Increasing gamma‐ and delta‐tocopherols in oils improves oxidative stability

Over the past two decades, plant geneticists have revolutionized how fatty acid compositions of vegetable oils are optimized to improve oxidative stability and functionality. Now, the expertise of plant geneticists is reaching beyond altering fatty acids to changing other oil components such as tocopherols. Basic lipid research on optimizing tocopherol profiles and ratios in vegetable oils is providing information for geneticists to breed the next generation of oxidatively stable vegetable oils. This review will discuss three studies; first, a basic study to determine the oxidative stability provided by the addition of pure gamma and delta tocopherols to oils treated to remove natural tocopherols; second, a practical study to evaluate the oxidative stability of mid‐oleic sunflower oil from seeds modified by plant breeding to contain high amounts of γ‐ and δ‐tocopherols; and third, a frying test to determine the effects of gamma tocopherol addition.     

Current advances in sunflower oil and its applications

The fatty acid and triacylglycerol composition of a vegetable oil determine its physical, chemical and nutritional properties. The applications of a specific oil depend mainly on its fatty acid composition and the way in which fatty acids are arranged in the glycerol backbone. Minor components, e. g. tocopherols, also modify oil properties such as thermo‐oxidative resistance. Sunflower seed commodity oils predominantly contain linoleic and oleic fatty acids with lower content of palmitic and stearic acids. High‐oleic sunflower oil, which can be considered as a commodity oil, has oleic acid up to around 90%. Additionally, new sunflower varieties with different fatty acids and tocopherols compositions have been selected. Due to these modifications sunflower oils possess new properties and are better adapted for direct home consumption, for the food industry, and for non‐food applications such as biolubricants and biodiesel production.     

Improving the oxidative stability of polyunsaturated vegetable oils by blending with high-oleic sunflower oil

Mixing different proportions of high-oleic sunflower oil (HOSO) with polyunsaturated vegetable oils provides a simple method to prepare more stable edible oils with a wide range of desired fatty acid composition. Oxidative stability of soybean, canola and corn oils, blended with different proportions of HOSO to lower the respective levels of linolenate and linoleate, was evaluated at 60°C. Oxidation was determined by two methods: peroxide value and volatiles (hexanal and propanal) by static headspace capillary gas chromatography. Determination of hexanal and propanal in mixtures of vegetable oils provided a sensitive index of linoleate and linolenate oxidation, respectively. Our evaluations demonstrated that all-cis oil compositions of improved oxidative stability can be formulated by blening soybean, canola and corn oils with different proportions of HOSO. On the basis of peroxide values, a partially hydrogenated soybean oil containing 4.5% linolenate was more stable than the mixture of soybean oil and HOSO containing 4.5% linolenate. However, on the basis of volatile analysis, mixtures of soybean and HOSO containing 2.0 and 4.5% linolenate were equivalent or better in oxidative stability than the hydrogenated soybean oil. Mixtures of canola oil and HOSO containing 1 and 2% linolenate had the same or better oxidative stability than did the hydrogenated canola oil containing 1% linolenate. These studies suggest that we can obviate catalytic hydrogenation of linolenate-containing vegetable oils by blending with HOSO. Presented at the AOCS/JOCS joint meeting, Anaheim, CA, April 25–29, 1993.     

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.     

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.     

The development and application of novel vegetable oils tailor‐made for specific human dietary needs

Conventional edible oils, such as sunflower, safflower, soya bean, rapeseed (canola) oils, were modified to obtain high‐oleic, low‐linoleic or even low‐linolenic oils. The aim was to develop salad, cooking and frying oils, that are very stable against lipid peroxidation. They are also suitable for margarine blends, as additives to cheeses and sausages, or even as feed components. Oils containing higher amounts of medium‐chain length or long‐chain polyunsaturated fish oil fatty acids are suitable as special dietetic oils or as nutraceuticals. High‐stearic oils are designed as trans‐fatty acid‐free substitutes for hydrogenated oils. New tailor‐made (designer) oils are thus a new series of vegetable oils suitable for edible purposes, where conventional oils are not suitable.     

