1,720,989 research outputs found
Development of stable isotope dilution assays for the simultaneous quantitation of biogenic amines and polyamines in foods by LC-MS/MS
No full textMicrobial amino acid metabolism may lead to substantial amounts of biogenic amines in either spontaneously fermented or spoiled foods. For products manufactured with starter cultures, it has been suggested that certain strains may produce higher amounts of such amines than others; however, to support efforts of food manufacturers in mitigating amine formation, reliable methods for amine quantitation are needed. Using 10 isotopically labeled biogenic amines as the internal standards, stable isotope dilution assays were developed for the quantitation of 12 biogenic amines and of the 2 polyamines, spermine and spermidine, in one LC-MS/MS run. Application of the method to several foods revealed high concentrations of, for example, tyramine and putrescine in salami and fermented cabbage, whereas histamine was highest in Parmesan cheese and fermented cabbage. On the other hand, ethanolamine was highest in red wine and Parmesan cheese. The results suggest that different amino acid decarboxylases are active in the respective foods depending on the microorganisms present. The polyamine spermine was highest in salami and tuna. © 2012 American Chemical Society
Fatigue strength of notched specimens made of 40CrMoV13.9 under multiaxial loading
No full textThe work deals with multiaxial fatigue strength of notched round bars made of 40CrMoV13.9 steel and tested under combined tension and torsion loading, both in-phase and out-of-phase. The axis-symmetric V-notches present a constant notch root radius, 1. mm, and a notch opening angle of 90°; the notch root radius is equal to 4. mm in the semi-circular notches where the strength in the high cycle fatigue regime is usually controlled by the theoretical stress concentration factor, being the notch root radius large enough to result in a notch sensitivity index equals to unity. In both geometries the diameter of the net transverse area is 12. mm.The results from multi-axial tests are discussed together with those obtained under pure tension and pure torsion loading from notched specimens with the same geometry. Altogether more than 120 new fatigue data are summarised in the present work, corresponding to a one-year of testing programme.All fatigue data are presented first in terms of nominal stress amplitudes referred to the net area and then re-analysed in terms of the mean value of the strain energy density evaluated over a given, crescent shape volume embracing the stress concentration region. For the specific steel, the radius of the control volume is found to be independent of the loading mode. © 2013 Elsevier Ltd
Brittle fracture of U-notched graphite plates under mixed mode loading
No full textBrittle fracture of isostatic polycrystalline graphite is studied experimentally, theoretically and numerically using U-notched samples under mode I and mixed mode loading (I. +. II) considering different combinations of the notch radius and the tilt angle of the notch. An experimental programme was performed to provide a new set of results. In total 60 new data are provided in the paper.The averaged value of the strain energy density over a control volume is used to assess the static strength of the specimens subjected to different mode mixities. The volume is centred where the principal stress reaches its maximum value on the notch edge, by rigidly rotating the crescent-shaped volume already used in the literature to analyse U- and V-shaped notches subject to mode I loading. The volume size depends on the fracture toughness and the ultimate tensile strength of the material. Good agreement is found between experimental data and theoretical predictions based on the constancy of the mean strain energy density over the control volume. © 2012 Elsevier Ltd
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
High-resolution mass spectrometry identification of secondary metabolites in four red grape varieties potentially useful as traceability markers of wines
Full text linkLiquid chromatography coupled to high-resolution mass spectrometry (LC-Q/TOF) is a powerful tool to perform chemotaxonomic studies through identification of grape secondary metabolites. In the present work, the metabolomes of four autochthonous Italian red grape varieties including the chemical classes of anthocyanins, flavonols/flavanols/flavanones, and terpenol glycosides, were studied. By using this information, the metabolites that can potentially be used as chemical markers for the traceability of the corresponding wines were proposed. In Raboso wines, relatively high abundance of both anthocyanic and non-anthocyanic acyl derivatives, is expected. Potentially, Primitivo wines are characterized by high tri-substituted flavonoids, while Corvina wines are characterized by higher di-substituted compounds and lower acyl derivatives. Negro Amaro wine’s volatile fraction is characterized by free monoterpenes, such as α-terpineol, linalool, geraniol, and Ho-diendiol I. A similar approach can be applied for the traceability of other high-quality wines
Changes in volatile compounds of grape pomace distillate (Italian grappa) during one-year ageing in oak and cherry barrels
No full textThe Italian grape pomace distillate grappa is often refined by ageing in wooden barrels. Chemical changes of the volatile profile of two samples produced from a Cabernet Sauvignon/Merlot blend and Prosecco pomace both at two ethanol contents (55% and 68%) were studied during one-year ageing in cherry and oak barriques. Grappa variety, ethanol content and barrel type strongly affected the volatiles profile of the distillates. Oak-aged grappa contained 10-fold the wood volatiles of the cherry-aged one, but the latter had higher levels of syringaldehyde, coniferaldehyde, and 3,4,5-trimethoxyphenol; 55% ethanol extracted higher levels of wood compounds and ethoxy-compounds were higher in the 68%-ethanol distillates. Prosecco grappa extracted higher wood compounds and showed no significant changes in the levels of fruity/floral esters and terpenols. Findings of this study can be also useful in the development of new ageing processes of distillates for which cherry barrels are still not used (e.g., brandy and whisky)
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