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)

Abstract

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.

Hop Compounds: Extraction Techniques, Chemical Analyses, Antioxidative, Antimicrobial, and Anticarcinogenic Effects

“…In spite of the fact that many believe that the last fraction of sulfur-containing compounds does not contain important biologically-active molecules, this may not be entirely true. Compounds from the sulfur fraction moreover proved to be important contributors to the hop and beer aroma and prevent its spoiling [ 34 , 134 ].…”

“…More than forty-one different volatile polyfunctional thiols, detected in various hop cultivars, also represent key contributors to the hop aroma in beer as their content rises during drying and brewing processes [ 142 , 144 ]. Polyfunctional thiols have been appreciated and widely studied in the enology field as the compounds providing desirable odor notes like rhubarb, citrus, passion fruit, or blackcurrant bud carried by 3-mercaptohexan-1-ol (3MH), 3-mercapto hexyl acetate, 4-methyl-4-mercaptopentan-2-one (4MMP), 3-sulfanyl-4-methyl pentane-1-ol, 3-sulfanylhexan-1-ol, and others [ 134 , 144 ]. In addition to releasing pleasant aromas, 3-mercaptohexan-1-ol also inhibits epigallocatechin gallate (EGCG) oxidation, thereby providing the necessary stability for EGCG to retain its beneficial biological activity [ 145 ].…”

“…Roland and coworkers [ 134 ] investigated in which form one can find thiols, especially 3MH and 4MMP in hops. For 4MMP the free-form represents the most important fraction (up to 95–100%) with precursors found in trace amounts only or even completely absent.…”

Characterization of odour‐active compounds in Timur (Zanthoxylum armatum DC.) fruits from Nepal

“… For 4‐MMP and 1,8‐PMT, the derivatization was operated with 4,4′‐dithiodipyridine as described by Capone et al . Thiols identification was confirmed by comparison of retention times, standard additions and 1 ratio of qualifier to quantifier in the MRM mode using the same transitions as previously reported. Quantification was performed by stable isotopic dilution analysis in the case of 3‐MH, 3‐MHA and 4‐MMP, and by internal calibration for 1.8‐MPT using 3‐MH‐d2, 3‐MHA‐d5 and 4‐MMP‐10, respectively, as internal standards.…”

Volatile constituents of yuzu (Citrus junos Sieb. ex Tanaka) peel oil: A review

“…Several Yuzu components were also identified in analytical studies which did not involve GC‐O, even if they were described as important odorant contributors and never appeared later in GC‐O studies: the two β ‐ketols 23 and 22 (‘very interesting Citrus flavour note’), 38 and 1‐ p ‐menthene‐8‐thiol 57 (a well‐known key odorant of grapefruits 75 ) providing the ‘characteristic pleasant and fresh odour’ 37 . Among the other sulphur compounds which are often key odorants in many fruit aromas, 4‐methyl‐4‐mercaptopentan‐2‐one 58 has been detected as an odour‐active compound in white wine 76 and hops 77 and reported to contribute also to the Yuzu odour with its tropical fruit‐like note 78 and a high FD value 33,34 . The three aldehydes 24 , 25 and 26 35 were also identified without the help of GC‐O as ‘a part of the essential odour of Yuzu’ with fresh green, bitter Citrus , and sweet notes and low detection thresholds.…”