Cinética de imbibición e isotermas de adsorción de humedad de la semilla de jamaica (Hibiscus sabdariffa L.)
Imbibition kinetics and moisture sorption isotherms of roselle seeds (Hibiscus sabdariffa L.)
S. Domínguez–Domínguez1, A. Domínguez–López1*, A. González–Huerta1 y S. Navarro–Galindo2
1 Programa de Maestría y Doctorado en Ciencias Agropecuarias y Recursos Naturales. Universidad Autónoma del Estado de México. Campus Universitario El Cerrillo A. P. 435. Toluca, Estado de México. C. P. 50200. México. * Autor para correspondencia: E–mail: adl@uaemex.mx Tel. y Fax: (722) 296 5518
2 Campo Experimental Chilpancingo. Delegación Estatal SAGARPA. Av. Ruffo Figueroa s/n, Col. Burócratas. Chilpancingo, Guerrero. Mexico.
]]>Recibido 15 de Diciembre 2006
Aceptado 23 de Noviembre 2007
Resumen
La jamaica es un arbusto que se cultiva para comercializar el cáliz de sus flores, pero como subproducto se obtienen las semillas, que por su valor nutritivo y alto rendimiento representan un potencial económico considerable. El objetivo de este trabajo fue describir la cinética de imbibición y las isotermas de adsorción de humedad a 25, 35 y 45°C en tres variedades cultivadas en México ("Criolla", "China" y "Sudán"). Los resultados mostraron que el proceso de imbibición describe una curva que se ajusta al modelo de Weibull, con coeficientes α de 12.99, 8.81 y 2.21 horas y β de 0.83, 1.70 y 0.72 para las variedades Criolla, China y Sudán, respectivamente. Los modelos de GAB, y de Chung–Pfost describieron adecuadamente las isotermas de adsorción. La humedad de la capa monomolecular (coeficiente a del modelo de GAB) resultó entre 3.97 y 5.71% b.s., lo cual representa una actividad de agua entre 0.1 y 0.30. Los calores isostéricos totales de adsorción obtenidos en el intervalo de humedades de equilibrio de 6 a 22% b.s., oscilaron entre 52.85 y 42.90 kJmol–1, 60.99 y 43.41 kJmol–1 y 51.23 y 43.20 kJmol–1para las variedades Criolla, China y Sudán, respectivamente. A humedades de equilibrio iguales o superiores a 12 % b.s., el calor isostérico fue similar a la entalpía de vaporización del agua, pero a humedades inferiores a 6% b.s., éste alcanzó los valores más elevados.
Palabras clave: Hibiscus sabdariffa L., semillas de jamaica, imbibición, isotermas de adsorción de humedad, distribución de Weibull, modelo de Guggenheim–Anderson–de Boer, modelo de Chung–Pfost.
Abstract
Roselle is a shrub cultivated with the purpose of using the calyx of their flowers. However, the seeds are obtained as by–product and have a considerable economic potential owing their nutritive value and yield. The aim of this work was to describe the imbibition kinetics and moisture sorption isotherms at 25, 35 and 45°C, of three Roselle seed cultivars produced in Mexico ("Criollo", "China" and "Sudan"). Results indicated that the imbibition process describes a curve that follows the Weibull distribution with a α coefficient of 12.99, 8.81 and 2.21 hours and a β coefficient of 0.83, 1.70 and 0.72 for the Criollo, China, and Sudan cultivars, respectively. The GAB and the Chung–Pfost models describe appropriately the moisture sorption isotherms. Monolayer moisture content (a coefficient of GAB model) was 3.97 to 5.71 d.b. which represents a water activity value ranging from 0.1 to 0.30. Total isosteric heats of sorption, in the equilibrium moisture content region of 6 to 22% d.b., ranging from 52.85 to 42.90 kJmol–1, for the Criollo cultivar, 60.99 to 43.41 kJmol–1, for the China cultivar and 51.23 to 43.20 kJmol–1, for the Sudan cultivar. At equilibrium moisture content up to 12% d.b., total isosteric heat of sorption was similar to the vaporization enthalpy of water, but at a moisture content lower to 6% d.b. this variable reached the highest values.
]]> Keywords: Hibiscus sabdariffa L., roselle seeds, imbibition, moisture sorption isotherms, Weibull distribution, Guggenheim–Anderson–de Boer model, Chung–Pfost model.
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