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.     

Physical Properties of Cocoa Butter/Vegetable Oil Blends Crystallized in a Scraped Surface Heat Exchanger

Blends of cocoa butter with soybean oil (CB/SO) or canola oil (CB/CO) were crystallized at either of two agitation rates (100 or 1,000 rpm) and at two process temperatures (14 or 17 °C) in a scraped surface heat exchanger (SSHE). The physical properties were characterized at the SSHE output and during storage (14 and 28 days) at 15 °C. At the SSHE output, the CB/CO and CB/SO systems that had been processed at 100 rpm presented a more solid-like character than systems processed at 1,000 rpm despite the fact that the former systems contained a higher solid fat content than the latter. The degree of secondary crystallization increased with increasing shear rate. Nevertheless, the polymorphic behavior of cocoa butter crystals resembled the behavior observed under static isothermal crystallization conditions. At the SSHE output, systems of either blend contained a mixture of β′ and β crystals. During storage, β′ converted to β in both blends, although it did so to a higher extent in the CB/CO systems. Crystal ripening, observed in the CB/CO blend, provided stability to the systems during storage. In contrast, the CB/SO system increased its hardness by a slow sintering process. The polymorphism and hardness evolution in the blends under study were found to be associated with the molecular compatibility of the triacylglycerols in the cocoa butter and the vegetable oils tested.     

Rapid Assessment of Frying Performance Using Small Size Samples of Oils/Fats

A rapid, effective test mimicking actual frying was developed to assess the frying performance of oils and fats using small size samples. To a small volume of the oil to be tested, a formulated food consisting of gelatinized potato starch, glucose and silica gel (4:1:1 w/w) were added and content heated at 185 ± 5 °C with mixing for 2 h. Thermo-oxidative degradation of the oil was assessed by the measurement of the total amount of polar components and their composition, including degradation of tocopherols. The developed fast test accurately mimics actual frying done using an institutional fryer as assessed by the accumulation and composition of total polar components and the amount of residual tocopherols. The validity of the test was assessed using the following oils: regular canola, high oleic– low linolenic canola, and high oleic sunflower. Comparison of data between the fast frying test and institutional frying revealed a lack of significant differences. The developed frying test provides reliable quantitative and qualitative data describing the performance of the frying oil/fat. The rapid frying procedure allows assessment of the frying performance of oils at the early stages of development where usually only small amounts of the sample are available and when a large number of samples have to be tested assessing effects of oil additives.     

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.     

A Novel Propolis Wax-Based Organogel: Effect of Oil Type on Its Formation,Crystal Structure and Thermal Properties

In this work, the potential application of propolis wax (PW) as a novel organogelator was investigated in different oils (canola, sesame, sunflower and flaxseed oil). PW at 2% (w/w) concentration produced a thick organogel at 5, 10 and 15 °C, with needle‐like crystals, suggesting that PW is a relatively efficient structuring agent for organogel formation. The oil binding capacity of the organogel with canola oil was lower than that of the other organogels, and the gelling time of flaxseed organogel with lower oil viscosity was shorter. The X‐ray diffraction measurements of the crystals showed β′‐form crystals, with no influence of oil type. In FTIR results, no chemical intermolecular interactions that were observed indicated physical bonds in the organogel network. DSC analysis was carried out to obtain greater insight into the thermal behavior of PW organogels. No significant differences were observed. The textural properties of PW organogels were stable over 30 days of storage. Flaxseed oil organogel had the greatest firmness and stickiness. These results showed the effect of oil viscosity on PW gel behavior.     

The Role of Water in Protection Against Thermal Deterioration of Liquid Margarine

The thermal stability of liquid margarine and vegetable oils was investigated by measuring the oxidative stability index (OSI) at temperatures ranging from 90 to 180 °C, whereas total polar compounds (TPC) and tocopherols (vitamin E) were measured during heating at 180 °C in frying trays. Results showed that the OSI of liquid margarine was in the same range as the OSI of vegetable oils at lower temperatures, but at 160 and 180 °C, liquid margarine had significantly higher thermal stability, close to that observed for hard margarine and butter. The increased stability was confirmed by lower levels of TPC and a smaller relative reduction in vitamin E content during heating. Variations between different vegetable oils could partly be explained by differences in degree of saturation and level of vitamin E, with high oleic sunflower oil being the most stable oil at all temperatures. The water in liquid margarine vaporized within 1.5 min at 160 °C, and it is hypothesized that volatile pro‐oxidants are removed with the water, inducing a delay in deterioration. The results indicate a role for water in preventing lipid oxidation and decomposition in fat emulsion products at 160–180 °C, suggesting that liquid margarine, low in saturated fat, may be the healthier and preferable alternative for pan‐frying compared to other liquid vegetable oils.     

