## 3 Results and Discussion
### Effects of Enzyme Treatments on the Levels of Gallic Acid and Catechins in Tea Extract  
Catechins, including gallated and non-gallated catechins, are the most abundant polyphenols in tea, which play a vital role in the taste and health benefits of tea. EGCG and ECG are the main contributors to bittermess, while non-gallated catechins and gallic acid provide a refreshing aftertaste [41]. Therefore, the catechin content of the tea extract after enzyme treatment was further analyzed. Based on the literature, the general pathways of action of tannase, tyrosinase, and lactose on four catechins (EGCG, ECG, EGC, and C) were plotted (Figure 8). Tannase can act on the galloyl groups of EGCG and ECG, breaking the ester bonds and producing EGC, C, and gallic acid [5] (Figure 8a). According to the catechin level results, the contents of the gallated catechins EGCG and ECG in TAN, TAN-TYR, TAN-LAC, and TAN-TYR-LAC treated tea extracts all decreased significantly, with the largest decreases being observed for EGCG and ECG, which dropped by 81.93% and 94.62%, respectively (Figure 9b). For these four samples, the content of the non-gallated catechin EGC significantly increased, with TAN showing the highest increase, which was 3.15 times that of the untreated group (Figure 9c). Additionally, the content of gallic acid in TAN was significantly increased, being 9.31 times that of the untreated group (Figure 9a). Catechins contain multiple phenolic hydroxyl groups in their molecular structure; moreover, polyphenol oxidase is believed to contribute to the decrease in the content of gallated catechins during oxidation [16]. Both tyrosinase and lactose can convert catechins into dimers (such as theaflavins), trimers, and other substances, which enhance the antioxidant properties and health benefits of tea extracts [18]. Tyrosine acts only on the dihydroxyl B-ring on ECG and C, while lactose has broader substrate specificity. In addition to the dihydroxyl B-ring on ECG and C, lactose  
Figure 7: Free radical scavenging rate of DPPH (**a**), ABTS (**b**), and (**c**) -OH. The error bar represents the standard error of the mean, and by the LSD test, the average of different lowercase letters indicates a significant difference (\(p<0.05\)). can also act on the trihydroxy B-ring and the gallic acid groups on the trihydroxy C-ring of EGC and EGCG [17] (Figure 8b). As shown in Figure 9b, the TYR, LAC, and TYR-LAC also reduced the EGCG and ECG contents to varying degrees, while increasing the concentration of gallic acid. Therefore, tyrosinase and laccase can also reduce the content of gallated catechins; however, their ability to convert gallated catechins is relatively lower than that of tannase. In summary, EGCG was significantly positively correlated with ECG (r = 0.983, \(p\) < 0.001) and was significantly negatively correlated with gallic acid (GA) (r = \(-\)0.974, \(p\) < 0.001) and EGC (r = \(-\)0.928, \(p\) < 0.001). This result further verifies the gradual transformation of gallated catechins to non-gallated catechins during the reaction with the enzyme, accompanied by an increase in the gallic acid content. This fully explains the series of changes in the taste of the tea extracts after the enzyme treatments. The sensory score indicated that TAN-TYR had the best taste improvement effect, with the overall flavor score increasing by about 40%. The contents of EGCG and ECG, which reflect the bitterness of tea, were the lowest in the TAN-TYR-treated extracts, being only 157.03 and 6.5 mg/kg, respectively (Figure 9b). The electronic tongue results showed that the bitterness, astringency,  
Figure 8: Pathway of action of tannase (**a**) and tyrosinase and laccase (**b**) on catechins [5; 17; 21]. bitterness aftertaste, astringency aftertaste, and sourness of all samples were significantly affected, with TAN-TYR leading to the most significant bitterness reduction.