Quality Differentiation and Mechanistic Insights Into Green Tea Processed by Different Fixation Methods

This research conducts a systematic exploration of the impacts of three fixation methods-50-type electric heating tube roller fixation (CQ), mixed fixation (HC), and steam fixation (ZQ)-on the quality formation of green tea. By means of quantitative analysis of aroma components, catechins, free amino acids, and alkaloids, in combination with electronic tongue taste fingerprint and untargeted metabolomics analysis, it is discovered that distinct fixation methods exert significant influences on the volatile and non-volatile metabolite profiles of green tea. CQ notably elevated the content of total polyphenols and gallic acid to 3.57 mg/g, intensifying its bitter and astringent taste profile. In contrast, ZQ produced the brightest green infusion and yielded the highest electronic tongue response value for sweetness. HC achieved a superior balance, retaining the highest levels of key aroma compounds like linalool (1.42 mg/kg) and D-limonene, while also preserving the highest total free amino acid content (13,983.2 µg/g). Metabolomics analysis further disclosed that fixation methods affect metabolite composition by regulating pathways such as phenylpropanoid biosynthesis and caffeine metabolism. Molecular docking experiments verify that the disparity in binding affinity between key differential metabolites (e.g., Chrysophanol 8-(6-galloylglucoside)) and taste receptors (TRPM5, TAS2R14, T1R1/T1R3) serves as the material foundation for taste differentiation. This study provides a theoretical basis for the development of precision processing technologies and quality control of green tea. PRACTICAL APPLICATIONS: This study provides a decision-making framework for green tea producers to select fixation techniques based on desired sensory profiles. To enhance floral and citrus notes, mixed fixation (HC) is recommended. Steam fixation (ZQ) is ideal for preserving a bright green color and sweeter taste, suitable for premium-grade teas. Roller fixation (CQ) can be applied where a stronger, more astringent profile is targeted. These insights enable the precision manufacturing of green teas with customized flavor characteristics.