Chemical Isotope Labeling Liquid Chromatograph-Mass Spectrometer: A Powerful Tool for Analyzing Non-Volatile Organic Acids in Baijiu

Non-volatile organic acids (NVOAs) are essential to the flavor profile of Baijiu. However, the low levels and diversity of NVOAs in Baijiu make their isolation, annotation, and quantification challenging. In this study, a well-established pipeline combining chemical derivatization, isotope labeling, and high-resolution mass spectrometry with a three-tier annotation process was used to quantify NVOAs in three typical flavor types of Baijiu with high coverage and confidence. The results revealed the annotation of 56, 145, and 1277 NVOAs in Baijiu at tier 1, tier 2, and tier 3 levels, respectively. Among them, a total of 166 high-confidence NVOAs were first reported in Baijiu. Furthermore, multivariate statistical analyses indicated that abundant NVOAs could potentially be used as biomarkers to distinguish between different flavor types of Baijiu. This study provides a powerful tool for the qualification and quantification of NVOAs in Baijiu. The results will greatly expand the understanding of NVOAs in Baijiu.