Formation and Accumulation of α-Acids, β-Acids, Desmethylxanthohumol, and Xanthohumol during Flowering of Hops (Humulus lupulus L.)

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Abstract
Important secondary metabolites, present in hops (Humulus lupulus L.), include α-acids and β-acids, which are essential for the brewing of beer, as well as the prenylated chalcones, desmethylxanthohumol, and xanthohumol, which exhibit interesting bioactive properties. Their formation and accumulation in five selected hop varieties, Wye Challenger, Wye Target, Golding, Admiral, and Whitbread Golding Variety, were quantitatively monitored by high-performance liquid chromatography using UV detection. All target compounds were present from the onset of flowering, not only in female hop cones but also in male inflorescences, albeit in low concentrations. During development from female inflorescences to cones, levels of α-acids, β-acids, desmethylxanthohumol, and xanthohumol gradually increased, while each hop variety exhibited individual accumulation rates. Furthermore, these compounds were present in leaves of fully grown hops as well. The study demonstrated that key compounds for flavor and potential beneficial health effects associated with beer not only reside in the glandular lupulin structures but also are distributed over various parts of the hop plant. Keywords: α-Acids; β-acids; desmethylxanthohumol; xanthohumol; hops (Humulus lupulus L.); high-performance liquid chromatography