Teas: Direct Test on Quality and Antioxidant Activity using Electron Paramagnetic Resonance Spectroscopy

M A Morsy

doi:10.1155/2002/384034

Abstract

The manufactured teas may conveniently be divided into three classes: Green teas, Oolongs (delicate black teas), and Black Teas. Several indirect methods are employed to measure the antioxidant activity of tea extracts that is basically takes place by monitoring the inhibition of oxidation of a suitable substrate using the extracts of antioxidant materials from the studies systems. This study is concerned with the results of electron paramagnetic resonance (EPR) spectroscopy that is utilized to investigate several categories of green and black teas: Twining Green Tea (TGT) of London, Rabea Green Tea (RGT) of Saudia, Chinese Green Tea (CGT) of China, English Breakfast Tea (EBT) of Ahmed Tea-London, and Rabea Black Tea (RBT) of Saudia. Three EPR signals from all the studied samples are observed. The assignment of these signals will discussed and correlated with the quality of leaves. Mainly, two paramagnetic species are considered to be responsible for the observed EPR signals; manganese(II)–protein system of the leaves and a stable free radical of aromatic origin. The study will provide facts on the dependency of radical signal on the oxidative degradation procedures of the studied samples. The intensity and feature of Mn(II)-EPR-signal is found to be related to the disintegration of tea leaves.

Highlights

China and Japan give large portions of the tea crop that is intended for export to foreign countries
In this study we extend our earlier electron paramagnetic resonance (EPR) spectroscopy studies utilized to monitor the generation and status of free radicals and paramagnetic species in natural fresh or partially fermented leaves [19,20,21,22]
All of the samples under investigation were recently collected from the local market and their production date is around 01/2002 except for the old twinning green tea that is produced around 01/2000

Summary

Introduction

China and Japan give large portions of the tea crop that is intended for export to foreign countries. Tea leaves in these countries are used as a daily beverage and crude medicine for thousands of years. Tea and green tea in particular is considered as an effective source of antioxidants that attracted much attention [6,7]. Green tea extracts showed enhanced antioxidant activity in vegetable oils and animal fats [8,9,10]. Several methods are employed to measure the antioxidant activity of tea extracts. The extracts antioxidant effectiveness is measured by monitoring the inhibition of oxidation of a suitable substrate. The intensity of manganese(II) EPR signal is found to be related to ageing and disintegration of the tea leaves

Experimental procedures

Results and discussion

Conclusion