Compounds In Model Systems Research Articles

Cis-Trans Isomerization of Unsaturated Fatty Acid Methyl Ester by Natural Sulfur Compounds in Model Systems.

Growing evidence indicates that the intake of trans fatty acids (TFAs) increases the risk of numerous diseases, such as cardiovascular diseases. Recently, our group found that certain natural sulfur compounds (allyl isothiocyanate [AITC] and diallyl disulfide [DADS]) promote cis to trans isomerization of fatty acid esters during heat treatment. However, little information is available on the fatty acid isomerization with them. In this study, we investigated the effects of oxygen and α-tocopherol (antioxidant) on isomerization of oleic acid (18:1) methyl ester (OA-ME) in the presence of AITC and DADS. Furthermore, the effect of the simultaneous use of AITC and DADS was evaluated. Our results indicate that oxygen enhances the AITC-induced trans isomerization, and DADS was found to promote trans isomerization but inhibit AITC-induced trans isomerization during heating. Both AITC- and DADS-induced trans isomerization were inhibited by α-tocopherol. These results indicate that the trans isomerization of fatty acids induced by sulfur compounds can be controlled by devising a cooking process and the food ingredients used together.

Investigation of molecular changes in wine during storage in refrigerated cabinets

Investigation of molecular changes in wine during storage in refrigerated cabinets

Formation of furanoic compounds in model systems with saccharides, amino acids, and fatty acids, analyzed with headspace-solid phase micro-extraction-gas chromatography–tandem mass spectrometry

Furan and furan derivatives are processing contaminants found in thermally processed food, such as coffee or canned products. For the determination of furan and ten derivatives, a sensitive headspace-solid phase micro-extraction-gas chromatography–tandem mass spectrometry method with stable isotope dilution analysis was developed. Different precursors such as saccharides, saccharide/amino acid mixtures, polyunsaturated fatty acids (PUFA), and oils were heat processed to investigate the formation of furanoic compounds via Maillard reaction and lipid oxidation. Therefore, a low moister (silica gel with 10% water content) and an aqueous (phosphate buffer, pH 4.5, 7, and 9) model system were chosen to study the effect of water content and pH value on the formation process. The formation of different furan derivatives could be attributed to distinct precursors; furfuryl alcohol was highly formed from 1,4-linked disaccharides, whereas PUFA formed the highest amounts of 2-ethylfuran and 2-pentylfuran.

Investigations on the effect of broccoli and wine sulphur compounds on glyoxal scavenging under simulated physiological conditions

Abstract This study aimed to investigate the glyoxal (GO) scavenging effect of broccoli and wine sulphur compounds in model systems under physiological conditions. The model systems composed of GO and different sulphur compounds both in pure forms and food extracts were subjected to simulated physiological conditions (37 °C & 7.4 pH, 2 h). The results revealed that some of these sulphur sources could scavenging GO under these conditions. From the pure sulphur compounds tested, potassium metabisulphite and cysteine was found as the most effective. Wine scavenged 18.01 ± 2.83% of GO (10 µmole) whereas potassium metabisulphite addition (7 µmole) to wine caused additional 20.81% scavenge. In addition, the results indicated that 11.70 ± 7.07% and 54.48 ± 6.38% of GO was scavenged by bioaccessible raw and steamed broccoli, respectively. High-resolution mass spectrometry scan analysis confirmed that it was attributed to the addition of GO to both amino acids and sulforaphane (SF)-amino acid adducts under physiological conditions.

High-intensity ultrasound production of Maillard reaction flavor compounds in a cysteine–xylose model system

Application of high intensity ultrasound has shown potential in the production of Maillard reaction odor-active flavor compounds in model systems. The impact of initial pH, sonication duration, and ultrasound intensity on the production of Maillard reaction products (MRPs) by ultrasound processing in a cysteine–xylose model system were evaluated using Response Surface Methodology (RSM) with a modified mathematical model. Generation of selected MRPs, 2-methylthiophene and tetramethyl pyrazine, was optimal at an initial pH of 6.00, accompanied with 78.1min of processing at an ultrasound intensity of 19.8Wcm−2. However, identification of volatiles using gas chromatography–mass spectrometry (GC/MS) revealed that ultrasound-assisted Maillard reactions generated fewer sulfur-containing volatile flavor compounds as compared to conventional heat treatment of the model system. Likely reasons for this difference in flavor profile include the expulsion of H2S due to ultrasonic degassing and inefficient transmission of ultrasonic energy.

