Screening of the antioxidant properties and polyphenol composition of aromatised green tea infusions

Aromatised green teas are widely sold and popular owing to their fragrance. In this study the antioxidant activity of six commercial green tea infusions was assessed by three complementary assays.

In order to evaluate the tea infusions as antioxidant sources, their phenolic content (Folin-Ciocalteu assay), cupric ion-reducing antioxidant capacity (CUPRAC) and 2,2-diphenyl-1-picryhydrazyl (DPPH) radical-scavenging ability were determined. Their content of polyphenols was also determined by high-performance liquid chromatography/mass spectrometry (HPLC/MS) in negative electrospray ionisation mode. Some teas with citrus aroma, besides having a relatively high content of catechins, also contain other phenolic compounds such as naringin and hesperidin. The three assays used to evaluate the antioxidant capacity of the tea infusions gave different rank orders. Therefore an antioxidant index was calculated for better correlation of the results, and its highest value was obtained for Clear Green Mint tea infusion.

The studied teas, besides having a relatively high content of catechins, also contain naringin and hesperidin, which are not present in 'pure' green tea. It is important to run multiple assays to get a better estimate of the antioxidant capacity of a given sample.