Evolution of thermograph parameters during the oxidation of extra virgin olive oil

The modulated differential scanning calorimetry (M‐DSC) was used as a rapid and effective method to characterize the olive oil at different levels of oxidation. Thermograph parameters have been related to oxidative degradation of the triglycerides. In this study, their relation to the characteristic off‐flavor compounds, correlated to the oxidative degradation of the oil, was also investigated. Extra virgin olive oil samples were subjected to the following oxidation treatments: a) purged with air using glass washing bottles at two flow rate values, b) heated in a conventional oven at two area/oil mass ratios, and c) heated in a microwave oven also at two area/oil mass ratios. Samples were withdrawn and analyzed at predetermined intervals. Flavor and off‐flavor compounds were isolated using a dynamic thermal stripping apparatus and transferred into a gas chromatograph by using a thermal desorption unit. All oil samples were analyzed by M‐DSC during cooling from 25 °C to ?60 °C at 7 °C/min, and heating back to 40 °C at 10 °C/min. High correlation values were obtained between various M‐DSC thermograph parameters and certain volatile compounds. Results showed that M‐DSC could be used as a simple method to indicate compositional changes in olive oil during oxidation.     

Characterization of the Volatile, Phenolic and Antioxidant Properties of Monovarietal Olive Oil Obtained from cv. Halhali

Volatile and phenolic compositions of olive oil obtained from the cv. Halhali were investigated in the present study. Fruits were harvested at the optimum maturity stage of ripeness and immediately processed with cold press. Simultaneous distillation/extraction (SDE) with dichloromethane was applied to the analysis of volatile compounds of olive oil. Sensory analysis showed that the aromatic extract obtained by SDE was representative of olive oil odour. In the olive oil, 40 and 44 volatile components were identified and quantified in 2010 and 2012 year, respectively. The total amount of volatile compounds was 18,007 and 19,178 μg kg^?1 for 2010 and 2012, respectively. Of these, 11 compounds in the 2010 and 12 in the 2012 harvest presented odour activity values (OAVs) greater than 1, with 1‐octen‐3‐ol, ethyl‐3‐methyl butanoate, (E)‐2‐heptenal and (E,Z)‐2,4‐decadienal being those with the highest OAVs in olive oil. The high‐performance liquid chromatographic method coupled with diode‐array detection was used to identify and quantify phenolic compounds of the olive oil. A total of 14 phenolic compounds in both years were identified and quantified in olive oil. The major phenolic compounds that were identified in both years were hydroxytyrosol, tyrosol, elenolic acid, luteolin, and apigenin. Antioxidant activity of olive oil was measured using the DPPH and ABTS methods.     

Stability of refined olive oil and olive‐pomace oil added by phenolic compounds from olive leaves

Refined olive oil and olive‐pomace oil were enriched with olive leaf phenolic compounds in order to enhance its quality and bring it closer to virgin olive oil. The changes that occurred in the concentrations of pure oleuropein, oleuropein aglycone, hydroxytyrosol acetyl and α‐tocopherol at 400 µg/kg of oil during the storage of refined olive oil and olive‐pomace oil under accelerated conditions (50 °C) were investigated. In a period of 4 months, α‐tocopherol decomposed by 75% whereas less than 40% of the phenols were lost. During storage, enzymatic olive leaf extract hydrolysate that contains two major compounds, hydroxytyrosol and oleuropein aglycone showed the highest antioxidant activity and the lowest detected stability, followed by oleuropein. The oleuropein in olive leaf extracts exhibited similar degradation profiles, reducing by 60–50% and 80% for the olive oil and olive‐pomace oil in 6 months, respectively. The acetylated extract, however, displayed a loss of 10 and 5% in olive oil and olive‐pomace oil, respectively. In the fatty acid composition, an increase in oleic acid and a decrease in linoleic acid were observed. The antiradical activities of the olive oil and olive‐pomace oil enriched with olive leaf phenolic compounds at 400 ppm showed that enzymatic hydrolysate extract had the highest protective effect against oil oxidation. Based on the Rancimat method, the oils with added leaf enzymatic hydrolysate extract had the lowest peroxide value and the highest stability. After 6 months of storage and at 120 °C, the oxidative resistance of refined olive oil and olive‐pomace oil reached 0.71 and 0.89 h, respectively, whereas that of the non‐enriched samples fell to zero.     

