Stability and radical‐scavenging activity of heated olive oil and other vegetable oils

The effect of heating at 180 °C on the antioxidant activity of virgin olive oil (VOO), refined olive oil (ROO) and other vegetable oil samples (sunflower, soybean, cottonseed oils, and a commercial blend specially produced for frying) was determined by measuring the radical‐scavenging activity (RSA) toward 1,1‐diphenyl‐2‐picrylhydrazyl radical (DPPH^?). The RSA of the soluble (polar) and insoluble (non‐polar) in methanol/water fractions of olive oil samples was also measured. The stability of heated oils was assessed by determining their total polar compound (TPC) content. VOO was the most thermostable oil. Total polar phenol content and the RSA of VOO heated for 2.5 h decreased by up to 70 and 78%, respectively, of their initial values; an up to 84% reduction in RSA of VOO polar and non‐polar fractions also occurred. Similar changes were observed in the RSA of ROO and its non‐polar fraction after 2.5 h of heating. The other oils retained their RSA to a relatively high extent (up to 40%) after 10 h of heating, but in the meantime they reached the rejection point (25–27% TPC). The results demonstrate that VOO has a remarkable thermal stability, but when a healthful effect is expected from the presence of phenolic compounds, heating has to be restricted as much as possible.     

Antioxidative activity of sage (Salvia officinalis L.), savory (Satureja hortensis L.) and borage (Borago officinalis L.) extracts in rapeseed oil

The antioxidant activity (AA) of acetone oleoresins (AcO) and deodorised acetone extracts (DAE) of sage (Salvia officinalis L.), savory (Satureja hortensis L.) and borage (Borago officinalis L.) were tested in refined, bleached and deodorised rapeseed oil applying the Schaal Oven Test and weight gain methods at 80 °C and the Rancimat method at 120 °C. The additives (0.1 wt‐%) of plant extracts stabilised rapeseed oil efficiently against its autoxidation; their effect was higher than that of the synthetic antioxidant butylated hydroxytoluene (0.02%). AcO and DAE obtained from the same herbal material extracted a different AA. The activity of sage and borage DAE was lower than that of AcO obtained from the same herb, whereas the AA of savory DAE was higher than that of savory AcO. The effect of the extracts on the oil oxidation rate measured by the Rancimat method was less significant. In that case higher concentrations (0.5 wt‐%) of sage and savory AcO were needed to achieve a more distinct oil stabilisation.     

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.     

Water Addition During Oil Extraction Affects on Virgin Olive Oil Ethanol Content,Quality and Composition

Ethanol is the alcoholic precursor of fatty acid ethyl esters (FAEEs) in virgin olive oil (VOO). Because of its miscibility, water addition during oil extraction may affect oil ethanol content and then, the FAEEs synthesis during oil storage. In this work, the effect of water addition on VOO ethanol content and composition is studied. Water addition at two extraction systems (two and three phases) is compared and for vertical centrifuge, water addition at different temperatures is assayed. Ethanol content, quality parameters, and healthy components are determined in the oils. Results indicate three phase system gives oils with a 25% lower ethanol content than two phases. Ethanol reduction because of water addition is more important for three phases system (≈14%). For vertical centrifugation, ethanol is lowered as water dose and temperature increase. In general, water addition for any of the extraction steps analyzed reduces the oil ethanol concentration but other aspects such as fruity intensity and phenol content are also lowered. Practical applications: Virgin olive oil final ethanol content, and then its FAEEs concentration, does not only depend on the health and conservation status of olives, but also on the extraction system used and the amount of water added to the extraction process. The knowledge of the impact on ethanol content of water addition during oil extraction can be useful for olive oil legislators in order to keep the approved limits of FAEEs or to modify them. For oil producers, results can help to reduce the oil ethanol content and then FAEEs synthesis during virgin olive oil storage.     

Fractionation of oligomeric triacylglycerides and the relation to rejection limits for used frying oils

Precipitates enriched in oligomeric triacylglycerides were separated from thermally oxidized olive residue oil, conventional and high-oleic sunflower oils, and soybean oil by solvent fractionation in methanol/acetone at 4–5°C for 16 h. Different fractionation conditions were evaluated in an effort to isolate the oligomeric triacylglycerides (OTG). OTG, formed in frying oils upon heating at low concentations, were not detectable with conventional methods to determine polymeric compounds. The best conditions found from the different assays were the following: (i) weight of oil sample-to-solvent volume ratio of 1∶20; and (ii) solvent system methanol/acetone 10∶90 (vol/vol) for monounsaturated oils and 15∶85 (vol/vol) for polyunsaturated oils. Precipitates, enriched in oligomers, were formed when heated oils and used frying oils contained more than 27% polar compounds, a value which is widely accepted as the upper limit for use of frying oils.     

