Oxidative Stability and Changes in Chemical Composition of Extra Virgin Olive Oils After Short‐Term Deep‐Frying of French Fries

We aimed at investigating oxidative stability and changes in fatty acid and tocopherol composition of extra virgin olive oil (EVOO) in comparison with refined seed oils during short‐term deep‐frying of French fries, and changes in the composition of the French fries deep‐fried in EVOO. EVOO samples from Spain, Brazil, and Portugal, and refined seed oils of soybean and sunflower were studied. Oil samples were used for deep‐frying of French fries at 180 °C, for up to 75 min of successive frying. Tocopherol and fatty acid composition were determined in fresh and spent vegetable oils. Tocopherol, fatty acid, and volatile composition (by SPME–GC–MS) were also determined in French fries deep‐fried in EVOO. Oil oxidation was monitored by peroxide, acid, and p‐anisidine values, and by Rancimat after deep‐frying. Differential scanning calorimetry (DSC) analysis was used as a proxy of the quality of the spent oils. EVOOs presented the lowest degree of oleic and linoleic acids losses, low formation of free fatty acids and carbonyl compounds, and were highly stable after deep‐frying. In addition, oleic acid, tocopherols, and flavor compounds were transferred from EVOO into the French fries. In conclusion, EVOOs were more stable than refined seed oils during short‐term deep‐frying of French fries and also contributed to enhance the nutritional value, and possibly improve the flavor, of the fries prepared in EVOO.     

Correlation between physicochemical analysis and radical‐scavenging activity of vegetable oil blends as affected by frying of French fries

The main goal of the present work was to compare and correlate the results of physicochemical parameters and antiradical performance of some oil blends during deep‐frying, which will be an initial indicator for applying antiradical tests for monitoring deep‐frying oils. Two oil blends were prepared. The first blend was a mixture (1 : 1, wt/wt) of sunflower seed oil and palm olein (SO/PO) and the second was a mixture (1 : 1, wt/wt) of cottonseed oil and palm olein (CO/PO). The oil blends were evaluated during intermittent frying of French fries on two consecutive days for 16 h, with oil replenishing after 8 h. Changes in the fatty acid profile and some physicochemical parameters (peroxide value, color index, viscosity, total polar compounds and UV absorbance at 232 and 270 nm) were used to evaluate the alterations during frying. A quick spectrophotometric method was developed to assess deep‐frying oil quality. With the 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) method, the neutralization of the stable radical DPPH by antioxidants present in the oil during frying was measured. Radical‐scavenging activity (RSA) of both oil blends was recorded during frying, wherein the results showed that the SO/PO blend had the highest RSA. It was evident from the results that a proportional correlation and positive relationship existed between the levels of fatty acids and the physicochemical characteristics of the vegetable oil blends and their RSA. The initial results obtained allow us to suggest that antiradical measurements could be used to quantify the oxidative and hydrolytic deterioration of vegetable oils upon frying.     

Content of trans,trans‐2,4‐decadienal in deep‐fried and pan‐fried potatoes

Trans,trans‐2,4‐decadienal is a by‐product of frying oil that is also transferred to fried food. This aldehyde has been found and quantified both in frying oils and fumes generated during frying. Furthermore, it has been reported that 2,4‐decadienal has cytotoxic and genotoxic effects and promotes LDL oxidation. In the present work trans,trans‐2,4‐decadienal was detected directly in fried potatoes (french‐fries). Moreover, the influence of frying conditions (deep‐frying, pan‐frying), the oil type (olive oil, sunflower oil, cottonseed oil, palm oil and a vegetable shortening) and the degree of thermal deterioration (eight successive frying sessions without replenishment) on the production of 2,4‐decadienal in oil and potatoes was studied. The isolation of the aldehyde was performed by methanol extraction, while the identification and quantification was performed by RP‐HPLC. The quantity of trans,trans‐2,4‐decadienal produced during successive pan‐frying demonstrated a peak at the third and fourth frying session. The highest concentration of trans,trans‐2,4‐decadienal was detected in potatoes fried in sunflower oil, and the lowest in olive oil. The quantity of trans,trans‐2,4‐decadienal in fried potatoes decreased during successive deep‐frying at the seventh frying session or remained stable, except for cottonseed oil. The quantity of trans,trans‐2,4‐decadienal in fried potatoes was considered to be dependent on the oil used, on the frying process and, to a lesser extent, on the oil deterioration. In all cases tested, the highest concentration of trans,trans‐2,4‐decadienal was detected during deep‐frying. The unsaturation degree of the frying oil was considered to promote the formation of trans,trans‐2,4‐decadienal. Considering the quantity of 2,4‐decadienal found in french‐fries and in the respective frying medium, direct quantification of 2,4‐decadienal is required in order to make an estimation of intake from french‐fries.     

