First identification and quantification of glutathionylated and cysteinylated precursors of 3-mercaptohexan-1-ol and 4-methyl-4-mercaptopentan-2-one in hops (Humulus lupulus)

Since ten years, many studies conducted on beers showed an important impact of polyfunctionnal thiols of the aroma profiles. Among them, three thiols responsible for blackcurrant bud, passion fruit, citrus and rhubarb notes have been intensively studied: the 4‐methyl‐4‐mercaptopentan‐2‐one (4MMP), the 3‐mercaptohexan‐1‐ol (3MH) and its corresponding acetate. Their origin was very complex in beers since they probably came from odourless precursors present either in hops or in malts. Our work focused on the formal identification of thiol precursors in hops and on their quantification. By using pure synthetic standards and mass spectrometry characterization, we formally identified for the first time the occurrence of glutathionylated conjugates of 4MMP and 3MH and the cysteinylated conjugate of 4MMP in hops. First quantification results obtained on 10 hop varieties, showed that 3MH conjugates were more ubiquitous than 4MMP ones. Conjugates of 3MH occurred at very high level until 20 mg kg‐1 in Cascade hop, which was considerably higher than concentrations found in grapes. Then, we compared the proportion of bound and free thiol fractions and we demonstrated that more than 99 % of 3MH occurred as precursors in hops. On the contrary, free 4MMP fraction represented the most important source of 4MMP in hops. Copyright © 2016 John Wiley & Sons, Ltd. Both cysteinylated and glutathionylated precursors of 3‐mercaptohexan‐1‐ol and 4‐methyl‐4‐mercaptopentan‐2‐one were identified and quantified for the first time in hops (Humulus lupulus). Substantial amounts of precursors were present in hops with concentration up to 20 mg.kg‐1. Contrary to 4MMP, more than 99% of 3MH was present as precursors and not as free form in hops.