LC-MS-Based Metabolomics Reveals the Chemical Changes of Polyphenols during High-Temperature Roasting of Large-Leaf Yellow Tea

Abstract

Large-leaf yellow tea (LYT) is made from mature tea leaves with stems and has unique sensory characteristics different from other teas. To study the chemical changes of LYT during processing, samples were collected from each step for quantitative and qualitative analyses by high-performance liquid chromatography and liquid chromatography−mass spectrometry (LC-MS). LC-MS-based nontargeted and targeted metabolomics analyses revealed that the tea sample after roasting was markedly different from samples before roasting, with the levels of epicatechins and free amino acids significantly decreased, but the epimerized catechins increased dramatically. After accounting for common compounds in tea, N-ethyl-2pyrrolidinone-substituted flavan-3-ols were found to be the marker compounds responsible for the classification of all samples, as they rapidly rose with increasing processing temperature. These findings suggested that the predominant changes in the tea constituents during large-leaf yellow tea roasting were the thermally induced degradation and epimerization of catechins and the formation of N-ethyl-2-pyrrolidinone-substituted flavan-3-ols from L-theanine.

Analytical strategy coupled to chemometrics to differentiate Camellia sinensis tea types based on phenolic composition, alkaloids, and amino acids

“…Furthermore, epimerization is another reason for the changes in catechins content in different type tea. some studies have reported that high‐temperature processing induces epimerization of tea catechins, such as 2,3‐ cis (EC, ECG, EGC, and EGCG), to form 2,3‐ trans configurations (C, GC, and GCG; Long et al., 2020; Zhou et al., 2018). Some report that the levels of EGCG, ECG, EC, and EGC were dramatically decreased.…”

“…Some studies have reported that evaluation of the secondary metabolomics of tea and the use of chemometric tools, such as principal component analysis (PCA) and linear discriminant analysis (LDA) can help in the exploratory study and classification of tea according to its cultivar, type, and geographical origin (Long et al., 2020; Zhang et al., 2019; Zhou et al., 2018, 2019). However, it is difficult for tea regulatory agencies and research institutions to use this method to distinguish tea types because of its higher technological and skill requirements.…”

Chemistry and Biological Activities of Processed Camellia sinensis Teas: A Comprehensive Review

“…At the A‐ring of flavan‐3‐ols, C 6 and C 8 are reactive carbons that can react with electron accepting compounds and produce many kinds of C 6 or C 8 substituted catechins. A series of N ‐ethyl‐pyrrolidinone substituted flavan‐3‐ols (EPSFs) has been isolated and identified from black, postfermented (dark tea), white, and yellow teas (Dai et al., ; Tanaka, Watarumi, Fujieda, & Kouno, ; Wang et al., ; Zhou et al., ). It is hypothesized that the Strecker degradation product of theanine is involved in the formation of N ‐ethyl‐pyrrolidinone substituted flavan‐3‐ols.…”

“…Recently, EPSFs were also identified from white and ripened pu‐erh teas, the substitution of N ‐ethyl‐2‐pyrrolidinone could be placed at the C 6 or C 8 of EGCG, EC, EGC, and ECG (Cheng et al., ; Wang et al., ; Zhou et al., ). These findings indicated that C 6 and C 8 are very reactive carbons, and then many other types of flavan‐3‐ols derivatives were also found.…”

Feature-Based Molecular Networking Analysis of the Metabolites Produced by In Vitro Solid-State Fermentation Reveals Pathways for the Bioconversion of Epigallocatechin Gallate

“…The similar phenomenon was reported in the high temperature treatment of large-leaf yellow tea. 3 No feature signals for FBRFAs or dihydromyricetin were observed from the network. The result validated that the hygrothermal effect was not the reason for generation of FBRFAs or flavan-3-ol C-ring oxidation products in tea leaves.…”