Yeast and Fermentation Session
Julia C Usbeck, Technische Universität München, Freising, Germany
Co-author(s): Jürgen Behr and Rudi Vogel, Technische Universität München, Freising, Germany
ABSTRACT: For the production of fermented beverages the most important industrially used yeast species belong to the genus Saccharomyces. Top-fermented ale-type beers are brewed with S. cerevisiae, while bottom-fermented lager beers, which are fermented at much lower temperatures, employ S. pastorianus. This yeast species is a genetic hybrid of S. bayanus and S. cerevisiae.
Apart from technological parameters, each specific strain affects
processing and the quality of the final product, e.g., flocculation
behavior, temperature optima, fermentation speed and rate, the spectrum
of secondary metabolites, and hence the aroma profile. These ecotypes
are differentiated by time-consuming and laborious biochemical and
DNA-based methods to enable a constant beverage quality and
characteristics. However, their physiological differences must also be
reflected in their enzymatic setting. Matrix assisted laser desorption
ionization–time-of-flight mass spectrometry (MALDI-TOF MS) offers a fast
and easy method to differentiate yeasts along their peptide mass
fingerprints. Therefore, we explored this method according to its
differentiating potential for brewing yeasts and their metabolic status.
Peptide mass fingerprints of top- and bottom-fermenting Saccharomyces
strains were generated by MALDI-TOF MS upon optimized sample
preparation and instrument settings and analyzed by a cluster analysis
for strain or ecotype level differentiation. Furthermore, we
investigated the effect of different culture conditions on selected
strains representative for different beer types in relation to specific
propagation or fermentation stages in the brewery, e.g., varying sugar
concentrations and availability of oxygen. The differentiation of top-
and bottom-fermenting brewing yeasts was achieved by >95% of more
than 400 samples. Top-fermenting S. cerevisiae strains could
further be subdivided into ecotypes according to their application in
the production of different beer types, like wheat or alt beer.
Differences within S. pastorianus strains were also present, but not as distinctive as for S. cerevisiae.
The status of yeast fermentation or respiration could be precisely
discriminated, while differences resulting from low and high sugar
concentrations were less decisive. These results enable fast
classification of unknown strains, improvement of quality control, and
pursuit of different physiological states in the yeast culture during
the brewing process.
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.
