Unraveling Variations in Primary Metabolites of Longjing Green Tea During Processing and from Different Geographical Origins

(1) Background: Primary metabolism is essential for tea quality formation, however systematic analysis of tea primary metabolites remains limited; (2) Methods: An orthogonal design was used to optimize the pre-column derivatization reaction conditions for the tea matrix. Using the optimized method, gas chromatography-mass spectrometry (GC-MS) was employed to analyze Longjing green tea (LJGT) samples from different processing stages and regions; (3) Results: Optimal derivatization was achieved with 75 μL of methoxamine hydrochloride pyridine solution at 30 °C for 1.5 h. A total of 52 primary metabolites were identified in LJGT. Processing analysis showed that 8 metabolites associated with carbohydrate metabolism significantly decreased during spreading. Five reducing sugars significantly decreased, while sucrose, turanose, and quinic acid significantly increased due to the thermal action during pan-fixation. Additionally, 15 key differential compounds were identified among three regions (Xihu, Qiantang, and Yuezhou) of LJGT. Quantitative analysis revealed that shikimic and quinic acid contents were significantly higher in the Xihu region compared to other regions; (4) Conclusions: This study established a pre-column derivatization GC-MS method for primary metabolite profiling, elucidated metabolic regulation during LJGT processing, and identified differences in primary metabolite content among LJGT from different geographical origins.