Concentration and Chemical Species of Manganese in Tea Leaves and Tea Infusion

Abstract

To evaluate a contribution of tea to manganese intake of Japanese, manganese contents in several types of tea leaves and tea infusions were determined and chemical species of this element in the tea infusions were examined. Thirty-five samples of green tea, 15 samples of black tea and 13 samples of oolong tea were collected. Their manganese contents were ranged in 200 to 1000 μg/g and were similar values to those listed in Standard Tables of Food Composition in Japan. Infusions prepared from these tea samples also showed similar manganese concentrations (2 to 5 μg/ml) to those listed in the Tables. However, manganese concentrations in tea infusions and commercial tea drinks consumed by healthy 108 university students were 0.5 to 2 μg/ml and were significantly less than those of tea infusions prepared in the laboratory or those listed in the Tables. Based on the present analytical results, manganese intake from tea is estimated to be less than half of total dietary manganese intake in Japanese. Most of manganese in the tea infusions prepared in the laboratory was filterable to an ultrafilter with molecular mass cut-off of 5kDa. In analysis of high-performance liquid chromatography using a column of molecular exclusive resin, manganese in the tea infusion was eluted at the same retention time of bivalent manganese ion.