Dear Clarence, I would suggest to use one standard substance of each phenolic subgroup in the test, i.e. 1 flavonol, 1 flavanol etc., in concentrations they occur in your samples (you need HPLC results for that, though). Then compare the "performance" of each phenol on an equimolar basis. This will help you estimating the impact each compound (phenolic subgroup) has on the different test systems.

Keep also in mind that the reactivity of Trolox is strongly dependent on pH, solvent etc., so this should be consitent throughout all tests as well.

Dear Clerance 

FRAP and  DPPH assays are easy to use and most favourite ones. There is one paper aleast published on this lemongrass. 

Form of sample  such ad dry or fresh samples will also have impact on result.

You must use also go through article by Chanda and Dave 2007

It will give lot of information on these methods 

Thanks 

Noted.

Thank you very much for your input! I really appreciate it.

 i think lemongrass is well studied already

To be more precise the goal of this study is to compare the methods (ABTS, DPPH, FRAP) and their efficiency towards evaluating the antioxidant capacity of lemongrass. Yes I agree that there are lots of studies on lemongrass. I have seen different methods applied with variations in declaring values making it hard to compare results. Part of the purpose of this study is to give a recommendation which method can be best used (gives reproducible results, precise, cost effective, simple and rapid, etc.) as part of the product development of a certain beverage. I was hoping to get an input about the practical concerns I need to consider before I go ahead with the experiments.

I also wonder about the sample concentration to be picked to calculate the activity as in the unit of e.g mg Trolox equivalent/g sample, for instance in DPPH assay.  As in the procedure, when you are not sure how much antioxidant containing in the sample, thus you have to dilute them into various conc before subjecting to the reaction.  Therefore each conc of sample will give you the different value of inhibition capacity.  So I am curious which value I should select to further calculate for the conc or amount of antioxidant in the sample expressed in xx mg Trp eq/g sample. Since normally what I found was different dilution of sample gave the different calculated conc of antioxidant in sample (calculation based on the standard curve Tro).

 I was also thinking if it will be suitable to use the value obtained from one that occurred the be the highest antioxidant capacity or the highest inhibition, to further calculate the conc of antioxidant in sample.

Please someone give me the light to this curiosity.  Thank you in advance.

What is the best method for determining antioxidant activity in elderberry juice? What is the procedure to be followed?

The best and single assay of antioxidant activity does NOT exist.  I'm an expert in kinetics of free radicals

The determination of total concentration and activity of antioxidants in foodstuffs

By: Geletii, YV; Balavoine, GGA; Efimov, ON; et al.

RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY   Volume: 28   Issue: 6   Pages: 501-514   Published: NOV-DEC 2002

Evaluation of antioxidant activity using peroxynitrite as a source of radicals

By: Geletii, YV; Balavoine, GGA

NITRIC OXIDE, PT D   Book Series: METHODS IN ENZYMOLOGY   Volume: 359   Pages: 366-379   Published: 2002

Peroxynitrite scavenging by different antioxidants. Part I: Convenient assay

By: Balavoine, GGA; Geletii, YV

NITRIC OXIDE-BIOLOGY AND CHEMISTRY   Volume: 3   Issue: 1   Pages: 40-54   Published: 1999. 

The latter paper has been cited about 100 times

Noted. Thank you all for your valuable input.