Effects of tocopherols, ascorbyl palmitate, and lecithin on autoxidation of fish oil

The effects of α-, γ/δ, and δ-tocopherol concentrates (0.2–2.0%) alone and in combination with ascorbyl palmitate (0.1%) and lecithin (0.5%) on oxidative stability and flavor of fish oil were studied. Stability was assessed on oil stored in air at 20°C by peroxide value (PV) and off-flavor formation. Polymer content, para-anisidine value, and conjugation were used to characterize selected samples. When used alone, the protective effect of the tocopherols, as measured by PV, was δ≫γ/δ≫α, especially at the 2% concentration. Binary systems of ascorbyl palmitate-lecithin and lecithin-γ/δ or-δ-tocopherol were strongly synergistic in delaying peroxidation. The ternary blends provided the greatest protection against autoxidation. Refined fish oil with 2% δ-tocopherol, 0.1% ascorbyl palmitate, and 0.5% lecithin showed no significant peroxidation at 20°C over a period of 6 mon. The original antioxidant effect noted for the ternary systems in delaying peroxidation was not reflected in improved flavor stability. Off-flavors developed within 3 wk, making the oils unsuitable for use at high concentrations in ambient products that are unprotected from air.     

Antioxidant synergism between butylated hydroxyanisole and butylated hydroxytoluene

Decay of the 2,6-di-tert-butyl-4-methylphenoxy radical [butylated hydroxytoluene (BHT)-radical] in the presence of butylated hydroxyanisole (BHA) was investigated in 1,2-dimethoxyethane with or without triethylamine. BHT-radical was conveniently generated by dissociation of its unstable dimer in solution. The products were BHT, 3,3′-di-tert-butyl-5,5′-dimethoxy-2,2′-dihydroxybiphenyl (BHA-dimer), 2,6-di-tert-butyl-p-quinone methide (QM), 1,2-bis(3,5-di-tert-butyl-4-hydroxyphenyl)ethane, and 3,3′,5,5′-tetra-tert-butyl-4,4′-stilbenequinone. The reaction without added triethylamine gave larger quantities of the last two products and BHA (recovery), whereas the reaction with it provided larger quantities of the first two products. The marked difference in the product distribution can be accounted for by a series of reactions including reversible dehydrogenation of BHA with BHT-radical, which generates 2-tert-butyl-4-methoxyphenoxy radical (BHA-radical) and BHT, reversible dimerization of BHA-radical, which affords an intermediarybis(cyclohexadienone), and spontaneous and base-catalyzed prototropic rearrangement of the intermediate into BHA-dimer. Products of coupling between BHT-radical and BHA-radical were not obtained. BHA was found to undergo facile acid-catalyzed addition to QM, providing two isomericbis(hydroxyphenyl)methanes. The results help to elucidate the mechanism of antioxidant synergism between BHA and BHT and may suggest that the synergism can be affected by base or acid.     

Antioxidant constituents of peanut oil

The components responsible for increased stability of raw peanut oil at a high relative humidity (RH) of 91% were examined in peanut oil and methyl linoleate systems. Of the constituents, the native gums, which were mostly phospholipids and glycolipids, showed increased antioxidant activity at 91% RH. The isolated components of the gums, namely phospholipids and glycolipids, were prooxidant individually or in combination. Tocopherols did not show increased antioxidant activity at 91% RH.     

Concentration of sterols and tocopherols from olive oil with supercritical carbon dioxide

A process based on the use of a semicontinuous countercurrent supercritical fluid extraction has been developed to isolate and concentrate minor compounds, such as sterols and tocopherols, from olive oil. In the present work, an evaluation of the efficiency of different random packing materials (Raschig rings, Dixon rings, Fenske rings, and glass beads) to selectively separate sterols and tocopherols from olive oil has been performed. Parameters such as recovery, enrichment, and selectivity vs. TG are discussed. Considering the importance of supercritical fluid extraction as a clean processing technology and the interest in minor compounds with nutraceutical properties from olive oil, the process studied represents an alternative to the reuse of low-quality olive oil to extract high added-value products.     

