In view of the growing tea consumption and the variety of tea brands available on the market, the aim of the study was to determine the content of selected minerals (K, Ca, P, Mg and Al) in black, white and green teas as well as to estimate the influence of brewing time and the addition of acid (lemon juice) during the process of tea brewing on the mobility of selected elements. The brands of fine quality leaf tea selected for the study included three brands of black tea (Assam Dagapur, Darjeeling Jungpana, Ceylon Uva), three brands of white tea (Pai Mu Tan, Ya Bao Yesheng, China White Snow Buds) and three brands of green tea (Pi Lo Chun, Gyokuro, Hojicha). The tea infusions were brewed for 5 or 15 minutes. The procedure was repeated using dry tea leaves with the addition of acid, i.e. 5 ml of lemon juice. The contents of mineral elements in tea infusions were examined with an ICP-OES Thermo iCAP Dual 6500 spectrometer, using a 3-point calibration curve for each element, as well as optical adjustment applied via the method of internal models provided by yttrium and ytterbium ions. Certified Reference Material, characteristic for the relevant matrix, was used to verify selected lengths of the measurement lines. Generally, the mineral content in decreasing order was K>Ca>P>Mg>Al, the one exception being white tea (Ya Bao Yesheng). Longer boiling time and the addition of lemon juice caused a higher mineral content in tea infusions. Among the macroelements tested, calcium content increased the most after the addition of lemon juice (2-3 times higher in black and green teas, 3.5-4 times higher in white teas). However, potassium extraction decreased by about 10% after the addition of lemon juice. The aluminium content, which is associated with human neurodegenerative diseases, increased from 19 to 50% in black teas, from 56 to 200% in white teas and from 27 to 41% in green teas.  

23.2.2018