Kinetics and thermodynamic properties related to the drying of 'Cabacinha' pepper fruits

Silva, Hellismar W. da; Rodovalho, Renato S.; Velasco, Marya F.; Silva, Camila F.; Vale, Luís S. R.

doi:10.1590/1807-1929/agriambi.v20n2p174-180

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STORAGE AND PROCESSING OF AGRICULTURAL PRODUCTS • Rev. bras. eng. agríc. ambient. 20 (2) • Feb 2016 • https://doi.org/10.1590/1807-1929/agriambi.v20n2p174-180 copy

Kinetics and thermodynamic properties related to the drying of 'Cabacinha' pepper fruits

Cinética e propriedades termodinâmicas relacionadas à secagem dos frutos de pimenta Cabacinha

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

The objective of this study was to determine and model the drying kinetics of 'Cabacinha' pepper fruits at different temperatures of the drying air, as well as obtain the thermodynamic properties involved in the drying process of the product. Drying was carried out under controlled conductions of temperature (60, 70, 80, 90 and 100 °C) using three samples of 130 g of fruit, which were weighed periodically until constant mass. The experimental data were adjusted to different mathematical models often used in the representation of fruit drying. Effective diffusion coefficients, calculated from the mathematical model of liquid diffusion, were used to obtain activation energy, enthalpy, entropy and Gibbs free energy. The Midilli model showed the best fit to the experimental data of drying of 'Cabacinha' pepper fruits. The increase in drying temperature promoted an increase in water removal rate, effective diffusion coefficient and Gibbs free energy, besides a reduction in fruit drying time and in the values of entropy and enthalpy. The activation energy for the drying of pepper fruits was 36.09 kJ mol^-1.

Key words:
Capsicum chinense L.; moisture ratio; enthalpy; activation energy

Model designation	Model	n°
Approximation of Diffusion	RX = a exp(-k t) + (1 - a) exp(-k b t)	(3)
Two-Term	RX = a exp(-k t) + b exp(-c t)	(4)
Logarithmic	RX = a exp(-k t) + b	(5)
Midilli	RX = a exp(-k tb) + c t	(6)
Modified Midilli	RX = exp(-k tn) + a t	(7)
Newton	RX = exp(-k t)	(8)
Page	RX = exp(-k tn)	(9)
Modified Page	RX = exp(-(k t)n)	(10)
Verna	RX = a exp(-k t) + (1 - a) exp(-b t)	(11)
Wang and Singh	RX = 1 + (a t) + (b t²)	(12)

Models	R²	SE	RSS	RD	R²	SE	RSS	RD	R²	SE	RSS	RD
	60 °C				70 °C				80 °C
Approximation of Diffusion	0.9977	0.024	0.054	BD	0.9944	0.041	0.154	BD	0.9908	0.054	0.270	BD
Two-Term	0.9846	0.062	0.361	BD	0.9855	0.066	0.397	BD	0.9974	0.030	0.078	RD
Logarithmic	0.9979	0.023	0.050	BD	0.9957	0.036	0.119	BD	0.9931	0.047	0.203	BD
Midilli	0.9991	0.015	0.020	RD	0.9990	0.018	0.029	RD	0.9991	0.017	0.026	RD
Modified Midilli	0.9990	0.016	0.025	RD	0.9988	0.019	0.033	RD	0.9989	0.019	0.032	RD
Newton	0.9797	0.070	0.477	BD	0.9792	0.076	0.569	BD	0.9793	0.079	0.604	BD
Page	0.9969	0.028	0.074	RD	0.9980	0.024	0.055	RD	0.9987	0.020	0.038	RD
Modified Page	0.9969	0.028	0.074	RD	0.9980	0.024	0.055	RD	0.9987	0.020	0.038	RD
Verna	0.9842	0.062	0.372	BD	0.9836	0.070	0.449	BD	0.9840	0.072	0.468	BD
Wang and Singh	0.9988	0.017	0.028	BD	0.9973	0.028	0.075	BD	0.9962	0.034	0.111	BD
	90 °C				100 °C
Approximation of diffusion	0.9889	0.060	0.329	BD	0.9888	0.061	0.329	BD	-	-	-	-
Two-term	0.9875	0.065	0.371	BD	0.9883	0.064	0.345	BD	-	-	-	-
Logarithmic	0.9916	0.052	0.248	BD	0.9916	0.053	0.247	BD	-	-	-	-
Midilli	0.9992	0.017	0.025	RD	0.9992	0.017	0.025	RD	-	-	-	-
Modified Midilli	0.9990	0.018	0.031	RD	0.9990	0.018	0.029	RD	-	-	-	-
Newton	0.9803	0.078	0.582	BD	0.9812	0.076	0.552	BD	-	-	-	-
Page	0.9989	0.019	0.033	RD	0.9990	0.018	0.030	RD	-	-	-	-
Modified Page	0.9989	0.019	0.033	RD	0.9990	0.018	0.030	RD	-	-	-	-
Verna	0.9846	0.071	0.454	BD	0.9883	0.076	0.510	BD	-	-	-	-
Wang and Singh	0.9944	0.042	0.167	BD	0.9927	0.048	0.217	BD	-	-	-	-

Coefficients	Temperature (°C)					Equations	R²
Coefficients	60	70	80	90	100	Equations	R²
a	0.9778	0.9814	0.9779	0.9765	0.9803	a = 0.979^* * Mean value;	^ns ns Not significant
k	0.0267	0.0503	0.0797	0.1235	0.2097	k = 0.001^ Significant at 0.01 by t-test; . exp(0.048^ Significant at 0.01 by t-test; . T)	0.9829
n	1.3754	1.5455	1.6604	1.6950	1.6713	n = -1.573^ Significant at 0.01 by t-test; + 0.073^ Significant at 0.01 by t-test; . T + (-4.054^ Significant at 0.01 by t-test; . 10-4) . T²	0.9342
b	-0.0029	-0.0021	-0.0010	-0.0006	-0.0005	b = -0.024^ Significant at 0.01 by t-test; + (5.049^ Significant at 0.01 by t-test; . 10-4) . T + (-2.685^ Significant at 0.01 by t-test; . 10-6) . T²	0.9787

Thermodynamic properties	Temperature (°C)
Thermodynamic properties	60	70	80	90	100
ΔH x 10² (J moL^-1)	333.233	332.402	331.571	330.739	329.908
ΔS (J moL^-1 K^-1)	-295.751	-295.997	-296.235	-296.468	-296.693
ΔG x 10³ (J moL^-1)	131.853	134.811	137.773	140.736	143.702

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[1] waksonhellismar@gmail.com (Corresponding author)