The influence of carotenoids and tocopherols on the stability of safflower seed oil during heat-catalyzed oxidation

The stability and antioxidant effects of carotenoids and tocopherols in safflower seed oil were evaluated under thermal (75°C) and oxidative conditions and the oxidative stability index (OSI) determined. The antioxidant capability of butylated hydroxytoluene (BHT) was also compared with that of β-carotene in a model system. Lycopene and β-carotene (1 to 2000 ppm) were heated (75°C) and exposed to air (2.5 psi) in an oxidative stability instrument. β-Carotene had no antioxidant effect at concentrations below 500 ppm, because it did not alter the induction time. Lycopene increased the induction time only slightly at low concentrations. However, at concentrations greater than 500 ppm, both β-carotene and lycopene acted as prooxidants, significantly decreasing the induction period. At the highest concentration, 2000 ppm, lycopene was more prooxidative than β-carotene. α- and γ-Tocopherol (concentration, 1000 ppm) delayed the induction time by 16 and 26 h, respectively. There was no cooperative interaction between α-tocopherol and β-carotene in delaying the onset of oxidation. Furthermore, BHT was significantly more antioxidative than β-carotene. Thus, under thermal and oxidative conditions, β-carotene could not delay the onset of oxidation. The tocopherols and BHT were effective in suppressing the onset of oxidation, as determined by the oxidative stability measurement.     

Effects of expeller-pressed/physically refined soybean oil on frying oil stability and flavor of french-fried potatoes

To determine effects of expeller pressing/physical refining of soybean oil (SBO) on frying, studies were conducted with expeller-pressed, physically refined, bleached, deodorized SBO (EPSBO); hexane-extracted, refined, bleached, deodorized SBO+TBHQ; and hydrogenated SBO (HSBO). Oils contained citric acid and dimethylpolysiloxane and were used for 35 h of frying french-fried potatoes. Polar compound levels in EPSBO were similar to SBO+TBHQ or HSBO. Flavor quality of potatoes was evaluated by trained, experienced, analytical sensory panelists. In early frying stages, potatoes fried in EPSBO had significantly lower intensities of fishiness than potatoes fried in SBO+TBHQ. Potatoes fried in HSBO were described as “hydrogenated”. Because of differences in flavor intensities and types, potatoes prepared in EPSBO had significantly better quality scores than those fried in SBO+TBHQ or HSBO during the first 15 h of frying. During later stages (25 and 35 h), potatoes fried in EPSBO had significantly better quality scores than potatoes fried in HSBO. Variations in minor oil constituents may partly explain these differences. EPSBO had less total tocopherols and phytosterols than did SBO at 0-time. During frying, TBHQ in SBO and Maillard reaction products in EPSBO probably inhibited tocopherol loss and therefore improved quality.     

Antioxidant effect of natural phenols on olive oil

The total polar fraction and individual phenols present in virgin olive oil were tested for their antioxidant effect in refined olive oil. Hydroxytyrosol and caffeic acid showed protection factors greater than BHT. Protocatechuic and syringic acid were also found to have antioxidant activity. Tyrosol, p-hydroxyphenylacetic acid, o-coumaric acid, p-coumaric acid, p-hydroxybenzoic acid and vanillic acid had very little or no effect, and their contribution to the stability of the oil is negligible.     

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.     

