## 5 Conclusions  
In summary, this study provided an in-depth understanding of the enzymes secreted by _A. niger_ PW-2, revealing the bioconversion and improvement in the quality of steamed green tea fermented by _A. niger_ PW-2 using proteomic analysis. The _A. niger_ PW-2 fermented steamed green tea had lower contents of linalool, geraniol and _L-\(\alpha\)_-terpineol which contribute to the \"green\" aroma, while it had higher contents of 1-octen-3-ol, nonanal, decanal and ethyl palmitate which contribute to mushroom, citrus-like and cheese-like odors. After fermentation, the as stringent taste was significantly weakened, mainly due to the decrease in the contents of polyphenols, such as catechins. The contents of theabrownins increased significantly, causing the tea infusion to have a reddish-brown color. _Aspergillus niger_ PW-2 was found to secret enzymes that can degrade plant polysaccharides and phenolic compounds, as well as those that can produce theabrownins. The strain also secreted enzymes involved in the biosynthesis and degradation of proteins, causing the amino acid contents to change. This study advances our understanding of the mechanism of _A. niger_ PW-2 that influences the conversion of chemical compounds and the formation of unique sensory characteristics of fermented steamed green tea.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/foods11060865/s1](https://www.mdpi.com/article/10.3390/foods11060865/s1)]([https://www.mdpi.com/article/10.3390/foods11060865/s1](https://www.mdpi.com/article/10.3390/foods11060865/s1)), Figure S1: Heatmap analysis based on all proteins detected in all fermented samples; Figure S2: GO annotation classification (A) and KEGG pathway classification of all proteins detected in all fermented samples; Figure S3: Heatmap analyses of enzymes related to the pathways of the biosynthesis of amino acids (A), ribosome (B), aminoacyl-tRNA biosynthesis (C), proteasome (D) and ubiquitin mediated proteolysis (E); Figure S4: Analysis of amino acids summed by sweet, bitter, umami and as stringent taste; Supplementary methods: The methods of proteomics analysis; Table S1: Contents of volatile compounds identified in fermented teas; Table S2: Physicochemical properties of fermented teas; Table S3: VIP values and \(p\) values of all chemical factors of analysis on samples of Day 0 and Day 21; Table S4: All proteins identified in fermented teas samples; Table S5: Annotations of proteins by GO, KEGG and CAZymes; Table S6: Enzymes involved in glycoside hydrolases (GHs); Table S7: Enzymes involved in TNS, COD, LCS and POD; Table S8: Enzymes related to amino acids metabolism.  
Conceptualization, M.L. and H.G.; methodology, M.L. and K.Z.; investigation, M.L. and Y.X.; software, M.L.; formal analysis, M.L. and Y.X.; writing--original draft preparation, M.L.; data curation, Y.X.; validation, K.Z.; supervision, K.Z., Y.W. and H.G.; resources, H.G.; funding acquisition, Y.W. and H.G.; writing--review and editing, Y.W. and H.G. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Science and Technology Plan Project of Sichuan Province of China, grant numbers 2020 YFG0073 and 2020 YJ0067; the Sichuan University and Luzhou City Strategic Cooperation Project, grant number 2021 CDLZ-20; and the Sichuan University and Dazhou City Strategic Cooperation Project, grant number 2021 CDDZ-18.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest.