Formation of oxidation compounds in sunflower and olive oils under oxidative stability index conditions

The objective of this work was to study the evolution of oxidation under oxidative stability index (OSI) conditions using the Rancimat apparatus. Sunflower oils with different degrees of unsaturation (conventional high‐linoleic sunflower oil, genetically modified high‐oleic sunflower oil, and a 1 : 1 mixture of both of them) and virgin olive oil were used. The sunflower oils were tested at 100 °C, while the olive oil was assayed at 100, 110 and 120 °C. Samples were analyzed at different time points and conductivity values, until the induction period (IP) was overpassed. A combination of adsorption and size‐exclusion chromatography was used for the quantification of oxidized triacylglycerol (TG) monomers, dimers and polymers. Additionally, peroxide values (PV) and ultraviolet absorption at 270 nm (K₂₇₀), as well as losses of tocopherols, were measured. The results showed that oxidized TG monomers were the only group of oxidation compounds that increased during the early oxidation stage. The end of the IP was marked by the initiation of polymerization after the exhaustion of tocopherols. In comparison with reported results obtained at room temperature, the main difference found was that the amounts of oxidation compounds at the end of the IP were much lower at OSI test temperatures. With the exception of the K₂₇₀ values, the results also showed that the IP endpoints provided by the OSI test were slightly higher than those obtained by quantification of oxidized TG monomers or by PV determination.     

Gekoppelte LC-GC für die Analyse von Olivenölen

Coupled LC-GC for the Analysis of Olive Oils The analysis of the so-called sterol fraction of fats and oils can be strongly improved by the application of on-line coupled LC-GC. LC replaces saponification, the (difficult) extraction of the non-saponifiable and the clean-up by preparative thin layer chromatography. The proposed method eliminates most of the manual sample preparation work, is more accurate, and provides more information at the same time, since the free and esterified components are analyzed separately. Analyzing olive oils, mostly small admixtures of other oils can be detected. For the determination of solvent extracted oil in “extra virgin” or “pure” olive oils, the method is more suitable than the conventional determination of the triterpenedialcohols erythrodiol and uvaol. Finally pressed oil of first quality (“extra virgin”) can be distinguished from that of second quality (“pure” olive oil). Oils of second quality are usually the result of pression with an excessive delay after harvesting the olives.     

Olive Oil Quality and Sensory Changes During House‐Use Simulation and Temporal Assessment Using an Electronic Tongue

During domestic usage, olive oil bottle manipulation may lead to a quality decrease due to agitation and oxygenation. Therefore, assessing the domestic consumption time period during which the initial quality grade is retained may allow including this information as a recommendation, ensuring olive oil consumers’ satisfaction. Temporal changes of physicochemical, chemical, and sensory parameters of extra‐virgin olive oils (EVOO) were monitored during 1‐month simulated house‐use conditions. It was observed that K₂₃₂ (R‐Pearson ≥+0.81) and ΔK increased resulting in a significant olive oil quality decrease from EVOO (during the initial 21 days of simulated usage) to lampante olive oil (after 28 days of simulated usage) as well as the appearance of rancid sensation. As lampante olive oils cannot be commercialized, it is pertinent to establish olive oil shelf life under usual home‐use conditions. Principal component analysis allowed grouping the olive oils according to home‐use time period and how bottles are stored after their first opening, showing that the overall olive oil physicochemical and sensory characteristics changed with the domestic‐use time period. Finally, a potentiometric electronic tongue coupled with linear discriminant analysis was used to discriminate olive oils according to the domestic‐use time period (leave‐one‐out cross‐validation sensitivities ≥95%). Thus, this device could be used to indirectly assess the quality of the remaining bottled olive oil by establishing for how long an olive oil bottle has been used under domestic conditions.     

