Formation Of Lipid Hydroperoxides Research Articles

Critical kinetic parameters and rate constants representing lipid peroxidation as affected by temperature

This study aimed to comparatively investigate the temperature effect on the kinetic parameters and rate constants representing lipid hydroperoxides (LOOH) formation and decomposition during initiation and propagation peroxidations. The initiation phase was characterized by induction period IP, overall initiation rate constant kIP, initiation oxidizability Oi, and the critical reverse micelle concentration of LOOH, CMCL. The propagation phase was characterized by its duration tp, the maximum rate of LOOH accumulation Rmax, maximum LOOH concentration [LOOH]max, propagation oxidizability Rn, composite rate constant kc, and LOOH decomposition rate constant kd. Oi and Rn indicated relatively high dependencies on temperature, respectively. Among the rate constants, kd better highlighted oxidizabilities as affected by temperature. The oxidizabilities had good correspondences with the Arrhenius kinetic (A and Ea) and Eyring thermodynamic (ΔS++ and ΔH++) parameters. The most endergonic reactions (ΔG++>0) were LOOH decompositions, followed by LOOH formations during the propagation and initiation phases, respectively.

Effects of histamine and sodium hypochlorite on prooxidand state in the rats erytrocytes

Abstract We studied the simultaneous influence of histamine and sodium hypochlorite (SH) on lipid peroxidation processes, as well as the level of structural changes in membranes (via the content of sialic acid) in rat erythrocytes. We established that histamine affects lipid peroxidation processes with the formation of lipid hydroperoxides, damages proteins and reduces the content of sialic acids, which leads to changes in the surface charge of red blood cells. However, the simultaneous action of histamine and low SH concentration has a positive effect in that it corrects the pro-oxidant state of erythrocytes. Hence, the content of lipid hydroperoxides, TBA-active products, carbonyl groups of proteins and sialic acids were mainly reduced after the simultaneous action of histamine and SH at all studied concentrations during the rehabilitation period.

Comparing DPPP fluorescence and UV based methods to assess oxidation degree of krill oil-in-water emulsions

In this study, lipid oxidation evaluation methods were compared for a krill-oil-in-water emulsion system. With this aim, thiocyanate and DPPP (diphenyl-1-pyrenylphosphine) fluorescence methods were comparatively examined to determine primary oxidation products. 2-thiobarbituric acid reactive substances (TBARS), hexanal and propanal formation were also monitored as secondary oxidations products. All oxidation experiments were performed via both auto-oxidation at 45 °C and light-riboflavin induced photooxidation at 37 °C. The results have shown that thiocyanate method was not suitable to measure lipid hydroperoxides by the both in auto- and photo-oxidation systems. On the other hand, fluorescence intensity of samples containing the DPPP probe increased during incubation period which indicates the formation of lipid hydroperoxides could be detected via this method. TBARS, hexanal and propanal concentrations also increased during storage period and the formation kinetics of secondary oxidation products was confirmed that the DPPP fluorescence method was accurate and reliable at different environmental conditions.

Deoxynivalenol-induced alterations in the redox status of HepG2 cells: identification of lipid hydroperoxides, the role of Nrf2-Keap1 signaling, and protective effects of zinc.

Deoxynivalenol (DON) is a type B trichothecenes that is widely contaminating human and animal foods, leading to several toxicological implications if ingested. Induction of oxidative stress and production of lipid peroxides were suggested to be the reasons for DON-induced cytotoxicity. However, detailed and comprehensive profiling of DON-related lipid hydroperoxides was not identified. Furthermore, the mechanisms behind DON-induced cytotoxicity and oxidative stress have received less attention. Zinc (Zn) is an essential element that has antioxidant activities; however, the protective effects of Zn against DON-induced adverse effects were not examined. Therefore, this study was undertaken to investigate DON-induced cytotoxicity and oxidative damage to human HepG2 cell lines. Furthermore, a quantitative estimation for the formed lipid hydroperoxides was conducted using LC-MS/MS. In addition, DON-induced transcriptomic changes on the inflammatory markers and antioxidant enzymes were quantitatively examined using qPCR. The protective effects of Zn against DON-induced cytotoxicity and oxidative stress, the formation of lipid hydroperoxides (LPOOH), and antioxidant status in HepG2 cells were investigated. Finally, the effects of DON and Zn on the Nrf2-Keap1 pathway were further explored. The achieved results indicated that DON caused significant cytotoxicity in HepG2 cells accompanied by significant oxidative damage and induction of the inflammatory markers. Identification of DON-related LPOOH revealed the formation of 22 LPOOH species including 14 phosphatidylcholine hydroperoxides, 5 triacylglycerol hydroperoxides, and 3 cholesteryl ester hydroperoxides. DON caused significant downregulation of Nrf2-regulated antioxidant enzymes. Zn administration led to significant protection of HepG2 cells against DON-induced adverse effects, probably via activation of the Nrf2-Keap1 pathway.

