Popular medicinal plants and their infusions have been the subject of significant scientific interest due to their therapeutic value for the prevention and treatment of diseases and health disorders. However, chemical compositions of medicinal plant species are complex.
In addition to being sources of organic compounds, such as polyphenols, flavonoids, proteins, vitamins carbohydrates among others, medicinal plant infusions are also rich sources of several elements, including major dietary metals (Ca, K and Mg), minor and trace minerals (Cu, Fe, Mn, Na, Sr, Zn) and heavy metals (Cd, Cr, Ni, Pb). Many of these elements are essential for the good health and thus, deficiency or excess of these elements may have significant health consequences.
Given the health implications of the mineral content in medicinal plant infusions it is not surprising that a number of studies have been performed to quantify their levels in tea leaves and their infusions using various analytical techniques. In a recent publication, we highlighted the analytical capabilities of a low-power total reflection X-ray fluorescence spectrometry (TXRF) method for multielemental analysis of vegetal foodstuff.
One of the major advantages of this analytical approach was the easy sample preparation (requiring only the suspension of 20 mg of the powdered sample in 1 mL of an aqueous internal standard) and the low operational costs (no consumables are needed for TXRF function). In a second study, we developed a similar method but for the analysis of black tea and mint infusions in order to study the effects of infusion parameters, tea origin and infusion type on leaching of elements of interest to human health.
In this case, for TXRF analysis, 1 mL of the infusion was mixed with 50 µL of a stock solution of Rh 100 mg/L (internal standard). The resulting solution was thoroughly homogenized and an aliquot of 10 µL was transferred onto a quartz glass sample carrier and dried using an infrared lamp for the later TXRF analysis. As an example, in the figure below, TXRF spectra obtained in the analysis of a black tea and a mint infusion are displayed.
Obtained results on Ca, Cu and Sr content in infusions showed up the significance of the water type used to prepare the infusion. Regarding the infusion time, it was demonstrated that element content in black tea and mint infusions is, in general, independent of infusion time (from 1 minute to 60 minutes). Only significant differences between the Mn, Rb, K and Ca content over time were observed. It was also demonstrated that Mn and Rb concentrations are significantly higher in tea infusions.
Therefore, tea infusions can be a source of these essential elements for human health. For instance, Mn participates in numerous metabolic and physiological processes and some studies have demonstrated that under stimulated intestinal conditions, a single serving of tea contributes to about 10% of the average daily dietary intake of Mn in a potentially bioavailable form.
Despite the fact that a large number of samples should be considered to study differences between infusions from different origin, compositional differences can be significantly detected using this simple and cost-effective developed methodology.
These findings are described in the articles entitled Multi-element analysis of vegetal foodstuff by means of low power total reflection X-ray fluorescence (TXRF) spectrometry and Multielement analysis of tea and mint infusions by total reflection X-ray fluorescence spectrometry, published in the journals Food Chemistry and Food Analytical Methods, respectively. This work was led by Eva Marguí & Mitko Voutchkov from the University of Girona and The University of the West Indies, respectively.