4.3.2. Sample Extraction Process

The leaves of *C. sinense* 'Red Sun' were vacuum freeze-dried and ground with a grinder (30 Hz for 1.5 min) to powder. The 0.1 g powder was dissolved in 70% methanol aqueous solution. The dissolved sample was swirled three times at 4 ◦C overnight to improve the extraction rate. After centrifugation (rotating speed 10,000× *g*, 10min), the supernatant was filtered with a microporous membrane (0.22 μ m pore size). The sample was stored in a sample injection bottle for UPLC-MS/MS analysis.