Oil-in-water emulsions formulated with sunflower lecithins: Vesicle formation and stability

Oil-in-water emulsions (30∶70, vol/vol) were formulated with sunflower lecithin to characterize the destabilization processes and the vesicles formed. Dispersions containing levels of 0.1% lecithin were more stable against coalescence than the control system. When the lecithin concentration was increased to 0.5%, the presence of spherical structures, such as vesicles, was recorded that occluded the emulsion inside. Vesicles underwent a creaming process, and a narrow coalescence zone was detected in the upper layers of the samples. As the lecithin concentration was increased, more vesicles were formed, representing as much as 80% of the system volume. A reduction in the average size of vesicles was observed at high lecithin concentrations (2.5 and 5.0%). The vesicle size distribution changed as a function of lecithin concentration, decreasing the ratio of large to small particles in the same way. Coalescence took place in zones where large-volume vesicles were in contact in the upper portion of the tube sample. The results obtained suggest that sunflower lecithins present interesting emulsifying properties that may prove useful in food technology.     

Predicting oxidative stability of vegetable oils using neural network system and endogenous oil components

The usefulness of Artificial Neural Network Systems (ANNW) to predict the stability of vegetable oil based on chemical composition was evaluated. The training set, comprised of a composition of major and minor components of vegetable oil as inputs and as outputs, induction period and values of slopes for initiation and propagation, was measured by oxygen consumption. The best predictability was achieved for oils stored at 35°C with light exposure, when the major fatty acids, chlorophylls, tocopherols, tocotrienols, and metals were used as predictors. For oils stored at 65°C without light, a good predictability was obtained when composition of the major fatty acids and the amounts of tocopherols and tocotrienols were used. These results suggest that vegetable oil stability can be successfully predicted by ANNW when partial oil composition is known.     

Regional distribution of tocopherols and fatty acids within soybean seeds

Seed coat, axis, and sections of cotyledons in three soybean cultivars were analyzed by high-performance liquid chromatography for tocopherols, and by gas-liquid chromatography for acyl lipids. Tocopherols were predominantly detected in axis, followed by cotyledons and seed coat. With a few exceptions, dominant components were γ- and δ-tocopherols, with much smaller amounts of α- and β-tocopherols. However, α-tocopherol was higher (P<0.05) for the Mikawajima cultivar than for Okuhara and Tsurunoko in all tissues. Triacylglycerols (TAG) were the major fraction of total lipids, representing 70% in axis and coat and 94% in cotyledons. A small difference (P<0.05) occurred in fatty acid composition of TAG when comparing seed coat to the axis. The fatty acid composition of phosphatidylinositol (PI) differed (P<0.05) from phosphatidylethanolamine (PE) and phosphatidylcholine (PC) in each tissue. Principally, the percentage of palmitic acid was higher, especially in axis and coat. In PE and PC, linoleic was greater, followed by palmitic, in all samples except for seed coat tissue in Mikawajima. The percentages of palmitic acid in both phospholipids were significant higher in the seed coat tissue from this cultivar than in cotyledon or axis of the other varieties. These results suggest that the differences in soybean cultivars could be appreciable, based on the distribution of tocopherols and fatty acids in each component part within soybean seeds.     

Effect of sunflower lecithins on the stability of water-in-oil and oil-in-water emulsions

Lecithins are frequently applied in the food industry as emulsifiers, viscosity regulators, and dispersing agents. The main aim of the present work was to study the emulsifying capability of diverse sunflower lecithins so as to evaluate the functionality of these by-products, which are not extensively used at present. The experimental results obtained for water-in-oil (W/O) emulsions showe that dispersions containing levels of 0.1% lecithins were more stable against coalescence than a control system, whereas those with 1% emulsifying agent exhibited the opposite behavior. On the other hand, faster sedimentation kinetics were observed at a concentration of 0.1% than at 1%. Lecithins with high phospholipid content, especially phosphatidylethanolamine and phosphatidylinositol, were found to be the best emulsifying agents for W/O dispersions. In the case of oil-in-water emulsions, it was possible to observe two processes: creaming of emulsions with the addition of 1% of lecithins, and instant creaming followed by coalescence of the cream phase in those cases corresponding to 0.1% added lecithin.     

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.     

