Effect of Greek sage and summer savory extracts on vegetable oil thermal stability

The effect of ethanol and acetone extracts obtained from Greek sage (Salvia fruticosa) and summer savory (Satureja hortensis L.) on the thermal stability of vegetable oils heated at frying temperature (180 °C) was studied. Virgin olive oil (VOO), refined olive oil (ROO), sunflower oil (SO), and a commercial oil blend suitable for frying (BL), enriched with each extract obtained from the two plant materials at a concentration of 3 g/kg oil, were heated at 180 °C for 10 h. Changes during heating were assessed by quantification of total polar materials and determination of p‐anisidine values. The acetone extract obtained from Greek sage showed a better inhibitory effect against thermal oxidation of heated refined oils (BL, ROO, SO) than the respective ethanol extract, although the latter was found to have a relatively higher total phenol content. Both summer savory extracts effectively retarded the thermal oxidation reactions during oil heating, showing a more pronounced effect than the Greek sage acetone extract. The activity of the acetone extract obtained from summer savory was stronger (SO, BL) or similar (ROO, VOO) to that of the summer savory ethanol extract, although the latter was found to have a higher total phenol content.     

Effect of Specific Oil Surface Area on the Thermal Stressing of Rapeseed Oil During Heating in an Electric Frying Pan

The effect of specific oil surface (SOS) during pan frying of rapeseed oil on its thermal stability and antioxidant capacity (AC) was evaluated. Rapeseed oils with different oil layer heights (OLH = 0.5, 1.0, 1.5, 2.0, and 2.5 cm) were heated on an electric frying pan coated with Teflon at 180 ± 10 °C until a selected end point of 25 % total polar compounds (TPC) was reached. The changes of chemical parameters of oil samples such as peroxide value, p‐anisidine value, Totox value, free fatty acids, TPC and AC using the 2,2‐diphenyl‐1‐picrylhydrazyl assay were determined. Irrespective of the applied methods, the highest changes in oil with OLH = 0.5 cm were observed. Heating in low OLH also led to the fastest time of TPC formation in rapeseed oil; the 0.5‐cm layer reached 25 % TPC in a relatively short time (71.5 min) compared to the highest OLH = 2.5 cm (t = 315.1 min). The SOS and the rate of change in the heated oils decreased with increasing OLH. Crucial effects of SOS on physicochemical oil changes were observed. The present study demonstrated the protective effect of increasing the OLH on the quality of the heated rapeseed 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.     

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).     

Antioxidative and synergistic effects of bene kernel and hull oils during oxidation of virgin olive oil

Total amounts of conjugated diene hydroperoxides and carbonyl compounds of a virgin olive oil (VOO) and its purified form as affected by 0.1–6% w/w bene kernel (BKO) and hull (BHO) oils were monitored during 16 h heating at 180°C. The VOO was more prone to the production of off‐flavour carbonyl compounds than to the formation of conjugated diene hydroperoxides. The VOOs oxidative stability decreased significantly due to the removal of the indigenous antioxidative compounds. Oxidative stability, especially regarding the secondary oxidation, significantly improved with increasing concentrations of the BKO than with those of the BHO.     

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.     

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.     

Influence of the extraction process on dissolved oxygen in olive oil

The influence of the olive oil processing steps [paste malaxation (PM), decanter centrifugation (DC), and vertical centrifugation (VC)] on the dissolved oxygen (DO) concentration in virgin olive oil (VOO) right after production was investigated at industrial plant scale for two successive years. The influence of this parameter on quality decay during shelf life, assessed by peroxide value (PV) analysis, was also monitored. The VC step showed the higher oxygenation effect (50% increase in comparison to the control), and a good linear regression (r² = 0.83) was found between the initial DO concentration and the PV after 2 days. An 18‐months shelf life test, performed on VOO sampled before and after the VC, indicated the slowest decay kinetics in the oils with the lower initial DO concentration, i.e. the non‐centrifuged oils.     

