顶空气相色谱-质谱测定橄榄调和油中橄榄油含量

建立了测定橄榄调和油中橄榄油含量的顶空气相色谱-质谱分析方法。对样品量、加热温度、加热时间、进样量、进样模式、色谱柱进行了优化。通过化学计量学方法发现了橄榄油的特征化合物。取1.0 g样品放置于20 m L顶空瓶中,在180℃加热振摇2 700 s,取1.0 m L顶空气体进样,通过HP-88色谱柱分离和质谱检测。结果表明,方法的线性范围为0~100%(橄榄油含量),线性相关系数(r2)大于0.995,检出限为1.26%~2.13%,模拟橄榄调和油中橄榄油含量测定的偏差为-0.65%~1.02%,相对偏差为-1.3%~6.8%,相对标准偏差为1.18%~4.26%(n=6)。该方法不使用任何溶剂,操作简单、快速、环保,灵敏度和准确度高,适用于橄榄调和油中橄榄油含量的测定。     

Direct olive oil authentication: detection of adulteration of olive oil with hazelnut oil by direct coupling of headspace and mass spectrometry, and multivariate regression techniques

Control of adulteration of olive oil, together with authentication and contamination, is one of the main aspects in the quality control of olive oil. Adulteration with hazelnut oil is one of the most difficult to detect due to the similar composition of hazelnut and olive oils; both virgin olive oil and olive oil are subjected to that kind of adulteration. The main objective of this work was to develop an analytical method able to detect adulteration of virgin olive oils and olive oils with hazelnut oil by means of its analysis by a headspace autosampler directly coupled to a mass spectrometer used as detector (ChemSensor). As no chromatographic separation of the individual components of the samples exists, a global signal of the sample is obtained and employed for its characterization by means of chemometric techniques. Four different crude hazelnut oils from Turkey were employed for the development of the method. Multivariate regression techniques (partial least squares and principal components analysis) were applied to generate adequate regression models. Good values were obtained in both techniques for the parameters employed (standard errors of prediction (SEP) and prediction residual error sum of squares (PRESS)) to evaluate its goodness. With the proposed method, minimum adulteration levels of 7 and 15% can be detected in refined and virgin olive oils, respectively. Once validated, the method was applied to the detection of such adulteration in commercial olive oil and virgin olive oil samples.     

Chemometrics-assisted gas chromatographic-mass spectrometric analysis of volatile components of olive leaf oil

Iranian olive leaf essential oil components were extracted by microwave-assisted hydrodistillation and analyzed using gas chromatography-mass spectrometry. Ninety-seven components were identified by direct similarity searches for olive leaf essential oil. Chemometrics was used to find more components with the help of multivariate curve resolution methods. Eigenvalues-based methods and Malinowski functions were used for chemical rank determination of GC–MS data. Multivariate curve resolution-alternative least squares as an iterative method was used for resolving the overlapped and embedded peaks. With the use of this method the number of 97 components was extended to 127 components. Major constituents in the olive leaf essential oil are 2-decenal-(E) (20.43 %), benzeneacetaldehyde (4.00 %), 2-undecenal (3.71 %) and valencen (3.31 %).     

MINOR SURFACE-ACTIVE LIPIDS OF OLIVE OIL AND VISCOELASTICITY OF PROTEIN FILMS AT THE OLIVE OIL-WATER INTERFACE

The influence of the minor surface-active lipids of olive oil on the viscoelastic parameters of bovine serum albumin, sodium caseinate and egg yolk films, formed following adsorption at the olive oil-protein solution interface, was studied. All the parameters substantialy decreased in the case of bovine serum albumin when surface-active lipids were removed from the olive oil while the absence of these components resulted in purely viscous films in the cases of sodium caseinate and egg yolk. Protein film viscoelasticity is probably influenced by olive oil surface-active lipids as a result of their interactions with adsorbed and unfolded protein molecules at the oil-protein solution interface.     

