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.     

A high performance size-exclusion chromatographic method for evaluating heated oils

High performance size-exclusion chromatography (HPSEC) was used to measure compounds with high-molecular weight (MW) formed during the heating of oil. Formation of the high-MW compounds is believed to be a reliable indicator of heat abuse in oils. The HPSEC method employs two μ-spherogel size-exclusion columns (500 and 1000 ?) in a series to separate the high-MW compounds which are detected at a wave-length of 234 nm by using a variable wavelength detector. The method was examined in the following study. Two sources of soybean oil were heated under laboratory conditions at 182 ± 2 C for eight 7-hr days. Samples were taken periodically and tested by using HPSEC. Oil samples from two commercial deep-fat frying operations were similarly tested. In all cases, size, number and apparent MW of the compounds formed increased with increasing frying time. The HPSEC procedure was compared with a method involving separation of polar and nonpolar components in a used frying fat by means of column chromatography on silica gel. This is Journal Paper No. J-11947 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA. Project No. 2568.     

Formation of a Δ7 triterpene alcohol in refined olive oils

The triterpene alcohol fraction in several virgin olive oils and the corresponding oils refined by alkali and by physical processes was analyzed by gas chromatography. A Δ⁷ compound was detected in all refined olive oils but not in virgin olive oils. This compound was tentatively identified by gas chromatography-mass spectrometry as 24-methyl-5α-lanosta-7,24-dien-3β-ol, a 24-methylenecycloartanol isomer produced during the refining process by the opening of the 9, 19 cyclopropane ring with formation of a double bond in the Δ⁷ position and the translocation of a double bond in the side chain from the 24–28 to the 24–25 position.     

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.     

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.     

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.     

Oil fractionation as a preliminary step in the characterization of vegetable oils by high-resolution 13C NMR spectroscopy

One hundred nine oil samples were separated chromatographically to obtain oil fractions with a decreased TAG content but with enhanced levels of the minor components that define oil genuineness and quality. The oils, which included virgin olive oils from different cultivars and regions of Europe and north Africa and refined olive, “lampante” olive, refined olive pomace, hazelnut, rapeseed, high-oleic sunflower, corn, grapeseed, soybean, and sunflower oils, were fractionated on a silica gel column with hexane/diethyl ether as the mobile phase eluent. The method was highly reproducible, and the fraction obtained contained about 15% unmodified TAG and 85% polar compounds, which included polymeric TAG, oxidized TAG, DAG, MAG, and FFA, in addition to other minor polar components of the oils. The presence of these compounds, in an enriched fraction, should provide information about the thermal, oxidative, and hydrolytic alterations of the oils, as well as many compounds of interest in determining oil genuineness. The results indicate that these fractions can provide more information than the original oils for NMR or other spectroscopic studies used in the determination of oil quality.     

The hydrocarbon fraction of virgin olive oil and changes resulting from refining

In numerous Spanish virgin olive oils, 6,10-dimethyl-1-undecene, various sesquiterpenes, the series ofn-alkanes from C14 to C35, n-8-heptadecene and squalene are the only less volatile components detected by gas chromatography in the hydrocarbon fraction. In oils from olives of the Arbequine variety, a series ofn-9-alkenes has also been found. In refined oils, notable features are the absence of the most volatile compounds and the appearance of other hydrocarbons produced during the refining process. Among these,n-alkanes, alkadienes (mainlyn-hexacosadiene), stigmasta-3,5-diene, isomerization products of squalene, isoprenoidal polyolefins coming from hydroxy derivatives of squalene and steroidal hydrocarbons derived from 24-methylene cycloartanol were identified. Physical refining produces larger amounts of degradation products and greater losses ofn-alkanes than chemical processing. Squalene is the major hydrocarbon component in all oils, both virgin and refined. The ranges of concentration for the different hydrocarbons found in Spanish virgin olive oils are presented.     

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.     

Characterization of sucrose polyesters-triacylglycerols mixtures

High-performance size-exclusion chromatography (HPSEC) and thin-layer chromatography/flame-ionization detection (TLC/FID) have been used for the characterization of mixtures of either monoacid sucrose octaesters with triacylglycerols (TAG) or sucrose polyesters (SPE) prepared from oils with natural oils. In mixtures of monoacid sucrose octaesters/TAG, no significant differences were found between the values obtained by either HPSEC or TLC/FID and the actual component proportions. Additionally, components could be separated by TLC, which was confirmed by fatty acid composition data of each fraction. Analysis of SPE/oil mixtures was attainable by HPSEC, but alternative quantitation by TLC/FID required previous silylation. Likewise, fatty acid composition could be determined only in the total mixture and in the sucrose octaester fraction. A formula derived for calculation of oil fatty acid composition, based on analytical data, showed the validity of the approach used in this study to determine component proportions in functional SPE/oil mixtures.     

