## 3 Results and Discussion  
### Catechin Content  
The four main catechins present in tea are EC, ECG, EGC, and EGCG [14]; therefore, the present study focused on these compounds. Catechins were identified using the LC-QTOF-MS method (Supplementary Materials: Table S1, Figure S1). The analyses allowed the determination of their abundance and the percentage of these compounds in the infusions. The profile of catechins (Figure 1) and their percentage of content in the initial non-supplemented samples (Figure 2) were determined, and then the effect of the additives on the extraction of the analysed catechins was estimated (Figure 3). In addition, multidimensional statistical techniques, including PCA, were used to monitor the relationship between the content of phenols and the antioxidant activity of the analysed teas [12; 27]. Figure 1: Catechin profile in the tea varieties identified by LC-QTOF-MS. EC—epicatechin; EGC—epigallocatechin; ECG—epicatechin gallate; EGCG—epigallocatechin gallate. It was observed that the analysed varieties of tea differed in the amount and percentage ratio of catechins contained therein (Figures 1 and 2). The lower content of catechins in the black tea can be explained by the fact that, in some types of deeply fermented tea, monomeric catechins are oxidised or condensed to theflavirus and thearubigins [28; 29]. Available research results also confirm that black tea may contain lower amounts of phenols that may be degraded in the fermentation process [30], but our research has shown that the differences between the varieties in the contents of catechins were much more pronounced than the differences in the contents of phenolic compounds. The white tea contained the largest amount of EC (40.6%) and the lowest level of ECG (15%), while the black tea contained 33.1% EC and 59.5% ECG. The infusions also differed in the content of EGC and EGCG, which was much higher in the white tea; this may explain its higher antioxidant properties. The obtained results are consistent with those obtained by other authors, who found dominant ECG concentrations in black and green teas [11]. In turn, [PERSON] et al. [4] analysed the concentrations of four catechins in six types of green teas and five types of black teas and showed that EGCG was the dominant catechin in all the analysed teas, with the content of this compound in green teas being almost three times higher than that in black teas [4]. The analysis of differences in the concentration of EGCG in infusions from three types of teas, black, green, and white, was conducted by [PERSON] et al. [31]. They noted the highest concentration of this compound in green tea, followed by white tea, in which it was about 1.5 times lower, while the concentration of EGCG in black tea was over 9 times lower [31]. In turn, [PERSON] et al. [32] analysed the chemical composition and antioxidant activity of five types of tea obtained from one tea bush and showed that white  
Figure 3: Changes in the catechin profile in the infusions of enriched teas identified by LC-QTOF-MS; (**a**) white tea, (**b**) black tea. EC—epicatechin; EGC—epigallocatechin; ECG—epicatechin gallate; EGCG—epigallocatechin gallate. Figure 2: Percentage of catechins in the tea infusions identified by LC-QTOF-MS; (**a**) white tea, (**b**) black tea. EC—epicatechin; EGC—epigallocatechin; ECG—epicatechin gallate; EGCG—epigallocatechin gallate. tea contained almost three times higher concentrations of total catechins than black tea and over two-fold lower amounts than that in green tea. An important issue in the present work was the evaluation of the effect of fruit additives on the catechin profile in the tea infusions. Figure 3 shows the results of the lemon, quince, strawberry, and sweet pepper additions on the content of the analysed compounds. The research results proved that all the additives used in the black tea increased the content of catechins. The quince additive had the most favourable effect on the content of three out of the four analysed catechins.