Structural Identification and Distribution of Proanthocyanidins in 13 Different Hops

Ten newly isolated hop proanthocyanidin oligomers and flavan-3-ol monomers from 13 different hops have been identified as gallocatechin, gallocatechin-(4α→8)-catechin, gallocatechin-(4α→6)-catechin, catechin-(4α→8)-gallocatechin, catechin-(4α→6)-gallocatechin, afzelechin-(4α→8)-catechin, catechin-(4α→8)-catechin-(4α→8)-catechin, epicatechin-(4β→8)-epicatechin-(4β→8)-catechin, catechin-(4α→8)-gallocatechin-(4α→8)-catechin, and gallocatechin-(4α→8)-gallocatechin-(4α→8)-catechin, together with seven previously isolated oligomers, namely, catechin, epicatechin, epicatechin-(4β→8)-catechin, epicatechin-(4β→8)-epicatechin, catechin-(4α→8)-catechin, catechin-(4α→8)-epicatechin, and epicatechin-(4β→8)-catechin-(4α→8)-catechin. These compounds were subjected to acid-catalyzed degradation in the presence of phloroglucinol or by partial or complete acid-catalyzed degradation and reaction with benzyl mercaptan followed by desulfurization. The resultant adducts when compared to authentic samples by high-performance liquid chromatography−atmospheric pressure chemical ionization tandem mass spectrometry and high-performance liquid chromatography−electrospray ionization tandem mass spectrometry served to identify the precursors. The composition of proanthocyanidins from 13 different hops was similar, but the concentration of individual compounds showed some differences, which indicated that hop proanthocyanidin profiles are affected by geographic origin and are variable depending on the cultivars. Keywords: Hops; proanthocyanidins; Humulus lupulus; Cannabinaceae; HPLC/APCI−MS/MS; HPLC/ESI−MS/MS