Influence of manufacturing process on the contents of iron, copper, chromium, nickel and manganese elements in Crush, Tear and Curl black tea, their transfer rates and health risk assessment

CTC (Crush, Tear and Curl) black tea, as one of the most representative black tea, is a very popular beverage in the world owing to its potential health benefits. However, the presence of toxic elements has gained more and more public health concerns. The contents of elements in tea were affected not only by growth environment but also by the technology of manufacturing process. Unfortunately, the studies of the influence of manufacturing process on the levels of elements in final tea products were very limited. In this study, the influence of manufacturing process on the levels of iron (Fe), copper (Cu), chromium (Cr), nickel (Ni) and manganese (Mn) in CTC black tea were determined by inductively coupled plasma mass spectrometry (ICP-MS). It was found that the concentrations of Fe and Cu in tea leaves could greatly increase after rolling by rotorvane, which was proved to be the key stage affecting the Fe and Cu levels in final made tea. However, Cr and Ni contents in tea leaves increased greatly after cutting by CTC rollers. There was no significant difference among Mn concentrations in tea samples obtained from different stages according to the one-way ANOVA analysis (p > 0.05). The effect of brewing time and brewing times on the transfer rates were investigated. Ni displayed the highest transfer rate with the value of 75.74%, while the transfer rates of Cu, Cr and Mn were 30.08%, 26.62% and 34.98%, respectively. With respect to the recommended daily allowance, the Fe, Cu, Cr and Ni in CTC black tea do not pose significant risk to human health while concerns should be paid to Mn since its HQ was still large than 1% even considering the bioavailability.