# Tea Infusions as a Source of Phenolic Compounds in the Human Diet
## 3 Results and Discussion
[PERSON] and [PERSON] [38] confirmed the dependence of a greater quantity of copper passing from the leaves to the green tea infusions as compared to black tea, which they attribute to the formation of different species of this element in different tea types. These authors also believe that the polymerized phenolic compounds found in black tea can form soluble and insoluble bonds with the metals contained in the leaves, which contributes to the different rates and degrees of extraction with water. It appears to be particularly important to identify the correlation relationships between the phenolic compound content and the levels of other components occurring in tea. Directly proportional correlation relationships were found between the total phenolics content and the oxalate, calcium, and sodium levels (Table 3). This means that as the oxalate, calcium, and sodium contents increase, the level of polyphenols found in tea infusions increases, which may indicate the similarity of chemical bonds formed by these compounds between one another and/or with other tea components. [PERSON] and [PERSON] [11] also demonstrated significant relationships between phenolic compounds and certain elements related to their similar chemical connections and interactions, which is important, especially during the metabolic processes occurring in the plants. The relationship between polyphenols and oxalates (r = 0.6209, Table 3) is also confirmed by Figure 3, which shows that particular relationships between these components are found in green and black tea infusions. Strong correlation relationships were also observed between phenolic compounds, calcium, and sodium, for which the determined correlation coefficients amount to r = 0.8516 and r = 0.8045, respectively (Table 3). The data presented in Figure 3 indicate the exceptional significance of these relationships in black and red tea infusions and a much weaker relationship in green tea. The relationships between phenolic compounds and minerals were also indicated by [PERSON] et al. [27] and [PERSON] [39], who stated that the direction of these relationships is determined by the phenolic compound type. In most of the cases analyzed by the authors, flavonoids formed inversely proportional relationships with mineral elements, whereas phenolic acids formed directly proportional relationships. The data presented in Figure 3 show that during the preparation of black tea infusions, the relationships between the phenolic compound levels and the calcium and sodium contents appear to be of particular importance. Certain relationships were also found between the polyphenics content and the manganese, calcium, and sodium contents in red tea infusions. The relationships noted between phenolic compounds and the sodium and copper contents found in green tea infusions appear to be only slightly significant. Analysis of the dendrogram also enables the conclusion that the oxalate level demonstrates close relationships with, primarily, the analyzed type of tea leaves and their of copper content and can be related to phenolics content, primarily in black and green tea infusions. The fact that there are various dependencies observed between the components present in infusions prepared from different types of tea confirms the considerable impact of technological leaf treatment on the level and properties of their components [12; 23; 26; 37]. Based on the individual component levels determined in this study, it is also important to identify the effect of average tea consumption, assumed to be three to four mugs (1 L) per day, on human health. The components that raise many doubts are oxalates. According to the American Dietetic Association, the levels of oxalates in people with increased risk of kidney  
Figure 3: Dendrogram of different tea infusions according to cluster analysis of similarity based on phenolic content, oxalates, and some minerals (Ca, Na, Cu, Mn). TPC—total phenolic compounds; O—oxalates; G, R, B—green, red (pu-erh), and black tea, respectively.