Comparison of the odor-active compounds in unhopped beer and beers hopped with different hop varieties

Odorants comprising the hop aromas of beers were examined. Strongly hopped beers with Saazer, Hersbrucker, and Cascade hops were compared with unhopped beer by gas chromatography-olfactometry (CharmAnalysis) and sensory evaluation. Twenty-seven odorants were revealed as hop-derived, which derived either directly from hops or via metabolization, and 19 components were identified. Of the components, linalool, geraniol, ethyl 2-methylbutanoate, ethyl 3-methylbutanoate, and ethyl 2-methylpropanoate were determined as odor-active components from their Charm values and aroma values. The muscat-like aroma of Cascade beer and the spicy aroma of Hersbrucker beer were predominant in sensory evaluation, and the contributors to these characteristics were investigated.     

Comparison of the most odor-active compounds in fresh and dried hop cones (Humulus lupulus L. variety spalter select) based on GC-olfactometry and odor dilution techniques

Application of aroma extract dilution analysis on the volatiles obtained from dried cones of Spalter Select hops grown in the German hop-growing area of Hallertau revealed 23 odorants in the flavor dilution (FD) factor range of 16-4096, 20 of which could be identified. On the basis of high FD factors, trans-4, 5-epoxy-(E)-2-decenal, linalool, and myrcene were identified as the most potent odorants, followed by ethyl 2-methylpropanoate, methyl 2-methylbutanoate, (Z)-1,5-octadien-3-one, nonanal, (E,Z)-1,3, 5-undecatriene, 1,3(E),5(Z),9-undecatetraene, propyl 2-methylbutanoate, 4-ethenyl-2-methoxyphenol, and 1-octen-3-one. Ten of the high-impact hop aroma compounds had previously not been identified as hop constituents and, in particular, 1,3(E),5(Z), 9-undecatetraene has not yet been reported as a food odorant. In an extract obtained from fresh hops, in addition to the odorants found in dry hops, (Z)-3-hexenal was characterized as a further key odorant rendering an additional green aroma note to the fresh material.     

Effects of beer and hop on ionotropic gamma-aminobutyric acid receptors

Beer induced the response of the ionotropic gamma-aminobutyric acid receptors (GABA(A) receptors) expressed in Xenopus oocytes, indicating the presence of gamma-aminobutyric acid (GABA)-like activity. Furthermore, the pentane extract of the beer, hop (Humulus lupulus L.) oil, and myrcenol potentiated the GABA(A) receptor response elicited by GABA. The GABA(A) receptor responses were also potentiated by the addition of aliphatic esters, most of which are reported to be present in beer flavor. Aliphatic esters showed the tendency to decrease in the potentiation of the GABA(A) receptor response with an increase in their carbon chain length. When myrcenol was injected to mice prior to intraperitoneal administration of pentobarbital, the pentobarbital-induced sleeping time of mice increased additionally. Therefore, the beer contained not only GABA-like activity but also the modulator(s) of the GABA(A) receptor response.     

Use of beer bran as an adsorbent for the removal of organic compounds from wastewater

Beer bran was found to effectively adsorb several organic compounds, such as dichloromethane, chloroform, trichloroethylene, benzene, pretilachlor, and esprocarb. Equilibrium adsorption isotherms conformed to the Freundlich isotherm (log-log linear). Adsorption of these organic compounds by beer bran was observed in the pH range of 1-11. At equilibrium, the adsorption efficiency of beer bran for benzene, chloroform, and dichiloromethane was higher than that of activated carbon. The removal of these organic compounds by beer bran was attributed to the uptake by intracellular particles called spherosomes. The object of this work was to investigate several adsorbents for the effective removal of organic compounds from wastewater.     

