Isotherms and thermodynamic properties of water adsorption in ‘Cumari-do-Pará’ pepper seeds

Rodrigues, Karen C.; Silva, Hellismar W. da; Silva, Isneider L.; Santos, Samuel G. F. dos; Silva, Daniel P. da; Rodovalho, Renato S.

doi:10.1590/1807-1929/agriambi.v24n4p280-285

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Articles • Rev. bras. eng. agríc. ambient. 24 (4) • Apr 2020 • https://doi.org/10.1590/1807-1929/agriambi.v24n4p280-285 copy

Isotherms and thermodynamic properties of water adsorption in ‘Cumari-do-Pará’ pepper seeds

Isotermas e propriedades termodinâmicas de adsorção de água em sementes de pimenta Cumari-do-Pará

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

Studies related to water sorption in seeds are essential for the design and optimization of storage systems. The objective of this research was to determine and model the adsorption isotherms and calculate the latent heat of water vaporization, differential enthalpy and entropy, the isokinetic theory and Gibbs free energy for ‘Cumari-do-Pará’ pepper seeds. The equilibrium moisture contents were obtained by the static gravimetric method at temperatures of 30, 35 and 40 °C and water activities between 0.290 and 0.900 (decimal). The Chen-Clayton model is the one that best represents the water adsorption isotherms in ‘Cumari-do-Pará’ pepper seeds under the studied conditions, with 9.94% mean relative error, 0.40 mean estimated error and random distribution of residuals. The latent heat of vaporization ranged from 2,555.669 to 3,162.180 kJ kg^-1. The enthalpy, entropy and Gibbs free energy increase with the reduction in the equilibrium moisture content of the seeds. The isokinetic theory is valid for the adsorption process.

Key words:
Capsicum chinense L.; hygroscopicity; latent heat; isokinetic

Model designation	Model
$X e = [- 1 / (c T^{d})] \ln [\ln (a_{w}) / (- a T^{b})]$	Chen-Clayton	(1)
$X e = a - b \ln [- (T + c) \ln (a_{w})]$	Chung-Pfost	(2)
$X e = (- 1 / b) \ln [(T + c) \ln (a_{w}) / (- a)]$	Modified Chung-Pfost	(3)
$X e = (a + b T) / [a_{w} / {(1 - a_{w})}^{1 / c}]$	Modified Oswin	(4)
$X e = a - (b T) - c \ln (1 - a_{w})$	Smith	(5)

Models	R²	P (%)	SE (decimal)	RD	Parameters
Models	R²	P (%)	SE (decimal)	RD	a	b	c	d
Chen-Clayton	0.9646	9.9368	0.4045	RN	4.6202	0.0536	0.0562	0.3883
Chung-Pfost	0.9637	10.0878	0.4730	RN	23.6614	4.4935	-0.1321	-
Modified Chung-Pfost	0.9637	10.0878	0.4730	RN	193.5895	0.2225	-0.1312	-
Modified Oswin	0.9669	10.0221	0.4520	RN	12.7664	-0.1006	3.2190	-
Smith	0.9648	10.2602	0.4658	RN	9.7339	0.1326	5.7179	-

Regression equation	R²
$L L^{' - 1} = 1 + 0.5140 * * e x p (- 0.0156 * * X e^{1.6544 * *})$	0.9999
$Δ h_{s t} = 465.3714 * * e x p (- 0.2262 * * X e) (X e^{1.1049 * *})$	0.9999
$Δ S = 0.7309 * * e x p (- 0.2401 * * X e) (X e^{1.4151 * *})$	0.9999
$Δ G = 9796 . 3510^{n s} e x p (- 0 . 0937^{n s} X e) [X e^{(- 0.0101 * * T - 1.3411 * *)}]$	0.9984

Unidade Acadêmica de Engenharia Agrícola 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
E-mail: revistagriambi@gmail.com

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[1] Hellismar W. da Silva - E-mail: waksonhellismar@gmail.com (Corresponding author)