Insights into the presence and distribution of polyfunctional thiols and their conjugates in different types of tea

Free polyfunctional thiols (PFTs) are a class of volatile sulfur-containing compounds known for potent tropical fruit-like aroma notes, even at trace concentrations. In this study, a QuEChERS extraction combined with 4,4'-dithiodipyridine (DTDP) derivatisation enabled simultaneous identification and quantification of three free PFTs (4-methyl-4-sulfanylpentan-2-one, 4MSP; 3-sulfanylhexan-1-ol, 3SH; 3-sulfanylhexyl acetate, 3SHA) and their conjugates (3-S-cysteinylhexan-1-ol, Cys-3SH; 3-S-glutathionylhexan-1-ol, Glut-3SH; and 3-S-γ-glutamylcysteinylhexan-1-ol, γ-GluCys-3SH) by UHPLC-MS/MS in five tea types using isotopically labelled standards. Generally, black tea showed the highest mean concentrations of conjugates (Cys-3SH at 472 ng/g, Glut-3SH at 14430 ng/g, γ-GluCys-3SH at 277 ng/g), while oolong tea exhibited the highest mean concentrations of free PFTs (4MSP at 15 ng/g, 3SH at 36 ng/g, 3SHA at 0.64 ng/g). Multivariate analysis revealed that enzymatic oxidation during processing plays a key role in shaping the levels of free PFTs and their conjugates. These findings provide new insights into their distribution in tea.