Esterification affects phytosterol oxidation

The effect of esterification with rapeseed oil fatty acids on the oxidation reactions of sitosterol, campesterol and sitostanol was investigated, as well as the interactions between phytosterol/stanol compounds and the saturated lipid matrix at 100 °C and 180 °C. Free and esterified phytosterols differed in their reactivity in terms of the formation and profile of secondary oxidation products. Phytosteryl esters were more reactive than free phytosterols during prolonged heating at 100 °C. In contrast, free phytosterols were slightly more reactive than phytosteryl esters at 180 °C. The oxidation reactions of phytostanol compounds were low under all conditions studied. Changes in the phytosterol compounds during heating were also studied via the losses in the original phytosterol contents. This study revealed that the formation of secondary oxides did not account for all the phytosterol losses; this indicates the presence of other oxidation products, especially at 180 °C, and during the heating of free sitosterol. Thus, in order to understand the overall deterioration of phytosterol and phytostanol compounds, both the secondary oxide formation and the sterol loss need to be studied. The deterioration of the saturated lipid matrix used in this study was rather low and was mainly associated with the heating temperature and time.     

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.     

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.     

Studies on phytosterol oxides. II: Content in some vegetable oils and in French fries prepared in these oils

Hydrogenated rapeseed oil/palm oil blend, sunflower oil and high-oleic sunflower oil, and French fries fried in these oils were assessed for contents of sterol oxidation products. Different oxidation products of phytosterols (7α- and 7β-hydroxy-sito-and campesterol, 7-ketosito- and 7-ketocampesterol, 5α,6α-epoxy-sito- and campesterol, 5β,6β-epoxy-sito-and campesterol, dihydroxysitosterol and dihydroxycampesterol) were identified and quantiated by gas chromatography (GC) and GC-mass spectroscopy. Rapeseed oil/palm oil blend contained 41 ppm total sterol oxides before frying operations. After two days of frying, this level was increased to 60 ppm. Sunflower oil and high-oleic sunflower oil had 40 and 46 ppm sterol oxides, respectively, before frying operations. After two days of frying operations, these levels increased to 57 and 56 ppm, respectively. In addition to campesterol and sitosterol oxidation products, small amounts of 7α- and 7β-hydroxystigmasterol were detected in the oil samples. Total sterol oxides in the lipids of French fries fried at 200°C in rapeseed oil/palm oil blend, sunflower oil, and high-oleic sunflower oil were 32, 37, and 54 ppm, respectively. The levels of total oxidized sterols, calculated per g sample, ranged from 2.4 to 4.0 ppm. In addition to the content of phytosterol oxides, full scan mass spectra of several oxidation products of stigmasterol are reported for the first time. Part of these results were presented at the 86th Annual Meeting of the AOCS, May 7–11, 1995, San Antonio, TX.     

Effect of Tocopherols on the Anti-Polymerization Activity of Oryzanol and Corn Steryl Ferulates in Soybean Oil

Steryl ferulates (SFs) are ferulic acid esters of phytosterols and/or triterpene alcohols which have potential as frying oil antioxidants. The objective of this study was to evaluate the anti-polymerization and antioxidant activity at frying temperatures of corn steryl ferulates (CSFs), rice steryl ferulates (oryzanol), and a mixture of CSFs with oryzanol, alone and with tocopherols. Antioxidant activity was measured by the reduction of polymerized triacylglycerol formation, and loss of olefinic and bisallylic protons from fatty acid double bonds by ¹H NMR. CSFs and oryzanol slowed the oxidation and polymerization of soybean oil triacylglycerols heated to 180 °C more effectively than a mixture of alpha and gamma tocopherols. CSFs were more effective at preventing polymerization than oryzanol, but when oryzanol was combined with tocopherols, they all had similar antioxidant activity. In addition, tocopherols had a protective effect on SFs. Corn SFs were degraded more quickly during heating than oryzanol, however, the phytosterol constituents of corn SFs, sitostanol and campestanol, were actually more resistant to degradation compared to the phytosterol constituents of rice SFs. Results demonstrate that corn and rice SFs may be effective antioxidants for use in frying oils, and that their activity is enhanced in the presence of tocopherols.     