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

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

Effect of oil replenishment during deep-fat frying of frozen foods in sunflower oil and high-oleic acid sunflower oil

Frying stability of sunflower oil (SO) with 23% oleic acid and 61% linoleic acid, and of high-oleic acid sunflower oil (HOSO) with 74% oleic acid and 13% linoleic acid was studied during 20 discontinuous deep-fat fryings of various frozen foods, with or without frequent replenishment of the used oil with fresh oil. Alterations of both oils were measured by column, gas-liquid and high-performance size-exclusion chromatography. Total polar content and compounds, related to thermoxidative changes, and diacylglycerides, related to hydrolytic changes, increased in all oils during frying but reached higher levels in SO than in HOSO. Nevertheless, the increased levels of diacylglycerides observed may result from the frozen potatoes prefried in palm oil. Oleic acid in HOSO and linoleic acid in SO significantly decreased, but the fatty acid modifications that occurred during the repeated fryings were not only related to thermoxidative alteration but also to interactions between the bath oil and the fat in the fried products. Data from this study also indicated that HOSO performed more satisfactorily than SO in repeated fryings of frozen foods. Moreover, frequent addition of fresh oil throughout the deep-frying process minimized thermoxidative and hydrolytic changes in the frying oils and extended the frying life of the oils.     

Cyclic fatty acids in sunflower oils during frying of frozen foods with oil replenishment

Frying of frozen foods has become popular because it considerably reduces cooking time. Polymers and cyclic fatty acid monomers (CFAM) formed during frying are potentially toxic and therefore their production should be minimized. Twenty discontinuous fryings of different frozen foods were carried out over ten consecutive days, in sunflower oil (SO) and in high‐oleic acid sunflower oil (HOSO), by adding fresh oil after each frying to bring the volume of the fryer oil back to 3 L. CFAM methyl ester derivates were hydrogenated, isolated, concentrated and quantified by HPLC using a reverse‐phase column, followed by gas chromatography. After 20 fryings, significantly higher contents of polar material, polymers and CFAM (all p <0.001) were found in SO than in HOSO. Bicyclic compound formation was four times higher in SO (p <0.001). The fat from the fried potatoes presented a polymer content very similar to that of their corresponding oils. The 100‐g rations of the SO‐fried potatoes from the 20^th frying supply 49 or 15%, respectively, more polymers and CFAM and 1 mg more bicyclic fatty acids than the 100‐g rations of HOSO‐fried potatoes. Because digestion and absorption of polar material, polymers and CFAM occur, the data clearly show the advantageousness and advisability of frying with HOSO rather than SO.     

Effect of after-cooking darkening inhibitors on stability of frying oil and quality of french fries

The effect of two after-cooking darkening inhibitors, sodium acid pyrophosphate (SAPP) and calcium acetate (CaAc), and their combined effect on frying oil stability and quality of french fries produced were evaluated over a period of 72 h. Samples of frying oil and par-fried french fries were taken at 3-h intervals through each experiment and analyzed for selected chemical and physical parameters. As the frying time increased, all the oil samples contained increased amounts of deterioration products. The color index and free fatty acid (FFA) values were highly correlated with frying time. There were no significant effects on oil properties in terms of FFA until 9 h of frying among the 4 pretreatments. However, from 12 to 72 h of frying, oil used to fry potatoes treated with SAPP contained less FFA than oils exposed to CaAc alone or in combination with SAPP. The fat content of par-fried french fries was approximately 0.11 g/g dry matter and remained relatively constant during extended frying. After-cooking darkening of par-fried french fries and final color of the fries were affected by the pretreatment, but not by the frying time.     

