Determination of potential migrants present in Nylon 'microwave and roasting bags' and migration into olive oil

Two groups of potential migrants were found in Nylon "microwave and roasting bags' (MRBs): volatile compounds were released at cooking temperatures and non-volatile compounds were extracted with methanol and/or water. A dynamic headspace system at 200 degrees C followed by gas chromatography (GC) coupled to mass spectrometry (MS) was used for determination of volatile compounds. Cyclopentanone (31.7 mg/bag), 2-cyclopentyl cyclopentanone (17.4 mg/bag), hexadecane (2.6 micrograms/bag), heptadecane (3.2 micrograms/bag), octadecane (3.0 micrograms/bag) and epsilon-caprolactam (5.0-35.5 mg/ bag) were the main volatile compounds present in the MRBs. High performance liquid chromatography (HPLC) and mass spectrometry were combined for identification and quantification of non-volatile compounds extracted with methanol (46.0 mg/bag). Nylon 6,6 cyclic monomer and cyclic oligomers up to the tetramer and Nylon 6 monomer and cyclic oligomers up to the octamer were identified and quantified, confirming that the plastic was made of Nylon 6,6 and Nylon 6 polymers. The same non-volatile compounds (except Nylon 6 heptamer and octamer) were found to migrate into olive oil at 175 degrees C for 1 h. A total of 0.916 mg/dm2 (19.2 mg/bag) of non-volatile compounds migrated into olive oil (41.8% of those quantified in the plastic material).     

Use of 13C nuclear magnetic resonance and gas chromatography to examine methionine catabolism by lactococci

Formation of methanethiol from methionine is widely believed to play a significant role in development of cheddar cheese flavor. However, the catabolism of methionine by cheese-related microorganisms has not been well characterized. Two independent methionine catabolic pathways are believed to be present in lactococci, one initiated by a lyase and the other initiated by an aminotransferase. To differentiate between these two pathways and to determine the possible distribution between the pathways, 13C nuclear magnetic resonance (NMR) performed with uniformly enriched [13C]methionine was utilized. The catabolism of methionine by whole cells and cell extracts of five strains of Lactococcus lactis was examined. Only the aminotransferase-initiated pathway was observed. The intermediate and major end products were determined to be 4-methylthio-2-oxobutyric acid and 2-hydroxyl-4-methylthiobutyric acid, respectively. Production of methanethiol was not observed in any of the 13C NMR studies. Gas chromatography was utilized to determine if the products of methionine catabolism in the aminotransferase pathway were precursors of methanethiol. The results suggest that the direct precursor of methanethiol is 4-methylthiol-2-oxobutyric acid. These results support the conclusion that an aminotransferase initiates the catabolism of methionine to methanethiol in lactococci.     

Evidence for S-adenosylmethionine independent catabolism of methionine in the rat

Experiments conducted with rats in vivo comparing the metabolism of methionine and S-methyl-L-cysteine and in vitro comparing methionine, S-methyl-L-cysteine and S-adenosyl-L-methionine indicate that a substantial portion of the oxidative metabolism of the methionine methyl group occurs by pathways that are independent of S-adenosylmethionine formation. Inclusion of 1.2% or 2.4% of S-methyl-L-cysteine in a diet containing 3% of L-methionine depressed the conversion of the methionine methyl and carboxyl carbons to CO2 by 39% and 28%, and 52% and 33%, respectively, for the two levels of S-methyl-L-cysteine. Inclusion of 1.65% of methionine in a diet containing 2.4% of S-methyl-L-cysteine did not affect the conversion of the methyl group of S-methylcysteine to CO2, but 3% of methionine depressed the conversion of the S-methylcysteine methyl group to CO2 to 87% of control values. Greater inhibitions were seen when these substrates were compared in a liver homogenate. In a rat liver homogenate system optimized for the conversion of the methyl group of methionine to CO2, the rate of conversion of the methyl group of S-adenosyl-L-methionine to CO2 was less than 1% of that of methionine even when the concentration of S-adenosylmethionine was saturating. Addition of saturating levels of unlabeled S-adenosymethionine to the homogenate system did not effect the rate of conversion of the methionine methyl carbon to CO2. Although S-adenosylmethionine-dependent metabolism of methionine, leading to incorporation of the methyl carbon into sarcosine and serine, could be demonstrated in liver homogenates, essentially all of the CO2 produced from the methionine methyl group was derived by a pathway or pathways independent of S-adenosylmethionine formation. Formaldehyde and formate have been tentatively identified as intermediates in catabolism of the methionine methyl group by this (these) pathway(s).     

