Use of RP-HPLC-ESI(–)-MS/MS to Differentiate Various Proanthocyanidin Isomers in Lager Beer Extracts

Abstract

Normal-phase high-performance liquid chromatography electrospray ionization(–) tandem mass spectrometry (NP-HPLC-ESI(–)-MS/MS) and thioacidolysis analyses recently have revealed the presence of (+)-catechin, (–)-epicatechin, procyanidin dimers, and prodelphinidin trimers in acetone/water (70/30, vol/vol) LH-20 extracts of lager beers. In this study, detailed structures were determined by reversed-phase (RP) HPLC-ESI(–)-MS/MS. Four dimers were identified: three procyanidins (B1, B3, and B4) and one prodelphinidin (B3). Previously detected in hop or malt, three trimers (the procyanidin C-4α-8-C-4α-8-C and two prodelphinidins, GC-4α-8-C-4α-8-C and GC-4α-8-GC-4α-8-C) were distinguished for the first time in beer. As expected based on previous thioacidolysis data, most beer proanthocyanidins carried a catechin as the terminal unit.