Effects of natural antioxidants on the lipid profile of electron beam‐irradiated beef burgers

The purpose of this study was to assess the efficacy of rosemary and oregano extracts in avoiding oxidative changes in beef burgers, and to evaluate the fatty acid profile of these products after electron beam exposition. Extracts, individually or in combination, were added to beef burgers and compared to synthetic antioxidants commonly used in food (butylated hydroxytoluene, butylated hydroxyanisole). The ground beef were submitted to electron beam irradiation at doses of 0, 3.5 and 7 kGy, and stored for 90 days. At regular time intervals, lipid oxidation and fatty acid composition were evaluated through measurement of thiobarbituric acid‐reactive substances (TBARS) and gas chromatography, respectively. The results indicate that, although the irradiation process triggers an increase in the lipid oxidation ratio expressed by TBARS values, great changes in the fatty acid profiles were not observed; instead, they continued to present characteristics very similar to that of non‐irradiated beef. Thus, as irradiation doses of up to 7 kGy for frozen meat can make foods safe from foodborne pathogens, natural antioxidants derived from spices are able to reduce and avoid lipid changes that may cause a deterioration of the sensory quality of these foods, and these natural extracts offer a good choice for replacing synthetic additives.     

Behaviour of cod liver oil during the autoxidation process

Prostaglandin‐like compounds, called isoprostanes, are generated by free enzyme‐independent radical peroxidation of the acids arachidonic (AA), eicosapentaenoic (EPA) and docosahexaenoic (DHA). Up to now, isoprostanes have been largely studied only in men and biological systems, but never in food. In this research, cod liver oil was used as a model system to study the oxidation mechanism in food containing high amounts of EPA and DHA. For comparison, under similar oxidation conditions, also the behaviour of a sunflower seed oil and an n‐3 long‐chain polyunsaturated fatty acid capsule supplement oil were studied. It was ascertained that EPA‐ and DHA‐derived compounds were formed during oxidation. These compounds were polar and easily isolatable by methanol from oxidised transmethylated oil. EPA and DHA oxidation derivatives showed maximal absorbance at 200 nm and were very potent pro‐oxidants at high temperatures. In oxidised sunflower oil, similar compounds did not form. Unfortunately, the chemical structures of the EPA and DHA oxidation derivatives were not discovered, but it is a realistic hypothesis that they could be isoprostane‐like compounds.     

Effect of synthetic antioxidants on cholesterol stability during the thermal-induced oxidation of a polyunsaturated vegetable oil

As a molecule with an unsaturated bond, cholesterol is prone to oxidation. Cholesterol oxidation products (COP) are found in many common foods and have been shown to be atherogenic, cytotoxic, mutagenic, and possibly carcinogenic. Efforts to reduce the formation of oxidation products are considered important during the manufacture and processing of foods. The effect of synthetic antioxidants on cholesterol oxidation has not been extensively studied. We assayed the effect of five commonly used antioxidants—BHT, BHA, the n-propyl ester of 3,4,5-trihydroxy benzoic acid (PG), TBHQ, and 6-ethoxy-1,2-dihydro-2,4-trimethylquinoline (EQ)—on cholesterol stability when oxidation is induced in a Rancimat 679 instrument by bubbling air through the sample at 150°C. The sample consisted of 200 mg cholesterol dispersed in 100 g of a polyunsaturated vegetable oil (soybean oil). Formation of six COP was measured at the induction period, and at the 50 and 100 μS conductivity values. Under the experimental conditions, BHT and TBHQ were the most effective inhibitors of cholesterol oxidation. BHA and EQ were less effective, and PG was unable to prevent cholesterol oxidation. Synthetic antioxidants were more effective in preventing COP formation at the nucleus of the cholesterol structure than at the lateral chain.     

