Study on the antioxidant activities of root extracts of Zizyphus lotus from the western region of Algeria

Objective: To find a new natural source of antioxidant, the phenolic contents and antioxidant activities of some secondary metabolites extracted from roots of Ziziphus lotus were evaluated. Methods: The total polyphenol contents were determined spectrophotometrically. Pyrrocatechol, catechin and cyanidin equivalents were used for these parameters. The antioxidant activities of the extracts were determined by several in vitro systems of assays, namely DPPH radical scavenging activity method, b-Carotene Bleaching assay (BCB), Ferric Reducing Antioxidant Power assay (FRA P) and Total Antioxidant capacity test (TAC). Results: The quantitative estimation showed that the roots of Z. lotus were rich in polyphenols ( 20.09 mg PE/g DW) and proanthocyannidins (1.56%) and they contained a small amount of flavonoids (0.02 mg CE/g DW). The most fractions exhibited high antioxidant activities, and some even showed higher potency than the standard synthetic antioxidants in some instances. In DPPH assay, all extracts had shown significant inhibition (58.535 – 94.730% at 1 mg/mL). In addition, the IC₅₀ values ranged from 0.211 to 0.816 mg/mL, compared to 0.110, 0.214, 0.214 and 0.413 mg/mL for gallic acid, tannic acid, butylated-hydroxyanisol and ascorbic acid respectively. In (BCB) assay, the extracts showed strong inhibition (55.55 – 100.00% at 1 mg/mL) and the IC₅₀ values ranging from 0.123 to 0.850 mg/mL compared to 0.433 mg/mL for gallic acid. A dose dependant curve was obtained for all extracts in the FRAP assay. However, the antioxidant potencies of ascorbic acid and extracts were comparable at low concentrations. The majority of extracts showed the highest value of antioxidant activity, based on TAC test (0.073 – 0.398 mg ascorbic acid / mg extract). Conclusion: The results indicate that Z. lotus roots could be an important sources of natural antioxidants.

Key words:Ziziphus lotus, Polyphenol contents, DPPH radical scavenging activity assay, b-Carotene Bleaching assay, Ferric Reducing Antioxidant Power assay, Total Antioxidant Capacity test.