Impact of Canolol‐Enriched Extract from Heat‐Treated Canola Meal to Enhance Oil Quality Parameters in Deep‐Frying: a Comparison with Rosemary Extract and TBHQ‐Fortified Oil Systems

Canolol‐enriched extracts obtained from the extraction of fluidized bed treated canola meal with supercritical carbon dioxide were added to high‐oleic canola oil in different concentrations (200, 500 and 750 mg/kg). After 30 h of deep‐fat frying, oils fortified with canolol‐enriched extracts showed a two to three times better frying performance in comparison to the commonly used antioxidants (TBHQ, 200 mg/kg; rosemary extract, 40 and 200 mg/kg) and a control without antioxidants with regards to the formation of di‐ and polymer triacylglycerols, total polar compounds, secondary degradation products (anisidine value) and the iodine value. The canolol‐enriched extracts were also able to slow down the degradation of α‐ and γ‐tocopherol during frying resulting in significant amounts of tocopherols after 30 h of frying in comparison to the other oils. The influence of the canolol‐enriched extracts indicated strongly concentration‐dependent performance. With increasing concentration of the extract, the thermal stability of the fortified oil was improved. The only disadvantage of the addition of the extracts was an increase in the initial acid value, but within the frying time, only oil fortified with 750 mg canolol‐enriched extract/kg reached the limit given in different countries.     

The Effect of Type of Oil and Degree of Degradation on Glycidyl Esters Content During the Frying of French Fries

The aim of the study was to determine the effect of oil degradation on the content of glycidyl esters (GEs) in oils used for the frying of French fries. As frying media, refined oils such as rapeseed, palm, palm olein and blend were used. French fries were fried for 40 h in oils heated to 180 °C in 30‐min cycles. After every 8 h of frying, fresh oil and samples were analyzed for acid and anisidine values, color, refractive index, fatty acid composition, and content and composition of the polar fraction. GEs were determined by LC–MS. Hydrolysis and polymerization occurred most intensively in palm olein, while oxidation was reported for rapeseed oil. The degradation of oil caused increased changes in the RI of frying oils. Losses of mono‐ and polyunsaturated fatty acids were observed in all samples, with the largest share in blend. The highest content of GE found in fresh oil was in palm olein (25 mg kg^?1) and the lowest content of GE was found in rapeseed oil (0.8 mg kg^?1). The palm oil, palm olein and blend were dominated by GEs of palmitic and oleic acids, while rapeseed oil was dominated by GE of oleic acid. With increasing frying time, the content of GEs decreased with losses from 47 % in rapeseed oil to 78 % in palm oil after finishing frying.     

Effect of Different Frying Methods on the Total <Emphasis Type="Italic">trans</Emphasis> Fatty Acid Content and Oxidative Stability of Oils

The main objective of this study was to determine the effect of different frying oils and frying methods on the formation of trans fatty acids and the oxidative stability of oils. Sunflower, canola and commercial frying oils, the most commonly used oils for frying potatoes in the fast food industry, were used as the frying medium. The value for total polar compounds was highest when commercial frying oil was used in the microwave oven (22.5 ± 1.1). The peroxide value, as an indicator of oil oxidation, was lowest for microwave oven frying (2.53 ± 0.03). The K₂₃₂ and K₂₇₀ values were 0.41 ± 0.04 and 0.18 ± 0.02, respectively, for commercial frying oil in the microwave oven. The lowest free fatty acid content was recorded for the commercial frying oil used in the deep‐fat fryer at 190 °C. The highest iodine value was measured for sunflower oil used in the deep‐fat fryer (148.14 ± 0.07), indicating a greater degree of unsaturation. The lowest trans fatty acid value was recorded for sunflower oil in the microwave oven (0.17 ± 0.05), with a higher overall amount of total trans fatty acids observed for oils after frying in the electrical deep‐fat fryer compared to the microwave. Sunflower oil was favourable for both frying methods in terms of the trans fatty acid content.     