Thai Tea Seed Oil and Virgin Olive Oil Similarly Reduce Plasma Lipids: A Pilot Study within a Healthy Adult Male Population

The potential cardiovascular benefit of virgin olive oil (VOO) is widely recognized. However, the use of VOO at very high cooking temperatures makes these oils poorly suited for many Asian dishes. The use of tea seed oil (TSO) is increasing in Thailand, with TSO having a higher smoke point than VOO. The current study examines the effects of daily TSO intake in healthy adults. In a randomized, single-blind crossover design, 12 men consumed for 3 weeks 40 g day⁻¹ of food prepared with either TSO or VOO as a cooking oil. Plasma lipids, thiobarbituric acid reactive substances (TBARS), and oxidant defense enzyme activities are measured before and after each 3-week intervention period. Gas chromatography analysis of TSO and VOO demonstrates that both oils are equally high in monounsaturated fatty acid. The dietary incorporation of TSO and VOO for three weeks reduces low-density lipoprotein cholesterol (LDL-C) concentrations by 15% and 13%, respectively; with total cholesterol (TC) levels lowered by 10% in both groups. No significant changes in TBARS or antioxidant enzyme activity is observed. These results support the concept that Thai TSO can be utilized as a suitable and healthy alternative oil for high-temperature cooking in many Thai and Asian diets. Practical Applications: Tea seed oil from Camellia oleifera grown in Thailand has been recently reported to favorably lower lipid profiles in hamsters fed a high-fat diet in a manner similar to feeding refined olive oil or grapeseed oil. A pilot crossover trial is conducted to compare the effects of three weeks of daily intake of either TSO or VOO in healthy human adults. Consumption of both oils produced significant reductions in TC and LDL-C. Thai TSO leads to favorable lipid profiles and is a reasonable choice for many Thai and Asian food recipes.     

Evaluation of virgin olive oil bitterness by total phenol content analysis

Bitterness is an important sensory attribute of virgin olive oil (VOO). It is usually assessed by tasting, which is a time‐consuming method and needs trained tasters. Bitterness is related to the phenolic compounds and can be estimated by the measurement of the specific absorbance at 225 nm (K₂₂₅). This paper proposes to evaluate oil bitterness intensity as estimated from the K₂₂₅ values measuring the phenol content. A significant relationship between phenol content and K₂₂₅ as well as a prediction model for bitterness intensity estimation from the phenol content was obtained. Classification of oil bitterness was based on the phenol content. Furthermore, when 12 VOO samples were classified by their bitterness intensities as estimated by the prediction model and by sensory analysis, more than 92% of the oil samples were correctly classified. Therefore, by measuring the phenol content, the bitterness intensity can be estimated and oils can be classified by their bitterness. This model may represent an easy method to evaluate the bitterness intensity without any sensory assessment.     

A non‐extractable condensed‐tannins fiber reduces thermal oxidation in oils at frying temperature

Several compounds presenting antioxidant properties have been tested in frying oils to delay thermal oxidation of the triglycerides containing unsaturated fatty acids. The present study was designed to evaluate, for the first time, the antioxidant and antipolymerizing effects of addition of Exxenterol®, a denatured carob fiber very rich in non‐extractable tannins, on olive oil (OO), sunflower oil (SO) and a homogeneous blend of both oils. Exxenterol was added to the three oils in amounts of 50, 250, 500 and 1000 mg/kg oil before heating. After 36 h of heating at 180 °C, there was a large and relevant increase of the polar material and the polymer contents, but tocopherol decreased to non‐detectable levels in all three oils. Polar content, polymer and thermal oxidation formation (p ≤0.004) and tocopherol degradation (p ≤0.022) were significantly and dose‐dependently inhibited by Exxenterol. Both polar material and polymer formation were inhibited (at least by 44%) in OO and SO and at least by 27% in the oil blend when 1000 mg/kg oil of this product was added. Small but detectable amounts of tocopherol were found in the oil blend containing 50 mg Exxenterol/kg. The results clearly show that this non‐extractable tannin‐rich fiber can be successfully employed as an additive to prolong oil shelf life at frying temperature.     

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.     