Determination of α-Tocopherol in Olive Oil by Solid-Phase Microextraction and Gas Chromatography–Mass Spectrometry

Olive oil has great human health benefits and is an important component of the Mediterranean diet. Its quality, sensory attributes, and oxidative stability are linked to the presence of minor compounds. Vitamin E (α-tocopherol) is a key component in these properties. In this work, solid-phase microextraction coupled to gas chromatography–mass spectrometry was used for the determination of α-tocopherol in olive oil. The analytical performance of the method has been assessed in fortified olive oil with negligible vitamin E concentrations. The calibration curve was linear from 0.020 to 0.500?mg/g. The limits of detection and quantification were 0.006 and 0.021?mg/g, respectively. Intraday and interday relative standard deviations were 3.2 and 10.0, respectively, and were concentration independent. The method was used for the determination of α-tocopherol in virgin and extra virgin olive oil, reporting average concentrations of 0.044?±?0.03 and 0.200?±?0.05?mg/g, respectively. Overall, the method is simple, sensitive, rapid, and solvent free, and provided high recoveries of 97.7?±?3.1%. In addition, vitamin E stability in extra-virgin olive oil was characterized by a shelf-life study.     

Independent components analysis coupled with 3D-front-face fluorescence spectroscopy to study the interaction between plastic food packaging and olive oil

Olive oil is one of the most valued sources of fats in the Mediterranean diet. Its storage was generally done using glass or metallic packaging materials. Nowadays, plastic packaging has gained worldwide spread for the storage of olive oil. However, plastics are not inert and interaction phenomena may occur between packaging materials and olive oil. In this study, extra virgin olive oil samples were submitted to accelerated interaction conditions, in contact with polypropylene (PP) and polylactide (PLA) plastic packaging materials. 3D-front-face fluorescence spectroscopy, being a simple, fast and non destructive analytical technique, was used to study this interaction. Independent components analysis (ICA) was used to analyze raw 3D-front-face fluorescence spectra of olive oil. ICA was able to highlight a probable effect of a migration of substances with antioxidant activity. The signals extracted by ICA corresponded to natural olive oil fluorophores (tocopherols and polyphenols) as well as newly formed ones which were tentatively identified as fluorescent oxidation products. Based on the extracted fluorescent signals, olive oil in contact with plastics had slower aging rates in comparison with reference oils. Peroxide and free acidity values validated the results obtained by ICA, related to olive oil oxidation rates. Sorbed olive oil in plastic was also quantified given that this sorption could induce a swelling of the polymer thus promoting migration.     

Determination of olive oil acidity by CE

In this work, a CE method for the determination of olive oil acidity was proposed. The method was based on an ethanolic extraction (at 60 degrees C) of the oil long-chain free fatty acids (LC-FFAs) components followed by CE determination in pH 6.86 phosphate buffer at 15 mmol/L concentration containing 4 mmol/L sodium dodecylbenzenesulfonate (SDBS), 10 mmol/L polyoxyethylene 23 lauryl ether (Brij 35), 2% v/v 1-octanol and 45% v/v ACN under indirect UV detection at 224 nm. Although this electrolyte promoted baseline separation of myristic acid (C14:0) (internal standard (IS)) and olive oil major components (palmitic acid (C16:0), oleic acid (C18:1c) and linoleic acid (C18:2cc)) in less than 8 min, after a few injections, the electropherogram profiles were severely altered (peak broadening, migration time shifts, etc.) and the current increased substantially. An adsorption study was conducted revealing that the dissolution of the capillary external polyimide coating during the electrophoretic run caused the detrimental effect. After removal of the capillary tip coating, ten consecutive injections could be performed without any disturbances and this simple procedure was, therefore, implemented during quantitative purposes. The reliability of the proposed method was further investigated by the determination of acidity of an extra virgin olive oil sample in comparison to the established methodology (AOCS method Ca 5a-40, alkaline volumetric titration (AVT)). No statistical differences were found within 95% confidence level. A % acidity of 0.39 +/- 0.02 was found for the olive oil sample under consideration.     

Oxidative stability and phenolic content of virgin olive oil: an analytical approach by traditional and high resolution techniques

The characteristic resistance to oxidation of virgin olive oil is related to its unique fatty acid composition in addition to several minor components that have antioxidant properties. Among the latter, phenols are the most important. Several factors can influence the chemical or enzymatic oxidative processes that extend or shorten the shelf-life of olive oil. Furthermore, the amount of phenolic compounds extracted during production is fundamental for the oxidative and nutritional quality of the oil. In fact, it is well known that different steps used for preparation of virgin olive oil may determine differences in the quantities of phenol. At present, various analytical methods are available to analyze the hydrophilic components, including spectrophotometric assays (traditional) and high resolution chromatographic techniques (HRGC, HPLC, HPCE). In this review we summarize these different methodologies and demonstrate that the amount of phenolic compounds in virgin olive oil as determined by both traditional and high resolution techniques can be influenced by different factors including the olive cultivar and degree of ripeness, as well as by production and extraction technologies.     