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.     

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.     

Effect of α- and γ-tocopherols on thermal polymerization of purified high-oleic sunflower triacylglycerols

The antipolymerization effects of α- and γ-tocopherols were compared in model systems composed of purified high-oleic sunflower triacylglycerols at 180°C. γ-Tocopherol was much more effective as an antipolymerization inhibitor than α-tocopherol, partly due to lower oxidizability/disappearance. Purified triacylglycerols of sunflower, rapeseed, and high-oleic sunflower oils were less stable than their nonpurified forms containing tocopherols. Results confirmed that tocopherols per se can act as antipolymerization agents in high-oleic oils at frying temperatures. No synergism was observed when α- and γ-tocopherols were present together although larger amounts of residuals were left for both tocols. Results suggested that high-oleic/high-γ-tocopherol oils (such as high-oleic canola and high-oleic soybean oils) may provide better frying oils than high-oleic/high-α-tocopherol oils (such as high-oleic sunflower oil).     

Formation of oxidation compounds in sunflower and olive oils under oxidative stability index conditions

The objective of this work was to study the evolution of oxidation under oxidative stability index (OSI) conditions using the Rancimat apparatus. Sunflower oils with different degrees of unsaturation (conventional high‐linoleic sunflower oil, genetically modified high‐oleic sunflower oil, and a 1 : 1 mixture of both of them) and virgin olive oil were used. The sunflower oils were tested at 100 °C, while the olive oil was assayed at 100, 110 and 120 °C. Samples were analyzed at different time points and conductivity values, until the induction period (IP) was overpassed. A combination of adsorption and size‐exclusion chromatography was used for the quantification of oxidized triacylglycerol (TG) monomers, dimers and polymers. Additionally, peroxide values (PV) and ultraviolet absorption at 270 nm (K₂₇₀), as well as losses of tocopherols, were measured. The results showed that oxidized TG monomers were the only group of oxidation compounds that increased during the early oxidation stage. The end of the IP was marked by the initiation of polymerization after the exhaustion of tocopherols. In comparison with reported results obtained at room temperature, the main difference found was that the amounts of oxidation compounds at the end of the IP were much lower at OSI test temperatures. With the exception of the K₂₇₀ values, the results also showed that the IP endpoints provided by the OSI test were slightly higher than those obtained by quantification of oxidized TG monomers or by PV determination.     

Effect of tocopherols on the frying stability of regular and modified canola oils

A study was conducted to compare the relationship between frying stability and levels and degradation rates of tocopherols in regular and three modified canola oils. Oils were heated at 175 ± 2°C for a total of 72 h, with french fries fried intermittently. Frying stability was compared based on the rates of formation of free fatty acids (FFA) and total polar compounds (TPC). Significant differences (P<0.05) were identified between oils using analysis of covariance and t-tests for multiple comparisons. No significant differences were observed in the rates of FFA formation among the canola oils during frying. Nevertheless, regular canola (RCO) and high-oleic, low-linolenic acid canola (HOLLCO) oils produced less FFA compared to higholeic LLCO and HOCO both had significantly (P<0.05) faster rates of TPC formation compared to HOLLCO or RCO. HOLLCO with the highest level of tocopherols (893 mg/kg) exhibited a slow rate of degradation which accounted for a halflife of 48–60 h of frying. RCO, with a lower level of tocopherols (565 mg/kg), however, had the slowest degradation rate with a half-liofe of >72 h. In contrast, HOCO and LLCO with 601 and 468 mg/kg tocopherols, respectively, both exhibited a half-life for tocopherols of 3–6 h of frying. An inverse relatioship was observed between TPC formation and the reduction of tocopherol. Thus, the greater frying stability of RCO and HOLLCO appears to be affected far more by the rate of tocopherol degradation than by any changes in fatty acid composition.     