Lipid aldehyde hydrophobicity affects apo-SOD1 modification and aggregation

Unsaturated lipids are oxidized by reactive oxygen species and enzymes, leading to the increased formation of lipid hydroperoxides and several electrophilic products. Lipid-derived electrophiles can modify macromolecules, such as proteins, resulting in the loss of function and/or aggregation. The accumulation of Cu,Zn-superoxide dismutase (SOD1) aggregates has been associated with familial cases of amyotrophic lateral sclerosis (ALS). The protein aggregation mechanisms in motor neurons remain unclear, although recent studies have shown that lipids and oxidized lipid derivatives may play roles in this process. Here, we aimed to compare the effects of different lipid aldehydes on the induction of SOD1 modifications and aggregation, in vitro. Human recombinant apo-SOD1 was incubated with 4-hydroxy-2-hexenal (HHE), 4-hydroxy-2-nonenal (HNE), 2-hexen-1-al (HEX), 2,4-nonadienal (NON), 2,4-decadienal (DEC), or secosterol aldehydes (SECO-A or SECO-B). High-molecular-weight apo-SOD1 aggregates dramatically increased in the presence of highly hydrophobic aldehydes (LogPcalc > 3). Notably, several Lys residues were modified by exposure to all aldehydes. The observed modifications were primarily observed on Lys residues located near the dimer interface (K3 and K9) and at the electrostatic loop (K122, K128, and K136). Moreover, HHE and HNE induced extensive apo-SOD1 modifications, by forming Schiff bases or Michael adducts with Lys, His, and Cys residues. However, these aldehydes were unable to induce large protein aggregates. Overall, our data shed light on the importance of lipid aldehyde hydrophobicity on the induction of apo-SOD1 aggregation and identified preferential sites of lipid aldehyde-induced modifications.

Interfacial performance of gallic acid and methyl gallate accompanied by lecithin in inhibiting bulk phase oil peroxidation

From an interfacial phenomena standpoint, gallic acid (GA), methyl gallate (MG), and their combination alone and together with lecithin (L) were evaluated for their inhibition against the formation of lipid hydroperoxides and carbonyl compounds in a stripped sunflower oil. Lecithin at a level (500 ppm) lower than its critical micelle concentration was able to protect the lipid system to some extent. GA (log P = –0.21), which was of higher capacity than MG (log P = – 0.14) in donating H/e− (IC50 = 36.4 vs. 39.9 μM and FRAP value = 598 vs. 514 μmol/L, respectively), exerted an antioxidant activity significantly better than MG in the bulk phase oil. Due to the improved interfacial performance, the inhibitory effect of the antioxidants was remarkably promoted in the presence of lecithin (L/GA/MG > L/GA > L/MG).

Supplementation with omega-3 fatty acids potentiates oxidative stress in human airway epithelial cells exposed to ozone

