## 3 Results and Discussion
### Effect of Infusion Temperature  
The antioxidant capacity for DPPH scavenging activity and the total phenols of black tea are dependent on infusion temperature. Figure 3 confirms that the DPPH scavenging ability of black tea was affected by infusion temperature. A higher DPPH scavenging ability was noted at higher temperatures, revealing that the scavenging activity for the DPPH radical of black tea prepared with boiling water was better than the others at the same tea concentration. However, Figure 3 indicates that the DPPH scavenging activity increased with tea concentration regardless of infusion temperature. Furthermore, the effects of tea concentration on the DPPH scavenging activity were more prominent at a higher infusion temperature. According to Figure 3, the IC\({}_{50}\) values were \(100.0\pm 13.7\), \(63.0\pm 4.2\), \(46.2\pm 5.5\), \(35.3\pm 5.2\), and \(28.4\pm 4.8\)\(\mu\)g/mL for temperatures from 60 to 100 \({}^{\circ}\)C (Figure 4). The total phenolic contents for 60 to 100 \({}^{\circ}\)C  
Figure 3: Effects of temperature on the DPPH scavenging activity of black tea. Figure 2: Relationship between 1,1-Diphenyl-2-picrylhydrazyl (DPPH) IC\({}_{50}\) and the water–tea leaves weight ratio. were \(50.4\pm 5.2\), \(72.6\pm 7.9\), \(104.1\pm 7.0\), \(135.2\pm 8.5\), and \(178.6\pm 16.4\) mg GAE/g dry leaf, respectively (Table 1). An increase in the DPPH scavenging ability and the total phenolic content associated with an increase in the infusion temperature concurred with the findings in previous reports [6; 8; 10; 23; 24; 25]. Thus, the infusion temperature of black tea is critical in the preparation process when aiming for high antioxidant capacity. Black tea with lower DPPH IC\({}_{50}\) had higher total phenols, and the IC\({}_{50}\) of DPPH scavenging ability showed a negative correlation with the value of the total phenolic content, as seen in Figure 5. This result concurred with previous reports [23; 26; 27; 28]. Theaflavins, a type of phenolic compound in black tea, may contribute to strong antioxidant properties that affect the DPPH scavenging activity and total phenols [23; 29; 30; 31; 32]. However, the therapeutic activities of black tea are attributed not only to the antioxidant activity of its components but also to the ability of bioactive molecules to interact with several biological targets [5; 33]. At a high temperature, chemical degradation can occur, changing the structure of temperature-sensitive molecules such as (-)-epigallocatechin-3-gallate. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{5}{c}{**Temperature (°C)**} \\ \cline{2-5}  & **60** & **70** & **80** & **90** & **100** \\ \hline Total phenolic content & \multirow{2}{*}{\(50.4\pm 5.2\)} & \multirow{2}{*}{\(72.6\pm 7.9\)} & \multirow{2}{*}{\(104.1\pm 7.0\)} & \multirow{2}{*}{\(135.2\pm 8.5\)} & \multirow{2}{*}{\(178.6\pm 16.4\)} \\ (mg GAE/g dry leaf) & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Effects of temperature on the total phenolic content of black tea. Figure 4: Effects of temperature on the DPPH IC\({}_{50}\) of black tea. Figure 5: Correlation between DPPH IC\({}_{50}\) and total phenolic content. Wide variations are noted among different kinds of black tea in terms of DPPH scavenging ability [9; 22; 34; 35; 36; 37; 23; 38] and total phenolic content [6; 20; 32; 36; 39]; these are highly dependent on the genetic background and growing conditions (such as temperature, nitrogen availability, and light conditions) of the plant material. The IC\({}_{50}\) of black tea in this study was 28.4 \(\pm\) 4.8 \(\upmu\)g/mL, and it falls within the range of 12.7-118.7 \(\upmu\)g/mL found by other authors [34; 38]. The total phenolic content in this study was 178.6 \(\pm\) 16.4 mg GAE/g dry leaf, and it was in the range from 50.9 \(\pm\) 4.1 mg GAE/g dry leaf [32] to 274.3 \(\pm\) 0.0 mg GAE/g dry leaf [20]. Different brewing conditions, including infusion temperature and time, may affect the DPPH IC\({}_{50}\) and total phenolic content. [PERSON] et al.