Evaluation and Comparison of the Antioxidant Activity of Extractable Polyphenolsand Non-extractable Polyphenols of Sour Orange Peel

Research on food polyphenols has experienced a huge development during thelast century. Most studies on polyphenolic compounds have focused on extractable polyphenols (EPP). However,an important polyphenolic fraction is ignored (Non-Extractable polyphenols (NEPP)) because they aretrapped in the corresponding extraction residues. In this study, the antioxidant EPP and NEPP of sour orangepeel, extracted by aqueous solvent and acid hydrolysis (with two different solvent systems) respectively, areevaluated and compared.

Antioxidant activity was evaluated by four tests of radical inhibition of 2, 2-diphenyl-1-picrylhydrazyl(DPPH), 2, 2-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), ferric reducing antioxidant power (FRAP)and iron chelating. The amount of polyphenolic compounds, flavonoids, oligomeric proanthocyanidins, andflavanones were respectively determined by folin-ciocalteu, Aluminium chloride (AlCl3) and Ultraviolet–visiblespectroscopy (UV-visible). Also, the anti-lipid peroxidation effect in rat liver was measured.

The results of antioxidant analysis showed that NEPP with methanol/Sulfuric Acid Solvent had thehighest level of antioxidant activity in sour orange peel. It can be due to the high polyphenolic compounds inthis extraction compared to the others.

All extracts had antioxidant activity and can be suggested as a potential natural source in food andpharmaceutical industries.