Dimeric catechins, such as theaflavin-3ʹ-gallate (TF-3ʹ-G), theaflavin-3,3ʹ-digallate (TF-DG), theaflavin-3-gallate (TF-3-G), theaflavin (TF), procyanidin B2, and procyanidin B1, were sourced from ChemFaces (Wuhan, Hubei, China). Additionally, the following compounds were procured from Sigma (St. Louis, MO, USA): nine flavanols, namely (−)-epigallocatechin (EGC), (−)-epicatechin (EC), (−)-gallocatechin gallate (GCG), (−)-epigallocatechin gallate (EGCG), (+)-catechin (C), (−)-gallocatechin (GC), (−)-epicatechin gallate (ECG), (−)-epigallocatechin-3-(4′'-O-methyl) gallate (EGCG-4′'-O-Me), and (−)-epiafzelechin 3-gallate; fifteen amino acids; eight kaempferol-O-glycosides and quercetin-O-glycosides; as well as flavone-C-glycosides, including vitexin and isovitexin. Other chemicals such as 1-ethyl-5-hydroxy-2-pyrrolidinone, quinic acid, benzyl primeveroside, pyroglutamic acid, pipecolic acid, choline, caffeine, and adenosine monophosphate (AMP), were procured from Yuanye Bio-Technology Co., Ltd. (Shanghai, China). Milli-Q water was used in this study (Millipore, Billerica, MA, USA). Liquid chromatography-mass spectrometry (LC-MS) grade formic acid, methanol, and acetonitrile of were obtained from Merck (Darmstadt, Germany) (Gao et al., 2022 (link), Gao et al., 2022 (link), Peng et al., 2021 (link)).
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