Trace elements in tea leaves, made tea and tea infusion: A review

Tea (Camellia sinensis L) is one of the most widely popular nonalcoholic beverage, consumed by over two-thirds of the world's population due to its medicinal, refreshing and mild stimulant effects. Mainly four types of made tea viz., black or red, oolong, green and white are used for tea infusion (water extract from fermented tea leaf) worldwide. Tea plays a major role in terms of the intake of a number of nutritional trace elements in humans. Besides essential macro- and microelements, experimental studies have demonstrated that the accumulation of significant amount of excess nonessential trace elements in tea leaves may eventually increase the metal body burden in humans. Different literatures have indicated that among different trace elements, levels of aluminium (Al), arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), fluoride (F) manganese (Mn), and nickel (Ni) in different tea infusions were 0.06–16.82 mg L− 1, trace—1.53 μg L− 1, trace—0.79 μg L− 1, below detectable limit—43.2 μg L− 1, 0.02–40.0 mg L− 1, 0.2–4.54 mg L− 1, 0.1–250 mg L− 1 and BDL—0.16 mg L− 1, respectively. It has also been reported that in some of the tea infusions, toxic metals exceed the maximum permissible limits stipulated for different countries. In the present review, an attempt has been made to update and evaluate the knowledge of the presence of some selected trace elements in tea leaves, made tea and tea infusion, based on the available literature. Existing reports suggested that the presence of trace elements in green tea is lower than the black tea in most cases. However, the available literatures still appear to have some limits and may need more detailed investigations before reaching the conclusions.