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1.
Effects of tocopherols on the oxidative stability of stripped vegetable oils were studied by adding pure tocopherols--alpha, beta, gamma, and delta--in their naturally occurring proportions in soybean and sunflower oils to the triacylglycerols (TAG) of soybean and sunflower oils. Soybean and sunflower oils were purified by stripping all minor constituents, leaving the triacylglycerols. Pure tocopherols in the proportion typical of sunflower oil--high alpha, low gamma, and low delta--were added to purified sunflower oil and to purified soybean oil. Pure tocopherols in the proportion typical of soybean oil--low alpha, high gamma, and high delta--were added to the purified oils. Oils were subjected to accelerated autoxidation using oven storage at 60 degrees C in the dark and accelerated photooxidation at 7500 lx light intensity at 30 degrees C. Oxidation levels of aged oils were measured by the formation of both peroxides and volatile compounds and by flavor analysis. Results from substituting the tocopherol profile from one oil type to another varied on the basis of whether they were oxidized in the dark or in the light. For example, during autoxidation in the dark, soybean oil with the typical soybean tocopherol profile had the lowest levels of peroxides and total volatile compounds, whereas sunflower oil with the sunflower tocopherol profile had the highest levels. In flavor analyses of the same oils, sunflower oil with the soybean tocopherol profile was the most stable. Soybean oil with the profile of sunflower tocopherols was the least stable in dark oxidation. In contrast to the data from autoxidation in the dark, addition of tocopherols typical of sunflower oil significantly improved light stability of both oil types compared to the addition of soybean tocopherols to sunflower oil. The tocopherol profile typical of soybean oil was significantly more effective in inhibiting autoxidation in the dark; however, the tocopherol profile typical of sunflower oil inhibited light oxidation significantly more than the soybean tocopherol profile.  相似文献   

2.
The oxidative stability of selected tree nut oils was examined. The oils of almond, Brazil nut, hazelnut, pecan, pine nut, pistachio, and walnut were extracted using two solvent extraction systems, namely, hexane and chloroform/methanol. The chloroform/methanol system afforded a higher oil yield for each tree nut type examined (pine nut had the highest oil content, whereas almond had the lowest). The fatty acid compositions of tree nut oils were analyzed using gas chromatography, showing that oleic acid was the predominant fatty acid in all samples except pine nut and walnut oils, which contained high amounts of linoleic acid. The tocopherol compositions were analyzed using high-performance liquid chromatography, showing that alpha- and gamma-tocopherols were the predominant tocopherol homologues present; however delta- and beta-tocopherols were also detected in some samples. The oxidative stability of nonstripped and stripped tree nut oils was examined under two conditions, namely, accelerated autoxidation and photooxidation. Progression of oxidation was monitored using tests for conjugated dienes, peroxide value, p-anisidine value, and headspace volatiles. Primary products of oxidation persisted in the earlier stages of oxidation, whereas secondary oxidation product levels increased dramatically during the later stages of oxidation. Hexanal was the major headspace aldehyde formed in all oxidized samples except walnut oil, which contained primarily propanal. Results showed that chloroform/methanol-extracted oils were more stable than hexane-extracted oils in both the accelerated autoxidation and photooxidation studies. Oils of pecan and pistachio were the most stable, whereas oils of pine nut and walnut were the least stable.  相似文献   

3.
The electron spin resonance (ESR) spin trapping technique was investigated as an analytical approach to follow lipid oxidation of rapeseed oil, sunflower oil, and fish oil during storage at 40 degrees C. Unlike previous investigations, alpha-phenyl-N-tert-butylnitrone (PBN), used as spin trap, was added to the fresh oils and formation of radicals was monitored during storage. Results were compared with the development in peroxide value (PV) and the thiobarbituric acid index (TBA). Increasing radical development was detected during the initial stages of oxidation, during which no significant changes in PV and TBA were observed. Evidence of spin adduct depletion was found during prolonged storage, suggesting that although spin trapping of radicals may be used to follow early events in lipid oxidation, it is not a suitable parameter for long periods of time. Addition of the spin trap after sequential samplings is recommended for getting an insight of oxidative changes during storage. Further, the influence of the spin trap (PBN) on lipid oxidation was studied in detail by application of PV and TBA and by following the depletion of naturally occurring tocopherol. PBN was found to possess a profound inhibiting effect on lipid oxidation. Such an effect was found to be dependent on the nature of the oil, and it was observed that the lower the oxidative stability, the larger the effect of PBN on lipid oxidation. This effect was interpreted in terms of the capability of PBN to react with peroxyl radicals, which in turn depends on the initial tocopherol content of the oils.  相似文献   

