Decomposition Of Lipid Hydroperoxides Research Articles

Impact of Nonthermal Plasma Treatment on the Oxidation of Lipids with Different Unsaturation Degrees.

Nonthermal plasma (NTP) treatment of food presents a new technology for the industry but raises concerns about lipid oxidation due to the presence of reactive species. Considering the critical role of the degree of unsaturation in lipid oxidation, this study investigates NTP-induced oxidation across various unsaturated lipids. These lipids are six oil samples primarily containing one of the following methylesters: oleate, linoleate, linolenate, arachidonate, eicosapentaenoate, and docosahexaenoate. Samples were treated with a nonthermal surface dielectric barrier discharge. Plasma-induced effects were first examined by classical lipid oxidation indicators, such as the peroxide value and p-anisidine value. The specific volatile oxidation products, including hexanal, nonanal, trans-2-hexenal, and methyl 9-oxononanoate, were determined to further elucidate the impact of ozone-related oxidation. Monitoring the production of selected nonvolatile oxidation products, such as epoxy-, oxo-, and hydroxy fatty acid methylesters, confirmed that plasma treatment facilitated the decomposition of lipid hydroperoxide. Generally, the level of plasma-induced oxidation increased in parallel with the unsaturation degree of the studied samples, except for the quantity of individual volatile carbonyls. The long-term effect of NTP treatment was investigated by a stability test, revealing that the oxidative stability depended on the input gas of plasma treatment, the sensitivity of the treated sample, and the presence of antioxidants. Except for the focus on the NTP impact, this study offered a case study of a comprehensive investigation into lipid oxidation.

Relationship between PAH4 formation and thermal reaction products in model lipids and possible pathways of PAHs formation

Lipids are closely related to the generation of PAHs during food thermal processing. During heating, lipids mainly triglycerides undergo hydrolysis, oxidation and decomposition. The relationship between the various products and the formation of PAHs is still unclear. This paper investigated the effect of different lipid standards on PAH4 production, and explored their thermal stability and reaction products to delve into nature of the differences in PAH4 production. Fatty acids were more prone to generate PAH4 than glycerides. The higher the degree of esterification of glycerides, the higher its thermal stability and the lower the content of PAH4 generated, implying that hydrolysis of glycerides promoted the generation of PAH4. In addition, there was a positive correlation between unsaturation in lipids and the PAH4 production. After heat treatment, hydroperoxides, unsaturated fatty alcohols and aldehydes, alkenes and aromatic substances were abundant in oleic acid and linoleic acid which produced the most PAH4. Thermal decomposition of lipid hydroperoxides was the pathway for the generation of conjugated hydrocarbon radicals, alcohols, aldehydes, and alkenes. The intramolecular cyclization and Diels-Alder reaction acted as ring-forming reactions, with consequent dehydrogenation, decarboxylation, side-chain breaks and radical reorganization, ultimately facilitating the amplification of the aromatic rings and the formation of PAHs.

Elucidation of decomposition pathways of linoleic acid hydroperoxide isomers by GC-MS and LC-MS/MS.

Food lipid oxidation provides various volatile compounds involved in food flavor via the decomposition of lipid hydroperoxide (LOOH). This study predicted the pathways which can coherently explain LOOH decomposition focusing on hydroperoxy octadecadienoic acid (HpODE) isomers (9-EZ-HpODE, 9-EE-HpODE, 10-HpODE, 12-HpODE, 13-ZE-HpODE, and 13-EE-HpODE) which are the major LOOH contained in edible oils. Each standard was first prepared and thermally decomposed. Generated volatile and non-volatile compounds were analyzed by GC-MS and LC-MS/MS. The results showed that all HpODE decomposition was based on the factors such as favorable scission, radical delocalization, and cyclization. Interestingly, the formation of 8-HpODE and 14-HpODE were demonstrated during HpODE decomposition. The insights obtained in this study would explain the generation pathways of flavor involved in food quality.

Biochemical attributes of fry-breaded pangagius (Pangasianodon hypophthalmus) steak during frozen storage

Pangasius (Pangasianodon hypophthalmus) is one kind of fresh water endemic to the waters of Mekong basin in South-East Asia. There is great demand for fish based products especially value added products. Breading is considered a protection against moisture and natural concentrate losses as it contrasts to effect of freezing. Fry-battered and breaded coating improved texture and flavour, reduced moisture loss and oil absorption. Total volatile base nitrogen (TVB-N) is often used as an indicator for seafood quality and deterioration. Thiobarbituric acid (TBA) is used as an indicator to determine the decomposition of lipid hydroperoxides formed during lipid oxidation. In our research, we examined the changes of biochemical attributes of fry-breaded pangagius steak by frying in soybean oil at 165°C for 30 sec and freezing at -18°C for 6 months. Our results revealed that pH decreased gradually in the first 2 months however it increased from the 3 to 6 months of frozen storage. There were significant changes of TVB-N and TBA values in fry-breaded Pangasius steaks preserved at -18°C for 6 months. Fortunately they all were within the acceptable limits.

Kinetics of oxidation of iron(II) ions with lipid hydroperoxides

AbstractOne of the pathways for excessive production of free radicals is the decomposition of lipid hydroperoxides catalyzed by iron. A number of hydroperoxides of unsaturated fatty acids (LOOH), some prepared in our laboratory and others extracted from biological materials, were used to determine the rate constants of Fe2+ oxidation by measuring the formation rate of Fe3+ ions in the presence of simple unidentate ligands, chloride, and thiocyanate as the [FeCl]2+ and [FeNCS]2+ complexes, in a deoxygenated dichloromethane:methanol (2:1, v/v) mixture. The rates of Fe2+ oxidation with prepared LOOHs via the [FeNCS]2+ complex were approximately the same‐the average second‐order reaction rate constant was 1390 ± 340 dm3 mol−1 s−1; the rate constants of LOOHs from different biological materials were in the same range. The rates measured as the [FeNCS]2+ complex were somewhat higher than the rates measured as the [FeCl]2+ complex, indicating that ligands could interact in the transition state, thus affecting the disruption of the intermediate complex. Since there were no significant differences in the activation thermodynamic parameters for reactions within the reaction series of studied hydroperoxides, it was assumed that the oxidation proceeded by an inner sphere mechanism, considering that the breakdown of the successor inner sphere complex with the homolytic cleavage of peroxide bonds of hydroperoxides forming reactive alkoxyl radicals was the rate‐limiting step. Based on this research, an indirect spectrophotometric method for quantitative determination of LOOH was reestimated. The microprocedure proposed for the lipid hydroperoxide assay could be applied to follow the early stages of lipid peroxidation processes in real biological samples.

Structure-Activity Relationship (SAR) of Phenolics for the Inhibition of 2-Phenylethylamine Formation in Model Systems Involving Phenylalanine and the 13-Hydroperoxide of Linoleic Acid.

Lipid hydroperoxides have been shown to produce amino acid decarboxylations. Because thermal decomposition of lipid hydroperoxides produces free radicals and reactive carbonyls, and phenolic compounds have been shown to scavenger both of them, phenolics are expected to inhibit these reactions and this protection should depend on the structures of the involved phenolics. In this study, the effect of a wide array of phenolics and their mixtures on 2-phenylethylamine formation by phenylalanine degradation in the presence of the 13-hydroperoxide of linoleic acid (LOOH) was studied. LOOH increased considerably the formation of the amine, and phenolics mostly exhibiting an inhibitory role that depended on their structure. Thus, 1,3-diphenols decreased the formation of 2-phenylethylamine because of their carbonyl trapping abilities. In contrast, the inhibition of 1,2- and 1,4-diphenols was lower because they could not trap the reactive carbonyls produced by LOOH decomposition. In addition, their free radical scavenging was likely accompanied by the formation of quinones, which acted as reactive carbonyls. The function of all other phenolics could be calculated by adding the individual functions of the different diphenols present in their structures. In fact, experimental values obtained for both mixtures of phenolics and complex phenolics correlated well with the calculated values obtained from their constituting diphenols. All of these results suggest that, when the reaction mechanisms are known, it is possible to predict the behavior of complex phenolics on the basis of their structure.

Lipid hydroperoxide decomposition in model emulsions stabilized with emulsifiers having various sizes of hydrophilic heads.

The vulnerability of oils in emulsions to oxidation depends on the structural and physicochemical properties of oil droplet interface. To evaluate the implications of the interfacial characteristics of emulsion droplets on lipid oxidation, particularly lipid hydroperoxide decomposition, emulsions were prepared using emulsifiers with various lengths of polar groups because the length of hydrophilic heads of emulsifiers could be an important factor in determining the thickness of the droplet surface. The decomposition rate constants of cumene hydroperoxide in emulsions showed that the cumene hydroperoxide in emulsions having a thick emulsion droplet interface was decomposed faster than in emulsions having a loosen one. Our findings also showed that the denseness of the droplet interface affected cumene hydroperoxide decomposition in emulsions. Conclusively, this study suggested that the interfacial thickness and denseness of the emulsion droplets influence oxidative stability of emulsions.

GPx4 is the controller of a specific form of programmed cell death executed by lipid peroxidation products

The recent identification of a routine of non-apoptotic controlled cell death recapitulates in a physiological perspective the long history of oxygen toxicity and lipid peroxidation. Due to the critical role of iron, this form of controlled non-apoptotic cell death had been named ferroptosis1. Ferroptosis executes cell death in major neurodegenerative diseases and ischemia-reoxygenation and accounts for of cytotoxicity of drug candidates for cancer treatment2. Moreover, evidence on embryo development indicates that ferroptosis is also involved in tissue homeostasis3. What we know is that oxygen, phospholipids containing ω-6 fatty acids, iron and a lipoxygenase active on membrane lipids are required. We also know that ferroptosis can only be executed by inactivation the selenoperoxidase GPx44. The reduction to hydroperoxy derivatives of lipid hydroperoxides inserted in membranes is, indeed, the critical anti-peroxidant reaction5. Seemingly, in the emerging scenario, oxygen metabolically activated in mitochondria, slowly but continuously generates species competent for free radical oxidation of a polyunsaturated fatty acid, evolving into a lipid hydroperoxide. This activates a lipoxygenase active on membrane lipids to produce more hydroperoxides. By decomposition of lipid hydroperoxides, iron propagates chain reactions and generates the electrophiles (aldehydes?) alleged executing cell death. All these events can only, take place when the reaction of GPx4 becomes limiting. The mechanism of GPx4 reaction has been analyzed up to quantum-mechanical level and calculated structures have been corroborated by MS6. The interaction of GPx4 with membrane phospholipid has been elucidated by Surface Plasmon Resonance (SPR), supported by molecular dynamics (MD) analysis. We know now how GPx4 works on membranes. A strong electrostatic interaction takes place between specific amino acid residues in the cationic area on the surface of GPx4 and polar head of phospholipids. This binding drives the orientation of the hydroperoxidic group flipping out of the membrane to precisely interact with the redox center of the enzyme7. Redox catalysis is operated by proton tunneling leading to the formation of a charge-separated species6. Interaction of the oxidized selenium with two GSH molecules reacting in sequence lessens the interaction with polar head of phospholipids and permits the “surfing” of the enzyme on the membrane surface to catch and reduce lipid hydroperoxides7. In conclusion, metabolism of oxygen in mitochondria provides metabolic energy but can also kill the cells when not sufficiently protected by GPx4 and GSH. About the mechanisms of induction of ferroptosis under physiological conditions we know that GSH concentration can be controlled by the efficiency of the import of cystine for the synthesis of GSH. What is still largely unknown, instead, is how expression/activity of GPx4 could be controlled under physiological conditions.

The Cytotoxic Action of Cytochrome C/Cardiolipin Nanocomplex (Cyt-CL) on Cancer Cells in Culture.

The effect of existing anti-cancer therapies is based mainly on the stimulation of apoptosis in cancer cells. Here, we have demonstrated the ability of a catalytically-reactive nanoparticle-based complex of cytochrome c with cardiolipin (Cyt-CL) to induce the apoptosis and killing of cancer cells in a monolayer cell culture. Cyt-CL nanoparticles were prepared by complexing CytC with different molar excesses of CL. Following characterization, cytotoxicity and apoptosis inducing effects of nanoparticles were investigated. In an attempt to identify the anticancer activity mechanism of Cyt-CL, pseudo-lipoxygenase and lipoperoxidase reaction kinetics were measured by chemiluminescence. Using chemiluminescence, we have demonstrated that the Cyt-CL complex produces lipoperoxide radicals in two reactions: by decomposition of lipid hydroperoxides, and by lipid peroxidation under the action of H2O2. Antioxidants inhibited the formation of lipid radicals. Cyt-CL nanoparticles, but not the CytC alone, dramatically enhanced the level of apoptosis and cell death in two cell lines: drug-sensitive (A2780) and doxorubicin-resistant (A2780-Adr). The proposed mechanism of the cytotoxic action of Cyt-CL involves either penetration through the cytoplasm and outer mitochondrial membrane and catalysis of lipid peroxidation reactions at the inner mitochondrial membrane, or/and activation of lipid peroxidation within the cytoplasmic membrane. Here we propose a new type of anticancer nano-formulation, with an action based on the catalytic action of Cyt-CL nanoparticles on the cell membrane and and/or mitochondrial membranes that results in lipid peroxidation reactions, which give rise to activation of apoptosis in cancer cells, including multidrug resistant cells.

