Abstract

DOMINGUEZ-DOMINGUEZ, S; DOMINGUEZ-LOPEZ, A; GONZALEZ-HUERTA, A  and  NAVARRO-GALINDO, S. Imbibition kinetics and moisture sorption isotherms of roselle seeds (Hibiscus sabdariffa L.). Rev. Mex. Ing. Quím [online]. 2007, vol.6, n.3, pp.309-316. ISSN 1665-2738.

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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