Recently, FRAP (Ferric Reducing Antioxidant Power Assay) is not accepted by some journals for the investigation of the antioxidant power of a sample like essential oil!
I don't know the reason behind this refusal!
Both FRAP and DPPH assays are performed under not physiological conditions. Personally, I don't consider the results obtained by these and by many other assays as valuable for biochemistry. I support such "some journals."
The ABTS is considered as the mosy appropriate method for determining both the lipophilic and hydrophilic antioxidants in samples. The DPPH method is widely preferred for its simplicity and the easiness of the formation of the DPPH radical.
The performance antioxidant activity of essential oil (EOs) is the result of a complex interplay between components and the oxidizable tested material. ABTS and DPPH are antioxidant assays to measure the activity of the compounds to scavenge free radicals. The essential oil especially terpenoid groups containing phenolic skeleton can react rapidly with peroxyl radical, therefore could protect oxidation by those radicals. Most of the phenolic compounds capable of scavenging free radicals by donating their electrons or H (from a hydroxyl (—OH) in the benzene ring) to the radicals. On the other hand, non-phenolic terpenoids can not protect lipid from oxidation due to (for example alpha-pinene or its similar compounds) undergo auto-oxidation. Furthermore, not all EOs have the ability to reduce Fe3+ to Fe2+ (as measured in FRAP assay), even the phenolic structure with ortho-dihydroxy moiety (ex. hydroxytyrosol) could chelate Fe2+ whereas the tyrasol that has only one OH does not show that ability. Knowing the structure of your ES is crucial in evaluating its antioxidant activity.
Antioxidant capacity or activity of a complex sample (essential oil, plant extract, etc) can not be fully studied with a single test, a full set of tests should be performed in order to have a better understanding. DPPH is a general method particularly sensitive to phenolics compounds and other species such as organic acids, ABTS is similar to DPPH with the advantage of evaluating water-soluble compounds, FRAP evaluates the reducing power. In essential oil, because of its nature (lipophilic), another test should be included to evaluate highly lipophilic compounds with antioxidant potential (TBARS, Inhibition of oleic acid oxidation, ORAC, etc). Therefore a combination of tests, instead of one test alone, is preferred.
- Badges
- Science topic
- Similar topics
- Phytochemistry
- Extracts