2.5. Detection of hydroxyl radicals by deoxyribose assay
The assay was performed as described by Halliwell, Gutteridge, and Aruoma (1987) with minor changes. All solutions were freshly prepared. One millimetre of the reaction mixture contained 100 μl of 28 mM 2-deoxy-d-ribose (dissolved in KH2PO4–K2HPO4 buffer, pH 7.4), 500 μl solution of various concentrations of the ginger extract, 200 μl of 200 μM FeCl3 and 1.04 mM EDTA (1:1 v/v), 100 μl H2O2 (1.0 mM) and 100 μl ascorbic acid (1.0 mM). After an incubation period of 1 h at 37 and 80 °C the extent of deoxyribose degradation was measured by the TBA reaction. 1.0 ml of TBA (1% in 50 mM NaOH) and 1.0 ml of TCA were added to the reaction mixture and the tubes were heated at 100 °C for 20 min. After cooling, the absorbance was read at 532 nm against a blank (containing only buffer and deoxyribose). The percentage inhibition was calculated by the formula:
I(%)=100-(Abs.sample/Abs.control)×100.I(%)=100-(Abs.sample/Abs.control)×100.
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The IC50 value represented the concentration of the compounds that caused 50% inhibition of radical formation. Quercetin was used as a positive control.
The data obtained at each point were the average of three measurements.