Rapid determination of BTEXS in olives and olive oil by headspace-gas chromatography/mass spectrometry (HS-GC-MS)

In this work, a straightforward, reliable and effective automated method has been developed for the direct determination of monoaromatic volatile BTEXS group (namely benzene, toluene, ethylbenzene, o-, m- and p-xylenes, and styrene) in olives and olive oil, based on headspace technique. Separation, identification and quantitation were carried out by headspace-gas chromatography-mass spectrometry (HS-GC-MS) in selected ion monitoring (SIM) mode. Sample pretreatment or clean-up were not necessary (besides olives milling) because the olives and olive oil samples are put directly into an HS vial, automatically processed by HS and then injected in the GC-MS for chromatographic analysis. The chemical and instrumental variables were optimized using spiked olives and olive oil samples at 50 μg kg⁻¹ of each targeted species. The method was validated to ensure the quality of the results. The precision was satisfactory with relative standard deviations (RSD (%)) in the range 1.6-5.2% and 10.3-14.2% for olive oil and olives, respectively. Limits of detection were in the range 0.1-7.4 and 0.4-4.4 μg kg⁻¹ for olive oil and olives, respectively. Finally, the proposed method was applied to the analysis of real olives and olive oil samples, finding positives of the studied compounds, with overall BTEXS concentration levels in the range 23-332 μg kg⁻¹ and 4.2-87 μg kg⁻¹ for olive oil and olives, respectively.     

13C nuclear magnetic resonance spectroscopy to determine olive oil grades

¹³C nuclear magnetic resonance spectroscopy was used in a first attempt to differentiate olive oil samples by grades. High resolution ¹³C NMR Distortionless Enhancement by Polarization Transfer (DEPT) spectra of 137 olive oil samples from the four grades, extra virgin olive oils, olive oils, olive pomace oils and lampante olive oils, were measured. The data relative to the resonance intensities (variables) of the unsaturated carbons of oleate (C-9 and C-10) and linoleate (L-9, L-10 and L-12) chains attached at the 1,3- and 2-positions of triacylglycerols were analyzed by linear discriminant analysis. The 1,3- and 2- carbons of the glycerol moiety of triacylglycerols along with the C-2, C-16 and C-18 resonance intensities of saturated, oleate and linoleate chains were also analyzed by linear discriminant analysis. The three discriminanting functions, which were calculated by using a stepwise variable selection algorithm, classified in the true group by cross-validation procedure, respectively, 76.9, 70.0, 94.4 and 100% of the extra virgin, olive oil, olive pomace oil and lampante olive oil grades.     

常压火焰离子化质谱技术对食用植物油快速分析的初探

建立了常压火焰离子化质谱(Ambient flame ionization mass spectrometry,AFI-MS)快速分析食用植物油(橄榄油、芝麻油、花生油和葵花籽油)的方法。AFI-MS检出食用植物油(橄榄油、芝麻油、花生油和葵花籽油)中的26种甘油三酯和11种甘油二脂。AFI-MS分析显示,不同的食用植物油(橄榄油、芝麻油、花生油和葵花籽油)得到的质谱图轮廓信息不同。通过对不同食用植物油的甘油三酯相对峰强度进行分析,可初步归纳出食用植物油的类型。AFI-MS分析食用植物油的操作简单,普通的打火机就可以作为离子源用于食用植物油的分析。这种便捷的离子化技术可以用于食用植物油的快速分析。     

Stabilization of nonaqueous foam with lamellar liquid crystal particles in diglycerol monolaurate/olive oil system