Simultaneous Analysis of Acrylamide and Its Key Precursors, Intermediates, and Products in Model Systems by Liquid Chromatography–Triple Quadrupole Mass Spectrometry

A new analytical setup allowing the simultaneous analysis of precursors, intermediates and products in Maillard reaction model systems was developed to investigate the formation and mitigation kinetics of acrylamide. It was based on high-performance liquid chromatography combined with electrospray ionization triple quadrupole tandem mass spectrometry (HPLC-MS/MS). Chromatography and mass spectrometry conditions were optimized to permit simultaneous monitoring of compounds relevant to acrylamide, such as asparagine, glucose, glycine, N-(1-deoxy-D-fructos-1-yl)-glycine (DFG), N-(1-deoxy-D-fructos-1-yl)-asparagine (DFA), and four reaction products between acrylamide and glycine. A fairly good separation was achieved on a Venusil MP-C18 column using an isocratic eluent of 0.5% formic acid in water at a flow rate of 0.4 mL/min. Triple quadrupole mass spectrometry in multiple reaction monitoring mode (MRM) was applied to obtain good sensitivity. All of the ten key reaction compounds were separated and determined in a single run within 15 min. High correlation coefficients (r > 0.99) of the ten analytes were obtained in their respective linear ranges. The method was capable to accurately quantify the ten key compounds in model systems during heating. The results showed that acrylamide formed in Maillard reaction could be reduced by reacting directly with glycine, and acrylamide concentration constantly decreased by about 60% within the 180 min heating at 150 °C when glycine was equal to asparagine and glucose in molecular concentration in model systems. This method helps achieve reduction in both time and labor of analysis of a large number of samples.

Influence of chemical composition of polysaccharides on aroma retention

The aim of this paper was to link physico-chemical characteristics of both xanthan and guar gums with the behaviour of aroma compounds in model systems. The chemical compositions of guar gums and xanthan gums were determined from several commercial samples. The guar samples differed mainly in their mannose/galactose (M/G) ratio, which varied from 1.23 to 1.83. The xanthan samples showed a large range of molecular weights, protein and acetate contents as well as pyruvate groups content. The impact of these variations on aroma retention was determined by measuring the partition coefficient of ethyl butanoate, ethyl hexanoate, ethyl octanoate and ethyl decanoate in polysaccharide solutions prepared at 0.1% (w/w). For guar samples, results clearly indicated that the M/G ratio could play a critical role in retention of ethyl hexanoate whatever the molecular weight of guar samples. Indeed, a low M/G ratio, i.e. a high density of galactose residues, induced a release of this non-polar compound. A competition between galactose residues and ethyl hexanoate to bind water molecules could explain this salting-out effect. On the contrary, the high retention of ethyl decanoate was clearly linked to the molecular weight of guar samples involving hydrophobic interactions with the macromolecules. In xanthan solutions, the intrinsic proteins could participate in the retention of ethyl hexanoate and ethyl decanoate while the different molecular weights of the polysaccharide samples seemed not to affect their retention. The different levels of acetate groups had apparently only an influence on ethyl hexanoate behaviour.

Thyroid hormone receptor isoform selectivity of thyroid hormone disrupting compounds quantified with an in vitro reporter gene assay

Some compounds, including brominated diphenyl ethers (BDEs), can interfere with thyroid hormone (TH) receptor (TR)-mediated TH-signalling. In this study, the TR isoform selectivity of some TH disrupting compounds was investigated with TRα/β specific reporter gene assays. For this purpose, the effects of compounds on 3,3′,5-triiodothyronine (T 3)-induced TRα- or TRβ-activation were tested in green monkey kidney fibroblast (CV-1) cells transiently transfected with Xenopus TRs and a luciferase reporter gene. The T 3-like BDE-OH and diiodobiphenyl (DIB) increased T 3-induced TRα-activation, but not T 3-induced TRβ-activation. BDE28 (100 nM) did not act via TRα, but almost tripled T 3-induced TRβ-activation relative to T 3 at its EC 50. BDE206 (100 nM) was antagonistic on both TRs with a maximum repression −54% relative to T 3 at its EC 50. Contrary to previous results obtained with the T-screen, HBCD was inactive. The present study illustrates the importance of testing potential TH disrupting compounds in model systems that enable independent characterization of effects on both T 3-induced TRs.

