Fast and reliable identification and differentiation of beverage spoiling yeasts by MALDI-TOF MS

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.