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.     

Influence of Water Deficit in Bioactive Compounds of Olive Paste and Oil Content

The main objective of this study was to evaluate the effect of different deficit irrigation treatments (control, regulated deficit irrigation [RDI]‐1, RDI‐2, and RDI‐3) on the phenolic profile of the olive paste and oil content. Irrigation treatments with more stress water led to a considerable increase in the phenolic compounds of olive paste, especially in oleuropein (60.24%), hydroxytyrosol (82%), tyrosol (195%), and verbascoside (223%) compared to control. A significant increase in the content of total flavonoids and phenolic acids was also observed for these samples. In virgin olive oils (VOO) elaborated from the most stressed olive trees (RDI‐2 and RDI‐3), a noticeable increase in phenolic substances with antioxidant properties (oleuropein, hydroxytyrosol, tyrosol, secoiridoid derivatives, and o‐vanillin) was observed. Consequently, water stress conditions improved antioxidant activity of VOO.     

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.     

The effect of phytosterol concentration on oxidative stability and thermal polymerization of heated oils

This study determined the effect of adding mixed phytosterols, at various concentrations, on the thermal polymerization and oxidative stability index (OSI) of soybean and high‐oleic sunflower oils. The indigenous tocopherols and phytosterols were removed from the oils by molecular distillation. Pure phytosterols were added back to these stripped oils at concentrations of 0.25, 0.5, 1, and 2.5 wt‐%. These oils were heated at 180 °C, and triacylglycerol dimers and polymers, fatty acid composition, and residual phytosterols were determined. Added phytosterols at 1 and 2.5% significantly decreased thermal polymerization of stripped soybean oil over 8 h. Phytosterols at 2.5% significantly increased polymerization of stripped high‐oleic sunflower oil over 12 h. Added phytosterols did not affect the loss of polyunsaturated fatty acids in either oil. The decomposition of the added phytosterols was followed in both oils during the heating study. The loss of phytosterols in soybean oil ranged from 7 to 13%, while loss in stripped high‐oleic sunflower oil ranged from 13 to 20%. Phytosterols added at 1 and 2.5% significantly decreased the OSI for stripped high‐oleic sunflower oil. This research shows that added phytosterols, especially at higher concentrations, will have an impact on the thermal and oxidative stability of oils.     

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.     

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.     

The effect of oxygen concentration on oxidative deterioration in heated high-oleic safflower oil

High-oleic safflower oil was heated at 180°C in atmospheres with four levels of oxygen concentration (2, 4, 10, and 20%) modified with nitrogen gas, to assess the effects of atmospheric oxygen concentration on the oxidative deterioration of deep-frying oils. Acid value, carbonyl value, polar materials, linoleic acid, tocopherol contents, and oxidative stability were measured to evaluate the quality of heated oils. These values were found to be correlated with both heating time and oxygen concentration. Acid and carbonyl values and polar material content of oils heated at oxygen concentrations of 2 and 4% were lower than those at 10 or 20%. On the other hand, linoleic acid and tocopherols were hardly reduced in oils after heating for 30 h at 2% O₂, whereas they were decomposed according to the oxygen concentration and heating time. Oxidative stability was well maintained in oils heated at 2 and 4% O₂. These results suggest that the oxidative deterioration of heated higholeic safflower oil depends on oxygen concentration.     

