DPPH assay was conducted with a method modified from Brand-Williams, Cuvelier, and Berset (1995).
1. Sample preparation : Dilute the fruit or vegetable juice sample to 10 times with distilled water.
2. A 1.0 mL aliquot of a 0.5 mmol/L DPPH in methanol (dissolved in 50% methanol solution) and 4.0 mL of the appropriately diluted sample were vigorously vortexed in a test tube with cap tube.
3. Held for 30 min of reaction at ambient temperature in the dark, the absorbance of the mixture was measured at 515 nm with the UV-Vis spectrophotometer.