Chemical Compositions of Oils from Several Wild Almond Species

Chemical compositions of oils extracted from three wild almond species [Amygdalus scoparia from Beyza, Iran (AZ); A. scoparia from Borazjan, Iran (AJ), and A. hausknechtii from the Firuzabad region, (AH)] and a domestic species, A. dulcis from Estahban, Iran (AD), as a reference, were investigated. Total oil content ranged from 44.4% in AJ to 51.4% in AD. Saponification numbers were in the range of 173.5 (for AJ) to 192.9 for AD. Oxidative stability, total phenolic contents and total wax contents were found to be within the ranges 11.7–14.0 h, 33.9–43.2 and 2.05–2.53%, respectively. The main monounsaturated fatty acid (MUFA) was oleic acid ranging from 66.7% for AH to 69.7% for AZ. The only polyunsaturated fatty acid (PUFA) was linoleic acid ranging from 18.2% for AZ to 23.0% for AD. The major saturated fatty acid was palmitic acid. MUFA contents and MUFA to PUFA ratio in the oils from wild almond species as well as those in the domestic one were found at higher levels than those in the common vegetable oils such as soybean, various nut oils, and also those from the seeds of pomegranate, grape, date and sesame. Oils from wild almond species investigated here are rich in oleic acid and can be considered as potential vegetable oils in the human diet.     

Chemical Characterization of a High‐Oleic Soybean Oil

High‐oleic low‐linolenic acid soybean oil (HOLLSB, Plenish^®) is an emerging new oil with projections of rapid expansion in the USA. HOLLSB has important technological advantages, which are expected to drive a gradual replacement of commodity oils used in food applications such as soybean oil. A key technological advantage of HOLLSB is its relatively high oxidation stability. This oxidation stability is the result of a favorable fatty acid composition, high (76%) oleic acid, low linoleic (6.7%), and alpha‐linolenic (1.6%) acids, and high concentration of tocopherols (936 ppm) after refining, enriched with the gamma‐homolog (586 ppm). A detailed analysis of the fatty acid composition of this HOLLSB by gas chromatography–mass spectrometry allowed the identification and structural determination of 9‐cis‐heptadecenoic acid (or 17:1n‐8). To our knowledge, this is the first time 9‐cis‐heptadecenoic acid has been unequivocally reported in soybean oil. This unusual fatty acid component has the potential to be used as a single authenticity marker for the quantitative assessment of soybean oil. The Rancimat induction period (IP) of Plenish^® (16.1 hours) was higher than those of other commercially available high‐oleic oils, such as canola (13.4 hours), and Vistive^® Gold (10 hours), a different variety of soybean oil. Plenish^® showed the same IP as high‐oleic sunflower oil. Plenish^® shows a modest increase in oxidation stability with the external addition or relatively high concentrations of tocopherols. The characteristic high oxidative stability of Plenish^® may be further enhanced with the use of nontocopherol antioxidants.     

Oxidative stability of fat substitutes and vegetable oils by the oxidative stability index method