Wax Ester Variation in Olive Oils Produced in Calabria (Southern Italy) During Olive Ripening

The wax ester composition of pressed olive oil and its variation during olive ripening were investigated by column chromatography/GC-on column technique. Six compounds were identified: C₃₆, C₃₈, C₄₀, C₄₂, C₄₄ and C₄₆ wax esters, which were grouped as total detected wax esters (TDWEs). The European Union (EU) includes C₄₀, C₄₂, C₄₄ and C₄₆ waxes (TEWEs) as a distinctive characteristic between different categories, with a maximum total content ≤250 mg/kg for an extra virgin olive oil. The International Olive Council (IOC) includes C₄₂, C₄₄ and C₄₆ waxes (TIOCWEs) as a purity parameter, with a maximum total content ≤150 mg/kg for an extra virgin olive oil. The analytical technique proposed by EU and IOC do not separate the wax esters from fatty acids esters with diterpenic alcohols (phytol and geranylgeraniol) that interfere with detected peaks. Although the examined cultivars were grown in the same geographical area and the same agricultural practices were applied to the trees, ANOVA analysis found significant differences among the oils extracted with the same machinery. The oil produced from the Itrana cultivar showed the lowest content in TEWEs (25.00–39.00 mg/kg) and in TIOCWEs (5.67–9.00 mg/kg). Wax content in Leccino and Pendolino cultivars showed a significant tendency to decrease during olive maturation, and a tendency to increase in all other cultivars from the first to the last harvest date when olive pigmentation changed from green to black.     

Development and Validation of a Simple Reversed‐Phase HPLC‐UV Method for Determination of Malondialdehyde in Olive Oil

A simple, precise, accurate and selective method was developed and validated for determination of malondialdehyde (MDA) in olive oil. Separation was achieved on a reversed‐phase C₈ column using a mobile phase consisting of methanol/0.8 % phosphoric acid (10:90, v/v), at a flow rate of 1.0 ml/min and UV detection at 220 nm. This method was validated according to the requirements for new methods, which include accuracy, precision, selectivity, robustness, a limit of detection, limit of quantitation (LOQ), linearity and range. The current method demonstrated good linearity over the range of 0.5–1000 ppm of MDA with r² greater than 0.999. The recovery of MDA in olive oil ranged from 97.1 to 99.1 %. The method was selective where MDA was distinctly separated from other compounds of the oil with good resolution. The method was also precise where the RSD of the peak areas of replicate injections of MDA standard solution were less than 1 %. The degree of reproducibility of the results obtained as a result of small deliberate variations in the method parameters and by changing the analytical operators proved that the method is robust and rugged. The low LOQ of MDA (0.5 ppm) using this method enables quantitation of MDA at low concentration.     

Investigation of the Effects of Virgin Olive Oil Cleaning Systems on the Secoiridoid Aglycone Content Using High Performance Liquid Chromatography–Mass Spectrometry

Phenolic compounds are useful markers to control olive oil technological processes, including the virgin olive oil (VOO)/water separation after olive oil extraction. In this investigation, VOO extracted from olives of cv. Coratina using a mild oil/water separator called the hydrocyclone sedimentation system (Hydroil) was compared with VOO obtained using a conventional vertical centrifuge separator (Cenoil), which is mostly used in the modern olive oil industry. Secoiridoid aglycones were selected, among phenolic compounds, as markers and analyzed using reversed‐phase liquid chromatography coupled to linear quadrupole ion‐trap mass spectrometry with electrospray ionization in the negative mode. VOO samples obtained using the Hydroil system were found to contain significantly higher levels of secoiridoid aglycones, compared to the Cenoyl‐type samples. In particular, the total content of the aglycones of decarboxymethyl oleuropein, decarboxymethyl ligstroside, ligstroside, and oleuropein, expressed in terms of oleuropein, was estimated as 35.40 ± 0.80 mg kg^?1, compared to 8.06 ± 0.41 mg kg^?1 in the Cenoil samples (n = 3). Since no significant difference in residual water (P < 0.05) was found between the two types of VOO samples, the higher amount of secoiridoids obtained for Hydroil‐type ones was explained by the lower extent of oxidation occurring during the mild oil/water separation achieved using the Hydroil system.     

