Chemistry and biology of hop flavonoids

The flavonoids of hops include flavonol glycosides, condensed tannins, and prenylflavonoids. The first two flavonoid classes are located intracellularly, while the prenylflavonoids are secreted along with bitter acids and essential oils by the lupulin glands of the inflorescences. The chemistry and biological activities of prenylflavonoids isolated from the lupulin fraction are reviewed. An LC-MS method was developed for quantitation of these phenolics in hops, hop-derived products, and beer. The fate of xanthohumol and related prenylflavonoids during the brewing process was investigated by LC-MS. The partial carryover of the prenylflavonoids from hops into beer was attributed mainly to incomplete extraction and adsorption to insoluble proteins and yeast. Moreover, the prenylchalcone-type flavonoids were largely converted into isomeric prenylflavanones during wort boiling. The biological activities of some of the prenylflavonoids isolated were examined using in vitro techniques. Some of the prenylflavonoi...

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