The Experts below are selected from a list of 198 Experts worldwide ranked by ideXlab platform
Denis De Keukeleire - One of the best experts on this subject based on the ideXlab platform.
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Reactivity of Beer Bitter Acids Toward the 1-Hydroxyethyl Radical as Probed by Spin-Trapping Electron Paramagnetic Resonance (EPR) and Electrospray Ionization−Tandem Mass Spectrometry (ESI−MS/MS)
Journal of agricultural and food chemistry, 2011Co-Authors: Natália E. C. De Almeida, Denis De Keukeleire, Paula Homem-de-mello, Daniel R. CardosoAbstract:The iso-α-acids or Isohumulones are the major contributors to the bitter taste of beer, and it is well-recognized that they are degraded during beer aging. In particular, the trans-Isohumulones see...
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Fate of flavins in sensitized photodegradation of Isohumulones and reduced derivatives: studies on formation of radicals via EPR combined with detailed product analyses.
Photochemical & photobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology, 2005Co-Authors: Arne Heyerick, Denis De Keukeleire, Kevin Huvaere, Malcolm D. E. ForbesAbstract:Photodegradation of Isohumulones accounts for formation of the lightstruck flavor in beer. The reactions involved are mediated by riboflavin, a natural photosensitizer present in beer in ppb quantities. The results of an investigation of this sensitized degradation process are presented herein. Product analyses and electron paramagnetic resonance spectroscopy, in steady-state as well as in time-resolved mode, offer extensive insight into the photophysical and photochemical details of the degradation mechanism. In contrast to energy transfer and Norrish type I α-cleavage reactions that take place on direct irradiation of Isohumulones, the sensitization pathway proceeds via one-electron redox chemistry involving the excited triplet state of riboflavin and derivatives. The flavin semiquinone radical thus formed could be readily detected, either by steady state or by time-resolved electron paramagnetic resonance spectroscopy. Superimposed signals in the spectra revealed the presence of radical fragments derived from Isohumulones or tetrahydroIsohumulones, which, on recombination with riboflavin semiquinone radicals, produced stable reaction products that were identified by HPLC-MS. However, no superimposed signals were observed on sensitized irradiation of dihydroIsohumulones.
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Photooxidative degradation of beer bittering principles: a key step on the route to lightstruck flavor formation in beer.
Journal of agricultural and food chemistry, 2005Co-Authors: Kevin Huvaere, Mogens L. Andersen, Leif H. Skibsted, And Arne Heyerick, Denis De KeukeleireAbstract: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 β-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. Keywords: Isohumulones; lightstruck flavor; EPR spectroscopy; photooxidation; beer
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Photooxidative degradation of beer bittering principles: product analysis with respect to lightstruck flavour formation
Photochemical & photobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology, 2004Co-Authors: Kevin Huvaere, Bart A. Sinnaeve, Jan Van Bocxlaer, Denis De KeukeleireAbstract:Isohumulones, the main bittering agents in beer, are decomposed by light-induced reactions, thereby leading to radical precursors on the pathway to lightstruck flavour formation. Excited flavins, formed on visible-light irradiation, readily interact with Isohumulones, as well as with reduced and oxidized derivatives thereof. From identification of both volatile and non-volatile reaction products thus formed, feasible degradation mechanisms are proposed.
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Riboflavin-sensitized photooxidation of Isohumulones and derivatives
Photochemical & photobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology, 2004Co-Authors: Kevin Huvaere, Mogens L. Andersen, Leif H. Skibsted, Arne Heyerick, Karsten Olsen, Denis De KeukeleireAbstract:Isohumulones, the bitter principles in beer, are decomposed by light-induced reactions, thereby adversely affecting beer quality. Upon absorption of visible light, riboflavin is excited and interacts with Isohumulones, as well as with oxidized and reduced derivatives thereof. Reaction kinetics were investigated by laser flash photolysis at 355 nm and at 440 nm, and analysis of kinetic data afforded detailed insights into the reaction mechanism.
