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1.
    
The method of headspace coupled with comprehensive two‐dimensional GC–time‐of‐flight MS (HS‐GC × GC–TOF/MS) was applied to differentiate the volatile flavor compounds of three types of pure vegetable oils (sesame oils, peanut oils, and soybean oils) and two types of adulterated oils (sesame oils and peanut oils adulterated with soybean oils). Thirty common volatiles, 14 particular flavors and two particular flavors were identified from the three types of pure oils, from the sesame oils, and from the soybean oils, respectively. Thirty‐one potential markers (variables), which are crucial to the forming of different vegetable oil flavors, were selected from volatiles in different pure and adulterated oils, and they were analyzed using the principal component analysis (PCA) and cluster analysis (CA) approaches. The samples of three types of pure vegetable oil were completely classified using the PCA and CA. In addition, minimum adulteration levels of 5 and 10% can be differentiated in the adulteration of peanut oils and sesame oils with soybean oils, respectively. Practical applications: The objective was to develop one kind of potential differentiated method to distinguish high cost vegetable oils from lower grade and cheaper oils of poorer quality such as soybean oils. The test result in this article is satisfactory in discriminating adulterated oils from pure vegetable oils, and the test method is proved to be effective in analyzing different compounds. Furthermore, the method can also be used to detect other adulterants such as hazelnut oil and rapeseed oil. The method is an important technical support for public health against profit‐driven illegal activities.  相似文献   

2.
    
The wax ester fraction of various plant oils was isolated by normal‐phase HPLC (NPLC) on‐line coupled to GC via the on‐column interface and applying concurrent eluent evaporation. The esters were analyzed by on‐line NPLC‐GC‐MS and by comprehensive two‐dimensional GC with flame ionization detection (GC×GC‐FID) off‐line combined with NPLC‐GC. GC×GC‐FID enables to group the various classes of wax esters, in particular the phytol esters, geranylgeraniol esters and the straight‐chain esters of palmitic acids and the unsaturated C18 acids. Optimization of the GC×GC columns and the conditions must take into account the limited thermostability of the diterpene esters. Chromatograms are shown for a range of oils, with particular focus on the various classes of wax esters in olive oil and the geranylgeraniol esters 22:0 and 24:0 in a variety of oils.  相似文献   

3.
Mazalli MR  Bragagnolo N 《Lipids》2007,42(5):483-490
A comparative study between two methods (lipid extraction followed by saponification and methylation, and direct methylation) to determine the fatty acids in egg yolk was evaluated. Direct methylation of the samples resulted in lower fatty acid content and greater variation in the results than the lipid extraction followed by saponification and methylation. The low repeatability observed for the direct HCl methylation method was probably due to a less efficient extraction and conversion of the fatty acids into their methyl esters as compared to the same procedure starting with the lipid extract. As the lipid extraction followed by esterification method was shown to be more precise it was validated using powdered egg certified as reference material (RM 8415, NIST) and applied to samples of egg, egg enriched with polyunsaturated omega-3 fatty acids (n-3 PUFA), and commercial spray-dried whole egg powder.  相似文献   

4.
    
A new hypothesis has been proposed in this work for hydrodynamic similarity that can be subsequently used for scale‐up of bubble column reactors. The proposed hypothesis takes into account both global (by matching overall gas holdup) as well as local hydrodynamics (by matching time‐averaged radial profile/cross‐sectional distribution of gas holdup) to maintain similarity in two systems. The evaluation of proposed hypothesis has been accomplished utilising advanced diagnostic techniques such as gamma‐ray computed tomography (CT) and computer automated radioactive particle tracking (CARPT). In this work, we experimentally demonstrate that similarity based only on global hydrodynamics does not necessarily ensure similar mixing and turbulence in two systems. It is essential to maintain similar global as well as local hydrodynamics. The hydrodynamic similarity that can be obtained by matching the commonly used dimensionless groups was also evaluated at these experimental conditions.  相似文献   

5.
    
