Hi, Arvind, one of the way is to measure activity of several antioxidant enzymes like catalase, peroxidase, SOd etc.

But remember, that activity of one enzyme may not give you correct picture, because enzymes have different localization (catalase is peroxisomal, APX is cytoplasmic, plastidic etc).

In  addition, you can also measure contents of low molecular weight antioxidants like ASC, GSH, tocopherol etc.

More information you can find in my profile.

See profile of Dr Guido Haenen

Dear Dr. Pasternak,

Thanks for your suggestion but as per my knowledge the antioxidant enzymes you mentioned are to access the activity in vivo and not in vitro. My query was regarding in vitro methods.

Methods Enzymol. 2002;359:366-79.

Evaluation of antioxidant activity using peroxynitrite as a source of radicals.

Geletii YV, Balavoine GG.

Russian Journal of Bioorganic Chemistry

November 2002, Volume 28, Issue 6, pp 501-514

The Determination of Total Concentration and Activity of Antioxidants in Foodstuffs

Yu. V. Geletii, G. G. A. Balavoine, O. N. Efimov, V. S. Kulikova

Nitric Oxide. 1999;3(1):40-54.

Peroxynitrite scavenging by different antioxidants. Part I: convenient assay.

Balavoine GG1, Geletii YV.

Hi arvind

For evaluation of in vitro antioxidant activity of plants, you should adopt the methods of

 DPPH free radical scavenging activity, nitric oxide scavenging activity, superoxide scavenging activity, hydroxyl radical scavenging activity etc. 

Dear Arvind

You can follow the following methods to evaluate in vitro antioxidant activity of plants.--

1. DPPH Free radical scavenging activity

2. Determination of total phenolic content

3. Determination of total flavonoid content

4. Reducing power assay & so on

You can read the following articles:

http://www.sciencedirect.com/science/article/pii/S0974694313002387

http://pelagiaresearchlibrary.com/european-journal-of-experimental-biology/vol3-iss1/EJEB-2013-3-1-449-454.pdf

10.5897/JMPR2014.5443

http://ajp.mums.ac.ir/jufile?c2hvd1BERj0xMDU2Jl9hY3Rpb249c2hvd1BERiZhcnRpY2xlPTEwNTYmX29iPTVjYWVmYTdmZGMwM2RmNjExZDE1YjJiZmI3NTUyODBlJmZpbGVOYW1lPWZ1bGxfdGV4dC5wZGY 

Dear Arvind,  In-vitro antioxidant assay are done through evaluation of radical-scavenging activity by DPPH colourimetry assay; Ferric reducing antioxidant potential (FRAP) and ABTS-FRS ability. 

Dear Dr. Arvind,

Based on the results of one assay of antioxidant activity, you may not the proper results, therefore you always have to perform at least more than one or two assay, to examine the radical scavenging profile of the different phytoconstitutes (because of their complex chemical nature and also mixture of different compounds in crude extracts); and most easiest assays are DPPH, TPC, TFC, FRAP and ABTS. For more information, see the files given below. All the best

Dear Arvind,

Whatever you read in answers, the best and simplest assay does not exist (see the profile of Dr Guido Haenen). Just use the assay(s)  you can use in your laboratory and which you understand well. When I developed my tube assay, the simplicity (skills of labor hands, instruments availability and the cost) was my first priority. On your request I can send you the copy of this paper;

Russian Journal of Bioorganic Chemistry

November 2002, Volume 28, Issue 6, pp 501-514

The Determination of Total Concentration and Activity of Antioxidants in Foodstuffs

Yu. V. Geletii, G. G. A. Balavoine, O. N. Efimov, V. S. Kulikova, 

where you can find a protocol applied for the  plant extracts

Hi

You can use the DPPH free radical scavenging activity

There are many ways to assess the antioxidant activity and easiest way to evaluate the DPPH or BBC and RP.

You can download these methods of research and  of  my research

Whatever method is suggested/recommended, make sure it is a published and recognized validated method. ORAC is such a method. Simple doesn't always meaning better. Science is about reproducibility. Getting different results from different labs using exactly the same methods, materials and procedures, the agree, is a step in the right direction. 

Following are the most easy and simple method for evaluation of in vitro antioxidant activity of plants..........

1. DDPH

2. Fe++ ion chelating ability

3. Determination of total phenolic content

4. Determination of flavonoid content

You can see the following articles :...

http://www.sciencedirect.com/science/article/pii/S0974694313002387

http://pelagiaresearchlibrary.com/european-journal-of-experimental-biology/vol3-iss1/EJEB-2013-3-1-449-454.pdf

http://www.academicjournals.org/journal/JMPR/article-abstract/E83A3E648091

http://ajp.mums.ac.ir/jufile?c2hvd1BERj0xMDU2Jl9hY3Rpb249c2hvd1BERiZhcnRpY2xlPTEwNTYmX29iPTVjYWVmYTdmZGMwM2RmNjExZDE1YjJiZmI3NTUyODBlJmZpbGVOYW1lPWZ1bGxfdGV4dC5wZGY

In our lab, we usually use DPPH method in order to investigate the antioxidative property of  the extracts from plants in vitro. Also, reducing power assay could be use to scan which initial material has ability of antioxidation.

DPPH

BBC

ABTS