Technical Session 02: Analytical I Session
Nils W Rettberg, TU Berlin / VLB Berlin
Co-author(s): Konrad Neumann and Leif Garbe, TU Berlin/VLB Berlin, Germany
ABSTRACT: Flavor active cis- and trans-4,5-epoxy-2E-decenal
isomers (epoxydecenals) are important (off)-flavor compounds in wheat
bread, popcorn, oils, beef meat, fruit juices, tomatoes, tea, etc. They
originate from linoleic acid oxidation; therefore, their presence in
wort and beer is likely. trans-4,5-Epoxy-2E-decenal has a very
intense metallic taste and smell. Its flavor threshold is reported at
0.6 pg/L in air and 20 ng/L in water, respectively. In the literature,
the aroma of cis-4,5-epoxy-2E-decenal is described as
citrus-like, sweet, fatty, and malty. So far there are no odor and
flavor thresholds published. The concentration of epoxydecenals in a
foodstuff varies widely. Fresh tomatoes contain up to 600 µg trans-epoxydecenal per kg in fruit juices, and black tea concentrations are considerably lower. In fresh grapefruit juice 3 µg/L trans-epoxydecenal
were traced; in black tea the sum of both isomers is in the 1 µg/L
range. Even at these comparatively low concentrations, epoxydecenal
isomers were identified as key odorants of these products. In fresh beer
we analyzed epoxydecenal concentrations at 20 pg/L. In wort we
quantified 3–4 µg/L of both isomers in sum. Determination of this
ultra-trace compound requires sophisticated analytical techniques. To
quantify epoxydecenals from beer, mash, and wort, we established a rapid
and effective solid phase extraction (SPE) procedure. A stable isotope
dilution assay (SIDA) was established for their quantification. Negative
chemical ionization–selected ion monitoring mass spectrometry
(NCI-SIM-MS) was used for analysis. This method increased the
sensitivity/selectivity and resulted in a reliable and ultra-trace
quantification. Epoxydecenals were quantified in mash and wort, as well
as in fresh and aged beers. We observed an increasing epoxydecenal
concentration during beer storage. The storage temperature, light, or
linoleic acid addition showed remarkable effects on their concentration
and their cis/trans ratio.
Nils W. Rettberg is a
trained brewer and maltster from Radeberger Gruppe, Germany. In 2011, he
received a diploma in biotechnology from the Berlin Institute of
Technology (TUB) and started as a Ph.D. student at the TUB Chair of
Bioanalytics. In addition, Nils is employed at the Research and Teaching
Institute for Brewing in Berlin (VLB), Department for Special Analyses.
His work includes courses for students of biotechnology and brewing
science ranging from basic chemical-technical analysis to more
sophisticated modern analytical techniques. As a member of
Leif-Alexander Garbe’s research group his scientific work focuses on
brewing-relevant special analyses using mass spectrometry and stable
isotope dilution assays. Initiated by his diploma thesis on “Flavor
Active Epoxydecenals,” he has developed a deep interest in lipid
oxidation, beer staling, and trace analysis in brewing.
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