In this study, the kinetics of the thermal decomposition of aminoguanidinium 5,5′‐azobis‐1H‐tetrazolate (AGAT), which is one of the promising fuel candidates of the new gas generating agents for airbags, was investigated. The kinetic model that fits the main decomposition of AGAT was examined, and the activation energy was obtained. The main decomposition of AGAT was a single elementary process according to the result of mass spectrometry. The recommended kinetic model for the main decomposition of AGAT is Avrami–Erofeev equation (n=4). The activation energies for the main decomposition obtained under helium by non‐isothermal analysis and isothermal analysis were 207 and 209 kJ mol−1, respectively.  相似文献   

6.
This study examined the effect of substituting vegetable oil for fish oil in feed, with subsequent re-introduction of fish oil-rich feed (finishing feeding) in late stages of growth, on the fatty acids of cultivated European whitefish (Coregonus lavaretus). Restorative finishing feeding with fish oil-rich feed for 15 and 25 weeks was sufficient to change the total content of nutritionally valuable long-chain n-3 fatty acids, eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3), to correspond to that of fish fed the fish oil-rich feed throughout their lifespan. Under natural conditions, 15 and 25 weeks correspond to weight gains of 75% and 100% (i.e. doubling), respectively. Also, the fatty acid profile of the fish was restored after finishing periods of 15 and 25 weeks. Limiting the use of fish oil by lowering the overall fat content of the feed (no vegetable oil added) resulted in a decrease in the long-chain n-3 fatty acids. Based on the results, after receiving a vegetable oil-rich diet, restorative fish oil-rich feeding in the last stages of growth in European whitefish is nutritionally justified in order to balance nutritional gain for consumers with sustainable use of finite marine oils. The results encourage commercial efforts to further utilize and optimize finishing feeding practices.  相似文献   

7.
    
Monolithic materials prepared from a mixture of n‐lauryl methacrylate (LMA) and ethylene glycol dimethacrylate (EGDMA) dedicated to nano‐liquid chromatography separation were synthesized using in situ UV polymerization in 75 µm inner diameter capillary tubing. A mixture of cyclohexanol and ethylene glycol was used as a porogen to control porosity. While the preparation conditions yielded satisfactory analytical results, values of pertinent parameters turned out to be critical for obtaining columns with efficient separation. In particular, the impact of two key parameters was studied here in an attempt to identify optimal preparation conditions: (a) different concentrations of the crosslinker EGDMA and (b) different porogen compositions while the monomer to porogen ratio was kept constant. Resulting monolithic phases were characterized in terms of permeability, mean pore diameter and swelling using three different eluents (water, acetonitrile and a mixture at maximum viscosity). First, the LMA/EGDMA monolithic phases present peculiar morphology and hydrodynamic properties for 37% by weight of EGDMA, as reflected by the peak observed for their permeability and mean pore diameter. Swelling experiments revealed the coexistence of two phases in the monolithic structure: a highly crosslinked rigid phase which was insensitive to swelling in the presence of solvent and a weakly crosslinked flexible phase exhibiting significant swelling, with a transition to such a biphasic behavior taking place at 37% by weight of EGDMA. The effects of porogen composition and network swelling properties are presented based on a combination of the Flory ? Huggins theory of isotropic mixing in polymer solutions and the Flory ? Rehner theory of rubber elasticity in the affine network approximation. © 2016 Society of Chemical Industry  相似文献   

8.
    
