Hallo Farida,
Antioxidant activity can be measured in both water-soluble and water-insoluble fractions using different methods, FRAP assay and free radical quenching activity assay. However, there are two easy ways to estimate ascorbic acid, wich is an important antioxidant in fruits. Both using titration method. One uses iodine and the other DCPI as reductor. I hope that the following links can help you.
http://www.sciencedirect.com/science/article/pii/S0308814603001651
http://www.outreach.canterbury.ac.nz/chemistry/documents/vitaminc_iodine.pdf
http://www.google.com.br/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CDEQFjAA&url=http%3A%2F%2Fseniorchem.com%2FvitaminC_DCPIP.doc&ei=V9o5UsDzDYTi8gTJvIH4BQ&usg=AFQjCNEMiEEBucCjQlZMuCbqEjQDQCmH2w&bvm=bv.52288139,d.dmg
Total carotenoids and lycopene content of fruits can be measured by spectrophotometer using wave length of 452 nm and 503 nm, respectively (Ranganna 1986). Antioxidant activity can be estimated by spectrophotometr using cupric reducing antioxidant capacity (CUPRAC) and CUPRAC assay is performed according to method developed by Apak et al. (2007). To 100 µL of sample aliquot, 1 ml each of copper (II) chloride solution (10-2M), neocuproine solution (705x10-3M) and ammonium acetate buffer solution (pH7) is mixed. The tubes are stopped and after 1h, absorbance at 450 nm is recorded against a reagent blank and the antioxidant activity is expressed as µmol Trolox (TE)/100g FW as suggested by Pentelidis et al. (2007).
Hi farida. Antioxidant capacity can be measured by spectrophotometery methods. you can use DPPH soloution. for more information you can study more articles about it.
good luck
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