Volatile flavor release from foods during eating

Classical analyses for volatile flavors (headspace or distillation/extract methods) give information on either the volatiles present in the air above a food before eating or the total volatile composition of the food. When foods are eaten, however, many changes take place (such as hydration/dilution with saliva, increase in surface area, etc.) that affect the release of volatiles from the food and therefore the profile of volatiles that are sensed in the nose. If we wish to study the relationship between flavor volatiles and the sensory properties of a food, it seems logical to measure the volatile profile that exists during eating. Although volatile flavor release during eating has been measured using a variety of sensory and psychophysiological analyses, only recently have instrumental methods been developed to measure the release of volatile compounds in humans as they eat. Whereas the sensory data give an overall measure of flavor perception, instrumental analyses can potentially follow the release of each and every flavor volatile and thus give a full picture of the aroma profiles generated during eating. From these instrumental measurements, a number of key factors have been identified. First, it has been shown that the volatile profile measured during eating is indeed different from the headspace profile of whole foods. Second, it is clear that the volatile profile in-mouth changes with time as the state of the food changes with chewing. Third, the volatile release from low-water foods is affected by the rate and extent of hydration in-mouth. The ability to measure aroma before, during, and after eating may lead to an understanding of the links between aroma release, interaction of volatiles with aroma sensors in the nose, and the overall perception of food flavor.     

Comparative analysis of the protein components from 5S rRNA.protein complexes of halophilic archaebacteria

The 5S RNA.protein complexes have been isolated from the 50S subunit of the halophilic archaebacteria Halobacterium cutirubrum, Halobacterium halobium, Halobacterium salinarium, Haloferax mediterranei, Haloferax volcanii and Haloarcula marismortui. The 50S subunits from most of the halophiles released a multiprotein ribonucleoprotein particle similar to that previously observed with the H. cutirubrum 5S RNA.protein complex, which contained proteins from the L5 and L18 ribosomal protein families. Ribosomes from H. marismortui, however, released an RNA.protein complex containing a single protein (L18) that is homologous to the single protein found in the eukaryotic 5S ribonucleoprotein complexes. N-terminal sequence analyses of the halophilic 5S RNA-binding proteins suggest that the L18 protein primary structure is highly conserved, with only the H. marismortui protein having a sequence difference in at least the first twenty amino acids. Although the L5 group of ribosomal proteins also shows a high conservation, it appears that the proteins may have had more freedom to diverge throughout evolution.     

Catalytic Incineration of C2H5SH and Its Mixture with CH3SH over a Pt/Al2O3 Catalyst

Catalytic incineration is one of the cost-effective technologies to solve troublesome volatile organic compounds. However, some sulfur containing volatile organic compounds, such as ethyl mercaptan, may deactivate the Pt catalyst that is commonly used in the catalytic incineration process. This paper provides information on the poisoning effect of ethyl mercaptan. The catalytic incineration of ethyl mercaptan, typically emitted from the petrochemical industry, over a Pt/Al2O3 fixed-bed catalytic reactor was studied. The effects of operating parameters including inlet temperature, space velocity, C2H5SH concentration, O2 concentration, and catalyst size were characterized. Catalytic incineration on a mixture of C2H5SH with CH3SH was also tested. The results show that the conversions of C2H5SH increase as the inlet temperature increases and the space velocity decreases. For the temperature from 200–260°C, the higher the C2H5SH concentration is, the lower its conversion. The O2 concentration has a positive effect on the conversion of C2H5SH. C2H5SH has a poisoning effect on the Pt/Al2O3 catalyst, especially at lower temperature. The existence of CH3SH has no effects on the conversion of C2H5SH.     