Two types of polymeric sols, resorcinol‐formaldehyde (RF) and resorcinol‐furfural (RFur), were mixed in a water‐containing medium with aqueous solutions of inorganic salts: NH4ClO4, Mg(ClO4)2, and NH4NO3. After gelation and an ambient pressure drying, hybrid nanocomposites with properties of energetic materials were obtained. It was stated that salt concentration and addition of a second solvent (e.g., methanol or N,N‐dimethylformamide) to the mixture of reagents have crucial meaning for gel formation. In the case when only water was used, the mixture of organic sol/inorganic salt did not transfer from sol to gel, and precipitates were formed. Conventional drying of wet gelled composites leads to rigid material called xerogels. The RF xerogels are red and RFur xerogels are black. Typically, xerogels are transparent at low salt concentration (below 30%). The microstructure, morphology, and some other properties of chosen composites were studied by means of HR SEM, AFM, XRD, DTA/TG, and N2 adsorption isotherm techniques. SEM observation revealed that sizes of the oxidizer particles vary from less than 100 nm to ca. 1000 nm. XRD analyses also confirmed the presence of nanometer‐sized crystals of oxidizers in some formulations. The specific surface area of polymeric matrix/oxidizer composites was found to be in the range from 0.002 to 0.3 m2 g−1. After removing the salt from the composites (by extraction with boiling water), the specific surface area grows even up to 210 m2 g−1. TG/DTA analyses showed that the tested composites decompose as typical energetic materials. If pre‐heated and exposed to flame, some of them (especially RF/Mg(ClO4)2 composites) undergo violent deflagration with loud sound and flash effect.  相似文献   

9.
A supercritical fluid extraction (SFE) method has been developed for the extraction of lipids in bilberry. Experimental design was used to optimize pressure, temperature and extraction time using CO2 as solvent. Best SFE condition for total lipids was 450 bar, 60 °C and 45 min. The SFE method was compared to conventional Bligh & Dyer (B&D) extraction. The amount of fatty acid methyl esters (FAME) was found to be 4.84 ± 0.06 mg and 4.564 ± 0.003 mg per g of the freeze‐dried bilberry sample for the developed SFE and B&D methods, respectively, while the amount of total lipids was found to be 54.40 ± 6.06 mg and 65.70 ± 0.67 mg per g of sample for SFE and B&D, respectively. This discrepancy between FAME and total lipids could be explained by the presence of wax esters, sterol esters, carotenoids and phospholipids, as determined by supercritical fluid chromatography.  相似文献   

10.
The salting‐out phase equilibria for acetone, 1‐butanol, and ethanol (ABE) from dilute aqueous solutions using potassium carbonate (K2CO3) and dipotassium hydrogen phosphate trihydrate (K2HPO4?3H2O) as outstanding salting‐out agents were investigated. Increasing the salt concentration strengthened the salting‐out effects and improved the distribution coefficients of all three solvents (ABE) significantly. Temperature had a slight effect on the phase equilibria. The K2HPO4 solution (69 wt %) showed a stronger salting‐out effect than the K2CO3 solution (56 wt %) on recovering ABE from dilute aqueous solutions. Dilute aqueous solutions containing more solvents increased the recoveries of acetone and 1‐butanol, while the results showed a negligible effect on the solubility of ABE. The solubility of ABE was also correlated well with the molar number of salt per gram of water in the aqueous phase. A new equation demonstrated this satisfactorily. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3470–3478, 2015  相似文献   

11.
    
Mullet bottarga is a food delicacy obtained by salting and drying the intact roes of mullet (Mugil spp.). The fatty acid and fatty alcohol compositions of different samples of bottarga were studied by means of gas chromatography (GC) and multivariate analysis (MVA). High percentages of beneficial n‐3 PUFA, among which docosahexaenoic acid (DHA) (22:6n‐3, 11.9%) and eicosapentaenoic acid (EPA) (20:5n‐3, 8.6%), were detected. Differences in the concentrations of unsaturated FA and FAL were observed among samples, while saturated components showed little variations. On the other hand, the total contents of saturated, monounsaturated and polyunsaturated components were similar. The principal component analysis loadings bi‐plot showed that n‐6 PUFA concentrations were inversely correlated to those of n‐3 PUFA, except for DHA that showed no correlations. Correlations between FAL concentrations were also observed. Furthermore, integrating our GC data with those from the literature on mullet and tuna bottarga, the MVA showed that both bottarga typologies exhibit a similar trend in the FA distribution and that 16:0 and 16:1n‐7 FA are the variables with the highest discriminant power. In this work, we demonstrated the usefulness of the application of MVA to GC data to extract meaningful information otherwise hidden in the amount of data.  相似文献   

12.
    
