I'm performing the antioxidant activity of essential oil by DPPH manner, and I was wondering about the value of IC50 it seems so high because that of reference which is ascorbic acid is around 0.018 mg/ml, whereas that of my sample is 2 mg/ml. There is a big difference!
When we can consider an essential oil as an antioxidant agent? Is there any intervale of IC50?
Is there any interest to say that this essential oil having an antioxidant activity?
There are water soluble (like vitamin C) and lipid soluble (like vitamin E) antioxidants. Essential oils are lipid soluble and therefore the assay designed for lipid soluble antioxidants must be performed. DPPH assay is performed under not physiological conditions. The value of data obtained by DPPH assay are questionable.
I think the ABTS method is more appropriate because it could be used for determining both the lipophilic and hydrophilic antioxidants in the sample. DPPH is generally used for hydrophilic antioxidants.
Of course, all these in vitro methods can't express the real biological value of the antioxidants because the conditions of experiment can't match those of the biological samples. However, by these in vitro methods we can have an idea about the potential antioxidant activity found in the sample, and these methods allow to classify the products/samples according to its potential antioxidant activity.
Duried Alwazeer ABTS is a di-sodium salt and present in solutions as a di-anion. It is slightly soluble in ethanol/methanol, which can't be considered as models of lipids. ABTS based assays have been developed to use in aqueous medium. The activity of antioxidants are strongly dependent on pH.
An additional function of lipophylic antioxidants is to remove peroxides. I would not use the same assay for two different families of antioxidants
A compound can be considered an antioxidant agent if it has at least two or more of the following mechanisms of action: radical scavenging, reducing agent, preventing lipid peroxidation, metal chelating, enhancing endogenous antioxidants. If only one action is dominant and the other action is very low, then the compound can only be called the compound with the dominant action, for example as a reducing agent. Your essential oil cannot be considered as an antioxidant agent only based on radical scavenging activity which is too low (the IC50 2 mg/ml in the DPPH assay is very high). You should examine it with other methods to conclude that the essential oil is an antioxidant agent.
Harto Widodo The definition of antioxidant can't not be based on the mechanism. There area thousands of molecules which fit your definition, but they are not antioxidants. The concept of antioxidants belongs to life-sciences. In the field of chemistry dealing with oxidation by dioxygen the term "inhibitor" is commonly used. I think that the best definition of an antioxidant was given by Halliwell and Gutteridge: "an antioxidant is any substance that delays, prevents or removes oxidative damage to a target molecule”
Yurii V Geletii thank you for your correction, however, my opinion is based on a growing consensus among scientists that evaluation of antioxidant should implement a combination mechanism action of antioxidant assays, rather than single entities according to the highly cited journal by Nur Alam et al 2013 https://pubmed.ncbi.nlm.nih.gov/24936134/
Harto Widodo
If you rely upon citation numbers, read this (Cited by 30087)
Free radicals in biology and medicine
B Halliwell, JMC Gutteridge - 2015 - books.google.com
Free Radicals in Biology and Medicine has become a classic text in the field of free radical and antioxidant research. Now in its fifth edition, the book has been comprehensively rewritten and updated whilst maintaining the clarity of its predecessors.
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