Extra Virgin Olive Oil Samples Research Articles

Pigments in extra virgin olive oils produced in different mediterranean countries in 2014: Near UV-vis spectroscopy versus HPLC-DAD

Carotenoids and chlorophyll derivatives play a key role in Extra Virgin Olive Oils (EVOOs). Many factors, such as cultivar, geographic origin, maturity of olives, climate and storage conditions, influence the pigments’ content. The quantification of pigments is usually done by chromatographic techniques. However, recent works evidenced the potentialities of UV-visible-related methodologies. In this research, a selection of EVOO samples produced from olives harvested at the beginning of November 2014 in Greece, Tunisia, Italy and Spain, was investigated in terms of pigments by means of two methods. The first one is a recent approach based on the mathematical treatment of near UV-vis absorption spectra of olive oils to quantify in a fast, cheap and non-destructive way four main pigments, namely β-carotene, lutein, pheophytin A and pheophytin B. The second one is a more standard HPLC-DAD method. From the comparison between the two methods, we can conclude that the new near UV-vis approach gives reliable results, with good precision and high reproducibility. Pigments quantified by these two methods in EVOOs produced in four countries from different cultivars are analyzed by principal component analysis (PCA). Results indicate that pigments can be correlated to several factors such as ripeness stage, geographic origin and cultivars.

Evaluation of MALDI‐TOF/MS Technology in Olive Oil Adulteration

AbstractAdulteration of extra virgin olive oil (EVOO) by addition of other vegetable oils or lower‐grade olive oils is a common problem of the oil market worldwide. Therefore, we developed a fast protocol for detection of EVOO adulteration by mass spectrometry fingerprinting of triacylglycerol (TAG) profiles based on MALDI‐TOF/MS. For that purpose, EVOO TAG profiles were compared with those of edible sunflower oil and olive oil composed of refined olive oil and virgin olive oils. Adulteration of EVOO was simulated by addition of sunflower and mixture of refined olive oil and virgin olive oils at 1, 10 and 20% w/w. Results of mass spectrometry TAG profiling were compared with routinely assessed K values for identification of adulteration. MALDI‐TOF/MS technology coupled with statistical analysis was proven as useful for detection of adulteration in EVOO at a rate down to 1%. In contrast, standard spectrophotometric methods failed to identify minor adulterations. In addition, the ability of MALDI‐TOF/MS in detection of adulteration was tested on EVOO samples from different geographical regions. Results demonstrated that MALDI‐TOF/MS technology coupled with statistical analysis is able to distinguish adulterated oils from other EVOO.

Resolution-optimized headspace gas chromatography-ion mobility spectrometry (HS-GC-IMS) for non-targeted olive oil profiling.

A prototype gas chromatography-ion mobility spectrometry (GC-IMS) system, hyphenating temperature-ramped headspace GC to a modified drift time IMS cell, was evaluated and compared to a conventional, isothermal capillary column (CC)-IMS system on the example of the geographical differentiation of extra virgin olive oils (EVOO) from Spain and Italy. It allows orthogonal, 2D separation of complex samples and individual detection of compounds in robust and compact benchtop systems. The information from the high-resolution 3D fingerprints of volatile organic compound (VOC) fractions of EVOO samples were extracted by specifically developed chemometric MATLAB® routines to differentiate between the different olive oil provenances. A combination of unsupervised principal component analysis (PCA) with two supervised procedures, linear discriminant analysis (LDA) and k-nearest neighbors (kNN), was applied to the experimental data. The results showed very good discrimination between oils of different geographical origins, featuring 98 and 92% overall correct classification rate for PCA-LDA and kNN classifier, respectively. Furthermore, the results showed that the higher resolved 3D fingerprints obtained from the GC-IMS system provide superior resolving power for non-targeted profiling of VOC fractions from highly complex samples such as olive oil. Graphical abstract Principle of the determination of geographic origins of olive oils by chemometric analysis of three-dimensional HS-GC-IMS fingerprints.

