Novel and efficient approach to identify hop cultivars (Humulus lupulus L.) using cultivar identification diagram strategy based on fingerprint of flavonol di- and tri-O-glycosides

Abstract

The profile of flavonoids in hops (Humulus lupulus L.) showed a significant cultivar diversity applicable for distinguishing cultivars. The aims of this study were (1) to identify and describe flavonol di- and tri-glycosides in hops; (2) to analyze the profile of flavonol glycosides in various hop cultivars; and (3) to develop a new approach for identifying hop cultivars using a manual cultivar identification diagram that consisted of the ratios between specific flavonol di- and tri-glycosides. The total of 22 different flavonol O-glucosides were detected and tentatively identified using liquid chromatography (RP-HPLC) coupled with high-resolution mass spectrometry (HR-MS/MS). The identified O-flavonol glycosides, mainly containing aglycones, quercetin, kaempferol and myricetin, were categorized into five groups according to their sugar moieties. Furthermore, fourteen characteristic peaks with a low sample-to-sample variation and acceptable coefficient of variation (< 20%) throughout growing seasons were selected for chemometric analysis. Hierarchical cluster analysis (HCA) was applied to two data sets to characterize the similarity and differences among samples: one data set contained five hop cultivars common in the Czech Republic and the second one consisted of 17 hop cultivars from around the world. The results of the HCA of flavonol di- and tri-glycosides proved the genotypic effect on their profile and allowed to select compounds primarily responsible for clustering hop cultivars into groups. These compounds were used for developing an efficient cultivar identification strategy based on the manual cultivar identification diagram. The functionality of the identification diagram was successfully tested and allowed, based on the specific ratios between flavonol glucosides, reliable discrimination among the five most common hop cultivars planted in the Czech Republic. Compared to the genetic or chemotaxonomic methods, the newly developed approach for the hop cultivar identification provided reliable results even if the tested materials were hop pellets or beer.