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  • 1
    ISSN: 1431-4630
    Keywords: Key words Collagen ; D-Amino acids ; Hydroxyproline stereoisomers ; Racemisation ; Food proteins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract  Using capillary gas chromatography on chiral stationary phases total hydrolysates of gelatins were investigated for their amounts of D-amino acids (D-AAs). Gelatins of different quality and origin were analysed including gelatin-containing final products like candies and meat products. In gelatins manufactured by stepwise extraction (first to fifth extract) with water of increasing temperature (ca. 55–95°C) amounts of 2.7–4.8% of D-aspartic acid (D-Asp) were determined in extracts obtained at ≤ 85°C. The amounts D-Asp were as high as 28.1% in fifth extracts obtained at 95°C (data corrected for 4.3% of D-Asp determined in native collagen as a result of acid-induced epimerisation of L-Asp during total hydrolysis). Epimerisation of aspartyl or asparaginyl residues of proteins in general on heating in water is assumed to proceed via formation of aspartyl succinimide, tautomerisation and release of D-Asp on total hydrolysis. The other AA residues of gelatin showed only a slight increase of epimerisation with increasing thermal treatment. Furthermore, amounts of 3–4% of cis-4-D-hydroxyproline, formed from native trans-4-L-hydroxyproline in collagen on hydrolysis, were detected in total hydrolysates of all gelatins.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1588-2780
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract A thick spherical target (R=25 cm) made of gabbro was irradiated isotropically with 1.6 GeV protons at the Saturne cyclotron at Laboratoire National Saturne (LNS)/CEN Saclay in order to simulate the interaction of galactic cosmic ray (GCR) protons with meteoroids in space. During a 2 weeks irradiation a proton-dose of 1.32 · 1014 cm−2 was received, which is equivalent to a cosmic-ray exposure age of 1.4 Ma. Production rates were measured by X- and gamma-spectrometry, by low-level counting and by conventional and accelerator mass spectrometry (AMS). Up to now, more than 200 target-product combinations were investigated. Theoretical production rates were derived on the basis of spectra of primary protons, secondary protons and secondary neutrons calculated by Monte Carlo techniques and thin-target cross sections of the underlying nuclear reactions. The model calculations excellently describe the production depth profiles in the artificial meteoroid, if reliable crosss sections are available. The thus validated model calculations allow for the interpretation of cosmogenic nuclide abundances in stony meteorites and lunar samples in terms of their exposure history and of the history of the radiation itself.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Amino acids ; Chiral separations ; Fruit juice adulteration ; Microorganisms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The configurations of free amino acids (AAs) in orange juice beverages (commercial products of satisfactory and unsatisfactory quality), an orange juice concentrate (bulk product suspected of being adulterated), and in an orange juice that has been contaminated by addition ofLactobacillus plantarum as a model for microbial spoilage, were determined, after derivatization, by means of gas-liquid chromatography (GC) using fused-silica capillary columns coated with Chirasil-L-Val or Chirasil-D-Val as stationary phases. AAs were isolated from juices by treatment with Dowex WX8 ion-exchanger and were investigated, by GC, as theirN(O)-pentafluoropropionylorN(O)-trifluoroacetyl 1-propyl esters. It was found that the high quality orange juice beverage contained L-AAs exclusively whereas this juice, after fermentation withLactobacillus, contained free D-Ala (32.7%), D-Val (62.3%), D-Phe (20.0%), D-Glu (24.3%), D-Ser (2.6%), D-Asp (0.8%), and significant amounts of D-Pro [% D=100 D/(D+L)]. D-Ala (8.8%) and D-Ser (4.2%) were found in a sensory and analytically unsatisfactory orange juice beverage, whilst D-Ala (27.5%) and D-Ser (14.3%) were detected in the orange juice concentrate suspected of being adulterated. Although capillary GC on chiral stationary phases is regarded as being highly suitable for the determination of AA enantiomers in fruit juice beverages, detection of D-AAs is currently not considered as conclusive proof of fruit juice adulteration caused by addition of AA racemates since a non-microbial origin of D-AAs in the respective juice, or an original occurrence of D-AAs, in either the free, substituted, or peptide-bonded form in the fruits, cannot be excluded with certainty.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Amino acid analysis ; Chirality ; Diastereoisomers ; Dipeptides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Using a robotic autosampler, free DL-amino acids were derivatized with highly reactive, urethane-protected, L-α-amino acidN-carboxyanhydrides (NACs) with structures: Boc-Phe-NCA, Boc-Asn(Trt)-NCA, Fmoc-Lys(Boc)-NCA, Fmoc-Met-NCA, Fmoc-Ala-NCA, Z-Ala-NCA, Z-Val-NCA and Z-Leu-NCA (Boc=tert-butyloxycarbonyl, Trt=trityl, Fmoc=9-(fluor-enylmethyl)oxycarbonyl, Z=benzyloxycarbonyl). Using sodium borate buffer and acetonitrile solvent, derivatization was complete in 3.5 min at room temperature. By selection of an appropriate reagent, the resulting diastereomeric,N-protected dipeptides were separated on an octylsilica stationary phase using mixtures of sodium acetate buffer and acetonitrile as eluents.
    Type of Medium: Electronic Resource
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