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Evaluation of Sideritis hyssopifolia antioxidant activity by using the FRAP method Introduction: Many medicinal plants contain polyphenolic compounds, mainly flavonoids, which exhibit high antioxidant activity and have many beneficial effects for the health. The aim of this study was to evaluate the antioxidant activity of the ether, methanol, chloroform and butanolic extracts obtained from the aerial parts of Sideritis hyssopifolia using FRAP method and ascorbic acid as the antioxidant standard. Material and Methods: For each extract and ascorbic acid different concentrations were dissolved in methanol for analysis. The FRAP reagent was prepared by mixing 300 mM acetate buffer (pH 3.6), 10 mM TPTZ solution in 40 mM HCl and 20 mM FeCl3.6H2O solution in a volume ratio of 10:1:1. Freshly prepared FRAP reagent (3 mL) was warmed to 37 ºC in a water bath before use and this volume was added to 100 µL of sample (extract or standard antioxidant) and to 300 µL of type I water. The absorbance was measured at 593 nm at 0, 4, 8, 15, 30 and 60 min at 37 ºC. The inhibitory concentration by 50% (IC50), defined as the antioxidant concentration that caused 50% loss of FRAP reagent activity, was calculated from the regression line obtained by representing the inhibition percentage against the concentration of the corresponding extract or antioxidant standard. Results and Conclusion: The reaction time for FRAP method was on 15 min. The results shown that the IC50 values obtained for the different extracts and antioxidant standard tested were: ascorbic acid.- 0.629 μg/mL; butanolic extract.- 1.371 μg/mL; methanol extract.- 4.045 μg/mL; ether extract.- 6.951 μg/mL and chloroform extract.- 14.734 μg/mL. From the results obtained in the present study, we can conclude that the best antioxidant activity was found in the butanolic extract, relative to our antioxidant standard, ascorbic acid.
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