Mechanism of Metal-independent Decomposition of Lipid Hydroperoxide by Halogenated Quinoid Carcinogens

Mechanism of Metal-independent Decomposition of Lipid Hydroperoxide by Halogenated Quinoid Carcinogens

Formation of oligomeric alkenylperoxides during the oxidation of unsaturated fatty acids: an electrospray ionization tandem mass spectrometry study

This study reports the identification of oligomeric alkenylperoxides by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (ESI-MS(2)), during the oxidation of oleic, linoleic and linolenic acids with Fenton's (Fe(2+)/H(2)O(2)) and Fe(2+)/O(2) systems. The reactions were followed by ferrous oxidation-xylenol orange method together with GC-MS and GC-FID, allowing to observe that both oxidation systems are different in terms of hydroperoxide evolution, probably due to the presence of different intermediate reactive species: perferryl ion and OH(·) radical responsible for the decomposition of lipid hydroperoxides and formation of new compounds. The analysis of ESI-MS in the negative mode, obtained after oxidation of each fatty acid, confirmed the presence of the monomeric oxidation products together with other compounds at high mass region above m/z 550. These new ions were attributed to oligomeric structures, identified by the fragmentation pathways observed in the tandem mass spectra.

Metal-independent Decomposition of Lipid Hydroperoxide (13-HPODE) and Formation of 4Hydroxy-2-Nonenal (4-HNE) by the Carcinogenic Halogenated Quinones

Metal-independent Decomposition of Lipid Hydroperoxide (13-HPODE) and Formation of 4Hydroxy-2-Nonenal (4-HNE) by the Carcinogenic Halogenated Quinones

5-Lipoxygenase-mediated Endogenous DNA Damage

Lipoxygenases (LOs) convert polyunsaturated fatty acids into lipid hydroperoxides. Homolytic decomposition of lipid hydroperoxides gives rise to endogenous genotoxins such as 4-oxo-2(E)-nonenal, which cause the formation of mutagenic DNA adducts. Chiral lipidomics analysis was employed to show that a 5-LO-derived lipid hydroperoxide was responsible for endogenous DNA-adduct formation. The study employed human lymphoblastoid CESS cells, which expressed both 5-LO and the required 5-LO-activating protein (FLAP). The major lipid peroxidation product was 5(S)-hydroperoxy-6,8,11,14-(E,Z,Z,Z)-eicosatetraenoic acid, which was analyzed as its reduction product, 5(S)-hydroxy-6,8,11,14-(E,Z,Z,Z)-eicosatetraenoic acid (5(S)-HETE)). Concentrations of 5(S)-HETE increased from 0.07 ± 0.01 to 45.50 ± 4.05 pmol/107 cells upon stimulation of the CESS cells with calcium ionophore A23187. There was a concomitant increase in the 4-oxo-2(E)-nonenal-derived DNA-adduct, heptanone-etheno-2′-deoxyguanosine (HϵdGuo) from 2.41 ± 0.35 to 6.31 ± 0.73 adducts/107 normal bases. Biosynthesis of prostaglandins, 11(R)-hydroxy-5,8,12,14-(Z,Z,E,Z)-eicosatetraenoic acid, and 15(R,S)-hydroxy-5,8,11,13-(Z,Z,Z,E)-eicosatetraenoic acid revealed that there was cyclooxygenase (COX) activity in the CESS cells. Western blot analysis revealed that COX-1 was expressed by the cells, but there was no COX-2 or 15-LO-1. FLAP inhibitor reduced HϵdGuo-adducts and 5(S)-HETE to basal levels. In contrast, aspirin, which had no effect on 5(S)-HETE, blocked the formation of prostaglandins, 15-HETE, and 11-HETE but did not inhibit HϵdGuo-adduct formation. These data showed that 5-LO was the enzyme responsible for the generation of the HϵdGuo DNA-adduct in CESS cells.