Determination of sterols by capillary column gas chromatography. Differentiation among different types of olive oil: Virgin,refined, and solvent-extracted

Compositional analysis of the sterol fraction of olive oil can be used to assess the degree of purity of the oil and the absence of admixture with other plant oils. This determination also permits characterization of the type of olive oil in question: virgin, refined, or solvent-extracted. In the present work, 130 samples of olive oil were analyzed, the sterol fractions were separated from the unsaponifiable fraction by silica gel plate chromatography, and later they were analyzed as the trimethylsilyl ether derivatives by capillary column gas chromatography. From the results obtained, it was concluded that this methodology is able to differentiate among virgin, refined, and solvent-extracted olive oils. Stigmasterol, clerosterol, Δ5-avenasterol, Δ7-stigmasterol, and Δ7-avenasterol permit the differentiation of the three types of oil from one another. Campesterol, Δ5, 23-stigmastadienol, β-sitosterol, and Δ5,24-stigmastadienol permit the differentiation of only two oils from each other but confirm the conclusions obtained for other sterols. Correlations between the different sterols of virgin, refined, and solven-extracted olive oil also have been obtained.     

Susceptibility of water-emulsified extra virgin olive oils to oxidation

The effect of emulsion structure on the susceptibility to oxidation of emulsified olive oils was tested. Olive oil samples were emulsified by adding a certain quantity of water in different ways. The resulting water-in-oil emulsions were then oxidized with UV light. The results revealed that the emulsion structure played a significant role in the oxidation process of emulsified olive oils. A kinetic mechanism is discussed based on the PV determined experimentally. The susceptibility of water-emulsified extra virgin olive oils to oxidation was quantified by means of a dimensionless parameter that displayed a characteristic dependence on the specific surface area of the water dispersed phase.     

Unmasking Sensory Defects of Olive Oils Flavored with Basil and Oregano Using an Electronic Tongue-Chemometric Tool

Olive oil price and consumers’ preference depend on the commercial grade classification that can decrease if any sensory defect is perceived leading to an economic loss. Enriched oils, obtained by incorporating dried aromatic herbs, spices, or essential oils, which is a common practice in the Mediterranean region, are commercially available. This practice may conceal the fraudulent purpose of masking the perception of sensory defects. The detection of this type of fraud is a difficult task, requiring sensory analysis. Thus, in this study, extra-virgin and lampante olive oils, the latter classification being due to the perception of an intense winey-vinegary defect, were deliberately enriched with different amounts of basil-dried herbs and oregano-dried herbs. Sensory analysis showed that, depending on the aromatic herb and on the added amount (0.011–0.110 g herb per kg oil), the defect intensity could be masked leading to an erroneous classification of flavored lampante oils as flavored virgin oils. In contrast, the electronic tongue-chemometric approach could unmask the defect in flavored oils (predictive sensitivities: 70–78%) and semiquantitatively discriminate flavored oils according to the added levels of basil or oregano (predictive sensitivities: 93–100%). The electronic tongue approach showed satisfactory unmasking performance when compared with the sensory panel, and so, its future application as a quality control taste-sensor device for disclosing olive oil sensory defects masked by the incorporation of flavoring agents may be forseen.     

Design and Characteristics of Novel Sensory and Nutritionally Oriented Olive,Seed, and Nut Virgin Oils’ Blendings

Virgin olive oil is considered a key component of the Mediterranean Diet, while nut and seed “cold-pressed” oils stand out as an interesting ingredient due to the growing consumer demand toward so-called gourmet and healthy oils. The main objective of this work is the development and characterization of novel virgin vegetal oils based on blendings of virgin olive oil with virgin oils obtained from seeds (sesame and flaxseed) and nuts (hazelnut and pistachio) of interest due to their peculiar nutritional and organoleptic characteristics. Oil formulations elaborated with 5% of sesame oils achieve a high content in vitamin E (842 mg kg⁻¹, 11.8 mg per standard 14 g oil dose, corresponding to an 80% of the recommended daily intake) and with 10% of flaxseed a high level in essential α-linolenic acid (6.4%, 0.90 mg per dose corresponding to a 66% of the recommended daily intake). In addition, sensory analysis shows that blends enriched with both 50% hazelnut oil and 75% pistachio oil not only maintain the typical aroma of virgin olive oil, but incorporate the characteristic nutty, roasty, seed-like, and sweet sensory attributes of nuts, providing an added value to the consumers.     

