## 2 Results
### Effect of drying Temperature on the Non-Volatile Components of LBT
This indicates that optimizing the content of soluble sugars and amino acids in tea can effectively enhance the quality of LBT, which can also be achieved through the controlled reduction in the drying temperature. The mellowness of the tea infusion can be partially characterized by the ratio of tea polyphenols to amino acids (T/A). Generally, a lower T/A indicates a higher level of umami and a mellower taste in the tea infusion. For LBT, the T/A decreased initially and then increased with a rising drying temperature, suggesting that a suitable drying temperature can enhance both the mellowness and umami levels in the tea infusion. Tea polysaccharide, an acidic polysaccharide or acidic glycoprotein combined with protein, exhibits diverse functionalities, such as antioxidant, blood sugar reduction, blood fat lowering, and immune enhancement. The content of tea polysaccharide increased with an increasing drying temperature due to the hydrolysis of the original pectin under high-temperature and acidic conditions, resulting in the formation of water-soluble pectin [23]. The properties of caffeine remained unchanged during drying, while the content of tea polyphenols significantly decreased due to the enhanced oxidation and degradation at higher temperatures [24]. Theaflavins, thearubigins, and theabrownin are crucial constituents related to the color, umami and mellow taste, as well as the astringency of black tea infusion [25]. With an increasing drying temperature, the levels of theaflavins and theabrownins followed a trend of decreasing first and then increasing at higher temperatures (120-130 \({}^{\circ}\)C). The content of thearubigins remained relatively stable between 70 and 120 \({}^{\circ}\)C, but significantly (\(p<0.05\)) increased at 130 \({}^{\circ}\)C. There was a positive correlation between the theaflavin content and the black tea quality, while there was a negative correlation between the theabrownin content and black tea quality, suggesting that LBT can achieve a superior quality through low-temperature drying. As the primary constituents of tea polyphenols, catechkins exert a pivotal influence on the overall tea quality. As shown in Table 3, with an increasing drying temperature, the EGCG content remained relatively stable, the ECG content gradually decreased, and the EGC content exhibited a significant decrease and then became undetectable at 120 and 130 \({}^{\circ}\)C, in contrast to a substantial increase in the GC content from 120 \({}^{\circ}\)C onwards. Additionally, the C content witnessed a notable reduction between 70 and 100 \({}^{\circ}\)C, but with  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Sample** & **70 \({}^{\circ}\)C** & **80 \({}^{\circ}\)C** & **90 \(  
no significant changes at 110 \({}^{\circ}\)C. Moreover, with an increasing drying temperature, the amount of total catechins exhibited a significant decrease, which was consistent with the observed trend in the tea polyphenols. The above results indicated that the conversion of non-ester catechins could be more significantly influenced by the drying temperature. The catechins undergo epimerization, hydrolysis, and oxidation/condensation reactions primarily under heating conditions, with their reaction degree varying with the drying temperature. Previous studies have demonstrated that EC and EGC are more heat-sensitive than other catechins, and their thermal instability can be mainly attributed to epimerization and oxidation/condensation reactions, respectively [26]. In the present study, an increase in the drying temperature led to a decrease in the contents of EGC, ECG, and C, indicating that higher temperatures exacerbated the intensity of epimerization and oxidation/condensation reactions. The significant rise in the GC content at 120 \({}^{\circ}\)C may be attributed to either epimerization or the degradation of other catechin monomers induced by the excessively high temperatures.