Metabolic Profiling of Non-volatile Compounds during Green Tea Processing from ‘Fuhuang 1’, a New Albino Tea Variety

This study aimed to evaluate the dynamic changes of non-volatile metabolites during green tea processing from the albino tea variety ‘Fuhuang 1’. Green tea was made from one bud with two leaves through three steps: natural drying, fixation and rolling. A total of 2 654 non-volatile metabolites were detected by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) in the raw material, intermediate products and final product. The total content of non-volatile metabolites showed an upward trend during tea processing. Our analysis showed that fixation was crucial for the conversion of non-volatile metabolites in green tea processing. A total of 292 important differential metabolites were selected before and after fixation, including amino acids and their derivatives (40), flavonoids (37), lipids (101), nucleotides and their derivatives (28), and phenolic acids (21). These metabolites were significantly enriched in pathways such as the biosynthesis of secondary metabolites, carbon metabolism, cysteine and methionine metabolism, arginine biosynthesis, alanine, aspartic acid and glutamic acid metabolism. They were categorized into three clusters by K-Means analysis. The metabolites in the first cluster accumulated significantly during fixation. The metabolites in the second cluster accumulated significantly during fixation and also accumulated during drying, but to a lesser extent. However, the metabolites in the third cluster significantly decreased during fixation. Amino acids and their derivatives accumulated significantly during fixation, especially reduced glutathione, which might be a signature compound of ‘Fuhuang 1’ green tea. Lipids were the most active compounds during green tea processing; their relative contents significantly increased, with lysophosphatidylethanolamine showing the greatest accumulation. Some flavonoids, nucleotides and their derivatives accumulated only during fixation, whereas others accumulated during both fixation and drying. This study provides a theoretical basis for the innovative utilization of tea albino mutants.