Equilibrium and thermodynamic studies of anthocyanin adsorption on fibrous cation exchanger FIBAN K-1

Abstract

In the last decades there has been an increased interest of researchers in the obtaining anthocyanins from available and low–cost plant materials, not only as natural food dyes but also for pharmaceutical products. Among plant sources of anthocyanins chokeberries and elderberries have attracted the interest of consumers due to abundant anthocyanin contents. In this study, adsorption equilibrium and thermodynamics of anthocyanins from chokeberry and elderberry extracts by fibrous cation exchanger FIBAN K–1 were investigated. The anthocyanin extracts were obtained by macerated in 0.1 M HCl under the follow extraction parameters: solid-liquid ratio = 1:2 at 293 K for 24 h. The total anthocyanin content in the extracts was determined by pH-differential method. Adsorption experiments were carried out under static conditions, shaking mixtures of anthocyanin extracts of the berries with FIBAN K–1. The adsorption isotherms were of L-type according to the classification of Giles. The adsorption capacity of FIBAN K– 1 for the chokeberry and elderberry anthocyanins increased as the temperature increased from 293 to 313 K. The Langmuir, Freundlich, and Temkin adsorption models were used to describe the experimental adsorption isotherms. These models had a good agreement with the experimental data for adsorption of the anthocyanins, but the Langmuir model was the most favorable model for studying the adsorption equilibrium of the chokeberry and elderberry anthocyanins on FIBAN K–1. Thermodynamic parameters of the anthocyanin adsorption, such as DG°, DH°_, and DS° were calculated. The ∆G° values were negative, thus indicating that the adsorption of the chokeberry and elderberry anthocyanins on FIBAN K-1 was spontaneous and favorable process under the experimental conditions. The decrease of the ΔG° values with increasing temperature shows that adsorption is more favorable at high temperature. The ∆H°values were positive for the anthocyanins of both kind of berries, which indicates the adsorption was an endothermic reaction. The ∆S°values were positive, which means that the anthocyanins in the aqueous phase are more organized than those in the adsorbent-liquid interface.