 45, 60, 75, 90 e 105 C e umidade relativa do ar de secagem de 14,5; 7,4; 3,8; 2,2 e 1,4% para os frutos e 15,6; 7,4; 4,0; 1,8 e 1,2%, para os grãos. O volume dos grãos e dos frutos de pinhão-manso, considerados esferoides, foi obtido por meio da medição dos três eixos ortogonais ao longo da redução do teor de água e a contração volumétrica avaliada por meio da redução do raio equivalente com o processo de secagem. Conclui-se que, o coeficiente de difusão efetivo dos grãos e dos frutos de pinhão-manso aumenta com a elevação da temperatura do ar, a inclusão da contração volumétrica promove um melhor ajuste do modelo da difusão líquida e a energia de ativação dos grãos e dos frutos de pinhão-manso são similares sendo que a inclusão da contração volumétrica praticamente não altera este parâmetro.