Zusammenfassung Das Modellsystem Cystein/Methionin/Furfural lieferte unter Röstbedingungen ein komplexes Reaktionsgemisch, das sich mittels Adsorptionschromatographie auf Kieselgel und Capillar-GC in ca. 130 Komponenten auftrennen ließ, von denen 85 capillargaschromatographisch-massenspektrometrisch charakterisiert wurden. Furfural und die aus Cystein und Methionin resultierenden reaktiven Abbauprodukte H2S, Cysteamin und Methylmercaptan sind wichtige Precursor für heterocyclische Flavorkomponenten. Neben Furanen, (Furan)-aldiminen und schwefelsubstituierten Furanderivaten werden auchN-Furfurylpyrrole, Pyridine, Thiazole, Thiazoline, Thiazolidine, Thiophene sowie aliphatische Schwefelverbindungen und cyclische Methylenpolysulfide gebildet. Beim Kaffeerösten entsteht Furfural als eine der Furanhauptkomponenten und spielt bei der Genese wesentlicher Kaffeearomastoffe eine zentrale Rolle.
Gaschromatographic-mass spectrometric investigation of aroma compounds from the reaction of cysteine and methionine with furfural under roasting conditions
Summary The model-system cysteine/methionine/furfural produced under roasting conditions a complex mixture of compounds which was separated by adsorption chromatography on silica gel, according to the increasing polarity of the components, into six fractions. The fractions were investigated by capillary gas chromatography with and without mass spectrometry. Of the approx. 130 compounds detected, 85 were identified and quantified. Furfural and the reactive degradation products H2S, cysteamine and methylmercaptan, resulting from cysteine and methionine, are important precursors for heterocyclic flavor components. Besides furans, (furan)aldimines, and sulphur-substituted furan derivates, the following compounds are also formed:N-furfurylpyrroles, pyridines, thiazoles, thiazolines, thiazolidines, thiophenes, as well as aliphatic sulphur compounds and cyclic methylene polysulfides. During coffee roasting, furfural is produced as one of the major components of the furans and is essential for the formation of important coffee aroma constituents.
Poster-Präsentation beim Deutschen Lebensmittelchemikertag in Bremen (14.–16. Sept. 1988) 相似文献
Zusammenfassung Es wird eine Methode zur Bestimmung von Glyphosat und dessen Hauptmetabolit Aminomethylphosphonsäure (AMPA) in Trinkwasser beschrieben, die es erlaubt, den in der Schweiz geforderten Toleranzwert von 0,1 g/1 zu erreichen (Nachweisgrenze 0,02 g/l). Die Wasserprobe wird dabei direkt mit 9-Fluorenylmethyl-chloroformaat (FMOCCI) versetzt, um extrahierbare und gleichzeitig fluorescierende Derivate zu erhalten. Diese werden nach Ausschütteln mit einem organischen Lösungsmittelgemisch durch HPLC mit Fluorescenzdetektor bestimmt. In bisher 151 untersuchten Trinkwasserproben des Kantons Bern konnten weder Glyphosat noch AMPA nachgewiesen werden.
Determination of glyphosate herbicide and its main metabolite aminomethylphosphonic acid (AMPA) in drinking water by HPLC
Summary A method for the determination of glyphosate and its major metabolite aminomethylphosphonic acid (AMPA) is described. With a detection limit of 0.02 g/l, the method suitably fulfills the requirements of the Swiss legislation (tolerance value of 0.1 g/l water). The compounds are derivatized directly in the original water sample with 9-fluorenylmethyl chloroformate (FMOCCI) in order to obtain extractable and fluorescent derivatives. These are extracted with organic solvents and determined by HPLC using a fluorescence detector. Neither of the compounds could be detected in 151 tap water samples from the Canton of Berne.
