where empty samples – 1 ml ethanol + 2.5 ml from various concentrations of ginger extract; control sample – 1 ml 0.3 mM DPPH + 2.5 ml ethanol.
The optic density of the samples, the control and the empty samples were measured in comparison with ethanol. One synthetic antioxidant, butylhydroxytoluene, was used as positive control.
2.4. Evaluation of antioxidant activity in linoleic acid model system
Linoleic acid emulsions were prepared by mixing 0.285 g of linoleic acid, 0.289 g of Tween 20 as emulsifier and 50 ml phosphate buffer (pH 7.2). The mixture was homogenized for 5 min according to Yen et al. (2003). The antioxidant was added at the final concentrations of 0%, 0.005%, 0.01%, 0.02% and 0.05% wt/vol of dry extract, BHT 0.01% was used as control. The mixture was incubated in an oven at 37 and 80 °C for 12 d and 10 h, respectively. The course of oxidation was monitored by measuring the conjugated dienes formation (CD) and thiobarbituric acid reactive substances (TBARS).
The antioxidative activity at the end of assay time was expressed for each indicator as reduction percent of peroxidation (RP%) with a control containing no antioxidant being 0%.
RP% = [(peroxidation indicator value without antioxidant) − (peroxidation indicator value with antioxidant)/(peroxidation indicator value without antioxidant)] × 100. A higher percentage indicates a higher antioxidant activity.