Modelling the temperature dependence of kinematic viscosity for refined canola oil

Viscosities of refined, bleached, deodorized (RBD) and refined, bleached, winterized (RBW) canola oils were measured at temperatures from 4 to 100°C. The viscosities of these refined canola oils were exponentially related to the oil temperature. Viscosity of the RBW oil was slightly greater than that of the RBD oil when the temperature was below 15°C. Compared to refined soybean oil, the canola oils were substantially more viscous. The viscosity of canola oil was modelled asv = exp(C₀ + C₁T + C₂T²). The maximum predicted error was less than 1.6% over the tested temperature range.     

Effect of fatty acids and tocopherols on the oxidative stability of vegetable oils

The oxidative stability of vegetable oils is determined by their fatty acid composition and antioxidants, mainly tocopherols but also other non‐saponifiable constituents. The effect of fatty acids on stability depends mainly on their degree of unsaturation and, to a lesser degree, on the position of the unsaturated functions within the triacylglycerol molecule. Vegetable oils contain tocopherols and tocotrienols, especially α‐ and γ‐tocopherols, as their main antioxidants. The antioxidant behavior of tocopherols represents a complex phenomenon as they are efficient antioxidants at low concentrations but they gradually lose efficacy as their concentrations in the vegetable oils increase. The “loss of efficacy” of tocopherols, sometimes referred to as a “pro‐oxidant effect”, is witnessed by an increase in the rate of oxidation during the induction period, despite elongation of this phase. The phenomenon is much obvious for α‐tocopherol, but is also evident for other tocopherols. In agreement with nature's wisdom, the tocopherol levels in vegetable oils seem to be close to the optimal levels needed for the stabilization of these oils. The presence of other antioxidants in the oils, e.g. carotenoids, phenolic compounds, and Maillard reaction products, may synergize with tocopherols and minimize this loss of efficacy.     

Oxidative Stability of Polyunsaturated Edible Oils Mixed With Microcrystalline Cellulose

The oxidative stability of mixtures of edible oils containing polyunsaturated fatty acids (PUFA) and microcrystalline cellulose (MCC) was investigated. The mixtures studied consisted of oils of either camelina (CAM), cod liver (CLO), or salmon (SO) mixed with either colloidal or powdered MCC. A 50:50 (w/w) ratio of oil:MCC resulted in an applicable mixture containing high levels of PUFA edible oil and dietary fiber. The oxidative stability of the formulated mixtures and the pure oils was investigated over a period of 28 days. The peroxide value (PV) was assessed as a parameter for primary oxidation products and dynamic headspace gas chromatography mass spectrometry (GC/MS) was used to analyze secondary volatile organic compounds (VOC). CAM and the respective mixtures were oxidatively stable at both 4 and 22 °C during the storage period. The marine oils and the respective mixtures were stable at 4 °C. At 22 °C, an increase in hydroperoxides was found, but no increase in VOC was detected during the time-frame investigated. At 42 °C, prominent increases in PV and VOC were found for all oils and mixtures. Hexanal, a common marker for the degradation of n-6 fatty acids, propanal and 2,4-heptadienal (E,E), common indicators for the degradation of n-3 fatty acids, were among the volatiles detected in the headspace of oils and mixtures. This study showed that a mixture containing a 50:50 ratio of oil:MCC can be obtained by a low-tech procedure that does not induce oxidation when stored at low temperatures during a period of 1 month.     

Thermal Antioxidative Kinetics of Hydroxytyrosol in Selected Lipid Systems of Different Unsaturation Degree

The oxidation kinetics of the purified triacylglycerols of olive, canola, and fish oils as affected by different concentrations of hydroxytyrosol were studied at 60–100 °C. On average, hydroxytyrosol improved the temperature susceptibility (temperature coefficient, T_C, and Q₁₀ number) of olive oil, whereas opposite results were observed for canola and fish oils. Despite the results observed in canola and fish oils, hydroxytyrosol caused much greater changes in the Arrhenius equation parameters (activation energy, E_a, and frequency factor, A) for the oxidation of olive oil. On the whole, the highest increase in the Gibbs free energy, ΔG⁺⁺, of the activated complex formation as affected by the antioxidant was for olive (9.7%), canola (8.9%), and fish (5.7%) oils, respectively.     