Transfer of multivariate classification models applied to digital images and fluorescence spectroscopy data

This work evaluates the use of transfer of classification models for identifying adulteration of extra virgin olive oil (EVOO) samples involving, separately, two analytical techniques: fluorescence spectroscopy and digital imaging. The chemometric procedures, including development of classification models and application of classification transfer methods, were performed individually for each analytical technique. Methods of direct standardization (DS) and piecewise direct standardization (PDS) were applied to transfer samples sets in order to estimate an adjustment function and apply it to a samples set measured by the secondary instrument. For purposes of comparison, classification models were built based on linear discriminant analysis (LDA) with previous selection of variables by the successive projections algorithm (SPA), and partial least squares discriminant analysis (PLS-DA). The performance of the classification models was evaluated according to the number of errors and correct classification rate (CCR) for the prediction set measured by the secondary instrument. Before standardization, SPA-LDA and PLS-DA models achieved the same CCR using two analytical techniques: 54% for fluorescence emission spectra and 47% for histograms of digital images. After the standardization, a substantial increase of the CCR was observed. For the SPA-LDA models, a CCR of 88% was obtained for the fluorescence emission spectra and 82% for the histograms of the digital images. The PLS-DA classification models reached 85% and 76% of CCR for the fluorescence and imaging data, respectively, after standardization. These results demonstrate the efficiency of standardization procedures applied to multivariate classification models developed from fluorescence spectroscopy and digital images.

Fast Fluorescence Spectroscopy Methodology to Monitor the Evolution of Extra Virgin Olive Oils Under Illumination

Detailed regions of excitation and emission wavelengths for extra virgin olive oil samples have been extracted from three dimensional front-face fluorescence spectra. Information was applied to establish a right-angle fluorescence procedure. A right-angle device was assembled and tested with simultaneous excitation from 200 to 400 nm and registration of the fluorescence signal emitted from 400 to 850 nm. A principal component analysis was performed on the signal ranging from 400 to 550 nm from spectra of olive oils officially categorized as extra virgin in order to model the expected variability of compounds related to oxidative processes. Such model was useful to monitor the spectral evolution of extra virgin olive oil samples acquired at retail markets, which were exposed to indirect light during 2 months, through the analysis of the effect on their scores. Three relevant peaks characterized such evolution, with local maxima at around 434 to 437, 464 to 469 and 510 to 518 nm. Polynomial relationship was found between the evolution of those peaks and that of the chlorophyll, at around 670 to 673 nm, with R2 values of 0.98 and 0.99.

Fast Automated Determination of Total Tocopherol Content in Virgin Olive Oil Using a Single Multicommuted Luminescent Flow Method

Tocopherols are natural fluorophores of great importance for the characterization and authentication of virgin olive oil. Herein, a single automatic multicommuted flow method has been developed for the determination of total tocopherol content as well as the semi-quantitative estimation of α-tocopherol in extra virgin olive oil (EVOO) samples. Only appropriate dilution of samples with 2-propanol was necessary for their direct analysis by a multicommuted flow injection (MCFIA) manifold based on three solenoid valves with fluorescence detection. The peak height at λ em = 330 nm (emission) with λ exc at 296 nm was used as analytical signal. Linear response was observed within the range from 50 to 350 mg of tocopherols (expressed as α-tocopherol kg−1 olive oil), suitable to cover the usual range for tocopherols in (extra) virgin olive oil ((E)VOO)). The results were consistent with those obtained by reversed-phase HPLC reference method, whereas the analysis time was significantly reduced. The sample frequency of the proposed automatic method was close to 40 samples h−1, in contrast to typically 15–30 min required by HPLC. The method is fast, straightforward, cost-effective, and easy to implement in routine laboratories for screening purposes.

Pedologic Factors Affecting Virgin Olive Oil Quality of “Chemlali” Olive Trees (<i>Olea europaea</i> L.)

The aim of this study examined the characterization of extra virgin olive oil samples from the main cultivar Chemlali, grown in five olive orchards with different soil type (Sandy, Clay, Stony, Brown, Limestone and Gypsum). Volatile compounds were studied using headspace-solid phase micro-extraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS) technics. Moreover, the sterol profile was established using gas chromatography-mass spectrometry. 35 different volatile compounds were identified: alcohols, esters, aldehydes, ketones and hydrocarbons. The chemical composition of the volatile fraction was characterized by the preeminence of 2-hexenal (32.75%) and 1-hexanol (31.88%). Three sterols were identified and characterized. For all olive oil samples, ß-sitosterol (302.25 mg/kg) was the most abundant sterol. Interestingly, our results showed significant qualitative and quantitative differences in the levels of the volatile compounds and sterols from oils obtained from olive trees grown in different soil type.

