Xanthohumol, isoxanthohumol, and 8-prenylnaringenin in beer, hop and hop pellet samples were analyzed by HPLC using an InertSustain phenyl column and the mobile phase containing 40% methanol and 12% 2-propanol. Fractions of isoxanthohumol and 8-prenylnaringenin obtained by the above HPLC were separately collected. Isoxanthohumol and 8-prenylnaringenin were enantioseparated by HPLC using a Chiralcel OD-H column with a mobile phase composed of hexane-ethanol (90:10, v/v) and a Chiralpak AD-RH column with a mobile phase composed of methanol-2-propanol-water (40:20:40, v/v/v), respectively. Isoxanthohumol and 8-prenylnaringenin from beer, hop and hop pellet samples were found to be present in a racemic mixture. This can be explained by the fact that the two analytes were produced by a nonenzymatic process. The effects of boiling conditions on the conversion of xanthohumol into isoxanthohumol were also studied. A higher concentration of ethanol in heating solvent resulted in a decrease in the conversion ratio and the conversion was stopped by addition of ethanol at >50% (v/v). The isomerization was significantly affected pH (2-10) and the boiling medium at pH 5 was minimum for the conversion. Therefore, it was suggested that xanthohumol was relatively difficult to convert to isoxanthohumol in wort (pH 5-5.5) during boiling.
Keywords: 8-prenylnaringenin; beer; enantioseparation; hops; isoxanthohumol.
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