Laurent Dagan (1), Stéphane Delpech (1), Florence Reillon (1), Aurélie Roland (1), Rémi Schneider (1), Clément Viel (1); (1) Nyseos, Montpellier, France
Malt and Grains
Barley (Hordeum vulgare) is the major source for brewing malts, which constitutes the single most important raw material for beer production. Mainly composed of starch (more than 65% of dry weight), it also contains proteins, cell wall polysaccharides, and, in smaller amounts, fat and minerals. Previous hypotheses suggested that some aroma precursors might occur in malts. Indeed, Kishimoto and co-workers demonstrated that 3-mercaptohexanol (3MH) occurred in unhopped beers, suggesting that 3MH precursors might be present in malts. Thus, the aim of this work was i) to identify cysteinylated and glutathionylated precursors of both 3-mercaptohexanol and 4-mercapto-4-methylpentan-2-one (4MMP); ii) to quantify each molecule; and iii) to study the relationship between glutathionylated and cysteinylated conjugates under enzymatic conditions. For this purpose, we used a high-throughput, accurate and sensitive method based on stable isotope dilution assay (SIDA), LC-MS/MS and multiple reaction monitoring (MRM) mode detection. Seven malt varieties (Pilsner 3EBC, Pale Ale 8EBC, Wheat Pale Ale 8EBC, Acide 9EBC, Munich 15 EBC, Melano 80 EBC, Carafa II 1150 EBC) with different levels of roasting were analyzed. For the first time, we identified only cysteinylated and glutathionylated precursors of 3MH. Under our conditions, we did not detect any trace of 4MMP precursors. As for the enology field, 3MH precursors seemed to be more ubiquitous than 4MMP ones and glutathionylated precursor (G3MH) was more abundant than the cysteinylated one (Cys3MH) for any of the considered malts. Malt roasting levels influenced considerably the amount of 3MH precursors; the more malt was roasted, the lower levels of precursors were found. Pilsner malt exhibited the highest aromatic potential, with Cys3MH and G3MH levels close to 2.5 and 700 ppb, respectively. According to the extraction procedure, we observed important precursor amount variations. Indeed, the use of methanol instead of water resulted in higher levels of G3MH, suggesting that some enzymatic activities could rapidly degrade this compound at room temperature. For this purpose, we spiked several crushed malts dissolved in water with G3MH-d2 (tracer), and we observed the kinetics for 1 hr at room temperature. We demonstrated for the first time the conversion of G3MH-d2 into Cys3MH-d2, with conversion rates up to 32%. These results opened an avenue to further experiments to better characterize the evolution of 3MH precursors during brewing. By characterizing the aromatic potential of malts, brewers would take advantage of thiol precursors during mashing (temperature, enzymes) to better pilot the subsequent release of fruity aromas in beers.
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.