Interactions of Phenolic Acids and β-Glucan: Studies of Adsorption Isotherms and Thermodynamics

P. Matić, Š. Ukić and L. Jakobek Baron

Abstract
Interactions between polyphenols and dietary fiber might play an important role in polyphenol bioactivities. These interactions can be studied through adsorption processes. The aim of this study was to investigate the adsorption of phenolic acids (p-coumaric acid, caffeic acid, chlorogenic acid) onto dietary fiber – β-glucan. Adsorption was carried out at different temperatures (25, 37, and 45 °C) and pH values (1.5, 5.5, and 10). Non-linear isotherm adsorption models (Langmuir, Freundlich, Dubinin-Radushkevich, Temkin, Hill) were applied to analyze the data. Experimentally determined adsorption capacities showed some fluctuations with temperature and pH. Adsorption isotherms modelled the experimentally determined adsorption capacities well. According to isotherm parameters, it can be suggested that the adsorption was a physical process with non-covalent bonding at all temperatures and pH. Thermodynamic parameters showed that the adsorption was spontaneous (except for chlorogenic acid) and exothermic. Adsorption isotherms and thermodynamics gave useful information about phenolic acid – β-glucan interactions.

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Keywords
adsorption mechanism, phenolic acids, dietary fiber, adsorption models