Evaluation of antioxidants for cod liver oil by chemiluminescence and the rancimat method

Commercial blends of natural antioxidants,viz., tocopherol concentrates, rosemary extracts, sage extracts, and lecithins, were tested for their ability to stabilize cod liver oil. The antioxidants were tested by using the Rancimat apparatus at 80°C and by a method based on hypochlorite-activated chemiluminescence analysis of samples stored at 35°C for 24 h in light. In addition, a stability study at 5°C in the dark for 8 wk, under conditions realistic for normal consumption of cod liver oil was carried out. A low correlation (r=0.339) was found between Rancimat induction times and chemiluminescence data for the sixteen antioxidant systems tested, probably due to temperature differences, and different ways of detecting oxidation products. Based on Rancimat induction times, δ-tocopherol-rich antioxidants and lecithin had the best stabilizing effect. However, based on the chemiluminescence method, the tocopherols acted as prooxidants, while tocopherols with lecithin increased the stability. Both Racimat and chemiluminescence data showed stabilizing effects with rosemary and sage extracts, but no synergistic effect between the herbal extracts and lecithin or tocopherol was observed. Analyses of oil aged at 5°C for 8 wk showed the highest stability for cod liver oil containing rose-mary extracts. The tocopherol mixtures showed only a minor effect on the stability. Ranking of antioxidants varied considerably depending on the method used, and increasing the temperature seemed to decrease the usefulness of the method. Antioxidant evaluation has to be done by using as many evaluation methods as possible under conditions relevant for normal storage and use.     

Oregano flavonoids as lipid antioxidants

Oregano (Origanum vulgare L.) leaves were successively extracted with hexane, ethyl ether, ethyl acetate and ethanol. The ethanol extract was reextracted in a separatory funnel with petroleum ether, ethyl ether, ethyl acetate and butanol. The ethyl ether layer was the most effective in stabilizing lard against oxidation, with activity equal to butylated hydroxytoluene. It also showed antioxidant activity when tested on vegetable oils under storage or frying conditions. The main antioxidant factors isolated from the ethyl ether layer consisted of flavonoids. Chromatographic and spectrophotometric analysis demonstrated the presence of the flavone apigenin, the flavanone, eriodictyol and the dihydroflavonols, dihydrokaempferol and dihydroquercetin.     

Oxidative stability of sunflower oil bodies

This study investigates the oxidative stability of sunflower oil body suspensions (10 wt‐% lipid). Two washed suspensions of oil bodies were evaluated over 8 days at three temperatures (5, 25 and 45 °C) against three comparable sunflower oil emulsions stabilized with dodecyltrimethylammonium bromide (DTAB), polyoxyethylene‐sorbitan monolaurate (Tween 20) and sodium dodecyl sulfate (SDS) (17 mM). The development of oxidation was monitored by measuring the presence of lipid hydroperoxides and the formation of hexanal. Lipid hydroperoxide concentrations in the DTAB, SDS and Tween 20 emulsions were consistently higher than in the oil body suspensions; furthermore, hexanal formation was not detected in the oil body emulsions, whereas hexanal was present in the headspace of the formulated emulsions. The reasons for the extended resistance to oxidation of the oil body suspensions are hypothesized to be due to the presence of residual seed proteins in the continuous phase and the presence of a strongly stabilized lipid‐water interface.     

Effect of maillard reaction volatile products on lipid oxidation

Maillard reaction volatile compounds (MRV), prepared by heating a glucose-glycine solution, were tested as antioxidants in soybean oil (SBO) thermoxidation. The volatiles were transferred into the oil by stripping with a stream of Nitrogen and substituting the atmosphere above the oil with air containing MRV. Standard accelerated oxidation was performed by heating the SBO. Peroxide value measurement and headspace gas Chromatographic analysis were carried out on all the samples. The MRV antioxidant activity was evaluated by determining the effect of the induction period and the kinetic rate constant of peroxide and oxidation volatiles formation. The MRV showed a significant antioxidant activity. The effectiveness was variable depending on MRV transfer method to the oil, and the Maillard reaction extent was related to the browning level of glucose/glycine solution. It was found that the maximum effect of MRV prolonged about three times the induction period and reduced the kinetic rate constant by half in relation to the control sample. MRV affects oxidative stability of soybean oil by lengthening the induction period as well as by decreasing the rate of oxidation at the propagation state and reducing the formation of hexanal.     

Inhibitory effect of boldine on fish oil oxidation

The antioxidative effect of boldine, an alkaloid extracted fromPeumus boldus Mol. (boldo), was assayed on the spontaneous and on the metal-induced oxidation of fish oil. The inhibitory effect of boldine was compared to those of dl-α tocopherol, the flavonoid quercetin and the synthetic antioxidants butylated hydroxytoluene and butylated hydroxyanisole. Boldine, in all assays, showed a good antioxidative effect, which was comparable to that of quercetin and even better than that of dl-α tocopherol and the synthetic antioxidants. Additive effects were observed when mixtures of boldine and quercetin or dl-α tocopherol were assayed. The present study supports the potential use of boldine as a novel natural antioxidant for fish oil.     

