Air-drying and rehydration characteristics of the brown seaweeds, Ascophylum nodosum and Undaria pinnatifida

Abstract

The water sorption isotherms (from 5 to 65 °C) and air-drying kinetics (from 35 to 75 °C) of the brown seaweeds, Ascophylum nodosum and Undaria pinnatifida (UNP), were determined. Rehydration kinetics of dried seaweeds at different temperatures were obtained at room temperature. The Caurie model was successfully applied to the experimental water adsorption and desorption data. Air-drying kinetics of both seaweeds were satisfactorily modelled using the Page model. The critical moisture contents (dry basis), 1.3 ± 0.2 for A. nodosum and 5.0 ± 0.4 for UNP, were invariant from 35 to 75 °C. Heat and mass transfer coefficients during constant drying rate period and effective coefficients of water diffusion during falling drying rate period were calculated, assuming cylinder geometry for A. nodosum and plane-sheet geometry for UNP, considering volumetric shrinkage in both cases. The Peleg model was employed for rehydration kinetic modelling at 25 °C employing dried seaweeds at 35 and 75 °C. A. nodosum showed adequate rehydration properties recovering its colour and final moisture content after drying at low temperature (35 °C).