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Quantifying the Radical Scavenging Activity of Tea

The antioxidant activity of the catechins found in white tea is much greater than that of ferulic acid, as determined using the spin trap method and electron paramagnetic resonance spectroscopy

Free radicals are formed when weak bonds within a molecule break, leaving an unpaired electron. They are very unstable and react quickly with other compounds in order to capture the needed electron and regain stability. Free radicals can be formed during normal metabolism, but the majority are formed as a consequence of environmental factors, such as pollution and cigarette smoking. High levels of free radicals cause damage to the body and it is the accumulation of such damage that gives rise to many of the effects of aging and can also lead to disease.

Antioxidants protect the body against the destructive effects of free radicals by donating one of their own electrons to neutralise the free radical. White tea, which is the least processed form of tea, is known to have good antioxidant activity by virtue of its high catechin content. The main catechins found in tea are epigallocatechin (EGC), catechin (C), epigallocatechin gallate (EGCG), epicatechin (EC), and epicatechin gallate (ECG).

A recent study by Azman et al. has compared the antioxidant activity of white tea with ferulic acid, one of the most powerful naturally occurring antioxidants. Ferulic acid is abundantly present in plant cell walls where it plays a key role in a plant’s self-preservation mechanism, protecting it from microbial and sun damage. It is consequently used in skin preparations and food supplements designed to delay the effects of ageing. Animal studies have also indicated that it may have anti-tumour activity.

The free radical neutralising activities were compared using the spin trap method and electron paramagnetic resonance (EPR) spectroscopy (using a Bruker EMX-Plus 10/12 spectrometer). The advantage of this technology is that it directly measures the reactive oxygen species that cause damage and disease in man. It is also able to detect very short-lived radical intermediates.

The comparison was repeated using four traditional methods of measuring radical scavenging activity that are based on more stable radicals. These were the trolox equivalent antioxidant capacity (TEAC) assay, the oxygen radical antioxidant capacity (ORAC) assay, 2,2-diphenyl-1-picrylhydrazyl (DPPH) EPR, and the ferric reducing ability of plasma assay.

The antioxidant efficiency of all the catechins found in white tea was much greater than that observed for ferulic acid. The greatest effect was observed for the catechins with the gallate group, ie, EGCG and ECG.

Good correlation of the data obtained using the spin trap EPR method was found with data from each of the experiments using traditional methods, confirming the reliability of the spin-trap EPR methodology. In fact, the spin trap EPR method was better able to detect differences in antioxidant activity between the different catechins.

With the bioavailability issues associated with ferulic acid, white tea may potentially provide a more effective option for protecting against the effects of aging, although this will need to be confirmed. Perhaps, now that its antioxidant activity has been quantified, white tea will reach superfood status?

Reference

Azman NAM, et al. J. Radical Scavenging of White Tea and Its Flavonoid Constituents by

Electron Paramagnetic Resonance (EPR) Spectroscopy. Agric. Food Chem. 2014, 62, 5743−5748.

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