Analysis of the Components of Hard Resin in Hops (Humulus lupulus L.) and Structural Elucidation of Their Transformation Products Formed during the Brewing Process

Abstract

The resins from hops (Humulus lupulus L.), which add the bitter taste to beer, are classified into two main sub-fractions, namely, soft and hard resins. α- and β-Acids in soft resin and their transformation during the wort boiling process are well-studied; however, other constituents in resins, especially hard resin, have been unidentified. In this study, we identified humulinones and hulupones as soft-resin components, in addition to 4'-hydroxyallohumulinones and tricyclooxyisohumulones A and B as hard-resin components. These compounds are all oxidation products derived from α- or β-acids. We also investigated compositional changes in the hard resin during the wort boiling process, which has a significant effect on the taste of the beer, by using model boiling experiments. The major changes were identified to be isomerization of 4'-hydroxyallohumulinones into 4'-hydroxyallo-cis-humulinones, followed by decomposition into cis-oxyhumulinic acids. These findings will be helpful in systematically evaluating and optimizing the effect of the hard resin on beer quality.

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

“…33) 4′-Hydroxyallohumulinones (6a-c), 4′-hydroxyallo-cis-cohumulinone (7a), 4′-hydroxyallo-cis-n-humulinone (7b), cis-oxycohumulinic acid (8a), and cis-oxy-n-humulinic acid (8b) were isolated in our laboratory. 34) Preparation of a MHBA fraction from stored hops. Hop pellets (600 g) were stored at 60°C for 120 h to oxidize αand β-acids and then extracted with prewarmed H 2 O (50°C, 6 L) for 1 h. During extraction, Fig.…”

“…Next, an aqueous solution of the extract was heated. The heating process induced chemical reactions that occur during the wort boiling process, such as transformation of unstable 4′-hydroxyallohumulinones (6a-c) into 4′-hydroxyallo-cis-humulinones (7a-c) and cis-oxyhumulinic acids (8a-c), 34) as well as potentially other reactions, resulting in the stabilization of the composition of the extract (Fig. 2D).…”

“…1). 34) Nonetheless, the chemical properties of a large number of other αand/or β-acid-derived oxidation products remain unknown. In order to evaluate the effects of bitter acid oxides on beer properties as well as their potential health benefits, the chemical structures of the main constituents of bitter acid oxides must be determined.…”

Potential of ATR-FTIR Spectroscopy for the Classification of Natural Resins

“…8,9 Alternatively, the cataloguing can be conducted according to their solubility in specific solvents: spirit soluble (shellac, rosin, sandarac); turpentine soluble (dammar and mastic); and oil soluble (copal from Congo).…”