Analytical Session
Jana H Gierds, Research and Teaching Institute for Brewing, Berlin, Germany
Co-author(s): Isil Baki, Research and Teaching Institute for Brewing,
Berlin, Germany; Christina Quandt, NovaBiotec Dr. Fechter GmbH, Berlin,
Germany; Erik Pollmann, Johannes Bader, Roland Folz, and Diedrich
Harms, Research and Teaching Institute for Brew
ABSTRACT: Reproducible production of beer and bakery
products is based on the application of specific culture yeast strains.
Microbiological purity and physiological fitness are strongly required
to ensure controlled processes and the production of desired products
including the aroma profile. Fast and reliable detection methods are
required to achieve process control. The presented detection method is
based on the determination of exact molecular masses of yeast proteins
using matrix assisted laser desorption ionization–time-of-flight mass
spectrometry (MALDI-TOF MS). For this purpose, a yeast sample is
solubilized and mixed with an appropriate organic matrix followed by a
co-crystallization directly on a sample plate. A laser beam (e.g.,
nitrogen laser) is focused and hits the sample in pulses. The absorption
of the photonic energy of each laser pulse leads to the desorption of
the crystal and the formation of partly ionized matrix and protein
molecules and the ionization of analyte molecules by charge transfer.
Ionized molecules are accelerated in an electromagnetic field, which is
the start of the separation process that is the basis of the
time-of-flight principle. This velocity depends on the mass of the ions
with heavier molecules having a higher moment of inertia and hence a
lower velocity. The mass spectrum can be used for yeast fingerprinting
and process monitoring. With the achieved spectra a database will be
built to enable fast and reliable identification of baker’s and brewer’s
yeasts. Furthermore, the detection of wild yeast or undesired bacteria
is a goal. This method is underpinned by PCR, a reproducible reference
analysis, based on the alignment of specific selected DNA sequences. The
described detection system is completed by a newly developed sampling
kit enabling safe shipping and conservation of the samples. This enables
small- and medium-sized enterprises to improve their process control
without having their own MALDI-TOF system.
Food chemist Jana H.
Gierds studied at the Technical University of Berlin. She started work
as a scientific assistant in the Central Laboratory of the Research and
Teaching Institute for Brewing in Berlin in 2010. Since September 2011
she has been working on the presented project “Identification of Yeast
by MALDI–TOF MS.” (ZIM [zentrales innovationsprogramm mittelstand]
KF2132320SK1).
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