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Air Exposure (air + exposure)
Selected AbstractsAutoxidation of linalyl acetate, the main component of lavender oil, creates potent contact allergensCONTACT DERMATITIS, Issue 1 2008Maria Sköld Background:, Fragrances are among the most common causes of allergic contact dermatitis. We have in previous studies shown that linalool, present in lavender oil, autoxidizes on air exposure, forming allergenic oxidation products. Oxidized linalool was found to be a frequent cause of contact allergy in a patch test study on consecutive dermatitis patients. Linalyl acetate, the main component of lavender oil is commonly used as a fragrance chemical in scented products. Because of structural similarities, linalyl acetate should also be susceptible to oxidation on air exposure, forming similar oxidation products as linalool. Objective:, The aim of the present study was to investigate the autoxidation of linalyl acetate and the influence of oxidation on its sensitizing potency. Methods:, Analyses were performed using gas chromatography, nuclear magnetic resonance spectrometry and mass spectrometry. Sensitizing potencies of compounds were determined using the local lymph node assay (LLNA) in mice. Results:, Analyses showed that the content of linalyl acetate decreased over time on air exposure and other compounds were formed. Hydroperoxides, an epoxide and an alcohol were identified as oxidation products from linalyl acetate. In the LLNA, linalyl acetate of high purity showed a weak sensitizing potency (EC3 25%). Autoxidation increased the sensitizing potency of linalyl acetate, and a 10 weeks oxidized sample gave an EC3 value of 3.6%. As for linalool, the hydroperoxides were shown to be the oxidation products with the highest sensitizing potency. Conclusion:, It is concluded that autoxidation of the weakly allergenic linalyl acetate leads to formation of allergenic oxidation products. [source] Contact allergy caused by air oxidation of common materials , diagnosis and preventionCONTACT DERMATITIS, Issue 3 2004Ann-Therese Karlberg When considering the allergenic activity of a compound not only the possibility of bioactivation by skin metabolism but also air activation by autoxidation must be taken into account. Natural compounds (terpenes) easily oxidize at air exposure. They are found in products that are common causes of allergic contact dermatitis (ACD) i.e. colophony and fragrances. The introduction of oxygen enables the molecules to form antigens with skin proteins via a nucleophilic- electrophilic interaction or via a radical reaction. The latter mechanism seems to be important since the primary oxidation products, the hydroperoxides, are the most potent sensitizers formed. Oxidative decomposition at air exposure resulting in allergenic oxidation products is observed also for other common compounds e.g. ethoxylated fatty alcohols used as surfactants. It is important to test the patient with the offending compounds for diagnosis of ACD. A negative diagnosis can be due to failure in testing with the correct substances. In the case of air activated compounds, testing should not be performed with the pure substances but rather with the oxidation mixture or the most sensitizing oxidation products (the hydroperoxides). We have in multicenter-studies shown that the common fragrance terpenes, limonene and linalool, are frequent sensitizers when oxidized. This is a challenge in clinical practice since such patch test materials are not easily standardized. Compounds, easily activated at air exposure, should be prevented from oxidative decomposition by addition of antioxidants and proper handling and storage. More research is needed in this area. [source] Storage stability of a high dietary fibre powder from orange by-productsINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 4 2009Juana Fernández-López Summary The goal of this investigation was to evaluate the effects of storage time and conditions on the physicochemical and microbiological properties of a high dietary fibre powder (HDFP). HDFP for this study was manufactured from orange juice industry by-products. The storage period was 11 months and samples were stored under vacuum or air exposure and under dark or light exposure. The HDFP is a stable product (based on chemical, microbiological and physicochemical properties) with large amounts of dietary fibre (71.62 ± 0.24 g 100 g,1 dry sample) and polyphenols content (40.67 ± 0.45 mg g,1 dry sample). Hesperidin is the major compound identified in HDFP (higher than 50% of total phenolic compounds). The packaging material used protects the HDFP only up to 6 months. After this time, the increase in moisture content decreases the quality of the product. The best storage conditions are packaging under vacuum and darkness. Both conditions preserve the colour of the fibres probably by means of avoiding pigment degradation. [source] PROPOSED NEW COLOR RETENTION METHOD FOR TILAPIA FILLETS (O. NILOTICUS, × O. AUREUS,) BY EUTHANATIZING WITH REDUCED CARBON MONOXIDEJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 5 2008LAIHAO LI ABSTRACT The conditions of color retention for tilapia fillets (O. niloticus, × O. aureus,) treated by euthanatizing with reduced carbon monoxide (CO) were investigated. Live tilapias were first exposed to water saturated with CO. After a certain amount of CO-saturated water had been pumped through the gills, the tilapias were timely picked out and killed following the industry guidelines. The color value of fillets was measured by colorimeter to evaluate the color retention. The results showed that (1) temperature did not have a significant effect on the color of the fillets; (2) the optimal conditions were a ratio of 3:1, v/w between water and fish, a CO flow rate of 80 mL/min and 10 min CO injection followed by 5 min air exposure. Under these conditions, a higher a*value (redness 19.44) and a better sensory evaluation value (4.8) were obtained; and (3) the proposed method shortened processing time by 30,35 min, reduced the frequency of sterilization to only once, significantly lowered microbial counts from 82.33 × 102 to 56.33 × 102 and reduced the CO requirement 25-fold, which has significant occupation, health, safety, and environmental implications. PRACTICAL APPLICATIONS Color retention for tilapias is conventionally accomplished by treating