Untargeted metabolomics reveals the formation pathways of bound sulfite in sodium metabisulfite-soaked Hemerocallis citrina Baroni

Hemerocallis citrina Baroni (HC) is usually soaked with sodium metabisulfite solution after harvest to keep its freshness. However, this will introduce bound sulfites with potential safety risks. In this study, formation pathways of bound sulfite in HC were explored using ultra-high performance liquid chromatography-Q-Exactive HF mass spectrometry (UHPLC-QE-MS) and statistical analysis. The results indicated that the chemical composition of HC changed the most at soaking times of 6–8 h and concentrations of 1.00–2.50 mg/mL. Primary metabolites and phenols in secondary metabolites were greatly affected during soaking. 71 compounds were identified in HC and 8 characteristic markers including 3 bound sulfites were screened which can be used to distinguish between non-soaked HC (NSHC) and sodium metabisulfite-soaked HC (SSHC). Among the 19 commercial HC samples analyzed, 79 % had been treated with sulfites. Mass spectrometry data further revealed two pathways of formation of bound sulfite in HC: one is the sulfonation of amino acids at the amino, the content initially increased with sulfite soaking time and concentration and then decreased until it disappeared; the other is that the addition of aldehyde at the carbonyl, the content increased continuously with sulfite soaking concentration. This study provides insight into bound sulfite formation in HC post‑sodium metabisulfite treatment.