Quantitation of Selected Terpenoids and Mercaptans in the Dual-Purpose Hop Varieties Amarillo, Citra, Hallertau Blanc, Mosaic, and Sorachi Ace

Abstract

Free terpenoids and both free and bound polyfunctional thiols were investigated in five selected dual-purpose hop cultivars. Surprisingly, the dual-purpose Sorachi Ace variety was found to contain higher amounts of farnesene (2101 mg/kg) than aromatic hops such as Saaz but only traces of 3-methylbutylisobutyrate, a compound that usually distinguishes all bitter varieties. All five cultivars investigated here showed an exceptional citrus-like potential explained by either monoterpenic alcohols or polyfunctional thiols. Among the monoterpenic alcohols, β-citronellol at concentrations above 7 mg/kg distinguished Amarillo, Citra, Hallertau Blanc, Mosaic, and Sorachi Ace from Nelson Sauvin and Tomahawk, two previously investigated dual-purpose hops, while linalool (312 mg/kg) and geraniol (211 mg/kg) remained good discriminating compounds for Nelson Sauvin and Tomahawk, respectively. Regarding polyfunctional thiols, higher amounts of 3-sulfanylhexyl acetate (27 μg/kg) characterized the Citra variety. Free 4-sulfanyl-4-methylpentan-2-one proved discriminant for Sorachi Ace, while the bound form is predominant in Nelson Sauvin. On the other hand, an S-conjugate of 3-sulfanylhexan-1-ol was found in Sorachi Ace at levels not far from those previously reported for Cascade, although the free form was undetected here. Both free and bound grapefruit-like 3-sulfanyl-4-methylpentan-1-ol (never evidenced before the present work) emerged as discriminating compounds for the Hallertau Blanc variety. The apotryptophanase assay also allowed us to evidence for the first time an S-conjugate of 2-sulfanylethan-1-ol.

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

“…As shown previously in studies on white wine, a large fraction of thiols are released from their non-aroma active cysteinylated and glutathionylated precursors also during beer fermentations with yeast (Cibaka et al. 2015, 2016). The levels of thiol-conjugates vary strongly in the different hop cultivars, leading to a significant difference in the final ratio and a unique thiol profile in beer.…”

“…Indeed, tryptophanase treatment could release the polyfunctional thiol 3-sulfanylhexan-1-ol (a key compound in passion fruit and grapefruit aroma) from extracts of aroma and dual-purpose hops (Gros, Tran and Collin 2013; Cibaka et al. 2015). When this enzyme is overexpressed in yeast, it leads to a very significant increase in release of the polyfunctional thiols in wine fermentations, suggesting that one of the bottlenecks is the CS β-lyase activity (Swiegers et al.…”

A comparison of sensory evaluation and an electronic nose assay in the assessment of aroma in dry hopped beers

“…Each sample was rated in each selected descriptor Total oils (ml/100 g) 1.5-2.7 1.5-1.9 0.7-1.4 2.1-2.3 1-2 Table 1 Description of the hop samples; the bitter acids content and the content of total oils and myrcene (Lutz et al, 2013;Van Holle et al, 2017;Lafontaine and Shellhammer, 2018;Hoplist, 2019;Krofta et al, (Takoi et al, 2016;Mikyška et al, 2017;Van Holle et al,2017;Vollmer et al, 2018) with a corresponding number of points in the intensity scale from 1 (threshold) to 9 (intense). The evaluators were asked to list the main odour and aroma impressions out of pre-defined aroma characteristics (hop, malt, yeast, spicy, floral, citrus, grapefruit, other) and flavour characteristics (sweet, caramel, citrus, spicy, yeast, general impression) were chosen based on the characteristics of hop varieties found in available literature (Kenny and Zimmermann, 1986;Nickerson and Van Engel, 1992;Kishimoto et al, 2006;Nesvadba et al, 2012;Lutz et al, 2013;Cibaka et al, 2015;Schnaitter et al, 2016) in order to detect differences in beer taste and aroma. The evaluators were also asked to give a score ranging from 1-9 for the bitterness intensity (smoothness -pleasant, not spiky and harsh; first impression -the intensity of bitterness perceived after 10 s; after-bitterness -30 s after swallowing the beer) (Oladokun et al, 2017;Van Holle et al, 2017).…”

Analysis of Potent Odour-Active Volatile Thiols in Foods and Beverages with a Focus on Wine

“…Other than retention index, MS spectra of peaks of interest can be compared to those in commercial databases (e.g., NIST [67] or Wiley [68]), or an in-house thiol database [23]. Accordingly, identity confirmation of new thiols then necessitates the synthesis of reference standards if they are not readily available from commercial suppliers [23,64,69]. The majority of GC-based quantitative analyses are conducted with MS detectors, with electron ionisation (EI) (Table 2, multiple entries) or less frequently used chemical ionisation (CI) (Entries 3, 5, 7, 8, 12) [18,25,29,30,31] being applied for volatile thiol detection.…”