Evaluation of anthocyanines antioxidant properties using chromatography

Abstract

A method for assessing the antioxidant properties of anthocyanins was proposed, using a reaction with an aqueous solution of potassium permanganate followed by chromatographic determination of the concentration of various anthocyanins in complex mixtures in comparison with the original solution. The main feature of the method is the exclusion of the occurrence of a chain of successive oxidation reactions of each initial anthocyanin, which is actually observed when using traditional methods for determining antioxidant properties. For this purpose, a lack of oxidant was used, which should be consumed mainly in the first stages for each antioxidant, under the assumption that the activity of the initial (least oxidized) anthocyanin is higher than that of the products formed from it. Only such a scheme allows comparing antioxidant activity (as a time-dependent parameter instead of the usually determined antioxidant capacity) depending on the structure of the molecule. Based on a study of the oxidation of 3-glucosides with potassium permanganate of five different main natural anthocyanidins (in extracts of grape fruits and leaves of Cercis canadensis), a dependence of antioxidant activity was established, which increased in the series: Pn3Glu<Cy3Glu<Mv3Glu<Pt3Glu<Dp3Glu. Consequently, the antioxidant activity of anthocyanins of the same type increased with the addition of an OH group to the B ring of the aglycone more strongly than the addition of a methoxy group. The analysis of anthocyanins from the fruits of grape variety Mercedes extract showed that the acylation of peonidin and malvidin 3-glucosides by p-coumaric acid did not lead to higher resistance. Therefore, the conclusion about higher stability of acylated anthocyanins are not always true. An analysis of the oxidability of various 3-glycosides by potassium permanganate was performed on the extract of black currant and red viburnum fruits and showed that in the first case, the oxidability does not reliably change when moving from 3-glucosides to 3-rutinoside. Moreover, in the second case, the addition of a second monoside to the existing 3-glucoside for both arabinoside and rhamnoside led to a decrease in activity. This indicates that accompanying extractives can alter the course of some reactions.