From herbal substance to infusion: The fate of polyphenols and trace elements

Abstract

ContextHerbal infusions are consumed worldwide owing to the beneficial properties often linked to their polyphenol content. However, whether cultivated or obtained from the wild, herbal substances may contain trace elements at various levels. This study relates to the release of polyphenols, and beneficial and toxic trace elements from herbal preparations during infusion of commercially-available herbal tea products. MethodsThe contents of 46 commercially-available herbal tea products were determined prior to and following infusion. Teabags (equal herb content) were infused in 200 mL boiling deionized water for 5 min in glass beakers. The total content of polyphenols was determined by using the Folin-Ciocalteu assay; heavy metals (Zn, Cd, Ba, Cu, Cr, Mn, Fe, and Pb) were determined by microwave plasma-atomic emission spectroscopy. ResultsA higher polyphenol content was detected in herbal infusions (0.97–8.80 % w/w) than in untreated herbal substances (0.32–1.52 % w/w) and residual herbal extracts (0.11–4.40 % w/w). The metals present in the highest concentrations were Mn, Fe, and Zn. Ba had the highest extractability, whereas Cr had the lowest extractability. ConclusionAccording to the Prevention of Herbal Tea Adulteration Act, Zn, Cd, and Pb in almost all samples exceeded the permissible limits, except for Fe. Furthermore, the higher the polyphenol content, the higher the copper and manganese contents in the untreated herbal substances and residual herbal extracts. The findings of this study imply that manufacturers need to analyze the finished product (consumer-prepared infusions) to verify the actual polyphenol content and whether trace elements are released.