Structural Elucidation of Humulone Autoxidation Products and Analysis of Their Occurrence in Stored Hops

Abstract

The transformation of α-acids [in hops (Humulus lupulus L.)] to iso-α-acids (in beer) during the brewing process is well known, but the occurrence and structure of the oxidized α-acids during hop storage are not well documented. Because an understanding of these oxidized compounds is essential to optimize the effects of oxidized hops on the quality of beer, we investigated the autoxidation products of humulone (a representative congener of α-acids) using a simplified autoxidation model. Among the oxidation products, tricyclooxyisohumulones A (1) and B (2), tricycloperoxyisohumulone A (3), deisopropyltricycloisohumulone (4), and the hemiacetal 5 of tricycloperoxyhumulone A (5') were isolated, and their structures were elucidated for the first time. The occurrence of compounds 1-4 in stored hops was verified using LC/MS/MS analysis. We also monitored the levels of compounds 1-4 during hop storage using LC/MS/MS analysis.

Genetic, acute and subchronic toxicity studies of matured hop extract produced by extraction from heat-treated hops

“…In contrast, oxidation of α-and β-acids produces bitter acid oxides, such as matured hop bitter acids (MHBA). All of the structurally elucidated compounds of MHBA possess a common β-tricarbonyl moiety similar to α-, β-, and isoα-acids (Taniguchi et al, 2013(Taniguchi et al, , 2014a(Taniguchi et al, , 2014b(Taniguchi et al, , 2015. We demonstrated that MHBA suppresses diet-induced body fat accumulation in animals (Morimoto-Kobayashi et al, 2015).…”

Development of preparative and analytical methods of the hop bitter acid oxide fraction and chemical properties of its components

“…The obtained respective solid was dissolved in EtOH (0.500 mg/mL) and analyzed by a Prominence UFLC system (Shimadzu, Kyoto, Japan). The analyses were performed using the following conditions 32,33) : column: 100 × 2.1 mm id, 3 μm, Alltima C 18 column (Systech, Tokyo, Japan); solvent: H 2 O/H 3 PO 4 (85%), 1000/0.2, (v/v) containing EDTA (0.02% w/v) (solvent A) and MeCN (solvent B), a linear gradient from 10 to 52% B in 0 → 26.7 min, 52% B for 26.7 → 30 min, 52 to 75% B in 30 → 32.7 min, 75 to 85% B in 32.7 → 36.7 min, and 85% B for 36.7 → 37.7 min; flow rate: 0.6 mL/min; detector: 270 nm; and column temperature: 40°C. The injection volume was 3.0 μL.…”

“…1). 32,33) We also revealed that 4′-hydroxyallohumulinones (6a-c) isomerize into 4′-hydroxyallo-cis-humulinones (7a-c) and degrade into cis-oxyhumulinic acids (8a-c) during the wort boiling process (Fig. 1).…”

Determination of Bitter Compounds in Hops - Effect of Crop Year and Hops Age

“…Ještě menší je pokles obsahu beta kyselin (8,3 % rel.). Je to dáno tím, že řada transformačních reakcí alfa kyselin, na rozdíl od beta kyselin, nevyžaduje přítomnost kyslíku (Taniguchi, 2014). Skladování granulovaného chmele za přístupu vzduchu při teplotách kolem 20 °C má na kvalitu chmele silně destruktivní vliv.…”

“…Even lower is the decrease in beta acid content (8.3% rel.). This is due to the fact that unlike in beta acids, a number of transformation reactions of alpha acids do not require the presence of oxygen (Taniguchi, 2014). Storage of granulated hop in air at temperatures around 20 °C has a strong destructive effect on the quality of hops.…”