Application of UHPLC-Q/TOF-MS-based metabolomics analysis for the evaluation of bitter-tasting Krausen metabolites during beer fermentation

Abstract

In this study, the evaluation of bitterness qualities and characteristic metabolite profiles in Krausen during beer fermentation were investigated using a UHPLC-Q/TOF-MS-based metabolomics approach and sensory evaluation analysis. Through sensory evaluation, Krausen was perceived as an extremely lingering bitterness character and exhibited impact on the bitter taste of beer and residue samples. Non-targeted metabolomics was employed to identify the potential bitter markers in Krausen through a differentiating approach across the metabolic profiles of Krausen, B1 (beer with Krausen removed), B2 (beer with Krausen retained), R1 (residue with Krausen removed), and R2 (residue with Krausen retained). Multivariate statistical analysis demonstrated that 41 of the screened key markers clustered towards the Krausen region were more or less hop bitter acid and its derivative. Subsequently, hop bitter acid and polyphenols were afterwards confirmed by quantification analysis. Both untargeted metabolomics and quantification results confirmed that isohumulones and humulinones contributed most towards the bitter profile of Krausen, while polyphenols may be not key compounds contributing to the bitter taste formation in Krausen. This study identified key bitter components of Krausen and may provided guidance for further research on taste quality of beer during fermentation.