Liquid chromatography/high resolution tandem mass spectrometry – Tool for the study of polyphenol profile changes during micro-scale biogas digestion of grape marcs

A microscale discontinuous fermenter was used for anaerobic digestion of wine waste – a hardly gasifiable feedstock material. Efficiency of biogas production, i.e. changes in content of nitrogen, oxygen, carbon dioxide and methane in gas phase, was monitored by gas chromatography/mass spectrometry. Liquid chromatography/high resolution tandem mass spectrometry in combination with principal component analysis and orthogonal projection to latent structures was used to reveal main chemical differences of gasified wine waste mixture from commonly used ones in agricultural biogas plants. Compounds with particular polyphenolic structures appeared among the most distinctive markers. Analysis of samples collected during acidogenic phase and unstabilized methanogenesis indicates formation of certain dihydro-flavonoids in early stages of the process and their consequent degradation. Due to formerly described higher toxicity of some dihydroflavonoids (e.g. taxifolin) compared to their more common counterparts (e.g. quercetin, malvidin etc.), unstabilized digestate would represent a potential environmental risk when used as a fertilizer deserving a proper control.