α-Tocopherol, β-carotene, lutein, squalene and secoiridoids in seven monocultivar Italian extra-virgin olive oils

Fatty acids and bioactive lipophilic and hydrophilic compounds (tocopherols, β-carotene, lutein, squalene, total polyphenols and secoiridoids) in monocultivar Italian extra-virgin olive oil (EVOO) samples produced from the Leccino cultivar and six other yet uncharacterised cultivars (Rustica, Carpinetana, Dritta, Gentile di Chieti and Intosso) were analysed, also taking into account the effect of the type of decanter used for the oil extraction. Significant differences among cultivars were found for α-tocopherol and squalene, but not for carotenoids. Among phenols, cultivars significantly influenced oleuropein and ligstroside aglycones contents, but not those of the dialdehydic form of decarboxymethyl elenolic acid linked neither to tyrosol nor hydroxytyrosol. As previously reported, phenol is quantitatively affected by the type of decanter used for oil extraction. Accordingly, we found that the two-phases decanter preserved in the oil 1.5 times more phenolic compounds as compared with three-phases, whereas it did not influence the amount of lipophilic compounds. Moreover, our data statistically support the finding that type of decanter affects phenols also qualitatively. In fact, the two-phases decanter preferably preserved more the hydroxytyrosol secoiridoid derivatives than the tyrosol ones. Our results from one hand characterise for the first time oils previously unreported, from the other give some new indications on the relative role of factors relevant for the achievement of biologically active extra-virgin oil, i.e. the cultivar and technological ones.

A paper-based platform with a pencil-drawn dual amperometric detector for the rapid quantification of ortho-diphenols in extravirgin olive oil

A simple, sensitive and fast responding device is described for the discrimination of hydrophilic ortho-diphenols, whose presence in abundant enough amounts is typical for extra virgin olive oils (EVOOs), from hydrophilic mono-phenols instead present in almost all vegetable oils. It consists of a dual electrode detector pencil-drawn at the end of a paper microfluidic channel, defined by hydrophobic barriers, where samples of these antioxidants, extracted from vegetable oils by a 80:20% v/v acetonitrile/water mixture, were applied. Thin-layer chromatographic runs conducted by using a 0.01 M H2SO4 + 1 M KCl running buffer allowed the selective detection of hydrophilic ortho-diphenols by profiting from the fact that they undergo reversible oxidation at less positive potentials than those required by monophenols for displaying their irreversible anodic process. On this basis, a potential for the oxidation of hydrophilic ortho-diphenols was applied to the upstream pencil-drawn electrode (W1) (at which a minor fraction of mono-phenols was also oxidized), while a potential for the reverse process involving the sole product (ortho-quinones) of the reversible oxidation of ortho-diphenols was imposed at the downstream pencil-drawn working electrode (W2). Thus, cathodic peak currents linearly dependent on analyte concentrations could be recorded at W2 which led to a satisfactory detection limit (8 μM, equivalent to 1.23 mg/L) even when working electrodes W1 and W2 with same dimensions were employed. Improved sensitivities and lower detection limits were achieved by increasing the dimensions of W2 with respect to W1, thanks to the improvement of the collection efficiency. Throughout this investigation, hydroxytyrosol (HTy) and tyrosol (Ty) were adopted as models of ortho-diphenols and mono-phenols, respectively, in view of their abundant presence in EVOOs. Real samples of EVOO from different production companies, of a simple olive oil and of a sunflower oil were analyzed. Different hydrophilic ortho-diphenol contents were found in EVOO samples (up to 40.8 mg/kg), while only a negligible amount turned out to be present in simple olive oil. No trace of these antioxidants were instead found in sunflower oil, as expected. All concentrations found were in good agreement with those detected by a more frequently employed spectrophotometric method used for the sake of comparison.