Chemical synthesis of phytosterol esters of polyunsaturated fatty acids with ideal oxidative stability

In this study, direct esterification of phytosterols with polyunsaturated fatty acid (PUFA) catalyzed by sodium bisulfate to produce sterol esters of PUFA was performed without organic solvent. Considering on both degree of esterification (DE) and oxidative stability, response surface methodology (RSM) was employed for modeling the phytosterol esters of PUFA production to obtain a food grade process. The optimal and mild reaction conditions were obtained as follows: mass ratio of PUFA:phytosterols = 4:1; amount of catalyst: 3% of the raw materials weight; reaction temperature 130°C; reaction time 8 h. Under these conditions, the degree of esterification was up to 96%, GC, TLC, NMR and GC‐MS results showed that purity of purified sterol ester was above 99%, and β‐sitosterol linolenate account for about 88%. Sterol ester of PUFA possessed low peroxide value (PV) (0.96 meq/kg) and conjugated diene (CD) value (2.15 mmol/kg), and high oxidative induction period (OIP) (10.4 h). Addition amount of sterol ester of PUFA into soybean oil, rapeseed oil, and flaxseed oil below 1, 1, and 3%, respectively, could increase OIP of the vegetable oil. The primrose phytosterol esters of PUFA possessed very low melting point, crystallization temperature, and greater solubility in oils. All the characteristics favored the wide application of sterol ester of PUFA produced by the food grade process in different formulations of functional foods.     

Utilization of high‐oleic rapeseed oil for deep‐fat frying of French fries compared to other commonly used edible oils

Changes in chemical, physical and sensory parameters of high‐oleic rapeseed oil (HORO) (NATREON?) during 72 h of deep‐fat frying of potatoes were compared with those of commonly used frying oils, palm olein (PO), high‐oleic sunflower oil (HOSO) and partially hydrogenated rapeseed oil (PHRO). In addition to the sensory evaluation of the oils and the potatoes, the content of polar compounds, oligomer triacylglycerols and free fatty acids, the oxidative stability by Rancimat, the smoke point and the anisidine value were determined. French fries obtained with HORO, PO and HOSO were still suitable for human consumption after 66 h of deep‐fat frying, while French fries fried in PHRO were inedible after 30 h. During the frying period, none of the oils exceeded the limit for the amount of polar compounds, oligomer triacylglycerols and free fatty acids recommended by the German Society of Fat Science (DGF) as criteria for rejection of used frying oils. After 72 h, the smoke point of all oils was below 150 °C, and the amount of tocopherols was reduced to 5 mg/100 g for PHRO and 15 mg/100 g for HORO and HOSO. Remarkable was the decrease of the oxidative stability of HOSO measured by Rancimat. During frying, the oxidative stability of this oil was reduced from 32 h for the fresh oil to below 1 h after 72 h of frying. Only HORO showed still an oxidative stability of more than 2 h. From the results, it can be concluded that the use of HORO for deep‐fat frying is comparable to other commonly used oils.     

Stability of Minor Lipid Components with Emphasis on Phytosterols During Chemical Interesterification of a Blend of Refined Olive Oil and Palm Stearin

