Optimization of Matrix-Assisted-Laser-Desorption–Ionization-Time-Of-Flight Mass Spectrometry for the identification of bacterial contaminants in beverages

• MALDI-TOF MS sample preparation method was optimized for beverage spoilage bacteria.
• Species level identification was not affected by cultivation parameters.
• MALDI-TOF MS allows reliable identification of beverage spoilage bacteria.

The growth of microbial contaminants in industrially produced beverages can cause turbidity, haze and off-flavors resulting in quality loss often rendering the product undrinkable. In this work Matrix-Assisted-Laser-Desorption–Ionization-Time-Of-Flight Mass Spectrometry (MALDI-TOF MS) based on the generation of peptide mass fingerprints, which form a distinctive protein peak pattern, is presented as a rapid, reliable and powerful tool for the identification of spoilage bacteria encountered in beverages.Lactobacillus brevis, Pediococcus claussenii and Leuconostoc mesenteroides were used to optimize sample preparation and MALDI-TOF MS-settings. Different sample preparation methods ranging from plain cell smears to more elaborate extraction procedures including mechanical and enzymatical disruption of cells were investigated. The effects of culturing time and the availability of oxygen and nutrients on the acquired protein peak patterns were studied.While cell smears at times hampered the acquisition of spectra for strain L. brevis all other procedures constantly delivered good quality spectra for all three strains. The extraction procedure allowed good reproducibility of spectra with high information content and enabled differentiation on the species level regardless of the culture conditions used. The application of specific culture conditions to microorganisms resulted in minor but stable changes in spectra, which were not sufficient to impair identification of isolates on the species level.