Determination of Squalene in Organic Extra Virgin Olive Oils (EVOOs) by UPLC/PDA Using a Single-Step SPE Sample Preparation

In this paper, a simple extraction and fast detection procedure was used to determine squalene (SQ) in extra virgin olive oils (EVOOs). SQ was purified from EVOOs by an efficient single-step solid phase extraction (SPE), and its content was determined using an UPLC-PDA instrument. The adopted technique was evaluated for accuracy, linearity, sensitivity, and repeatability. The precision of the SPE extraction was satisfactory and the mean recoveries were 91.9 ± 0.4 and 96.3 ± 0.3 % for 25 and 50 mg L−1 level of addition, respectively. The selected chromatographic conditions allowed a very fast SQ determination; in fact, it was well separated in ∼0.54 min with good resolution. The UPLC method showed a good linearity in the range 50–500 mg L−1 (R 2 = 0.9998). Method sensitivity was evaluated by measuring the limits of detection (LOD) that was 0.3 mg L−1. The method was utilized for SQ determination in 33 different organic EVOO samples, coming from different countries (Turkey, Tunisia, Spain, Portugal, Greece, USA, Slovenia, Albania, Israel, Italy) and the data were statistically evaluated.

Geographical discrimination of extra-virgin olive oils from the Italian coasts by combining stable isotope data and carotenoid content within a multivariate analysis

We have determined the isotopic composition and the carotenoid contents of 38 extra-virgin olive oils (EVOOs) from seven regions along the Italian coasts, by means of isotope ratio mass spectrometry (IRMS) and resonant Raman spectroscopy (RRS), respectively. The application of linear discriminant analysis to our overall results demonstrated the combination of isotope and carotenoid data is a promising method to discriminate EVOOs from production sites that are impacted by similar geographical and climatic parameters. In particular, this dual approach allowed correct classification of 82% EVOO samples, while separate IRMS and RRS investigations were able to discriminate only samples from Sicily and Latium, respectively.

Combined untargeted and targeted fingerprinting with comprehensive two-dimensional chromatography for volatiles and ripening indicators in olive oil

Comprehensive two-dimensional gas chromatography (GC × GC) is the most effective multidimensional separation technique for in-depth investigations of complex samples of volatiles (VOC) in food. However, each analytical run produces dense, multi-dimensional data, so elaboration and interpretation of chemical information is challenging.This study exploits recent advances of GC × GC-MS chromatographic fingerprinting to study VOCs distributions from Extra Virgin Olive Oil (EVOO) samples of a single botanical origin (Picual), cultivated in well-defined plots in Granada (Spain), and harvested at different maturation stages. A new integrated work-flow, fully supported by dedicated and automated software tools, combines untargeted and targeted (UT) approaches based on peak-region features to achieve the most inclusive fingerprinting.Combined results from untargeted and targeted methods are consistent, reliable, and informative on discriminant features (analytes) correlated with optimal ripening of olive fruits and sensory quality of EVOOs. The great flexibility of the UT fingerprinting here adopted enables retrospective analysis with great confidence and provides data to validate the transferability of ripening indicators ((Z)-3-hexenal, (Z)-2-hexenal, (E)-2-pentenal, nonanal, 6-methyl-5-hepten-2-one, octane) to external samples sets. Direct image comparison, based on visual features, also is investigated for quick and effective pair-wise investigations. Its implementation with reliable metadata generated by UT fingerprinting confirms the maturity of 2D data elaboration tools and makes advanced image processing a real perspective.

Determination of Bitterness of Extra Virgin Olive Oils by Amperometric Detection

AbstractA flow injection system with amperometric detection at potentials poised at +0.4 and +0.9 V was used to evaluate intensity of the bitter taste in monovarietal Extra Virgin Olive Oils (EVOO). Results from the proposed method were based on the extraction of the bitter constituents of the virgin olive oil samples in methanol‐water, followed by the direct amperometric measurement. These potentials were selected according to the hydrodynamic voltammogram of oleuropein, one of the most prominent and bitter phenolic compound found in EVOO. The amperometric detection was applied on 32 monovariatal EVOO samples. Results were correlated with the phenolic profile measured by high performance liquid chromatography (HPLC). The amperometric signal at +0.9 V mainly correlated with the total phenols of the samples (R2=0.81), whereas the signal at +0.4 V mainly correlated with oleuropein aglycone (3,4 DHPEA‐EDA, R2=0.79). Bitterness intensity of the samples was evaluated by a trained sensory panel of experts and the results compared to those obtained by the amperometric flow system. The best correlation with the bitter taste was achieved by the sensor at +0.4 V (R2=0.72). A calibration model based on partial least squares was built with three variables, namely the sensors set at +0.4 and +0.9 V and the total phenol content of the EVOO extracts. The model showed a moderate capacity to predict the bitterness of the EVOO samples using leave one out method, (R2=0.75) and in prediction of a test set of samples (R2=0.7). Such approach is very promising for future studies.

