M. L. Kankolongo Cibaka (1), T. T. Tran (1), J. Gros (1), R. Robiette (2), S. COLLIN (1); (1) Unité de Brasserie et des Industries Alimentaires, Earth and Life Institute, Université Catholique de Louvain, Louvain-la-Neuve, Belgium; (2) Institute of Condensed Matter and Nanosciences, Université Catholique de Louvain, Louvain-la-Neuve, Belgium

Poster

Polyfunctional thiols contribute to the hop varietal aroma of beers (Gros, J., et al. J. Agric. Food Chem. 59:8853, 2011), especially when dry-hopping (Collin, S., et al. Cerevisia 36:119, 2012) or bottle-refermenting (Nizet, S., et al. J. Am. Soc. Brew. Chem. 71:15, 2013) are applied. Very recently, a cysteine-S-conjugate (S-3-(1-hydroxyhexyl)-cysteine) has been identified by HPLC/MS/MS in the Cascade variety (Gros, J., et al. J. Agric. Food Chem. 60:7805, 2012). Other cysteine adducts have been evidenced in Saaz, Nelson Sauvin, and Tomahawk hops by enzymatic release assays (Gros, J., et al. J. Inst. Brew. 119:221, 2013). Both methods were here applied on new dual hop varieties, including Citra, Amarillo, Mosaïc, and Hallertau Blanc. S-Cysteine conjugates were purified from hydroalcoholic extracts to be analyzed by HPLC/MS/MS. Free thiols issued from the reaction of a beta-lyase enzyme (apotryptophanase) were extracted and quantified by gas chromatography connected to a pulsed-flame photometric detector (GC-PFPD). Commercially unavailable cysteine-S-conjugates (S-3-(1-hydroxyhexyl)-cysteine, S-3-(hexanal)-cysteine, S-2-(1-hydroxyethyl)-cysteine, S-3-(1-hydroxypropyl)-cysteine, and S-1-(3-methyl-2-butene)-cysteine) have been synthesized by the addition of N-Boc-cysteine to an alpha,beta-unsaturated carbonyl or by cysteine nucleophilic substitution of halogenides. These pure standards allowed us to compare the cysteine beta-lyase activities of different top- and bottom-fermenting yeasts. The flavor stability of beers with different thiol potentials were also assessed through storage (with or without refermenting yeasts).

In 1988, Sonia Collin received a Ph.D. degree in chemical sciences. She started her career as chercheur qualifié at the FNRS. A professeur ordinaire at the Université Catholique de Louvain (Belgium), she is responsible of the master in brewing sciences. She chaired the last De Clerck symposium devoted to the “Belgian Beer Paradox.” She has published more than 100 papers in peer-reviewed publications, mainly on flavor stability, sulfur aroma, pyrazines, hops, and polyphenols.