BackgroundDietary intake of the omega-3 family of polyunsaturated fatty acids (ω-3 FA) is associated with anti-inflammatory effects. However, unsaturated fatty acids are susceptible to oxidation, which produces pro-inflammatory mediators. Ozone (O3) is a tropospheric pollutant that reacts rapidly with unsaturated fatty acids to produce electrophilic and oxidative mediators of inflammation. ObjectiveDetermine whether supplementation with ω-3 FA alters O3-induced oxidative stress in human airway epithelial cells (HAEC). Methods16-HBE cells expressing a genetically encoded sensor of the reduced to oxidized glutathione ratio (GSH/GSSG, EGSH) were supplemented with saturated, monounsaturated, or ω-3 FA prior to exposure to 0, 0.08, 0.1, or 0.3 ppm O3. Lipid peroxidation was measured in cellular lipid extracts and intact cells following O3 exposure. ResultsRelative to cells incubated with the saturated or monounsaturated fatty acids, cells supplemented with ω-3 FA containing 5 or 6 double bonds showed a marked increase in EGSH during exposure to O3 concentrations as low as 0.08 ppm. Consistent with this finding, the concentration of lipid hydroperoxides produced following O3 exposure was significantly elevated in ω-3 FA supplemented cells. DiscussionSupplementation with polyunsaturated ω-3 FA potentiates oxidative responses, as indicated by EGSH, in HAEC exposed to environmentally relevant concentrations of O3. This effect is mediated by the increased formation of lipid hydroperoxides produced by the reaction of O3 with polyunsaturated fatty acids. Given the inflammatory activity of lipid hydroperoxides, these findings have implications for the potential role of ω-3 FA in increasing human susceptibility to the adverse health effects of O3 exposure.

Reactive Sterol Electrophiles: Mechanisms of Formation and Reactions with Proteins and Amino Acid Nucleophiles.

Radical-mediated lipid oxidation and the formation of lipid hydroperoxides has been a focal point in the investigation of a number of human pathologies. Lipid peroxidation has long been linked to the inflammatory response and more recently, has been identified as the central tenet of the oxidative cell death mechanism known as ferroptosis. The formation of lipid electrophile-protein adducts has been associated with many of the disorders that involve perturbations of the cellular redox status, but the identities of adducted proteins and the effects of adduction on protein function are mostly unknown. Both cholesterol and 7-dehydrocholesterol (7-DHC), which is the immediate biosynthetic precursor to cholesterol, are oxidizable by species such as ozone and oxygen-centered free radicals. Product mixtures from radical chain processes are particularly complex, with recent studies having expanded the sets of electrophilic compounds formed. Here, we describe recent developments related to the formation of sterol-derived electrophiles and the adduction of these electrophiles to proteins. A framework for understanding sterol peroxidation mechanisms, which has significantly advanced in recent years, as well as the methods for the study of sterol electrophile-protein adduction, are presented in this review.

Effect of enzymatic degraded polysaccharides from Enteromorpha prolifera on the physical and oxidative stability of fish oil-in-water emulsions

To explore the potential application of enzymatic degraded polysaccharides from Enteromorpha prolifra (EEP) as antioxidant in fish oils, a stable fish oil emulsion system incorporating EEP was established. Effects of emulsifier (Tween 80, gum arabic and lecithin) and EEP concentration on the physical characteristics of fish oil emulsions were investigated. The results indicated that Tween 80 was the best choice, and 1% (w/w) of EEP was the optimum concentration for the preparation of fish oil emulsions. Influence of EEP on the oxidative stability and physical stability of fish oil emulsions was compared with that of antioxidants VE and TBHQ by determining the physical properties, lipid hydroperoxide formation, secondary reaction products formation, pH and long chain polyunsaturated fatty acid content, during storage at 45 °C. The results indicated that the fish oil emulsion system (5% oil, 1% EEP and 1% Tween 80, w/w) possessed good physical and oxidative stabilities.

Understanding neuromuscular disorders in chronic fatigue syndrome.

Muscle failure has been demonstrated in patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Neurophysiological tools demonstrate the existence of both central and peripheral fatigue in these patients. Central fatigue is deduced from the reduced amplitude of myopotentials evoked by transcranial magnetic stimulation of the motor cortex as well as by the muscle response to interpolated twitches during sustained fatiguing efforts. An impaired muscle membrane conduction velocity assessed by the reduced amplitude and lengthened duration of myopotentials evoked by direct muscle stimulation is the defining feature of peripheral fatigue. Some patients with ME/CFS show an increased oxidative stress response to exercise. The formation of lipid hydroperoxides in the sarcolemma, which alters ionic fluxes, could explain the reduction of muscle membrane excitability and potassium outflow often measured in these patients. In patients with ME/CFS, the formation of heat shock proteins (HSPs) is also reduced. Because HSPs protect muscle cells against the deleterious effects of reactive oxygen species, the lack of their production could explain the augmented oxidative stress and the consecutive alterations of myopotentials which could open a way for future treatment of ME/CFS.