Towards green analysis of virgin olive oil phenolic compounds: Extraction by a natural deep eutectic solvent and direct spectrophotometric detection

The determination of phenolic compounds in extra virgin olive oils (EVOO) by means of rapid, low-cost, environment-free methods would be a desirable achievement. A natural deep eutectic solvent (DES) based on glucose and lactic acid was considered as extraction solvent for phenolic compounds in EVOO. DESs are green solvents characterized by high availability, biodegradability, safety, and low cost. The spectrophotometric characteristics of DES extracts of 65 EVOO samples were related to the total phenolic content of the oils, assessed by methanol-water extraction coupled to the Folin-Ciocalteu assay. A regression model (ncalibration=45, nvalidation=20), including the absorbance at two wavelengths (257, 324nm), was obtained, with an adjusted R2=0.762. Therefore the DES could provide a promising and viable approach for a green screening method of phenolic compounds in EVOO, by means of simple spectrophotometric measurements of extracts, even for on-field analysis (for example in olive mills).

Non-thermal plasma as preparative technique to evaluate olive oil adulteration

In recent years adulteration of pure extra virgin olive oil (EVOO) with other types of vegetable oils has become an important issue. In this study, non-thermal plasma (NTP) is investigated as an innovative preparative analytical technique enabling classification of adulterated olive oil from an ascertained authentic batch of olive oil in a more sensitive manner. Non-thermal plasma discharges are a source of highly oxidative species such as singlet oxygen, and atomic oxygen. It was assumed that NTP-induced oxidation triggers unique lipid oxidation mechanisms depending on the specific composition of the oil matrix and minor constituents. In this work EVOO samples were adulterated with sunflower oil (1–3%) and submitted to NTP treatment. Results showed that while untreated samples could not be classified from the authentic olive oil reference, NTP treatments of 60min (Ar/O2 0.1%) on the oil batches resulted in the formation of a unique set of secondary volatile lipid oxidation products enabling classification of adulterated oil samples.

Evaluating the potential of phenolic profiles as discriminant features among extra virgin olive oils from Moroccan controlled designations of origin

Herewith, the potential of an approach based on the combination of the determination of phenolic compounds and the use of chemometric treatments has been evaluated to establish, for the first time, promising models to authenticate the provenance of Moroccan monovarietal olive oils produced under different geographical origin indication systems. To achieve this purpose, 136 commercial extra virgin olive oil samples from three diverse production areas (Meknès territory; the Protected Geographical Indication Ouazzane; and the Protected Designation of Origin Tyout-Chiadma) were collected over two consecutive crop seasons (2012/2013 and 2013/2014). Their phenolic fraction composition was investigated by using high performance liquid chromatography coupled to mass spectrometry (HPLC-ESI-IT MS). The results showed that geographical provenance and harvest season had a marked influence on the content of identified phenolic compounds. Principal components analysis (PCA) and linear discriminant analysis (LDA) were applied to test the potential of the determined compounds as geographical discriminant features, achieving a noticeable discrimination among the three evaluated regions. The contribution of each analyte to the statistic model has been evaluated in depth.

The effect of thermal treatment on the enhancement of detection of adulteration in extra virgin olive oils by synchronous fluorescence spectroscopy and chemometric analysis

In this study the effect of thermal treatment on the enhancement of synchronous fluorescence spectroscopic method for discrimination and quantification of pure extra virgin olive oil (EVOO) samples from EVOO samples adulterated with refined oil was investigated. Two groups of samples were used. One group was analyzed at room temperature (25°C) and the other group was thermally treated in a thermostatic water bath at 75°C for 8h, in contact with air and with light exposure, to favor oxidation. All the samples were then measured with synchronous fluorescence spectroscopy. Synchronous fluorescence spectra were acquired by varying the wavelength in the region from 250 to 720nm at 20nm wavelength differential interval of excitation and emission. Pure and adulterated olive oils were discriminated by using partial least-squares discriminant analysis (PLS-DA). It was found that the best PLS-DA models were those built with the difference spectra (75°C–25°C), which were able to discriminate pure from adulterated oils at a 2% level of adulteration of refined olive oils. Furthermore, PLS regression models were also built to quantify the level of adulteration. Again, the best model was the one built with the difference spectra, with a prediction error of 3.18% of adulteration.

