Comparative Investigation of Antioxidant Effects in Different Binary Systems: Does Quercetin Stabilize Ascorbic Acid/Resveratrol in Their Binary Mixtures?

Background: In recent decades, research concerning the antioxidant properties of phenolic compounds has increased, but data about their interaction in mixture systems are still rare. It has been found that in the case of a mixture of antioxidants, the antioxidant activity is not always the sum of the activity of each compound. Methods: This study considered the antioxidant activity of individual antioxidants, including quercetin, resveratrol, and ascorbic acid. Additionally, their binary mixtures, such as quercetin/resveratrol (Q/R), quercetin/ascorbic acid (Q/A), and resveratrol/ascorbic acid (R/A), were applied to understand the antioxidant effect between these compounds. The antioxidant capacity was assayed for different concentrations and ratios of these compounds using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) tests. Results: The results showed the superiority of quercetin by both methods, followed by ascorbic acid and resveratrol using the DPPH test, and resveratrol and ascorbic acid using the FRAP test. Also, the antagonism effect was confirmed for all antioxidant mixtures at different concentrations and ratios, and the ratio of 5:1 of stronger antioxidants to weaker antioxidants showed lower antagonism in binary mixtures. The magnitude of this effect is affected by the antioxidant activity assay method, type of antioxidant, compound concentration, their ratios, and mutual interactions between antioxidants. This indicates that the antioxidant activity of antioxidant mixtures is not predictable based on the antioxidant capacity of individual compounds. Moreover, a high correlation was obtained between DPPH and FRAP antioxidant assay methods for binary mixtures of quercetin/resveratrol and quercetin/ascorbic acid. Conclusions: The obtained results can be helpful for the proper design of functional foods, food supplements, and applications in other industries such as skincare.