# Effect of Fermentation Humidity on Quality of Congou Black Tea
## Materials and Methods
### Chemical Composition Determination  
The Folin-Ciocalteu method was used for determining the total amount of polyphenols; the ninhydrin colorimetric method for determining the total free amino acid content; the colorimetric approach involving anthrone and sulfuric acid for determining the amount of soluble sugar; the colorimetric method of aluminium trichloride for measuring the total amount of flavones in tea. Ethyl acetate, n-butanol and ethanol were used for extraction of theaflavins, thearubigins and theabrownines, and the total contents were detected by systematic analysis. The chromatic aberration of the tea infusion was determined with a CS-820N spectrophotometer for color measurement (Hangzhou Caipu Technology Co., Ltd., Hangzhou, China) and the tea infusion was prepared as described for sensory evaluation. Theaflavin and catechin components were detected by high-performance liquid chromatography (HPLC) (1260 Infinity, Agilent, Santa Clara, CA, USA). Determination of the components of theaflavins was based on GB/T 31740.3-2015 with conditions as follows: column, AgilentTC-C18 (250 mm \(\times\) 4.6 mm \(\times\) 5 \(\upmu\)m); 35 \({}^{\circ}\)C column temperature, 0.7 mL/min flow rate, 278 nm detection wavelength, 5 \(\upmu\)Li injection volume, mobile phase A consisted of 90 mL acetonitrile with 20 mL glacial acetic acid and 2 mL EDTA-2 Na (10 mg/mL), with ultrapure water fixed to 1000 mL; mobile phase B consisted of 800 mL acetonitrile with 20 mL glacial acetic acid and 2 mL EDTA-2 Na (10 mg/mL). Determination of catechin components was based on GB/T 8313-2018 with conditions as follows: AgilentTC-C18 column (250 mm \(\times\) 4.6 mm \(\times\) 5 \(\upmu\)m); 35 \({}^{\circ}\)C column temperature, 0.7 mL/min flow rate,5 \(\upmu\)L injection volume, 278 nm detection wavelength, mobile phase A was ultrapure water (involving 0.1% formic acid), and mobile phase B was methanol (involving 0.1% formic acid). The elution gradient of theaflavins and catechins consisted of 100% A from 0-10 min, 100-68% A from 10-25 min and 68-100% A from 25-35 min. The volatile compounds were detected by gas chromatography-mass spectrometer (GC-MS), Thermo MS DSQ II (Thermo Fisher Scientific, Waltham, MA, USA). Briefly, aroma components were adsorbed by headspace solid-phase microextraction (HS-SPME), and PDMS/DVB extraction fibers (PDMS/DVB 65 \(\upmu\)m) were first aged at 250 \({}^{\circ}\)C for 1 h at the GC inlet. Meanwhile, the sample of crushed tea (1.0 g) was placed into a headspace vial (20 mL) and extracted with 5 mL of boiled supersaturated NaCl solution, followed by adding 500 \(\upmu\)L of cyclohexanone internal standard solution (0.1 \(\upmu\)L/mL), placing the bottle in a 60 \({}^{\circ}\)C water bath for 60 min after sealing it promptly and tightly. Finally, SPME was transferred to the GC-MS injection section for the separation, identification and quantification of volatile compounds. Chromotagraphic conditions: 30 mm \(\times\) 0.25 mm \(\times\) 0.22 \(\upmu\)D-5 MS column; 230 \({}^{\circ}\)C inlet temperature; high purity (\(\geq\)99.99%) helium carrier gas; 1.0 mL/min column flow rate; an initial temperature at 45 \({}^{\circ}\)C and held for 2 min, then 7 \({}^{\circ}\)C/min to 80\({}^{\circ}\)C with no hold, 2 \({}^{\circ}\)C/min to 90 \({}^{\circ}\)C and held for 2 min, 3 \({}^{\circ}\)C/min to 100 \({}^{\circ}\)C and held for 2 min, 3 \({}^{\circ}\)C/min to 130 \({}^{\circ}\)C and held for 2 min, 3 \({}^{\circ}\)C/min to 150 \({}^{\circ}\)C, and finally 10 \({}^{\circ}\)C/min to 230 \({}^{\circ}\)C and held for 5 min; 40 \({}^{\circ}\)C the column chamber temperature; splitless injection mode. Mass spectrometry conditions: Electron Ionization (EI) ion source; 70 eV electron energy; 230 \({}^{\circ}\)C ion source temperature; \(m/z\) 30-500 mass scan range. Electron collision ionization was used for GC-MS analysis.