A spectroelectrochemical and chemical study on oxidation of hydroxycinnamic acids in aprotic medium

Electrochemical and chemical oxidation of hydroxycinnamic acids (HCAs) was studied to investigate the mechanisms occurring in their antioxidant activities in a protons poor medium. Electrolyses and chemical reactions were followed on-line by monitoring the UV-spectral changes with time; final solutions were analysed by HPLC-MS. Anodic oxidation of mono- and di-HCAs, studied by cyclic voltammetry and controlled potential electrolyses, occurs via a reversible one-step two-electrons process, yielding the corresponding stable phenoxonium cation. A cyclization product was also proposed, as supported by ESR studies. Chemical oxidation with lead dioxide leads to different oxidation products according to the starting substrate. Di-HCAs like chlorogenic and rosmarinic acids and the ethyl ester of caffeic acid gave the corresponding neutral o-quinones, while mono-HCAs like cumaric, ferulic and sinapinic acids yielded the corresponding unstable neutral phenoxyl radical, as supported by the formation of dimerization products evidenced by HPLC-MS. In the case of caffeic acid, traces of the dimerization product suggest that the neutral phenoxyl radical may competitively undergo dimerization or decomposition of the neutral quinone.Chemical oxidation of HCAs was also followed by ESR spectroscopy: the di-HCAs radical anions were generated and detected, whereas among the mono-HCAs only the phenoxyl radical of the sinapinic acid was recorded.     

Autoxidation of cod liver oil with tocopherol and ascorbyl palmitate

Cod liver oil (CLO) with no added antioxidants (REF), 200 mg/kg ascorbyl palmitate (AP), and/or 800 mg/kg tocopherol concentrate (TOH) were stored in sealed bottles with a small headspace of air at 25°C in the dark. A binary mix of TOH +AP affected the sensory perception of CLO by leading to a more grass/cucumber-like and less herring oil-like impression, whereas TOH alone had no effect. This was caused by the different influence of the antioxidants with regard to formation of volatile oxidation products. TOH+AP promoted formation of, e.g., hexanal, 2-hexenal, and 2,6-nonadienal and inhibited formation of, e.g., 2,4-heptadienal. TOH affected the proportions of trans, cis-and trans,trans-2,4-heptadienal that were formed and inhibited formation of, e.g., 1-penten-3-ol, whereas formation of acetic acid and some other volatiles was inhibited by both antioxidants. The total amount of volatiles increased during the experiment, and with REF were significantly higher (P<0.05) than with TOH. The PV increased during the first 2 wk of storage. PV levels were in the order of TOH>REF>TOH+AP. The observed effects could partly be explained by hydrogen donation from TOH to peroxyl radicals, but the mode of action for AP was unclear.     

Kinetics of lipid oxidation in the presence of cinnamic acid derivatives

The effects of seven (prenyl‐ and methoxy‐) derivatives of cinnamic acid (0.1 mM) on the kinetics of lipid (sunflower oil triacylglycerols, TGSO) bulk phase oxidation at 80 °C have been compared. Synthesis of prenyl cinnamic acid derivatives: 3‐prenyl‐4‐hydroxy‐cinnamic acid (PHC), 3,5‐diprenyl‐4‐hydroxy‐cinnamic acid (DPHC), 2,2‐di‐methyl‐6‐carboxy‐ethenyl‐2H‐benzopyran (DMCB), 2,2‐dimethyl‐6‐carboxy‐ethenyl‐8‐prenyl‐2H‐benzopyran (DCEPB) present in Brazilian propolis has been performed. The monoprenyl derivative (PHC) has been found to exert a higher antioxidant activity as compared to the diprenyl derivative (DPHC). However, cinnamic acid derivatives DMCB and DCEPB have caused no change in the kinetics of TGSO oxidation. The results obtained have been compared with those on related compounds containing a cinnamic acid moiety as a structural feature, such as 4‐hydroxy‐cinnamic (p‐coumaric), 3‐methoxy‐4‐hydroxy‐cinnamic (ferulic) and 3,5‐dimethoxy‐4‐hydroxy‐cinnamic (sinapic) acids, as well as with data on butylated hydroxytoluene (BHT) and α‐tocopherol (αToc). PHC has shown a stronger antioxidant efficiency than BHT, p‐coumaric and ferulic acid, but a weaker antioxidant efficiency than α‐Toc and sinapic acid. The observed antioxidant effect of DPHC was stronger than that of p‐coumaric and ferulic acids and weaker than that of α‐Toc, BHT and sinapic acid.     