Identification of alloantibodies associated with an autoantibody: profile of 2 quality control programs in French blood transfusion facilities

Aroma release from a cream style dressing, consisting of a thickening agent dispersed in the water phase of an oil in water (o/w) emulsion, has been studied by a purge-and-trap (PT) and a dynamic headspace mastication (DHM) model using two representative volatile compounds, viz. diacetyl and 2-heptanone. These isolations have been carried out from three systems: the dressing, the thickening agent dispersion and the o/w type of emulsion after adding different volumes of artificial saliva. Dilution of the samples with artificial saliva influences the amounts released for diacetyl and 2-heptanone differently: diacetyl decreases upon dilution of the thickening agent dispersion, emulsion and dressing. However, the amount of released 2-heptanone decreased only in the case of the thickening agent dispersion. These differences are caused by the distribution of diacetyl and 2-heptanone between the water and the oil phases. The distribution is not so important, when the DHM model is used for the release from dressings. The viscosity of the mixture of dressing and artificial saliva then plays an essential role. In general, the viscosity is considered to suppress the release of flavour. However, it has been found that the amount of volatile compounds released from the more viscous dressing was greater than from the emulsion. Most probably, the DHM model creates a large surface area by adhesion of the dressing on the wall of the sampling flask and the plunger head. This result suggests that the DHM equipment, which mimics the mouth movement, might be used to predict the real release of flavour in the mouth more precisely than other mouth models.     

Measurement of polyene antibiotic-mediated erythrocyte damage by release of hemoglobin and radioactive chromium

Polyene antifungal antibiotics produce various degrees of membrane damage in sheep erythrocytes in vitro. Mediocidin, filipin, amphotericin B, and candicidin were found to result in greater damage than nystatin, pimaricin, and amphotericin B methyl ester. The degree of sensitivity of the cells varied by 100-fold for mediocidin verus amphotericin B methyl ester as measured by curves of hemoglobin release versus drug concentration. In erythrocytes prelabeled with radioactive chromium, release of the isotope through polyene-damaged cell membranes was found to occur at lower drug concentrations than measurable hemoglobin release, and the percentage of isotope released at the highest drug dose was consistently greater than the percentage of hemoglobin released. Thus, the isotope assay is a more sensitive indicator of polyene-induced membrane damage in the test system. These significant differences in release of molecules through polyene-induced membrane lesions indicate the complex nature of the binding and further interactions of this class of drugs with the plasma membrane.     

The determination of methionine in proteins by gas-liquid chromatography

Intact methionine residues in proteins were rapidly and precisely determined by measuring methyl thiocyanate released during the reaction with CNBr and separated by g.l.c. Conditions for the reaction and for chromatography on columns of Porapak P-S are described. The recovery of methyl thiocyanate from several methionine derivatives and analogues were examined. Carbamoylmethionine was adopted as a stable primary standard and ethyl thiocyanate as internal standard. The measured methionine content of several isolated proteins was close to the theoretical value indicated by previous work and the results for these and a range of food proteins agreed well with results obtained by ion-exchange chromatography after performic acid oxidation. Since CNBr does not react with methionine sulphoxide and a preliminary hydrolysis is not required, the method discriminates between methionine and any methionine sulphoxide that may be present. It could be useful in studies on the nutritional availability of methionine in processed foods.     

Disturbances of affective prosody in patients with schizophrenia; a cross sectional study

The solutions of nine alpha, omega-bis(3-alkyl(aryl)-4,5-dihydro-1H-1,2,4-triazol-5-on-4-yl) alkanes were titrated with tetrabutylammoniumhydroxide (TBAH) in methanol, using potentiometric methods. The half neutralization potentials values were found for all cases. Potentiometric titration curves of compounds in methanol with 0.03 M TBAH are similar to those of weak acids obtained in aqueous media with strong bases. Methanol is found to be a suitable medium for the weakly acidic compounds titrated since they are poorly dissolved in other organic solvents. A comparison among the compounds having the same alkyl chains between the two ring systems has shown that basicity increases and acidity decreases as the size of alkyl chains increases. However, the compound with a substituted phenyl group was found to be the most acidic one among the examined compounds indicating that phenyl group donates ring electrons less effectively to the system. This can be attributed to the stability of the benzene ring.     

