Validation of an ultra-high-performance liquid chromatography-mass spectrometry method for the quantification of cysteinylated aldehydes and application to malt and beer samples

•Validation of a methodology for the quantification of cysteinylated aldehydes by liquid–chromatography mass–spectrometry was obtained.•Cysteinylated aldehydes were, for the first time, quantified in malt and beer.•Quantification of cysteinylated aldehydes in malt supports the hypothesis of bound-state aldehydes as potential contributors to beer flavor deterioration. This paper describes the method validation for the simultaneous determination of seven cysteinylated aldehydes, i.e. 2-substituted 1,3-thiazolidines-4-carboxylic acids, using ultra-high-performance liquid chromatography-mass spectrometry (UHPLC–MS). Authentic reference compounds were first synthesized for identification and quantification purposes. Moreover, nuclear magnetic resonance (1H NMR and 13C NMR) was applied for verification of their structure, while ultra-high-performance liquid chromatography–mass spectrometry (UHPLC–MS) was applied for estimation of the purity. The method for quantification of cysteinylated aldehydes in model solutions has been validated according to the criteria and procedures described in international standards. The synthesized compounds were successfully identified via UHPLC–MS by comparing retention time and MS spectra with the commercial reference compounds. Method validation revealed good linearity (R2 > 0.995) over the range of 0.4–2.2 µg/L to approximately 1000 µg/L, depending on the analyte. The limits of quantification varied from 0.9 to 4.3 µg/L depending on the nature of the compound. Furthermore, evaluation of the method showed good accuracy and stability of the standard solutions. Reported chromatographic recoveries ranged from 112 to 120%. Consequently, the currently described method was applied on malt and beer samples. For the first time, quantification of cysteinylated aldehydes was obtained in malt. In contrast, in fresh beers unambiguous identification of these compounds was not achieved.