Protein post-translational modifications (PTMs) play key roles in eukaryotes since they finely regulate numerous mechanisms used to diversify the protein functions and to modulate their signaling networks. Besides, these chemical modifications also take part in the viral hijacking of the host, and also contribute to the cellular response to viral infections. All domains of the human immunodeficiency virus type 1 (HIV-1) Gag precursor of 55-kDa (Pr55Gag), which is the central actor for viral RNA specific recruitment and genome packaging, are post-translationally modified. In this review, we summarize the current knowledge about HIV-1 Pr55Gag PTMs such as myristoylation, phosphorylation, ubiquitination, sumoylation, methylation, and ISGylation in order to figure out how these modifications affect the precursor functions and viral replication. Indeed, in HIV-1, PTMs regulate the precursor trafficking between cell compartments and its anchoring at the plasma membrane, where viral assembly occurs. Interestingly, PTMs also allow Pr55Gag to hijack the cell machinery to achieve viral budding as they drive recognition between viral proteins or cellular components such as the ESCRT machinery. Finally, we will describe and compare PTMs of several other retroviral Gag proteins to give a global overview of their role in the retroviral life cycle. 相似文献
A mathematical model and its numerical solution is presented to describe adiabatic adsorption—desorption processes in a fixed bed when the mass and heat transfer can be described by external film transfer coefficients only, which is especially interesting in the case of non-uniform, irregular particles. A new method to measure such rates is presented, based on continuous weighing of a through-circulated bed. The measured rates can be checked against the difference in humidity and temperature between the outlet and inlet air in order to minimize errors.The comparison between experimental results and calculations showed that the adsorption process in a bed of molecular sieve pellets can not be described with a constant mass transfer coefficient; the desorption process is better described although not entirely satisfactorily. In the case of a honeycomb molecular sieve, a constant mass transfer coefficient described both the adsorption and desorption processes satisfactorily. 相似文献
This study aims to determine whether indirect touch device can be used to interact with graphical objects displayed on another screen in an air traffic control (ATC) context. The introduction of such a device likely requires an adaptation of the sensory-motor system. The operator has to simultaneously perform movements on the horizontal plane while assessing them on the vertical plane. Thirty-six right-handed participants performed movement training with either constant or variable practice and with or without visual feedback of the displacement of their actions. Participants then performed a test phase without visual feedback. Performance improved in both practice conditions, but accuracy was higher with visual feedback. During the test phase, movement time was longer for those who had practiced with feedback, suggesting an element of dependency. However, this ‘cost’ of feedback did not extend to movement accuracy. Finally, participants who had received variable training performed better in the test phase, but accuracy was still unsatisfactory. We conclude that continuous visual feedback on the stylus position is necessary if tablets are to be introduced in ATC. 相似文献
Cellular signal transduction proceeds through a complex network of molecular interactions and enzymatic activities. The timing of these molecular events is critical for the propagation of a signal and the generation of a specific cellular response. To define the timing of signalling events, we introduce the combination of high-resolution confocal microscopy with the application of small-molecule inhibitors at various stages of signal transduction in T cells. Inhibitors of Src-family tyrosine kinases and actin dynamics were employed to dissect the role of the lymphocyte-specific tyrosine kinase Lck in the formation and maintenance of T cell receptor/CD3-dependent contacts. Anti-CD3epsilon-coated coverslips served as a highly defined stimulus. The kinetics of the recruitment of the yellow fluorescent protein-tagged signalling protein ZAP-70 were detected by high-resolution confocal microscopy. The analysis revealed that at 5 min after receptor engagement, Lck activity was required for maintenance of contacts. In contrast, after 20 min of receptor engagement, the contacts were Lck-independent. The relevance of the timing of inhibitor application provides a pharmacological concept for the maturation of T cell-substrate contacts. 相似文献
Hybrid MalEGVP is a bifunctional protein in vitro sinceit binds maltose as protein MalE of Escherichia coli and sinceit is dimeric and specifically binds single-stranded DNA asprotein GVP of phage M13. The oxidation rate of a unique cysteineresidue was used to compare the stabilities of GVP in its freeand hybrid forms, under conditions where MalE was either foldedor unfolded by a denaturing agent. The results showed that boththe covalent link and tertiary non-covalent interactions betweenMalE and GVP destabilized GVP in MalEGVP. To test whetherGVP had identical structures in its free and hybrid forms, mutationswere used as local conformational probes. The effects of thesemutations on the capabilities of MalEGVP to dimerizeand to bind single-stranded DNA were assayed in vitro. Theywere compatible with the effects of the same mutations on theglobal activity of free GVP in vivo and with the effects thatcould be predicted from the known data on free GVP, in particularits crystal structure. Thus, one partner of a hybrid proteincan be destabilized by the other partner while maintaining itsstructural and functional characteristics. 相似文献
The role of ozone was studied for two different configurations combining non-thermal plasma (NTP) and heterogeneous catalysis, namely the use of a gas phase plasma with subsequent exposure of the effluent to a catalyst in a packed-bed reactor (post-plasma treatment) and the placement of the catalyst directly in the discharge zone (in-plasma catalysis). Non-porous and porous alumina and silica were deployed as model catalysts. The oxidation of immobilised hydrocarbons, toluene as a volatile organic compound and CO as an inorganic pollutant were studied in both operational modes.
While conversion and selectivity of hydrocarbon oxidation in the case of catalytic post-plasma treatment can be fully explained by the catalytic decomposition of O3 on γ-Al2O3, the conversion processes for in-plasma catalysis are more complex and significant oxidation was also measured for the other three materials (-Al2O3, quartz and silica gel). It became obvious that additional synergetic effects can be utilised in the case of in-plasma catalysis due to short-lived species formed in the NTP.
The capability of porous alumina for ozone decomposition was found to be correlated with its activity for oxidation of carbon-containing agents. It could be clearly shown that the reaction product CO2 poisons the catalytic sites at the γ-Al2O3 surface. The catalytic activity for O3 decomposition can be partially re-established by NTP treatment. However, for practical purposes the additional reaction pathways provided by in-plasma catalytic processes are essential for satisfactory conversion and selectivity. 相似文献