Use of gas chromatography-olfactometry to identify key odorant compounds in dark chocolate. Comparison of samples before and after conching

After vacuum distillation and liquid-liquid extraction, the volatile fractions of dark chocolates were analyzed by gas chromatography-olfactometry and gas chromatography-mass spectrometry. Aroma extract dilution analysis revealed the presence of 33 potent odorants in the neutral/basic fraction. Three of these had a strong chocolate flavor: 2-methylpropanal, 2-methylbutanal, and 3-methylbutanal. Many others were characterized by cocoa/praline-flavored/nutty/coffee notes: 2,3-dimethylpyrazine, trimethylpyrazine, tetramethylpyrazine, 3(or 2),5-dimethyl-2(or 3)-ethylpyrazine, 3,5(or 6)-diethyl-2-methylpyrazine, and furfurylpyrrole. Comparisons carried out before and after conching indicate that although no new key odorant is synthesized during the heating process, levels of 2-phenyl-5-methyl-2-hexenal, Furaneol, and branched pyrazines are significantly increased while most Strecker aldehydes are lost by evaporation.     

Formation of alpha-dicarbonyl compounds in beer during storage of Pilsner

With the aim of determining the formation of alpha-dicarbonyl intermediates during beer aging on the shelf, alpha-dicarbonyls were identified and quantified after derivatization with 1,2-diaminobenze to generate quinoxalines. The sensory effects of alpha-dicarbonyls were evaluated by the quantification of key Strecker aldehydes and by GC-olfactometry (GCO)analysis of beer headspace using solid phase microextraction. Four alpha-dicarbonyls, reported here for the first time, were detected in fresh and aged beers, three were derived from the 2,3-enolization pathway of mono- and disaccharides, and the fourth was derived from the epimerization of 3-deoxy-2-hexosulose. Ten alpha-dicarbonyls were quantified during beer processing and during different periods of beer aging at 28 degrees C. The aging periods were from 15 to 105 days. During beer aging, 1-deoxydiuloses were produced and degraded, while 1,4-dideoxydiuloses were produced at the highest rates. The GCO analysis indicated that forced beer aging increased the amounts of furaneol, trans-2-nonenal, and phenylacetaldehyde. The blockage of alpha-dicarbonyls inhibited the accumulation of sensory-active aldehydes in the beer headspace.     

Determination of volatile compounds in different hop varieties by headspace-trap GC/MS--in comparison with conventional hop essential oil analysis

A headspace (HS)-trap method in combination with gas chromatography (GC)-mass spectrometry (MS) was developed for the determination of volatile constituents in hops. The highly sensitive HS-trap system reduces the detection limit by using up to four trap enrichment cycles. Seventy hop samples of different varieties and cultivation regions, from the 2008 harvest, were examined using the HS-trap-GC-MS method and the established "European Brewery Convention" (EBC) method for hop essential oil analysis. Twenty-one different volatiles were quantified for each hop sample. For all compounds, except caryophyllene oxide, a strong correlation was found between the results of the HS-trap method and the EBC method. Experiments have revealed that the EBC method using steam distillation is not appropriate for thermolabile compounds, such as caryophyllene oxide, due to decomposition during boiling. The HS-trap method is fast and sensitive, requires small sample amounts and minimal sample preparation, and is easy to apply.     

Analysis of hop acids and their oxidized derivatives and iso-alpha-acids in beer by capillary electrophoresis-electrospray ionization mass spectrometry

This study investigates the applicability of on-line coupling of capillary electrophoresis with electrospray ionization tandem mass spectrometry (CZE-ESI-MS) for the separation and characterization of alpha- and beta-acids and oxidized hop acids from crude extracts of different hop varieties. CZE-ESI-MS with negative-ion electrospray ionization proved to be a suitable technique for the determination of these types of natural compounds and their oxidized derivatives. The CZE parameters (pH, concentration, and buffer type) and ESI-MS parameters (nature and flow rate of the sheath liquid, nebulizer pressure, drying gas flow rate, temperature, and compound stability) were optimized. The optimized method provides the potential for a fast qualitative determination of hop acids and their oxidation compounds. The method was also applied to the determination of iso-alpha-acids in beer.     

