## 2 Materials and Methods
### Processing and Decaffeination of Green and Black  
The fresh leaves were harvested from the Yongchuan district, Chongqing, China. The same batch of fresh leaves was used to manufacture green and black teas. The green and black teas were processed using typical manufacturing approaches. Briefly, a portion of fresh leaves was fixed at 150-180 \({}^{\circ}\)C for 3 min to fixate the endogenous enzymes, followed by a rolling procedure for 50 min, and then dried at 95-110 \({}^{\circ}\)C for 5 min into the green tea. Another portion of fresh leaves was withered at 25 \(\pm\) 2 \({}^{\circ}\)C and 70% humidity for 5 h and then rolled for 30 min. After that, the leaves were fermented at 28 \(\pm\) 2 \({}^{\circ}\)C and 95% humidity for 3 h, followed by drying at 90-100 \({}^{\circ}\)C for 5 min to obtain the black tea. The obtained tea was stored at \(-\)80 \({}^{\circ}\)C until further use. The tea leaves were slowly ground in a mortar. The particle sizes in the range of 0.3 to 0.6 mm in the tea samples were obtained using a sieve shaker. Then, the tea samples were decaffeinated using a supercritical CO\({}_{2}\) extraction system (HA220-50-06, Nantong Huaan Supercritical Extraction Co. Ltd., Nantong, China). An amount of 500 g of tea samples was put into the extraction kettle, and then 150 mL of distilled water was pumped as the co-solvent into the extraction kettle. The system parameters were set as follows: extraction pressure, 32 MPa; temperature, 50 \({}^{\circ}\)C; time, 3.5 h; flow rate of CO\({}_{2}\), 5 L/h. Next, the extraction system was opened, and then supercritical CO2 was introduced, and the extraction was completed after 3 h. The obtained tea leaves were dried in a vacuum dryer (SCIENTZ-30 ND, Ningbo Scientz Biotechnology Co., Ltd., Ningbo, China) to obtain decaffeinated tea samples. Total Water-Soluble Solid Content (TWSSC), Phenolics, Theaflavins, Theabrownins, Thearbugins, and Total Free Amino Acids (TFAAs)  
TWSSC was measured using a previous method [16]. The tea was extracted twice at a tea-to-water ratio of 1 g/50 mL for 30 min at 80 \({}^{\circ}\)C. Then the extracts were combined and dried at 103 \({}^{\circ}\)C until constant weight. TWSSC of tea samples was expressed as mg/g DW. Total phenolics of tea samples were analyzed using the Folin-Ciocalteu method [17]. Briefly, 1 mL of 10% Folin-Ciocalteu reagent was added to 0.02 mL of the tea extract solution or water as a blank, followed by 0.18 mL of water. 0.8 mL of a 7.5% Na\({}_{2}\)CO\({}_{3}\) solution was added after 5 min. Utilizing a Synergy H1 MG microplate reader (BioTek Instruments Inc., Winooski, VT, USA), samples were incubated at 25 \(\pm\) 2 \({}^{\circ}\)C for 60 min in the dark. The results were calculated using the gallic acid (GA) standard curve. Total theaflavins and thearubigins of tea samples were analyzed according to the previous method [18; 19]. Three grams tea sample was extracted with 125 mL boiling water for 10 min and then immediately filtered to obtain the tea extract. The extract was mixed with 25 mL of ethyl acetate (EA) and then shaken for 5 min. The extract was allowed to stand for separation to obtain the EA extract and water extract. Mix 95% ethanol with 2 mL of EA extract until the total volume is 25 mL to obtain the Solution A. Mix 15 mL of EA extract with 15 mL of 2.5% NaHCO\({}_{3}\) solution and shake rapidly for 30 s. After standing and layering, take 4 mL of EA extract and mix with 95% ethanol until the total volume is 25 mL to obtain the Solution C. Take 2 mL of the aqueous layer extract obtained from the first extraction and mix with 2 mL of saturated oxal acid solution and 6 mL of water, then add 95% ethanol and mix until the total volume is 25 mL to obtain the Solution D. Mix 25 mL of tea extract with 25 mL of n-butanol and shake for 3 min. After separation, mix 2 mL of the aqueous layer with 2 mL of saturated oxal acid solution and 6 mL of distilled water, then add 95% ethanol and mix until the total volume is 25 mL to obtain the Solution B.