Cyclic FA monomers in high-oleic acid sunflower oil and extra virgin olive oil used in repeated frying of fresh potatoes

The measurement of FA profile, polar material, oligomers, oxidized triacylglycerols (OTG), total polyphenols, and cyclic FA monomers (CFAM) was used to evaluate the alteration of a high-oleic sunflower oil (HOSO) and an extra virgin olive oil (EVOO) used in 75 domestic fryings of fresh potatoes with frequent replenishment (FR) of unused oil. CFAM were absent in the unused EVOO but appeared in small amounts in the unused HOSO. Although polar material, oligomers, OTG, and CTAM contents increased and linoleic acid and polyphenols content decreased in both oils during repeated frying, the changes produced should be considered small and related to the use of very stable oils and FR. Throughout the 75 fryings, the total CFAM concentration was higher in HOSO than in EVOO. OTG increased more quickly in EVOO, whereas oligomers increased more quickly in HOSO. Polar material and oligomer content appear significantly correlated (r=0.9678 and r=0.9739, respectively; for both, P<0.001) with the CFAM content. A 25% polar material and 12% oligomer content would correspond to about 1 mg·kg⁻¹ oil of CFAM. Data suggest that both oils, particularly EVOO, perform very well in frying, with a low production of oligomers, polar materials, and CFAM.     

Formation of 4‐Hydroxy‐2‐Trans‐Nonenal,a Toxic Aldehyde,in Thermally Treated Olive and Sunflower Oils

4‐Hydroxy‐2‐trans‐nonenal (HNE) is a toxic aldehyde produced mostly in oils containing polyunsaturated fatty acid due to heat‐induced lipid peroxidation. The present study examined the effects of the heating time, the degree of unsaturation, and the antioxidant potential on the formation of HNE in two light olive oils (LOO) and two sunflower oils (one high oleic and one regular) at frying temperature. HNE concentrations in these oil samples heated for 0, 1, 3, and 5 hours at 185 °C were measured using high‐performance liquid chromatography. The fatty‐acid distribution and the antioxidant capacity of these four oils were also analyzed. The results showed that all oils had very low HNE concentrations (<0.5 μg g^?1 oil) before heating. After 5 hours of heating at 185 °C, HNE concentrations were increased to 17.98, 25.00, 12.51, and 40.00 μg g^?1 in the two LOO, high‐oleic sunflower oil (HOSO), and regular sunflower oil (RSO), respectively. Extending the heating time increased HNE formation in all oils tested. It is related to their fatty‐acid distributions and antioxidant capacities. RSO, which contained high levels of linoleic acid (59.60%), a precursor for HNE, was more susceptible to degradation and HNE formation than HOSO and LOO, which contained only 6–8% linoleic acid.     

Comparison of the Frying Performance of High Oleic Oils Subjected to Discontinuous and Prolonged Thermal Treatment

Frying is a popular practice because of its unique sensory characteristics and low cost. The high temperature reached with this cooking method alters molecules present in the oil. The deterioration of the oil depends primarily on its chemical composition. The aim of this study was to evaluate the thermal stability of high oleic sunflower oil (HOSO), sunflower oil (SO) and mixed oil (MIX) during deep frying of French fries. Octanoic acid and unsaturated fatty acid (UFA)/saturated fatty acid (SFA) ratio showed a good correlation with total polar compounds (TPC) for all frying samples analyzed. HOSO and MIX were characterized by reduced levels of thermal degradation, while SO resulted in the highest values of oxidation products (highest TPC values). SO was also the oil more retained by the food matrix, whereas MIX was the least absorbed. HOSO and MIX, having a high oleic acid content (77.58 and 59.92 %, respectively) and a low linoleic acid content (13.42 and 25.70 %, respectively), showed the best characteristics for the frying process.     

Optimising the baking and frying process using oil‐improving agents

Despite slimness mania and acrylamide scare, the market of fried products is still growing. Frying is an extremely effective way to cook food. A fried product tastes good, has a good flavour and is prepared within a few minutes. Every effort has been made to optimise the frying process. With regard to the quality of the fried food, the quality of the frying oil is very important. In the past, important characteristics of industrial frying oils were oxidative stability, high smoke point and low foaming. Nowadays, new frying fats with various additives, with a healthier fatty acid profile and higher heat stability are emerging. Emulsifiers, anti‐polymerising agents, and natural and synthetic antioxidants improve the performance during frying. Sesamol, rosemary and other natural extracts display strong stabilising effects during the frying operations. Filtration and the use of heat‐stabilising additives help to retard fat degradation and give the producer a larger time‐window for optimum frying. The effectiveness of the treatment with filter aids or mineral adsorbents and the stabilising effects of synthetic and natural agents were compared by using the Rancimat test for testing oxidative stability and the OSET (oxidative stability at elevated temperature) test to determine the stability at the frying temperature.     