Flavonoids as stabilizers of fish oil: An alternative to synthetic antioxidants

The antioxidant activities against fish oil oxidation of six commercially available flavonoids and of five flavonoids purified from two Chilean native plants were compared to those ofdl-α-tocopherol and of two synthetic antioxidants, butylated hydroxytoluene and butylated hydroxyanisole. Among the commercial flavonoids, catechin, morin and quercetin showed a higher activity when fish oil oxidation (either spontaneous or Fe²⁺-induced) was assessed from the formation of peroxides or thiobarbituric acid-reactive substances. Among the native flavonoids, the 5,3′,4′-trihydroxy-7-methoxy flavanone (designated as Pt-2) showed the highest antioxidant activity. Mixtures of quercetin or of Pt-2 withdl-α-tocopherol produced better inhibitory effects when compared to that of each substance assayed by itself. Also, when Pt-2 and quercetin were assayed in combination (0.3 g/kg oil and 0.7 g/kg oil, respectively), a synergistic antioxidant effect was observed. Results indicate that several flavonoids could be used as natural antioxidants as a means to replace those synthetic antioxidants, the use of which has been questioned.     

Impact of antioxidant additives on the oxidation stability of biodiesel produced from Croton Megalocarpus oil

The increase in crude petroleum prices, limited resources of fossil fuels and environmental concerns have led to the search of alternative fuels, which promise a harmonious correlation with sustainable development, energy conservation, efficiency and environmental preservation. Biodiesel is well positioned to replace petroleum-based diesel. Biodiesel is a non-toxic, biodegradable and renewable biofuel. But the outstanding technical problem with biodiesel is that, it is more susceptible to oxidation owing to its exposure to oxygen present in the air and high temperature. This happens mainly due to the presence of varying numbers of double bonds in the free fatty acid molecules. This study evaluates oxidation stability of biodiesel produced from Croton megalocarpus oil. Thermal and Oxidation stability of Croton Oil Methyl Ester (COME) were determined by Rancimat and Thermogravimetry Analysis methods respectively. It was found that oxidation stability of COME did not meet the specifications of EN 14214 (6 h). This study also investigated the effectiveness of three antioxidants: 1,2,3 tri-hydroxy benzene (Pyrogallol, PY), 3,4,5-tri hydroxy benzoic acid (Propyl Gallate, PG) and 2-tert butyl-4-methoxy phenol (Butylated Hydroxyanisole, BHA) on oxidation stability of COME. The result showed that the effectiveness of these antioxidants was in the order of PY > PG > BHA.     

Are natural antioxidants better – and safer – than synthetic antioxidants?

Antioxidants are necessary in the Western diet as it is rich in polyenoic fatty acids, which are easily oxidized with formation of free radicals that are harmful if present in higher amounts. Consumers prefer natural antioxidants to synthetic antioxidants, mainly for emotional reasons. The common Western daily diet contains about 1 g natural antioxidants even if no natural antioxidants have been added for lipid stabilization. Their main sources are cereals, fruits, vegetables, and beverages. Only a part of the natural antioxidants is absorbed and used as free‐radical scavengers in vivo. Natural antioxidants should be added to food in larger amounts than synthetic antioxidants as they are less active, but the actual activity depends very much on particular conditions and food composition. Nevertheless, the addition of additional antioxidants is still negligible in comparison with the dietary supply of native antioxidants. The safety limits of natural antioxidants are mostly not known, but they are hardly safer than synthetic antioxidants. The best protection would be to replace high‐polyenoic oils in the diet with high‐oleic oils, and to use alternative methods of food protection against autoxidation.     

