Epicatechin 3 gallate

The chemical standards caffeic acid, p-coumaric acid, trans-caftaric acid, trans-piceid, (−)-epigallocatechin (EGC), (−)-gallocatechin (GC), and procyanidin B1 (PB1) (Phytolab, Vestenbergsgreuth, Germany); cyanidin-3-glucoside (cy-3-glc), procyanidin B2 (PB2), quercetin (Q), kaempferol (K), isorhamnetin (I), the 3-glucosides of Q, K, I and 3-galactosides of Q, K, and I (−)-catechin 3-gallate (CG), (−)-epicatechin 3-gallate (ECG), and (−)-epigallocatechin 3-gallate (EGCG) (Extrasynthese, Genay, France); gallic acid, trans-resveratrol, (+)-catechin (C), (−)-epicatechin (EC), and (−)-gallocatechin 3-gallate (GCG) (Sigma-Aldrich, Steinheim, Germany) were used. The non-commercial flavonol standard of quercetin 3-glucuronide (Q-3-glcU) was previously isolated from the skin of Petit Verdot grapes, and the Procyanidin B4 (PB4) was kindly supplied by the Department of Biochemistry and Biotechnology, Universitat Rovira i Virgili, Spain. The trans- isomers of resveratrol and its 3-glucosides (piceid) were obtained according to the methodology previously described [36 (link)]. All solvents used were chromatographic grade (>99%); the chemical standard was analytical grade (>95%) and ultrapure water (Milli-Q system) was used.

The following chemicals were commercially obtained: KH₂PO₄ (Merck KGaA, Darmstadt, Germany); Na₂HPO₄, citric acid, NaN₃, sodium carboxymethyl cellulose (CMC, molecular weight ≈ 250 kDa), mucin from bovine submaxillary glands (type I-S) with a molecular weight between 0.4 and 4.0 MDa [22 (link), 23 ], (-)-epicatechin (EC), (-)-epigallocatechin-3-gallate (EGCG), methyl gallate, saccharin (Sigma-Aldrich, Steinheim, Germany); quercetin-3-O-rutinoside (rutin) (Carl Roth, Karlsruhe, Germany); (-)-epicatechin-3-gallate (ECG), (-)-epigallocatechin (EGC) (Extrasynthese, Genay, France); acetonitrile (J.T. Baker, Deventer, Netherlands); D₂O, DMSO-d₆, and 3-(trimethylsilyl)propionic acid sodium salt (TMSP) (Euriso-top, Gif-sur-Yvette, France). All chemicals were of analytical grade or better and were used without further purification. Ultrapure water was prepared with a Milli-Q Gradient A10 system (Millipore, Schwalbach, Germany).

Sodium hydroxide solution (0.1 mol/L) was purchased from Sigma-Aldrich (Poznań, Poland). Buffer solutions of pH 2, 4 and 7 were purchased from POCH (Gliwice, Poland). Sucrose, glucose, fructose, tartaric, malic, lactic, acetic, citric and succinic acids were obtained from Sigma-Aldrich (Poznań, Poland), all with a purity level of ≥98%. Analytical standards of cyanidin-3-O-glucoside, peonidin-3-Oglucoside, petunidin-3-O-glucoside, malvidin-3-O-glucoside, delphinidin-3-O-glucoside, myricetin-3-O-glucoside, quercetin-3-O-rutinoside, quercetin-4′-O-glucoside, quercetin-3-O-glucoside, kaempferol-3-O-glucoside, isorhamnetin-3-O-glucoside, (+)-catechin, (−)-epicatechin, (−)-epicatechin-3-gallate, procyanidin A1 and A2, trans-resveratrol, and trans-piceid, were purchased from Extrasynthese (Lyon, France). The analytic standards of gallic acid, caftaric acid, protocatechuic acid, coutaric acid, caffeic acid, p-coumaric acid, and ferulic acid were purchased from PhytoLab (Vestenbergsgreuth, Germany). Acetonitrile (HPLC gradient grade) was purchased from POCH (Gliwice, Poland). Formic acid (LC–MS grade) was purchased from Fischer Scientific (Schwerte, Germany).