Factors affecting the concentration of acrylamide during deep‐fat frying of potatoes

The paper describes the effect of different factors influencing the concentration of acrylamide in deep‐fat fried potato products. In French fries the amount of acrylamide increased with the temperature as well as the frying time, especially at temperatures higher than 175 °C. The increase of acrylamide with the time followed a linear function, whereas a non‐linear relationship was given with the temperature of frying. As a result, a reduction of the processing temperature led to lower concentrations of acrylamide in the product. Both, oil type and silicon oil as antifoaming agents had no significant influence upon the acrylamide concentration in the food. The variety of potatoes had a strong effect on the acrylamide concentration in potato crisps and French fries. The investigation showed a significant correlation (r = 0.73) between the concentration of acrylamide and reducing sugars in raw potatoes, and no significant correlation with the asparagine concentration. The storage temperature of the raw material had an effect on the acrylamide concentration in the product. Lowering of the storage temperature from 8 to 4 °C resulted in an increase of the concentration of reducing sugars in the raw material, which led to a higher potential of acrylamide formation in the products. The experiments showed that the acrylamide concentration of French fries depended on the surface‐to‐volume ratio (SVR).     

Carbon dioxide blanketing impedes the formation of 4‐hydroxynonenal and acrylamide during frying. A novel procedure for HNE quantification

Acrylamide and 4‐hydroxynonenal (HNE) are among the most detrimental compounds formed during high temperature processing of food. The effect of carbon dioxide blanketing (CDB) on the formation and accumulation in food of these compounds during deep‐fat frying was investigated. French fries were fried for 7 h daily and for 7 days in canola oil at 185 ± 5°C without and with CO₂ protection. The amount of acrylamide and HNE accumulated in the French fries were analyzed. Compared to standard frying conditions (SFC), frying under CDB reduced the amount of HNE by 62%. On the 3rd day of frying, the amount of acrylamide in fries fried under SFC was 3.3 times higher compared to frying with CO₂ protection. Frying with carbon dioxide protection is an effective and practical way to impede formation of toxic components during deep‐fat frying. To assess formation of HNE a simple, sensitive and reliable procedure for HNE analysis in frying oils and fried products was developed and evaluated. Practical applications : The toxicity of HNE and acrylamide, coupled with the increasing consumption of fried foods necessitates that measures be taken to reduce their formation and subsequent accumulation in fried foods. The frying method proposed in this study is very effective and requires only a simple modification to the fryer. Developed rapid and simple procedure for HNE analysis allows more accurate quantification.     

Comparison of near‐infrared emission spectroscopy and the Rancimat method for the determination of oxidative stability

This work presents a comparison between a new method for the determination of the oxidative stability of edible oils at frying temperatures, based on near‐infrared emission spectroscopy (NIRES), and the Rancimat method at 110 °C. In the NIRES‐based method, the induction time (IT) is determined by means of the variation of the emission band at 2900 nm during heating at 160 °C. The comparison between the IT values obtained with the two methods for 12 samples of edible oils shows some correlation for samples of the same type once there is an agreement on the sequence of highest to lowest IT values between the methods, but a poor correlation considering all samples (correlation coefficient of 0.78). This lack of correlation demonstrates that the results obtained with the Rancimat method cannot be used as an indication of the oxidative stability, or the resistance to degradation, of edible oils at frying temperatures. The difference in the heating temperatures used in the two methods leads to 20–36 times higher IT values for the Rancimat method in relation to the NIRES‐based method, but with similar repeatabilities (2.0 and 2.8%, respectively).     