Oxidative Stability Index (OSI) of carbohydrate fatty acid polyesters, fat substitutes and vegetable oils were measured with the Omnion Oxidative Stability Instrument according to the new AOCS Standard Method Cd 12 B-92 (The Official Methods and Recommended Practices of the American Oil Chemists' Society, edited by D. Firestone, AOCS, Champaign, 1991). The stability of crude and refined, bleached and deodorized (RBD) vegetable oils (soybean, hydrogenated soybean and peanut) were determined at 110°C. In addition, OSI times for sucrose polyesters of soybean oil, butterfat, oleate:stearate and methyl glucoside polyester of soybean oil were determined in the absence and in the presence of 0.02 wt% antioxidants, [Tenox TBHQ (tertiary butylhydroquinone, Tenox GT-2 (from Eastman Chemical Products (Kingsport, TN); and vitamin E (from BASF, Wyandotte, MI)], and the results were compared with those of vegetable oils. Crude oils were most stable (20.4–25.9 h), followed by RBD oils (9.3–10.4 h) for soybean and peanut oils, respectively, and fat substitutes (3.8–6.8 h). Overall, Tenox TBHQ was the best antioxidant for improving the oxidative stability of both vegetable oils and fat substitutes. The sucrose polyester made with oleic and stearic acid was more stable than fat substitutes containing more polyunsaturated fatty acids, such as those from soybean oil, or from short-chain fatty acids, such as from butterfat. Antioxidants enhanced the stability of RBD oils (222% increase) and synthetic fat substitutes (421–424% increase) more than that of crude oils (33% increase). The shapes of the induction curves, not the actual OSI times for fat substitutes and vegetable oils, were similar and sharply defined.     

Alternatives to tropical fats based on high‐stearic sunflower oils

New high‐oleic high‐stearic sunflower lines produce oils that could be a source of disaturated triacylglycerol alternatives to tropical fats. These oils can be fractionated to produce stearins enriched in stearic acid with physical properties similar to cocoa butter and other confectionary fats without hydrogenation or transesterification. These fats can be produced in temperate countries from a well‐established crop like sunflower, and represent a healthy source of saturated fatty acids.     

Manoeuvring the physicochemical and nutritional properties of vegetable oils through blending

Modification of vegetable oils is carried out to make them suitable according to their specific end use as most of the vegetable oils in original forms do not meet the recommended dietary allowance of saturated (SFA), monounsaturated (MUFA) and polyunsaturated (PUFA) fatty acids. Vegetable oils are modified using a variety of techniques including hydrogenation, interesterification, fractionation, and blending. However, blending is the most widely accepted method for improving the physicochemical properties, nutritive value and oxidative stability of vegetable oils because it is simple, cost-effective, non-destructive, and does not involve chemical treatments. Blending vegetable oils with contrasting fatty acid compositions or blending omega 3 fatty acids and antioxidants rich minor oils with major oils are two common strategies to formulate blends. Blended oil with balanced fatty acids could play substantial role in improving the consumers' health. However, while designing vegetable oil blends, it is important to keep in mind the intended application of the formulated blend, consumer's demands and also food laws. This review paper covers the literature related to blending of vegetable oils with a focus on effect of vegetable oils blending on their physicochemical and nutritional properties, health benefits and utility in food industries.     

Effects of frying oil composition on potato chip stability

Potato chips were fried in six canola (low-erucic acid rape-seed) oils under pilot-plant process settings that represented commercial conditions. Oil samples included an unmodified canola oil and oils with fatty acid compositions modified by mutation breeding or hydrogenation. Chips were fried for a 2-d, 18-h cycle for each oil. Chips and oil were sampled periodically for sensory, gas-chromatographic volatiles and chemical analyses. Unmodified canola oil produced chips with lower flavor stability and oxidative stability than the other oils. The hydrogenated oil imparted a typical hydrogenation flavor to the chips that slightly affected overall quality. the modified canola oil (IMC 129) with the highest oleic acid level (78%) had the lowest content of total polar compounds and the lowest total volatile compounds at most of the storage times; however, the sensory quality of the potato chip was only fair. The potato chip with the best flavor stability was fried in a modified/blended oil (IMC 01-4.5/129) with 68% oleic acid, 20% linoleic acid and 3% linolenic acid.     