4.
Salmon fillets were steamed, or pan-fried without oil, with olive oil, with corn oil, or with partially hydrogenated plant oil. The exchange between the salmon and the pan-frying oils was marginal, but it was detectable as slight modifications in the fatty acid pattern and the tocopherol contents according to the oil used. Primary and secondary oxidation products were only slightly increased or remained unchanged, which indicated a slight lipid oxidation effect due to the heating procedures applied. The same was observed for tocopherol levels, which remained almost stable and were not affected by the oxidation process. The sum of cholesterol oxidation products (COPs) increased after the heating processes from 0.9 microg/g in the raw sample to 6.0, 4.0, 4.4, 3.3, and 9.9 microg/g extracted fat in pan-fried without oil, with olive oil, corn oil, partially hydrogenated plant oil, and steamed, respectively. A highly significant correlation was found between the fatty acid pattern and the total amount of COPs (r2 = 0.973, p < 0.001). No change has been determined in the n-3 fatty acids content and in the polyunsaturated/saturated-ratio of the cooked salmon fillets. Moderate pan-frying (6 min total) and steaming (12 min) of salmon did not accelerate lipid oxidation but significantly increased the content of COPs. The highest increase of COPs was found through steaming, mainly due to the longer heat exposure. The used frying oils did not influence the outcome; no significant difference between heat treatment with or without oil has been determined.  相似文献   

5.
采用中压快速制备型色谱-高效体积排阻色谱技术,探索了煎炸次数对大豆油及薯条表面所吸附油脂中极性化合物总量(total polar compounds,TPC)及其组分的影响。结果表明,煎炸薯条后剩余的大豆油中的TPC总量随着煎炸次数的增加而是逐渐增加,而薯条表面所吸附油脂中的TPC含量也随之逐渐增加;同时,煎炸次数的增加,显著改变了极性组分氧化甘油三酯寡聚物(oxidized triglyceride oligomers,TGO)、氧化甘油三酯二聚物(oxidized triglyceride dimers,TGD)、氧化甘油三酯单体(oxidized triglyceride monomers,ox-TG)在大豆油中的分布,而甘油二酯(diacylglycerols,DG)的含量增加缓慢,游离脂肪酸和甾醇(free fatty acids and sterols,FFAsterols)和其他未知小分子化合物的含量呈现波动性变化。煎炸次数严重影响了大豆油和薯条表面所吸附油脂中的TPC及其组分分布,也在一定程度上影响了薯条的健康价值。  相似文献   

6.
Western diets contain substantial amounts of lipid oxidation products. The effects of fasting status and oil oxidation on short-term digestibility of oxidized fatty acids (ox-FA) and ketolinoleic acids (keto-LA) of sunflower oils were evaluated. Twelve rats were fasted overnight for 3 days, whereas another 12 rats had free access to diet. From day 4, and for 4 days, two groups of rats, nonfasted (NFT) and fasted (FT), received 1 g/100 g body weight of sunflower oil reused from 40 deep-frying processes, and two control groups of rats, nonfasted (NFC) and fasted (FC), received the same amount of fresh oil. Ox-FA and keto-LA were determined 5 h after the last administration in the various gastrointestinal compartments together with the intraintestinal MDA. Oil digestibility was highest in NFC and lowest in FT rats. NFT and FT rats had higher (at least P < 0.05) intraintestinal MDA, ox-FA, and keto-LA than NFC and FC; MDA and keto-LA concentrations correlated with each other (P < 0.05). Ox-FA and keto-LA levels found in the gastric lumen suggest that digestion contributes to the formation of these compounds. Total ox-FA and keto-LA were efficiently absorbed during the first 5 h after test oil administration, but poorly absorbed in the case of fresh oils. Oil alteration influenced the digestibility of these compounds more than fasting, although the digestibility of oxidized oil was significantly affected by fasting.  相似文献   