Histamine H3-receptor-mediated inhibition of calcitonin gene-related peptide release from cardiac C fibers. A regulatory negative-feedback loop

Antidromic stimulation of cardiac sensory C fibers releases calcitonin gene-related peptide (CGRP), which increases heart rate, contractility, and coronary flow. C-fiber endings are closely associated with mast cells, and CGRP may release mast-cell histamine. Because prejunctional histamine H3-receptors inhibit transmitter release from autonomic nerves, we tested the hypothesis that H3-receptors modulate CGRP release in the heart. CGRP released by bradykinin in the electrically paced guinea pig left atrium and by capsaicin in the spontaneously beating isolated heart caused marked positive inotropic and chronotropic effects, respectively. Capsaicin significantly enhanced the overflow of CGRP (fivefold) and histamine (twofold) into the coronary effluent. All of these effects were prevented by prior chemical destruction of C fibers in vivo. The H3-receptor agonist imetit attenuated the inotropic response to bradykinin by 50%. Imetit also decreased the capsaicin-induced tachycardia and the increase in CGRP overflow by 50%. Imetit, however, did not modify the response to exogenous CGRP. The effects of imetit were blocked by the H3-receptor antagonist thioperamide. Notably, thioperamide by itself potentiated the capsaicin-evoked increases in heart rate and CGRP overflow (by 25% and 50%, respectively). Thus, our findings identify a negative-feedback loop, whereby CGRP releases histamine from cardiac mast cells and histamine in turn inhibits CGRP releases by activating H3-receptors on C-fiber terminals. Because CGRP release is augmented in pathophysiological conditions, such as septic shock, heart failure, and acute myocardial infarction, modulation of CGRP release may be clinically relevant.     

Multistaged Anaerobic Sludge Digestion Processes

Two multistaged anaerobic digestion systems, a four-stage thermophilic anaerobic digestion (4TAD), all at 55°C, and a four-stage anaerobic digestion with a tapered temperature configuration (4ADT) at 55, 49, 43, and 37°C, respectively, were studied to evaluate their solids, volatile organic sulfur compounds, and indicator organism (E. coli and fecal coliform) reduction potentials. The 4TAD system removed significantly more volatile solids from sludges than the 4ADT system (6%). However, the dewatered biosolids cakes from the 4ADT system generated fewer organic sulfur compounds than those from the 4TAD system. Both multistage systems showed better digestion efficiencies than single-stage mesophilic or single-stage thermophilic anaerobic digesters at the same overall retention time. However, the lowest organic sulfur compounds were observed from the single mesophilic system. Both multistage anaerobic digestion systems failed to dramatically remove DNA of the indicator organism, E. coli, quantified by real time polymerase chain reaction, even though the indicator organism densities measured by standard culturing methods satisfied EPA Class A biosolids requirements.     

Effects of chronic ethanol exposure on oxidation and NMDA-stimulated neuronal death in primary cortical neuronal cultures

Two enzymes of detoxification were studied in blood samples from 27 patients with ulcerative colitis (UC) and 18 controls to determine whether there is an abnormality in sulfur metabolism in UC. Thiol methyltransferase (TMT) activity was measured in erythrocyte membranes as the extent of conversion of 2-mercaptoethanol to S-methyl-2-mercaptoethanol with [3H]methyl-S-adenosyl methionine as methyl donor. Phenol sulfotransferase (PST) activity was measured in platelet homogenates as the extent of sulfation of p-nitrophenol with 3-phosphoadenosine 5-phospho[35S]sulfate (PAPS) as sulfate donor. TMT activity was significantly higher in UC patients (27.0 vs 17.1 nmol/mg protein/hr; P < 0.005). No difference in PST activity was found. We conclude that TMT may be up-regulated in UC to detoxify excess hydrogen sulfide exposed to the peripheral blood compartment. This may arise from either increased luminal sulfide production or reduced colonic detoxification.     

Applications of the PM3 semi-empirical method to the study of triethylenediamine

Charcoal filters impregnated with triethylenediamine (TEDA) are known to be efficient for the collection of volatile methyl iodide, which may be released under a hypothetical loss-of-coolant accident in a nuclear generating station. The structure and thermodynamic stability of the products of the TEDA-methyl iodide reaction have thus been studied using semi-empirical techniques. The reaction of TEDA with two molecules of methyl iodide leads to a quaternization reaction at each of the nitrogens. Moreover, it is shown that substitution of the hydrogens on TEDA with electron-donating groups can lead to enhanced stability of the quaternary ammonium reaction products. The semi-empirical method PM3 (Parametric Method 3) was used as the basis for all calculations. Molecular systems and simulations were constructed using HyperChem 4.5 for Silicon Graphics workstations. Enthalpy determination and geometry optimization were some of the calculations performed on a system.     