Polymeric and oxidized triglyceride content of crude and refined vegetable oils — An overview

High-pressure size-exclusion chromatography (HPSEC) was used in combination with column chromatography on silica to determine the polymeric and oxidized triglyceride content of 19 refined vegetable oil samples of different origin (corn, sun, soy, peanut, rapeseed, palm and olive oil). The evolution of these compounds during the labscale physical refining of corn oil was also studied. Dimeric and oxidized triglyceride levels of the refined oils ranged between 0.32–2.01% (mean = 1.07%) and 1.53–4.83% (mean = 3.11%), respectively. A major increase of polymeric triglycerides was observed during the deacidification-deodorization step, while the oxidized triglycerides increased mainly during bleaching. Further studies to determine the exact influence of refining conditions on the formation of polymeric and oxidized triglycerides are necessary.     

Formation and distribution of oxidized fatty acids during deep‐ and pan‐frying of potatoes

The formation of cis‐9,10‐epoxystearate, trans‐9,10‐epoxystearate, cis‐9,10‐epoxyoleate, cis‐12,13‐epoxyoleate, trans‐9,10‐epoxyoleate, trans‐12,13‐epoxyoleate and the co‐eluting 9‐ and 10‐ketostearates during eight successive pan‐ and deep‐frying sessions of pre‐fried potatoes in five different types of vegetable oils – namely cottonseed oil, sunflower oil, vegetable shortening, palm oil and virgin olive oil – was followed and quantified both in fried oils and in fried potatoes by GC/MS after derivatization to methyl esters. These oxidized fatty acids were present at relatively low concentrations in the fresh oils and pre‐fried potatoes while they increased linearly with frying time, reaching up to 1140.8 µg/g in virgin olive oil (VOO) and 186.9 µg/g in potatoes pan‐fried in VOO after eight pan‐frying sessions, with trans‐9,10‐epoxystearate predominating in all cases. The formation of polymerized triacylglycerols (PTG) was also quantified in frying oils by size exclusion HPLC. Pan‐frying caused higher oxidized fatty acid and PTG formation compared to deep‐frying. Epoxyoleates and PTG concentrations were increased after frying in polyunsaturated oils, while epoxystearate and 9‐ and 10‐ketostearate concentrations were increased after frying in monounsaturated oils. No specific absorption of the oxidized fatty acids by the fried potatoes seems to occur. The dietary intake of oxidized fatty acids and PTG by the consumption of fried potatoes was discussed.     

Effect of natural antioxidants in virgin olive oil on oxidative stability of refined,bleached, and deodorized olive oil

The factors influencing the oxidative stability of different commercial olive oils were evaluated. Comparisons were made of (i) the oxidative stability of commercial olive oils with that of a refined, bleached, and deodorized (RBD) olive oil, and (ii) the antioxidant activity of a mixture of phenolic compounds extracted from virgin olive oil with that of pure compounds andα-tocopherol added to RBD olive oil. The progress of oxidation at 60°C was followed by measuring both the formation (peroxide value, PV) and the decomposition (hexanal and volatiles) of hydroperoxides. The trends in antioxidant activity were different according to whether PV or hexanal were measured. Although the virgin olive oils contained higher levels of phenolic compounds than did the refined and RBD oils, their oxidative stability was significantly decreased by their high initial PV. Phenolic compounds extracted from virgin olive oils increased the oxidative stability of RBD olive oil. On the basis of PV, the phenol extract had the best antioxidant activity at 50 ppm, as gallic acid equivalents, but on the basis of hexanal formation, better antioxidant activity was observed at 100 and 200 ppm.α-Tocopherol behaved as a prooxidant at high concentrations (>250 ppm) on the basis of PV, but was more effective than the other antioxidants in inhibiting hexanal formation in RBD olive oil.o-Diphenols (caffeic acid) and, to a lesser extent, substitutedo-diphenols (ferulic and vanillic acids), showed better antioxidant activity than monophenols (p- ando-coumaric), based on both PV and hexanal formation. This study emphasizes the need to measure at least two oxidation parameters to better evaluate antioxidants and the oxidative stability of olive oils. The antioxidant effectiveness of phenolic compounds in virgin olive oils can be significantly diminished in oils if their initial PV are too high.     

