Equilibrium studies for the adsorption of fructo-oligosaccharides on a Dowex Monosphere calcium resin

Abstract

Fructo-oligosaccharides (FOS), namely kestose, nystose and fructo-furanosylnystose, are prebiotic sugars that can be obtained from sucrose by fermentation. The resulting fermentative broth is a complex mixture containing also salts and other smaller sugars that must be removed. In this study, a Dowex Monosphere calcium resin was evaluated for the separation of sugars. The adsorption behavior of FOS contained in a fermentative broth was compared with FOS from purified mixtures. Experiments were performed in static batch mode at 60ºC. Experimental isotherms data were analyzed using linear, Langmuir/anti-Langmuir, Freundlich, Redlich & Peterson, and Toth type models. Isotherm parameters were estimated using linear and non-linear correlations for the minimization of several error functions. The non-linear correlations were found to provide the best isotherm parameters for the models. FOS adsorption showed different behaviors depending on the complexity of the liquid phase of the FOS mixtures studied. The experimental adsorption data of FOS contained in purified mixtures were well fitted with the anti-Langmuir isotherm, while FOS in a fermentative broth were better fitted with Toth and Langmuir isotherms.