2.4. Electronic Nose Analysis

The electronic nose analysis was based on a previous study with slight modifications [14]. The gas detectors of the electronic nose system (Supplementary Materials Figure S1) consisted of ten metal oxide sensors, which were individually sensitive to different volatile organic compounds (Table 1). Typically, a precise amount of 2 g of tea powder was weighed and placed into a 40 mL headspace flask, which was then sealed with a silicone cap. The headspace flask was equilibrated in an electrically heated constant temperature blast drying oven at 60 °C for 60 min for the extraction. Subsequently, both the injection and gas-filling needle of the electronic nose (cNose, Shanghai Baosheng Industrial Development Co., Ltd., Shanghai, China) were simultaneously inserted into the headspace flask. Manual headspace injection was performed with an interval of 1 min between injections, a sample collection time of 90 s, an instrument cleaning time of 120 s, a gas flow rate of 0.8 L/min, and an operating ambient temperature maintained at 25 ± 2 °C.

Sensitive substances of electronic nose sensor.