Keiji Kondo - One of the best experts on this subject based on the ideXlab platform.
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Isohumulones, the bitter component of beer, improve hyperglycemia and decrease body fat in Japanese subjects with prediabetes.
Clinical nutrition (Edinburgh Scotland), 2009Co-Authors: Kuniaki Obara, Hiroaki Yajima, Mai Mizutani, Yoshitaka Hitomi, Keiji KondoAbstract:Summary Background & aims A recent study reported that Isohumulones, the bitter component of beer, activate peroxisome proliferator-activated receptor alpha (PPARα) and PPARγ in vitro and decrease plasma glucose and lipid levels in diabetic mice. This study was to investigate the efficacy and safety of Isohumulones for subjects with prediabetes. Methods Ninety-four subjects with prediabetes were randomly divided into four groups. A 12-week double-blind dose-finding study was performed in which subjects ingested placebo capsules or test capsules containing 16 mg, 32 mg or 48 mg of Isohumulones per day. Result After treatment, fasting blood glucose was decreased in the 32 mg and 48 mg groups after 4 weeks, but did not change in the placebo group. HbA1c was also significantly decreased after 4 weeks in the 16 mg group and after 8 weeks in the 32 mg and 48 mg groups. Body mass index (BMI) was significantly decreased in the 48 mg group as compared with the placebo group at 12 weeks. The decrease in total fat area was also significantly greater in the 48 mg group than in the placebo group at 12 weeks. Conclusion The present study suggests that ingestion of Isohumulones has beneficial effects in diabetes and obesity.
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Isohumulones modulate blood lipid status through the activation of PPARα
Biochimica et biophysica acta, 2005Co-Authors: Masako Shimura, Shinichi Oikawa, Keiji Kondo, Yutaka Miura, Mayu Hosono, Akiko Hasumi, Toshiko Minato, Satoru Mizutani, Aruto YoshidaAbstract:Abstract Isohumulones derived from hops are the major bitter compounds in beer. It was recently reported that Isohumulones activated peroxisome proliferator-activated receptors (PPARs) α and γ in vitro and modulated glucose and lipid metabolism in vivo. In this study, we examined the effects of isomerized hop extract (IHE) primarily containing Isohumulones in C57BL/6N male mice and found that such treatment increased their liver weight and reduced their plasma triglyceride and free fatty acid levels. Microarray analysis and quantitative real time PCR (QPCR) showed that IHE dose-dependently upregulated the expression of a battery of hepatic genes that are involved in microsomal ω-oxidation and peroxisomal and mitochondrial β-oxidation. These effects were common in both genders and very similar to those found with the PPARα agonist, fenofibrate (FF). Moreover, these effects were not found in PPARα-deficient mice. Thus, our results strongly suggest that IHE intake upregulates the expression of key genes that are involved in hepatic fatty acid oxidation, and that it ameliorates the blood lipid profile by activating PPARα.
