Determination of desorption isotherms, latent heat and isosteric heat of pequi diaspore

Sousa, Kelly A. de; Resende, Osvaldo; Carvalho, Bruno de S.

doi:10.1590/1807-1929/agriambi.v20n5p493-498

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STORAGE AND PROCESSING OF AGRICULTURAL PRODUCTS • Rev. bras. eng. agríc. ambient. 20 (5) • May 2016 • https://doi.org/10.1590/1807-1929/agriambi.v20n5p493-498 copy

Determination of desorption isotherms, latent heat and isosteric heat of pequi diaspore

Determinação das isotermas de dessorção, calor latente e calor isostérico de diásporos de pequi

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

The objective was to determine water sorption isotherms of diaspores of pequi fruits in order to obtain information on the amount of water that this product desorbs at the temperatures of 10, 20, 30 and 40 °C and water activities from 0.20 to 0.89, adjusting different mathematical models to experimental data, and to determine its latent heat and isosteric heat. The equilibrium moisture content was obtained through the indirect static method, using the device Hygropalm Model Aw 1. The Modified Henderson model was the one that best fitted the data and was selected to predict the equilibrium moisture content of pequi diaspore. It was observed that the higher the temperature for the same equilibrium moisture content (% d.b.), the higher the water activity values. As temperature values increased, there was a reduction in the vaporization latent heat of the product. Isosteric heat values of diaspores of pequi fruits in the moisture content range of 4.02 to 16.63 (% d.b.) varied from 2,776.49 to 2,558.39 kJ kg^-1.

Key words:
hygroscopic equilibrium; water activity; thermodynamic properties

Water activity (decimal)	Temperature (°C)
Water activity (decimal)	10	20	30	40
0.20	4.02	-	-	-
0.22	-	4.02	-	-
0.25	-	-	4.32	-
0.26	-	-	-	4.27
0.28	6.06	-	-	-
0.31	-	6.05	-	-
0.32	-	-	6.22	-
0.33	-	-	-	6.21
0.41	8.33	-	-	-
0.43	-	-	7.84	-
0.44	-	8.29	-	7.7
0.65	-	-	10.83	-
0.68	13.39	-	-	10.72
0.70	-	13.41	-	-
0.84	-	-	15.14	15.2

Models	Coefficients	R²	P (%)	SE (decimal)	χ²
Modified BET	a = 12.18877^* * Significant at 0.05 by t-test;	0.9753	6.095	1.916	0.480
	b = 1.86850^ns ns Not significant
	c = 0.50383^ Significant at 0.01 by t-test;
BET	a = 61.73712^ Significant at 0.01 by t-test;	0.5530	25.754	33.591	8.147
BET	b = 0.34823^ Significant at 0.01 by t-test;	0.5530	25.754	33.591	8.147
Chung Pfost	a = 31.89414^ Significant at 0.01 by t-test;	0.9819	6.612	1.404	0.351
	b = 5.26625^ Significant at 0.01 by t-test;
	c = 93.57341^* * Significant at 0.05 by t-test;
Copace	a = 1.329342^ Significant at 0.01 by t-test;	0.9762	8.396	1.843	0.461
	b = 0.005294^ Significant at 0.01 by t-test;
	c = 1.879629^ Significant at 0.01 by t-test;
Modified Halsey	a = 4.124731^ Significant at 0.01 by t-test;	0.9335	12.872	5.152	1.288
	b = 0.010170^ns ns Not significant
	c = 2.020375^ Significant at 0.01 by t-test;
Henderson	a = 0.000067^ Significant at 0.01 by t-test;	0.9799	6.658	1.511	0.367
Henderson	b = 1.637354^ Significant at 0.01 by t-test;	0.9799	6.658	1.511	0.367
Modified Henderson	a = 0.00019^ Significant at 0.01 by t-test;	0.9869	5.973	1.01	0.253
	b = 86.30364^ Significant at 0.01 by t-test;
	c = 1.62142^ Significant at 0.01 by t-test;
Modified Oswin	a = 9.514117^ Significant at 0.01 by t-test;	0.9624	9.651	2.909	0.727
	b = -0.043465^* * Significant at 0.05 by t-test;
	c = 2.558607^ Significant at 0.01 by t-test;
Peleg	a = 5748.253^ns ns Not significant	0.9771	5.690	1.835	0.474
	b = 58.158^ns ns Not significant
	c = 17.485^ Significant at 0.01 by t-test;
	d= 0.932^ Significant at 0.01 by t-test;
Kuhn	a = 1.927009^ Significant at 0.01 by t-test;	0.8382	18.692	12.54	3.134
Kuhn	b = 4.841493^ Significant at 0.01 by t-test;	0.8382	18.692	12.54	3.134
Sigma Copace	a = 0.533370^ Significant at 0.01 by t-test;	0.9539	11.417	3.571	0.893
	b = 0.005234^* * Significant at 0.05 by t-test;
	c = 1.028713^ Significant at 0.01 by t-test;
Smith	a = 3.467185^ Significant at 0.01 by t-test;	0.9434	10.582	4.253	1.031
Smith	b = 6.846135^ Significant at 0.01 by t-test;	0.9434	10.582	4.253	1.031

X_e (% d.b.)	Temperature (°C)
X_e (% d.b.)	10	20	30	40
04.016	0.160	0.175	0.190	0.204
04.021	0.160	0.175	0.190	0.205
04.268	0.175	0.191	0.207	0.223
04.320	0.178	0.195	0.211	0.227
06.047	0.287	0.312	0.336	0.359
06.060	0.288	0.313	0.337	0.360
06.214	0.298	0.323	0.348	0.371
06.220	0.298	0.324	0.348	0.372
07.701	0.394	0.425	0.454	0.482
07.839	0.403	0.434	0.464	0.491
08.291	0.431	0.464	0.494	0.523
08.334	0.434	0.467	0.497	0.526
10.720	0.575	0.611	0.644	0.675
10.830	0.581	0.618	0.651	0.681
13.390	0.707	0.742	0.773	0.800
13.410	0.708	0.743	0.774	0.801
15.140	0.777	0.809	0.836	0.860
15.200	0.779	0.811	0.838	0.862
16.630	0.825	0.854	0.879	0.899

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[1] kellyapsousa@yahoo.com.br (Corresponding author)