Thiolysis-HPLC characterization of apple procyanidins covering a large range of polymerization states

Procyanidins from the cortex of two cider apple varieties (Malus domestica; Kermerrien and Avrolles) were extracted by solvents. After a solid-phase extraction step, they were fractionated by normal-or reversed-phase HPLC at the semipreparative scale to obtain a series of purified fractions covering a wide range of polymerization states. Freeze-dried fractions were characterized by reversed-phase HPLC following thiolysis. Elution on normal-phase HPLC gave oligomeric procyanidins fractions with (DPn) over bar (average degree of polymerization) values varying from 2 to 8, whereas polymeric fractions ((DPn) over bar values varying from 7 to 190) were obtained by reversed-phase HPLC. Constitutive units were mainly (-)-epicatechin with a proportion above 95% for all fractions. Thiolysis yields were wholly homogeneous with an average value of 75%, which indicates that the efficiency of the reaction did not depend on the polymerization state of the procyanidin fractions.