食用植物油中溶剂残留量的顶空气相色谱标准加入法测定研究

对食用植物油中的溶剂残留测定方法进行了改进。用样品作基体配制标准溶液,采用顶空进样气相色谱测定,标准加入法定量。方法线性范围在ofμg／g-200μg/g,检测低限1．0μg/g,在1-μg／g-200μg／g浓度范围内,标准添加回收率为87．8％-107．4％．相对标准偏差6．06％-11．8％。本方法采用标准加入法进行定量,样品和标准的基体一致,避免了基体的影响,该法简便、快速,适合食用植物油中的溶剂残留的分析。     

Separation of wax esters from olive oils by high-performance liquid chromatography

To detect adulteration of olive oil with solvent-extracted oils, the determination of the wax ester content has become more important during recent years. Hence, a greater number of wax ester analyses need to be performed by quality control laboratories. The most common method in use requires a liquid chromatographic (LC) separation of the less polar fraction, which contains the wax esters, from the glyceride matter on a hand-filled silica gel column. The aim of this project was to verify the possibility of replacing LC with high-performance liquid chromatography by taking advantage of the greater reliability and repeatability of this technique, as well as of the possibility of making the separation automatic. The paper describes how to perform the analysis and the statistical test that was carried out; furthermore, a comparison has been made with the usual method and results are in good agreement.     

Quantitative determination of castor oil in edible and heat-abused oils by13C nuclear magnetic resonance spectroscopy

Application of¹³C nuclear magnetic resonance (NMR) spectroscopy for detection of castor oil (CO) in various edible oils, such as coconut oil, palm oil, groundnut oil and mustard oil, is described. Characteristic signals observed at δ 132.4, δ 125.6, δ 71.3, δ 36.8 and δ 35.4 ppm, due to C10, C9, C12, C13 and C11 carbons of ricinoleic acid (RA) in CO, were selected for distinguishing it from edible oils. Quantitative¹³C NMR spectra of oils were recorded in CDCl₃ with a gated decoupling technique. The minimum detection limits for qualitative and quantitative analyses were 2.0 and 3.0%, respectively. The proposed method is simple, nondestructive and requires no sample pretreatment. Its application to heat-abused oils has also been demonstrated successfully without any of the interferences observed in most other methods.     

Physical refining of edible oils

Physical refining of edible oils offers several advantages over alkali refining. The method described for physical refining of rapeseed oil involves several novel factors, including the availability of cold-pressed rapeseed oil low in phosphatide content and deacidification/deodorization in a film molecular evaporator. Parameters are presented from a pilot plant unit with an output of 500 metric tons per year. Further applications of the technology are proposed, including the processing of oils to pharmaceutical-grade products.     

Interfacial tension of edible oils in supercritical carbon dioxide

Interfacial properties essentially influence fluid‐liquid separation processes. Thereby, interfacial tension is an important parameter that is associated with mass transfer and mutual solubility of participating compounds. For this reason, interfacial tension of a virgin olive oil with a known amount of free fatty acids was measured in supercritical carbon dioxide atmosphere at 313 K and 353 K and pressures up to 40 MPa. The obtained values were compared to different oils some of which contain appreciable amounts of volatile components. In general, interfacial tension behaviour is dominated by the effect of pressure, whereas differences between oil compositions are secondary. Besides mutual solubility interfacial tension is supposed to be associated with the compressibility of the dense fluid phase. For predicting mass transfer area some general comments on the colloidal behaviour of systems containing supercritical CO₂ are made     

Ultrasonic attenuation of edible oils

The frequency dependence (1–60 MHz) of the ultrasonic attenuation coefficient of canola oil, corn oil, olive oil, peanut oil, safflower oil, soybean oil, and sunflower oil was measured at 25°C. The attenuation coefficient of all the oils could be described by the relation: α ∼ Af ⁿ(with A between 6 and 40 × 10⁻¹², and n between 1.74 and 1.86).     

Quantitative determination of phospholipids in sunflower oil

Phospholipids from sunflower oil samples were enriched by using solid-phase extraction (SPE) cartridges and subsequently separated and analyzed by high-performance liquid chromatography (HPLC) with an ultraviolet detector. The recovery of individual phospholipids at different total concentrations in model oils and the repeatability of the method were investigated. The results demonstrated the utility of SPE-HPLC for quantitative analysis of phospholipids in sunflower oil and the effectiveness for concentrating, separating, identifying, and quantitating phospholipids in samples with phosphatide contents as low as 0.1%. Samples of sunflower oil at different stages of processing were analyzed, and phospholipid profiles in hexane-extracted oil, hot-pressed oil, and water-degummed oils were compared.     

