From herbal substance to infusion : the fate of polyphenols and heavy metals

Abstract

The content of polyphenols and concentration of heavy metals (Zn, Cd, Ba, Cu, Cr, Mn, Fe and Pb) in 46 commercially available herbal tea products were investigated in this study. The total content of polyphenols was determined by using the Folin-Ciocalteu assay and the concentration of heavy metals was determined by Microwave-Plasma Atomic Emission Spectroscopy. Principal Component Analysis (PCA) varied between untreated herbal substances, herbal infusions and residual herbal extracts. A higher content of polyphenols was exhibited in herbal infusions (<8.799% w/w) than the untreated herbal substances (<1.517% w/w) and residual herbal extracts (<4.402% w/w), and the higher the polyphenolic content in the untreated herbal substances, the higher was the content of polyphenols extracted in the infusion (r=0.732). The metals present in the highest concentration were Mn (0.0005 – 0.0786 %w/w), Fe (0.0005 – 0.0570% w/w) and Zn (0.0004 – 0.0398% w/w), whereas Cr (<0.0003% w/w), Cu (<0.0026% w/w), Cd (<0.0003% w/w) and Pb (<0.0022% w/w) were the least abundant. Ba showed the highest extractability (5.26-100%), whereas Cr showed the poorest extractability (0%, except for sample 02b).The concentration of Zn, Cd and Pb in almost all samples exceeded the permissible limits defined by the Prevention of Herbal Tea Adulteration Act, except for Fe, which was found to be below the permissible limit. Furthermore, the higher the polyphenolic content, the higher is the copper and manganese content in the untreated herbal substances and residual herbal extracts.