Enthalpy-entropy compensation models for sorption and browning of garlic

Madamba, Ponciano S.; Driscoll, R. H.; Buckle, K. A.

doi:10.1016/0260-8774(94)00072-7

Cited by 133 publications

(151 citation statements)

References 16 publications

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“…Quando ocorre aumento na temperatura do ar de secagem, a viscosidade, que representa a resistência do fluído ao escoamento da água, diminui, o que resulta em alterações na difusão da água nos capilares das folhas, favorecendo a movimentação deste fluído no produto (Goneli et Madamba et al (1996), os valores do coeficiente de difusão efetivo para a secagem de produtos agrícolas apresentam-se na ordem de 10 -9 m 2 s -1 a 10 -11 m 2 s -1 . Por outro lado, para a secagem de folhas de aroeira, Goneli et al (2014), encontraram magnitudes de coeficientes de difusão efetivo variando entre 0,1476 × 10 -11 m 2 s -1 e 1,5811 × 10 -11 m 2 s -1 , para a faixa de temperatura de 40 a 70 ºC.…”

Section: Resultsunclassified

Cinética de secagem e difusividade efetiva em folhas de jenipapo (Genipa americana L.)

Silva

Resende

Virgolino

et al. 2015

Rev. bras. plantas med.

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1Recebido para publicação em 28/08/2014 Aceito para publicação em 14/04/2015 RESUMO: O jenipapo (Genipa americana L.) é uma espécie nativa com importância medicinal, sendo amplamente utilizada no Brasil. Em função da necessidade de conhecimento à cerca do pré-processamento desta espécie, este trabalho foi desenvolvido com o objetivo de avaliar a cinética de secagem de folhas de jenipapo (G. americana L.), bem como determinar a difusividade efetiva da água durante o processo. As folhas foram coletadas com teor de água inicial de 2,30±0,05 (decimal b.s.), e submetidas à secagem em três condições de temperatura do ar (35,3; 46,0 e 65,0°C) até atingirem o teor de água de equilíbrio. Aos dados experimentais, ajustaram-se doze modelos matemáticos, recomendados para representar o processo de secagem de produtos agrícolas. As magnitudes do coeficiente de determinação (R 2 ), do erro médio relativo (P), do erro médio estimado (SE) e do teste do qui-quadrado (χ²), foram utilizadas para verificar o grau de ajuste dos modelos. Os modelos de Henderson e Pabis modificado e Midilli apresentaram ajustes adequados aos dados experimentais, sendo o modelo de Midilli, em função de sua simplicidade, escolhido para representar a cinética de secagem das folhas de jenipapo. Aumentando a temperatura do ar de secagem de 35,3 para 46,0 e 65,0ºC houve redução no tempo de secagem das folhas de jenipapo de 91,1 para 62,5 e 24,2 horas, respectivamente. O coeficiente de difusão efetivo aumenta com a elevação da temperatura, e esta relação é descrita pela equação de Arrhenius, que apresenta energia de ativação para a difusão líquida de 33,9 kJ mol -1 . Palavras-chave:Modelo de Midilli, desidratação, plantas medicinais, energia de ativação ABSTRACT: Drying kinetics and effective diffusivity in jenipapo sheets (Genipa americana L.). The jenipapo (Genipa americana L.) is a native species with medicinal importance and is widely used in Brazil. Due to the need for knowledge about the preprocessing of this species, this work was developed to evaluate the drying kinetics of the jenipapo leaves (G. americana L.), and also to determine the effective diffusivity of water during the process. The leaves were collected with an initial moisture content of 2.30 ± 0.05 (decimal db), and dried in three conditions of air temperature (35.3, 46.0 and 65.0°C) until they reach the equilibrium moisture content. The experimental data set were twelve mathematical models, recommended to represent the drying process of agricultural products. The magnitudes of the coefficient of determination (R²), the mean relative error (P), the average estimated error (SE) and the chi-square (X²), were used in order to verify the adequacy level of the models. The Henderson, modified Pabis and Midilli models presented appropriate adjustments to the experimental data, with the model Midilli, due to its simplicity, chosen to represent the drying kinetics of the jenipapo leaves. By increasing the temperature of the drying air from 35.3 to 46.0 and 65.0ºC, there was a reduction in the dryin...

