Generally speaking you have to prepare an extract of antioxidants using for e.g. methanol/water mixure (or others, is depends on you) then you can use this extract for the antioxidant assay. For the assay let the extract react with the radical in fixed conditions. Give a look at the attached paper. It regards oil. For quantification you can report the results as % of inhibition or maybe better by means of a calibration curve (as in the paper). Hope this may help.

You can use the multivariate calibration methods principal component regression and partial least squares for the prediction of antioxidant capacities of fruit juices. You can use high-performance liquid chromatography and spectrophotometric approaches.

The DPPH scavenging activity could be determined as follows:

* first of all, you make the standard curve of Ascorbic acid by using 5-7 different Ascorbic acid solutions. The scavenging activity of both Ascorbic acid solutions and your food sample (extract) could be measured as follows:

* 500 ul of sample extract (or Ascorbic acid solution) is mixed with 2.5 ml of 6×10^-5 M methanolic solution of DPPH.

* The reaction mixture is

incubated in the dark at room temperature for 90 min.

* then the absorbance is measured by spectrophotometry at 515 nm.

*The DPPH scavenging activity value of sample (or Ascorbic acid solution) (%) = 1- ( Absorbance of sample/absorbance of control)×100

Control sample contains all reagents excluding the sample.

* By the previous equation you first draw the curve of DPPH scavenging activity of Ascorbic acid. Then, from this curve and by using the absorbance value of your sample you can find the DPPH scavenging activity of your sample.

Best wishes

Duried

interesting question

Following the answers