# Tea Infusions as a Source of Phenolic Compounds in the Human Diet
## 3 Results and Discussion
For this type of tea, the production process involves the complete fermentation of the leaves, during which catechins are converted, under the influence of polyphenol oxidase, into compounds of higher molecular weight that can be difficult to extract from the tea leaves with water [50]. \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline \multirow{2}{*}{**Tea Type**} & \multirow{2}{*}{\ \begin{tabular}{c} **Extraction** \\ **Time [min]** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **Total Phenolic** \\ **Compounds [\%] * \\ \end{tabular}  } & \multirow{2}{*}{**Oxalates [\%] *} & \multicolumn{5}{c}{**Mineral Elements [\%] *} \\ \cline{5-8}  & & & & **Ca** & **Na** & **Cu** & **Mn** \\ \hline green & 6 & * & * & * & * & * & * \\  & 10 & \(\uparrow\) 27 & \(\uparrow\) 34 & \(\uparrow\) 9 & \(\downarrow\) 5 & \(\uparrow\) 5 & \(\uparrow\) 27 \\  & 20 & \(\uparrow\) 75 & \(\uparrow\) 49 & \(\uparrow\) 24 & \(\downarrow\) 6 & \(\uparrow\) 57 & \(\uparrow\) 51 \\  & 30 & \(\uparrow\) 41 & \(\uparrow\) 71 & \(\uparrow\) 35 & \(\downarrow\) 6 & \(\uparrow\) 50 & \(\uparrow\) 45 \\ \hline red &One of the components whose content in the infusions of all analyzed tea types increased steadily over the entire duration of leaf extraction with water was calcium, the levels of which in black tea infusions prepared for 30 min were higher by almost 60% as compared to infusions prepared for 6 min. An almost two times lower increase in the content of this element was observed during the prolonged leaf extraction process in green tea infusions, whereas an almost five times lower rate of increase was determined in red tea infusions. Differences in the levels of calcium passing from the leaves to the infusions of different tea types were also noted by [PERSON] et al. [13], who attributed them primarily to leaf structure and age (black tea is produced using older and harder leaves), whereas [PERSON] et al. [51] additionally linked this phenomenon to the distribution of calcium in individual leaf tissues. A clear increasing trend with increased time of leaf contact with water was also observed for oxalates and manganese. Red tea infusions prepared for 20 and 30 min contained almost two times more oxalates than the 6 min infusions, with the smallest (15%) increase in the content of these compounds noted in black tea infusions. A similar degree of increase in oxalate content in tea infusions prepared for a longer time was also indicated in a study by [PERSON] et al. [19]. Moreover, [PERSON] et al. [13] confirmed the particularly high content of these compounds in red tea infusions, which they linked to the specific structure of red tea leaves. Manganese content increased by almost 50% in the green and black tea infusions prepared for the longest time, whereas an almost 70% increase in the levels of this component was observed as the duration of red tea leaf extraction increased. The trend of a steady increase in manganese with duration of leaf contact with water was also confirmed by [PERSON] [39], who demonstrated that depending on the analyzed tea type, the level of this element can increase by 20-49% of its initial quantity. As for copper, no clear dependencies could be demonstrated as regards the change in its content as the time of extraction of the various types of tea leaves increased. Increased duration of green tea leaf contact with water resulted in increased levels of copper by 57% after 20 min of infusion, remaining almost unchanged for another 10 min. Different trends were observed for black tea, in which the copper content decreased with increased leaf extraction time, with the changes being the most intense at the beginning of the process. Initially, the level of this element in the red tea infusions increased (by almost 30% between 6 and 10 min of leaf contact with water); then, it decreased by almost 30%, finally increasing by approximately 10%.