7.
Factors contributing to the oxidative stability of phytosterols were studied. Unsaturated stigmasterol and saturated sitostanol were used as model compounds and were heated at different temperatures in different lipid matrices for various periods of time. Accumulations of the major secondary oxidation products were used as a marker of the stability of heated compounds, and the products were analyzed by gas chromatography-mass spectrometry. The results showed that both temperature and heating time, as well as sterol structure and lipid matrix composition, affected phytosterol oxidation. In particular, the interactions between different lipid matrices and temperatures had drastic effects on the total contents of the phytosterol oxides formed and also on the reaction pathways of oxidation. During heating at high temperatures for prolonged periods, >20% of stigmasterol was oxidized. At moderate temperatures the oxidation of stigmasterol was rather slow. Sitostanol oxide contents were low under all heating conditions studied.  相似文献   

8.
The effects of oxidized dietary lipid and the role of vitamin E on lipid profile, retained tocopherol levels, and lipid oxidation of juvenile Atlantic cod (Gadus morhua) were evaluated following a 9-week feeding trial. Four isonitrogenous experimental diets containing fresh or oxidized (peroxide value of 94 mequiv/kg) fish oil with or without added vitamin E (alpha-tocopherol or mixed tocopherols) were fed to juvenile cod in duplicate tanks. There was no significant (P > 0.05) influence on major lipid classes of cod liver and muscle by diet with the exception of sterols. Sterols content was increased in liver but decreased in muscle by oxidized dietary oil in the absence of vitamin E. Dietary vitamin E supplementation decreased the sterols level in cod liver but with no significant (P > 0.05) effect on their level in the muscle. Fatty acid composition varied between lipid fractions in muscle tissue and was affected by the diet. Oxidized oil significantly (P < 0.05) decreased the deposition of alpha-tocopherol in liver but not in muscle. gamma- and delta-Tocopherols from dietary tocopherol mixtures were retained at very low levels in liver, but higher retention was observed in muscle tissue. The oxidative state of both liver and muscle, as measured by the 2-thiobarbituric acid reactive substances (TBARS) and headspace propanal, negatively correlated with tissue vitamin E levels. It is suggested that oxidized oil affected juvenile Atlantic cod by causing vitamin E deficiency in certain tissues and that these effects could be alleviated by supplementation of a sufficient amount of dietary vitamin E. The results also indicate that mixed tocopherols were good antioxidants for Atlantic cod, although less effective than alpha-tocopherol alone in many tissues with the exception of muscle, where gamma- and delta-tocopherols were deposited at relatively high levels.  相似文献   

9.
Phosphatidylethanolamine (PE), phosphatidylcholine (PC), lysine (Lys), and mixtures of them were tested for antioxidative activity in a tocopherol-stripped olive oil (TSO) and the same oil after addition of 250 microg of alpha-tocopherol g of oil/(tocopherol-added olive oil, TAO) to evaluate the role of tocopherol in the antioxidant activity of oxidized lipid-amine products. Neither PE nor PC nor Lys protected TSO when tested alone, but both PE and Lys increased the induction period (IP) of TAO. On the contrary, PE/Lys and PC/Lys mixtures, but not PC/PE mixtures, protected both TSO and TAO. These results were a consequence of both the formation of oxidized lipid-amine products, which were determined by gas chromatography-mass spectrometry after their conversion into volatile derivatives, and a synergism between alpha-tocopherol and the produced compounds. These results were confirmed by analyzing the antioxidative activity of two of the produced carbonyl-amine products: 6-amino-2-(1H-pyrrol-1-yl)hexanoic acid (1) and 2,3-dipalmitoylpropyl 2-(1H-pyrrol-1-yl)ethyl phosphate (2). The hydrophilic compound 1 was more antioxidant than the analogous lipophilic compound 2, and this antioxidative activity was observed in TAO and not in TSO. All these results suggested that antioxidative activity of carbonyl-amine products may be greatly increased with the addition of tocopherols, and those products derived from Lys are more antioxidant in bulk oils than those derived from PE.  相似文献   

