Antioxidant ability of fractionated apple peel phenolics to inhibit fish oil oxidation

Polyphenols isolated from frozen and dried apple peels were studied as potential natural antioxidants to stabilize omega-3 polyunsaturated fatty acid (ω3 PUFA) enriched fish oil. The ethanolic extracts of apple peels were fractionated by reversed phase chromatography using gradient elution of 20–100% aqueous ethanol. The collected fractions were analyzed by ultra pressure liquid chromatography coupled with tandem mass spectrometry (UPLC–MS/MS). The total phenolic content and antioxidant capacity of each fraction were evaluated by Folin–Ciocalteu (FC), ferric reducing antioxidant power (FRAP) and 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) scavenging assays. Inhibition of fish oil oxidation was studied using the thiobarbituric acid reactive substances (TBARS) assay. Polyphenols fractionated using frozen apple peel extract had significantly higher FC, FRAP and DPPH· scavenging values than those of dried apple peel (p < 0.05). The flavonol-rich fractions inhibited fish oil oxidation by 40–62% at a total phenolic concentration of 200 μg/ml. The fractionated polyphenols from both dried and frozen apple peel showed higher inhibition of lipid oxidation compared to α-tocopherol, butylated hydroxytoluene and crude apple peel extracts.

► Processing methods influence the antioxidant properties of fractionated apple peel polyphenols.
► Polyphenol fractions had stronger antioxidant properties than the crude apple peel extract.
► The fractions showed stronger inhibitory effect on fish oil oxidation than BHT and α-tocopherol.
► Quercetin glycosides and epicatechin combination showed the greatest antioxidant capacity.