Comprehensive sensomics analysis of hop-derived bitter compounds during storage of beer

For the first time, quantitative LC-MS/MS profiling of 56 hop-derived sensometabolites contributing to the bitter taste of beer revealed a comprehensive insight into the transformation of individual bitter compounds during storage of beer. The proton-catalyzed cyclization of trans-iso-α-acids was identified to be the quantitatively predominant reaction leading to lingering, harsh bitter tasting tri- and tetracyclic compounds such as, e.g. the cocongeners tricyclocohumol, tricyclocohumene, isotricyclocohumene, tetracyclocohumol, and epitetracyclocohumol, accumulating in beer during storage with increasing time and temperature. The key role of these transformation products in storage-induced trans-iso-α-acid degradation was verified for the first time by multivariate statistics and hierarchical cluster analysis of the sensomics data obtained for a series of commercial beer samples stored under controlled conditions. The present study offers the scientific basis for a knowledge-based extension of the shelf life of the desirable beer's bitter taste and the delay of the onset of the less preferred harsh bitter aftertaste by controlling the initial pH value of the beer and by keeping the temperature as low as possible during storage of the final beverage.     

Degradation of certain aromatic compounds by rhizobia

The ability of 22 strains of Rhizobium to degrade catechol, protocatechuic acid, p-hydroxybenzoic acid and salicylic acid all at 1 mm concentration was examined. In the presence of 4.8 mm Na-glutamate, all rhizobia tested degraded catechol (99–100%), p-hvdroxybenzoic acid (79–99%), protocatechuic acid (81 97%) and salicylic acid (20–83%).The concentration of Na glutamate in the medium affected the degradation of the phenolic compounds at 1 mm concentration. Increased glutamate favoured degradation of p-hydroxybenzoic and salicylic acids but had little effect on catechol. Degradation of protocatechuic acid was inhibited by increased glutamate concentration.Rhizobium phaseoli 405 grown with 8.0 mM Na-glutamate, directly cleaved catechol and protocatechuic acid. p-Hydroxybenzoic acid was converted to protocatechuic acid before ring cleavage. Salicylic acid was converted to gentisic acid before further oxidation. O₂ uptake experiments showed that R. phaseoli 405 grown with p-hydroxybenzoic acid was adapted to this compound and protocatechuic acid. A lag of 30 min was required for catechol and salicylic acid.     

Approaches to spirit aroma: contribution of some aromatic compounds to the primary aroma in samples of orujo spirits

Terpenes and C(13) norisoprenoids are among the most important aromatic compounds found in a volatile and nonvolatile form in grapes. Aromatic typicity of a spirit could be attributed to these compounds despite the very important presence of volatile compounds produced during alcoholic fermentation. In this study, following a solid phase extraction stage, the determination of the varietal aromatic compounds by gas chromatography was performed on 15 samples of Galician orujo spirits. The results show that significant differences (p < 0.05) exist in the concentrations of varietal aromatic compounds in Galician spirits obtained from different varieties of grapes. alpha-Ionona is the varietal aromatic compound that is most likely to contribute to the aroma of all of the spirits studied. The spirits from Catalan Roxo are the most aromatic, with floral and fruity nuances, while the spirits from Godello were the less aromatic group as far as the varietal compounds studied are concerned. Spirits from Mencia and Treixadura show a similar profile, but the former has a more intensive aroma due to beta-pinene, citronellol, and alpha-ionone. Albari?o spirits stand out because of their profile that is marked by the contributions of eugenol and linalool.     