10.
The objectives of this study were to investigate the effects of dietary fat (6% soy oil or rapeseed oil or tallow) and alpha-tocopheryl acetate supplementation at two levels (30 or 200 ppm) on radical production, measured by ESR spectroscopy, and on lipid and protein oxidation in turkey muscle extracts oxidized by an enzymic system (NADPH, ADP, FeSO(4)/cytochrome P450 reductase). Two muscles were tested: pectoralis major (glycolytic) and sartorius (oxidative) muscles. Radical production measured by ESR was higher in pectoralis major muscle than in sartorius muscle, whereas lipid and protein oxidation was more important in sartorius muscle, showing the importance of the pro-/antioxidant ratio in oxidative processes in muscular cells and of the measurement methodology to appreciate the free radical production. Dietary fat had no effect on the level of ESR signals, whereas feeding of animals with soy oil induced higher oxidation of lipids. Protein oxidation was less sensitive to the nature of the dietary fat than lipid oxidation. Vitamin E supplementation significantly decreased radical production, as measured by ESR spectroscopy. Vitamin E also decreased lipid and protein oxidation, but the effect of vitamin E on protein oxidation was less pronounced than on lipid oxidation.  相似文献   

11.
The impact of lipid oxidation on yellow pigment formation in squid lipids and proteins was studied. When the squid microsomes were oxidized with iron and ascorbate, thiobarbituric acid reactive substance were observed to increase simultaneously with b values (yellowness) and pyrrole compounds concomitantly with a decrease in free amines. Oxidized microsomes were not able to change the solubility, sulfhydryl content, or color of salt-soluble squid myofibrillar proteins. Aldehydic lipid oxidation products were able to decrease solubility and sulfhydryl content of salt-soluble squid myofibrillar proteins but had no impact on color. Aldehydic lipid oxidation products increased b values (yellowness) and pyrrole compounds and decreased free amines in both squid phospholipid and egg yolk lecithin liposomes. The ability of aldehydic lipid oxidation products to change the physical and chemical properties of egg yolk lecithin liposomes increased with increasing level of unsaturation and when the carbon number was increased from 6 to 7. These data suggest that off-color formation in squid muscle could be due to nonenzymatic browning reactions occurring between aldehydic lipid oxidation products and the amines on phospholipids headgroups.  相似文献   

12.
The emergence of primary and secondary oxidation products in New Zealand extra virgin olive oil during accelerated thermal oxidation was measured and correlated with the concentrations of 13 headspace volatile compounds measured by selected ion flow tube mass spectrometry (SIFT-MS). SIFT-MS is a mass spectrometric technique that permits qualitative and absolute quantitative measurements to be made from whole air, headspace, or breath samples in real-time down to several parts per billion (ppb). It is well-suited to high-throughput analysis of headspace samples. Propanal, hexanal, and acetone were found at high concentrations in a rancid standard oil, while propanal, acetone, and acetic acid showed marked increases with oxidation time for the oils used in this study. A partial least-squares (PLS) regression model was constructed, which allowed the prediction of peroxide values (PV) for three separate oxidized oils. Sensory rancidity was also measured, although the correlations of headspace volatile compounds with sensory rancidity score were less satisfactory, and too few results were available for the construction of a PLS regression model. A fast (approximately 1 min), reliable method for prediction of olive oil PVs by SIFT-MS was developed.  相似文献   

