Thermodynamic properties and drying kinetics of ‘okara’

Guimarães, Rafaiane M.; Oliveira, Daniel E. C. de; Resende, Osvaldo; Silva, Jhessika de S.; Rezende, Thaisa A. M. de; Egea, Mariana B.

doi:10.1590/1807-1929/agriambi.v22n6p418-423

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ARTICLE • Rev. bras. eng. agríc. ambient. 22 (6) • June 2018 • https://doi.org/10.1590/1807-1929/agriambi.v22n6p418-423 copy

Thermodynamic properties and drying kinetics of ‘okara’

Propriedades termodinâmicas e cinética de secagem de okara

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

‘Okara’ is the insoluble part obtained after the aqueous extraction of soybeans, generated in large quantities as a by-product of the ‘tofu’ industry or soybean water-soluble extract. This work aimed to study ‘okara’ convective drying kinetics, determine the effective diffusion coefficient, and obtain activation energy and thermodynamic properties under different drying conditions. The by-product ‘okara’ was obtained from the processing of BRS 257 soybean water-soluble extract, homogenized and dried in a forced-air oven at temperatures of 40, 50, 60 and 70 °C until constant weight. Among the analysed models, Wang & Singh was selected to represent the drying phenomenon. Effective diffusion coefficient increased with the temperature rise, and the activation energy for the net diffusion in the drying was 28.15 kJ mol^-1. Enthalpy and Gibbs free energy increased with the elevation of drying temperature.

Key words:
mathematical modeling; activation energy; diffusion coefficient

Model	Temperature (°C)
	40			50			60			70
	P	R²	SE	P	R²	SE	P	R²	SE	P	R²	SE
Wang & Singh	1.98	0.9993	0.010	1.53	0.9992	0.010	5.98	0.9995	0.007	2.06	0.9992	0.009
Verma	31.20	0.9870	0.043	20.08	0.9958	0.023	18.68	0.9980	0.015	4.09	0.9987	0.011
Thompson	31.20	0.9870	0.042	40.20	0.9861	0.041	60.08	0.9840	0.042	25.61	0.9783	0.046
Page	14.72	0.9960	0.024	20.66	0.9948	0.025	25.82	0.9968	0.019	10.69	0.9969	0.017
Newton	31.20	0.9870	0.041	40.20	0.9861	0.040	60.07	0.9840	0.040	25.60	0.9783	0.044
Midilli	5.15	0.9990	0.012	7.44	0.9991	0.011	9.57	0.9991	0.011	1.04	0.9999	0.004
Logarithmic	7.22	0.9988	0.013	8.56	0.9991	0.011	16.82	0.9984	0.014	2.59	0.9995	0.007
Henderson & Pabis	28.77	0.9887	0.040	36.97	0.9877	0.038	51.65	0.9886	0.035	21.37	0.9860	0.037
Two-Term Exponential	16.33	0.9963	0.023	40.20	0.9861	0.041	60.07	0.9840	0.042	25.61	0.9783	0.046
Two Terms	13.66	0.9973	0.020	36.96	0.9877	0.041	25.42	0.9973	0.018	21.37	0.9860	0.039
Approximation of Diffusion	14.84	0.9967	0.022	20.08	0.9958	0.023	18.68	0.9980	0.015	4.09	0.9987	0.011

Parameters	Temperature (°C)
Parameters	40	50	60	70
a	-0.041815**	-0.070555**	-0.09207**	-0.123793**
b	0.000435**	0.001248**	0.002109**	0.003557**

Temperature (°C)	Thermodynamic properties
Temperature (°C)	∆H (J mol^-1)	∆S (J mol^-1 K^-1)	∆G (J mol^-1)
40	25548.51	-168.39	78281.17
50	25465.37	-168.66	79966.42
60	25382.23	-168.91	81654.25
70	25299.09	-169.15	83344.58

Departamento de Engenharia Agrícola - UFCG Unidade Acadêmica de Engenharia Agrícola, UFCG, Av. Aprígio Veloso 882, Bodocongó, Bloco CM, 1º andar, CEP 58429-140, Campina Grande, PB, Brasil, Tel. +55 83 2101 1056 - Campina Grande - PB - Brazil
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[1] rafaiane.guimaraes@ifgoiano.edu.br (Corresponding author)