Combination of silver ion and reversed-phase high-performance liquid chromatography in the fractionation of herring oil triacylglycerols

Triacylglycerols from North Atlantic herring (Clupea harengus) were separated according to the degree of unsaturation by high performance liquid chromatography (HPLC) in the silver ion mode. Each of the eleven fractions collected was then separated by reversed- phase HPLC, which in these circumstances separated the molecules according to the combined chain- lengths of the fatty acyl residues only. One hundred thirty fractions were obtained for fatty acid analysis. Almost 50% of the triacylglycerol molecules had six or more double bonds in their fatty acyl residues. Saturated-dimonoenes and disaturated- monoenes, 18.9% and 10.4%, respectively, were the most plentiful fractions of the more saturated species. Such a complex mixture of molecules was present that the most abundant subfractions from reversed- phase HPLC represented less than 5% of the total. Indeed, the largest single molecular species [16:0- 22:l- 22:6(n− 3)] represented only 2.8% of the total. These sequential analyses by complementary techniques made it possible to obtain a considerable amount of information on the composition of molecular species, but it was still not possible to identify all components.     

Simultaneous determination of lipophilic aldehydes by high-performance liquid chromatography in vegetable oil

A very sensitive high-performance liquid chromatography (HPLC) method was developed for the simultaneous separation and measurement of nonpolar and polar lipophilic secondary lipid peroxidation products in vegetable oil. Seventeen nonpolar and 13 polar lipophilic aldehydes and related carbonyl compounds, derived from thermally oxidized soybean oil as 2,4-dinitrophenyl hydrazones, were separated simultaneously by reversed-phase HPLC. Detection limit for the individual compounds is 1 ng. Thirteen of the nonpolar carbonyl compounds were identified as: butanal, 2-butanone, pentanal, 2-pentanone, hexenal, hexanal, 2,4-heptadienal, 2-heptenal, octanal, 2-nonenal, 2,4-decadienal, decanal, and undecanal. Three of the polar carbonyl compounds were identified as: 4-hydroxy-2-hexenal, 4-hydroxy-2-octenal, and 4-hydroxy-2-nonenal. The detection of the toxic 4-hydroxy-2-nonenal, a major compound, and 4-hydroxy-2-hexenal, a minor compound, in heated soybean oil is of particular importance because these toxic compounds have been shown to be absorbed from the diet.     

Rapid determination of oxidative stability of edible oils by FTIR spectroscopy using disposable IR cards

Disposable polytetrafluoroethylene (PTFE) polymer IR (PIR) cards were used as substrates to rapidly oxidize edible oils and simultaneously monitor the extent of oxidation by FTIR spectroscopy. Four edible oils were oxidized on PIR cards and in bulk at moderate temperature (58°C), and real-time oxidation plots were obtained by measuring changes in the IR hydroperoxide (ROOH) absorbance as a function of time. The relationship between the ROOH absorbance and PV was developed using a reference method to define absorbances corresponding to PV end points of 100 and 200 meq ROOH/kg for the oils oxidized in bulk and on cards, respectively. The real-time oxidation plots obtained for the oils oxidized in bulk and on cards were similar in appearance, but the oils on the cards reached the PV end point 20 times faster than the oils oxidized in bulk. The results indicate that the use of disposable PIR cards coupled with moderate heating and aeration provides a simple, practical, and rapid means for monitoring oxidation and determining the oxidative stability of edible oils at a normal storage temperature.     