The Effect of Regular Exercise Training on Serum Level of Malondialdehyde

Background and objective: Poly unsaturated fatty acids(PUFAs ) that contain two or more double bonds are particularly susceptible to oxidation by free radicals and other highly reactive species. Malondialdehyde( MDA) is one of many low molecular weight endproducts of lipid hydroperoxide decomposition and is the most often measured as an index of lipid peroxidation. The aim of the present study was to measure the serum level of MDA in healthy non athletics and athletics. Methods : This study was carried out during the period from April 2007 to September 2007 on 53 healthy non athletics (27 males and 26 females), and 31 healthy athletics (16 males and 15 females). Serum MDA level was measured colorimetrically using thiobarbituric acid method . Results: The mean value of serum MDA was significantly higher in healthy athletics than that of healthy non athletics (p<0.05). The mean value of serum MDA in females was non significantly higher than that of males (p>0.05) in both groups . The mean value of serum MDA was significantly higher in healthy non athletic smokers than that of non smokers (p<0.001) . Conclusion: Based on the findings of the present study , it can be concluded that regular exercise training causes excess lipid peroxidation and generation of significant amounts of MDA, one of the most important harmful free radicals .Therefore athletics should take a diet rich in antioxidants or appropriate amount of antioxidant vitamins ( A, C,and E) .

Profiles of volatile compounds in milk containing fish oil analyzed by HS‐SPME‐GC/MS

AbstractLong‐chain polyunsaturated fatty acids (LC‐PUFA) have various positive biological effects. Fish oil represents a major source of LC‐PUFA; therefore it is extensively used to enrich food products as, for example, infant formulae, dairy products and fruit juices. However, in the presence of oxygen and metals, LC‐PUFA readily degrade, producing off‐flavors and decreasing the nutritional value of the product. The deterioration of sensory properties (taste and odor) can be easily perceived by the consumer, due to the formation of volatile compounds that are formed by decomposition of lipid hydroperoxides, also known as primary oxidation products. In this study, we used the headspace solid‐phase microextraction‐gas chromatography/mass spectrometry technique (HS‐SPME‐GC/MS) to characterize and quantify volatile compounds in a food matrix supplemented with fish oil. We demonstrated that the HS‐SPME‐GC/MS method is a valuable tool to monitor lipid oxidation at early stages. We identified t‐2‐hexenal and c‐4‐heptenal as possible oxidation markers during the storage of milk enriched with 5% of cod oil.

명태건조방법에 따른 갈변화 관련 물질의 변화

건조된 명태들은 전반적으로 다가불포화지방산이 감소하고 단일불포화지방산은 증가하는 경향을 보였다. 특히 주기적인 자연냉동과 해동을 반복하면서 건조된 명태(미숙성황태)를 장기간 숙성하여 완성한 황태의 지방산 조성은 북어나 미숙성황태와 비교해 볼 때, 원료시료(명태)간의 차이를 감안하더라도 특징적인 차이를 보였다. 총 유리아미노산 함량도 황태가 북어나 미숙성황태보다 낮게 나타나 불포화지방산과 유리아미노산의 반응에 의한 점진적인 갈변화 현상을 설명해 주는 것으로 판단된다. 황태의 수용성 갈변물질은 주로 숙성단계에서 많이 형성되는 것으로 추정되었다.

Mechanism of the antioxidant to pro-oxidant switch in the behavior of dehydroascorbate during LDL oxidation by copper(II) ions

Oxidised low density lipoprotein (LDL) may be involved in the pathogenesis of atherosclerosis. We have therefore investigated the mechanisms underlying the antioxidant/pro-oxidant behavior of dehydroascorbate, the oxidation product of ascorbic acid, toward LDL incubated with Cu 2+ ions. By monitoring lipid peroxidation through the formation of conjugated dienes and lipid hydroperoxides, we show that the pro-oxidant activity of dehydroascorbate is critically dependent on the presence of lipid hydroperoxides, which accumulate during the early stages of oxidation. Using electron paramagnetic resonance spectroscopy, we show that dehydroascorbate amplifies the generation of alkoxyl radicals during the interaction of copper ions with the model alkyl hydroperoxide, tert-butylhydroperoxide. Under continuous-flow conditions, a prominent doublet signal was detected, which we attribute to both the erythroascorbate and ascorbate free radicals. On this basis, we propose that the pro-oxidant activity of dehydroascorbate toward LDL is due to its known spontaneous interconversion to erythroascorbate and ascorbate, which reduce Cu 2+ to Cu + and thereby promote the decomposition of lipid hydroperoxides. Various mechanisms, including copper chelation and Cu + oxidation, are suggested to underlie the antioxidant behavior of dehydroascorbate in LDL that is essentially free of lipid hydroperoxides.