Headspace concentration of selected dry-cured aroma compounds in model systems as affected by curing agents

The effect of curing agents (sodium chloride, nitrate, nitrite, glucose, and ascorbic acid) on the headspace concentration of six volatile compounds (2-methyl-butanal, 3-methyl-butanal, 2-pentanone, hexanal, methional, and octanal) has been studied. These volatile compounds were selected based on their presence and contribution to the flavour of typical Spanish dry-cured meat products. The release of volatile compounds to the headspace has been studied by using solid-phase microextraction (SPME) and gas chromatography analysis. The main effect was produced by sodium chloride, because it produced a salting-out effect on all the volatile compounds studied. Furthermore, the presence of nitrite, nitrate, and ascorbic acid in the solution also produced an increase in the headspace concentration of the volatile compounds while glucose decreased the headspace concentration of octanal and hexanal. The changes in the relative proportions of volatile compounds due to the effect of curing agents should be taken into account as they may change the flavour perception of dry-cured meat products.

Interaction of Soluble Peptides and Proteins from Skeletal Muscle with Volatile Compounds in Model Systems As Affected by Curing Agents

The effect of curing agents (salt, glucose, nitrate, nitrite, and ascorbic acid) on the binding of skeletal peptides (carnosine and anserine) and a sarcoplasmic protein (myoglobin) with key flavor compounds (hexanal, octanal, 2-pentanone, 2-methylbutanal, and 3-methylbutanal) has been studied by solid-phase microextraction (SPME). Curing agents had an effect on the interaction process between carnosine and volatile compounds, which was higher than the interactions observed with anserine and myoglobin. Sodium chloride decreased the interaction of volatiles with carnosine except for octanal, which was increased, and 2-pentanone, which was unaltered. Ascorbic acid exerted the highest effect by decreasing the interaction of carnosine with all of the volatile compounds except for octanal and 2-pentanone. The interaction with anserine was affected by sodium chloride, nitrate, and nitrite, producing a decrease in the interaction with hexanal, octanal, and methional. Finally, sodium chloride, glucose, and nitrite increased the interaction of myoglobin with hexanal, octanal, and methional. The effect of simulated stages of the curing process on the binding was also studied. A combined effect of the curing agents resulted in a change in the relative proportions of volatile compounds that can lead to different flavor perceptions of dry-cured meat products.

Simultaneous analysis of phytohormones, phytotoxins, and volatile organic compounds in plants.

Phytohormones regulate the protective responses of plants against both biotic and abiotic stresses by means of synergistic or antagonistic actions referred to as signaling crosstalk. A bottleneck in crosstalk research is the quantification of numerous interacting phytohormones and regulators. The chemical analysis of salicylic acid, jasmonic acid, indole-3-acetic acid, and abscisic acid is typically achieved by using separate and complex methodologies. Moreover, pathogen-produced phytohormone mimics, such as the phytotoxin coronatine (COR), have not been directly quantified in plant tissues. We address these problems by using a simple preparation and a GC-MS-based metabolic profiling approach. Plant tissue is extracted in aqueous 1-propanol and mixed with dichloromethane. Carboxylic acids present in the organic layer are methylated by using trimethylsilyldiazomethane; analytes are volatilized under heat, collected on a polymeric absorbent, and eluted with solvent into a sample vial. Analytes are separated by using gas chromatography and quantified by using chemical-ionization mass spectrometry that produces predominantly [M+H]+ parent ions. We use this technique to examine levels of COR, phytohormones, and volatile organic compounds in model systems, including Arabidopsis thaliana during infection with Pseudomonas syringae pv. tomato DC3000, corn (Zea mays) under herbivory by corn earworm (Helicoverpa zea), tobacco (Nicotiana tabacum) after mechanical damage, and tomato (Lycopersicon esculentum) during drought stress. Numerous complex changes induced by pathogen infection, including the accumulation of COR, salicylic acid, jasmonic acid, indole-3-acetic acid, and abscisic acid illustrate the potential and simplicity of this approach in quantifying signaling crosstalk interactions that occur at the level of synthesis and accumulation.

