Title: The application of adsorption isotherms with proper fitting to interpret polyphenol bioaccessibility in vitro

Lidija Jakobek

Josip Juraj Strossmayer University of Osijek, Croatia


Lidija Jakobek is an associate professor at the Department of Applied Chemistry and Ecology, Faculty of Food Technology, Josip Juraj Strossmayer University of Osijek, Croatia. She has a PhD in a food technology from Josip Juraj Strossmayer University of Osijek. Her research interests are food science, particularly polyphenols, their bioaccessibility and health effects, and polyphenol characterization.


Bioaccessibility of polyphenols is described as their accessibility for absorption in the digestive tract. Dietary fibers, together with some other food components, can affect bioaccessibility since they can interact with polyphenols.

One of the ways of studying these complex reactions in vitro is to study the adsorption of polyphenols onto dietary fiber. The experimental results (the amount of polyphenols adsorbed onto dietary fiber qe, and the amount non-adsorbed ce) can be modelled with adsorption isotherm equations. Parameters obtained from these equations can help in the attempt to interpret adsorption process and by that to interpret bioaccessibility in vitro. But, adsorption isotherms require proper fitting to lower the error of models and to obtained correct parameters of adsorption equations.

The aim of this work was to study the adsorption between apple polyphenols and b-glucan, to model the experimental data with Langmuir, Dubinin-Radushkevich, and Hill adsorption isotherms with improved fitting, and to use corrected parameters from adsorption isotherms to interpret the adsorption process. Polyphenols were extracted from the flesh and peel of apples by using ultrasound assisted extraction and adsorbed onto b-glucan until the adsorption reached the equilibrium. The amount of total free polyphenols before and after adsorption were determined by using Folin-Ciocalteu method. The qe (adsorption capacity, mg g-1) and ce (polyphenol concentration in equilibrium, mg l-1) were modelled with equations of adsorption isotherms. Experimental data fitting (qe and ce) was conducted by using improved minimization of the sum of square errors. According to the results, polyphenols from peel adsorbed in a higher amount onto b-glucan than flesh polyphenols. Adsorption isotherms fitted according to the new, improved fitting, showed lower standard error and can be considered more accurate and precise for the interpretation of adsorption. According to new parameters, peel polyphenols showed higher theoretical, maximal adsorption capacity (qm) and theoretical capacity of saturation (qs). Parameter nH points to the negatively cooperated bonding for almost all polyphenols. New, more accurate fitting allows safer insight into the bonding between polyphenols and dietary fibers and accordingly into the bioaccessibility explanation, in vitro.

Audience take away:

  • The audience will understand the importance of proper fitting of data from adsorption process
  • The results of this study are interesting for many areas in which adsorption isotherms can be applied (like in chemistry, ecology, biochemistry etc.).
  • The presentation will also give an insight into the bioaccessibility process and its importance in polyphenol bioactivities