Characterization of olive paste volatiles to predict the sensory quality of virgin olive oil

One of the main challenges that virgin olive oil producers face today is an accurate prediction of the sensory quality of the final product prior to the milling of the olives. The possibility that olive paste aroma can be used as a predictive measurement of virgin olive oil quality is studied in this paper. The study was centered on distinguishing the aroma of olive pastes that produced virgin olive oils without sensory defects from the aroma of olive pastes the virgin olive oils of which showed sensory defects. Olive pastes were analyzed by solid‐phase microextraction‐gas chromatography and a sensor system based on metal oxide sensors. Forty‐four volatile compounds were identified in olive pastes, all of them being also present in virgin olive oil. Six volatile compounds – acetic acid, octane, methyl benzene, (E)‐2‐hexenal, hexyl acetate and 3‐methyl‐1‐butanol – distinguished both kinds of pastes with only five misclassified samples. Five metal oxide sensors were able to classify the olive pastes with only two erroneous classifications.     

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.     

Oligopolymer,diglyceride and oxidized triglyceride contents as measures of olive oil quality

The objective of this study was to test the qualities of olive oils of different commercial grades by quantifying oligopolymer compounds by high-performance size-exclusion chromatography (HPSEC). The method required no sample manipulation and was accurate and rapid. The mean level of oligopolymers in refined olive oils was 0.70% and was more than twice as high in refined olive pomace oils. Conversely, edible virgin olive oils had no oligopolymer compounds. HPSEC analyses of polar compounds by silica gel column chromatography also allowed determination of oxidized triglycerides and partial glycerides, which help define levels of oxidative degradation and hydrolysis. Research supported by National Research Council of Italy, Special Project RAISA, Sub-project 4, Paper No. 321.     

Use of high-resolution 13C nuclear magnetic resonance spectroscopy for the screening of virgin olive oils

¹³C Nuclear magnetic resonance (NMR) spectra of 104 oil samples were obtained and analyzed in order to study the use of this technique for routine screening of virgin olive oils. The oils studied included the following: virgin olive oils from different cultivars and regions of Europe and north Africa, and refined olive, “lampante” olive, refined olive pomace, high-oleic sunflower, hazelnut, sunflower, corn, soybean, rapeseed, grapeseed, and peanut oils, as well as mixtures of virgin olive oils from different geographical origins and mixtures of 5–50% hazelnut oil in virgin olive oil. The analysis of the spectra allowed us to distinguish among virgin olive oils, oils with a high content of oleic acid, and oils with a high content of linoleic acid, by using stepwise discriminant analysis. This parametric method gave 97.1% correct validated classifications for the oils. In addition, it classified correctly all the hazelnut oil samples and the mixtures of hazelnut oil in virgin olive oil assayed. All of these results suggested that ¹³C NMR may be used satisfactorily for discriminating some specific groups of oils, but to obtain 100% correct classifications for the different oils and mixtures, more information than that obtained from the direct spectra of the oils is needed.     

Detection of pressed hazelnut oil in admixtures with virgin olive oil by analysis of polar components

Analysis of the polar fraction from virgin olive oil and pressed hazelnut oil by high-performance liquid chromatography showed marked differences in the chromatograms of the polar components in the two oils. Six commercial samples of pressed hazelnut oil and 12 samples of virgin olive oil (or blended olive oil including virgin olive oil) were analyzed. The phenolic content of the pressed hazelnut oil samples was 161±6 mg·kg⁻¹. Inspection of the chromatograms showed that the pressed hazelnut oil extracts contained a component that eluted in a region of the chromatogram that was clear in the olive oil samples, and consequently this component could be used to detect adulteration of virgin olive oil by pressed hazelnut oil. The component had a relative retention time of 0.9 relative to 4-hydroxybenzoic acid added to the oil as an internal standard. The ultraviolet spectrum of the component showed a maximum at 293.8 nm, but the component could not be identified. Analysis of blends of oils showed that adulteration of virgin olive oil by commercial pressed hazelnut oil could be detected at a level of about 2.5%.     