Formation of Polar Compounds During Deep‐frying—Determination by 1H NMR and ESR

The present study aims to elucidate the factors influencing the generation of polar compounds in oils during deep‐frying. Oils with different fatty acid compositions, including palm oil (PO), refined palm kernel oil (RPKO), and refined coconut oil (RCO), are applied in successive frying processes. ¹H NMR spectra reveal that heated PO has a higher percentage of allyl acyl group and is more prone to formation of non‐polar dimeric triglycerides as compared to other types of oils. In addition, electron spin resonance (ESR) spectra indicate that alkyl radicals are more predominant than alkoxy radicals in heated PO. In contrast, RPKO and RCO are inclined to generation of alkoxy radicals during the thermal treatment. The results reveal that oils with high unsaturated fatty acid content are more prone to generation and oxidation of non‐polar dimeric triglycerides. Practical Applications: The change in free radical profile and concentration is one of the indicators of lipid oxidation and polymerization. Alterations in the levels of alkyl and alkoxyl radicals, revealed by ESR, can be used to illustrate the formation of polar compounds in deep‐fried oils with different fatty acid compositions. The percentage of allyl acyl group, revealed by ¹H NMR, can be used to predict the generation of polar compounds. Therefore, this study provides useful information for the development of different methods to reduce polar compound formation in oils during thermal processing depending on the fatty acid composition of different deep‐fried oils.     

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.     

Contribution of Compositional Parameters to the Oxidative Stability of Olive and Walnut Oil Blends

Oil blending was conducted to study the effects of changes in fatty acid composition (FAC), tocopherols and total phenol content (TPC) on oxidative stability of virgin olive oil (VOO):walnut oil (WO) blends. The measurement of the antioxidant activity of bioactive components present in the parent oils and blends was achieved by their ability to scavenge the free stable 2,2-diphenyl-1-picrylhydrazyl radical (DPPH·). The highest percentage of DPPH· inhibition was found for pure VOO, and the lowest one for pure WO. EC₅₀ values obtained from the DPPH assay correlated significantly and inversely with TPC. The generation of volatile flavor components in VOO indicated the predominance of C₆ compounds produced through biochemical (enzymatic) pathways, whereas WO showed increased concentrations of medium chain (C₇–C₁₁) aldehydes produced through chemical (oxidative) pathways. The results obtained confirm the importance of VOO phenolics in providing protection against oxidation in VOO and VOO/WO blends. However, considering the impact of FAC and the content of endogenous antioxidant substances mentioned previously on the oxidative stability of the oils analyzed, the effect of an elevated unsaturation level (WO) prevails over a high amount of such bioactive components (VOO).     

Separation and concentration of natural antioxidants from the rape of olives

Polyphenols were extracted from the rape of Israeli olive oil using hexane, acetone and ethanol in a simple sequential procedure yielding three fractions (A,B,C). Fraction A (extracted with hexane) contained few polyphenols (0.05%), while Fraction B (extracted with acetone) and Fraction C (extracted with ethanol) contained about 5% polyphenols each. Fractions B and C were also found to contain the highest ortho-di-phenol concentration (about 3%). The addition of purified Fraction B at a level of 100 ppm to refined olive or soybean oils partially inhibited the oxidative deterioration when the oils were stored in the dark at 100 C.     

Proposed parameters for monitoring quality of virgin olive oil (Koroneiki cv)

The overall quality of virgin olive oil (VOO) is closely related to its oxidative stability that is usually evaluated through the stability index measured by the Rancimat apparatus. Quality characteristics and also pro‐oxidant and antioxidant content for 52 Greek VOO samples (Koroneiki cv) were used to build up a model capable of predicting stability. Collinearity diagnostics, variable selection, and regression analysis were applied to the experimental data to locate the contribution of each parameter to the keeping quality of the samples. The predictive ability of the model was confirmed for a second VOO ample set of the same cultivar. It was found that except for the peroxide value, which negatively influences the stability, other important parameters were α‐tocopherol, total polar phenol and total chlorophyll content. It is concluded that the colorimetric determination of total polar phenols, the spectrometric determination of total chlorophylls and the high‐performance liquid chromatography analysis of α‐tocopherol, not presently included in the established methods of official analysis, can be used for a better evaluation of VOO quality. These parameters, which can be easily adopted as routine methods by the industry, seem to be of utmost importance for shelf life prediction and expiration dating if applied for the promotion of the most competitive products in the international olive oil market.     

Frying stability of canola oil in presence of pumpkin seed and olive oils

Frying performance of canola oil (CO) was investigated in the presence of 5, 10, and 15% levels of virgin olive oil (VOO) and pumpkin seed oil (PSO) during frying of potatoes at 180°C. Acid value, carbonyl value, total polar compounds content, and total tocopherols content of the oil samples were determined during the frying process. VOO and PSO addition improved the frying stability of the CO. Frying performance of the CO increased more in the presence of PSO than in the presence of the VOO. The PSO levels higher than 5% exerted pro‐oxidant effects, indicating the necessity of investigation at lower levels. The better antioxidative effect of PSO was attributed to its probably different phenolic composition.     

