Potential of polyphenols from an aqueous extract of apple peel as inhibitors of free radicals: An experimental and computational study

The apple peel, which is an agro-industrial byproduct, has a high content of natural antioxidants and could be a source of functional ingredients for easily oxidizable foods, as well as a source of nutraceuticals for the treatment of diseases of oxidative origin. The ability to inhibit free radicals of an apple peel aqueous extract (APAE) and its fraction of procyanidins (P) was investigated, based on both the second-order rate constants (Ks) and inhibition of lipid peroxidation (ILP). For this purpose, ultraviolet–visible spectrophotometry (UV–Vis) adapted to stopped-flow, and computational methodologies as Density Functional Theory (DFT) were used. It was found that the P fraction was the one that showed the highest Ks in aqueous medium, while the largest percentage of ILP in emulsion was accomplished by the APAE. The compounds which could confer the high antiradical activity to apple peel are mainly quercetin-3-galactoside, quercetin-3-glucoside, procyanidin B-2 and cyanidin-3-glucoside.

► The fraction of procyanidins showed the highest Ks (172.80 (mg/mL)−1 s−1).
► The apple polyphenol aqueous extract showed the highest percentage of ILP (91.94%).
► In the fraction of procyanidins the HAT was the favored mechanism in aqueous medium.
► Quercetin glycosides and procyanidin B2 confer the antiradical activity to apple peel.