Autophagy Modulation for Precision Cancer (immuno)Therapy

Unsaturated lipids are oxidized by reactive oxygen species and enzymes, leading to the increased formation of lipid hydroperoxides and several electrophilic products. Lipid-derived electrophiles can modify macromolecules, such as proteins, resulting in the loss of function and/or aggregation. The accumulation of Cu,Zn-superoxide dismutase (SOD1) aggregates has been associated with familial cases of amyotrophic lateral sclerosis (ALS). The protein aggregation mechanisms in motor neurons remain unclear, although recent studies have shown that lipids and oxidized lipid derivatives may play roles in this process. Here, we aimed to compare the effects of different lipid aldehydes on the induction of SOD1 modifications and aggregation, in vitro. Human recombinant apo-SOD1 was incubated with 4-hydroxy-2-hexenal (HHE), 4-hydroxy-2-nonenal (HNE), 2-hexen-1-al (HEX), 2,4-nonadienal (NON), 2,4-decadienal (DEC), or secosterol aldehydes (SECO-A or SECO-B). High-molecular-weight apo-SOD1 aggregates dramatically increased in the presence of highly hydrophobic aldehydes (LogPcalc > 3). Notably, several Lys residues were modified by exposure to all aldehydes. The observed modifications were primarily observed on Lys residues located near the dimer interface (K3 and K9) and at the electrostatic loop (K122, K128, and K136). Moreover, HHE and HNE induced extensive apo-SOD1 modifications, by forming Schiff bases or Michael adducts with Lys, His, and Cys residues. However, these aldehydes were unable to induce large protein aggregates. Overall, our data shed light on the importance of lipid aldehyde hydrophobicity on the induction of apo-SOD1 aggregation and identified preferential sites of lipid aldehyde-induced modifications.

Effects of partial and complete replacement of added phosphates with encapsulated phosphates on lipid oxidation inhibition in cooked ground meat during storage.

The objective of this research was to investigate the influence of various levels (0.0, 0.1, 0.2, 0.3, 0.4, 0.5%) of added encapsulated polyphosphates (sodium tripolyphosphate; sodium pyrophosphate) combined with unencapsulated polyphosphate to total 0.5% on the inhibition of lipid oxidation in cooked ground meat (beef, chicken) during refrigerated storage (0, 1, 7 d). The use of sodium tripolyphosphate (encapsulated sodium tripolyphosphate, unencapsulated sodium tripolyphosphate) led to lower cooking loss compared to sodium pyrophosphate in both meat species (p < 0.05). Increasing encapsulated sodium tripolyphosphate up to 0.3% decreased cooking loss in ground beef (p < 0.05). Added encapsulated polyphosphate at 0.5% had the same effect on pH as 0.5% unencapsulated polyphosphate in the cooked ground beef and chicken. A higher accumulation of orthophosphate was determined in the samples with sodium tripolyphosphate compared to those with sodium pyrophosphate (p < 0.05). Inclusion of a minimum of 0.1% encapsulated polyphosphate decreased thiobarbituric acid reactive substances and lipid hydroperoxides on 7 d. Increasing encapsulated sodium tripolyphosphate and encapsulated sodium pyrophosphate up to 0.2% in beef decreased thiobarbituric acid reactive substances at 7 d. Addition of 0.4% encapsulated sodium tripolyphosphate and 0.3% encapsulated sodium pyrophosphate in chicken prevented any increase in TBARS during storage. Incorporating encapsulated sodium pyrophosphate at 0.3% inhibited lipid hydroperoxide formation in beef and chicken. The meat industry could achieve enhanced lipid oxidation inhibition by replacing some of the unencapsulated polyphosphate with encapsulated polyphosphate in their product formulations.