Detection of adulteration of olive oil with seed oils by a combination of column and gas liquid chromatography

Samples of virgin olive oil and refined seed oils, as well as mixtures of olive oil with 10 and 5% seed oils were fractionated by column chromatography on silicic acid impregnated with ammoniacal silver nitrate. It was possible to isolate a characteristic fraction enriched in polyunsaturated triglycerides. Its linoleic acid content in pure olive oil never exceeds 9.3%, whereas in pure seed oils, it varies between 38.1 and 70.1%; in mixtures of olive oil with 10 and 5% of seed oils, the respective values are 22.3–38.2% and 15.6–32.1%. The oleic-to-linoleic acid ratios of the same fraction are more than 7.6 (olive oil), 0.2–0.8 (seed oils), 1.1–2.0 (olive oil with 10% seed oils) and 1.4–3.6 (olive oil with 5% seed oils). These analytical values may be used as a safe criterion for the eventual adulteration of olive oil with seed oils. This work was taken in part from the doctoral dissertation of S. Passaloglou-Emmanouilidou.     

Chemical Composition of Turkish Olive Oil––Ayvalik

Although large amounts of olive oil are produced in Turkey, not much information on its chemical composition is available in the literature to date. The aim of this study was to evaluate the chemical composition of commercial olive oils produced from the Ayvalik olive cultivar in Canakkale, Turkey. Five different samples corresponding to the olive oil categories of extra virgin (conventional, extra virgin olive oil (EVOO), and organic extra virgin olive oil (OGOO) production), virgin olive oil (OO-1), ordinary virgin olive oil (OO-2) and refined olive oil (RFOO) were evaluated. Olive oils were collected from two consecutive production years. According to the free fatty acids, the absorbance values (K₂₃₂ and K₂₇₀), and peroxide values of all the samples conformed to the European standards for olive oil. The level of oleic acid was in the range of 68–73%; while the linoleic acid content was significantly lower in the refined olive oils. The tocopherol and polyphenol content was in the lower range of some European olive oils. However, pinoresinol was a major phenolic compound (5–77 mg/kg depending on the oil category). Its content was markedly higher than in many other oils, which would be a useful finding for olive oil authentication purposes.     

On the composition of Iranian olive oil

Two samples of virgin olive oil and one sample of hexane-extracted husk oil coming from Iran were examined. The analyses included physical and chemical characteristics, the composition of total fatty acids and fatty acids at the glyceride 2-position by gas liquid chromatography (GLC) of methyl esters, the triglycerides composition calculation according to Vander Wal theory, the separation of the alcoholic fractions (sterols, 4-methylsterols, triterpene alcohols, triterpene dialcohols and aliphatic alcohols) of the unsaponifiable matter by thin layer chromatography (TLC), the quantitation and the composition of these fractions by GLC of TMS derivatives. The results were in line with data from literature for olive oils of different origin, with the exception of: a high content of unsaponifiable matter (1.75 and 1.95% for virgin oils, 5.33% for husk oil); a high amount of sterols for husk oil (562 mg/100 g oil); a low content of SE 30 apparent β-sitosterol for husk oil (91.1%); a low amount of triterpene dialcohols (1 mg/100 g oil) and triterpene alcohols (78 and 91 mg/100 g oil) for virgin oils; a content of cycloartenol (60.2–66.9%) higher than the 24-methylenecycloartanol one (22.8–26.6%; a content of C₂₄ linear saturated alcohol (33.9–38.0%) slightly higher than the C₂₆ alcohol one (29.3–32.8%).     

Pinoresinol and 1-acetoxypinoresinol, two new phenolic compounds identified in olive oil

Polyphenols of olive oil show autoprotective, sensory, and nutritional-therapeutic effects. Two new phenolic compounds have been isolated from virgin olive oils by preparative high-performance liquid chromatography and their structures established on the basis of their mass spectra and nuclear magnetic resonance spectral data. The compounds identified are the lignans pinoresinol and 1-acetoxypinoresinol. Both have been found in all the commercial virgin olive oils analyzed. Pinoresinol concentration was rather similar in all the oils. In contrast, 1-acetoxypinoresinol concentration was higher in oils of the Arbequina and Empeltre cultivars than in Picual or Picudo cultivars. Pinoresinol and 1-acetoxypinoresinol may represent the major phenolic compounds in some Arbequina and Empeltre oils. Lignans possess biological and pharmacological properties and, therefore, the two new compounds identified in olive oils may contribute to the reported beneficial effects which are attributed to polyphenols on human health of a diet rich in olive oil.