Oxidation Products of Isohumulones

Vanhoey, M.; Vandewalle, M.; Verzele, M.

doi:10.1002/bscb.19700790901

Cited by 12 publications

(5 citation statements)

References 11 publications

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“…5,61 The recent reports of Intelmann and Hofmann on the identification of degradation products of IAA formed upon beer ageing 62 indicates the proneness of IAA to oxidative degradation, partly based on findings already established much earlier by several authors. [63][64][65][66][67][68][69][70] Although phase-II conjugation of IAA and THIAA cannot be completely ruled out, in none of the plasma, urine, and faecal samples proof for sulfation or glucuronidation could be demonstrated. This corresponds also with the results of the enzymatic hydrolysis of Caco-2 monolayer samples.…”

Section: Discussionmentioning

confidence: 99%

Bioavailability of hop-derived iso-α-acids and reduced derivatives

et al. 2011

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Iso-α-acids (IAA) and their reduced derivatives (dihydro-iso-α-acids (DHIAA) and tetrahydro-iso-α-acids (THIAA)) have been administered to Caco-2 cell monolayers (30, 60, and 120 μM) to investigate epithelial transport, in both absorptive and secretive directions. In addition, 25 mg kg(-1) IAA, DHIAA, and THIAA were applied to New Zealand white rabbits (±3-3.5 kg) in a single intravenous and oral dose. The most important pharmacokinetic parameters (C(max), t(max), half life, clearance, and AUC(0-∞)) and the absolute bioavailability were determined for each class of hop acid. The results from the in vitro Caco-2 study of IAA, DHIAA, and THIAA, showed a higher membrane permeability for IAA and THIAA, both in absorptive (P(appAB) range 1.6-5.6 × 10(-6) cm s(-1)) and secretive directions (P(appBA) range 5.7-16.3 × 10(-6) cm s(-1)), when compared to DHIAA. Factors limiting transport of DHIAA could include phase II metabolism. After oral and i.v. dosing to New Zealand white rabbits, the absolute bioavailability for IAA was determined to be 13.0%. The reduced derivatives reached higher bioavailabilities with 28.0% for DHIAA and 23.0% for THIAA. The area under curve AUC(0-∞) upon oral gavage for DHIAA and THIAA was 70.7 ± 48.4 μg h ml(-1) and 57.4 ± 9.0 μg h ml(-1), respectively, while that for IAA was 10.6 ± 5.3 μg h ml(-1). Phase I metabolism was indicated as the main factor limiting the bioavailability of IAA. Bioavailability of DHIAA is mostly influenced by phase-II metabolism as shown by enzymatic hydrolysis of plasma samples upon administration of DHIAA.

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Section: Discussionmentioning

confidence: 99%

Bioavailability of hop-derived iso-α-acids and reduced derivatives

et al. 2011

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“…Multiple studies have demonstrated that the aging of beer induces a decrease of the amounts of trans-iso-a-acids (3), whereas the corresponding cis-iso-a-acids (2) seem to be comparatively stable. [8,[10][11][12][13][14][15][16] Although numerous publications have proposed chemical structures of putative degradation products of isoa-acids obtained from model experiments, [17][18][19][20] most of these studies have been performed under rather artificial conditions, for example, iso-a-acids were degraded at highly alkaline pH values or in the presence of hydrogen peroxide. Consequently, the presence of a majority of these compounds could not been unambiguously verified in authentic beer samples.…”

Section: Introductionmentioning

confidence: 99%

Structures of Storage‐Induced Transformation Products of the Beer’s Bitter Principles, Revealed by Sophisticated NMR Spectroscopic and LC–MS Techniques

Intelmann

Kummerlöwe

Haseleu

et al. 2009

Chemistry A European J

108

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Besides undesirable changes in the attractive aroma, a significant decrease in the intensity of the bitterness as well as a change of the taste into a lingering, harsh bitterness has long been known as a shelf-life limiting factor of beer. Multiple studies have demonstrated that the aging of beer induces a decrease of the total amount of cis- and trans-iso-alpha-acids, the well-known bitter principles of beer. Although the trans-iso-alpha-acids exclusively, not the cis-iso-alpha-acids, were found to be degraded upon storage of beer, the key transformation products formed exclusively from the trans isomers in beer are not known. In the present study, suitable model experiments followed by LC-MS/MS and sophisticated NMR spectroscopic experiments, including the measurement of residual dipolar couplings (RDCs) in gel-based alignment media as well as a novel broadband and B(1)-field-compensated incredible natural abundance double-quantum transfer experiment (INADEQUATE) pulse sequence, enabled the identification of a series of previously unknown trans-specific iso-alpha-acid transformation products, namely, tricyclocohumol, tricyclocohumene, isotricyclocohumene, tetracyclocohumol, and epitetracyclocohumol, respectively. HPLC-MS/MS analysis of these compounds, which exhibit the aforementioned harsh lingering bitter taste and have threshold concentrations ranging from 5 to 70 micromol L(-1), confirmed their generation during aging of beer and, for the first time, explained the storage-induced changes of the beer's bitter taste on a molecular level.

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“…E-mail: thomas.hofmann@wzw.tum.de. Although numerous publications proposed chemical structures of putative degradation products formed from both cis-and trans-iso-R-acids such as alloisohumulones and humulinic acids (19)(20)(21), respectively, most of these compounds have been isolated from model experiments performed under rather artificial model conditions, and only a few of them have been structurally confirmed by means of NMR spectroscopy (22)(23)(24)(25)(26). The objective of the present study was, therefore, to answer the question as to whether oxidative reactions are involved in the depletion of iso-R-acids during beer aging, to isolate and identify the oxidation products formed from model systems, and to determine their amounts in authentic beer samples stored under defined conditions.…”

Section: Introductionmentioning

confidence: 99%

On the Autoxidation of Bitter-Tasting Iso-α-acids in Beer

Intelmann

Hofmann

2010

J. Agric. Food Chem.

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The iso-alpha-acids, the major contributor to bitter beer taste, is well-known to strongly degrade during beer aging. The storage of beer in brown glass bottles revealed a strong depletion of the trans-configured isomers in a highly specific manner, whereas the corresponding cis-iso-alpha-acids seemed to be hardly affected. In comparison, storage of beer in polyethylene terephthalate bottles, which are known to be permeable to oxygen, induced a drastic degradation of both isomers independent of their cis/trans configuration. To investigate the chemical transformation of iso-alpha-acids under oxidative storage conditions, suitable model experiments were performed, and the reaction products that formed were identified as previously not reported hydroperoxy- and hydroxyl-allo-iso-alpha-acids by means of one-/two-dimensional NMR and liquid chromatography-mass spectrometry experiments; for example, cis- and trans-configured hydroperoxy-alloisohumulone as well as the corresponding hydroxy-alloisohumulones were generated upon oxidation of cis- and trans-isohumulone independent of their cis/trans configuration. In addition, the oxidation products formed from the various iso-alpha-acid congeners were quantitatively determined in a series of beer samples stored under defined conditions. For the first time, these data help to understand the molecular mechanism involved in the autoxidative degradation of iso-alpha-acids in beer.

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Oxidation Products of Isohumulones

Cited by 12 publications

References 11 publications

Bioavailability of hop-derived iso-α-acids and reduced derivatives

Bioavailability of hop-derived iso-α-acids and reduced derivatives

Structures of Storage‐Induced Transformation Products of the Beer’s Bitter Principles, Revealed by Sophisticated NMR Spectroscopic and LC–MS Techniques

On the Autoxidation of Bitter-Tasting Iso-α-acids in Beer

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