Assessment of the Role of Oxidative Stress Indicators and Early Markers of Myocardial Injury and Disfunction in Patients with Lymphoproliferative Diseases

to study dynamics of indicators of oxidative stress and their role in development of cardiotoxicity in patients with lympho-proliferative diseases at the background of polychemotherapy. We included into this study 30 patients with newly detected Non-Hodgkin lymphomas. The control group comprised 15 healthy volunteers. For registration of dynamics of formation of oxygen active forms (OAF), we used highly sensitive chemiluminescence assay. The state of initial stage of lipoperoxidation OAF and radicals of organic compounds) was assessed by dynamics of the leukocyte chemiluminescence. The state of final stage of lipoperoxidation (formation of nonmetabolizing lipid hydroperoxides and other compounds) was assessed by the level of malonic dialdehyde. We also determined indicator of leukocyte chemiluminescence intensity (both basal and zymosan-stimulated). For assessment of the cardiovascular system functional state before and after chemotherapy we used electrocardiography (ECG), echocardiography (EchoCG) and 24-hour ECG monitoring. The data obtained were indicative of increased generation of free radicals by leukocytes during polychemotherapy. After chemotherapy course we detected various types of cardiotoxicity. We noted substantial elevation of frequency of supraventricular and ventricular extrasystoles. There was direct correlation between rate of appearance of supraventricular extrasystoles and level of chemiluminescence of leukocytes (r=0.7; p=0.03). According to data of EchoCG although the left ventricular ejection fraction remained within the normal range during chemotherapy, there was a persistent tendency to its decrease (р&lt;0.001). In this study we for the first time in patients with Non-Hodgkin lymphomas detected an elevation of level of free radical reactions and lipid peroxidation with simultaneous lowering of antiperoxidative activity of blood plasma and their relation to development of cardiotoxic effects. The results obtained indicate to necessity of search for novel early markers of oxidative stress activation, myocardial injury and disfunction able to help to substantially decrease risk of development of cardiovascular complications during and after chemotherapy.

Determining the effects of encapsulated polyphosphates on quality parameters and oxidative stability of cooked ground beef during storage

Abstract Effects of encapsulated (e) sodium tripolyphosphate (STP), sodium pyrophosphate (SPP) and various combinations of encapsulated and un-encapsulated (u) forms of these polyphosphates on lipid oxidation in the cooked ground beef during storage (0, 1, 7 d at 4 0C) were determined. pH, color, cooking loss (CL), thiobarbituric acid reactive substances (TBARS), lipid hydroperoxide (LPO) and soluble orthophosphate (OP) analysis were conducted. Study results indicated that STP increased pH, whereas SPP decreased pH compared to control (p<0.05). SPP was determined as the most effective polyphosphate type to inhibit lipid oxidation (p<0.05). In addition, the use of eSPP significantly reduced OP content compared to uSPP (p<0.05). The lowest TBARS and LPO formation were determined in the groups produced with only eSPP or its combinations with uSPP or uSTP or eSTP (p<0.05). Since the group containing a combination of 0.25% eSTP and 0.25% eSPP was found to have lower CL than the other groups produced with only eSPP or its combinations with uSPP or uSTP, this group was suggested as the most appropriate group which can be used in ready to eat meat product processing by the meat industry.

In Vitro Antioxidant and Cancer Inhibitory Activity of a Colored Avocado Seed Extract.

Avocado (Persea americana) seeds have been used traditionally for a number of health-related indications. Because of its high polyphenol content, we investigated the potential antioxidant and anticancer effects of a colored avocado seed extract (CASE). CASE exhibited an oxygen radical acceptance capacity value of 2012 ± 300 trolox equivalents/mg. CASE reduced lipid hydroperoxide formation in an oil-in-water emulsion (33% reduction at 500 μg/mL). CASE dose-dependently reduced the viability of human breast (MCF7), lung (H1299), colon (HT29), and prostate (LNCaP) cancer cells in vitro. The half maximal inhibitory concentrations ranged from 19 to 132 μg/mL after treatment for 48 h. CASE treatment downregulated the expression of cyclin D1 and E2 in LNCaP cells. This was associated with cell G0/G1 phase cycle arrest. CASE also dose-dependently induced apoptosis in LNCaP cells. CASE reduced nuclear translocation of nuclear factor κB, a prosurvival signal. Further studies are needed to examine these effects in in vivo models.