Minor compounds such as tocopherols and phytosterols in vegetable oils play an important role in their stability and nutritional value. This study monitored the effects of chemical interesterification on the levels of tocopherols, tocotrienols, phytosterols and phytosterol oxidation products (POPs) in an olive oil and palm stearin blend (50/50 w/w). Tocopherols and tocotrienols were dominated by α-tocopherol (192 ppm) and γ-tocotrienol (70 ppm) and decreased during interesterification. Among the tocopherols, δ-tocotrienol had the highest decrease (35%) at 120 °C. During interesterification at 90 and 120 °C, total sterol content in the oil blend (509 ppm) declined slightly, by 3 and 5%, respectively. Phytosterols were esterified at a higher level at 120 °C (7%) than at 90 °C (4%) during this process. Distribution of fatty acids in the esterified sterols followed the fatty acid composition of the oil blend. Total POP content was 4.3 ppm, and remained generally unchanged during interesterification. Among the nine POPs tentatively identified by their mass spectra, 6-hydroxysitostanol and 6-hydroxycampestanol dominated in the oil blend and in the interesterified product. The formation pathways of these saturated di-hydroxyphytosterols have yet to be identified. Although the interesterification process comprised several treatments, there were only minor losses of tocopherols and phytosterols and virtually no increases in the POPs.     

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.     

Accumulation of 5-Hydroxymethylfurfural in Oil During Frying of Model Dough

5-Hydroxymethylfurfural (HMF), a thermal process contaminant, forms in food during frying as a result of the Maillard reaction and caramelization. Owing to its chemical properties, HMF formed in foods during frying partially transfers into frying oil. This study aimed to investigate the accumulation of HMF in oil during repetitive frying operations. A model dough composed of 25 % of glucose was fried at 160, 170, 180 °C for 50 frying cycles. Apart from total polar compounds (TPC), accumulation of HMF was determined in oils during repetitive frying operations. Increasing frying temperature also increased the amount of HMF formed in dough, and those transferred to oil. Prolonging frying cycles to 150, increasing amount of dough being fried to 100 g and frying time to 10 min caused the TPC content to reach 25 % at the 130th frying cycle at 180 °C. Under the same frying conditions, the concentration of HMF showed a rapid increase at the first 10th frying cycle. Its increase was at a slower rate until the 50th frying cycle reaching a plateau level exceeding 5.0 mg/L. The results revealed that HMF transferred and accumulated in the frying oil during repetitive frying. The HMF concentration exceeding 5.0 mg/L in oil may be considered as an indicator for heavily used frying oil. Correlation between TPC and HMF contents of frying oil showed no linear correlation.     

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.     

Effect of Deep-Fat Frying on Phytosterol Content in Oils with Differing Fatty Acid Composition

The objective of this study was to determine the fate of phytosterols in vegetable oils with varying fatty acid composition used for frying. High oleic sunflower (HOSun), corn (Corn), hydrogenated soybean (HSBO), expeller pressed soybean (ESBO), and expeller pressed low-linolenic acid soybean oil (ELLSBO) were used for frying potato chips in a pilot plant-scale continuous fryer. The same oils, and regular soybean oil (SBO) were also used in intermittent batch frying of tortilla chips. Phytosterols were measured in oils collected at various times during frying by GC to determine their loss. The formation of polymerized triacylglycerides (PTAGs) and total polar compounds (TPC) were analyzed to determine the extent of oil degradation. In the continuous frying system, phytosterol loss ranged between 4 and 6% in ESBO, ELLSBO, HOSun, and Corn, with no loss in HSBO. PTAGs and TPC were highest in ESBO and ELLSBO, followed by Corn, HOSun, and HSBO. In the batch frying experiment, phytosterol loss ranged from 1 to 15%, and was highest in Corn followed by SBO and HSBO. There was no significant loss of phytosterols in ESBO, ELLSBO, and HOSun. Formation of PTAGs and TPC during batch frying was highest in SBO and ESBO, followed by Corn, ELLSBO, HOSun, and HSBO. In conclusion, phytosterol loss in both the continuous fryer and in the batch frying system appeared to be unrelated either to fatty acid composition, or to the extent of oil degradation. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the US Department of Agriculture.     

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.     

