Modelling the effect of temperature on the water sorption isotherms of chitosan films

AGUIRRE-LOREDO, Rocio Yaneli; RODRIGUEZ-HERNANDEZ, Adriana Inés; VELAZQUEZ, Gonzalo

doi:10.1590/1678-457X.09416

Rocio Yaneli AGUIRRE-LOREDO

Centro de Investigación en Ciencia Aplicada y Tecnología Avanzada Unidad Querétaro – CICATA, Instituto Politécnico Nacional – IPN, Querétaro, Qro., México

Adriana Inés RODRIGUEZ-HERNANDEZ

Instituto de Ciencias Agropecuarias, Universidad Autónoma del Estado de Hidalgo – UAEH, Tulancingo, Hidalgo, México

Gonzalo VELAZQUEZ ^**Corresponding author: gvelazquezd@ipn.mx

Centro de Investigación en Ciencia Aplicada y Tecnología Avanzada Unidad Querétaro – CICATA, Instituto Politécnico Nacional – IPN, Querétaro, Qro., México

*Corresponding author: gvelazquezd@ipn.mx

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Figure 1
Moisture adsorption isotherms of chitosan films as a function of the temperature (symbols), fitted to the original GAB model (lines).

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Figure 2
Monolayer moisture content of chitosan films as a function of the temperature calculated from the GAB and BET models.

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Table 1
a_w values of several salts as a function of temperature.

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Table 2
Isotherm models used for experimental data fitting (Aviara et al., 2004Aviara, N. A., Ajibola, O. O., & Oni, S. A. (2004). Sorption equilibrium and thermodynamic characteristics of soya bean. Biosystems Engineering, 87(2), 179-190. http://dx.doi.org/10.1016/j.biosystemseng.2003.11.006.
http://dx.doi.org/10.1016/j.biosystemsen... ; Ayala Aponte et al., 2011Ayala Aponte, A., Serna Cock, L., & Rodriguez de la Pava, G. (2011). Moisture adsorption isotherms in yellow pitahaya (Selenicereus megalanthus). DYNA, 78, 7-14.; Furmaniak et al., 2007Furmaniak, S., Terzyk, A. P., Gauden, P. A., & Rychlicki, G. (2007). Applicability of the generalised D’Arcy and Watt model to description of water sorption on pineapple and other foodstuffs. Journal of Food Engineering, 79(2), 718-723. http://dx.doi.org/10.1016/j.jfoodeng.2006.02.036.
http://dx.doi.org/10.1016/j.jfoodeng.200... ; Gálvez et al., 2006Gálvez, A. V., Aravena, E. L., & Mondaca, R. L. (2006). Isotermas de adsorción en harina de maíz ( L.). Zea maysFood Science and Technology, 26(4), 821-827. http://dx.doi.org/10.1590/S0101-20612006000400017.
http://dx.doi.org/10.1590/S0101-20612006... ; Timmermann et al., 2001Timmermann, E. O., Chirife, J., & Iglesias, H. A. (2001). Water sorption isotherms of foods and foodstuffs: BET or GAB parameters? Journal of Food Engineering, 48(1), 19-31. http://dx.doi.org/10.1016/S0260-8774(00)00139-4.
http://dx.doi.org/10.1016/S0260-8774(00)... ).

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Table 3
Sorption isotherm model parameters and coefficient of regression R² values for chitosan films.

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(11)

Salt	Preparation amount		aw
	Salt (g)	Water (mL)	15 °C	20 °C	25 °C	30 °C
CH₃COOK	200	70	0.2340	0.2311	0.2251	0.2161
MgCl₂	200	25	0.3330	0.3307	0.3278	0.3244
K₂CO₃	200	90	0.4315	0.4316	0.4316	0.4317
NaBr	200	100	0.6070	0.5910	0.5760	0.5600
NaCl	200	60	0.7561	0.7547	0.7529	0.7509
KCl	200	80	0.8592	0.8511	0.8434	0.8362
BaCl₂	200	70	0.9110	0.9050	0.9040	0.9010

