47. Hops (Humulus lupulus) provide important sources of thiol precursors: A key ingredient to obtain fruity beers

Laurent Dagan (1), Stéphane Delpech (1), Florence Reillon (1), Aurélie Roland (1), Rémi Schneider (1), Clément Viel (1); (1) Nyseos, Montpellier, France

Technical Session 14: Hops II
Tuesday, August 16  •  9:45–11:30 a.m.
Plaza Building, Concourse Level, Governor’s Square 14

Varietal thiols such as 3-mercaptohexan-1-ol (3MH), 3-mercaptohexylacetate (3MHA) and 4-mercapto-4-methylpentan-2-one (4MMP) have been described as key aroma compounds due to the pleasant notes conferred to beers made with aromatic hops like Cascade or Nelson Sauvin. 3MH and 4MMP concentrations increased during brewing suggesting that hops could be a key ingredient susceptible to bringing thiol precursors. This hypothesis was verified by demonstrating the occurrence of S-cysteinylated precursor of 3MH (Cys3MH) in several hop varieties such as Cascade, Saaz, Nelson Sauvin or Tomahawk. Enzymatic release of 3MH from hops by apotryptophanase suggested that Cys3MH might occur at levels ranging from 450 to 2,750 mg/kg. By analogy with enology, we hypothesized that other precursors of 3MH and 4MMP might occur in hops. The aim of this work was (i) to identify both cysteinylated and glutathionylated precursors of 3MH and 4MMP in hops; (ii) to quantify them in several varieties; (iii) to study their kinetics during boiling and fermentation; and (iv) to investigate the impact of dry-hopping on such molecules. For this purpose, we used a very sensitive, high-throughput and accurate method based on stable isotope dilution assay, LC-MS/MS and multiple monitoring reaction detection. 4) First results showed that both cysteinylated and glutathionylated precursors of 3MH and 4MMP occurred in hops based on comparison of mass spectra obtained from synthetic precursors and hop extracts. As for grapes, 3MH precursors seemed to be more ubiquitous than 4MMP precursors. Generally, glutathionylated precursors were more abundant than cysteinylated ones whatever the hop variety, and 3MH precursors occurred always at higher levels than 4MMP ones. In a different experiment, we studied the evolution of 3MH precursors during boiling and fermentation under real conditions in pilot-scale trials (120 L). Surprisingly, we observed important amounts of both cysteinylated and glutathionylated (G3MH) precursors of 3MH at the beginning of boiling, suggesting that these precursors might also occur in malts. During boiling, G3MH levels slightly increased, whereas Cys3MH levels did not change. It is also important to note that both 3MH precursors remained present at the end of the first fermentation. Finally, we investigated the influence of hopping on thiol precursors. First results showed that dry-hopping considerably increased 3MH precursor concentrations. These results opened avenues to further studies to better understand the role played by glutathionylated and cysteinylated precursors of 3MH and 4MMP (degradation, conversion rate, enzymes). These new analytical parameters provide new technical solutions for beer makers in order to drive aromatic potential of beer ingredients.

Laurent Dagan obtained his Ph.D. degree in food sciences in 2006 focused on aromatic potential of Petit and Gros Manseng grapes. He was a cofounder of Nyseos in 2007, a private company specializing in aroma compound analysis in the enology field but also in food matrices. He participated in the development in 2013 of an original tool able to simulate wine blending called Kallosmé.