Evaluating Electron Paramagnetic Resonance (EPR) to Measure Lipid Oxidation Lag Phase for Shelf-Life Determination of Oils

Lipid oxidation is one of the major causes of oil deterioration causing off-flavors and consumer rejection. Fast, easy, and dependable assays for predicting lipid oxidation rates in foods are important for shelf-life prediction. In this study, an electron paramagnetic resonance (EPR) spin-trapping technique with N-tert-butyl-α-phenylnitrone (PBN) was tested to determine the lag phase of lipid oxidation in stripped soybean oil (SSO), SSO with added α-tocopherol, and commercial soybean, canola and corn oils. EPR intensity of spin-trapped products from SSO correlated well with lipid hydroperoxides formation for samples stored at 37 and 55 °C respectively. When the antioxidant α-tocopherol was added, the EPR signal intensity of oil samples increased—indicating sample deterioration—after 50–65% of α-tocopherol was consumed. When using the EPR method with commercial soybean, canola or corn oil stored at 55 °C, there was a poor relationship between EPR intensity and lipid hydroperoxides lag phases. However, a linear correlation was found between EPR signal intensity and hexanal formation. For example, EPR signal intensity lag phases were 5, 13 and 27 days for soybean, canola and corn oils, respectively which was similar to the hexanal lag phases of 5, 13 and 25 days for the same oils. The EPR spin-trapping assay method has several advantages over headspace hexanal measurements, especially with regard to easier sample handling and shorter analysis times.     

Thin-film test to investigate liquid oxypolymerization of nonvolatile analytes: Assessment of vegetable oils and biodegradable lubricants

A thin-film oxidation test was developed to investigate liquid oxypolymerization of nonvolatile analytes. Gel permeation chromatography (GPC) showed that the test delivered the required degree of oxidation with better than ±5% accuracy. The following oils were ranked according to their decreasing resistance to oxypolymer formation at 150°C: 90% oleic sunflower oil, triolein, meadowfoam oil, castor oil, canola oil, lesquerella oil, and soybean oil. Higher degrees of oxidation demonstrated the occurrence of oxidative gelation. Oxypolymerization tendencies of hydraulic fluids based on canola and rapeseed oils were comparable to those of canola oil without additives. The relative amount of C-C polyunsaturation present in the fatty acid chain was a major differentiating factor. However, oxidation inhibitors also reduced the rates of oxypolymerization, as demonstrated by sunflower oil-based hydraulic fluid. Canola and rapeseed lubricants needed better oxypolymerization control.     

Oxidation Rates of Triacylglycerol and Ethyl Ester Fish Oils

Fish oil is available primarily as triacylglycerols (TAG) or ethyl esters (EE). Anecdotal evidence suggests that TAG have superior bioavailability and oxidative stability compared to EE. In this work, peroxide value (PV) and p‐anisidine value (AV) were used to monitor oxidation in commercially available TAG and EE fish oils incubated at temperatures from 5 to 60 °C. Pseudo first‐order kinetics were assumed and rate constants were calculated for each temperature. At all temperatures, the rates of oxidation were higher for EE oils than TAG oils. For PV and AV measured in both oils, non‐linear Arrhenius models were plotted, generating activation energies that ranged from 7 to 103 and 2 to 159 kJ/mol for PV and AV, respectively. Although TAG were more resistant to oxidation than EE, they had lower activation energies (E_a) at ≤15 °C for reactions measured with PV and AV. The E_a for EE was negative at temperatures ≥45 °C, indicating that reaction rate was influenced by factors in addition to temperature.     

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.     

Antioxidant activity of amino acid sodium and potassium salts in vegetable oils at frying temperatures

Previous studies reported that several amino acids had strong antioxidant activity in vegetable oils under frying conditions. In this study, amino acids were converted to their sodium or potassium salts, and a heating study was conducted with 5.5 mM amino acid salts in soybean oil (SBO) at 180°C. Sodium salts of amino acids including alanine, phenylalanine, and proline and disodium glutamate had significantly stronger antioxidant activity than the corresponding amino acids, and potassium salts had stronger antioxidant activity than sodium salts. Potassium salts of alanine and phenylalanine more effectively retained tocopherols in SBO than the corresponding amino acids during heating. Phenylalanine potassium salt had stronger antioxidant activity than phenylalanine in other vegetable oils including olive, high oleic soybean, canola, avocado, and corn oils. Phenylalanine potassium salt at 5.5 mM more effectively prevented oil oxidation than tert-butyl hydroquinone, a synthetic antioxidant, at its legal concentration limit (0.02%) indicating its feasibility as a new antioxidant for frying.