13.
The similarities and differences of eight vegetable oils produced in China were investigated in terms of their fatty acid, sterol, and tocopherol compositions and subsequent data processing by hierarchical clustering analysis and principal component analysis. The lipid profiles, acquired by analytical techniques tailored to each lipid class, revealed great similarities among the fatty acid profiles of corn and sesame oil as well as few differences in their sterol profiles. It turns out that not only was there great similarity between the fatty acid profiles of corn oil and sesame oil but also there were not too many differences for the sterol profiles. Sunflower and tea-seed oil showed similar sterol compositions, while the tea-seed oil tocopherol was very similar to palm oil. The results demonstrated that the use of only one of these profiles was unreliable for indentifying oil origin and authenticity. In contrast, the use of the sterol or tocopherol profile together with the fatty acid profile more accurately discriminates these oils.  相似文献   

14.
The phenolic fraction of virgin olive oil influences both its quality and oxidative stability. One of the principal threats of the quality of olive fruit is the olive fly ( Bactrocera oleae) as it alters the chemical composition. The attack of this olive pest has been studied in order to evaluate its influence on the quality of virgin olive oil (free acidity, peroxide value, fatty acid composition, water content, oxidative stability, phenols, and antioxidant power of phenolic fraction). The study was performed using several virgin olive oils obtained from olives with different degrees of fly infestation. They were acquired in different Italian industrial mills from the Abruzzo region. Qualitative and quantitative analyses of phenolic profiles were performed by capillary electrophoresis-diode array detection, and electrochemical evaluation of the antioxidant power of the phenolic fraction was also carried out. These analyses demonstrated that the degree of fly attack was positively correlated with free acidity ( r = 0.77, p < 0.05) and oxidized products ( r = 0.58, p < 0.05), and negatively related to the oxidative stability index ( r = -0.54, p < 0.05) and phenolic content ( r = -0.50, p < 0.05), mainly with secoiridoid compounds. However, it has been confirmed that the phenolic fraction of olive oil depends on several parameters and that a clear correlation does not exist between the percentages of fly attack and phenolic content.  相似文献   

15.
Virgin olive oil is valued for its flavor, but unacceptable off-flavors may develop on storage in food products containing this oil due to oxidation. The oxidative stability of oil-in-water emulsions containing bovine serum albumin (BSA) and virgin olive oil phenolic compounds was studied. Four oil-in-water emulsions with and without BSA and phenols isolated from virgin olive oil were prepared. These model systems were stored at 60 degrees C to speed up lipid oxidation. Primary and secondary oxidation products were monitored every three days. Peroxide values and conjugated diene contents were determined as measures of the primary oxidation products. p-Anisidine values and volatile compounds were determined as measures of the secondary oxidation products. This latter determination was carried out by headspace solid-phase microextraction coupled with gas chromatography. Although olive oil phenolic compounds and BSA contributed some antioxidant activity when present as individual additives, the combination of BSA with phenols in an emulsion showed 58-127% synergy, depending on which analytical method was used in the calculation. The emulsion containing phenolic compounds and BSA showed a low level of deterioration after 45 days of storage at 60 degrees C.  相似文献   

16.
The effect of natural phenolic compounds on the antioxidant and prooxidant activity of lactoferrin was studied in liposomes and oil-in-water emulsions containing iron. The antioxidants tested with lactoferrin were alpha-tocopherol, ferulic acid, coumaric acid, tyrosol, and natural phenolic extracts obtained from three different extra-virgin olive oils and olive mill wastewater. The natural extracts of olive oils and mill wastewaters were composed mainly of polyphenols and simple phenolics, respectively. Lipid oxidation at 30 degrees C was determined by the formation of hydroperoxides and fluorescent compounds resulting from oxidized lipid interactions. All phenolic compounds showed synergistic properties in reinforcing the antioxidant activity of lactoferrin in lipid systems containing iron. The highest synergistic effects were observed for the phenolic extracts rich in polyphenols of extra-virgin olive oils and lactoferrin. This synergistic effect was higher in liposomes than in emulsions.  相似文献   