芳香族化合物对土壤硝化作用的抑制研究

Aromatic compounds (ACs) in soil can induce competitive inhibition for soil NH₃ oxidation, and nitrification inhibitors can be used to this end. A laboratory incubation experiment was performed with 12 nitroaromatic compounds (NACs), 15 amidoaromatic compounds (AACs) and 20 hydroxyaromatic compounds (HACs) to assess the inhibitory effects of ACs on soil nitrification. Based on these results, the critical and optimal concentrations of ACs were determined for better inhibitory effects. Most of the test ACs were able to inhibit soil nitrification; the effectiveness differed with soil type. Among the ACs, the NACs with m-nitryl, amino or hydroxyl and the AACs with a nitro group or a chlorine atom on aromatic ring or with a p-hydroxyl were more effective. 3-nitroaniline, 4-aminophenol and 3-nitrophenol showed the greatest potential as nitrification inhibitors. The critical concentration of these compounds in brown soil and cinnamon soil was found to be 0.5 mg kg^-1 soil. Due to the toxicity, carcinogenicity and mutagenicity of ACs, further toxicological and ecotoxicological research is necessary before ACs are used as nitrification inhibitors in agricultural and horticultural practices.     

Photooxidative degradation of beer bittering principles: a key step on the route to lightstruck flavor formation in beer

Isohumulones, dihydroisohumulones, tetrahydroisohumulones, and humulinones, important hop-derived bittering compounds in beer, were shown to give rise to reactive triacylmethyl radicals on interaction with triplet-excited riboflavin after spin trapping by 5,5-dimethyl-1-pyrroline N-oxide or 2-methyl-2-nitrosopropane, followed by electron paramagentic resonance spectroscopy combined with spectral simulation. Electron abstraction from the ionized beta-tricarbonyl chromophore, which is common to all five-membered ring hop derivatives, is the initial event on photoinduced degradation. Radicaloid decomposition of isohumulones leads to precursors for 3-methylbut-2-ene-1-thiol, the lightstruck constituent in beer. Interaction of reduced derivatives of isohumulones with triplet-excited riboflavin furnished radical precursors of volatile aldehydes, which may lead to the development of unpleasant stale or cardboard flavors.     

Use of fatty acid profiles to identify food-borne bacterial pathogens and aerobic endospore-forming bacilli

Capillary gas chromatography (GC) with flame ionization detection was used to determine the cellular fatty acid profiles of various food-borne microbial pathogens and to compare the fatty acid profiles of spores and vegetative cells of the same endospore-forming bacilli. Fifteen bacteria, representing eight genera (Staphylococcus, Listeria, Bacillus, Yersinia, Salmonella, Shigella, Escherichia, and Vibrio) and 11 species were used to compare the extracted fatty acid methyl esters (FAMEs). Endospore-forming bacilli were processed to obtain pure spores and whole cell FAMEs for GC analysis. A data set for each bacterial agent was prepared using fatty acid profiles from five replicates prepared on different days. The results showed that these fatty acid intensity profiles were unique for each of the 11 species and that they could be used as a fingerprint for the organisms. The cellular fatty acid profiles for Bacillus anthracis and Bacillus cereus show that there are two branched chain fatty acids, iso 17:1 omega10c and 17:1 anteiso, which are unique in these species. Iso 17:1 omega10c is present in B. cereus vegetative cells and spores but is not observed in B. anthracis. The 17:1 anteiso fatty acid is present in B. anthracis cells but not in B. cereus cells. Fatty acids 16:0 2OH and 17:0 iso 3OH are present in B. anthracis and B. cereus spores but not in the vegetative cells. In summary, analysis of FAMEs from bacteria and spores can provide a sensitive procedure for the identification of food-borne pathogens.     