Effects of Ergothioneine-Rich Mushroom Extract on the Oxidative Stability of Astaxanthin in Liposomes.

Ergothioneine-rich crude extracts of Pleurotus cornucopiae were used as a source of antioxidative components to control the effects of lipid oxidation in astaxanthin-containing liposomes. This study aimed to elucidate the interactions of liposomal astaxanthin and lipids with ergothioneine-rich mushroom extract (ME) under radical oxidation-induced conditions to provide a better understanding of the agricultural and postharvest applications of this strategy. Azo compounds (2,2'-azobis(2-methylpropionamidine) dihydrochloride and 2,2'-azobis(2,4-dimethylvaleronitrile) were used as hydrophilic and lipophilic radical initiators, respectively. Results of this study demonstrate that the presence of ME significantly delayed the oxidative degradation of astaxanthin and controlled the progress of lipid oxidation in a liposomal system. The lipid hydroperoxide formation was significantly suppressed, while polyunsaturated fatty acids were protected from degradation. In addition, Crude ME also demonstrated more potent DPPH radical scavenging activities and EC50 than the equimolar concentrations of ergothioneine alone, which suggested the presence of additional compounds with antioxidative properties.

Rosmarinic acid and its esters inhibit membrane cholesterol domain formation through an antioxidant mechanism based, in nonlinear fashion, on alkyl chain length

BackgroundUnder conditions of oxidative stress, cholesterol aggregates into discrete membrane bilayer domains that precipitate the formation of extracellular crystals, a feature of advanced atheroma in cardiovascular disease. Therapeutic interventions using membrane-directed antioxidants, such as polyphenolic esters, may reduce cholesterol domains and crystal formation. In this study, the effects of rosmarinic acid (RC0) and rosmarinic esters, with alkyl chain lengths ranging from 4 to 16‑carbons (RC4-RC16), on membrane lipid oxidation and cholesterol domain formation were investigated. MethodsModel membranes were prepared with 1,2-dilinoleoyl-sn-glycero-3-phosphocholine and cholesterol at different cholesterol-to-phospholipid mole ratios (0.3:1, 0.9:1, and 1.2:1), in the absence or presence of each molecule and exposed to 72 h of oxidation. Changes in lipid hydroperoxide (LOOH) and cholesterol domain formation were measured using iodometric and small angle x-ray diffraction approaches, respectively. ResultsRosmarinic acid and its esters had differential effects on LOOH formation based on alkyl chain length. RC8 exhibited the greatest antioxidant effect, reducing LOOH levels by 82%, and inhibited cholesterol domain formation. By contrast, RC0 and RC16 failed to inhibit either LOOH formation or cholesterol domain formation. ConclusionThese data indicate that the membrane antioxidant and cholesterol domain inhibition activities of rosmarinic acid esters are dependent, nonlinearly, on alkyl chain length. The mechanism for this effect is attributed to the influence of alkyl chain length on the optimal depth of the polyphenols into the lipid bilayer for trapping free radicals. General significanceThese findings provide insight into novel atheroprotective benefits of polyphenol esters that are dependent on their membrane location.

Impaired enzymatic reactive aldehyde-detoxifying capacity and glutathione peroxidase activity in the aged human arterial tissue.

It is not known whether aging alters the enzymatic reactive aldehyde- and lipid hydroperoxide-detoxifying capacity of the human arterial tissue favoring vascular oxidative stress. To address this issue, we studied the specific enzymatic activities of class 1, 2 and 3 aldehyde dehydrogenase (ALDH1, ALDH2 and ALDH3), glutathione S‑transferase (isozyme A4-4, GSTA4-4) and aldose reductase (AR), namely the major reactive aldehyde-scavenging enzymes, together with the activity of the lipid hydroperoxide-removing enzyme glutathione peroxidase (GSH-Px), in superior thyroid arteries (STA) specimens obtained in the thyroid surgery setting in aged subjects (age 72.3 ± 3.6 years) and young adult controls (age 31.9 ± 3.5 years). Vascular lipid peroxidation was also studied by assessing in STA fluorescent damage products of lipid peroxidation (FDPL), which reflect oxidant-induced 4‑hydroxynonenal and lipid hydroperoxide formation. Remarkably, the activities of ALDH1, ALDH2, ALDH3, GSTA4-4, AR and GSH-Px were significantly lower, and FDPL levels higher, in the arterial tissue of the aged subjects than in that of the young adult controls. Moreover, the enzymatic activities were inversely and significantly correlated with the levels of FDPL in the arterial tissue of both the aged and young subjects, highlighting their vascular antioxidant/antilipoperoxidative role in vivo. Thus, aging impairs the enzymatic reactive aldehyde-detoxifying capacity and GSH-Px activity of the human arterial tissue eventually favoring vascular oxidative stress.