The antioxidant effects of phospholipids on perilla oil

Antioxidant effect of phospholipids on the oxidation of refined perilla oil (PO;α-18:3, 54.5%; 16:0, 7.2%; 18:0, 2.6%; 18:1, 18.6%; 18:2, 15.5%), tocopherol-free (POF) and tocopherol-enriched (POR) perilla oil were investigated by measuring weight-gains and by the oven test at 37°C. The oxidative stability of PO was especially increased by additions of phosphatidylethanolamine (PE) and phosphatidylserine (PS), but phosphatidylcholine (PC) scarcely showed an antioxidant effect. The oxidative stability of POF was markedly low, and none of the phospholipids (PC, PE, PS) showed an antioxidant effect on the oxidation of POF. The stability of POR was lower than that of PO regardless of its higher tocopherol contents. However, the oxidation of POR was significantly suppressed by additions of PE and PS, as was observed with PO. PC showed a small antioxidant effect on the oxidation of POR. Therefore, it seems that the antioxidant effects of phospholipids, especially of PE and PS, was due to the presence of tocopherols in the perilla oil.     

Antioxidant activity of tocopherols and phenolic compounds of virgin olive oil

The antioxidant effects of hydrophilic phenols and tocopherols on the oxidative stability in virgin olive oils and in purified olive oil have been evaluated. Total hydrophilic phenols and the oleosidic forms of 3,4-dihydroxyphenolethanol (3,4-DHPEA) were correlated (r=0.97) with the oxidative stability of virgin olive oil. On the contrary, tocopherols showed low correlation (r=0.05). Purified olive oil with the dialdehydic form of elenolic acid linked to 3,4-DHPEA, an isomer of oleuropeine aglycon, and 3,4-DHPEA had good oxidative stability. A synergistic effect was observed in the mixture of 3,4-DHPEA and its oleosidic forms with α-tocopherol in purified olive oil by the Rancimat method at 120°C.     

Analysis of tocopherols in vegetable oils by high-performance liquid chromatography: Comparison of fluorescence and evaporative light-scattering detection

A comparison of the responses of an evaporative light-scattering detector (ELSD) and a fluorescence detector for tocopherols in vegetable oils by high-performance liquid chromatography is presented. The tocopherols were separated from acylglycerols by gel-permeation chromatography (GPC). The tocopherol fraction was collected off a set of four GPC columns with a mobile phase of methylene chloride before separation on a normal-phase silica column with a mobile phase of hexane/isopropanol, 99.7∶0.3 (vol/vol). An internal standard of 5,7 dimethyltocol, which was detected by both the ELSD and fluorescence detector, was used to obtain quantitative data. The fluorescence detector was ten times more sensitive than the ELSD. γ-Tocopherol was the major tocopherol detected in the vegetable oils studied and ranged from 24.1–93.3 mg/100 g. The amounts of tocopherols found in the vegetable oils agreed favorably with the literature values.     

Antioxidant activity of rapeseed phenolics and their interactions with tocopherols during lipid oxidation

Commercial rapeseed press cakes are rich sources of phenolic compounds, namely, sinapic acid derivatives, which can be extracted as free sinapic acid and its bound forms (such as sinapine, the choline ester of sinapic acid). Fractionated rapeseed extracts rich in sinapic acid and sinapine were compared for their capacity to inhibit the formation of lipid oxidation products. Oxidation at 40°C was monitored by the formation of hydroperoxides (indicating primary oxidation products) and propanal (secondary oxidation products). The 70% methanolic extract of rapeseed meal, added as an equivalent of 500 μmol/kg oil (based on sinapic acid equivalent for sinapic acid-rich extracts or sinapine equivalent for sinapinerich extracts) showed good antioxidative activity compared with the addition of 500 μmol/kg oil sinapic acid. Apart from this, the interaction between a mixture of α-/γ-tocopherol and sinapic acid was investigated using response surface methodology for the experimental design. The experiments indicated that the addition of sinapic acid (concentration dependent) caused inhibition of peroxide formation, complementing further lower endogenous tocopherol concentration in oils. This paper was initially presented at the 95th AOCS Annual Meeting and Expo in Cincinnati, Ohio, May 1–4, 2004.     

