Humulinic Acid Research Articles

Impact of Different Hop Compounds on the Overfoaming Volume of Beer Caused by Primary Gushing

When weather conditions favour the growth of moulds on barley, beers brewed from the resulting malts often tend to gush. Certain Fusarium species (e.g., F. graminearum and F. culmorum) may cause this problem. Supersaturated with CO 2 , a primary beer contains an overcritical concentration of microbubbles; these are reputed to be stabilised by Fusarium-derived hydrophobins. Research with varying brewhouse parameters has been performed to investigate the factors of primary gushing. As hops are known to contribute to a wide range of both positive and negative substances in beer, the hopping regime has emerged as an important aspect. This paper examines the impact of different hop varieties on gushing. Hop oils and unsaturated fatty acids are reputed to be gushing-suppressors. Compounds such as dehydrated humulinic acid can intensify the effect. Hop pellets, with a prevalent range of conductometric values (5―10% α-acid), commonly employed in breweries to adjust bitterness and aroma were selected. By working with the same gushing malt, the spectrum of compounds in the finished beer only differed through the hop product used. The overfoaming volumes of different samples were determined according to MEBAK guidelines. Respective hop oil and fatty acid concentrations (by GC) and iso-α-acid contents (by HPLC) were compared and a chronological sequence of the changing percentages of beer loss is shown.

Solid-Phase Extraction of Hop Acids from Beer or Wort for Subsequent Analysis

A procedure for extracting hop acids from beer or wort was developed. A solid-phase extraction procedure employing a 3.0-ml Bakerbond spe* octyl column was used to absorb the hop compounds. After the concentrated hop compounds were washed, they were desorbed with methanol. UV measurement of either international bitterness units or high-performance liquid chromatography (HPLC) was used to determine the amount of hop acids present. UV analysis could be correlated with the ASBC-recommended procedure for bitterness units. HPLC analysis allowed quantitation of hulupones, humulinic acid, isohumulones, humulones, lupulones, ρ-isohumulones, and tetrahydro-isohumulones. Recovery of isohumulones is better than 90%, and recovery of other specific hop compounds is better than 75%.

The relation between the molecular structure and gushing potential of dehydrated humulinic acid

Dehydrated humulinic acid, 2-isovaleroyl-4-(3-methylbut-2-enyliden)-cyclopentane-1.3-dione (DNA) sometimes occurs in isomerised hop extract. The use of any such extract can cause beer gushing. It was attempted to establish whether this gushing-releasing characteristic is related to specific functional groups of the molecule. Two hydrogenated derivatives of DHA, 2-isovaleroyl-4-(3-methylbutyl)-cyclopentane-1.3-dione (IMCD) and 2.4-di-(3-methylbutyl)-cyclopentane-1.3-dione (DMCD) were prepared and their gushing-releasing potential was compared with that of DHA in various types of beer. These three components released gushing but DMCD, probably on account of elimination of a carbonyl group, reacted differently from DNA and from IMCD. The gushing potential of IMCD was lower than that of DHA.Since both the DHA and the IMCD molecules contain the β-tricarbonyl system of isohumulone but lack a hydrophilic hydroxyl group on the cyclopentane ring, it was suggested that the gushing potential of DHA was due to the β-tricarbonyl system and to the absence of the hydrophilic hydroxyl group. The results also indicate that gushing caused by DHA occurs if concentrations of certain DHA protein complexes are sufficiently high in the beer.It was shown that DMCD-induced gushing is released by DMCD crystals and consequently is different in nature from that of DHA-induced gushing.

HOP RESIN ANALYSIS BY HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY ON MICROPARTICULATE SILICA

A high-performance liquid chromatographic separation of hop resins on a commercially available microparticulate silica has been developed. The chromatography involves a new mechanism in hop resin separation. A solvent containing di-n-butylammonium acetate is used. The method gives good separation of α-acid, iso-α-acid, β-acid and humulinic acid, and has been used for the quantitative analysis of α-acid and iso-α-acid in hop extracts and isomerised hop extracts.

Membrane leakage in Bacillus subtilis 168 induced by the hop constituents lupulone, humulone, isohumulone and humulinic acid.

The bactericidal activity of the hop constituents lupulone, humulone, isohumulone and humulinic acid against Bacillus subtilis 168 is shown to result from primary membrane leakage. This process leads to complete inhibition of active transport of α-methyl-d-glucopyranoside and several amino acids into whole bacteria and isolated membrane vesicles within 5 min at 37°C at the corresponding minimal inhibitory concentrations of 1, 2, 25 and 250 μg/ml, respectively. Inhibition of the respiratory chain, of protein, RNA and DNA synthesis seems to be a secondary event.

Preparation of Humulinic Acid: Effect on Analytical and Flavor Characteristics of Beer

Preparation of Humulinic Acid: Effect on Analytical and Flavor Characteristics of Beer

Humulinic Acids: IX. Formation and Isomerization

AbstractThis paper discusses the formation and isomerization of humulinic acids and the origin of positive and negative optically active trans humulinic acid in humulone hydrolysis mixtures. The separation of the cis humulinic acid stereoisomers is described.

HUMULINIC ACID IN ISOMERIZED HOP EXTRACTS

Humulinic acid, which is not bitter, behaves similarly to iso-α-acids in some analytical estimations of beer bitterness. The humulinic acid content of a number of isomerized hop extracts was estimated using thin layer chromatography.

