From my point of view, RACI does not make much chemical or physical sense. There are two different values, the antioxidant capacity and antioxidant activity. Let's look at the simplest case with a single antioxidant in a sample. The antioxidant capacity measures how many radicals can be scavenged by a sample. The capacity is calibrated against a standard antioxidant (Trolox, ascorbic acid, or whatever) and expressed in mole/L equivalents of your standard. The antioxidant activity is the relative rate, with which a given radical reacts with your antioxidant, and measured relatively a standard antioxidant. More accurately, the antioxidant activity is the reaction rate constant, with which an antioxidant reacts with a given radical. The general protocol to characterize the antioxidants in your sample includes two steps. First is the measurement of the total antioxidant capacity of your sample in mol/L equivalents of a standard. Second is the measurement of the average activity of antioxidants in your sample. This is a very tricky procedure and I would advise you to measure the total antioxidant capacity of your sample. The best assays is based on ABTS.

The details in this my publication Russian Journal of Bioorganic Chemistry, Vol. 28, No. 6, 2002, pp. 501–514. I can send a copy, if you request by email.

The comparison the data obtained by different assays is useless because assays are based on different chemistry. While, it might be some correlations between different assays. Don't bother yourself with RACI.

The parameter can be determined by using different antioxidant activity determination methods viz DPPH free radical scavenging activity, Inhibition of Lipid per oxide, Superoxide anion radical scavenging activity etc in reference to any postive control/Ascorbic acid etc

You can assess your samples antioxidant potential by performing different types of radical scavenging assays such as FRAP, ORAC, DPPH, and ABTS free radical scavenging assays. Moreover, B-carotene bleaching and lipid peroxidation assays would also be performed. The antioxidant capacity is calibrated against standard antioxidant (control) trolox or ascorbic acid.

Hello everybody!

Relative Antioxidant Capacity Index (RACI), calculated by assigning equal weight to all applied assays and Phenolic Antioxidant Coefficients (PAC), calculated as a ratio between particular AO capacity and TPC, were used to achieve more comprehensive comparison between analyzed samples, as well as applied assays.

I feel, that the people who posted answers completely ignored my first response. Each assay is based on its own chemistry, designed for certain goals, and used in different conditions. You need to understand well what you are measuring. Otherwise, you put into a basket apples, oranges, pears and unknown fruits and want to compare your and someone's else baskets. How you can say which basket is better? My point is that the RACI does not have any chemical sense.