Nonaqueous foams stabilized by lamellar liquid crystal (L alpha) dispersion in diglycerol monolaurate (designated as C12G2)/olive oil systems are presented. Foamability and foam stability depending on composition and the effects of added water on the nonaqueous foaming behavior were systematically studied. It was found that the foamability increases with increasing C12G2 concentration from 1 to 3 wt% and then decreases with further increasing concentration, but the foam stability increases continuously with concentration. Depending on compositions, foams are stable for a few minutes to several hours. Foams produced by 10 wt% C12G2/olive oil system are stable for more than 6 h. In the study of effects of added water on the foaming properties of 5 wt% C12G2/olive oil system, it was found that the foamability and foam stability of 5 wt% C12G2/olive oil decreases upon addition of 1 wt% water, but with further increasing water, both the foamability and foam stability increase. Foams with 10% water added system are stable for approximately 4 h. Phase behavior study of the C12G2 in olive oil has shown the dispersion of L alpha particles in the dilute regions at 25 degrees C. Thus, stable foams in the C12G2/olive oil system can be attributed to L alpha particle, which adsorb at the gas-liquid interface as confirmed by surface tension measurements and optical microscopy. Laser diffraction particle size analyzer has shown that the average particle diameter decreases with increasing the C12G2 concentration and, hence, the foams are more stable at higher surfactant concentration. Judging from foaming test, optical micrographs, and particle size, it can be concluded that stable nonaqueous foams in the studied systems are mainly caused by the dispersion of L alpha particles and depending on the particle size the foam stability largely differs.     

Differential scanning calorimetry: a potential tool for discrimination of olive oil commercial categories

Differential scanning calorimetry thermograms of five commercial categories of olive oils (extra virgin olive oil, olive oil, refined olive oil, olive-pomace oil and refined olive-pomace oil) were performed in both cooling and heating regimes. Overlapping transitions were resolved by deconvolution analysis and all thermal properties were related to major (triacylglycerols, total fatty acids) and minor (diacylglycerols, lipid oxidation products) chemical components.All oils showed two well distinguishable exothermic events upon cooling. Crystallization enthalpies were significantly lower in olive oils due to a more ordered crystal structure, which may be related to the higher triolein content. Pomace oils exhibited a significantly higher crystallization onset temperature and a larger transition range, possibly associated to the higher amount of diacylglycerols. Heating thermograms were more complex: all oils exhibited complex exo- and endothermic transitions that could differentiate samples especially with respect to the highest temperature endotherm.These preliminary results suggest that both cooling and heating thermograms obtained by means of differential scanning calorimetry may be useful for discriminating among olive oils of different commercial categories.     

A New Definition of the Term “High-Phenolic Olive Oil” Based on Large Scale Statistical Data of Greek Olive Oils Analyzed by qNMR

In the last few years, a new term, “High-phenolic olive oil”, has appeared in scientific literature and in the market. However, there is no available definition of that term regarding the concentration limits of the phenolic ingredients of olive oil. For this purpose, we performed a large-scale screening and statistical evaluation of 5764 olive oil samples from Greece coming from >30 varieties for an eleven-year period with precisely measured phenolic content by qNMR. Although there is a large variation among the different cultivars, the mean concentration of total phenolic content was 483 mg/kg. The maximum concentration recorded in Greece reached 4003 mg/kg. We also observed a statistically significant correlation of the phenolic content with the harvest period and we also identified varieties affording olive oils with higher phenolic content. In addition, we performed a study of phenolic content loss during usual storage and we found an average loss of 46% in 12 months. We propose that the term high-phenolic should be used for olive oils with phenolic content > 500 mg/kg that will be able to retain the health claim limit (250 mg/kg) for at least 12 months after bottling. The term exceptionally high phenolic olive oil should be used for olive oil with phenolic content > 1200 mg/kg (top 5%).     

Multivariate analysis of HT/GC-(IT)MS chromatographic profiles of triacylglycerol for classification of olive oil varieties

The ability of multivariate analysis methods such as hierarchical cluster analysis, principal component analysis and partial least squares-discriminant analysis (PLS-DA) to achieve olive oil classification based on the olive fruit varieties from their triacylglycerols profile, have been investigated. The variations in the raw chromatographic data sets of 56 olive oil samples were studied by high-temperature gas chromatography with (ion trap) mass spectrometry detection. The olive oil samples were of four different categories (“extra-virgin olive oil”, “virgin olive oil”, “olive oil” and “olive-pomace” oil), and for the “extra-virgin” category, six different well-identified olive oil varieties (“hojiblanca”, “manzanilla”, “picual”, “cornicabra”, “arbequina” and “frantoio”) and some blends of unidentified varieties. Moreover, by pre-processing methods of chemometric (to linearise the response of the variables) such as peak-shifting, baseline (weighted least squares) and mean centering, it was possible to improve the model and grouping between different varieties of olive oils. By using the first three principal components, it was possible to account for 79.50% of the information on the original data. The fitted PLS-DA model succeeded in classifying the samples. Correct classification rates were assessed by cross-validation.     

