30D-22 |
Determination of water sorption isosteric heat in papaya (Carica papaya ) by thermal analysis |
M. A. GARCÍA-ALVARADO1, M. A. Salgado-Cervantes, G. C. Rodríguez-Jimenes, J. M. Tejero-Andrade, and T. L. Rosado-Zarrabal. (1) UNIDA, Instituto Tecnológico de Veracruz, Av. Miguel Angel de Quevedo 2779, P.O. Box 1420, Veracruz, 91860, Mexico A common method used in the evaluation of water sorption isosteric heat in foods is the estimation from sorption isotherms and Clausius-Clapeyron equation. However this method has long times for experimental (until two weeks), and presents uncertainties at low moistures levels. Thermal analysis represents an alternative for the evaluation of this thermodynamic property, which application in foods is not generalized. In this work the water sorption isosteric heat in papaya fruit (Carica papaya ) was evaluated by means of thermal analysis (DSC and TGA). The values obtained were compared with those obtained from sorption isotherms and Clausius-Clapeyron equation. Experimental sorption isotherms were obtained by static gravimetric method. The isotherms were obtained with 5g samples of mature papaya both by dehydratation and rehydratation. Saturated salt and sulfuric acid solutions were used at temperatures of 5, 15, 25, 30 and 40 C. The papaya samples at different moisture content were ground and placed into DSC and TGA sample dishes in 5 mg portions. The thermal analysis was run at heating rate of 2 C/min and temperatures of 25-150 C in both equipments. Experimental sorption isotherms did not show evidence of temperature effect, like it has been reported by other authors in fruits with high sugars content. Therefore, by Clausius-Clapeyron equation the water isosteric sorption heat must be equal to water latent heat. The integral water sorption isosteric heat evaluated by thermal analysis did not show significant difference with respect to a thermal analysis of pure water. Then, the thermal analysis confirms the thermodynamic behavior of water estimated from sorption isotherm. These results confirm the sorption isotherms of fruits reported by several authors in which the temperature effect is not evident.
Session 30D, Food Engineering: Physical and chemical properties
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