Procyanidin b2

1,10-Phenantroline, (-)-epicatechin, Thiamine, Flufenamic acid, Vanillic acid and Protocatechuic acid were purchased from Sigma (Barcelona, Spain). Procyanidin B2 gallate, Epigallocatechin gallate (EGCG) and epicatechin gallate were purchased from Extrasynthese (Genay, France) and Procyanidin B2 was purchased from Adooq-Bioscience (Irvine, CA, USA).
We used Krebs–Ringer bicarbonate (KRB) buffer (Hepes 11.5 mM, CaCl₂ 2.6 mM, MgCl₂ 1.2 mM, KCl 5.5 mM, NaCl 138 mM, NaHCO₃ 4.2 mM, NaH₂PO₄ 1.2 mM) pH 7.4, supplemented with either 10 mM D-Glucose (KRB-D-Glucose buffer) or 10 mM D-Mannitol (KRB-D-Mannitol buffer). For enterohormone secretion studies, KRB-D-Glucose was supplemented with protease inhibitors: 10 µM amastatin (Enzo Life Sciences, Madrid, Spain), 100 KIU aprotinin (Sigma, Barcelona, Spain) and 0.1% fatty acid free-bovine serum albumin.

(+)-Catechin and (−)-epicatechin were purchased from YuanYe Biotechnology (Shanghai, China). Procyanidin B2, procyanidin B3 and (+)-dihydroquercetin were purchased from Adooq BioScience (Irvine, CA, USA). Cysteine and L-ascorbate were purchased from Sigma Aldrich (St Louis, MO, USA).