Influence of duration and temperature of infusion on the heavy metal contents of some groups of tea in Nigeria

Abstract

Consumption of tea has been recommended not only for its taste and aroma but also for its medicinal importance, and these factors may contribute to public health concerns. The physicochemical characteristics of tea groups (green, black, and medicinal tea) were investigated using standard procedures. 2 g of each tea group and type were infused for 10 min at 60 and 80°C, and the extract was digested with a 2:1 mixture of HNO3 (65%) and H2O2 (30%) and then analyzed using Flame Atomic Absorption Spectrophotometry (FAAS) for Cd, Pb, Cu, Zn and Fe. The moisture content for green tea ranged from 6.75 to 7.50%, black tea from 5.50 to 8.50%, and medicinal/herbal tea from 7.50 to 13.25%, while the pH of the infusion at 60 and 80°C was found to be 7.0. The moisture content of medicinal tea was higher among the tea groups, as was their ash content, which was less than 8% for all groups and types of tea products. Furthermore, it was also found that the heavy metal content increases with an increase in infusion temperature for all similar brands of tea, except for some brands of medicinal tea. This may be due to plant species, soil conditions, and other environmental factors. There is no carcinogenic or noncarcinogenic health risk from elements in all tea brands and groups for both adults and children. However, there is a relative risk for children over adults, especially from Pb. Therefore, frequent consumption of all tea types and groups under investigation should be discouraged among children. Key words: Green tea, black tea, medicinal tea, infusion characteristics, health risk, Nigeria.