Identification des interactions flavonoïde-flavonoïde par évaluation in vitro du pouvoir antioxydant de mélanges binaires

Résumé

Identification of flavonoid-flavonoid interactions through in vitro assessment of the antioxidant capacity of binary mixtures

Flavonoids co-present in plant extract create molecular interactions between themselves. Investigation of these flavonoid-flavonoid interactions was carried out by in vitro evaluation of the antioxidant activity of binary mixtures with nine flavonoids prepared in methanol. Antioxidant capacity was assessed by two spectrophotometric methods using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS). Ferric reducing power was also assessed using Ferric Reducing Antioxidant Power (FRAP) method.  Based on the 50% inhibitory concentration (IC₅₀) values, the antioxidant activities of the various molecules were determined. The different values of IC₅₀ obtained make it possible to classify the molecules into three main groups: active flavonoids (FA), moderately active flavonoids (FMA) and non-active flavonoids (FNA). Quercetin exhibits the highest value for antioxidant activity, with IC₅₀ values (μM) of 95.5 ± 0.3; 38.0 ± 0.4 and 32.2 ± 0.2 obtained for the DPPH, ABTS and FRAP methods, respectively. From the combination indices (CI) of binary mixtures, the antagonistic interaction was more observed with the DPPH method, the synergy interaction was observed with the FRAP method, while the ABTS method is more marked with additive effects. These trends are particularly noticeable with quercetin and catechin, both belonging to the FA group. In ABTS analysis, with a CI value of 0.74, the most synergistic effect was revealed by the binary mixture eriodictyol-hesperetin. The strongest antagonistic effect was obtained with the apigenin-luteolin-7-glucoside combination (CI =1.72) in DPPH analysis. Glycosylation and methylation are structural factors favourable to antagonism. The diversity of flavonoid interactions expressed through antagonistic or synergistic effects revealed by antioxidant capacities should be taken into account when blending botanical extracts for application.

 Keywords: Phenolic compounds; Interaction; Anti-radical capacity; Reduction; Binary combination.