Nitration and inactivation of cytochrome P450BM‐3 by peroxynitrite

Peroxynitrite (PN) is likely to be generated in vivo from nitric oxide and superoxide. We have previously shown that prostacyclin synthase, a heme-thiolate enzyme essential for regulation of vascular tone, is nitrated and inactivated by submicromolar concentrations of PN [Zou, M.-H. & Ullrich, V. (1996) FEBS Lett. 382, 101-104] and we have studied the effect of heme proteins on the PN-mediated nitration of phenolic compounds in model systems [Mehl, M., Daiber, A. & Ullrich, V. (1999) Nitric Oxide: Biol. Chem. 2, 259-269]. In the present work we show that bolus additions of PN or PN-generating systems, such as SIN-1, can induce the nitration of P450BM-3 (wild-type and F87Y variant), for which we suggest an autocatalytic mechanism. HPLC and MS-analysis revealed that the wild-type protein is selectively nitrated at Y334, which was found at the entrance of a water channel connected to the active site iron center. In the F87Y variant, Y87, which is directly located at the active site, was nitrated in addition to Y334. According to Western blots stained with a nitrotyrosine antibody, this nitration started at 0.5 microM of PN and was half-maximal between 100 and 150 microM of PN. Furthermore, PN caused inactivation of the P450BM-3 monooxygenase as well as the reductase activity with an IC50 value of 2-3 microM. As two thiol residues/protein molecule were oxidized by PN and the inactivation was prevented by GSH or dithiothreitol, but not by uric acid (a powerful inhibitor of the nitration), our data strongly indicate that the inactivation is due to thiol oxidation at the reductase domain rather then to nitration of Y residues. Stopped-flow data presented here support our previous hypothesis that ferryl-species are involved as intermediates during the reactions of P450 enzymes with PN.

Identification and quantification of aminophospholipid-linked Maillard compounds in model systems and egg yolk products.

While the Maillard reaction of free amino acids and proteins is a well-established process, no defined structures from the nonenzymatic browning of aminophospholipids in foodstuffs have been described so far. Phosphatidylethanolamine (PE)-linked glucosylamines (Schiff-PE), Amadori products (Amadori-PE), 5-hydroxymethylpyrrole-2-carbaldehydes (Pyrrole-PE), and carboxymethyl (CM-PE) as well as carboxyethyl (CE-PE) derivatives were detected and quantified by liquid chromatography- electrospray mass spectrometry (LC-(ESI)MS). Model incubations of soy-PE and D-glucose were employed to firmly establish the LC-(ESI)MS procedure. Analyses of spray-dried egg yolk powders and lecithin products derived therefrom show one-fourth of the native D-glucose content of egg yolk to be transformed to Amadori-PE, corresponding to a PE derivatization quota of 11-15.5 mol %. Schiff-PE and Pyrrole-PE were present only in low amounts, no CM-PE and CE-PE could be identified in any of the investigated samples. The high glycation rate of egg yolk PE will influence the emulsifying properties and perhaps even the oxidation resistance of the respective products.

Specific Inhibition of Photobacterium phosphoreum Extends the Shelf Life of Modified-Atmosphere-Packed Cod Fillets

Inhibition of the specific spoilage organism, Photobacterium phosphoreum, was studied in model substrates and in modified-atmosphere-packed cod fillets. The objective was to determine how inhibition of this organism influenced spoilage. The spoilage reactions limiting shelf life were studied rather than the development of a new product. In naturally contaminated modified-atmosphere-packed cod fillets, 500 ppm Na2CaEDTA reduced the growth rate of P. phosphoreum by 40% and shelf life was increased proportionally by 40%, from 15 to 17 days to 21 to 23 days at 0°C. In aerobically stored cod fillets other microorganisms were responsible for spoilage and Na2CaEDTA had no effect on shelf life. The extension of the shelf life of modified-atmosphere-packed cod therefore was a result of the reduced growth of P. phosphoreum and no other microbial or nonmicrobial spoilage reactions limited shelf life. These results confirmed P. phosphoreum as the specific spoilage organism in modified-atmosphere-packed cod and showed the organism to have an extensive spoilage domain. Consequently, any preservation procedure able to reduce growth of P. phosphoreum is likely to extend shelf life of packed cod. However, the effect of different inhibitory compounds in model systems as well as results from packed cod indicated the need to include product studies in the screening of antimicrobials and in the development of preservation procedures.