枞酸氧化反应及其抗氧剂的研究

采用紫外分光光度分析方法研究了枞酸在聚乙烯膜上的氧化反应,考察了MBP,FMH,DBH,DSB3,DSB65种抗氧剂对枞酸氧化反应的影响,提出了用抗氧化值AO考核抗氧剂的抗氧化能力。实验结果表明,枞酸氧化反应动力学在初期阶段呈表观一级,后期受氧化膜影响不呈表观一级。当反应温度为35,40,45,50,55℃时,5种抗氧剂都表现出不同程度的抗氧化能力,其中MBP,DBH,DSB6抗氧剂的抗氧化能力显著,在35℃下其抗氧化值AO分别是109.92,50.93,209.84。     

Influence of oxygen and copper concentration on lipid oxidation in rapeseed oil

The influence of oxygen concentration and copper on lipid oxidation in rapeseed oil during storage at 40°C was investigated. The oil was stored in air, or with 1.1%, 0.17%, or 0.04% oxygen in the headspace, and 70 or 0.07 ppm copper was added. Volatile oxidation products and oxygen consumption were monitored. Addition of 70 ppm copper to the sample in air resulted in a 70-fold higher hexanal concentration after 35 d of storage, compared to the sample without added copper. The addition of 0.07 ppm copper to the sample stored in air gave a doubled hexanal concentration, compared to the sample without copper, after 35 d of storage. For the samples with 70 ppm copper at 0.17% and 0.04% oxygen, all oxygen was consumed after 7 d of storage. The results show the importance of minimizing the oxygen available for oxidation, especially when pro-oxidants are present. In the sample with 70 ppm added copper, in air, the hexanal increase was 65 times larger than for the same sample in 0.04% oxygen. A comparison of the effect of oxygen or copper on oxidation shows that the addition of 70 ppm copper to the 0.04% oxygen sample gave the same increase in hexanal content as an oxygen increase to 0.17%.     

Effects of natural antioxidants on iron-catalyzed lipid oxidation of structured lipid-based emulsions

The effects of iron, pH, and natural antioxidants (α-tocopherol, gallic acid, and quercetin) on oxidation of structured lipid-based emulsions were evaluated. Ten percent oil-in-water emulsions were formulated with a canola oil/caprylic acid structured lipid and stabilized with 0.5% whey protein isolate. The PV, anisidine values, and Totox values of emulsions stored at 50°C were measured over a 15-d period. Iron significantly (P<0.05) increased lipid oxidation rates compared to control emulsions. Greater iron-catalyzed lipid oxidation occurred in the pH 3.0 emulsions compared to their pH 7.0 counterparts. Quercetin and gallic acid exhibited significant (P<0.05) prooxidant effects on total oxidation in the pH 3.0 emulsions. Emulsions at pH 7.0 were relatively stable to oxidation throughout the storage period. Because of the ability of some of these natural antioxidants to exhibit prooxidant activity, care should be exercised when adding them to food systems containing transition metals.     

The supramolecular chemistry of lipid oxidation and antioxidation in bulk oils

The microenvironment formed by surface active compounds is being recognized as the active site of lipid oxidation. Trace amounts of water occupy the core of micro micelles and several amphiphilic minor components (e.g., phospholipids, monoacylglycerols, free fatty acids, etc.) act as surfactants and affect lipid oxidation in a complex fashion dependent on the structure and stability of the microemulsions in a continuous lipid phase such as bulk oil. The structures of the triacylglycerols and other lipid‐soluble molecules affect their organization and play important roles during the course of the oxidation reactions. Antioxidant head groups, variably located near the water‐oil colloidal interfaces, trap and scavenge radicals according to their location and concentration. According to this scenario, antioxidants inhibit lipid oxidation not only by scavenging radicals via hydrogen donation but also by physically stabilizing the micelles at the microenvironments of the reaction sites. There is a cut‐off effect (optimum value) governing the inhibitory effects of antioxidants depending inter alias on their hydrophilic/lipophilic balance and their concentrations. These complex effects, previously considered as paradoxes in antioxidants research, are now better explained by the supramolecular chemistry of lipid oxidation and antioxidants, which is discussed in this review. The evolution of micellar size and number during and after the induction period of lipid oxidation. Amphiphilic compounds, including lipid hydroperoxides, contribute to micelle formation and act as prooxidants. Antioxidants and retarders stabilize micelles and prevent their breakdown.