*3.4. ECG and L-Theanine Quantification*

A targeted quantification method based on a PRM assay was carried out to measure the ECG and L-theanine content in the CBP samples. The established calibration curve showed good linearity for ECG (*r*<sup>2</sup> = 0.9965) and L-theanine (*r*<sup>2</sup> = 0.9932). A significant difference was observed in the ECG (94.08–401.82 mg/kg) and L-theanine (864.83–2204.26 mg/kg) content among the CBP samples (Figure 3). The highest ECG content was found in the CBP samples from Anhui Province (387.04–430.70 mg/kg), followed by Sichuan Province (272.52–280.56 mg/kg), and the lowest content was found in the samples from Zhejiang Province (90.95–98.33 mg/kg). The CBP samples from Sichuan Province had the highest L-theanine content (2138.56–2314.01 mg/kg), while those from Jiangsu and Zhejiang Provinces had the lowest content (819.45–964.43 mg/kg).

**Figure 3.** ECG and L-theanine content (mean ± standard error) in the CBP samples from different locations. Different letters indicate statistically significant differences (*p* < 0.05 in ANOVA).
