Identification of yeast by MALDI–TOF MS

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).