Phenolic acid content and sensory properties of two Spanish monovarietal virgin olive oils

In recent years, phenolic acids have received considerable attention as they are essential to olive oil quality and nutritional properties. This study aims to validate a rapid and sensitive method based on ultra‐performance liquid chromatography/time‐of‐flight mass spectrometry (UPLC–TOF‐MS) for analyzing the phenolic acid content of olive oil and assessing its impact on virgin olive oil (VOO) sensory attributes. Once this method was validated, we used it to evaluate the phenolic acid composition of several Spanish monovarietal virgin olive oils in relation to nine different olive ripening stages. The results obtained confirm that the methodology developed in this study is valid for extracting and analyzing phenolic acids from VOO. The phenolic acid content of the virgin olive oils sampled was proven to be influenced by the type of cultivar and olive harvest date. Therefore, phenolic acids might be used as potential markers for olive oil cultivar or ripening stage. Finally, the data obtained indicate that the sensory properties of VOO may be differently affected by its phenolic acid content depending on the type of cultivar. Practical applications: The method validated in the present study – based on UPLC‐TOF‐MS – allows experts to assess the phenolic acid content of different VOO cultivars (varieties). This application will probably be very useful to the olive oil industry. The reason is that our study revealed that phenolic acids have an impact on the sensory quality of VOO, which is essential to consumer preferences and choice. In addition, there are phenolic acids that are only found in a particular variety of olive oil obtained from fruits at a specific ripening stage. Consequently, phenolic acids could be used as potential markers for olive oil variety and harvest time.     

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.     

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.     

Changes in Total Polar Compounds,Peroxide Value,Total Phenols and Antioxidant Activity of Various Oils Used in Deep Fat Frying

In this study, the effect of deep fat frying on oil degradation, total phenols (TP) and total antioxidant activity (TAA) of hazelnut, corn, soybean and olive oils were investigated. Oil degradation and oxidation were monitored by measuring the total polar compounds (TPC) and the peroxide value (PV). The amount of TPC in corn, soybean and olive oils increased significantly with the time increment (p < 0.05). The PV of the oils did not exceed the maximum acceptable limit of 10 mequiv O₂/kg after 125 min frying except for hazelnut oil (10.64 mequiv O₂/kg). Deep-fat frying did not cause any significant change in the TP of corn oil, soybean oil and olive oil (p < 0.05). A significant decrease in the antioxidant activity was observed after 50 min frying using hazelnut oil and corn oil (p < 0.05). However, the antioxidant activity of soybean oil and olive oil significantly decreased after 75 and 25 min frying, respectively.     

Effect of Clarification System on the Conservation of Virgin Olive Oil during Its Storage

The results obtained in this work explain how clarification systems can affect the conservation of virgin olive oils (VOOs) during the storage step. The evolution of the quality and sensory properties during the storage of VOOs clarified by different systems, vertical centrifugal separator (VCS) with minimal water addition and conical bottom settling tank (CBST), is studied at industrial scale for two different crop years. In general, VCS oils show a slight higher moisture and solid impurities content at the end of the storage step due to a higher emulsion grade (because of the emulsion generated) caused by the rotating movement of this clarification system. For the studied clarification systems, no remarkable differences are observed between the oils during their storage for quality indexes. However, these systems show differences regarding oil sensory properties. The VOOs clarified by VCS are characterized by a higher presence of phenol components, higher positive sensory attributes intensity, and higher lipoxygenase (LOX) aldehydes content during their storage. VOOs from CBST show lower phenol content, a higher “non‐LOX” volatiles content, and the presence of sensory defects during storage. Practical Applications: The results obtained in this work are very important in order to provide specific recommendations and scientific support based on objective data to improve VOO quality. As described in this study, the VCS with a minimal water addition can be a better option to produce VOO of improved quality. This clarification system is an efficient and quick operation that reduces the contact between oil and the remaining water and impurities during the storage step. The minimal water addition used in this clarification system allows obtaining VOOs with higher phenol content and positive sensory notes. This leads to prolong VOO shelf‐life and conservation during the storage stage, due to preservation of the quality indexes and minor components with antioxidant activity. Besides, this clarification system reduces the water consumption during oil clarification and generates a lower wastewater volume regarding conventional vertical centrifugation, and therefore can be considered more environmentally friendly.