Conjugated Autoxidizable Triene‐Based (CAT and ApoCAT) Assays: Their Practical Application for Screening of Crude Plant Extracts with Antioxidant Functions in Relevant to Oil‐in‐Water Emulsions

Many previous reports suggested that conventional antioxidant assays could not forecast antioxidant performance of plant extracts, especially when it came to a real food system such as oil‐in‐water emulsion. In this study, antioxidant activities of aqueous and ethanolic plant extracts are investigated using multiple conventional assays (TPC, ABTS, FRAP, ORAC) and the oil‐in‐water (O/W) emulsion‐based high throughput assays (the CAT and ApoCAT) in a comparison with an autoxidative O/W emulsion model monitored by formation of lipid hydroperoxide and TBARS values. Results suggest that only the ApoCAT assay is able to forecast the antioxidative performances of the extracts in O/W emulsions, regardless of the differences in extraction solvents, while the CAT assay can explain only the performance of ethanolic plant extracts in O/W emulsions. According to untargeted metabolite analysis, the antioxidants activities of plant extracts might be strongly influenced by extraction solvents. As a result, not only is the quantity of particular metabolites impacted, but also the whole metabolite (antioxidant) profiles of the extracts are modified. In addition, this study demonstrates that both the chemical reaction scheme and physical‐state of a model are important parameters for designing a better antioxidant assay in the future.Practical Applications: The ApoCAT assay would be a more practical method for screening antioxidant compounds and/or crude plant extracts than conventional antioxidant assays and the original CAT assay. The antioxidant capacity of plant extracts obtaining from the ApoCAT can be used to represent their antioxidant performances in food emulsions regardless of their extraction solvents.Several crude plant extracts using different solvents are used to validate the performance of the CAT and the ApoCAT assays in comparisons with multiple conventional antioxidant assays. These assays differ from each other in terms of scheme of reaction and physical state of the test. In addition, oil‐in‐water (O/W) emulsion model is used as a reference method representing the antioxidant activities in food matrices. Principal component analysis (PCA) is performed to better understand the relationship among all assays. The results suggest that only the ApoCAT assay exhibits a close relationship with O/W emulsion model in both crude ethanolic and aqueous plant extracts. Furthermore, putative metabolite profiles of crude plant extracts are identified using LC‐orbitrap MS/MS.

The role of tocopherol on photooxidation reactions palm oil emulsion in water

Lipid oxidation is one of the main deteriorative reactions that takes place during preparation and storage of many food products. This can make it unacceptable for human consumption.. In food emulsion, oxidation reaction can be occurred by either diradical triplet oxygen or nonradical singlet oxygen. The singlet oxygen can be formed from triplet oxygen by photooxidation. The purpose of this research was to study the effect of singlet oxygen quencher such as tocopherol on lipid oxidation rate in the erythrosine-sensitized photooxidation of oil-in-water emulsion. Palm oil-in-water emulsion, containing erythrosine 100 ppm and tocopherol 0, 25, 50, 75 and 100 ppm, were prepared with polyoxyethylene sorbitan monolaurate (Tween 20). The mixtures were stored under 4,000 lux fluorescent light for 10 h and peroxide values were measured at 2 h interval. Erythrosine greatly increased the photooxidation of palm oil-in-water emulsion, as expected. Lipid oxidation rates, as determined by the formation of lipid hydroperoxides in palm oil-in-water emulsions containing erythrosine decreased with increasing tocopherol concentration. At pH 3, the peroxide value was higher than at pH 7, ie., from 8,03 to 6.08 respectively. The results indicate that tocopherol is an effectively singlet oxygen quencher in palm oil-in-water emulsion.