Seed roasting improves the oxidative stability of canola (B. napus) and mustard (B. juncea) seed oils

Animal fats and partially hydrogenated vegetable oils (PHVO) have preferentially been used for deep‐frying of food because of their relatively high oxidative stability compared to natural vegetable oils. However, animal fats and PHVO are abundant sources of saturated fatty acids and trans fatty acids, respectively, both of which are detrimental to human health. Canola (Brassica napus) is the primary oilseed crop currently grown in Australia. Canola quality Indian mustard (Brassica juncea) is also being developed for cultivation in hot and low‐rainfall areas of the country where canola does not perform well. A major impediment to using these oils for deep‐frying is their relatively high susceptibility to oxidation, and so any processing interventions that would improve the oxidative stability would increase their prospects of use in commercial deep‐frying. The oxidative stability of both B. napus and B. juncea crude oils can be improved dramatically by roasting the seeds (165 °C, 5 min) prior to oil extraction. Roasting did not alter the fatty acid composition or the tocopherol content of the oils. The enhanced oxidative stability of the oil, solvent‐extracted from roasted seeds, is probably due to 2,6‐dimethoxy‐4‐vinylphenol produced by thermal decarboxylation of the sinapic acid naturally occurring in the canola seed.     

Oxidative decomposition of cholesterol in fish products

Cholesterol oxides in fish products popular in Japan, including salted and dried, boiled and dried and smoked products, were qualitatively and quantitatively determined as trimethylsilyl ether derivatives by gas-liquid chromatography and mass spectrometry. The level of total cholesterol oxides ranged widely between 8.3 ppm in boiled and dried shrimp and 188.0 ppm in boiled and dried anchovy. 7β-Hydroxycholesterol and 7-ketocholesterol were the most prominent oxidative decomposition products of cholesterol. The levels of epimeric epoxides, cholestane triol and 25-hydroxycholesterol were relatively low. To elucidate a mechanism of cholesterol oxidation proceeding during fish processing and subsequent preservation, four model systems, consisting of a mixture of purified cod liver triglycerides plus cholesterol, of a mixture of authentic triolein plus cholesterol, of triolein alone and of cholesterol alone, were stored separately at 25°C in dry air for up to 104 d. The residual fatty acids of the triglycerides, and the cholesterol oxides produced, were recovered and determined. Oxygen uptake remained almost unchanged for the mixture of triolein plus cholesterol. No detectable amount of cholesterol oxides was produced, and the fatty acid content of the residual oleic acid, measured by an internal standard, remained almost unchanged. For the mixture of cod liver triglycerides plus cholesterol, a remarkable increase in oxygen uptake was observed. A continuous increase in the amount of cholesterol oxides was observed, accompanied by a remarkable concurrent decrease in polyunsaturated fatty acid residues, as well as of the oleic acid naturally present. These results strongly suggest that cholesterol oxidation in fish products proceeds in conjunction with oxidative decomposition of the coexisting polyunsaturated fatty acids of fish oils.     

Antioxidant properties of individual phospholipids in a salmon oil model system

The antioxidant properties of phospholipids (PL) in a refined salmon oil model system were measured by determining changes in the 2-thiobarbituric acid number and decreases in the ratio of docosahexaenoic acid (DHA)/palmitic acid (22:6/16:0) of a fish oil system incubated at 180°C for up to 3 h. The more phosphatidylcholine (PC) added to the oil system, the higher the oxidative stability obtained. The order of effectiveness of commercial phospholipids in inhibiting oxidation and the loss of polyunsaturated fatty acids was as follows: sphingomyelin (SPH)=lysophosphatidylcholine (LPC)=phosphatidylcholine (PC)=phosphatidylethanolamine (PE)>phosphatidylserine (PS)>phosphatidylinositol (PI)>phosphatidylglycerol (PG)>control salmon oil. Nitrogen containing PL, including PE, PC, LPC and SPH, were equally effective in exerting greater antioxidant properties than PS, PG and PI. The inverse relationship observed between the oxidation index (C22:6/C16:0) and color intensity for treatments following 2 h of heating suggests that Maillard-type reaction products may have contributed to the oxidative stability of PL-supplemented fish oils.     