Transfer of Phenolic Compounds from Olive Mill Wastewater to Olive Cake Oil

The transfer of the phenolic compounds from olive mill wastewater (OMW) to oil extracted under microwave from olive cake (OC) was carried out by using the following operations: mixing of the olive mill wastewater with the olive cake, drying of the mixture and recovery by solvent of the olive cake oil enriched by phenolic compounds. In the first part of this work, we made a screening design using a Hadamard matrix to quickly locate the factors influencing the process. Among five potentially influential parameters, we found that only three were actually active (OMW/OC ratio noted R, mixing velocity of mixture Vm and mixing time Tm). In the second part, fractional factorial design (2^5?1) was performed to evaluate the effects of five variables (three of them being selected by screening with exposition time Te and radiation power P) and their eventual interactions. The p value (p < 0.05) indicated that R, P,Te, Vm and Tm had significant effects on the response followed by the interaction effects between R‐P, P‐Te, R‐Vm, Te‐Vm, Te‐Tm, and Vm‐Tm. Under optimal conditions, the addition of OMW to OC increased the phenolic compounds content in the oil from 0.04 ± 0.01 to 0.13 ± 0.02 g/L.     

Zinc and nickel determination in liquid edible oils by FAAS after the extraction

A new method has been developed for the extraction and determination of zinc and nickel in liquid edible oils by using the complexation of these metals with [N,N′‐bis(salicylidene)‐2,2′‐dimethyl‐1,3‐propanediaminato]. Zn(II) and Ni(II) complexes with a tetradentate Schiff base have been investigated spectrophotometrically. Experimental extraction conditions for these metals from liquid oil standards were optimized using central composite design. Optimum conditions for Zn(II) and Ni(II) extractions from oil have been found close to each other. The ratio of the volume of used Schiff base solution to the amount of oil (V_LDM/m_oil; mL/g), the stirring time and the temperature were round about 1.00 mL/g, 55 min, 32°C, respectively, for simultaneous determination of both metals in same sample. The recovery percentages at the optimum experimental conditions were found 98.9 ± 2.8 and 101.8 ± 4.7 for Zn(II) and Ni(II), respectively. The proposed method was applied on the raw and spiked samples such as olive oil, sunflower oil, corn oil, canola oil and obtained recovery values were between 93.7–107.2 and 93.1–101.1% for Zn(II) and Ni(II), respectively. Practical applications: There is interest in the determination of metals in liquid edible oils because of their catalytic effect on the oxidation reaction of oils. A new method for the determination of Zn(II) and Ni(II) in liquid edible oils which does not require any digestion or decomposition was developed. This study offeres a cheap, rapid, accurate, sensitive, risk‐free, and practical metal determination method after the extraction.     

Column and high-performance size exclusion chromatography applications to the in vivo digestibility study of a thermoxidized and polymerized olive oil

This study aimed (i) to design an in vivo model to study fat digestibility, and (ii) to apply this design to test the in vivo digestibility of a highly thermoxidized olive oil. True digestibility of unheated olive oil was tested 2, 4, 6, and 7 h after administering 1 g of olive oil/100 g body weight to young adult Wistar rats by means of esophageal probes. Remaining gastrointestinal lumen fat showed an inversely linear relationship (t=−0.9932; P<0.001) with the length of the experiment. A 4-h test was considered adequate because after this period, half of the oil administer still temains in the lumen, making it possible to accurately measure the different nondigested, nonabsorbed themoxidized compounds. In a second experiment, fresh olive oil (3.6 mg polar content/100 mg oil) was heated at 180°C for 50 h in the presence of air; the polar content in this oil rose to 46.0 mg/100 mg oil. After 4 h, the true digestibility coefficient of 50-h heated olive oil did not significantly change, although it tended to decrease (24%) with respect to the unheated oil. Silica gel column chromatography and high-performance size exclusion chromatography were used to quantify nonthermoxidized and thermoxidized products present in the oils and in the gastrointestinal lumen after these test periods. True digestibility of the different thermoxidized compounds from the heated oil was 30–40%, whereas that of thermoxidized compounds from the fresh oil was much higher (∼80%). Nonoxidized triacylglycerol hydrolysis was negatively affected by the presence of large amounts of thermoxidized compounds. The present proposed model seems to be a useful tool for the study of thermoxidized oils. Data also show that thermoxidized compounds from abused olive oil are poorly but actively hydrolyzed and absorbed in vivo.     