Soybean oil triacylglycerol analysis by reversed-phase high-performance liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometry

Soybean oil triacylglycerols from genetically modified soybean lines were conclusively identified by reversed-phase high-performance liquid chromatography coupled with mass spectrometry with atmospheric pressure chemical ionization. Atmospheric pressure chemical ionization is a soft ionization technique which gives simple spectra for triacylglycerols. Spectral identification of the triacylglycerols was based on the molecular [M+1]⁺ ion and the 1(2)-, 2(3)- and 1(3)-diacylglycerol fragments. Triacylglycerols identified in high-stearic and high-palmitic soybean varieties were quantitated by reversed-phase high-performance liquid chromatography with flame-ionization detection. There was excellent agreement between the fatty acid composition calculated from the triacylglycerol composition and the fatty acid composition obtained by gas chromatography of the transmethylated oils. The oils of the modified soybean varieties, compared to typical soybean oil, contained increased content of triacylglycerols known to be more oxidatively stable, such as linoleoyloleoylstearoyl, linoleoylpalmitoylstearoyl, and linoleoyldipalmitoyl glycerols, and less triacylglycerols like trilinoleoylglycerol, known to decrease oxidative stability. This study showed that the atmospheric pressure chemical ionization technique is suitable for mass spectral identification of neutral molecules, such as triacylglycerols, which do not contain a chargeable functional group.     

Physical properties of liquid edible oils

Literature values of density, viscosity, adiabatic expansion coefficient, thermal conductivity, specific heat (constant pressure), ultrasonic velocity, and ultrasonic attenuation coefficient are compiled for a range of food oils and water at 20°C, and a series of empirical equations are suggested to calculate the temperature dependency of these parameters. The importance of these data to the application of ultrasonic particle-sizing instruments to food emulsions is discussed.     

Application of high-performance size-exclusion chromatography to study the autoxidation of unsaturated triacylglycerols

A combination of solid-phase extraction (SPE) and high-performance size-exclusion chromatography (HPSEC) was used to study the autoxidation of triacylglycerol (TAG) mixtures separated from low-erucic acid rapeseed oil and butter oil. The samples were autoxidized in the dark at 40°C for four weeks. The polar compounds of the autoxidated samples were separated by SPE (NH₂ stationary phase), and the polar fraction was further characterized by HPSEC with a series of three size-exclusion columns and an evaporative light-scattering detector. The polar fraction contained TAG polymers, polar TAG monomers (PTAG) and diacylglycerols. Peroxide values and anisidine values of the samples were also measured. By using three different types of TAG mixtures, it could be demonstrated that the PTAG content of the TAGs increases during autoxidation. A slight increase was also detected in polymer content. The correlation between PTAG content and the comparative measurements was considered significant. The results indicate that the measurement of PTAG and polymeric material content by HPSEC analysis can be used when studying the autoxidation level of edible oils and in characterizing the autoxidation products of different molecular sizes.     

Silver ion high-performance liquid chromatography of the triacylglycerols ofCrepis alpina seed oil

The triacylglycerols ofCrepis alpina oil were characterized because this oil has a high concentration of crepenynic (cis-9-octadecen-12-ynoic) acid, a fatty acid useful in the chemical synthesis of deuterated fats for human metabolism studies. The triacylglycerols were separated from the crude oil by solid-phase extraction. Resolution, quantitation and isolation of the individual triacylglycerols were performed by silver ion high-performance liquid chromatography on a commercial column, an acetonitrile in hexane isocratic mobile phase and flame-ionization detection. Isolated triacylglycerols were identified by capillary gas chromatography of their fatty acid methyl esters. Of the eleven eluted triacylglycerols ofCrepis alpina oil, 85% included 35% tricrepenynoyl, 34% linoleoyldicrepenynoyl and 16% dilinoleoylcrepenynoyl glycerols. Triacylglycerols eluted according to the numbers of alkene and alkyne bonds. Elution times, resolution and quantitation were reproducible over a three-month period. The flame-ionization detector response required no response factors for quantitation of the triacylglycerols present inCrepis alpina oil. The silver ion chromatography system permitted the identification of 95% of the triacylglycerols compared to 70% of the triacylglycerols previously identified with reversed-phase high-performance liquid chromatography.     

Catalytic hydroprocessing of cottonseed oil in petroleum diesel mixtures for production of renewable diesel

The conversion of the esters included in refined cottonseed oil into hydrocarbon molecules compatible with petroleum diesel, which are named renewable diesel, has been studied at conventional hydrotreatment conditions. The vegetable oil was fed in mixture with desulphurized petroleum diesel to the hydrotreater containing a conventional CoMo/Al₂O₃ hydrotreatment catalyst. Conversion of esters was determined in the temperature range of 305-345 °C, at 30 bar and for 5 h⁻¹ < WHSV < 25 h⁻¹. Catalyst deactivation was followed for a period of 450 h in operation. A simple kinetic model of ester conversion suitable for scale-up and simulation studies has been tested.     

