Catechin gallate

Reagents needed for cultivation of in vitro cultures, e.g., MS and SH basal media, agar, PGRs, and sucrose were acquired from Duchefa Farma B.V. (Haarlem, The Netherlands).
Ultrapure water was obtained using Millipore Milli-Q system (Merck Millipore, Molsheim, France). Acetonitrile and methanol were purchased from Thermo Fisher Scientific (Illkirch-Graffenstaden, France). Standard compounds L-leucine, L-isoleucine, L-phenylalanine, L-tyrosine, L-tryptophan, L-proline, citric acid, gallic acid, coutaric acid, trans-resveratrol, cis-resveratrol, E-piceid, catechin, epicatechin, catechin gallate, tyrosinase, and L-DOPA were purchased from Sigma-Aldrich (St. Louis, MO, USA). Rhamnetin, E-ε-viniferin, quercetin 3-O-glucoside, quercetin 3-O-glucuronide, quercetin-3-O-galactoside, procyanidin B1, procyanidin B2, procyanidin B3, and procyanidin C1 were obtained from ExtraSynthèse (Genay, France); caftaric acid was delivered by Carbosynth (Compton, Berkshire, UK), while E-ε-viniferin, Z/E-vitisin B, ampelopsin A, and hopeaphenol were obtained by previous extraction from grape stems [50 (link)].

Catechin, epiCatechin gallate (ECG), EC epiCatechin (EC), epigalloCatechin (EGC), galloCatechin (GC), Catechin gallate (CG), EGCG, and galloCatechin gallate (GCG) were acquired from Sigma-Aldrich Co. (St. Louis, MO, United States). High-Performance Liquid Chromatography (HPLC)-grade methanol was obtained from Merck (Darmstadt, Germany). All other chemicals and reagents were of analytical grade. FBT is mainly consumed in Shaanxi province, Hunan province, Guizhou province, Zhejiang province, and Guangxi Zhuang Autonomous Region in China. From these main producing areas, five FBT samples were collected from large factories and named as SX (Shaanxi Xianxi Lamu Tea Co., Ltd.), HN (Anhua Yuntiange Tea Industry Co., Ltd.), GZ (Guizhou Fanjin Tea Industry Co., Ltd.), ZJ (Zhejiang Wuyi Luotuo Jiulong Brick Tea Co., Ltd.), and GX (Guangxi Jinhua Tea Co., Ltd.). All tea samples used in this study were produced in 2018.

The chemicals for the determination of ferric-reducing antioxidant power (FRAP), Trolox equivalent antioxidant capacity (TEAC), TPC, TFC and phenol analysis were bought according to the paper [17 (link)] we published previously. Eighteen standard phenolic compounds, including gallic acid, protocatechuic acid, gallo catechin, chlorogenic acid, cyanidin-3-glucoside, caffeic acid, epicatechin, catechin gallate, p-coumaric acid, ferulaic acid, melatonin, 2-hydroxycinnamic acid, rutin, resveratrol, daidzein, equol, quercetin, and genistein were purchased from Sigma-Aldrich (St. Louis, MO, USA). Standard organic acids, including ascorbic acid, lactic acid, citric acid, and succinic acid, were obtained from Sigma-Aldrich, and oxalic acid, tartaric acid, and malic acid were bought from National Institutes for Food and Drug Control (Beijing, China). Phosphoric acid and potassium phosphate monobasic used for organic acid analysis were of analytical grade and bought from Damao Chemical Factory (Tianjin, China) and Yongda Chemical Reagent Company (Tianjin, China), respectively. Double-distilled water was used in all the experiments. The 23 fruit vinegars (Table 1) were bought from online shopping platforms and local markets in Guangzhou, China, and were stored at 4 °C before use.