Mechanisms of cancer chemoprevention by hop bitter acids (beer aroma) through induction of apoptosis mediated by Fas and caspase cascades

The bitter acids of hops (Humulus lupulus L.) mainly consist of alpha-acids, beta-acids, and their oxidation products that contribute the unique aroma of the beer beverage. Hop bitter acids displayed a strong growth inhibitory effect against human leukemia HL-60 cells, with an estimated IC(50) value of 8.67 microg/mL, but were less effective against human histolytic lymphoma U937 cells. Induction of apoptosis was confirmed in HL-60 cells by DNA fragmentation and the appearance of a sub-G1 DNA peak, which were preceded by dissipation of mitochondrial membrane potential, cytochrome c release, and subsequent induction of pro-caspase-9 and -3 processing. Cleavages of PARP and DFF-45 were accompanied with activation of caspase-9 and -3 triggered by hop bitter acids in HL-60 cells. The change in the expression of Bcl-2, Bcl-X(L), and Bax in response to hop bitter acids was studied, and the Bcl-2 protein level slightly decreased; however, the Bcl-X(L) protein level was obviously decreased, whereas the Bax protein level was dramatically increased, indicating that the control of Bcl-2 family proteins by hop bitter acids might participate in the disruption of mitochondrial integrity. In addition, the results showed that hop bitter acids promoted the up-regulation of Fas and FasL prior to the processing and activation of pro-caspase-8 and cleavage of Bid, suggesting the involvement of a Fas-mediated pathway in hop bitter acids-induced cells. Taken together, these findings suggest that a certain intimate link might exist between receptor- and mitochondria-mediated death signalings that committed to cell death induced by hop bitter acids. The induction of apoptosis by hop bitter acids may offer a pivotal mechanism for their chemopreventive action.     

High levels of chlorinated aromatic compounds in deep rhine sediments with special reference to microbial transformations

Sediment cores were taken from the Ketelmeer, a sedimentation area of the River Rhine located in the central part of the Netherlands. Chlorinated benzenes, biphenyls, dibenzo-p-dioxins and furans were determined in all or in a selected number of core samples. Levels of these compounds since the late 1930s were established using radionuclide tracers and area-specific geological time markers. Unexpectedly high concentrations of chlorinated dioxins and furans were found in layers that were deposited in the 1960s and 1970s. the highly toxic 2,3,7,8-TCDD reached concentrations up to 400 ng kg⁻¹ in the mid-1960s. Post-depositional redistribution of pollutants was verified by analysing deeper layers that were unpolluted at the time of deposition. Downward transport was only found for some di- and trichlorobenzenes. Possible transformations in the anaerobic sediment were evaluated by analysing sediment top-layer samples taken in 1972. Supported by laboratory experiments, it became clear that some polychlorinated biphenyls and chlorobenzenes had been microbially dechlorinated in the anaerobic sediments. Up to 80 per cent of the input in the early 1970s has disappeared. on the other hand, The accumulation of a dechlorination product, 1,3,5-trichlorobenzene, from hexachlorobenzene transformation was found. This dechlorination product is less hydrophobic and therefore more mobile than the parent compound. This phenomenon is of particular concern with respect to groundwater quality.     

Comparison of odor-active compounds in the spicy fraction of hop (Humulus lupulus L.) essential oil from four different varieties

The "spicy" character of hops is considered to be a desirable attribute in beer, associated with "noble hop aroma". However, the compounds responsible have yet to be adequately identified. Odorants in four samples of the spicy fraction of hop essential oil were characterized using gas chromatography-olfactometry (GC-O) and CharmAnalysis. Four hop varieties were compared, namely, Target, Saaz, Hallertauer Hersbrucker, and Cascade. Odor-active compounds were tentatively identified using comprehensive two-dimensional gas chromatography (GCxGC) combined with time-of-flight mass spectrometry (TOFMS). An intense "woody, cedarwood" odor was determined to be the most potent odorant in three of the four spicy fraction samples. This odor coincided with a complex region where between 8 and 13 compounds were coeluting in each of the four spicy fractions. The peak responsible was determined by (i) correlating peak areas with Charm values in eight hop samples and (ii) heart-cut multidimensional gas chromatography-olfactometry (MDGC-O). The compound responsible was tentatively identified as 14-hydroxy-beta-caryophyllene. Other important odorants identified were geraniol, linalool, beta-ionone, and eugenol.