A laboratory study of the bleaching process in stigmasta-3,5-diene concentration in olive oils

The bleaching effect was simulated in pilot plant by measuring the influence of temperature (40, 50, 60, 70, 80, and 90°C), time (5, 10, 15, 20, 25, and 30 min), and concentration of solid adsorbent [1.5 and 8% (w/w) of Tonsil supreme NFF] on stigmasta-3,5-diene (STIG) obtained by dehydration of steroidal compounds. Conditions were chosen to simulate those used in industrial operations. The presence of refined oils in extra virgin olive oil can be detected by these newly formed steroid hydrocarbons. Experimental results indicated that STIG did not exceed an imposed limit of 0.15 mg/kg in extra virgin olive oil, when oils were bleached with 1.5% earth at temperatures ≤80°C for 30 min in admixed to oils sold as virgin. A large proportion of the adulterations were not detectable by the official methods. Color determinations (CIE-1931) chromatic coordinates) were replicated on a refined oil and in admixed extra virgin olive oil. Color of olive oil was not significantly affected by mixing with refined oil (≤20%).     

Frying Quality Characteristics of French Fries Prepared in Refined Olive Oil and Palm Olein

The objective of this study was to compare two oils with different polyunsaturated/saturated (P/S) fatty acid ratios, refined olive oil (P/S 0.75) and palm olein (P/S 0.25), in frying French fries. The chemical qualities of the oil residues extracted from the French fries were assayed for five consecutive batches fried at 1-h intervals. The levels of total polar compounds, free fatty acids, p-anisidine value and phytosterol oxidation products (POPs) were elevated in French fries fried in both oils. The level of total polar compounds increased from 4.6 in fresh refined olive oil to 7.3% in final batches of French fries. The corresponding figures for palm olein were 9.8–13.8%. The level of free fatty acid in fresh refined olive oil increased from 0.06 to 0.11% in final products. These figures for palm olein were 0.04–0.13%. The p-anisidine value increased from 3.7 to 32.8 and 2.5 to 53.4 in fresh oils and in final batches of French fries in refined olive oil and palm olein, respectively. The total amount of POPs in fresh refined olive oil increased from 5.1 to 9.6 μg/g oil in final products. These figures were 1.9 to 5.3 μg/g oil for palm olein.     

Low molecular weight polypeptides in virgin and refined olive oils

Twenty-eight virgin olive oils—from different regions of Spain and prepared from olive drupes of different varieties—and six refined olive oils were analyzed to determine the presence of proteins in these oils. All oils studied showed the presence of proteins in the range of 7–51 μ/100 g of oil. There were no significant differences in protein content in oils from different varieties or between virgin or refined oils. In addition, all oils exhibited analogous amino acid patterns, suggesting a similarity among protein fractions obtained from different oils. A polypeptide with an apparent M.W. of 4600 Da was common to the isolated protein fractions. These results suggest that this polypeptide is a previously unknown minor component in olive oils. No clear influence of this component on oil stability was observed when oil stabilities were estimated as a function of phenol, tocopherol, phosphorus, and protein contents of the oils.     

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.     

A study of rancidity of olive oils

Summary The Wheeler test for peroxides proved to be relatively the most reliable method for the examination of olive oils for rancidity. The Issoglio test, although of no value for testing rancidity, can be of use in differentiating the natural olive oils from the refined olive oils. There is a wide variation in the susceptibility to fat oxidation of the oils from different sources. Infestation of the olives by mold induces the susceptibility of the oils to rancidity. Alcoholic extracts of anise seed showed antioxidant properties. Negative results were obtained using alcoholic extracts of mustard seed.     

Characterization of Volatile Compounds of Virgin Olive Oil Originating from the USA

The volatile profiles of virgin olive oils originating from the USA were first studied: 71 volatile compounds were identified in 21 monovarietal virgin olive oils using solid‐phase microextraction–gas chromatography/mass spectrometry, representing 100 % of the headspace composition. Principal component analysis (PCA) allowed for the grouping of olive oils based on geographical origin, and also the distinguishing of olive oil varieties by their relative positions in the group; 17 distinguishable volatile compounds that significantly contributed to the olive oil classification were found to be distributed on a PCA plot according to their sensory attributes. Moreover, the major volatile components were compared among varieties and origins to clarify the genetic and geographic influences. Our results indicate the significant effects of both origin and cultivar on the volatile composition of olive oil as well as the dominant role of the geographic effect compared to the genetic effect on applied samples.     

Evolution of phenolic compounds in virgin olive oil during storage

Phenolic compounds are of fundamental importance to the shelf life of virgin olive oils because of their antioxidative properties. In this paper, the evolution of simple and complex olive oil phenols during 18 mon of storage is studied by high-performance liquid chromatography (HPLC) analysis. The olive oils under examination were from various olive cultivars, harvested in two sectors in the same region at different stages of ripeness. The findings indicate that it is not the variety but rather the ripeness of the olives and the soil and climate that influence the phenol composition of virgin olive oil. In addition, a positive correlation was found between the age of the oils and the tyrosol to total phenols ratio. Lastly, gas chromatography-mass spectrometry analysis confirmed that the unidentified peaks detected by HPLC were of a phenolic nature.     

