Characterization by HPLC–ESI–MS2 of native and oxidized procyanidins from litchi (Litchi chinensis) pericarp

•About 60% of extracted litchi pericarp polyphenols corresponded to procyanidins.•A first molecular structure of the oxidized procyanidins in litchi was achieved.•Five oxidation markers of procyanidins were clearly identified.•Thioglycolysis–HPLC–ESI–MS is a useful method to characterize oxidized procyanidins.