Effect of phytosterol structure on thermal polymerization of heated soybean oil

This study determined the effect of phytosterol structure, including the degree of unsaturation and the presence of an ethylidene group in the side chain, on the thermal polymerization of heated soybean oil. Indigenous tocopherols and phytosterols were removed from soybean oil by molecular distillation. Pure phytosterols were added back to the stripped soybean oil at concentrations of 0.5, 1.0, and 5 mg/g oil (0.05, 0.1, and 0.5 wt-%). These oils were heated at 180 °C over a period of 8 h, and triacylglycerol dimers and polymers, fatty acid composition, and residual phytosterol content were determined. None of the phytosterols prevented triacylglycerol dimer and polymer formation when used at 0.5 mg/g; however, phytosterols with two or more double bonds, regardless of the presence of an ethylidene group in the side chain, provided slight protection when added at 1 mg/g. Ergosterol addition at 5 mg/g reduced polymer formation by 16–20% compared to the control oil, but at this level none of the other phytosterols provided protection of any practical significance. Thus, under the conditions used for this heating study, the degree of phytosterol unsaturation was more important for its anti-polymerization activity than the presence of an ethylidene group.     

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.     

Testing the Antioxidant Effect of Essential Oils and BHT on Corn Oil at Frying Temperatures: a Response Surface Methodology

Food habits worldwide have increased the demand for oxidative-resistant oils that can be used for deep-frying. Oxidative stability in oils can be improved by changing the fatty acid composition of the oil or by adding natural antioxidants to the oil. In this study, the effect of essential oils of seven plants; cinnamon, rosemary, sage, turmeric, clove, thyme and oregano enriched with carvacrol on the oxidative stability of corn oil at frying temperatures were studied. Experiments were conducted by using a PetroOxy device, a rapid small scale oxidation stability test. A central composite design was used to evaluate the effects of concentration of essential oil (X1: 1,500–5,000 ppm) and temperature (X2: 150–180 °C), on the induction time of corn oil. In order to compare the results with the synthetic antioxidant, butylated hydroxy toluene (BHT), another design was made with a concentration range (60–350 ppm) containing the legal upper limit of BHT, 200 ppm. Induction periods obtained from the accelerated oxidation test revealed that increasing temperature decreased the induction time of all the samples. However, the essential oils except for oregano oil had no significant antioxidative effect on corn oil, probably due to a lower content of their active components. The antioxidative effect of oregano oil was also found to be higher compared to BHT. At very high temperatures (e.g., 180 °C), the concentration of antioxidants had no effect on the induction periods.     

Performance of Regular and Modified Canola and Soybean Oils in Rotational Frying

Canola and soybean oils both regular and with modified fatty acid compositions by genetic modifications and hydrogenation were compared for frying performance. The frying was conducted at 185 ± 5 °C for up to 12 days where French fries, battered chicken and fish sticks were fried in succession. Modified canola oils, with reduced levels of linolenic acid, accumulated significantly lower amounts of polar components compared to the other tested oils. Canola oils generally displayed lower amounts of oligomers in their polar fraction. Higher rates of free fatty acids formation were observed for the hydrogenated oils compared to the other oils, with canola frying shortening showing the highest amount at the end of the frying period. The half-life of tocopherols for both regular and modified soybean oils was 1–2 days compared to 6 days observed for high-oleic low-linolenic canola oil. The highest anisidine values were observed for soybean oil with the maximum reached on the 10th day of frying. Canola and soybean frying shortenings exhibited a faster rate of color formation at any of the frying times. The high-oleic low-linolenic canola oil exhibited the greatest frying stability as assessed by polar components, oligomers and non-volatile carbonyl components formation. Moreover, food fried in the high-oleic low-linolenic canola oil obtained the best scores in the sensory acceptance assessment.