Epigallocatechin

Methanol HPLC grade was obtained from Panreac Química (Barcelona, Spain). Acetonitrile HPLC grade, formic acid HPLC grade, SYBR safe DNA gel stain, and the primers MatK-1RKIM-f and MatK-3FKIM-r were from Thermo Fisher Scientific (Runcorn, Cheshire, UK). Agarose MB 250 was purchased from Biotools Biotechnological and Medical Laboratories SA (Madrid, Spain). Apigenin-7-glucoside, epigallocatechin, and tiliroside were acquired from Extrasynthese (Genay Cedex, France). Acetoxy acid was from Sigma-Aldrich (St. Louis, MO, USA), and valerenic acid was from Chromadex (Irvine, CA, USA).

All chemicals were at least of analytical grade. Toluene, 1-propanol, formic acid, acetic acid, hydrochloric acid (37%) and 4-dimethylaminocinnamaldehyde (DMACA) were from Merck (Darmstadt, Germany). Ethanol, acetone, as well as HPLC grade acetonitrile and mEthanol were purchased from Sigma-Aldrich (St. Louis, MO, USA). LC-MS grade acetonitrile and mEthanol used for MS analyses were from Fluka (Buchs, Switzerland). MilliQ 18.2 MΩ water (Millipore, Bedford, MA, USA) was also used.
Standards of (−)-epicatechin gallate, (−)-epigallocatechin, (−)-epigallocatechin gallate, (−)-catechin gallate, (−)-gallocatechin, (−)-gallocatechin gallate, procyanidin B1, procyanidin B2, procyanidin B3 and procyanidin C1 were obtained from Extrasynthèse (Genay, France), while (−)-epicatechin was from Sigma-Aldrich and (+)-catechin from Carl Roth (Karlsruhe, Germany).

All chemicals used were of high-performance liquid chromatography (HPLC) analytical grade. Acetonitrile was purchased from from J.T. Baker (Deventer, The Netherlands). Formic acid and orthophosphoric acid (85% w/w) were purchased from Fluka (Buchs, Switzerland) and ethanol from Kemika (Zagreb, Croatia). Phenolic standard compounds of analytical standard grade used for identification and quantification were: delphinidin-3-O-glucoside, cyanidin-3-O-glucoside, peonidin-3-O-glucoside, malvidin-3-O-glucoside, epigallocatechin, procyanidin B1, procyanidin B2, rutin (quercetin 3-O-rutinoside) and myricetin from Extrasynthese (Lyon, France); (–)-epicatechin, (+)-catechin and (–)-and epicatechin-gallate from Sigma-Aldrich (St. Louis, MO, USA); kaempferol, quercetin and isorhamnetin from Fluka (Steinheim, Germany) and quercetin-3-O-glucoside from Sigma (St. Louis, MO, USA).

All chemicals were at least of analytical grade. Acetic acid, formic acid, hydrochloric acid (37%), toluene, 1-propanol, and 4-dimethylaminocinnamaldehyde (DMACA) were from Merck (Darmstadt, Germany). Acetone, ethanol as well as HPLC grade acetonitrile and methanol were purchased from Sigma-Aldrich (St. Louis, MO, USA). LC–MS grade acetonitrile and methanol used for MS analyses were from Fluka (Buchs, Switzerland). MilliQ 18.2 MΩ water (Millipore, Bedford, MA, USA) was also used.
Standard of (−)-epicatechin was obtained from Sigma-Aldrich and (+)-catechin from Carl Roth (Karlsruhe, Germany). Standards of procyanidin B1, procyanidin B2, procyanidin B3, procyanidin C1, (−)-catechin gallate, (−)-gallocatechin, (−)-gallocatechin gallate, (−)-epicatechin gallate, (−)-epigallocatechin and (−)-epigallocatechin gallate were obtained from Extrasynthèse (Genay, France).

MEM with Earle's salts, DMEM, fetal bovine serum (FBS), trypsin‐EDTA, and antibiotics were purchased from Biochrom GmbH (Berlin, Germany). Entero‐STIM Intestinal Epithelium Differentiation Medium and MITO+ Serum Extender were purchased from Corning (Wiesbaden, Germany). Hesperetin, peltatoside, hyperoside, kaempferol, ellagic acid, isoquercitrin, quercitrin, phloretin, (−)‐epicatechin, epigallocatechin, epicatechin gallate, procyanidin B1, procyanidin B2, epigallocatechin gallate, gallocatechin, and morine were obtained from Extrasynthese (Genay Cedex, France). Phloridzin, chlorogenic acid, caffeic acid, quercetin, (+)‐catechin, gallic acid, 2‐mercaptoethanol, NaCl, MgSO₄, KCl, CaCl₂, HEPES, and xylitol were purchased from Sigma‐Aldrich (Schnelldorf, Germany). Guaijaverin and avicularin were obtained from Glentham Life Sciences (Corsham, United Kingdom). Purified and concentrated GLE (cGLE) was provided by Belan GmbH (Wels, Austria).30 Guava fruit puree for preparation of fruit extracts was obtained from Tradework BV (Rotterdam, The Netherlands), commercially available GLE and apple extract (AE) were purchased from Pfannenschmidt (Hamburg, Germany). Transwell inserts (12 mm, collagen‐treated, 0.4 μm pore size) and 12‐well plates were obtained from Corning (Wiesbaden, Germany).

Chromatographic solvents were of high-performance liquid chromatography (HPLC) grade, and chemicals were of analytical reagent grade. Acetonitrile, acetone, chloroform, methanol, ethanol, formic acid, and trifluoracetic acid were from Merck (Darmstadt, Germany). The phloroglucinol reagent and tris-HCl equilibrated phenol pH 6.7 were sourced from Sigma Aldrich (St. Louis, MO, USA). Sodium acetate was from J.T. Baker (Deventer, The Netherlands). The (+)-catechin, (−)-epicatechin, (−)-epicatechin gallate and (−)-epigallocatechin standards were obtained from Extrasynthese (Genay, France). Galacturonic acid was from Sigma (St. Louis, MO, USA) and Bovine serum albumin (BSA) fraction V from J.T. Baker (Deventer, Holland). For glucose determination, an enzymatic analysis kit from R-biopharm (Darmstadt, Germany) was used.

HPLC grade ethyl acetate, methyl alcohol, acetic acid (99%), formic acid (98–100%) and toluene as well as analytical grade hydrochloric acid (37%), phosphoric acid (85%), ethyl alcohol and dichloromethane were purchased from Sigma-Aldrich (St. Louis, MO, USA) and Merck (Darmstadt, Germany). The anthocyanin standards (cyanidin-3,5-O-diglucoside, cyanidin-3-O-glucoside, delphinidin-3-O-glucoside, malvidin-3,5-O-diglucoside, malvidin-3-O-glucoside, delphinidin) and also (+)-catechin, (−)-epicatechin, (−)-epigallocatechin and (−)-epigallocatechin gallate were provided by Extrasynthese (Genay, Lyon area, France). The reagents for derivatization steps, namely 2-aminoethyl diphenylborinate (natural product reagent A, NP) and polyethylene glycol 400 (PEG 400), were obtained from Sigma Aldrich, while vanillin was bought from BDH (Poole, UK). Bidistilled water was used as solvent for each type of application method, i.e., extraction and sample preparation.