Stabilization of refined olive oil by enrichment with chlorophyll pigments extracted from Chemlali olive leaves

This paper presents the first investigation on the effect of enrichment refined olive oil by chlorophyll pigment extracted from Chemlali olive leaves during storage (6 months). The changes that occurred in the quality indices, fatty acids, sterol, and phenolic content were investigated during the storage of refined olive oil under RT (20°C) and accelerated conditions (50°C) in the dark. Additionally, the pigments (chlorophyll and carotene) changes during 6 months of oil storage were evaluated. At the end of the storage, more than 90% of chlorophyll pigments decomposed in all samples, while, carotene pigment loss was lower showing up to 60 and 85% loss for oil stored at 20 and 50°C, respectively, at the end of storage. The reduction of total phenolic compounds exhibited similar degradation profiles, being reduced by 5% and up to 60% for the enriched refined olive oil stored at 20 and 50°C in 6 months, respectively. In the fatty acid composition, an increase in oleic acid and a decrease in linoleic and linolenic acids were less significant in enriched than non‐enriched refined olive oil. On the other hand, sterol composition was less affected by storage in enriched oil samples. However, the sterol concentration of the oil samples showed an increase in β‐sitosterol, 24‐methylene cholesterol, stigmasterol, and a decrease in cholesterol, Δ5, 24‐stigmastadienol percentage at the end of storage. Based on the Rancimat method, the oils with added leaf pigment extract had the lowest peroxide value and the highest stability. After 6 months of storage, the oxidative resistance of refined olive oil fell to 0.2 and to zero for enriched refined olive oil stored at 20 and 50°C, respectively.     

Separation of Triacylglycerols from Edible Oil Using a Liquid Chromatography–Mass Spectrometry System with a Porous Graphitic Carbon Column and a Toluene–Isopropanol Gradient Mobile Phase

This study presented a rapid and practical method of separating triacylglycerol (TAG) from edible oil using high‐performance liquid chromatography (LC) coupled with atmospheric‐pressure chemical ionization (APCI)/mass spectrometry (MS) system with a porous graphitic carbon column (150 mm × 2.1 mm, 5 μm) and a toluene–isopropanol–formic acid mobile phase. After investigating the experimental conditions, the gradient toluene–isopropanol mobile phase containing 0.1% formic acid was changed from 50:50 to 80:20 in 30 min; the column temperature was set to 35 °C, and APCI/MS was used in the positive‐ion acquisition mode. The TAG retention displayed a special order and was summarized to fit as follows: S‐ECN (special equivalent carbon number) = 2CN (carbon number) ? 3dB (double bond number) – 5uFA (unsaturated fatty‐acid number). Then, the LC–MS method was applied to separate TAG in 6 vegetable oils, resulting in the recognition of 27 TAG in corn oil, 21 TAGs in olive oil, 22 TAG in sunflower seed oil, 28 TAG in soybean oil, 25 TAG in sesame oil, and 31 TAG in peanut oil. The TAG separation through the LC–MS method was rapid, reproducible, and durable.     

