First evidence of the glutathione S-conjugate of 3-sulfanylheptanol in green malt: discrepancy with the ubiquitous 5-and 6-C analogues

While cysteinylated (Cys-) and glutathionylated (G-) precursors of 3-sulfanylhexanol (3SHol) and 3-sulfanylpentanol (3SPol) appear to be ubiquitous in hop varieties, no data are available on precursors of their seven-carbon analogue 3-sulfanylheptanol (3SHptol), although the free form has been found in both hops and beer. Chemical synthesis of Cys- and G-3SHptol enabled determination of their chromatographic elution times (14.3-14.8 and 16.2-17.1 min, respectively) and ESI(+) mass spectra (main m/z fragments: 219 and 293, for Cys- and G- 3SHptol, respectively). Here, for the first time, we report the occurrence of G-3SHptol in a natural matrix. RP-HPLC-ESI(+) MRM analysis of selective extracts eluted from a cation exchange resin quantified G-3SHptol in green malt (0.10 mg/kg), while no trace was found after kilning. Neither the cysteinylated nor the glutathionylated conjugate was found in hop or grape extracts. G-3SHptol is formed in-situ from trans-2-heptenal and free glutathione, and its synthesis most likely involves aldol condensation between acetaldehyde and pentanal instead of lipid oxidation. (c) 2022 The Institute of Brewing & Distilling.