Fate of Xanthohumol and Related Prenylflavonoids from Hops to Beer

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Abstract
The fate of three prenylated flavonoids of the chalcone type, xanthohumol, desmethylxanthohumol, and 3‘-geranylchalconaringenin, was monitored with LC/MS-MS from hops (Humulus lupulus L.) to beer in two brewing trials. The three prenylchalcones were largely converted into their isomeric flavanones, isoxanthohumol, prenylnaringenins, and geranylnaringenins, respectively, in the boiling wort. Losses of prenylflavonoids were due to incomplete extraction from the hops into the wort (13−25%), adsorption to insoluble malt proteins (18−26%), and adsorption to yeast cells (11−32%) during fermentation. The overall yield of xanthohumol, after lagering of the beer and largely in the form of isoxanthohumol, amounted to 22−30% of the hops' xanthohumol. About 10% of the hops' desmethylxanthohumol, completely converted into prenylnaringenins, remained in the beers. 3‘-Geranylchalconaringenin behaved similarly to desmethylxanthohumol. Solubility experiments indicated that (1) malt carbohydrates form soluble complexes with xanthohumol and isoxanthohumol and (2) solubility does not dictate the isoxanthohumol levels of finished beers. Keywords: Beer; hops; Humulus lupulus; prenylated flavonoids; xanthohumol