First Evidence of the Cysteine and Glutathione Conjugates of 3-Sulfanylpentan-1-ol in Hop (Humulus lupulus L.)

Abstract

After evidence of the cysteinylated precursors of 3-sulfanyl-4-methylpentan-1-ol (Cys-26) and 3-sulfanylhexan-1ol (Cys-23) in hop, S-glutathione precursors (G-23 and G-26) were recently discovered in different dual-purpose hop varieties. Because free 3-sulfanylpentan-1-ol (21) has also been detected in hop, the present work aimed to identify its potential precursors. The compounds S-3-(1-hydroxylpentyl)cysteine (Cys-21) and S-3-(1-hydroxylpentyl)glutathione (G-21) were first synthesized and characterized by nuclear magnetic resonance and high-resolution mass spectrometry. High-performance liquid chromatography−positive electrospray ionization−tandem mass spectrometry evidenced both for the first time in hop. Both S conjugates were further quantitated in six hop samples: the well-known Saaz, Amarillo, Citra, Hallertau Blanc, Nelson Sauvin, and Polaris. Similar to G-23, G-21 appeared ubiquitous to all varieties. Of all of the samples investigated here, Citra (harvest 2017) emerged as the richest in G-21, with 18 mg/kg of dry matter. Cys-21 was found in all samples at a much lower concentration (up to 0.2 mg/kg of dry matter in Polaris, harvest 2017). Model media spiked with Cys-21 or G-21 allowed for the confirmation that brewing yeast is able to release free compound 21 from them.

Ability of the Mandarina Bavaria hop variety to release free odorant polyfunctional thiols in late‐hopped beers

“…Also noteworthy is that the G‐3SHol content reached 3 to 6 times the G‐3SPol content ( 17 ) . As recently reported for Polaris, trans ‐2‐hexenal (precursor of G‐3SHol) is from the major oxidation pathway of linolenic acid, while G‐3SPol requires the involvement of minor routes ( 17 ) . Both the Astec® Cyclobond® I 2000 RSP HPLC column and the apotryptophanase enzymatic assay revealed the total absence of 3S4MPol adducts (Cys‐ and G‐3S4MPol) in Mandarina Bavaria, despite the presence of 8.7 μg/kg free form.…”

“…For quantification of precursors, a strategy using two HPLC columns was applied as previously described for analysis of Polaris ( 17 ) . With the first column (Hypersil GOLD TM aQ column), both cysteine and glutathione adduct can be quantitated (Figure 4a, two peaks not always completely resolved for each adduct, because of diastereoisomers).…”

“…Extraction of cysteinylated and glutathionylated thiol precursors from hop pellets was performed according to ( 17 ) (Figure 2b). Milled pellets (100 g) were stirred with 1000 mL H 2 O:EtOH:HCOOH (79:20:1, v/v/v) for 2 h at 45°C.…”

“…The previously synthesised ( 17, 20, 21 ) cysteinylated and glutathionylated precursors of 3SPol, 3SHol, and 3S4MPol were used for identification and quantitation. The two complementary columns ‐ strategy described by ( 17 ) ‐ was applied to identify and quantify these molecules in hop samples.…”

“…The aim of this paper was to complete the reported thiol adduct profile of Mandarina Bavaria hop using two complementary HPLC‐MS methods recently applied to Polaris ( 17 ) , another German dual hop. These analyses focused especially on the cysteinylated and glutathionylated adducts of three sulfanylalkyl alcohols, recently reported in other dual hop varieties (structures and abbreviations detailed in Figure 1).…”