Analytical Session
Jennifer Koob, Research Center Weihenstephan for Brewing- and Food-Quality, TU Muenchen, Freising, Germany
Co-author(s): Robert Riedl, Mathias Hutzler, Mehmet Coelhan, and
Fritz Jacob, Research Center Weihenstephan for Brewing- and
Food-Quality, TU Muenchen, Freising, Germany
ABSTRACT: A few bacteria, especially species of the genera Lactobacillus and Pediococcus,
are able to spoil beer. Procedures to detect and identify these
bacteria are numerous, but nearly all of them are based on the presence
of living or augmentable cells. This study attempts to detect beer
spoiling microorganisms indirectly using chemical fingerprints. Nine
different, as determined by real time-PCR (polymerase chain reaction)
and DNA-sequencing, strains of beer spoiling bacteria were inoculated in
bottled beer and incubated for a period of at least 2 weeks. As
reference samples, uncontaminated blank beers were processed and
analyzed in the same way as the contaminated samples. After the
formation of turbidity by the beer spoiling bacteria the sample was
chemically analyzed. Several chromatographic methods were applied to
detect the differences between the contaminated media and the blank
samples. The accumulation or degradation of compounds had to be caused
by microbial growth. The analyses performed were, for example, the
determination of the fatty acid content and the concentrations of
aging-relevant substances by GC and flame ionization detector (FID)
after steam distillation. In addition, the contents of amino acids,
dimethyl sulfide, organic acids, and fermentation by-products were
determined by chromatographic methods. The major differences (±60% of
the initial values of the blank samples) were collected and transferred
to a profile that is specific for every bacteria strain used in this
study. The results for L. brevis and L. backi differed
particularly with regard to organic acid, fatty acid, and aging-relevant
compound contents. The profiles or chemical fingerprints can be
regarded as a novel tool to identify a certain beer spoiling
microorganism by recovering them in contaminated beer samples that don’t
have to contain living cells. This work establishes the basic
experimental setup and analysis for further studies on the chemical
detection of microbial infections in unfiltered and filtered sections in
breweries.
Jennifer Koob was born in Bad Kissingen, Germany,
in 1986. From 2005 until 2010 she studied brewing science and beverage
technology at TU München and graduated with a Dipl.-Ing. degree. After
her studies she worked as an assistant manager for the Lang Brewery,
Waltershausen. Since October 2011 she has been a scientific assistant at
the Research Center Weihenstephan for Brewing and Food Quality. Her
main research topics are beer spoiling microorganisms and their chemical
identification.
VIEW PRESENTATION 98
