Petra Krivak

The influence of interactions among phenolic compounds on the antiradical activity of chokeberries (Aronia melanocarpa)

In the present work, interactions between phenolic compounds from chokeberries and their influence on the antiradical activity was studied. Three fractions were isolated from chokeberries containing different classes of phenolic compounds. The first fraction contained a major part of phenolic acids and flavonols, the second anthocyanins, and the third insoluble phenols and proanthocyanidins. The phenolic compound content was determined using high-performance liquid chromatography, and the antiradical activity using the DPPH test. In order to evaluate the effects of interactions between phenolic compounds on the antiradical activity, the antiradical activity of individual phenolic fractions was compared with that obtained by mixing phenolic fractions. Phenolic mixtures showed the decrease in the antiradical activity in comparison with the individual phenolic fractions. These results suggest the existence of complex interactions among phenolic compounds that caused the decrease of the antiradical activity. Interactions among chokeberry phenols promoted a negative synergism.

Polyphenols and β-glucan interactions through linear adsorption models

The aim of this work was to obtain information about interactions between polyphenols and β- glucan through linear adsorption equilibrium models. Polyphenolic compounds can interact with various food ingredients such as carbohydrates, proteins and lipids and this interactions can affect polyphenol bioactivities. Interactions can be studied through adsorption process at constant temperature and adsorption isotherms can be obtained. In this work the interactions between polyphenols like gallic acid, cyanidin-3- galactoside and cyanidin-3-glucoside and β- glucan as natural dietary fiber were studied through Freundlichs, Langmuirs, Dubinin- Radushkevichs, Tempkins and Hills models. Adsorption was carried out through model solutions of different concentrations of polyphenols and β-glucan in 16 hours at 25°C. After the adsorption, unadsorbed polyphenols were separated from adsorbed polyphenols by ultrafiltration. Concentration of unadsorbed polyphenols were determined by spectrophotometric Folin-Ciocalteu method for gallic acid and pH differential method for cyanidin-3-galactoside and cyanidin-3- glucoside. The results of adsorption isotherm parameters showed that adsorption between all polyphenols and β-glucan were physical and all interactions were favorized. Gallic acid showed the highest maximum adsorption capacity onto β- glucan. This study showed that information about interactions between polyphenols and dietary fibers can be obtained through the linear adsorption equilibrium isotherms.