Discriminating olive and non-olive oils using HPLC-CAD and chemometrics

This work presents a method for an efficient differentiation of olive oil and several types of vegetable oils using chemometric tools. Triacylglycerides (TAGs) profiles of 126 samples of different categories and varieties of olive oils, and types of edible oils, including corn, sunflower, peanut, soybean, rapeseed, canola, seed, sesame, grape seed, and some mixed oils, have been analyzed. High-performance liquid chromatography coupled to a charged aerosol detector was used to characterize TAGs. The complete chromatograms were evaluated by PCA, PLS-DA, and MCR in combination with suitable preprocessing. The chromatographic data show two clusters; one for olive oil samples and another for the non-olive oils. Commercial oil blends are located between the groups, depending on the concentration of olive oil in the sample. As a result, a good classification among olive oils and non-olive oils and a chemical justification of such classification was achieved.     

Determination of pesticide residues by GC-MS using analyte protectants to counteract the matrix effect.

An analytical method was developed to determine pesticides of various chemical classes in soil, juice and honey using analyte protectants to counteract the enhancement of the chromatographic response produced by the presence of matrix components (matrix effect). This effect was more pronounced for soil and honey samples than for juice samples; regarding the pesticide chemical class, organochlorine pesticides were less affected by the presence of matrix components than triazines and organophosphorus pesticides. Several analyte protectants (2,3-butanediol, L-gulonic acid gamma-lactone, corn oil and olive oil) were tested for counteracting the observed matrix effect. L-Gulonic acid gamma-lactone was an effective protecting agent for most of the pesticides studied in soil and honey samples, whereas olive oil was very effective for juice samples. The combination of these two protectants was found to be an effective analyte protectant for all compounds in soil and honey samples.     

The variability of composition of the volatile fraction of olive oil

Aroma of olive oil is a very complex mixture of components. Analysis of head space of a series of virgin olive oil samples indicate a great variability of volatile substances composition in olives and these data probably should be related to the story of olives after collecting.     

Direct olive oil analysis by low‐temperature plasma (LTP) ambient ionization mass spectrometry

A fast, reagentless, and direct method is presented for the mass spectrometric analysis of olive oil without any sample pretreatment whatsoever. An ambient ionization technique, the low‐temperature plasma (LTP) probe, based on dielectric barrier discharge, is used to detect both minor and trace components (free fatty acids, phenolics and volatiles) in raw untreated olive oil. The method allows the measurement of free fatty acids (the main quality control parameter used to grade olive oil according to quality classes), selected bioactive phenolic compounds, and volatiles. The advantages and limitations of the direct analysis of extremely complex mixtures by the ambient ionization/tandem mass spectrometry combination are discussed and illustrated. The data presage the possible large‐scale application of direct mass spectrometric analysis methods in the characterization of olive oil and other foodstuffs. Copyright © 2009 John Wiley & Sons, Ltd.     

Comparative study of electrospray and photospray ionization sources coupled to quadrupole time-of-flight mass spectrometer for olive oil authentication

The use of fast and reliable analytical procedures for olive oil authentication is a priority demand due to its wide consumption and healthy benefits. Olive oil adulteration with other cheaper vegetable oils is a common practice that has to be detected and controlled. Rapid screening methods based on high resolution tandem mass spectrometry constitute today the option of choice due to sample handling simplicity and the elimination of the chromatographic step. The selection of the ionization source is critical and the comparison of their reliability necessary. The possibilities of the direct infusion electrospray ionization (ESI) and the recently introduced atmospheric pressure photospray ionization source (APPI), coupled to quadrupole time-of-flight (QqTOF), have been critically studied and compared to control olive oil adulteration. These techniques are very rapid (approximately 1 min per sample) and have high discrimination power to elucidate key components in the edible oils studied (olive, hazelnut, sunflower and corn). Nevertheless, both sources are complementary, being APPI more sensitive for monoacyl- and diacylglycerol fragment ions and ESI for triacylglycerols. In addition, methods reproducibility's are very high, especially for APPI source. Mixtures of olive oil with the others vegetable oils can be easily discriminated which has been tested by using principal components analysis (PCA) with both ESI-MS and APPI-MS spectra. Analogously, linear discriminant analysis (LDA) confirms methods reproducibility and detection of other oils used as adulterants, in particular hazelnut oil, which is especially difficult given its chemical similarity with olive oil.