Field Measurements and Modeling of Two-Stage Biofilter that Treats Odorous Sulfur Air Emissions

Because the presence of hydrogen sulfide (H2S) and methyl mercaptan (MeSH) inhibits the removal of some organic reduced sulfur compounds (e.g., dimethyl sulfide, Me2S) in biofilters, a two-stage biofilter may be an appropriate method to treat a mixture of reduced sulfur compounds. This work studied the treatment of odorous air emissions [a mixture of H2S, MeSH, Me2S, and dimethyl disulfide (Me2S2)] using a two-stage biofilter. H2S had the highest overall removal efficiency (96%) followed by MeSH and Me2S (90 and 91% removal, respectively) and Me2S2 (81%). Most of the removal of H2S, MeSH, and Me2S2 occurred in the primary biofilter (72% H2S, 66% MeSH, and 52% Me2S2), while most of the Me2S removal occurred in the secondary biofilter (64% Me2S). A dynamic model that describes biofiltration was calibrated and validated to H2S and MeSH field data. This is the first time a model was evaluated with organic odor-causing sulfur compound data obtained from a biofilter packed with compost and wood chips. Model simulations showed that H2S removal in a lava rock packed biofilter would be better than in a similar biofilter packed with compost and wood chips.     

Insulinotropic action of the D-glucosyl and 3-O-methyl-D-glucosyl monomethyl esters of succinic acid

Succinic acid methyl esters are currently under investigation as potential insulinotropic tools in animal models of non-insulin-dependent diabetes mellitus. The in vivo administration of these esters may result in the undesirable generation of methanol through their intracellular hydrolysis. As a first attempt to circumvert this drawback, we have now investigated whether the esterification of the carboxylic group of succinic acid monomethyl ester by D-glucose or 3-O-methyl-D-glucose affects its insulin-otropic action. Both the 6-O-D-glucosyl and 6-O-(3-O-methyl)-D-glucosyl esters were found to stimulate insulin release in pancreatic islets and the isolated perfused pancreas. The 6-O-D-glucosyl ester also stimulated insulin release after intravenous administration to anaesthetized rats. These findings suggest that the undersirable generation of methanol from the methyl esters of succinic acid could eventually be avoided by using other esters of this dicarboxylic acid, whilst keeping the benefit of their insulinotropic action.     

Utilization of inorganic sulfur sources by Staphylococcus aureus strains

Staphylococcus aureus strains of different host-adapted variants (Meyer 1966) have been tested for their ability to use inorganic sulfur sources. All the 25 strains tested were able to utilize sodium sulfide as sulfur source in a medium similar to that described by Kloos and Pattee (1965). Using S. aureus strain 116/74 grown in a medium containing Na2-35S as the only sulfur source we studied incorporation and insertion of inorganic sulfide into sulfur containing amino acids. In disintegrated and fractionated cellular material we could find 35S labelled homocystine and methionine as major compounds, and cystine, cysteic acid, homocysteic acid, and beta-sulphopyruvate as minor compounds. The occurrence of homocystine and the sulfonic acids in bacterial proteins is rather uncommon.     

The structure of the C-terminal domain of methionine synthase: presenting S-adenosylmethionine for reductive methylation of B12

