Objectives: The study investigated the free radical scavenging and antioxidant potential of the methanol, ethanol and ethyl acetate extracts of turmeric rhizome. Methods: We assessed the phytochemical constituents, total polyphenol and flavonoid content in these turmeric extracts using standard phytochemical analyses. Phytochemical screening of turmeric extracts showed the presence of carbohydrates, proteins, sterols, tannins, flavonoids and saponins. Results: Ethanol extracts showed the highest polyphenol content (71.7 ± 3.0 mg of gallic acid equivalents/g of extract) and flavonoid content (28.5 ± 2.1 mg quercetin equivalents/g of extract) when compared to other extracts of turmeric rhizome. Similarly, ethanol extract of turmeric possessed the higher antioxidant activity (463.25 ± 36.15 μM Fe(II)/g of extract) in FRAP assay. The inhibitory concentration (EC50) of gallic acid, ethanol, methanol and ethyl acetate extract were found to be 27μg, 30μg, 38μg and 47μg respectively in DPPH assay. The H2O2 scavenging activity of the extract (20, 40, 50, 100 and 200g/ml) was increased in a dose dependent manner and ethanol extracts found superior hydrogen peroxide scavenging activity similar to gallic acid standard. The curcuminoids (standard) and the turmeric extracts were separated in Thin layer Chromotography (TLC). The Curcuminoids were separated into curcumin, dimethoxycurcumin, bis demethoxycurcumin with Rf value of 0.91, 0.65 and 0.44 respectively. The composition of turmeric extracts was consistent with the composition of curcuminiods as shown by the Rf values. Conclusion: The study concludes that ethanol extract of turmeric showed high polyphenol and flavonoid content which is attributed to its higher antioxidant properties.
Key words: Turmeric, Phenolic content, Flavonoids, Ferric reducing antioxidant power assay, DPPH radical scavenging assay.