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.
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