Model	Original equation	Modified equation	Parameters
BET	$X = \frac{x_{m} c a_{w}}{(1 - a_{w}) (1 + (c - 1) a_{w})}$ (1)	$X = \frac{(A + B T) C a_{w}}{(1 - a_{w}) (1 - a_{w} + C a_{w})}$ (2)	x_m: monolayer water content c: energy difference between the upper layers and the monolayer A, B y C: empirical parameters
GAB	$X = \frac{x_{m} c k a_{w}}{(1 - k a_{w}) (1 - k a_{w} + c k a_{w})}$ (3)	$X = \frac{x_{m} + k \frac{c}{T} a_{w}}{(1 - k a_{w}) (1 - k a_{w} + \frac{c}{T} k a_{w})}$ (4)	x_m: monolayer water content c: energy difference between the upper layers and the monolayer k: degree of freedom of water molecules
Henderson	$X = 0.01 {(\frac{- \log (1 - a_{w})}{10^{A}})}^{\frac{1}{B}}$ (5)	$X = {[- \frac{\ln (1 - a_{w})}{A * (B + T)}]}^{\frac{1}{C}}$ (6)	A, B y C: empirical parameters
Halsey	$X = {[\frac{A}{\ln (1 / a_{w})}]}^{\frac{1}{B}}$ (7)	$X = {[- \frac{\exp (A + B T)}{\ln a_{w}}]}^{\frac{1}{C}}$ (8)	A, B y C: empirical parameters
Oswin	$X = A {(\frac{a_{w}}{1 - a_{w}})}^{B}$ (9)	$X = (A + B T) {[\frac{a_{w}}{1 - a_{w}}]}^{\frac{1}{C}}$ (10)	A, B y C: empirical parameters

Model				Parameters
			Temp (°C)	x_m	c	k	A	B	C
T	a_w Range	0-0.75	15	10.99	15,985.16	-	-	-	-
	R²=	0.9244	20	10.29	1,757.52	-	-	-	-
	%E=	20.1029	25	8.03	13,361.27	-	-	-	-
			30	6.75	6,281.44	-	-	-	-
Modified BET	a_w Range	0-0.75	15	9.59	4,490.89	-	-	-	-
	R²=	0.9215	20	8.35	3,181.96	-	-	-	-
	%E=	13.9420	25	6.38	2,637.54	-	-	-	-
			30	5.74	1,787.79	-	-	-	-
GAB	a_w Range	0-0.9	15	16.74	9.15	0.84	-	-	-
	R²=	0.9714	20	15.27	9.37	0.82	-	-	-
	%E=	7.9196	25	10.15	3,887.34	0.85	-	-	-
			30	7.81	482.41	0.89	-	-	-
Modified GAB	a_w Range	0-0.9	15	16.27	10.94	0.85	-	-	-
	R²=	0.9847	20	16.79	7.84	0.80	-	-	-
	%E=	8.3945	25	11.22	18.40	0.84	-	-	-
			30	8.31	15.33	0.90	-	-	-
Henderson	a_w Range	0-0.9	15	-	-	-	1.28	-4.90	-
	R²=	0.9666	20	-	-	-	1.34	-5.05	-
	%E=	11.8945	25	-	-	-	1.47	-5.38	-
			30	-	-	-	1.21	-4.38	-
Modified Henderson	a_w Range	0-0.9	15-30	-	-	-	0.00055	1.15	1.31
	R²=	0.9729
	%E=	11.0574
Halsey	a_w Range	0-0.9	15	-	-	-	321.11	1.89	-
	R²=	0.9807	20	-	-	-	283.75	1.92	-
	%E=	12.4197	25	-	-	-	255.68	2.03	-
			30	-	-	-	77.50	1.74	-
Modified Halsey	a_w Range	0-0.9	15-30	-	-	-	6.79	-0.06	1.90
	R²=	0.9703
	%E=	9.9392
Oswin	a_w Range	0-0.9	15	-	-	-	25.96	0.44	-
	R²=	0.9813	20	-	-	-	23.27	0.43	-
	%E=	8.6661	25	-	-	-	18.77	0.40	-
			30	-	-	-	15.17	0.47	-
Modified Oswin	a_w Range	0-0.9	15-30	-	-	-	33.38	2.13	-0.61
	R²=	0.9781
	%E=	9.6822

[1] *Corresponding author: gvelazquezd@ipn.mx

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Modelling the effect of temperature on the water sorption isotherms of chitosan films

Abstract