Estimated Contributions of Rooibos Tea to the Daily Manganese and Zinc Intakes Determined in Tea Leaves and Tea Infusions by Inductively Coupled Plasma-Mass Spectrometry

Rooibos tea, scientific name Aspalathus linearis, is a popular tea grown in South Africa and consumed worldwide for its unique taste and presumed health benefits. There is a growing interest in using rooibos tea as a supplement for the deficiency of metallic nutrients in South Africa. In this study, the total concentrations of manganese (Mn) and zinc (Zn) in acid-digested tea leaves and the corresponding tea infusions were determined by inductively coupled plasma-mass spectrometry (ICP-MS) to estimate the contribution of rooibos tea consumption to the recommended daily allowance (RDA) of Mn and Zn in consumers. The accuracy of microwave-assisted acid digestion and tea infusion methods were checked by analyzing INCT-TL-1 tea leaves certified reference material (CRM) and samples spiked with standards, respectively. Both methods yielded quantitative percentage recoveries for Mn and Zn. Rooibos tea leaves and the corresponding infusions are composed of higher levels of Mn than Zn where 40.9 to 85.7 μg Mn/g and 4.15 to 12.2 μg Zn/g were found in digested tea leaves and 11.8 to 30.2 μg Mn/g and 1.51 to 4.59 μg Zn/g in tea infusions. These results indicate the contribution of about 1.0 to 3.2% Mn and 0.03 to 0.08% Zn in males approximately ≥ 9 years of age and 1.3 to 3.8% Mn and 0.04 to 0.11% Zn in females of the same age group as males of the RDA from drinking a cup of tea obtained by infusing a 2-g bag of rooibos tea.