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Dietary Isohumulones, the bitter components of beer, raise plasma HDL-cholesterol levels and reduce liver cholesterol and triacylglycerol contents similar to PPARα activations in C57BL/6 mice
The British journal of nutrition, 2005Co-Authors: Yutaka Miura, Hideharu Odai, Shinichi Oikawa, Mayu Hosono, Chiaki Oyamada, Keiji KondoAbstract:The effects of dietary Isohumulones, the main components accounting for the bitter taste of beer, on lipid metabolism were examined. Young female C57BL/6N mice were fed diets containing isomerized hop extract (IHE), which consists mainly of Isohumulones. Administration of IHE with an atherogenic (high-fat and high-cholesterol) diet for 2 weeks resulted in a significant increase in plasma HDL-cholesterol (P
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Dietary supplement of Isohumulones inhibits the formation of aberrant crypt foci with a concomitant decrease in prostaglandin E2 level in rat colon
Molecular nutrition & food research, 2005Co-Authors: Hajime Nozawa, Wakako Nakao, Feng Zhao, Keiji KondoAbstract:Male Fischer 344 rats were subcutaneously injected with azoxymethane (AOM) twice weekly at a dose of 15 mg/kg and were fed with freeze-dried (FD) samples of beer brewed without hops (non-hops beer), beer with hops at 4 times the amount of regular lager beer (x 4-hops beer), and isomerized hop extract (IHE) for the whole experimental period (I/PI) or for the post-initiation period (PI) only. Feeding FD beer samples at a dose of 1% significantly decreased the number of aberrant cryp foci (ACF) in the PI protocol over five weeks.x4-hops beer showed stronger inhibitory effects on the development of the numbers of aberrant crypts per focus and large ACF with four or more crypts than non-hops beer. Feeding IHE to rats at a dose of 0.01% or 0.05% in either the I/PI or PI experiment significantly reduced the numbers of ACF. Prostaglandin E2 (PGE2) levels in colonic mucosa of AOM-treated rats were significantly reduced by feeding of IHE. PGE2 production induced by lipopolysaccharide/interferon-gamma (LPS/IFN-gamma) in RAW264.7 cells was also reduced by treatment with IHE and Isohumulone in a dose-dependent manner. These observations suggest that Isohumulones show chemopreventive effects on ACF formation in rat colon by inhibiting the production of PGE2.
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Isohumulones, Bitter Acids Derived from Hops, Activate Both Peroxisome Proliferator-activated Receptor α and γ and Reduce Insulin Resistance
The Journal of biological chemistry, 2004Co-Authors: Hiroaki Yajima, Emiko Ikeshima, Maho Shiraki, Tomoka Kanaya, Daisuke Fujiwara, Hideharu Odai, Nobuyo Tsuboyama-kasaoka, Osamu Ezaki, Shinichi Oikawa, Keiji KondoAbstract:The peroxisome proliferator-activated receptors (PPARs) are dietary lipid sensors that regulate fatty acid and carbohydrate metabolism. The hypolipidemic effects of fibrate drugs and the therapeutic benefits of the thiazolidinedione drugs are due to their activation of PPARα and -γ, respectively. In this study, Isohumulones, the bitter compounds derived from hops that are present in beer, were found to activate PPARα and -γ in transient co-transfection studies. Among the three major Isohumulone homologs, Isohumulone and isocohumulone were found to activate PPARα and -γ. Diabetic KK-Ay mice that were treated with Isohumulones (Isohumulone and isocohumulone) showed reduced plasma glucose, triglyceride, and free fatty acid levels (65.3, 62.6, and 73.1%, respectively, for Isohumulone); similar reductions were found following treatment with the thiazolidinedione drug, pioglitazone. Isohumulone treatment did not result in significant body weight gain, although pioglitazone treatment did increase body weight (10.6% increase versus control group). C57BL/6N mice fed a high fat diet that were treated with Isohumulones showed improved glucose tolerance and reduced insulin resistance. Furthermore, these animals showed increased liver fatty acid oxidation and a decrease in size and an increase in apoptosis of their hypertrophic adipocytes. A double-blind, placebo-controlled pilot study for studying the effect of Isohumulones on diabetes suggested that Isohumulones significantly decreased blood glucose and hemoglobin A1c levels after 8 weeks (by 10.1 and 6.4%, respectively, versus week 0). These results suggest that Isohumulones can improve insulin sensitivity in high fat diet-fed mice with insulin resistance and in patients with type 2 diabetes.
W. J. Simpson - One of the best experts on this subject based on the ideXlab platform.
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Bitterness of congeners and stereoisomers of hop-derived bitter acids found in beer
Journal of the American Society of Brewing Chemists, 1996Co-Authors: P.s. Hughes, W. J. SimpsonAbstract:The sensory bitterness intensity of the major hop bitter acids has been shown to vary. The cis- and trans-isomers of isocohumulone and Isohumulone were isolated and purified by preparative high-per...
