Analytical Session
Nils W Rettberg, TU Berlin / VLB Berlin
Co-author(s): Leif Garbe, TU Berlin/VLB Berlin, Germany
ABSTRACT: For decades fatty acids (FA) and their oxidation
products have attracted the attention of brewers. They strongly
influence beer foam and fermentation, are closely linked to beer flavor
(in)stability, and may promote beer gushing. Data from free and
oxygenated hydroxy fatty acids (HFA) are known from the literature.
However, analytical approaches differ considerably in time and chemicals
required. In the current paper we present two user-friendly sample
preparation procedures for low-level quantification of C12-C20 fatty
acids and their abundant oxidation products. The aim of the study was a
significant reduction in the amount of sample, chemicals, and costs
required. We compare a modified and miniaturized Bligh and Dyer
extraction with a solid phase extraction (SPE) assay. Additionally, we
introduced a mild and efficient derivatization procedure that enables
simultaneous methylation of all free organic acids. Quantification of FA
and HFA can be done by GC-FID/internal standard methods. Here, we
present a convenient GC-MS route with stable isotope dilution techniques
(SIDA). Lab synthesis of deuterium labeled FA and O-18 labeled HFA was
performed. Selected ion monitoring mass spectrometry (SIM-MS) strongly
increased the sensitivity and selectivity of our analysis. We analyzed
wort, beer, and several intermediates to validate our experimental setup
and to underline its advantages. High recovery rates and excellent
repeatability prove that both sample preparation procedures are very
suitable and useful. Compared to assays that have been presented in the
past we could strongly reduce solvents, waste, and harmful reagents.
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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