# Effect of Leaf Grade on Taste and Aroma of Shaken Hunan Black Tea
## Materials and Methods
### Analysis of Hunan Black Tea Aroma-Active Compounds  
5.1 Hunan Black Tea Volatile Compounds Extraction by Headspace Solid-Phase Microextraction (HS-SPME)  
The 50/30 \(\upmu\)m DVB/CAR/PDMS extraction head was positioned within the gas chromatograph's inlet port and subjected to an aging process at a temperature of 270 \({}^{\circ}\)C for 30 min. Each tea sample, weighing 3.00 g, was carefully measured and deposited into a 250 mL beaker equipped with a magnetic rotor. Subsequently, 10 g of NaCl was added to the beaker, which was then filled with 150 mL of boiled water. A 20 \(\upmu\)L solution of ethyl caprate at a concentration of 8.68 \(\upmu\)g/mL, dissolved in a solvent consisting of 10% ethanol, was injected into the beaker. The extraction head was expeditiously enveloped with a sealing film and positioned on a magnetic stirring heating stage, where it was subjected to heating and stirring at a temperature of 80 \({}^{\circ}\)C and a stirring rate of 600 r-min-1 for 10 min. Subsequently, the aged extraction head was introduced into the headspace region of the beaker. Following 50 min of adsorption of the extractor head in the sample bottle at a temperature of 80 \({}^{\circ}\)C and a stirring rate of 600 r/min, the extractor head was inserted into the gas chromatograph's inlet and thermally resolved at a temperature of 250 \({}^{\circ}\)C for 5 min [2; 3; 4].  
5.2 Qualitative and Quantitative Analysis of the Volatiles by Gas Chromatography-Mass Spectrometry (GC-MS)  
The analysis was conducted using an HP-5 MS capillary column with a carrier gas consisting of 99.999% helium at a flow rate of 1.7 mL/min. The sample was injected without a shunt, and the inlet temperature was set at 250 \({}^{\circ}\)C. The heating program consisted of initially maintaining a temperature of 50 \({}^{\circ}\)C for 2 min, followed by a gradual increase to 60 \({}^{\circ}\)C at a rate of 1 \({}^{\circ}\)C/min and another 2 min hold. Subsequently, the temperature was further increased to 104 \({}^{\circ}\)C at a rate of 2 \({}^{\circ}\)C/min. The overall heating procedure involved the following steps: starting at 50 \({}^{\circ}\)C with a 2 min hold, increasing to 60 \({}^{\circ}\)C at a rate of 1 \({}^{\circ}\)C/min with another 2 min hold, further increasing to 104 \({}^{\circ}\)C at a rate of 2 \({}^{\circ}\)C/min with a 1 min hold, increasing to 150 \({}^{\circ}\)C at a rate of 5 \({}^{\circ}\)C/min with a 1 min hold, and finally increasing to 220 \({}^{\circ}\)C at a rate of 15 \({}^{\circ}\)C/min with a 5-min hold. The quadrupole temperature was maintained at 150 \({}^{\circ}\)C, while the ion source temperature was set to 230 \({}^{\circ}\)C. The ion source utilized in this study was an EI source, characterized by an electronic energy of 70 eV and an ionization voltage of 1540 mV. The scanning range for mass-to-charge ratio (\(m/z\)) was set between 33 and 400. The NIST 2017 spectral library was employed for comparison, resulting in a matching error of 20. Additionally, the retention index was verified.  
For quantitative analysis, a semi-quantitative approach was adopted using the internal standard method. The internal standard employed was 20 \(\upmu\)L of decanoic acid ethyl ester with a concentration of 8.68 \(\upmu\)g/mL.