# Enhancing the Flavor Profile of Summer Green Tea via Fermentation with _Aspergillus niger_ RAF106
## 3 Results
### Changes of Non-Volatile Components in Light Fermentation Tea  
To further investigate the impact of _A. niger_ RAF106 fermentation on the nonvolatile compounds present in SGT, we conducted a comprehensive analysis to observe the dynamic changes occurring throughout the fermentation process (Table 2).  
The content of non-ester catechin and gallic acid (GA) gradually increased during fermentation, while the content of ester catechin decreased progressively. The (-)-epigallocatechin (EGC) content exhibited a time-dependent increase, reaching its peak after 6 days of fermentation with a significant increase of 123.29% (\(p<0.05\)) compared to the control group (CK). Similarly, (-)-epicatechin (EC) content showed an initial rise followed by a decline during fermentation, reaching its maximum value after 4 days with a significant increase of 133.53% (\(p<0.05\)) compared to CK. The GA content displayed a gradual increase and reached an astounding increment of 3775% (\(p<0.05\)) after 6 days of fermentation. On the other hand, both the (-)-epigallocatechin gallate (EGCG) and (-)-epicatechin gallate (ECG) contents decreased gradually as fermentation progressed, with reductions of 83.25% and 79.39%, respectively (\(p<0.05\)), observed after 6 days.  
The content of lactic acid and acetic acid was significantly increased in _A. niger_ RAF106 fermented tea, establishing them as predominant organic acids following fermentation (\(p<0.05\)). Compared to CK, there was a significant increase in the content of lactic acid, acetic acid, and citric acid after fermentation. Lactic acid content reached its peak at 4 days of fermentation with a remarkable increase of 524.58% (\(p<0.05\)), while the acetic acid content peaked at 2 days of fermentation with an increase of 411.41% (\(p<0.05\)). Additionally, citric acid content increased by 544.39% (\(p<0.05\)) at 6 days of fermentation. The content of oxal acid and fumaric acid in tea exhibited fluctuations during fermentation, with a decrease of 36.82% and 45.98%, respectively, at day 6 (\(p<0.05\)). Gradual reductions were observed in the content of quinic acid and malic acid throughout the fermentation process, with a decrease of 30.90% (\(p<0.05\)) in quinic acid after 6 days of fermentation and a reduction of 72.20% (\(p<0.05\)) in malic acid after the same duration.  
The total polyphenol content remained stable throughout the fermentation process. The free amino acid content exhibited a significant increase with a prolonged fermenttation time, reaching its peak after 6 days of fermentation and showing an 18.09% increase (\(p<0.05\)) compared to the control group (CK). The caffeine content did not show any significant changes during the initial 4 days of fermentation but decreased by 7.46% (\(p<0.05\)) on the 6 th day compared to CK. The soluble sugar and total flavonoid contents initially increased and then decreased as fermentation progressed, with their highest values observed at 4 days of fermentation, exhibiting a remarkable increase of 95.59% and 54.70%, respectively, compared to CK (\(p<0.05\)).