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CAMBRIDGE PRIZE LECTURE. STUDIES ON THE SENSITIVITY OF LACTIC ACID BACTERIA TO HOP BITTER ACIDS
Journal of the Institute of Brewing, 1993Co-Authors: W. J. SimpsonAbstract:Hop bitter acids act as mobile-carrier ionophores. They inhibit the growth of beer-spoilage bacteria by dissipating the transmembrane pH gradient. Their activity is pH dependent. Low pH favours antibacterial activity but high pH reduces it. Resistance to hop bitter acids is a stable character, associated only with beer-spoilage lactic acid bacteria. Hop-resistant organisms can maintain a larger transmembrane pH gradient and ATP pool than can hop-sensitive organisms. Prior exposure of bacteria to trans-Isohumulone does not influence the degree of resistance to hop bitter acids. However, in some strains, exposure to trans-Isohumulone does induce the ability to spoil beer. The chemistry of these compounds is more complex than previously thought. In aqueous solutions, such as beer, hop acids bind to metal ions and may be covalently hydrated.
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IONIZATION BEHAVIOUR OF HOP COMPOUNDS AND HOP‐DERIVED COMPOUNDS
Journal of the Institute of Brewing, 1993Co-Authors: W. J. SimpsonAbstract:The ionization behaviour of colupulone, (−)-humulone, trans-Isohumulone and trans-humulinic acid was investigated using a number of techniques. When a potentiometric technique was employed, precise estimates of pKa could not be obtained for any of the compounds, since a drift in the observed pKa values occurred during the titrations. Approximate, or equilibrium pKa values for the most acidic function of each of the compounds were: colupulone, 6.1; (−)-humulone, 5.0; trans-Isohumulone, 3.1; trans-humulinic acid, 2.7. Evidence from spectroscopic measurements (UV, 1H-NMR, 13C-NMR), conductiometric experiments and measurements of the pH dependency of solvent partition behaviour and aqueous solubility of the compounds is consistent with the possibility that, in aqueous solution, compounds such as trans-Isohumulone are present as covalent hydrates. It is likely that reversible hydration occurs at one or more carbonyl groups. As a consequence of this behaviour, no single pKa value is sufficient to describe the behaviour of any one hop compound or hop-derived compound. The potential significance of this phenomenon is discussed.
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Ionophoric action of trans-Isohumulone on Lactobacillus brevis
Journal of General Microbiology, 1993Co-Authors: W. J. SimpsonAbstract:Summary: Compounds (e.g. trans-Isohumulone) derived from flowers of the hop plant (Humulus lupulus L.) protect beer from spoilage. Cells of Lactobacillus brevis IFO 3960 did not die when they were exposed to 40 μM-trans-Isohumulone for up to 120 h. At higher concentrations (80, 120 μM) death occurred after a lag period of about 30 h. trans-Isohumulone dissipated the transmembrane pH gradient of non-growing cells and reduced their ability to accumulate L-[U-14C]leucine. The membrane potential was dissipated to a smaller extent. Addition of trans-Isohumulone to cells that had accumulated L[U-14C]leucine, under conditions in which no synthesis of protein took place, caused slow leakage of radiolabelled leucine. trans-Isohumulone did not inhibit the activity of the proton-translocating membrane ATPase. Potentiometric experiments with resting cell suspensions suggested that trans-Isohumulone acted as an ionophore of the mobile-carrier type, causing electroneutral exchange of H+ for divalent cations such as Mn2+. A second monovalent cation (e.g. K+) was essential for protonophoric activity.
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Application of in vivo bioluminescence to the study of ionophoretic action.
