Dear Mihai, Kindly follow the following question of Zongo Cheikna,

Can anyone suggest the best technique to estimate the level of antioxidant compounds in a plant extract?

You will get useful discussions of peers there.

There is no technique considered as best for determination of antioxidant potential of plant extracts. researchers have used collection of techniques to show this activity in plants both in vitro and in vivo.

Hi, it's a bit complicated to pinpoint one particular method for the measurement of antioxidant activity. However, the Trolox-Equivalent Antioxidant Capacity Assay (TEAC) is thus far the commonest in cereal research (despite its setbacks). This could allow you to easily compare your results with previous studies. I found this article that might help you out. 

http://www.sciencedirect.com/science/article/pii/S0023643811003641

Well there are perhaps two ways to go about doing this.

1. do a solid/ liquid extraction of your bread ingredients and measure the antioxidant activity (AOA).

2. Make the bread and bake it. Then extract the bread using solid/ liquid extraction and measure the (AOA). 

As suggested by the previous answers, there is no one true way to measure AOA of a sample. This is because the  reagents involved in the assay scavenge for different reactive oxygen species (ROS). Therefore a selection of assays might be of benefit. Although the results between assays will differ you should see a distinct correlation (i.e. pattern) between high/ low antioxidant extracts. Some commonly used assays include DDPH and ABTS assays (radical scavenging), FRAP and CUPRAC assays (redox reactions), and ORAC assay (Fluorescence decay). 

http://www.sciencedirect.com.ucd.idm.oclc.org/science/article/pii/S0308814613009370 

I can send on additional info if required for these and other assays 

First you can identify which plant parts you have taken for antioxidant activity , then further you prepared extracts in suitable solvents and go further for Total antioxidant activity and some parameters of it DPPH, scavenging activity , Reducing ion exchange activity, ( Enzymatic and non enzymatic activity).etc.  

I recommend you to read the articles given below. We are actively using QUENCHER method in cereal products. 

http://www.sciencedirect.com/science/article/pii/S0889157512000208

http://www.sciencedirect.com/science/article/pii/S0924224409001289

http://www.sciencedirect.com/science/article/pii/S0733521008001008