Isoscapes of carbon and oxygen stable isotope compositions in tracing authenticity and geographical origin of Italian extra-virgin olive oils

The authentication and verification of the geographical origin of food commodities are important topics in the food sector. This study shows the spatial variability in δ13C and δ18O of 387 samples of Italian extra-virgin olive oil (EVOO) collected from 2009 to 2011. EVOOs’ δ13C and δ18O values were related to GIS (Geographic Information System) layers of source water δ18O and climate data (mean monthly temperature and precipitation, altitude, xerothermic index) to evaluate the impact of the most significant large-scale drivers for the isotopic composition of Italian EVOOs. A geospatial model of δ18O and δ13C was developed for the authentication and verification of the geographical origin of EVOOs. The geospatial model identified EVOOs from four distinct areas: north, south-central Tyrrhenian, central Adriatic and islands, highlighting the zonation of the expected isotopic signatures. This geospatial approach can be used to define a protocol for analyzing the isotopic composition of EVOOs in order to certify their origin and prevent food fraud. Limits and perspectives of the model are discussed.

Protected Designation of Origin Extra Virgin Olive Oils Assessment by Nuclear Magnetic Resonance and Multivariate Statistical Analysis: “Terra di Bari”, an Apulian (Southeast Italy) Case Study

AbstractWe report a study on the chemical characterization of 102 monovarietal micro‐extracted and genetically characterized extra virgin olive oils (EVOOs) from Coratina, Ogliarola Barese and Cima di Mola cultivar, according to “Terra di Bari” (Apulia, southeast Italy) PDO requirement. Three additional geographical mentions, all belonging to the same Bari district (Bitonto, Castel del Monte and Murgia dei Trulli e delle Grotte), were studied and potential microclimate differences were evaluated. Our results indicate the possibility of distinguishing EVOOs from the same “Terra di Bari” PDO with respect to different cultivars and (to some extent) different subareas. In particular, two cultivars (Ogliarola Barese and Coratina), obtained from the same Bitonto area, and a single cultivar (Coratina), obtained from Bitonto and Castel del Monte subareas, were compared to investigate the micro‐area pedoclimatic effect. Finally, 1H NMR data were found significant for classification purposes of unknown EVOO samples, the results of which were included in the model space, as they were correctly predicted by the OPLS‐DA obtained by 1H NMR data. This work aims to classify commercial “Terra di Bari” PDO EVOOs by comparison of the declared cultivar and geographical origin with a reference dataset of genetically characterized micro‐extracted monovarietal oils. In conclusion, the effect of the pedoclimatic micro‐areas of origin on the Coratina cultivar, which is the main component of the “Terra di Bari” PDO, has been studied in order to improve the traceability of the raw material used to produce this valuable food.

Sensory and Volatile Profiles of Monovarietal North Tunisian Extra Virgin Olive Oils from 'Chétoui' Cultivar.

The quality of olive oil is defined as a combination of characteristics that significantly determine its acceptance by consumers. This study was carried out to compare sensorial and chemical characteristics of sixty 'Chétoui' extra virgin olive oils (EVOOc) samples from six northern areas in Tunisia (Tebourba (EVOOT); Other regions (EVOON): Mornag, Sidi Amor, El Kef, Béjà and Jendouba). Trained panel taste detected ten sensory attributes. EVOOT and EVOON were defined by 'tomato' and 'grass/ leave notes, respectively. Twenty one volatile compounds from EVOOc were extracted and identified by Headspace Solid-Phase Microextraction followed by Gas Chromatography- Flame Ionization Detector. Principal component and cluster analysis of all studied parameters showed that EVOOT differed from EVOON. Sensory and volatile profiles of EVOOc revealed that the perception of different aromas, in monovarietal olive oil, was the result of synergic effect of oils' various components, whose composition was influenced by the geographical growing area.