fillets with CO. Recently, euthanatizing tilapias with CO has been assumed to be an effective way to shorten processing time and to lessen product handling process. Many factories have been searching for a way to solve the problem of color retention for tilapias or other red muscle treatment, but there has been a lack of information on how euthanasia affects fish quality, especially red muscle color. The objective of this experiment was to explore the application of the new method. [source] ,-Irradiation of ultrahigh-molecular-weight polyethylene: Electron paramagnetic resonance and nuclear magnetic resonance spectroscopy and imaging studies of the mechanism of subsurface oxidationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2004Todd M. Alam Abstract The shelf aging of irradiated ultrahigh-molecular-weight polyethylene (UHMWPE) causes subsurface oxidation, which leads to failure in UHMWPE orthopedic components, yet the mechanisms causing subsurface oxidation remain unclear. The shelf aging of ,-irradiated UHMWPE bars has been studied with electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) imaging and with microtoming and Fourier transform infrared microscopy. The bars initially contained only allyl radicals, and upon air exposure, a surface layer of peroxyl radicals formed through the reaction of allyl radicals with oxygen. Importantly, a band of low radical intensity just beneath the peroxyl layer became apparent. NMR imaging showed a zone of altered proton relaxation in this zone. With increasing time, surface peroxyl radicals persisted in comparison with the interior allyl radicals, although oxygen did not appear to penetrate any more deeply into the bar. The area of maximal oxidation and mechanical disruption, measured after 3 years, was at the interface between the zone of exterior peroxyl radicals and the zone of low radical intensity. We present a mechanism involving the intermediacy of sterically strained reactive dialkyl peroxides at this interface to explain subsurface oxidation. We also demonstrate that EPR and NMR imaging provides information that could potentially be used to identify subsurface oxidized UHMWPE components before failure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5929,5941, 2004 [source] Fluorescence EXAFS for the in situ study on the state of promotors in catalysisJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001Jan-Dierk Grunwaldt The fluorescence EXAFS (FLEXAFS) technique has been combined with an in situ cell and on-line gas analysis. For this purpose a seven-element silicon drift detector has been used, which has high count rate capabilities and can be operated at room temperature. The potential of this technique is shown by the study of the state of copper promoter atoms in Fe-Cr based high temperature shift (HTS) catalysts. The FLEXAFS measurements revealed that Cu (0.17,1.5 wt%) is present in the metallic state under working conditions of the catalysts but easily re-oxidizes upon air exposure. The reduction behaviour of copper depends strongly on the copper concentration and the pre-treatment, i.e. if the catalysts have been calcined or used in the HTS reaction. For used catalysts, a Cu(I) phase was detected as intermediate during reduction. Its stability was especially high at low copper concentration. [source] Metastable alumina formation during oxidation of FeCrAl and its suppression by surface treatmentsMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 12 2005E. N'Dah Abstract The influence of various surface treatments of industrial FeCrAl grades was investigated in order to reduce the formation of transition aluminas during thermal oxidation in the 800,950°C temperature range. High temperature gas phase annealing in H2 -H2O mixtures promoted the initial formation of an alpha thin film and no transition alumina formed during subsequent oxidation at lower temperatures, showing very low weight gains compared to non-treated grades. Such a treatment was shown to be efficient for isothermal oxidation in oxygen of laboratory foil specimens but also for cyclic air exposure of fiber mats in near-real operating conditions. Surface modification by application of a slurry TiO2 coating before oxidation was also shown to greatly reduce the amount of transition alumina, observed by X-Ray Diffraction and Laser Induced Optical Spectroscopy. For both treatments, the optimal conditions were determined and the influence on oxidation rate was assessed. [source] Effects of air exposure on the lysosomal membrane stability of haemocytes in blacklip abalone, Haliotis rubra (Leach)AQUACULTURE RESEARCH, Issue 3 2007Liang Song Abstract The neutral red retention (NRR) assay was used to evaluate the effects of air exposure on lysosomal membrane integrity in the haemolymph of blacklip abalone, Haliotis rubra, and its subsequent recovery in water. After acclimation in 16°C water for 7 days, abalone were exposed to an air temperature of 7, 16 or 23°C for 12 h in the air exposure experiment or to these three air temperatures, e.g., for 12, 24 or 36 h, followed by re-immersion in 16°C water in the lysosomal membrane stability recovery experiment. Statistical analyses of the air exposure experiment showed that when abalone were exposed to different air temperatures (7, 16 or 23°C), the lysosomal membrane stability was significantly affected by the air temperature, the exposure duration and their interaction. Air temperature similar to the acclimation temperature had a significantly lower impact on the lysosomal membrane stability within the initial 4.5 h in comparison with the other two temperatures in the same period. The lysosomal membrane stability recovery experiment showed that after air exposure durations of 12, 24 or 36 h, the re-stabilization of the lysosomal membrane was faster in the animals exposed to lower temperatures than those exposed to higher temperatures. The recovery of the lysosomal membrane stability in abalone exposed to lower 7°C air temperature was not significantly affected (F2, 66=0.251, P=0.779) by the exposure durations (12, 24 and 36 h) used in this study. Alternatively, the lysosomal membrane stability in abalone exposed to higher air temperatures of 16 or 23°C recovered at a faster rate when subjected to shorter durations of air exposure (F2, 66=3.663, P=0.031 and F1, 44=17.057, P<0.001 for 16 and 23°C respectively). [source] | |||||||||||||