Rapid screening and annotation of the carbonyl submetabolome via bromine isotope-based derivatization sensitization...

Carbonyl compounds (CCs) are extensively present in biological and food samples with broad concentration range and high reactivity. Despite advances in chemical isotope labelling assistant liquid chromatography-mass spectrometry (CIL-LC-MS) to address poor ionization efficiency and weak chromatographic retention, challenges remain in defining potential CCs by report ion and further accurately annotating labelled products due to the lack of experimental spectra. Improved strategies are needed to enhance the annotation of CCs. On the other hand, Chinese Baijiu (liquor) contains a lot of CCs, understanding CC composition and concentration can provides insights into the chemical basis of its sensory characteristic.

A comprehensive strategy that integrates CIL-LC-MS detection with structure-guided molecular network (SGMN) strategy annotation was developed for CC characterization. A novel Br-based reagent - 3-bromo-1-(3-(5-hydrazinyl-5-oxopentanamido)propyl)quinolin-1-ium with three MS features was synthesized with intensity ratio1:1 in MS¹, highest report ion and stable neutral loss fragment in MS² for rapid screening of CCs. Furthermore, a SGMN established based on structural similarity for the annotation. Employing this strategy, more than 1000 CCs were defined in 6 grades of Sauce-Flavor Baijiu (SFB), and further annotated by SGMN strategy with 100 standards as seed, showcasing superior coverage. Quantitative analysis reveals positive correlations between most CC contents and SFB grades, such as furfural and (E)-oct-2-enal. Traceability analysis indicated that CCs changed greatly during different fermentation rounds, especially 3rd to 5th rounds of base liquors contribute most to the SFB characters.

This study developed a novel, multi-characteristic derivatization reagent and demonstrated the significant role of SGMN strategy in labelled product annotation, providing comprehensive strategy for profiling of the submetabolome. Qualitative and quantitative analysis of CCs in Baijiu enhances our understanding of the overall profile of CCs and are helpful to trace the fermentation process and improve the quality.