Magda Costa
Universiteit Gent

MICROBIOLOGY
Keywords: brewer’s yeast, fermentation follow-up, LC-ESI-MS

Fermentation is an important step in beer production and so are thus the wort composition and fermentation conditions. As yeast behaviour can be very unpredictable, wort fermentation must be controlled through careful management of yeast quantity and health. Yeast’ well-being needs to be correctly assessed since poor quality negatively affects attenuation, the final beer quality, and the beer flavour profile due to off-flavour production. Measuring the specific gravity, extract, alcohol content, pH and colour of the fermenting wort are the traditional methods to follow-up the fermentation progress, due to their easy performance compared to reliable yeast viability and vitality tests, or carbohydrate profiling of the fermenting wort. As it is known that brewer’s yeast behaves differently in terms of proteome depending on the stage of fermentation, the aim of this research work is to explore the use of LC-ESI-MS (Liquid Chromatography Electrospray Ionization Mass Spectrometry) for targeting yeast internal proteins during fermentation as a new technique for follow-up of brewer’s yeast fermentation. LC-ESI-MS is already described for fingerprinting of carbohydrates and iso-alpha-acids[1] and for identification of polyphenols in beer[2]. Also, Saccharomyces cerevisiae had its metabolic footprinting documented using this technique.[3] Following the progress of specific proteins by LC-MS from each stage of the fermentation will help us to draw a more precise map of yeast metabolism and connect it with yeast metabolites from this important step in the brewing process. In order to investigate this, yeast samples at specific time points of fermentation from different brews will be analysed by LC-MS, in addition to analysis of the fermenting wort: carbohydrates by HPAEC-PAD (high-performance anion-exchange chromatography coupled with pulsed amperometric detection), amino acids by UPLC MS/MS (ultra-high-performance liquid chromatography tandem mass spectrometry), and esters and higher alcohols by GC-MS (gas chromatography mass spectrometry). It is excepted that this study will contribute to the implementation of a new analysis method for yeast performance in brewing science.

References:
[1] A. S. Araújo et al., “Electrospray ionization mass spectrometry fingerprinting of beer,” Analyst, vol. 130, no. 6, p. 884, 2005.
[2] P. Quifer-Rada et al., “A comprehensive characterisation of beer polyphenols by high resolution mass spectrometry (LC-ESI-LTQ-Orbitrap-MS).,” Food Chem., vol. 169, pp. 336–343, Feb. 2015.
[3] J. Højer-Pedersen, J. Smedsgaard, and J. Nielsen, “The yeast metabolome addressed by electrospray ionization mass spectrometry: Initiation of a mass spectral library and its applications for metabolic footprinting by direct infusion mass spectrometry,” Metabolomics, vol. 4, no. 4, pp. 393–405, 2008.