Perspectives on mycotoxin decontamination procedures.

Unquestionably, prevention is the best method for controlling mycotoxin contamination. Should the contamination occur, however, the hazard associated with the toxin must be removed if the product is to be used for food or feed purposes. Decontamination procedures currently used are based on (a) physical, chemical, or biological removal, or (c) physical or chemical inactivation. Ammoniation of corn, peanuts, cottonseed, and meals to alter the toxic and carcinogenic effects of aflatoxin contamination has been the subject of intense research effort by scientists in various government agencies and universities worldwide. Engineers have devised workable systems of treatment of whole seeds, kernels, or meals; chemists have identified and characterized products formed from the reaction of aflatoxin B1 with ammonia with and without a meal matrix; biochemists have studied the biological effects of these compounds in model systems; and nutritionists have studied animal responses to rations containing ammoniated or non-ammoniated components. This review describes these studies as well as other potentially useful decontamination processes. The results of aflatoxin/ammonia decontamination research demonstrate the efficiency and safety of ammoniation as a practical solution to aflatoxin detoxification in foods and animal feeds.

Review of the Decontamination of Aflatoxins by Ammoniation: Current Status and Regulation

Ammoniation of corn, peanuts, cottonseed, and meals to alter the toxic and carcinogenic effects of aflatoxin contamination has been the subject of intense research effort by scientists in various government agencies and universities, both in the United States and abroad. Results of these studies have been well documented over the last 20 years. Engineers have devised workable systems of treatment of whole seeds, kernels, or meals; chemists have identified and characterized products formed from the reaction of aflatoxin B1 with ammonia with and without a meal matrix; biochemists have studied the biological effects of these compounds in model systems; and nutritionists have studied animal responses to rations containing ammoniated or non-ammoniated components. This review describes these studies. Results demonstrate overwhelming support for the efficacy and safety of ammoniation as a practical solution to aflatoxin detoxification in animal feeds.

Retro‐aldol degradations of unsaturated aldehydes: Role in the formation ofc4‐heptenal fromt2,c6‐nonadienal in fish, oyster and other flavors

AbstractAlterations of cucumber‐, melon‐like notes in aromas and flavors caused by retro‐aldol degradations oft2,c6‐nonadienal were confirmed using gas chromatographic measurements of volatile compounds in model systems. The data indicated that 3‐hydroxy‐c6‐nonenal was formed first by the addition of water to the alpha/beta double bond oft2,c6‐nonadienal, and this was followed by a retro‐aldol condensation of 3‐hydroxy‐c6‐nonenal to yieldc4‐heptenal and ethanal. Compared to the reaction rate in aqueous systems at neutral pH, formation ofc4‐heptenal was enhanced substantially at alkaline pH, but was greatly diminished at acidic pH values. Heating (to 90 C) of aqueous model systems oft2,c6‐nonadienal held at neutral pH also enhanced the rate of formation ofc4‐heptenal substantially compared to that at ambient temperature (21 C). Rates of formation ofc4‐heptenal in aqueous model systems held under air or nitrogen atmospheres were similar.c4‐Heptenal was not formed whent2,c6‐nonadienal was held at 21 C for 96 hr under air or nitrogen in nonaqueous commercial corn oil.

Isolation of flavor compounds in model systems by countercurrent continuous dialysis

Isolation of flavor compounds in model systems by countercurrent continuous dialysis

Dispersed liquid phase referencing of NMR spectra

It is shown that suitable liquids, when dispersed through samples with which they are immiscible, can be used as otherwise uncontained references for the measurement of chemical shifts. These shifts are independent of the volume magnetic susceptibility of the components of the heterogeneous sample. The 1H chemical shifts for various compounds in model systems have been measured using both the traditional external reference and the new dispersed methods and the differences between these are explained.

Radiolysis of iodine compounds in model systems of PWR

The paper gives a survey of experimental results concerning the chemical behaviour and radiation chemical reactions of inorganic iodine compounds in a model WWER coolant, the reactions of iodine with methane taking place in the gas phase on irradiation and the radiolysis of inorganic iodine compounds as well as of CH 3I in the spray solutions.