Oxidation Of Edible Oils Research Articles

Effects of Moisture and Amphiphilic Compounds on the Oxidative Stability of Microwave‐Treated Corn Oil

AbstractEffects of moisture and amphiphilic compounds, including oleic acid, lecithin, and monoacylglycerols (MAGs), on the oxidative stability are evaluated in microwave‐treated corn oil. Moreover, the physical properties including critical micelle concentration (CMC) and moisture content are determined in oils treated by microwave irradiation. The CMC of lecithin and moisture content of oils decreases remarkably, whereas the temperature of the oil increases rapidly with microwave irradiation. The addition of lecithin results in increased moisture content significantly in the edible oils, whereas oleic acid and MAGs do not exhibit these effects. Primary oxidation products in all the oil samples increase, despite the type of amphiphilic compounds used. Corn oil containing oleic acid and samples with lecithin exhibits lower and higher p‐anisidine values (p‐AV), respectively. Remarkably high moisture content in corn oils containing lecithin may contribute to the formation of volatile compounds and high p‐AV. Collectively, moisture and amphiphilic compounds affect the degree of lipid oxidation in microwave‐irradiated bulk oils.Practical application: A microwave oven is an irreplaceable home appliance and is widely used in households nowadays. Effects of amphiphilic compounds and moisture on the oxidative stability are evaluated and it is found that the amphiphilic compounds in lipids affect heat transfer and oxidative stability of oils. The results of this study can provide fundamental insights into lipid oxidation in edible oils, and can provide a direction to the food industry with respect to the development of more efficient and safe methods for the preparation of microwavable foods.

Study on antioxidant activity of crude peanut oils and refined cottonseed oils from Burkina Faso

<abstract> <p>Vegetable oils are among the foodstuffs produced and consumed in abundance by the population in Burkina Faso. These edible oils are nutrient sources for health. However, the oxidation of edible oils is a phenomenon that leads to their degradation. Hence, the objectives of this study were to determine the antioxidants compounds, to evaluate the antioxidant activity of vegetable oils produced in Burkina Faso and to propose good manufacturing practices. Thus, 32 samples of crude peanut oils and refined cottonseed oils were analyzed. α-Tocopherol was determined by High performance liquid chromatography (HPLC), total phenolic compounds and DPPH by spectrophotometry. The α-tocopherol averages are 10.89 and 56.44 mg/100 g for peanut oils and cottonseed oils, respectively (<italic>p</italic> < 0.05). For total phenolic compounds, the averages are 2.91 and 0.64 mg/100 g of gallic acid equivalent for peanut oils and cottonseed oils, respectively (<italic>p</italic> < 0.05). The inhibition percentages are respectively 17.97% and 5.58% (<italic>p</italic> < 0.05) for peanut oils and cottonseed oils. For antioxidant activity, the averages are 0.81 and 0.27 mg trolox/100 g for peanut oils and cottonseed oils, respectively (<italic>p</italic> < 0.05). Cottonseed oils have the highest levels of α-tocopherol while peanut oils have high levels of total phenolic compounds and antioxidant activity. Vegetable oils contain acceptable levels of α-tocopherol and total phenolic compounds for their oxidative stability and health benefits for the consumer. However, the levels of biomolecules will be higher if production and preservation conditions are improved and controlled. The results could be used for future recommendations about human feeding programs in Burkina Faso.</p> </abstract>

Quantitative determination of peroxide value of edible oil by algorithm-assisted liquid interfacial surface enhanced Raman spectroscopy

Edible oil is an indispensable food in daily life but early detection of its lipid oxidation is difficult. Developing new, rapid and accurate screening technique is urgently needed for oil quality control. Here we developed a surface-enhanced Raman spectroscopy analyzer based on plasmonic metal liquid-like platform (PML-SERS), which could directly analyze the oil sample in ca. 3 min. This analyzer has the ability and sensitivity to identify fingerprint peak changes. Moreover, the relative Raman intensity, I1265/1436, has a good correlation with peroxide value (POV), which is used for quantitative detection. The fitting model combined with principal component analysis (PCA) realized rapid spectral recognition for determining POV in edible oil oxidation. The relative deviation between the POV measured by PML-SERS and the national standard method (NSM) was less than 10%. Our platform provided a practical solution for ultra-sensitive and fast analysis of POV in oil oxidation.

Visual determination of oxidation of edible oil by a nanofiber mat prepared from polyvinyl alcohol and Schiff's reagent.

A fiber mat was developed to visually determine the oxidation of edible oils, based on the colorimetric reaction of Schiff's reagent and aldehydes - the major volatile formed during lipid oxidation. The mixtures of polyvinyl alcohol (PVA) and Schiff's reagent containing various amounts of glycerol were electrospun to form the fiber mats. The response of the PVA/Schiff's reagent fiber mats to gaseous hexanal (model aldehyde) was investigated. Oxidized soybean oils were used to evaluate the effectiveness of the PVA/Schiff's reagent fiber mat for indicating oxidation of the oils. The results showed that the fiber mats obtained had average fiber diameters of less than 100nm. Upon hexanal exposure, the fiber mats turned from white to purple. Higher amount of glycerol led to larger color change of the fiber mats and shorter response time to hexanal. A linear relationship (R2 = 0.96) was observed between the color change of the mat and hexanal concentration (15-117μmolL-1). The visual determination limit of the mat for hexanal was 29μmolL-1. The color change of the PVA/Schiff's reagent fiber mat was increased with an increase of soybean oil oxidation. Out of the seven soybean oils tested, the PVA/Schiff's reagent fiber mat was able to correctly indicate the oxidation states of six oils. The result suggested that the visual determination method developed is a promising method to indicate the oxidation of edible oils, which can be performed easily by non-experts.Graphical abstract.

