Please try Chang et al. (2001).

Namskar Pauline and Rishikes and thanks for your suggestion

Actually i am looking to determine the antioxidant activity of colored fruit juice which give negative absorbance.

Hello Pravin

I faced the same problem,. Generally we do antioxidant assay using different concentrations of samples. You do one thing, maintain control also for each concentration. Controls should consist of everything expect DPPH. instead of DPPH, add same volume of solvent what you used to prepare DPPH solution. While reading the absorbance. for each concentration, you need to nullify the absorbance of the corresponding control. Then you will get exact activity of the sample. 

Good luck

Thank You Mr Rajesh

It is well known that polyphenols are one of the major contributors to the antioxidant activity of fruits, vegetables and mushrooms. For this reason, in this study, total phenols concentration, and antioxidant activity of plants and its products is determined, reduction means a higher antioxidant activity.  Vegetables and fruits juices antioxidant activity,is measured using the free radical 2,2- diphenyl- 1-picrylhydrazyl (DPPH) method, and correlation of the results withby  the C  vitamin concentration in the sample.  It is determined, by the iodometric method, the vitamin C concentration both in the raw materials (apple, beetroot, red cabbage, tomatoes and pink grapefruit) and in

the juices.