HUMULINIC ACIDS. VIII. STEREOISOMERS OF HUMULINIC ACIDS

Humulinic acid contains chiral centra at C4 and C5 and can therefore theoretically occur in four optically active stereoisomers. The diastereoisomeric forms are at the same time trans and cis isomers of each other (formerly humulinic acids A and B).5 This paper concerns the isolation and characterization of the trans and cis co- and ad-humulinic acids and the separation of racemic trans humulinic acid in its enantiomorphs.

ISOHUMULONES*

Isomerization of humulone in wort or in buffer solution produces a mixture of two pairs of stereoisomers, which are named following a nomenclature based on the humulinic acid series, isohumulone A (melting point 62° C.) and isohumulone B (an oil) are formed in the largest amounts. The second pair is present in smaller quantities (e.g., 4.5–8%) and comprises alloisohumulone A and allisohumulone B.

The humulinic acids. V. Specific catalytic reductions methyl allohumulinic acid D.

AbstractMethyl allohumulinic acid D (I) was isolated after acid treatment of either humulinic A (HAA) or humulinic acid B (HAB). Some specific reductions on this and other humulinic acids are reported. Dihydromethylhumulinic acid D (IV) is described. A new route to dihydro‐HAB was developed.

1205. Chemistry of hop constituents. Part XXVII. Further model compounds of hulupone and humulinic acid

1205. Chemistry of hop constituents. Part XXVII. Further model compounds of hulupone and humulinic acid

223. Chemistry of hop constituents. Part XXIII. The structure of humulinic acid C and other acid-transformation products of humulinic acids

223. Chemistry of hop constituents. Part XXIII. The structure of humulinic acid C and other acid-transformation products of humulinic acids

ISOLATION AND CHARACTERIZATION OF TWOISOHUMULONE ISOMERS

Isohumulones may be prepared by boiling humulone in a buffer solution of medium pH or by the methods of Howard and of Windisch et al., who use alkaline solutions. Medium pH is to be preferred as no humulinic acid is formed. The reaction product may be resolved by reversed-phase partition chromatography into two isomeric substances, one optically inactive and one dextrorotatory isohumulone with very similar properties. When purified humulone is used, small amounts of co- and ad-humulone are present and give rise to the corresponding iso-compounds. The same six isohumulones are present in beer. An isooctane extract of beer which is resolved into three fractions by countercurrent distribution thus gives five to six peaks when an efficient chromatographic procedure is used. No substance corresponding to the resin B of Windisch et al. has been observed in the isomerization mixture at any pH.

CHEMISTRY OF HOP CONSTITUENTS: XXII. PROTON MAGNETIC RESONANCE SPECTROSCOPY OFISOHUMULONE A

Knowledge of the structure of isohumulone A is reviewed. Its proton magnetic resonance spectrum has been interpreted with the aid of the spectra of the two isomers of humulinic acid. It is concluded that isohumulone A consists of a mixture of stereoisomers, trans and cis with respect to the 4-isohexenoyl and 5-isopentenyl chains, in the ratio of about 60% trans (i.e., with the stereochemistry of humulinic acid B) to 40% cis (i.e., humulinic acid A stereochemistry). Humulone has been isomerized into isohumulone A in deuterium oxide, and unlabelled isohumulone A has been hydrolysed into humulinic acid A using sodium deuteroxide in deuterium oxide. The modified spectra assisted some of the assignments.

The Humulinic Acids IV. Humulinic acids C, D.

AbstractHumulinic acids C and D have respectively stucture III and IV. The methyl derivative of HAD(2) has structure V. The assignments are based on physical and chemical evidence. A mechanism for the formation of these substances is advanced.The preparation and isolation of a number of humulinic acid isomers or derivatives called humulinic acids A, B, C, D (HAA, HAB, HAC, HAD) was reported by us before (2). The structure elucidation of humulinic acids A and B showing them to be trans and cis isomers I and II was also reported by our laboratory (1). The recent structure attribution to humulinic acid C by English authors (3) prompts us now to publish our further results.

The Humulinic Acids III. The NMR Spectra and the Structure of HAA and HAB

AbstractA detailed analysis of the proton magnetic resonance (PMR) spectra of humulinic acid A and humulinic B shows that the former is the trans and the the latter the cis form with structures I and II respectively. Evidence is advanced that J trans is smaller than J cis in ring compounds with several sp2 carbon atoms in the ring.

731. Chemistry of hop constituents. Part XX. The constitution of humulinic acid A and B as indicated by proton magnetic resonance spectroscopy

731. Chemistry of hop constituents. Part XX. The constitution of humulinic acid A and B as indicated by proton magnetic resonance spectroscopy

ATTEMPTED FRACTIONATION OF HUMULINIC ACID INTO ISOMERS

Although isohumulone can be resolved into two isomers by reversed-phase partition chromatography, humulinic acid behaves as a homogeneous substance. Most certainly, therefore, only one of the two theoretically possible isomers of humulinic acid exists as a transformation product of humulone. The two isohumulone isomers are accordingly derivatives of one and the same humulinic acid.

The Humulinic Acids Part 1. Isolation and preparation of humulinic acid isomers

AbstractThe isolation and preparation of several humulinic acid isomers named humulinic acid A, B, C and D is reported. They can be obtained by isomerization of the known degradation product of humulone which is the humulinic acid A of the above series.