29. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for brewing microbiology

Anita Van Landschoot (1), Anneleen Decloedt (1), Freek Spitaels (1), Koenraad Van Hoorde (1), Peter Vandamme (1), Anneleen Wieme (1); (1) Ghent University, Ghent, Belgium

Technical Session 9: Brewing Microbiology
Monday, August 15  •  9:45–11:30 a.m.
Plaza Building, Concourse Level, Governor’s Square 14

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was used for dereplication of microbial brewery isolates and for identification of beer spoilage bacteria, microbiota of beers of spontaneous fermentation and microorganisms in old beers and beer ferment. The applicability of MALDI-TOF MS was investigated for controlling the purity of pitching yeast and for the follow-up of beer fermentation. To achieve the goals, an extensive identification database was constructed comprising more than 5,000 mass spectra, including biological and technical replicates derived from lactic acid bacteria (LAB), acetic acid bacteria (AAB) and yeasts, covering more than 50 species. MALDI-TOF MS spectra allowed a straightforward species identification of 327 (94.0%) isolates of spoiled beer and brewery samples (Wieme et al. 2014a). The remaining isolates clustered separately and were assigned through sequence analysis of protein coding genes either to species not known as beer spoilage bacteria, and thus not present in the database, or to novel AAB species. The microbiota involved in the fermentation of lambic beers, products of spontaneous fermentation, were studied by sampling fermentation batches over a period of two years. Although lambic sour beers showed minor variations in the microbiota between casks and batches and a considerable species diversity, a characteristic microbial succession was identified. This succession started with a dominance of Enterobacteriaceae in the first month (for the most traditional lambic brewery of Belgium), which were replaced at 2 months by Pediococcus damnosus and Saccharomyces spp., the latter being replaced by Dekkera bruxellensis at 6 months fermentation duration (Spitaels et al. 2014). The isolates of 37 different Belgian beers that were more than 25 years old and a Nepal beer ferment comprised strains of nine different species: Acetobacter sp., Enterococcus faecium, Lactobacillus brevis, Lactobacillus plantarum, Pediococcus acidilactici, Dekkera anomala, Dekkera bruxellensis, Pichia sp. and Saccharomyces cerevisiae. Most isolates were related to brewing microbiota either as described fermentation cultures and/or as brewing spoilage microorganisms. The proof of concept was delivered that MALDI-TOF MS is a suitable fast tool to monitor the purity of brewer’s yeast cultures (Wieme et al. 2014b). This was examined for a brewer’s yeast strain contaminated with wild-type yeast and for bottled beer refermented with that particular contaminated brewer’s yeast strain. The method for follow-up of fermentations with MALDI-TOF MS was optimized at small-scale fermentations with top-fermenting yeast. During a 4-day fermentation the MALDI-TOF MS spectra demonstrated a clear shift with final spectra at day 4 that resemble best the spectra of the starting yeast. It can be concluded that MALDI-TOF MS is a suitable rapid high-throughput tool for detection, identification and differentiation of microbiota in the brewing industry. Wieme et al. (2014a) Int. J. Food Microbiol. 185:41-50; Spitaels et al. (2014) PlosONE 9 (4) e95384; Wieme et al. (2014b) JIB 120(4):438-443.

Anneleen Decloedt graduated magna cum laude with a masters degree in science, biochemistry, and biotechnology (Ghent University, Belgium) in 2011 with a thesis within the Food Safety department. Her great passion for biochemical research led her to take up an international doctoral research project, that she finished in 2015 as a Ph.D. graduate at Ghent University. Since then she has been working as a postdoc at the Laboratory of Biochemistry and Brewing at Ghent University/Ghent University College and she is involved in diverse brewery research projects.