Oxidative stability of olive oil flavoured by Capsicum frutescens supercritical fluid extracts

The effect of red pepper supercritical fluid extracts (SFE) on the oxidative stability of extra‐virgin olive oil was evaluated using accelerated stability tests [Rancimat and differential scanning calorimetry (DSC) methods] and by measuring the changes in the levels of polyunsaturated fatty acid primary and secondary oxidation products during storage under ambient conditions. SFE were produced according to a central composite rotatable design, at a constant temperature (40 °C), different pressures (15–23 MPa) and superficial velocities (0.04–0.08 cm/s). The results showed that the red pepper extracts produced at low extraction pressure and superficial velocity (e.g. 16.2 MPa and 0.046 cm/s) containing low/intermediate capsaicinoid levels did not affect olive oil stability. The extracts produced at higher pressure showed a slight pro‐oxidant activity. The K₂₃₂ and K₂₇₀ values always fell within the limit set by the European legislation for the quality characteristics of olive oil containing no additives. Evaluation of oxidative stability using DSC was found to be a useful methodology, which demands smaller oil samples and shorter times in comparison with the methodology using the Rancimat apparatus. Red pepper SFE obtained at low extraction pressures can be used in order to produce stable flavoured olive oils.     

Improvement of fluidized‐bed dryers for drying solid waste (olive pomace) in olive oil mills

Olive pomace from the two‐phase method of olive oil extraction (two‐phase olive pomace) must be dried from about 65% [wet basis (wb)] to about 8%, in order to extract part of the remaining pomace oil (about 3 wb‐%). An innovative dryer based on a fluidized bed is developed in this study. The objective is to improve olive pomace drying with low energy cost and high product quality by using optimal operating conditions, e.g. temperature and air flow rate, feeding solid moisture, and a control system. The bed operating temperature was set at 125 °C to obtain a good olive pomace oil quality and to reduce the thermal power consumption and drying time. The dried material is rather homogeneous and contains a negligible amount of polycyclic aromatic hydrocarbons. The fluidized bed was further improved with a moving bed joined by a conical device to the fluidized‐bed freeboard. This is a powerful combination in which the moving bed acts as a pre‐dryer of the wet solid and also as a filter of the output gas, with more than 99.9% of fines retention. The mean power consumption of the improved fluidized‐moving‐bed plant is 1 kWh/kg_water; this means a significant reduction of power cost with respect to the rotary dryers, which require about 1.4 kWh/kg_water.     

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.     

Malaxing temperature affects volatile and phenol composition as well as other analytical features of virgin olive oil

Three Italian olive varieties (Caroleo, Leccino and Dritta) were processed by centrifugation in the oil mill. The olive paste was kneaded at 20, 25, 30 and 35 °C. The results achieved revealed that the oil content in green volatiles from lipoxygenase pathway (including C₅ and C₆ compounds and especially unsaturated C₆ aldehydes) decreased progressively as the kneading temperature increased, dropping markedly at 35 °C. The content of phenols, o‐diphenols and secoiridoids showed an opposite trend, but the temperature of 35 °C was critical also for them, as it was for the majority of the other components, analytical parameters and indices related to quality, typicality and genuineness. In general, an increasing kneading temperatures increased the release of oil constituents from the vegetable tissue. This factor also affected the oil extraction yields. The best overall results were achieved by malaxing the olive paste at 30 °C. In fact, this temperature level led to achieving both pleasant green virgin olive oils and satisfactory oil extraction outputs.     

Analysis of neutral lipids and glycerolysis products from olive oil by liquid chromatography

A simple method was developed to separate model triglycerides, 1,3-diglycerides, 1,2-diglycerides, monoglycerides and free fatty acids and products generated in enzymatic glycerolysis of olive oil by high-performance liquid chromatography with a laser light-scattering detector. The separation was carried out with a silica column at 30°C. A gradient elution with mobile phase A (hex-ane/chloroform/formic acid) and mobile phase B (hex-ane/acetone/chloroform) can separate the compounds into distinct peaks in less than 20 min.     

