Freshly prepared FRAP solution contained 25 mL of acetate buffer
(0.3 mol/L, pH 3.6) plus 2.5 mL of TPTZ (10 mmol/L, dissolved in 40 mmol/L HCl) and 2.5 mL of ferric chloride (FeCl3·6H2O, 20 mmol/L).
Four milliliters of FRAP solution at 37 °C wasmixed with 100 μL ascorbic
acid solution or diluted strawberry juice. Ten minutes later, the ferric
reducing ability of strawberry juice was measured by monitoring the
increase of absorbance at 593 nm with a spectrophotometer (UV-726,
T6, PG General, Beijing, China) and the FRAP solution was used as blank.
Results were expressed as equivalents ofmg of ascorbic acid per 100 mL
of juice.