# Enhancing the Flavor Profile of Summer Green Tea via Fermentation with _Aspergillus niger_ RAF106
## 3 Results
### Changes of Tea Volatiles during Fermentation
#### 3.1.2 Volatile Compounds Identified by HS-SPME-GC-MS  
To investigate the distinctive flavor profile of fermented tea at various fermentation durations, we conducted tea extraction to obtain volatile compounds, which were subsequently analyzed using GC-MS. A total of 86 different types of compounds were detected, including 26 alkanes, 16 alkenes, 17 alcohols, 7 aldehydes, 11 ketones, 3 esters, 3 nitrogen oxides, and 3 other substances, were identified. The CK tea leaves, fermented for 2 days, 4 days, and 6 days, respectively, contained a total of 50, 44, 41, and 48 volatile compounds (Figure 3A, Table 1). The proportion of volatile substances in tea leaves increased with the fermentation time, with alcohol compounds being the most abundant. The content of alcohol compounds in CK, D2, D4, and 6D accounted for 39.25%, 41.80%, 48.88%, and 54.80%, respectively. Alcohol compounds gradually became the main volatile substance during a fermentation period of up to 6 days. Ketones and alkanes were found in CK, accounting for the relative contents of 21.65% and 13.71%, respectively. The content of alkanes and nitrogen oxides progressively increased with fermentation time, reaching 24.32% and 8.95%, respectively, on the sixth day of fermentation (Figure 3B). Additionally, we conducted a principal component analysis on these 86 compounds. Two principal components (PCs) were obtained from the PCA analysis, namely PC1 and PC2. They accounted for 64.85% and 22.24% of the total variance, respectively. The samples in the CK group exhibited a negative distribution along the PC1 direction, indicating dynamic changes in the relevant products at D2 (Figure 3C). Alcohol, predominantly characterized by floral and fruity aromas, constitutes the primary aroma compound in most teas. During fermentation, linalool and its derivatives emerged as the dominant alcohol, and the linalool content peaked at D4 relative to CK, showing a significant increase of 35.16% (\(p<0.05\)). The pyranic and furan oxidation of linalool exhibited a gradual increment over time during fermentation, demonstrating a significant rise of 70.71% and 225.12%, respectively, compared to CK (\(p<0.05\)). However, the relative content of dihydrolinalool gradually declined throughout the fermentation process, with a decrease of 77.14% after 6 days of fermentation (\(p<0.05\)). The substances that underwent the most significant changes during fermentation were (Z)-\(\alpha\),\(\alpha\),5-trimethyl-5-vinyltetrahydrofuran-2-methanol. Its content gradually increased throughout the process, starting at 1.62% in CK and rising to 5.32% after 6 days of fermentation (\(p<0.05\)). Post-fermentation analysis did not detect substances such as 1-octene-3-ol, 1-methylcycloheptanol, \(\alpha\)-terpinol, however, (+)-\(\alpha\)-terpinol, ionol, and phenylethanol were all detectable during the fermentation process. The gradual increase in the (+)-\(\alpha\)-terpineol content during fermentation could be attributed to the transformation of \(\alpha\)-terpineol into its isomer (+)-\(\alpha\)-terpineol. After 6 days of fermentation, the content of (+)-\(\alpha\)-terpineol reached 3.13% (\(p<0.05\)). Ionol content increased to 3.38% (\(p<0.05\)), while the phenylethanol content peaked at 8.05% (\(p<0.05\)) and decreased to 4.77% after 6 days of fermentation (\(p<0.05\)). Figure 3: Effect of fermentation time on volatiles in tea (**A**) Amount of different volatile compounds during fermentation (**B**) Proportion of different volatile compounds during fermentation (**C**) PCA plot of volatiles during fermentation (**D**) Thermogram of relative. a, b, c, d different lowercase letters indicate significant differences between groups (\(p<0.05\)). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{1}{c}{**No.