Ozonated Olive Oil with a High Peroxide Value for Topical Applications: In-Vitro Cytotoxicity Analysis with L929 Cells

Previous studies have shown that ozonated vegetable oils have been used topically for healing of cutenous wounds. The aim of this study is to evaluate the dose dependent use of ozonated olive oil with high peroxide value (OZ) on the viability of cells for preventing side effects in topical applications. To the best of our knowledge, there are no reports investigaing the effect of peroxide value of ozonated olive oil associated with its cytotoxic activity on mouse non-neoplastc fibroblast cell lines (L929). Therefore, the present study was carried out by using OZ alone and/or in combination with glycerol and olive oil. In our study OZ was prepared by using pure olive oil. Both olive oil and glycerol are non-toxic and can be mixed with OZ uniformly. The cytotoxic activity of samples against L929 fibroblasts was assessed using the tetrazolium salt 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyltetrazolium bromide (MTT) assay. The peroxide value of synthesized OZ was found to be in the range of 2700–2900 mEq O₂/kg oil. The OZ/olive oil group did not show any cell death at all concentrations tested (p > 0.05) however OZ/glycerol group showed statistically significant reductions in viability at higher concentrations (p = 0.004–0.006) compared to the control group. Conclusively, using OZ/olive oil with a peroxide value of 2700–2900 mEq O₂/kg oil for short-term incubation was non-cytotoxic to the L929 fibroblast cell line.     

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.     

Phenolic Composition and Antioxidant Activity of Monovarietal and Commercial Portuguese Olive Oils

Olive oil composition has been investigated using chemical approaches, since the composition has a direct impact on its quality and safety and it may be used for certification purposes. In this paper, eleven monovarietal and twelve commercial Portuguese olive oils were analyzed to determine spectrophotometrically their total polyphenol content, ortho-diphenols and antioxidant activity. The phenolic profiles of these olive oils were also studied by high performance liquid chromatography. The lowest phenolic content and antioxidant activity were observed for monovarietal olive oils, however, among these group, ‘Cobrançosa’ and ‘Redondil’ cultivars showed the highest values of these two chemical parameters. In commercial olive oils, the concentration of polyphenols, determined according to the Folin–Ciocalteu method, and the antioxidant activity (ABTS method) ranged from 97.37 ± 1.10 to 219.7 ± 1.50 mg GAE/kg of oil and from 387.2 ± 20.00 to 997.5 ± 30.90 µmol Trolox/kg, respectively. The study of the phenolic profile demonstrated that the highest concentrations of the most abundant compounds in olive oil (tyrosol, hydroxytyrosol and oleuropein) are present in commercial olive oils. The correlation coefficient between total phenolics and antioxidant activity was statistically significant (r = 0.95, p < 0.0001). The same was observed for ortho-diphenol content and antioxidant capacity (r = 0.94, p < 0.0001).     

Quantitation and Distribution of Polar Compounds in an Extra Virgin Olive Oil Used in Fryings with Turnover of Fresh Oil

The alteration of an extra virgin olive oil used in 75 repeated and intermittent deep-fat fryings of potatoes (with a frequent turnover of fresh oil) was measured by column and high-performance size-exclusion chromatography (HPSEC). Total polar content increased slightly but continuously in the fryer's oil during the first 30 fryings from 2.76 ± 0.01 mg/100 mg oil (mean ± SD) to 6.60 ± 0.00 mg/100 mg used oil, followed by a tendency to reach a near steady state after a large number of fryings. Compounds related to thermoxidative alteration also increased significantly in the oil used 75 times to fry potatoes. Triglyceride dimers increased from 0.03 ± 0.01 mg/100 mg unused oil to 1.65 ± 0.05 mg/100 mg oil at the thirtieth fryings while triglyceride polymers and oxidized triglycerides did so during the first 60 fryings (0.07 ± 0.01 mg/100 mg oil and 0.56 ± 0.03 mg/100 mg oil in the unused oil respectively to 0.38 ± 0.01 mg/100 mg oil or 2.95 ± 0.15 mg/100 mg oil in the used oil, respectively). Both of these changes were followed by a tendency of these polar compounds to reach a near steady state in later successive fryings. Nevertheless, diglycerides and free fatty acids related to hydrolytic alteration remained quite stable throughout the frying process. Data from this study indicate that repeated fryings of potatoes in extra virgin olive oil with a frequent turnover of fresh oil throughout the frying slightly increased the level of polar material in the fryer oil during the first fryings followed by minor changes and by a tendency to reach a near steady state in successive fryings.