17.
Proteins dispersed in the continuous phase of oil-in-water emulsions are capable of inhibiting lipid oxidation reactions. The antioxidant activity of these proteins is thought to encompass both free radical scavenging by amino acid residues and chelation of prooxidative transition metals; however, the precise mechanism by which this occurs remains unclear. In this study, the oxidative stability of cysteine, tryptophan, and methionine residues in continuous phase beta-lactoglobulin (beta-Lg) in a Brij-stabilized menhaden oil-in-water emulsion was determined. The presence of low concentrations of continuous phase beta-Lg (250 and 750 microg/mL) significantly inhibited lipid oxidation as determined by lipid hydroperoxides and thiobarbituric acid reactive substances analysis. It was observed that cysteine oxidized before tryptophan in beta-Lg, and both residues oxidized before lipid oxidation could be detected. No oxidation of the methionine residues of beta-Lg was observed despite its reported high oxidative susceptibility. It is conceivable that surface exposure of amino acid residues greatly affects their oxidation kinetics, which may explain why some residues are preferentially oxidized relative to others. Further elucidation of the mechanisms governing free radical scavenging of amino acids could lead to more effective applications of proteins as antioxidants within oil-in-water food emulsions.  相似文献   

18.
The objective of this study was to investigate approaches to protect selected flavor compounds from deterioration when stored in an oil matrix. An aroma compound model mixture was prepared in a medium-chain triglyceride (MCT) or sunflower oil (SfO) matrix and stored under either an ambient air or argon atmosphere containing, respectively, ca. 20 and <0.5% residual oxygen as controls or containing a natural antioxidant, delta-tocopherol (0.01%). Samples were analyzed by static headspace GC/FID to determine the stability over time of the compounds in mixture. It was found that the type of oil had the greatest effect (P < 0.01) on overall compound stability. A low-oxygen atmosphere also had a significant (P < 0.05) protective effect on the aroma compounds in both oils. The addition of delta-tocopherol generally offered little additional protection. No significant relationship could be determined between the oxidation of the lipid matrix and the loss of oxidation-sensitive thiol compounds.  相似文献   

19.
Some important edible oils (extra virgin olive oil, canola oil, and sunflower oil) were added to aqueous glucose-lysine or xylose-lysine model systems to investigate their effect on the formation of volatiles from the Maillard reaction (MR). The volatile compounds were extracted by a Likens-Nickerson apparatus and quantified. Pyrazines, Maillard reaction products with an important impact on food flavor, appeared to be particularly sensitive to the presence of the oils in both the xylose-lysine and glucose-lysine model systems. The unsubstituted pyrazine was formed more with olive oil, less with canola oil, and even less with sunflower oil, whereas 2-methylpyrazine, 2,5-methylpyrazine, and 2,3-dimethylpyrazine were formed less with olive oil, more with canola oil, and even more with sunflower. The oxidative states of the oils and their fatty acid fingerprints were determined: the results indicated that the relative amounts of the pyrazines are sensitive to the degree of unsaturation of the oil. The autoxidation of the volatile compounds generated from the MR, investigated by the addition of free radical modulators (antioxidants alpha-tocopherol, 2,6-di-tert-butyl-4-methylphenol, and rosemary extract; or pro-oxidant alpha,alpha'-azobis-isobutyronitrile, a free radical initiator), was limited in respect to aqueous model systems.  相似文献   

20.
Lipid oxidation is a major deteriorative factor in meats. Sources of natural antioxidants that are as effective as commercially available antioxidants are desired. The objective of this research was to investigate honey as an inhibitor of lipid oxidation in ground poultry. The antioxidant content of different varieties of honey was investigated spectrophotometrically and honey's effectiveness in reducing oxidation of ground poultry determined by monitoring thiobarbituric acid reactive substances (TBARS). Buckwheat honey had the highest antioxidant content and acacia honey the lowest. Honeys of different floral sources differed in their protection against lipid oxidation. Buckwheat honey (5%, w/w) reduced TBARS approximately 70%, whereas acacia honey reduced TBARS approximately 34% at 3 days of storage at 4 degrees C. In comparison to butylated hydroxytoluene and tocopherol (0.02% of total fat), honey (at 5% of the weight of the meat) was much more effective at preventing oxidation. Honey has great potential as an antioxidant source and may result in greater acceptability of meat products and prevent negative health implications of oxidized meats.  相似文献   

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