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Section: Resultsunclassified

Cinética de secagem e difusividade efetiva em folhas de jenipapo (Genipa americana L.)

Silva

Resende

Virgolino

et al. 2015

Rev. bras. plantas med.

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“…The differential entropy (ΔS) was obtained by fitting Eq. (15) to equilibrium moisture content data from the bestfitting equation (Madamba et al 1996).…”

Section: Differential Entropymentioning

confidence: 99%

“…Since there is a high degree of linear correlation between enthalpy and entropy, the compensation theory was assumed to be valid for sorption (Madamba et al 1996;Vishwakarma et al 2011). To corroborate the compensation theory, a statistical analysis test (Eq.…”

Section: Enthalpy-entropy Compensation Theorymentioning

confidence: 99%

Thermodynamic analysis of sorption isotherms of cassava (Manihot esculenta)

et al. 2012

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Sorption isotherms of cassava were determined experimentally using a static gravimetric method at 30, 45 and 60°C and within the range of 0.10-0.90 water activity. At a constant water activity, equilibrium moisture content decreased with increasing temperature. The equilibrium moisture content increased with increasing water activity at a given temperature. The experimental results were modelled using seven sorption models using non-linear regression technique. Results demonstrated that the GAB model adequately predicted equilibrium moisture content of cassava for the range of temperatures and water activities studied. The thermodynamic functions such as net isosteric heat of sorption, differential entropy of sorption, net integral enthalpy and entropy were evaluated to provide an understanding of the properties of water and energy requirements associated with the sorption behaviour. Net isosteric heat and differential entropy decreased with increasing equilibrium moisture content. The net integral enthalpy decreased while net integral entropy increased with increasing equilibrium moisture content. Net integral entropy was negative in value. All thermodynamic functions were adequately characterised by a power law model. The point of maximum stability was found between 0.053 and 0.154 kg water/kg db for cassava.

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“…where: q st is the net isosteric heat of sorption in kJ mol -1 ; a w is the water activity; R is the universal gas constant (8.314 J mol -1 K -1 ); T is the temperature in K. Net isosteric heats (q st ) and the differential entropy (S d ) of sorption at each moisture content were obtained by fitting Equation 6 to equilibrium data from the best-fitting equation (Madamba et al, 1996).…”

Section: Methodsmentioning

confidence: 99%

Moisture sorption characteristics of microalgae Spirulina platensis

Oliveira

Rosa

Moraes

et al. 2009

Braz. J. Chem. Eng.

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-In recent times, the microalgae Spirulina platensis has been used as a functional ingredient in several food applications; its process involving drying and storage steps. Moisture equilibrium data for adsorption isotherms of microalgae Spirulina were investigated at 10, 20 and 30°C and for desorption, at 40, 50 and 60°C, using the gravimetric static method. The experimental data were analyzed by GAB and BET models. The GAB equation showed the best fitting to the experimental data with R² ≈ 99% and MRE < 10%. The water surface area values calculated by GAB and BET models were very similar. The isosteric heats were determined by application of Clausius-Clapeyron equation to sorption isotherms obtained from the best-fitting equation. The isosteric heat and the entropy of desorption isotherm presented similar behavior, with a sharp change in an equilibrium moisture content of 10%. The enthalpy-entropy compensation theory was applied to the isotherms, indicating that they are enthalpy-controlled.

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Enthalpy-entropy compensation models for sorption and browning of garlic

Cited by 133 publications

References 16 publications

Cinética de secagem e difusividade efetiva em folhas de jenipapo (Genipa americana L.)

Cinética de secagem e difusividade efetiva em folhas de jenipapo (Genipa americana L.)

Thermodynamic analysis of sorption isotherms of cassava (Manihot esculenta)

Moisture sorption characteristics of microalgae Spirulina platensis

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