3-Sulfanyl-4-methylpentan-1-ol in Dry-Hopped Beers: First Evidence of Glutathione S-Conjugates in Hop (Humulus lupulus L.)

Abstract

Monovarietal dry-hopped beers were produced with the dual-purpose hop cultivars Amarillo, Hallertau Blanc, and Mosaic. The grapefruit-like 3-sulfanyl-4-methylpentan-1-ol was found in all three beers at concentrations much higher than expected on the basis of the free thiol content in hop. Even cysteinylated precursors proved unable to explain our results. As observed in wine, the occurrence of S-glutathione precursors was therefore suspected in hop. The analytical standards of S-3-(4-methyl-1-hydroxypentyl)glutathione, never described before, and of S-3-(1-hydroxyhexyl)glutathione, previously evidenced in grapes, were chemically synthesized. An optimized extraction of glutathionylated precursors was then applied to Amarillo, Hallertau Blanc, and Mosaic hop samples. HPLC-ESI(+)MS/MS revealed, for the first time, the occurrence of S-3-(1-hydroxyhexyl)glutathione and S-3-(4-methyl-1-hydroxypentyl)glutathione in hop, at levels well above those reported for their cysteinylated counterparts. S-3-(1-Hydroxyhexyl)glutathione emerged in all cases as the major adduct in hop. Yet, although 3-sulfanylhexan-1-ol seems relatively ubiquitous in free, cysteinylated, and glutathionylated forms, the glutathione adduct of 3-sulfanyl-4-methylpentan-1-ol, never evidenced in other plants up to now, was found only in the Hallertau Blanc variety.

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

“…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].…”

“…Free 3MH represents less than 1% in all hop varieties, although some studies reported up to 7.1% of the free fraction [134]. In plants in general and also in hops, it is more common to encounter cysteine-S-conjugates as they represent the final product of the glutathione detoxification pathway [144]. Since from glutathione-S-conjugates free glutathione can be released, consumed thiol precursors from hops may importantly contribute to the organism’s detoxification processes and therefore prevent the oxidative stress and other diseases like cancer.…”

The molecular biology of fruity and floral aromas in beer and other alcoholic beverages

“…This thiol was also identified in significant quantities in the Hallertau Blanc and Tomahawk hop cultivars and was found at higher levels in dry-hopped beers (Gros, Nizet and Collin 2011; Cibaka et al. 2016). Beer made with other hop varieties such as Simcoe, Summit and Cascade contains considerable amounts of another extremely potent thiol, 4-methyl-4-sulfanyl-2-pentanone (Fig.…”

Impact of Copper Fungicide Use in Hop Production on the Total Metal Content and Stability of Wort and Dry-Hopped Beer

“…Various hop-derived polyfunctional thiols commonly referred to as "varietal thiols," impart desirable aroma traits such as passionfruit, grapefruit, or black currant and are present in perceivable concentrations in a variety of heavily hopped and hop-forward beer styles [30][31][32]. Several types of hops used in dry-hopping have appreciable amounts of these thiols, and their precursors [33][34][35], and preservation of those aromas in a dry-hopped beer is vital to brewers [36]. Therefore, dry hopping with large quantities of hops treated with CBFs with the goal of increasing characteristic thiol aromas may be futile as the increased copper load may result in a more rapid loss of these compounds.…”