# Enhancing the Flavor Profile of Summer Green Tea via Fermentation with _Aspergillus niger_ RAF106
## 3 Results
### Sensory Evaluation  
Based on the color, aroma, and taste of tea, a sensory evaluation was conducted for tea at different fermentation times. Although no statistically significant difference was observed, the sensory evaluation scores of teas fermented by _A. niger_ RAF106 exhibited an improvement. The color gradually brightened with prolonged fermentation time. The aroma of the tea intensified with prolonged fermentation, exhibiting a sweet fragrance that aligned with the presence of floral and fruity volatile nitrogen oxides and alcohol in the tea. With an extended fermentation time, the taste gradually evolved into a mellower and sweeter aftertaste accompanied by a balanced level of acidity. This transformation could be attributed to a significant reduction in ester-type catechins, coupled with an increase in the content of free amino acids and soluble sugars (Table 3). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Compound** & \multicolumn{4}{c}{**Content (\%)**} \\  & **CK** & **D2** & **D4** & **D6** \\ \hline \multicolumn{5}{c}{Catechins and gallic acid *} \\  & 1.46 \(\pm\) 0.089 c & 2.79 \(\pm\) 0.153 b & 3.15 \(\pm\) 0.239 a & 3.26 \(\pm\) 0.101 a \\ C & 0.45 \(\pm\) 0.027 a & 0.52 \(\pm\) 0.031 a & 0.45 \(\pm\) 0.008 a & 0.41 \(\pm\) 0.062 a \\ EC & 1.67 \(\pm\) 0.092 b & 3.96 \(\pm\) 0.143 a & 4.09 \(\pm\) 0.196 a & 3.90 \(\pm\) 0.18 a \\ Non-ester catechins & 3.58 \(\pm\) 0.123 c & 7.27 \(\pm\) 0.181 b & 7.69 \(\pm\) 0.437 a & 7.57 \(\pm\) 0.161 ab \\ EGCG & 3.88 \(\pm\) 0.236 a & 1.32 \(\pm\) 0.08 b & 0.89 \(\pm\) 0.025 c & 0.65 \(\pm\) 0.034 c \\ ECG & 4.27 \(\pm\) 0.208 a & 1.86 \(\pm\) 0.103 b & 1.13 \(\pm\) 0.044 c & 0.88 \(\pm\) 0.006 c \\ Ester catechins & 8.15 \(\pm\) 0.441 a & 3.17 \(\pm\) 0.181 b & 2.02 \(\pm\) 0.066 c & 1.53 \(\pm\) 0.033 d \\ GA & 0.12 \(\pm\) 0.003 c & 3.35 \(\pm\) 0.086 b & 4.30 \(\pm\) 0.218 a & 4.65 \(\pm\) 0.139 a \\ Organic acid & & & & \\ Oxalic acid & 1.04 \(\pm\) 0.074 a & 0.42 \(\pm\) 0.097 c & 0.87 \(\pm\) 0.161 ab & 0.66 \(\pm\) 0.055 bc \\ Quinic acid & 3.73 \(\pm\) 0.272 a & 3.14 \(\pm\) 0.299 b & 2.22 \(\pm\) 0.103 d & 2.57 \(\pm\) 0.154 c \\ Malic acid & 4.04 \(\pm\) 0.394 a & 3.03 \(\pm\) 0.201 b & 1.74 \(\pm\) 0.074 c & 1.12 \(\pm\) 0.086 d \\ Lactic acid & 4.63 \(\pm\) 0.71 c & 24.83 \(\pm\) 1.84 b & 28.89 \(\pm\) 1.083 a & 24.1 \(\pm\) 3.075 b \\ Acetic acid & 3.13 \(\pm\) 0.476 d & 16 \(\pm\) 0.991 a & 13.05 \(\pm\) 1.316 b & 9.48 \(\pm\) 1.532 c \\ Fumaric acid & 0.36 \(\pm\) 0.043 b & 0.34 \(\pm\) 0.061 b & 0.5 \(\pm\) 0.033 a & 0.2 \(\pm\) 0.017 c \\ Citric acid & 0.21 \(\pm\) 0.017 c & 0.23 \(\pm\) 0.03 c & 0.86 \(\pm\) 0.064 b & 1.38 \(\pm\) 0.073 a \\ Others & & & & \\ Tea polyphenols & 18.34 \(\pm\) 0.33 a & 20.59 \(\pm\) 0.644 a & 19.66 \(\pm\) 1.032 a & 20 \(\pm\) 0.692 a \\ Amino acid & 4.73 \(\pm\) 0.138 c & 5.11 \(\pm\) 0.181 bc & 5.18 \(\pm\) 0.071 ab & 5.59 \(\pm\) 0.137 a \\ Caffe & 3.86 \(\pm\) 0.015 a & 3.82 \(\pm\) 0.044 a & 3.93 \(\pm\) 0.023 a & 3.57 \(\pm\) 0.023 b \\ Soluble sugar & 0.68 \(\pm\) 0.044 c & 1.29 \(\pm\) 0.085 ab & 1.33 \(\pm\) 0.045 a & 1.16 \(\pm\) 0.010 \\ Total flavone & 0.75 \(\pm\) 0.06 c & 1.04 \(\pm\) 0.074 ab & 1.16 \(\pm\) 0.08 a & 0.84 \(\pm\) 0.03 bc \\ \hline \hline \end{tabular}  
* (+)-catechin (C), (+)-epigallocatechin (ECC), (-)-epigatechin (EC), non-ester catechins (EGC, C and EC), (-)-epicatechin gallate (EGCG), ester catechins (EGCG and ECG), and gallic acid (GA). a, b, c, d different lowercase letters indicate significant differences between groups (\(p<0.05\)).  
\end{table} 
Table 2: Changes of non-volatile components during fermentation.