We propose a new volatility model, which is called the mixture memory generalized autoregressive conditional heteroskedasticity (MM‐GARCH) model. The MM‐GARCH model has two mixture components, of which one is a short‐memory GARCH and the other is the long‐memory fractionally integrated GARCH. The new model, a special ARCH( ∞ ) process with random coefficients, possesses both the properties of long‐memory volatility and covariance stationarity. The existence of its stationary solution is discussed. A dynamic mixture of the proposed model is also introduced. Other issues, such as the expectation–maximization algorithm as a parameter estimation procedure, the observed information matrix, which is relevant in calculating the theoretical standard errors, and a model selection criterion, are also investigated. Monte Carlo experiments demonstrate our theoretical findings. Empirical application of the MM‐GARCH model to the daily S&P 500 index illustrates its capabilities.  相似文献   

13.
    
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14.
    
The seasonal variation of the fatty acids composition of butters were investigated over three seasons during a 12‐month study in the protected designation of origin Parmigiano‐Reggiano cheese area. Fatty acids were analyzed by GC‐FID, and then computed by artificial neural networks (ANN). Compared with spring and winter, butter manufactured from summer milk creams showed an optimal saturated/un‐saturated fatty acids ratio (?8.89 and ?5.79%), lower levels of saturated fatty acids (?2.63 and ?1.68%) and higher levels of mono‐unsaturated (+5.50 and +3.45%), poly‐unsaturated fatty acids (+0.65 and +0.17%), and rumenic acid (+0.55 and +3.41%), while vaccenic acid had lower levels in spring and higher in winter (?2.94 and +2.91%). Moreover, the ANN models were able to predict the season of production of milk creams, and classify butters obtained from spring and summer milk creams on the basis of the type of feeding regimens. Practical applications: The investigation on variables that affect the milk fatty acids composition can improve the quality of milk across all systems, and the combination of chromatographic and computational techniques will ensure a secure traceability enabling producers to characterize dairy products.  相似文献   

15.
    
The effect of metal nanopowders (Al, Fe, W, Ni, Cu, and Cu‐Ni alloys) on the decomposition of energetic materials (HMX, AP, and AN) with DTA–TGA method was studied and it was found that the catalytic action appears in the case of Cu‐Ni nanopowders with the three studied energetic materials. The temperature of decomposition of energetic materials with the addition of metal nanopowders could be lowered by 82 °C for AN, 161 °C for AP, and 96 °C for HMX. The reaction mechanism of metal nanopowders enhancing the decomposition of energetic materials is discussed.  相似文献   

16.
    
Porous nanocomposite films based on polypropylene (PP) and titanium dioxide (TiO2) nanoparticles were prepared by melt extrusion followed by uniaxial stretching. The effects of drawing temperature, extension rate, stretching ratio and composition of the base films on the final properties and microstructure of the stretched films were studied. Water vapor permeability (WVP) results showed a significant decrease in permeability of the films stretched at temperatures higher than 60 °C. Porosity, pore size and water vapor transmission rate in the porous nanocomposite films had a direct relation with nanoparticle content, extension rate and stretching ratio. Study of the morphology of the stretched films, using SEM, revealed that the pores form due to PP/TiO2 interfacial debonding at low stretching ratios. Higher stretching ratios cause an enlargement of the pores and the formation of a PP fibril structure parallel to the stretching direction. Quantification of dye adsorption revealed that the quantity of adsorbed dye increased with porosity and surface area of the pores. © 2014 Society of Chemical Industry  相似文献   

17.
    