Detection of Soft‐Deodorized Olive Oil and Refined Vegetable Oils in Virgin Olive Oil Using Near Infrared Spectroscopy and Traditional Analytical Parameters

The European Parliament identifies virgin olive oil (VOO) as one of the foods which are often subject to fraudulent activities. Possibilities of adulteration are the application of illegal soft deodorization of extra virgin olive oil (EVOO) or the commercialization of blends of EVOO with soft‐deodorized EVOO or refined vegetable oils. Despite the search for possibilities to prove the illegal soft deodorization of EVOO or the addition of cheaper vegetable oils to EVOO, suitable methods are still missing. Therefore, the aim of the study is to develop a new analytical and statistical approach addressing detection of mild deodorization or addition of refined foreign oils. For this purpose, VOOs are treated in lab‐scale for 1 h up to 28 days at different temperatures (20, 50, 60, 80,100, 110, and 170 °C) in order to simulate and study the effect of heat treatment on known analytical parameters by near infrared spectroscopy (NIR). A logit regression model enabling the calculation of the probability for a heat treatment is developed. This new methodology allows detecting both soft deodorized olive oils and blends of EVOO with cheaper full refined vegetable oils. Adding only 10% of full refined oil could be detected in extra VOO. Practical Applications: NIR methods combined with chemometrics have become one of the most attractive analytical tools to control quality of food. It is a simple, precise, and rapid method. All relevant analytical parameters of oxidative and thermal fat degradation can be determined in a single run and be used to detect adulterated virgin olive oils (VOOs). The use of a simple equation developed from the logistic regression using peroxide value, K‐values, p‐anisidine value, pyropheophytine, 1,2‐diacylglycerols, total polar compounds and monomeric oxidized triacylglycerols, and other well‐known parameters allows to detect mild deodorized olive oils or also blends of VOO with soft‐deodorized ones or the addition of low amounts of foreign vegetable oils. This technique has potential to be used as a screening method for the detection of adulterated olive oils using both the traditional laboratory methods and the corresponding NIR‐methods.     

A 3-year Study on Quality,Nutritional and Organoleptic Evaluation of Organic and Conventional Extra-Virgin Olive Oils

The quality of extra-virgin olive oils (EVOO) from organic and conventional farming was investigated in this 3-year (2001–2003) study. The oils were extracted from Leccino and Frantoio olive (Olea europaea) cultivars, grown in the same geographical area under either organic or conventional methods. Extra-virgin olive oils (EVOO) were produced with the same technology and samples were analyzed for nutritional and quality parameters. Volatile compounds were measured with solid-phase microextraction combined with gas chromatography and mass spectrometry (SPME–GC–MS). Sensory evaluation was also completed by a trained panel. Significant differences were found in these parameters between organic and conventional oils in some years, but no consistent trends across the 3 years were found. The acidity of organic Leccino oils was higher than conventional oils in 2001 and 2002 but not in 2003; Frantoio oils were never different. Organic Leccino oils had higher peroxide index than conventional oils in 2001 and 2002 but it was the reverse in 2003. Organic Frantoio oils had lower peroxide index in 2001, but values were not statistically different in the other years. The concentrations of phenols, o-diphenols, tocopherols, the antioxidant capacity and the volatile compounds showed differences in some years and no difference, or opposite differences, in others. Sensory analysis showed only slight differences in few aromatic notes. Our results showed that organic versus conventional cultivation did not affect consistently the quality of the high quality EVOO considered in this study, at least in the measured parameters. Genotype and year-to-year changes in climate, instead, had more marked effects.     

Applications of chromatographic techniques to evaluate enzymatic hydrolysis of oxidized and polymeric triglycerides by pancreatic lipase in vitro

With the aim of studying the susceptibility to enzymatic hydrolysis of oxidized and polymeric triglycerides (TG) that are formed during frying, various chromatographic techniques were applied in combination, i.e., adsorption chromatography, high-performance size-exclusion chromatography (HPSEC), and thin-layer chromatography-flame ionization detection (TLC-FID). Polar fractions, isolated by adsorption chromatography from thermoxidized trilinolein as model system, and real used frying fats and oils, were analyzed by HPSEC before and after incubation with pancreatic lipase in vitro. Also, the influence of degradation level of used frying oils on hydrolysis of intact TG was investigated with the additional aid of TLC-FID. Results showed the high hydrolysis rate of oxidized TG monomers in contrast to the significant discrimination of pancreatic lipase against TG dimers and, particularly, TG polymers. On the other hand, hydrolysis of intact TG can be affected by the presence of dimers and polymers in abused frying oils.