Deterioration of diacylglycerol‐ and triacylglycerol‐rich oils during frying of potatoes

The stabilities of a commercial diacylglycerol‐rich oil (DAG) and a salad oil (TAG) that had been prepared from a mixture of rapeseed and soybean oils were compared while frying potatoes at 180 °C for 3 h. The representative chemical and physical characteristics of the oils were assessed before and after frying, together with the amount of volatile aldehydes in the exhaust of frying. Among the deterioration indications, the carbonyl value, polymer content, and residual polyunsaturated fatty acid content were similar and not significantly different between the TAG and DAG. On the other hand, the characteristics relating to free fatty acids, i.e. the acid value and emission of chemiluminescence at 100 °C, were greater and the smoke and flash points were lower in the DAG than in the TAG. An irritating odor was generated from the DAG after 1 h of frying and got stronger as frying continued. These results suggested that DAG more easily forms free fatty acids under frying conditions than TAG.     

Effects of frying on the trans‐fatty acid formation in soybean oils

To evaluate the effects of repeated deep‐frying on the trans‐fatty acid (TFA) formation in soybean oils, simultaneous frying experiments were carried out. French fries were prepared using three different types of soybean oil (pressed soybean oil, PSBO; first‐grade solvent extracted soybean oil, FG‐SESBO; and third‐grade solvent extracted soybean oil, TG‐SESBO). French fries were fried intermittently at 180–185°C for a total frying time of 32 h and at an interval time of 30 min. It was found that the initial amount of total TFAs was 0.29 g/100 g, 0.31 g/100 g, and 0.90 g/100 g in PSBO, TG‐SESBO, and FG‐SESBO, respectively. Before the frying started, the C18:1,t‐9, trans‐linoleic acid (TLA), trans‐linolenic acid (TLNA), and total TFA content of the PSBO and TG‐SESBO were significantly lower than in the FG‐SESBO (p<0.05). However, in the frying oil samples, the final concentration of total TFA in the PSBO, TG‐SESBO, and FG‐SESBO were 1.79 ± 0.17 g/100 g, 1.12 ± 0.10 g/100 g, and 1.70 ± 0.07 g/100 g, which was 6.17‐, 3.61‐, and 1.89‐fold higher that in fresh oil, respectively. The highest increasing slopes of C18:1,t‐9, TLA, TLNA, and total TFA were observed in the PSBO. Practical applications : A high intake of TFAs has been shown to lead to an increased risk of coronary heart disease. Plant oils, particularly soybean oil, have been widely used in the food industry in China. Frying is one of the most common methods to cook food. The formation of TFAs during frying has been shown to be closely related to the temperature and duration of the frying process. However, the effects of frying on the formation of TFAs in different soybean oils have not been well studied. In the present study, we demonstrated that increasing the number of frying cycles can cause an intensive increase in the concentration of TFAs in different types of soybean oil, but especially in PSBO.     

Monitoring of 2,4‐decadienal in oils and fats used for frying in restaurants in Athens,Greece

Some frying by‐products of medium polarity, so‐called medium‐polarity materials (MPM), produced during domestic deep‐frying of French‐fried potatoes in edible vegetable oils, have recently been isolated and linearly correlated to % total polar materials and % polymerized triglycerides. The in vitro oxidation of low‐density lipoproteins in a dose‐dependent manner by MPM has also been reported. In the present study, the MPM constituents were identified after extraction of MPM from the oils, subsequent purification by RP‐HPLC, and GC‐MS analysis. The main constituent of MPM was trans,trans‐2,4‐decadienal, a compound that has previously been reported to be formed during peroxidation of linoleic and arachidonic acid. 2,4‐Decadienal was also quantified in oils and fats used for frying in restaurants in Athens, Greece, by direct injection of oil sample solutions in HPLC. For the most commonly used frying oils, 2,4‐decadienal concentration ranges were 0.3–119.7 mg/kg for sunflower oil, 13.3–92.7 mg/kg for cottonseed oil, 4.1–44.9 mg/kg for palm oil, and 2.0–11.3 mg/kg for vegetable cooking fats. Considering the common catering practices of frying, 2,4‐decadienal was more likely to be found in sunflower oil after deep‐frying of potatoes. Comparing the amounts of this aldehyde found in oils from restaurants to the amounts previously found for domestic frying (up to 30 mg/kg after the 8^th successive frying session in sunflower oil), the probability of consuming a level of 2,4‐decadienal in restaurant‐prepared food that is higher than the level in home‐fried food was determined to be approximately one third.