K. NEUMANN (1), L. A. Garbe (1); (1) VLB-Berlin/TU-Berlin, Berlin, Germany

Sensory II
Thursday, June 5 - 10:00 a.m.-11:45 a.m.
Lobby Level, Empire Ballroom

Many aroma compounds contribute to the characteristic taste of beer, whereas certain compounds contribute to off-flavor notes that develop during aging of beer. Two of them, cis- and trans-4,5-epoxy-2E-decenal, have very low odor thresholds and, therefore, contribute to the aroma profile of aging beers. They can be monitored during aging processes in sub-ppb levels by GC-NCI-MS methods. Until now the origin of these aging products remained unknown, although theories of formation in beer have been published. Its appearance in beer linoleic acid is recognized as a possible source of flavor-active aldehydes generally and epoxydecenals in particular. In a set of experiments we confirmed the role of linoleic acid as a precursor for epoxydecenals and incorporation of oxygen applied to the headspace of the bottles in these aldehydes during oxidative degradation processes. In a first experiment we spiked pilsner-type beer with ¹³C-labeled linoleic acid. In the case of degradation of linoleic acid to cis- and trans-4,5-epoxy-2E-decenal the ¹³C-labels should be found in the epoxydecenal molecules. The second part of this set involved flushing the headspace of swing-top beer bottles with ¹⁸O₂. In the case of oxidative degradation processes the ¹⁸O-label should appear in the epoxydecenals either incorporated once at the epoxide ring or twice additionally at the carbonyl function (C-1). In case of an exchange reaction at C-1 the ¹⁸O-label should disappear and not be visible. After incubation at 40°C samples were worked up at certain times via SPE. GC-NCI-MS analysis and quantification using ²H₃-labeled isotopomers revealed the incorporation of the isotope labels in the epoxydecenal isomers. We found ¹³C-labels in the epoxydecenal produced by degradation of ¹³C-labeled linoleic acid. Additionally, we observed one ¹⁸O-label in the epoxydecenal at the epoxide ring. Stable incorporation of ¹⁸O at C1 could not be confirmed. These results show that oxidative degradation processes of linoleic acid leads to formation of cis- and trans-4,5-epoxy-2E-decenal.

In 2005, Konrad Neumann graduated from the Technische Universität Berlin (TUB), Germany, with a Dipl.-Ing. degree in biotechnology. Since 2005 he has been working at the Research and Teaching Institute for Brewing in Berlin (VLB) in a research group led by Professor Tressl and Leif-Alexander Garbe. The focus of his work is the characterization of reactive carbonyl compounds like 2E-nonenal, 2,4-decadienal, and epoxydecenals and their interactions with peptides and proteins by means of GC-O, GC-MS, and proton and carbon-13 NMR, as well as LC-ESI-MS.

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