BACKGROUND: In both mammalian and microbial species, B12-dependent methionine synthase catalyzes methyl transfer from methyltetrahydrofolate (CH3-H4folate) to homocysteine. The B12 (cobalamin) cofactor plays an essential role in this reaction, accepting the methyl group from CH3-H4folate to form methylcob(III)alamin and in turn donating the methyl group to homocysteine to generate methionine and cob(I)alamin. Occasionally the highly reactive cob(I)alamin intermediate is oxidized to the catalytically inactive cob(II)alamin form. Reactivation to sustain enzyme activity is achieved by a reductive methylation, requiring S-adenosylmethionine (AdoMet) as the methyl donor and, in Esherichia coli, flavodoxin as an electron donor. The intact system is controlled and organized so that AdoMet, rather than methyltetrahydrofolate, is the methyl donor in the reactivation reaction. AdoMet is not wasted as a methyl donor in the catalytic cycle in which methionine is synthesized from homocysteine. The structures of the AdoMet binding site and the cobalamin-binding domains (previously determined) provide a starting point for understanding the methyl transfer reactions of methionine synthase. RESULTS: We report the crystal structure of the 38 kDa C-terminal fragment of E.coli methionine synthase that comprises the AdoMet-binding site and is essential for reactivation. The structure, which includes residues 901-1227 of methionine synthase, is a C-shaped single domain whose central feature is a bent antiparallel betasheet. Database searches indicate that the observed polypeptide has no close relatives. AdoMet binds near the center of the inner surface of the domain and is held in place by both side chain and backbone interactions. CONCLUSIONS: The conformation of bound AdoMet, and the interactions that determine its binding, differ from those found in other AdoMet-dependent enzymes. The sequence Arg-x-x-x-Gly-Tyr is critical for the binding of AdoMet to methionine synthase. The position of bound AdoMet suggests that large areas of the C-terminal and cobalamin-binding fragments must come in contact in order to transfer the methyl group of AdoMet to cobalamin. The catalytic and activation cycles may be turned off and on by alternating physical separation and approach of the reactants.     

Coronary artery stenosis in rats affects beta-adrenergic receptor signaling in myocytes

The rotational spectrum of (CH3OH)2 has been observed in the 8 to 24 GHz region with a pulsed-beam Fabry-Perot cavity Fourier-transform microwave spectrometer. Previously we demonstrated that each transition of the a-type R(J), Ka = 0 is split into 15 states of the 16 theoretically expected states by tunneling motions. Here we show that the K = 1 states are split into the 16 expected states through the assignment of the Ka = 1 a-type transitions and DeltaKa = 1 b-type transitions. The internal-rotation analysis of the two inequivalent methyl groups presented here was guided by the previous experimental observations and theory for multidimensional tunneling, which predicts 16 tunneling components for each R(J) transition from 25 distinct tunneling motions. The effective barrier to internal rotation for the donor methyl group of (CH3OH)2 is V3 = 183.0 cm-1, and is one-half of the value for the methanol monomer (370 cm-1), while the barrier to internal rotation of the acceptor methyl group is 120 cm-1, one-third of the methanol monomer. The structure of the methanol dimer complex is similar to that of water dimer with a hydrogen bond distance of 1.96(2) A and tilt of the acceptor methanol of 77(2)degrees from the O-H-O axis (one standard deviation uncertainty). This structure shows good agreement with the angular orientation of the methyl groups derived in the internal-rotation analysis. Copyright 1997 Academic Press. Copyright 1997Academic Press     

Human hydrometry: comparison of multifrequency bioelectrical impedance with 2H2O and bromine dilution

The renal transport and fractional reabsorption of inorganic sulfate is altered under conditions of sulfate deficiency or excess. The objective of this study was to examine the cellular mechanisms of adaptation of renal sodium/sulfate cotransport after varying dietary intakes of a sulfur containing amino acid, methionine. Female Lewis rats were divided into four groups and fed diets containing various concentrations of methionine (0, 0.3, 0.82 and 2.46%) for 8 days. Urinary excretion rates and renal clearance of sulfate were significantly decreased in the animals fed a 0% methionine diet or a 0.3% methionine diet, and significantly increased in the animals fed a 2.46% methionine diet when evaluated on days 4 and 7. Serum sulfate concentrations were unchanged by diet treatment in all animals. The fractional reabsorption of sulfate was significantly increased in the animals fed the 0% methionine diet and the 0.3% methionine diets, and decreased in the animals fed the 2.46% methionine diet. Increased mRNA and protein levels for the sodium/sulfate transporter (NaSi-1) were found in the kidney cortex following treatment with the 0 and 0.3% methionine diet groups. Sulfate homeostasis by renal reabsorption is maintained by an up-regulation of steady state levels of NaSi-1 mRNA and protein when the diet is low in methionine.