Isolation and separation of tocopherols from olive by-products with supercritical fluids

Supercritical fluid extraction of olive pomace, the semisolid residue obtained using two-phase olive oil production systems, and supercritical fluid chromatographic separation of the extracts were performed to study the content of tocopherols, a group of compounds of interest for the food industry owing to their antioxidant activity. The developed method consists of supercritical CO₂ extraction at pilot plant scale and subsequent fractionation by two successive depressurizations. Enrichment of α-, β-, and γ-tocopherol was achieved in separator 2 when working at low densities in the first separator. Fractions obtained using high densities in separator 1 contained major proportions of triglycerides, waxes, and sterols. Tocopherols from olive by-products were separated and quantified in an environmentally friendly way by using supercritical fluid chromatography with packed capillary columns coated with polyethylene glycol and neat CO₂ according to a method previously optimized in our laboratory. The studied olive by-products can be considered a natural source of antioxidants because substantial concentration of tocopherols have been obtained in the extracts. The isolation and separation of tocopherols from olive pomace by applying supercritical fluid technology provides an interesting approach to exploit such by-products in an environmentally friendly way.     

Oxidative stability of sardine and mackerel lipids with reference to synergism between phospholipids and α-tocopherol

Relationships between oxidative stability and the compositions of sardine and mackerel lipids were investigated in view of possible synergism between phospholipids andα-tocopherol (α-Toc). The total lipids extracted from viscera were highly susceptible to autoxidation, compared with lipids of white and red muscles and of skin. This seemed to be due to lower concentrations ofα-Toc and phosphatidylethanolamine (PE) in the tissue, but not to the level of polyunsaturated fatty acids. The synergistic effect of PE withα-Toc seemed to be slightly affected by the degree of unsaturation of its fatty acyl chains. The synergistic ability ofO-phosphoethanolamine, the base moiety of PE, was higher than that ofO-phosphoserine.O-Phosphocholine was only slightly effective. During the induction period of autoxidation, theα-Toc level decreased rapidly, and rapid lipid oxidation began only afterα-Toc was almost exhausted.     

Antioxidant properties of myricetin and quercetin in oil and emulsions

The effect of quercetin and myricetin on the stability of sunflower oil and oil-in-water emulsions was studied by storage experiments monitored by measurement of peroxide values, conjugated dienes, and headspace volatile analysis. Myricetin showed strong antioxidant activity in oils stored at 60 or 30°C and in oil-in-water emulsions stored at 30°C, whether tocopherols or citric acid were present or not; however, quercetin showed similar antioxidant activity in stripped sunflower oil but no activity in oils that contained tocopherols and citric acid. This showed that myricetin is effective owing to strong radical scavenging and metal-chelating properties, whereas quercetin has weaker radical scavenging activity, although it is also active by metal-chelation. The effects of copper and iron salts on the antioxidant activity of myricetin and quercetin were studied in sunflower oil and oil-in-water emulsions. Quercetin and myricetin enhanced the prooxidant effect of cupric chloride in oil-in-water emulsions (pH 7.4), but this effect was not observed with cupric stearate. The addition of myricetin to emulsions that contained ferric chloride at pH 5.4 also produced a strong prooxidant effect, and small prooxidant effects of flavonols were also detected in the presence of cupric chloride under these conditions. However, myricetin and quercetin reduced the prooxidant effect of ferric palmitate in oils. Myricetin also showed a strong antioxidant effect in oil that contained cupric stearate, although quercetin had no significant effect on the oxidative stability of this system. It therefore appears that flavonols may exert a prooxidant effect in the presence of metal salts, but the nature of the metal salt is important in determining whether a prooxidant effect occurs.