Journal of Bioluminescence and Chemiluminescence, 1993Co-Authors: W. J. SimpsonAbstract:: Ionophores (carbonyl cyanide m-chlorophenylhydrazone; valinomycin; and the hop-derived compounds colupulone, trans-Isohumulone and trans-humulinic acid) reduced the rate of dodecanal-dependent light emission from IuxA/B-transformed cells of Lactococcus lactis subsp. diacetylactis F712 when the cells were suspended in a buffered medium (pH 6.4) containing glucose. This allowed an assay for ionophores to be devised and permitted measurement of the effects of such compounds on the test organism by the use of a non-destructive technique in real time.
M. Verzele - One of the best experts on this subject based on the ideXlab platform.
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The isomerization products of humulone
Bulletin des Sociétés Chimiques Belges, 2010Co-Authors: F. Alderweireldt, M. Verzele, M. J. O. Anteunis, J. DierckensAbstract:The substance known as “Isohumulone” is in fact a mixture of four components. They were separated by C.C.D. According to a new nomenclature based mainly on the chemically related humulinic acids A,B, C etc. series they are the stereoisomers Isohumulone A and B (IV and V) and alloIsohumulone A and B (VI and VII).
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The Isomerization Mechanism of Humulone
Bulletin des Sociétés Chimiques Belges, 2010Co-Authors: M. Verzele, M. Van BovenAbstract:The first step in the isomerization of humulone in mildly acid or alkaline media is the formation of a mono anion. This is followed by stereospecific ketonization and only then by the ring contraction, producing trans and cis Isohumulone, in a 32/68 ratio. In strong alkaline medium the reaction proceeds over a dianion form and the isomer ratio is then 50/50.
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Oxidation Products of Isohumulones
Bulletin des Sociétés Chimiques Belges, 2010Co-Authors: M. Vanhoey, M. Vandewalle, M. VerzeleAbstract:Humulone is oxidised in conditions which parallel the hops treatment conditions in brewing. A number of products can be isolated from the reaction mixture by counter current distribution. These are oxidation products of Isohumulones; this paper is about their preparation, isolation and identification.
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Spiro‐Isohumulones: Isohumulones with a 3‐Keto Tetrahydrofurane Moiety
Bulletin des Sociétés Chimiques Belges, 2010Co-Authors: L. Maes, M. J. O. Anteunis, M. VerzeleAbstract:Since 1951 it is known that methanolic alkaline isomerization of humulone produces a mixture of crystalline isomers. This paper shows that the mixture contains the four diastereoisomers with structures 12, 13, 14 and 15 of chart III. It is proposed to name these substances trans-spiro-Isohumulone I and II and cis-spiro-Isohumulone I and II respectively.
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Borohydride Reduction of Isohumulones
Bulletin des Sociétés Chimiques Belges, 2010Co-Authors: A. Khokher, M. J. O. Anteunis, M. VerzeleAbstract:Following chart 1 the borohydride reduction of Isohumulones A and B gives four diastereoisomeric reaction products, (ρ-Isohumulones A1, A2, B1 and B2).
Kevin Huvaere - One of the best experts on this subject based on the ideXlab platform.
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Fate of flavins in sensitized photodegradation of Isohumulones and reduced derivatives: studies on formation of radicals via EPR combined with detailed product analyses.
Photochemical & photobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology, 2005Co-Authors: Arne Heyerick, Denis De Keukeleire, Kevin Huvaere, Malcolm D. E. ForbesAbstract:Photodegradation of Isohumulones accounts for formation of the lightstruck flavor in beer. The reactions involved are mediated by riboflavin, a natural photosensitizer present in beer in ppb quantities. The results of an investigation of this sensitized degradation process are presented herein. Product analyses and electron paramagnetic resonance spectroscopy, in steady-state as well as in time-resolved mode, offer extensive insight into the photophysical and photochemical details of the degradation mechanism. In contrast to energy transfer and Norrish type I α-cleavage reactions that take place on direct irradiation of Isohumulones, the sensitization pathway proceeds via one-electron redox chemistry involving the excited triplet state of riboflavin and derivatives. The flavin semiquinone radical thus formed could be readily detected, either by steady state or by time-resolved electron paramagnetic resonance spectroscopy. Superimposed signals in the spectra revealed the presence of radical fragments derived from Isohumulones or tetrahydroIsohumulones, which, on recombination with riboflavin semiquinone radicals, produced stable reaction products that were identified by HPLC-MS. However, no superimposed signals were observed on sensitized irradiation of dihydroIsohumulones.