Emission of Volatile Aldehydes from DAG-Rich and TAG-Rich Oils with Different Degrees of Unsaturation During Deep-Frying

The purpose of the present study was to compare the emission of volatile aldehydes from diacylglycerol-rich oils (DAG-OILs) and triacylglycerol-rich oils (TAG-OILs) with different degrees of unsaturation of fatty acid moieties during the deep-frying of sliced potatoes. To examine the effect of fatty acid composition, four kinds of oils with different fatty acid compositions were selected: rape seed (RS); sunflower oil as a high oleic (HO); safflower oil as high linoleic (HL); and, perilla oil as high linolenic (HLn) oils. The emissions of volatile aldehydes were determined during the deep-frying of sliced potatoes by using the above fresh test oils or deteriorated RS oils. The statistical analysis showed no significant difference in volatile aldehyde emission and profile between the DAG-OIL and TAG-OIL with the fatty acid composition of RS, HL, and HLn. Although a statistically significant difference was noted in the volatile aldehyde emission between the DAG-OIL and TAG-OIL with HO, this difference was extremely small when compared to the variations found in the oils with four types of fatty acid composition. Finally, no difference was found in the volatile aldehyde emissions between the deteriorated DAG-OIL and TAG-OIL, although volatile aldehyde emissions increased with frying time. In addition, the acrylamide contents in potato chips prepared with RS–DAG or RS–TAG were at comparable levels.     

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.     

Effect of fatty acid composition of oils on flavor and stability of fried foods

Effects of fatty acid composition of frying oils on intensities of fried-food flavor and off-flavors in potato chips and french-fried potatoes were determined. Commercially processed cottonseed oil (CSO) and high-oleic sunflower oil (HOSUN) were blended to produce oils with 12 to 55% linoleic acid and 16 to 78% oleic acid. Analytical sensory panels evaluated french-fried potatoes and pilot plant-processed potato chips. Initially, both foods prepared in CSO (16% oleic/55% linoleic acid) had the highest intensities of fried-food flavor; however, this positive flavor decreased with decreasing levels of linoleic acid. 2,4-Decadienal in potato chips also decreased with decreasing linoleic acid in the oils. Frying oil stability, measured by total polar compounds (TPC), and oxidative stability of potato chips, measured by volatile compounds, showed that HOSUN (78% oleic acid) produced the lowest levels of TPC and the lowest levels of hexanal and pentanal, indicating greater frying oil stability and oxidative stability of the food. However, fresh potato chips fried in HOSUN had the lowest intensities of fried-food flavor and lowest overall flavor quality. Fried-food flavor intensity was the best indicator of overall flavor quality in fresh potato chips. Volatile compounds, TPC, and oxidative stability index directly varied with increasing oleic acid, and were therefore not directly indicative of flavor quality. No oil analysis predicted flavor stability of aged potato chips. Compositions of 16 to 42% oleic acid and 37 to 55% linoleic acid produced fresh fried-food with moderate fried food flavor intensity, good overall flavor quality, and low to moderate TPC levels (chips only). However, in aged food or food fried in deteriorated oil, compositions of 42 to 63% oleic and 23 to 37% linoleic provided the best flavor stability.     

Oxidative stability of high oleic sunflower and safflower oils

High oleic sunflower seed progenies derived from normal seed by chemical mutagenesis were extracted and their oils refined by standard laboratory procedures. Oxidative stability was related directly to linoleic acid content with an AOM value of 100 hr obtained at 1% linoleate. Data is presented comparing linoleate concentration and oxidative stability of oils obtained from normal sunflower seed and high linoleic (normal) and high oleic (naturally induced mutations) varieties of safflower seed.     