Assessment of olive oil adulteration by reversed-phase high-performance liquid chromatography/amperometric detection of tocopherols and tocotrienols

A method involving reversed-phase high-performance liquid chromatography with amperometric detection has been developed for the analysis of tocopherols and tocotrienols in vegetable oils. The sample preparation avoids saponification. Recoveries of α-tocotrienol and γ-tocotrienol in extra virgin olive oil were 97.0 and 102.0%, respectively. No tocotrienols were detected in olive, hazelnut, sunflower, and soybean oils, whether virgin or refined. However, relatively high levels of tocotrienols were found in palm and grapeseed oils. This method could detect small quantities (1–2%) of palm and grapeseed oils in olive oil or in any tocotrienol-free vegetable oil and might, therefore, help assess authenticity of vegetable oils.     

Detection of olive oil adulteration with canola oil from triacylglycerol analysis by reversed-phase high-performance liquid chromatography

The objective of this study was to explore the use of reversed-phase high-performance liquid chromatography (RP-HPLC) as a means to detect adulteration of olive oil with less expensive canola oil. Previously this method has been shown to be useful in the detection of some other added seed oils; however, the detection of adulteration with canola oil might be more difficult due to similarities in fatty acid composition between canola oil and olive oil. Various mixtures of canola oil with olive oils were prepared, and RP-HPLC profiles were obtained. Adulteration of olive oil samples with less than 7.5% (w/w) canola oil could not be detected.     

The triacylglycerol structure of olive oil determined by silver ion high-performance liquid chromatography in combination with stereospecific analysis

The compositions of positionssn-1,sn-2 andsn-3 of triacylglycerols from “extra-virgin” olive oil (Olea europaea) were determined. The procedure involved preparation of diacyl-rac-glycerols by partial hydrolysis with ethyl magnesium bromide; 1,3-, 1,2- and 2,3-diacyl-sn-glycerols as (S)-(+)-1-(1-naphthyl)ethyl urethanes were isolated by highperformance liquid chromatography (HPLC) on silica, and their fatty acid compositions were determined. The same procedure was also carried out on the five main triacylglycerol fractions of olive oil after separation according to the degree of unsaturation by HPLC in the silver ion mode. Although stereospecific analysis of the intact triacyl-sn-glycerols indicated that the compositions of positionssn-1 andsn-3 were similar, the analyses of the molecular species demonstrated marked asymmetry. The data indicate that the “1-random, 2-random, 3-random” distribution theory is not always applicable to vegetable oils.     

Principal component analysis in fast atom bombardment-mass spectrometry of triacylglycerols in edible oils

Positive-ion fast atom bombardment-mass spectrometry, withm-nitrobenzyl alcohol as matrix and a methanolic sodium iodide (Nal) solution, was used to characterize edible oils by their triacylglycerol composition. Cationized triacylglycerols gave characteristic spectra for olive (57 samples), sunflower (9 samples), soybean (9 samples), corn (12 samples), and peanut (10 samples) oils. Relative abundance of [M + Na]⁺ ions showed relevant differences among the oils. The obtained data were analyzed with the aid of chemometrics by using principal component analysis (PCA) to evaluate the differentiation. Twelve variables were reduced to two principal components, accounting for 82% of the total variance. A two-dimensional plot of 97 PCA scores allowed the separation of the edible oils. The analysis is both fast and reproducible.     

Analysis of the monoenoic fatty acid distribution in hydrogenated vegetable oils by silver-ion high-performance liquid chromatography

A silver-ion high-performance liquid chromatography column (hexane/acetonitrile as solvent, ultraviolet detection) was used to analyze the fatty acid distribution (as fatty acid methyl esters) of a representative sample of hydrogenated oil. Fractions containingcis- andtrans-18:1 isomers were readily separated. The positional fatty acid isomers were separated by rechromatographing these fractions. The elution order and percent compositions were compared with results obtained by gas chromatography. Of the Δ8 to Δ14trans-18:1 isomers, only the Δ8 and Δ9 pair could not be separated. The Δ8 and Δ9cis-18:1 pair also could not be separated, and the Δ10 isomer was poorly separated from this pair. Area percents were comparable to results obtained by gas chromatography.