Abstract: An ultra-high performance liquid chromatography-high resolution mass spectrometric (UPLC-HRMS) method was developed, optimized and applied to analyze the bitter compound trihydroxyoctadecenoic acid in Chinese baijiu. The samples were diluted and filtered through a 0.22 μm membrane before analysis. Acetonitrile was selected as the organic phase and 0.1% formic acid as the aqueous phase with a flow rate of 0.3 mL/min and an injection volume of 2 μL. The analyte was separated on a Hypersic Gold (100 mm × 2.1 mm, 1.9 μm) column by gradient elution, and qualitative analysis was achieved by comparison of secondary daughter ions and theoretical simulation of molecular ion fragment structures using the Mass Frontier 8.0 software, which could avoid false positive results. This method had the advantages of simple pretreatment, fast analysis, low detection limit (0.2 ng/mL) and high accuracy, and could meet the requirements for the detection of baijiu samples. This method was used to study the change in the content of trihydroxyoctaenoic acid during the production process of Maotai-flavor baijiu. The results showed that with the prolongation of fermentation time, a large amount of linoleic acid in the raw materials was likely to be oxidized and decomposed into trihydroxyoctadecenoic acid, and then transferred into the base liquor by distillation. The content of trihydroxyoctadecenoic acid in the base liquor did not obviously change during storage, indicating that it was affected little by storage time. The content of trihydroxyoctadecenoic acid in Maotai-flavor base liquor was lowest among the three typical bodies of Maotai-flavor baijiu, so Maotai-flavor base liquor could be used as one of the major base liquors for packaged products.

Key words: bitterness; trihydroxyoctadecenoic acid; Chinese baijiu; method optimization