Selective hydrogenation of sunflower seed oil in a three-phase catalytic membrane reactor

Continuous hydrogenation of sunflower seed oil has been carried out in a novel three-phase catalytic membrane hydrogenation reactor. The membrane reactor consisted of a membrane impregnated with Pd as the active catalyst, which provided a catalytic interface between the gas phase (H₂) and the oil. Hydrogenations were carried out at different pressures, temperatures, and selectivities, and the formation of trans isomers was monitored during the hydrogenation runs. For the three-phase catalytic membrane reactor, interfacial transport resistances and intraparticle diffusion limitations did not influence the hydrogenation reaction. Hydrogenation runs under kinetically controlled conditions showed that oleic and elaidic acid were not hydrogenated in the presence of linoleic acid. Initial formation of stearic acid was caused by direct conversion of linoleic acid into stearic acid by a shunt reaction. Furthermore, high selectivities led to high trans levels, which is in accordance with the many published data on hydrogenation of vegetable oils in slurry reactors. Finally, the catalytic membrane showed severe catalyst deactivation. Only partial recovery of the catalyst activity was possible.     

Thermoxidative stability of triacylglycerols from mutant sunflower seeds

Thermoxidative stability was evaluated in triaclyglycerols (TAG) from the oils of the mutant sunflower lines CAS-3, CAS-4, and CAS-8 (with a high percentage of stearic acid), CAS-5 (with a high percentage of palmitic acid), all from standard highlinoleic genetic backgrounds, and the mutant sunflower line CAS-12 (with a high percentage of palmitic acid), from a high-oleic genetic background. These oils contained unusually high contents of TAG molecular species with one or two saturated fatty acids at the sn-1,3 positions. Purified total TAG devoid of tocopherols were subjected to controlled thermoxidative treatment at 180°C. Polymerized TAG were determined at 2-h intervals for 10 h. After this time, total polar compounds, oxidized TAG monomers, TAG dimers, and TAG oligomers were determined. TAG from highly saturated sunflower oils with levels of linoleic acid similar to those found in conventional sunflower oils (40–50%) showed enhanced thermal stability. In these TAG, the amount of polar compounds formed during the thermoxidative treatment was similar to that formed in the high oleic acid line. Excellent results were obtained for the TAG of the CAS-12 oil, which had the highest thermal stability, producing half the amount of polar compounds as the conventional line and less than two-thirds that of the high-oleic line.     

Biological utilization of fatty acid isomers

Summary A review of the literature has shown that in the hydrogenation of vegetable oils, positional and stereoisomers of the unsaturated fatty acids are formed in appreciable quantities and that some isomers are intermediates in the development of others as hydrogenation proceeds. Using a microbiological assay technique, it was demonstrated that the iso-oleic acids formed during hydrogenation are not antimetabolites for natural oleic acid but are utilized as nutrients. Fatty acids with conjugated double bonds are not antimetabolites for the essential fatty acids but are readily metabolized to carbon dioxide and water. Hydrogenated fats compare favorably with a natural fat of comparable firmness in serving as a source of essential fatty acids. In hydrogenating vegetable oils, isomers of linoleic acid can be formed which resist spectrophotometric detection but exhibit essential fatty acid activity. Paper presented at the 1953 Conference on Food and Nutrition, Gordon Research Conferences, AAAS, Colby Junior College, New London, N. H. Contribution 351 of the Department of Biochemistry and Nutrition, University of Southern California.     

Some chemical processes utilizing oleic safflower oil

Oleic safflower seed (UC-1) produces an oil containing approximately 80% oleic acid and 12% linoleic acid. The oil is a source of high quality oleic acid, and fatty acids from the oil may be used without further separation in some applications where technical oleic acid is now used, since oleic safflower free fatty acids have a a higher oleic acid content than good commercial grades of oleic acid. A high purity oleic acid can be produced by urea fractionation. Ozonization of the oil followed by reductive cleavage yields pelargonaldehyde and nearly colorless aldehyde oils. Ozonization of a crude mixture of oleic safflower acids followed by oxidative cleavage provides high yields of azelaic acid and pelargonic acid. In contrast, ozonization of free fatty acids from polyunsaturated vegetable oils produces azelaic acid and mixtures of lower molecular weight carboxylic acids with smaller amounts of pelargonic acid. Furtherore, ozone consumption is lower and reaction time is shorter when oleic safflower acids are used in place of more highly unsaturated fatty acids.