Effects of Filtration on the Quality Properties of Extra Virgin Olive Oils during Storage

In this study, the effects of filtration on quality parameters, chemical characteristics, antioxidant activity, and oxidative stability (OS) of Turkish olive oils during the storage period of 12 months were investigated. The olive oil free acidity (% oleic acid per 100 g of olive oil) (free fatty acidity, FFA), peroxide values (PV) (meq O₂ kg⁻¹ oil), and UV spectrophotometric indices (K₂₃₂ and K₂₇₀ measurements) were used for evaluating the quality parameters of olive oils. α-tocopherol analysis, total phenolic content (TPC), total chlorophyll and carotenoid analyses, and 2,2-diphenyl-1-picrylhydrazyl (DPPH•) radical-scavenging activity (RSA) assays were carried out. Chromatographic methods were applied to determine the fatty-acid and triacylglycerol (TAG) composition, the content of methyl and ethyl esters (FAEE and FAME), and the content of fatty acids of olive oils. Univariate and multivariate statistical methods were performed to evaluate results. Univariate data analysis results showed that filtration of Ayvalık, Memecik, and Domat olive oils had no considerable influence on quality parameters, antioxidant compounds, FAEE and FAME, antioxidant activity, and OS, except TPC (P < 0.05). A significant difference between the samples was determined regarding storage times of the olive oils. Principal component analysis (PCA) analysis revealed that olive oils were grouped according to storage periods of the olive oils regarding fatty-acid and triacylglycerol (TAG) composition while there was no clear separation among the samples according to the filtration process. However, qualitative and quantitative changes took place on minor and major components of olive oils during the storage period.     

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.     

Hydrophilic antioxidants of virgin olive oil. Part 1: Hydrophilic phenols: A key factor for virgin olive oil quality

Virgin olive oil (VOO) consumption is increasing all over the world due to its excellent organoleptic and nutraceutical properties. These beneficial traits stand from a prominent and well‐balanced chemical composition, which is a blend of major (98% of total oil weight) and minor compounds including antioxidants. The main antioxidants are phenolic compounds, which can be divided into lipophilic and hydrophilic phenols. While lipophilic phenols such as tocopherols can be found in other vegetable oils, most hydrophilic phenols in olive oil are exclusive of the Olea europaea species endowing it with a chemotaxonomic interest. This review is focused on VOO antioxidant profile and, particularly, on hydrophilic phenols that are divided into different sub‐families such as phenolic acids and alcohols, hydroxy‐isochromans, flavonoids, secoiridoids, lignans and pigments. Analytical methods for qualitative and/or quantitative determination of these compounds are assessed. The implementation of efficient sample preparation protocols, separation techniques such as liquid chromatography, GC and capillary electrophoresis, as well as detection techniques such as ultraviolet absorption, fluorescence or MS are critical to succeed in the quality of the results. The effects of hydrophilic phenols on increasing VOO stability, its nutraceutical interest and organoleptic properties are also considered.     

Determination of nonvolatile components of heated soybean oils separated with high-efficiency mixed-bed polystyrene/divinylbenzene columns

Whole heated soybean oils and their polar fractions were analyzed for nonvolatile components by high-performance size-exclusion chromatography (HPSEC) with evaporative light scattering detection (ELSD). High molecular-weight (MW) polymer compounds with MW ≥ trimer were efficiently separated with new 3-μm mixed-bed styrene/divinylbenzene copolymer columns. Peaks of high MW polymer components in the new column system appeared to be sharper and more symmetrical than those obtained with other columns. In the model systems studied, continuous addition of water to partially simulate frying conditions resulted in a significant increase (up to 30%) in the polar lipid content of the heated oils evaluated. Due to relatively high concentrations of monomeric triglycerides (84.6–93.5%) present in the whole unfractionated oils, small but erratic variations in the compositional distribution of components were observed in oils containing different amounts of added water. On the other hand, HPSEC-ELSD analyses of the polar fractions (monomeric triglycerides, 25.4–62.6%) showed significant changes in the content and composition of nonvolatile components with the amount of water added. In general, prolonged heating with increasing amounts of water accelerated hydrolysis and polymerization of heated soybean oils. Discrepancies in total polymerization of heated soybean oils. Discrepancies in total polymeric materials obtained from HPSEC composition data for whole oils and polar fractions are discussed in terms of nonuniformity in sample matrices, detection limitations for minor components, and a nonlinear ELSD response rationale.