The 2,2′-azinobis(3-ethylbenothiazoline-6-sulphonic acid) diammonium salt (ABTS), 6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid (Trolox), 2,4,6-tri(2-pyridyl)-s-triazine (TPTZ), Folin-Ciocalteu’s phenol reagent, and the standard compounds (gallic acid, protocatechuic acid, gallo catechin, chlorogenic acid, cyanidin-3-glucoside, caffeic acid, epicatechin, catechin gallate, p-coumaric acid, ferulaic acid, melatonin, 2-hydroxycinnamic acid, rutin, resveratrol, daidzein, equol, quercetin and genistein) were provided by Sigma-Aldrich (St. Louis, MO, USA). Tetrahydrofuran, methanol, formic acid, diethyl ether and ethyl acetate were provided by Kermel Chemical Factory (Tianjin, China). Acetic acid, sodium acetate, potassium acetate, sodium hydroxide, hydrochloric acid, ethylenediaminetetraacetic acid (EDTA), ascorbic acid, iron (III) chloride hexahydrate (FeCl₃·6H₂O), iron(II) sulphate heptahydrate (FeSO₄·7H₂O), potassium persulphate, sodium carbonate, aluminum chloride hexahydrate (AlCl₃·6H₂O), ethanol and n-hexane were provided by Damao Chemical Factory (Tianjin, China). All chemical reagents used in the tests were of analytical or chromatographic grade, and the water used was double distilled.

Acetonitrile, formic acid, and methanol were all HPLC grade and from Merck (Darmstadt, Germany). Authentic standards were purchased from Sigma–Aldrich (Shanghai, China), including caffeine, gallic acid, (+)-Catechin (C), (−)-epicatechin (EC), (−)-gallocatechin (GC), (−)-epigallocatechin (EGC), (−)-catechin gallate (CG), (−)-epicatechin gallate (ECG), (−)-gallocatechin gallate (GCG), (−)-epigallocatechin gallate (EGCG). Acetic acid was purchased from Aladdin Co., Ltd (Shanghai, China). Ethyl caprate (decanoate; 99 %) and n-alkanes (C7-C40) were purchased from Beijing Zhongsheng Ruitai Technology Co., Ltd. (Beijing, China).

All chemicals and standards described below were of either HPLC or LC-MS grade. (+)-Catechin (≥98%, HPLC grade, cat# C1251), (−)-catechin (≥98%, HPLC grade, cat# C0567), (−)-epicatechin (≥98%, HPLC grade, cat# E4018), (−)-epigallcatechin (≥98%, HPLC grade, cat# E3768), (−)-gallocatechin (≥98%, HPLC grade, cat# G6657), (−)-catechin gallate (≥98%, HPLC grade, cat# C0692), (−)-epigallocatechin gallate (≥80%, HPLC grade, cat# E4268) and (−)-gallocatechin gallate (≥98%, HPLC grade, cat# G6782) were purchased from Sigma-Aldrich^® (St Louis, MO, USA). Procyanidin B1 and B2 (HPLC grade, cat# ASB-16230 and 16231, respectively) were purchased from Chroma Dex™ (Irvine, CA, USA). Acetonitrile (LC-MS grade, cat#: 9829-03), glacial acetic acid (HPLC grade, cat#: 9515-03), and methanol (LC-MS grade, cat#: 9830-03) were purchased from Avantor^® (Center Valley, PA, USA). Ethyl alcohol (200 proof, cat#: EX0276-1) was purchased from EMD (Burlington, MA, USA). Water (LC-MC grade, cat#BJLC365) was purchased from VWR^® (Radnor, PA, USA).

N‐nitrosodiethylamine, EGCG, EGC, ECG, EC, C, gallocatechin (GC), catechin gallate (CG), gallocatechin gallate (GCG), and caffeine (at least 98% purity) were purchased from Sigma‐Aldrich. The immunohistochemical SP‐HRP kit, ECL plus Western blot kit purchased from Dingguo Biological Technology. All other chemicals were purchased from local commercial sources in China.