Development and validation of an efficient HILIC-QQQ-MS/MS method for quantitative and comparative profiling of 45 hydrophilic compounds in four types of tea (Camellia sentences).

Hydrophilic constituents are significant for the taste and nutrition of tea, but their simultaneous quantification remains challenging due to the lack of efficient methods. Based on the hydrophilic interaction chromatography coupled with triple quadrupole-tandem mass spectrometry, this work developed and validated an efficient (8.5 min per run), sensitive (LOQ: 0.002-0.493 µg/mL) and accurate method. This method was successfully used to determine the contents of 45 hydrophilic constituents in Yunnan large-leaf tea. Umami amino acids and umami-enhanced nucleotides generally exhibited higher content in green tea and Pu-erh raw tea. By contrast, a few number of amino acids (e.g., proline and γ-aminobutyric acid) and most alkaloids and nucleosides showed significantly higher contents in black tea or Pu-erh ripen tea. By performing the orthogonal partial least squares discriminant analysis, classification models for distinguishing four types of tea, and green tea from Pu-erh raw tea were established.

Chemical profiling and discrimination of green tea and Pu-erh raw tea based on UPLC-Q-Orbitrap-MS/MS and chemometrics.

To reveal the characteristic chemical profiles of Pu-erh raw tea (PRT) and traditional green tea (TGT), a high-throughput analytical method based on UPLC-Q-Orbitrap-MS/MS was proposed. 145 components were characterized with a three-level qualitative strategy and the integrated filtering strategy combining nitrogen rule, mass defect, and diagnostic ions information. 124 components were quantified using an internal standard method. The total contents of flavan-3-ols and derivatives, phenolic acids and derivatives were higher in PRT than TGT, while flavonoids were reversed. Furthermore, partial least squares-discriminant analysis (PLS-DA) models were established to classify TGT and PRT. 23 characteristic components were revealed by variable importance in projection method. Their difference in content is between 1.5 and 7.3 times for PRT and TGT. The results showed the chemical characteristics of TGT and PRT clearly and comprehensively. The high-throughput method demonstrated considerable potential in the analysis of complex chemical system, such as food and herbs.

Uncovering the antioxidant characteristics of black tea by coupling in vitro free radical scavenging assay with UHPLC-HRMS analysis.

Black tea (BT) is rich in dietary antioxidants, but its antioxidant composition has not been fully understood. To identify the true antioxidants occurring in BT, we established an approach based on 2,2-diphenyl-1-picrylhydrazyl radical scavenging assay coupled with ultra-high performance liquid chromatography-high resolution mass spectrometry (DPPH-UHPLC-HRMS). The employment of HRMS enable us to detect trace antioxidants, resolve co-eluted antioxidants, and characterize chemical structures of unknown antioxidants. In total, 56 phenolic compounds were screened as potential antioxidants from 106 compounds identified in BT. Catechol and pyrogallol were revealed as the key substructures in enhancing the antioxidant abilities of phenolic compounds. During BT brewing, high temperature with extended time promote antioxidant leaching but may induce the degradation of esterified and glycosylated compounds such as theaflavin-3-gallate and rutin. In conclusion, this work identified the true antioxidant constituents of BT, their structural characteristics, and their dynamic changes under various brewing conditions.