Fruit of the bine: exploring the chemodiversity of cultivated hops ( Humulus lupulus L.)

Hops ( Humulus lupulus L.) is widely used in the brewing industry for its aromatic and bittering properties associated with hops’s unique phytochemistry. Although the brewing properties of different cultivars are believed to reflect total and relative amounts of bitter acids and prenylated flavonoids, few studies have investigated the relationship between these compounds among hop cultivars. A collection of hop samples (commercial pellets and field-grown infructescence) was extracted and analyzed using targeted profiling and untargeted metabolomic techniques for phytochemical comparisons based on cultivar use (aroma vs. bittering) and origin (Europe vs. North America). Marker compounds correlated positively with one another, most notably co- and ad-humulone (α-acids, r = 0.90) and co- and ad-lupulone (ß-acids, r = 0.72), each with xanthohumol. Relative to aroma cultivars, bittering hops contained higher levels of α-acids and, as revealed by untargeted metabolomics, certain ß-acid derivatives. North American hops had more adhumulone and a higher α-to-ß-acid ratio than European hops. Untargeted metabolomic analysis revealed higher levels of bitter acid metabolites in bitter and North American hops than aroma or European hop varieties. This study was the first to systematically compare various categories of hops using both targeted profiling and untargeted metabolomic approaches.