The accumulation of space charge in high voltage direct current cable will bring the insulation to failure; the addition of nanoparticles can markedly improve the space charge distribution characteristics inside the cable insulation, but particle agglomeration and cavitation lead to difficulty in controlling the properties of nanocomposites. In this paper, polypropylene (PP)/propylene‐ethylene copolymer (PEC) and PP/ethylene‐octene copolymer (EOC) blends were prepared by mechanical blending in order to improve both mechanical properties and space charge distribution. Dynamic mechanical thermal analysis shows that both blends have excellent mechanical properties for recyclable power cable. Pulsed electro‐acoustic and thermally stimulated depolarization current tests illustrate that PP/EOC blends significantly decrease space charge accumulation and remarkably increase the trap density in the bulk compared with PP and PP/PEC blends. The increase of the trap density in PP/EOC blends can be explained as the result of the shallow traps introduced by the crystalline ? amorphous interface existing in the boundaries of spherulites. The shallow traps can act as hopping sites to improve the transportation of space charges. © 2016 Society of Chemical Industry  相似文献   

18.
Historically, a complete analysis of cottonseed fatty acids required two separate analyses: gas chromatography (GC) for nutritional fatty acids and a separate analysis for cyclopropenoid fatty acids (CPFA). Using base esterification and optimized GC conditions, the method presented combines both analyses into a single GC procedure that improves analytical processes and streamlines workflow. While there were challenges, the resolution of critical pairs malvalic/stearic and dihydrosterculic/alpha linolenic methyl esters were adequately separated, allowing for accurate quantitation. Single lab reproducibility measurements (RSD) for major nutritional fatty acids ranged from 0.7 to 2.0 %. For CPFA the RSD ranged from 1.1 to 5.4 %, with the higher variability seen in the extracted cottonseed. In oils, the precision was similar between nutritional fatty acids and CPFA at equivalent concentrations, indicating the variation comes from the extraction process. Average spiked recovery results ranged from 93.3 to 106.5 % for selected fatty acids. In addition, complete fatty acid profile results compare favorably with other methodologies and historical data, demonstrating that it is possible to combine two legacy methods into one.  相似文献   

19.
    
A series of new vanadium‐silsesquioxanes ( 2a ? 2d ) was prepared by reacting VCl4 with not fully condensed silsesquioxanes (having from one to four silanol groups) and evaluated as pre‐catalysts in olefin polymerization. The activation of 2a ? 2d with EtAlCl2 generated highly active catalysts for ethylene polymerization, yielding high molar mass polymers with narrow dispersity. Ultra‐high molar mass polyethylenes, M w up to 4 × 106 g mol?1, were obtained with methylaluminoxane and Al(i Bu)3/[Ph3C][B(C6F5)4] as activators. Upon treatment with methylaluminoxane and boron compounds, all vanadium pre‐catalysts were active in 1‐octene polymerization as well, and produced isotactic‐rich poly(1‐octene)s with moderate monomer conversion (up to 23%). The polymerization parameters were optimized and the effect of the silsesquioxane structure on the catalytic activity and polymer properties was studied. © 2017 Society of Chemical Industry  相似文献   

20.
    
The environmentally friendly Mn2(CO)10‐based visible light photoinitiating system is a powerful method for the preparation of linear and crosslinked polymeric structures. From a practical point of view, the most important feature of this initiating system is its optical characteristics in the visible range with high quantum yield and good solubility properties. This photoinitiating system is applicable for a variety of monomers that can be polymerized via either radical or cationic mechanisms. Various complex macromolecular structures such as telechelic polymers, block and graft copolymers, polymer networks and surface modifications can be simply prepared by using halogenated precursors. This photoinitiating system is also combined with controlled radical polymerization techniques providing a mild and efficient method for polymer synthesis. © 2016 Society of Chemical Industry  相似文献   

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