Microbiology Session
Julia C Usbeck, Technische Universität München, Freising, Germany
Co-author(s): Carola Kern, Rudi Vogel, and Jürgen Behr, Technische Universität München, Freising, Germany
ABSTRACT: The growth of beverage spoiling yeasts in
beverages during the production process or upon packaging leads to
defects such as formation of estery off-flavors, hazes, and turbidity,
which result in economic and image losses. Therefore, species-specific
biochemical and DNA-based identification methods have been developed
that are widely applied in microbiological quality control. However,
these methods are generally time-consuming and laborious. Matrix
assisted laser desorption ionization–time-of-flight mass spectrometry
(MALDI-TOF MS) could deliver discriminative peptide mass fingerprints
within minutes and could thus be a rapid and reliable tool for the
identification and differentiation of beverage spoiling yeasts. Up to
now, routine analysis of yeasts by MALDI-TOF MS has been impaired by low
reproducibility of data acquisition. Furthermore, the effects of
differences in the physiological state of the organism on the
reliability of the identification method are still unknown. It was
therefore the aim of this study to optimize sample preparation, as well
as the MALDI-TOF MS parameterization, by using three strains of yeasts
commonly associated with spoilage incidents belonging to the species Saccharomyces cerevisiae var. diastaticus, Wickerhamomyces anomalus, and Debaryomyces hansenii.
Especially the influences of varying physiological conditions like
respiration or fermentation and different nutrients on protein mass
signatures were analyzed. Routine identification for yeast samples was
established by optimized sample preparation and MALDI-TOF MS settings.
Environmental or physiologic parameters including the availability of
oxygen, different nutrients, yeast cell density, or growth phase
revealed small differences in the peptide mass fingerprint. The status
of a spoilage yeast performing fermentation or respiration could be
precisely differentiated along these small differences (biomarkers) in
the mass spectrum. Still a core of mass peaks remained constant under
all tested conditions enabling reliable identification. Yeast cell
concentration did not affect the spectra distinctly and an influence of
available nutrients could not be measured in each case. Significant
differences caused by specific culture or environmental conditions can
be connected to their respective origins.
Julia C. Usbeck was
born in 1984 in Wuppertal, North Rhine-Westphalia, Germany. In 2009 she
finished her studies in food chemistry at the Westfälische
Wilhelms-Universität, Münster, followed by a mandatory practical year to
accomplish the second state examination. Currently she is working on
her Ph.D. thesis on the ability to detect beverage spoiling yeasts using
MALDI-TOF mass spectrometry at Technische Universität München under the
supervision of Rudi F. Vogel at the Chair of Technische Mikrobiologie
in Weihenstephan.
