<b>Adsorption isotherms and thermodynamic properties of <i>Carthamus tinctorius</i> L. seeds</b>

Bessa, Jaqueline F. V.; Resende, Osvaldo; Oliveira, Daniel E. C. de; Lima, Rayr R. de; Quequeto, Wellytton D.; Siqueira, Valdiney C.

doi:10.1590/1807-1929/agriambi.v25n10p696-702

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Articles • Rev. bras. eng. agríc. ambient. 25 (10) • Oct 2021 • https://doi.org/10.1590/1807-1929/agriambi.v25n10p696-702 copy

**Adsorption isotherms and thermodynamic properties of Carthamus tinctorius L. seeds** ¹ 1 Research developed at Instituto Federal de Educação, Ciência e Tecnologia Goiano, Rio Verde, GO, Brazil

Isotermas de adsorção e propriedades termodinâmicas de sementes de Carthamus tinctorius L.

Authorship SCIMAGO INSTITUTIONS RANKINGS

HIGHLIGHTS:

The Chung-Pfost model showed the best fit to describe the phenomenon of adsorption of safflower seeds.

For constant water activity, the values of the equilibrium moisture content decreased with increasing temperature.

The thermodynamic properties were influenced by the moisture content of the seeds.

ABSTRACT

Safflower is a crop of high economic value with high oil concentration in its seeds and great industrial versatility, besides various benefits to human health. As with other agricultural crops, it is common to store safflower to make it available in different periods of the year and, due to its hygroscopic characteristics, studies evaluating the effect of temperature and air relative humidity on its moisture content become relevant. Thus, the objective of the present study was to determine the water adsorption isotherms of safflower seeds and analyze their thermodynamic properties. Moisture contents of 6.5, 6.9, 7.3, 7.7, 8.3 and 9.1% (dry basis) were obtained by adsorption under controlled conditions of temperature (30 °C) and relative air humidity (90%). The adsorption isotherms were obtained by the indirect static method at different temperatures (10, 20, 30 and 40 °C). As temperature increased, for the same moisture content, there was an increase in water activity and, for constant water activity, the values of equilibrium moisture content decreased with increasing temperature. Chung-Pfost model showed the best fit to describe the phenomenon of hygroscopicity of safflower seeds. The thermodynamic properties were influenced by the moisture content of the seeds, reducing the energy necessary for water absorption in the product with the increase in adsorption, and the enthalpy-entropy theory was controlled by enthalpy.

Key words:
equilibrium moisture content; hygroscopicity; oilseed

Model	Model designation
$X e = a - b \ln [- (T + c) \ln (a_{w})]$	Chung-Pfost	(1)
$X e = e x p [a - (b T) + (c a_{w})]$	Copace	(2)
$X e = (a b c a_{w}) / [(1 - c a_{w}) (1 - c a_{w} + b c a_{w})]$	GAB	(3)
$X e = {[e x p (a - b T) / - \ln (a_{w})]}^{1 / c}$	Modified Halsey	(4)
$X e = a (a_{w}^{b / T c})$	Sabbah	(5)
$X e = e x p \{a - (b T) + [c e x p (a_{w})]\}$	Sigma Copace	(6)
$X e * = (a + b T) / {[a_{w} / (1 - a_{w})]}^{1 / c}$	Modified Oswin	(7)
$X e = {[\ln (1 - a_{w}) / (a (T^{b}))]}^{1 / c}$	Cavalcanti Mata	(8)
$X e = {[\ln (1 - a_{w}) / (- a (T + b))]}^{1 / c}$	Modified Henderson	(9)
$X e = {[\ln (1 - a_{w}) / (- a (T + 273.16))]}^{1 / b}$	Henderson	(10)
$X e = [1 / [(1 - a_{w}) (1 / a b + ((a - 1) / a b))]]$	BET	(11)

Moisture content (% d.b.)	Temperature (°C)
Moisture content (% d.b.)	10	20	30	40
7.21	0.333	-	-	-
7.34	-	0.378	-	-
7.31	-	-	0.400	-
7.25	-	-	-	0.422
9.63	0.433	-	-	-
9.62	-	0.497	-	-
9.67	-	-	0.521	-
9.49	-	-	-	0.538
11.93	-	-	-	0.622
12.06	-	0.573	-	-
12.07	-	-	0.611	-
12.19	0.527	-	-	-
12.99	0.558	-	-	-
13.29	-	0.620	-	-
13.31	-	-	0.650	-
13.03	-	-	-	0.669

Models	Parameters		SE (decimal)	P (%)	χ² (decimal)	R² (%)	Residual distribution
Chung-Pfost	a =	23.1706**	0.069	0.677	0.0047	99.45	R
	b =	3.6272**
	c =	117.0422**
Copace	a =	1.1790**	0.088	0.885	0.0077	99.09	R
	b =	0.0032**
	c =	1.560965**
GAB	a =	3.659**	0.292	2.992	0.0855	89.96	B
	b =	-18.2981^ns
	c =	0.8135**
Modified Halsey	a =	3.887411**	0.083	0.749	0.0070	99.18	R
	b =	0.006902**
	c =	2.16336**
Sabbah	a =	15.42607**	0.132	1.291	0.0175	97.95	R
	b =	0.93362**
	c =	0.07015**
Sigma Copace	a =	0.564856**	0.077	0.763	0.0060	99.25	R
	b =	0.003199**
	c =	0.84816**
Modified Oswin	a =	7.105151**	0.081	0.784	0.0066	99.22	R
	b =	-0.021172**
	c =	2.737047**
Cavalcanti Mata	a =	-0.017103**	0.103	0.997	0.0105	98.76	R
	b =	0.1225**
	c =	1.769402**
Modified Henderson	a =	0.0001**	0.092	0.936	0.0084	99.02	R
	b =	148.8543**
	c =	1.7671**
Henderson	a =	0.000081**	0.152	1.590	0.0230	97.18	R
Henderson	b =	1.789511**	0.152	1.590	0.0230	97.18	R
BET	a =	52.29137**	0.776	7.190	0.6018	25.96	B
BET	b =	0.34238**	0.776	7.190	0.6018	25.96	B

Xe (% d.b.)	L/L’	Xe (% d.b.)	L/L’
6.57	1.0816	7.8300	1.0576
6.60	1.0808	8.3400	1.0500
6.89	1.0747	8.3900	1.0494
6.90	1.0745	8.4000	1.0493
6.91	1.0742	8.4200	1.0449
7.30	1.0667	9.0300	1.0414
7.31	1.0665	9.0900	1.0407
7.75	1.0589	9.1000	1.0405
7.78	1.0583	9.1400	1.0401
7.80	1.0582

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] * Corresponding author - E-mail: wellytton_quequeto@hotmail.com

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Adsorption isotherms and thermodynamic properties of Carthamus tinctorius L. seeds 1 1 Research developed at Instituto Federal de Educação, Ciência e Tecnologia Goiano, Rio Verde, GO, Brazil

Isotermas de adsorção e propriedades termodinâmicas de sementes de Carthamus tinctorius L.

HIGHLIGHTS:

ABSTRACT

**Adsorption isotherms and thermodynamic properties of Carthamus tinctorius L. seeds** ¹ 1 Research developed at Instituto Federal de Educação, Ciência e Tecnologia Goiano, Rio Verde, GO, Brazil