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Photooxidative degradation of beer bittering principles: a key step on the route to lightstruck flavor formation in beer.
Journal of agricultural and food chemistry, 2005Co-Authors: Kevin Huvaere, Mogens L. Andersen, Leif H. Skibsted, And Arne Heyerick, Denis De KeukeleireAbstract: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 β-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. Keywords: Isohumulones; lightstruck flavor; EPR spectroscopy; photooxidation; beer
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Photooxidative degradation of beer bittering principles: product analysis with respect to lightstruck flavour formation
Photochemical & photobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology, 2004Co-Authors: Kevin Huvaere, Bart A. Sinnaeve, Jan Van Bocxlaer, Denis De KeukeleireAbstract:Isohumulones, the main bittering agents in beer, are decomposed by light-induced reactions, thereby leading to radical precursors on the pathway to lightstruck flavour formation. Excited flavins, formed on visible-light irradiation, readily interact with Isohumulones, as well as with reduced and oxidized derivatives thereof. From identification of both volatile and non-volatile reaction products thus formed, feasible degradation mechanisms are proposed.
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Riboflavin-sensitized photooxidation of Isohumulones and derivatives
Photochemical & photobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology, 2004Co-Authors: Kevin Huvaere, Mogens L. Andersen, Leif H. Skibsted, Arne Heyerick, Karsten Olsen, Denis De KeukeleireAbstract:Isohumulones, the bitter principles in beer, are decomposed by light-induced reactions, thereby adversely affecting beer quality. Upon absorption of visible light, riboflavin is excited and interacts with Isohumulones, as well as with oxidized and reduced derivatives thereof. Reaction kinetics were investigated by laser flash photolysis at 355 nm and at 440 nm, and analysis of kinetic data afforded detailed insights into the reaction mechanism.
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Photolysis of hop-derived trans-iso-alpha-acids and trans-tetrahydroiso-alpha-acids: product identification in relation to the lightstruck flavour of beer.
Photochemical and Photobiological Sciences, 2003Co-Authors: Arne Heyerick, Kevin Huvaere, Yining Zhao, Pat Sandra, Frederik Roelens, Denis De KeukeleireAbstract:The photolysis of hop-derived trans-iso-α-acids (2a–c; naturally occurring bitter compounds present in beer) and of trans-tetrahydroiso-α-acids (5a–c; semi-synthetic advanced hop products) was investigated at 300 nm in methanol. The complex photoreaction mixtures were separated by high-performance liquid chromatography (HPLC) using diode array detection and the major photoreaction products were identified by HPLC–mass spectroscopy. The main part of the mixture consisted of compounds, which originated from recombination of radicals derived from Norrish Type I photocleavage of the acyloin moiety in both trans-iso-α-acids and trans-tetrahydroiso-α-acids. The results confirm the intermediacy of radicals that were previously identified by time-resolved electron paramagnetic resonance and they bear relevance to the formation of the lightstruck flavour that is generated when beer is exposed to light. Additionally, new photoproducts were found that are formed by photochemical reactions hitherto undiscovered in hop chemistry, including photoenolization of trans-Isohumulone (2a) leading to trans-alloIsohumulone (13a) and a retro oxa-di-π-methane rearrangement in trans-Isohumulone (2a) and trans-tetrahydroiso-α-acids to humulone (1a) and tetrahydro-α-acids (23a–b), respectively.
