期刊
JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY
卷 58, 期 8, 页码 5059-5067出版社
AMER CHEMICAL SOC
DOI: 10.1021/jf100083e
关键词
Iso-alpha-acids; hop; beer; hydroperoxides; alloisohumulone; tricyclocohumol
The iso-alpha-acids, the major contributor to bitter beer taste, is well-known to strongly degrade during beer aging. The storage of beer in brown glass bottles revealed a strong depletion of the trans-configured isomers in a highly specific manner, whereas the corresponding cis-iso-alpha-acids seemed to be hardly affected. In comparison, storage of beer in polyethylene terephthalate bottles, which are known to be permeable to oxygen, induced a drastic degradation of both isomers independent of their cis/trans configuration. To investigate the chemical transformation of iso-alpha-acids under oxidative storage conditions, suitable model experiments were performed, and the reaction products that formed were identified as previously not reported hydroperoxy- and hydroxyl-allo-iso-alpha-acids by means of one-/two-dimensional NMR and liquid chromatography mass spectrometry experiments; for example, cis- and trans-configured hydroperoxy-alloisohumulone as well as the corresponding hydroxy-alloisohumulones were generated upon oxidation of cis- and trans-isohumulone independent of their cis/trans configuration. In addition, the oxidation products formed from the various iso-alpha-acid congeners were quantitatively determined in a series of beer samples stored under defined conditions. For the first time, these data help to understand the molecular mechanism involved in the autoxidative degradation of iso-alpha-acids in beer.
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