Biological hydroperoxides and singlet molecular oxygen generation

The decomposition of lipid hydroperoxides (LOOH) into peroxyl radicals is a potential source of singlet molecular oxygen ((1)O(2)) in biological systems. Recently, we have clearly demonstrated the generation of (1)O(2) in the reaction of lipid hydroperoxides with biologically important oxidants such as metal ions, peroxynitrite and hypochlorous acid. The approach used to unequivocally demonstrate the generation of (1)O(2) in these reactions was the use of an isotopic labeled hydroperoxide, the (18)O-labeled linoleic acid hydroperoxide, the detection of labeled compounds by HPLC coupled to tandem mass spectrometry (HPLC-MS/MS) and the direct spectroscopic detection and characterization of (1)O(2) light emission. Using this approach we have observed the formation of (18)O-labeled (1)O(2) by chemical trapping of (1)O(2) with anthracene derivatives and detection of the corresponding labeled endoperoxide by HPLC-MS/MS. The generation of (1)O(2) was also demonstrated by direct spectral characterization of (1)O(2) monomol light emission in the near-infrared region (lambda = 1270 nm). In summary, our studies demonstrated that LOOH can originate (1)O(2). The experimental evidences indicate that (1)O(2) is generated at a yield close to 10% by the Russell mechanism, where a linear tetraoxide intermediate is formed in the combination of two peroxyl radicals. In addition to LOOH, other biological hydroperoxides, including hydroperoxides formed in proteins and nucleic acids, may also participate in reactions leading to the generation (1)O(2). This hypothesis is currently being investigated in our laboratory.

Lipid Oxidation in a Menhaden Oil-in-Water Emulsion Stabilized by Sodium Caseinate Cross-Linked with Transglutaminase

Transglutaminase-catalyzed cross-linking of interfacial proteins in oil-in-water has been shown to influence physical stability, but little is known about how this reaction impacts lipid oxidation. Therefore, this study evaluated the influence of transglutaminase-induced interfacial protein cross-linking on the oxidative stability of casein-stabilized menhaden oil-in-water emulsions. Interfacial casein in menhaden oil-in-water emulsions cross-linked by transglutaminase (pH 7.0) produced a cohesive interfacial protein layer that could not be removed from the emulsion droplet by Tween 20. Although transglutaminase cross-linked the interfacial casein, these emulsions did not show increased oxidative stability when compared to untreated emulsions as determined by measurement of lipid hydroperoxides and thiobarbituric acid reactive substances. These results indicate that increasing the cohesiveness of proteins at the interface of oil-in-water emulsions does not inhibit lipid oxidation. This could be due to the ability of prooxidative species such as iron to diffuse through the cross-linked protein layer where it could promote the decomposition of lipid hydroperoxides into free radicals that could oxidize unsaturated fatty acids in the emulsion droplet core.

Role of Proteins in Oil-in-Water Emulsions on the Stability of Lipid Hydroperoxides

The purpose of this research was to better understand the mechanisms by which proteins affect the rates of lipid oxidation in order to develop protein-stabilized emulsion delivery systems with maximal oxidative stability. This study evaluated the affect of pH and emulsifier concentration on the stability of cumene hydroperoxide in hexadecane-in-water emulsions stabilized by beta-lactoglobulin (beta-Lg). Emulsions prepared with 0.2 wt % beta-Lg (at pH 7.0) showed a 26.9% decrease in hydroperoxide concentrations 5 min after 0.25 mM ferrous ion was added to the emulsion. EDTA, but not continuous phase beta-Lg, could inhibit iron-promoted lipid hydroperoxide decomposition. Lipid hydroperoxides were more stable to iron-promoted degradation at pH values below the pI of beta-Lg, where the emulsion droplet would be cationic and thus able to repel iron away from the lipid hydroperoxides. Heating the beta-Lg-stabilized emulsions to produce a cohesive protein layer on the emulsion droplet surface did not alter the ability of iron to decompose lipid hydroperoxides. These results suggest that proteins at the interface of emulsion droplets primarily stabilize lipid hydroperoxides by electrostatically inhibiting iron-hydroperoxide interactions.