Oxidation Products of Isohumulones

Abstract

A complex mixture of oxidation products is formed from iso-a-acids during wort boiling. These substances are already present in hops and persist to beer. Seven major constituents of such a mixture, obtained from pure humulone, were isolated by countercurrent distribution and their structures were elucidated, mainly by mass spectroscopy. The bitterness of the new beer substances was evaluated against trans isohumulone as a reference standard. These oxidation products of iso-a-acids are not extracted with iso-octane and they therefore escape the usual beer bitterness assay.

18O Stable Isotope Labeling, Quantitative Model Experiments, and Molecular Dynamics Simulation Studies on the Trans-Specific Degradation of the Bitter Tasting Iso-α-acids of Beer

“…There are only a few proposals on the structures of iso-R-acid degradation products as well as their underlying formation mechanisms such as, e.g., photolytic cleavage of the isohexenoyl side chain (9) or the alkalicatalyzed formation of humulinic acids (22,23). Although numerous publications proposed chemical structures of putative iso-R-acid degradation products, most of these model experiments have been done using rather artificial model conditions (24)(25)(26)(27). Most important, the compounds previously identified do not at all explain the different reactivity of trans-iso-R-acids (3) and cis-iso-R-acids (2) as well as the trans-specificity formation of iso-R-acid degradation products.…”