Catechin

Catechin (C, ≥98%), galloCatechin (GC, ≥98%), galloCatechin-3-gallate (GCG, ≥98%), epiCatechin (EC, ≥98%), epiCatechin-3-gallate (ECG, ≥98%), epigalloCatechin (EGC, ≥98%), epigalloCatechin-3-gallate (EGCG, ≥98%), caffeine (CAF, ≥98%), theaflavins (TF, ≥95%), theaflavins-3-gallate (TF3G, ≥98%), theaflavin-3′-gallate (TF3′G, ≥98%), theaflavine-3,3′-digallate (TFDG, ≥98%), quercetin-3-O-galactoside (≥98%), myricetin-3-O-galactoside (≥98%), kaempferol-3-O-rutinoside (≥98%), vitexin (≥98%), astragaloside (≥98%), quercetin (≥98%), and kaempferol (≥98%) were purchased from Shanghai yuanye Bio-Technology Co., Ltd. (Shanghai, China). l-alanine, l-arginine, l-aspartic acid, l-cystine, l-glutamic acid, glycine, l-histidine, l-isoleucine, l-leucine, l-lysine, l-methionine, l-phenylalanine, l-proline, l-serine, l-threonine, l-tyrosine, l-valine, l-asparagine, l-glutamine, theanine, γ-aminobutyric acid, and l-tryptophan were purchased from Sigma (Sigma-Aldrich Co., St. Louis, MO, USA). Anthrone reagent and ninhydrin/formic acid reducing agent were purchased from BeiJing DingGuochangSheng Biotech. Co., Ltd. (Bejing, China). Ethyl caprate (≥99%) was purchased from Shanghai Macklin Biochemical Technology Co., Ltd. (Shanghai, China), and n-alkane mixed standard C7-C40 was purchased from o2si (o2si smart solutions—an LGC Standards Company, Charleston, SC, USA).

Vanillin, hydrochloric acid, glacial acetic acid, ferric chloride, sulfuric acid, anhydrous sodium carbonate, sodium nitrite, sodium acetate, and other reagents were purchased from Bodi Chemical (Tianjin, China) and were analytically pure. HPLC-grade methanol and acetonitrile were purchased from Sigma-Aldrich (Saint Louis, MO, USA). The Folin–Ciocalteu regent, Trolox, 2, 4, 6-tris(2-pyridyl)-s-triazine (TPTZ), 1,1-diphenyl-2-picrylhydrazyl (DPPH), gallic acid, rutin, catechin, and 2, 2′-azinobis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) were acquired from Yuanye Bio-Technology (Shanghai, China).