Abstract
M.Sc. (Chemistry)
Rooibos tea, also known by its botanical name as Asphalanthus linearis is an indigenous plant to South Africa exclusively grown in the Clanwilliam district and its surroundings in the Western Cape and Northern Cape Provinces. Among other things, rooibos tea is loved for being caffeine free, good flavor when consumed as steeped beverage and as herbal remedy and a potential source of essential elements. There is a growing interest to use rooibos tea as a potential supplement for deficiency of metallic nutrients faced by South Africa. Manganese (Mn) and zinc (Zn), which are the focus of this study, are regarded essential in human metabolism. Manganese deficiency leads to bones deformation and its overdose to neurotoxicity, while zinc deficiency leads to growth retardation and its overdose to reduced copper in the body. The combined use of fractionation and speciation techniques will provide information on accessible levels and forms of Mn and Zn to consumers, which may in turn ward off their deficiency. The purpose of this study was to quantify, fractionate (separate into a group of compounds) and speciate (separate into individual compounds) Mn and Zn in rooibos tea with a view to estimating the actual amounts and forms of the metals available to rooibos tea consumers.
Advocates of rooibos tea claim multiple uses in such products as beverages, salads, cosmetic products, rooibos-infused dishes and as a dying agent but its primary use remains to be consumed as brewed tea (infusion). The proportion of Mn and Zn accessible to consumers through the consumption of rooibos tea can reasonably be assessed by comparing the levels in acid-digested tea leaves (total concentration) and in brewed infusions (dissolved portion). In this study, the total concentrations of Mn and Zn in tea infusions and digested tea leaves were determined using the inductively coupled plasma mass spectrometry (ICP-MS). The accuracy of these results was checked by analyzing tea leaves certified reference material (CRM) (INCT-TL-1) for the digested samples. Due to the absence of suitable CRMs, spiking experiments were conducted to ensure accuracy of results for the infusions. The percentage recoveries were within 80 - 120% for both metals in digested CRM but relatively lower recoveries were obtained with the infusions for Mn (75%) and Zn (73%). In general, higher concentrations were found for Mn than Zn in both digested and infused rooibos tea...