Qualitative analysis of edible oil oxidation using an olfactory machine

Oil oxidation is an undesirable series of chemical reactions involving oxygen that degrades the quality of an oil. Oxidation eventually produces rancidity in oil, with accompanying off-flavors and smells. An electronic nose was used in this study to detect the adulterations in edible oils. The acidity, peroxide, anisidine and Totox values of the edible oil samples were measured according to the official American Oil Chemist Society (AOCS) standard. The results were analyzed using cluster analysis, principal component analysis, support vector machine, quadratic discriminant analysis, and Partial least squares regression technique. In the sensor array, the TGS2602, and MQ136 sensors had the highest values of the Loudness coefficient and the MQ9, TGS822, TGS813, and TGS2620 had the lowest values. Based on the results obtained, the accuracy of the three methods; Support vector machine (SVM), Quadratic discriminant analysis and Partial least squares were 97%, 98.33%, and 100%, respectively. The results for the linear vector kernel support machine, training accuracy and validation for C-SVM and Nu-SVM were 98, 97, 97 and 95%, respectively. The results also indicated that the proposed method can be used as an alternative to the official AOCS methods to innovatively detect the edible oil oxidation with high accuracy.

Analysis of Reaction Kinetics of Edible Oil Oxidation at Ambient Temperature by FTIR Spectroscopy

AbstractEdible oils are studied to analyze their reaction kinetics during oxidation and predict shelf life at ambient temperature. Rapeseed oil (RO), soybean oil (SO), linseed oil (LO), and peanut oil (PO) are detected via Fourier transform infrared spectroscopy with a mesh cell as spectral acquisition accessory. The reaction kinetics of ROOH bonds, C═O bonds, trans double bonds (TDBs), and carbon chain skeletons (CCSs) are determined by absorbance changes in their characteristic absorption peaks. Prediction models for shelf life based on various characteristic absorption peaks are converted via the reaction kinetics equations of the oils. Results show that first‐order reaction kinetics are used to describe absorbance changes of ROOH bonds in PO, SO, and LO, while zero‐order reaction kinetics are used to describe the absorbance changes in RO. Both C═O bonds and CCS absorbance changes in the four oils satisfy first‐order reaction kinetics. TDBs absorbance changes in PO, SO, and LO are in accordance with zero‐order reaction kinetics. The regression equations of reaction kinetics exhibit good fitting degree (coefficient of determination, R2 > 0.9000) and statistical significance (p < 0.001), indicating that the proposed method can be used to analyze the reaction kinetics of oil oxidation and predict shelf life.Practical Applications: The reaction kinetics of RO, SO, LO, and PO are studied at ambient temperature and the shelf life is predicted by using FTIR spectroscopy based on the absorbance changes of ROOH bonds, C═O bonds, TDB bonds, and CCS in the oils. The shelf life of edible oils can be more effectively predicted in this case and provide a practical reference for food industries. Furthermore, the proposed technique is rapid, green, and accurate, and allows real‐time characterization of absorbance changes in various characteristic absorption peaks, which corresponded to different oxidation products. By this method, it is possible to reflect real‐time information for different quality indices (such as peroxides and acid values) of oil oxidation simultaneously, and unnecessary to measure these indices directly one by one, saving manpower and material resources. Therefore, FTIR spectroscopy is convenient for the rapid evaluation of oxidation stability and shelf life of edible oils under ambient temperature.

Machine learning-driven Raman spectroscopy for rapidly detecting type, adulteration, and oxidation of edible oils

Machine learning-driven Raman spectroscopy for rapidly detecting type, adulteration, and oxidation of edible oils

Effect of Star Fruit (Averrhoa carambola L.)By-product on Oxidative Stability of Sesame (Sesamum indicum) Oil under Accelerated Oven Storage and during Frying.

Aim of this study was to evaluate the effect of star fruit (Averrhoa carambola L.) by-products (peel and residue) on stability of sesame (Sesamum indicum) oil against oxidation. Antioxidant properties of extract of peel and residue at different time durations of extraction were determined and found that peel contains higher antioxidant potential than residue. Thus, extract of peel obtained after 24 h extraction was used to study its effectiveness on oxidative stability of sesame oil during accelerated oven storage and frying using the butylated hydroxytoluene (BHT) (200 ppm) as the reference antioxidant (positive control) and oil without added antioxidant as the negative control. The oxidative stability of the oil was determined by evaluating peroxide value, p-anisidine value, thiobarbituric acid reactive substances (TBARS) value, total oxidation (TOTOX) value, conjugated diene (CD) and conjugated triene (CT) values, and iodine value. Peel extract at different concentrations (200-1000 ppm) was tested. The oil added with peel extract exhibited higher stability against oxidation than the controls during oven storage test. Extract at 1000 ppm significantly increased the stability of sesame oil during frying as compared with controls. Thus, star fruit peel extract could be an alternative to synthetic antioxidants to suppress oxidation of edible oils.

Direct Discrimination of Edible Oil Type, Oxidation, and Adulteration by Liquid Interfacial Surface-Enhanced Raman Spectroscopy.

The quality and safety of edible oils is a momentous but formidable challenge, especially regarding identification of oil type, oxidation, and adulteration. Most conventional analytical methods have bottlenecks in sensitivity, specificity, accessibility, or reliability. Surface-enhanced Raman spectroscopy (SERS) is promising as an unlabeled and ultrasensitive technique but limited by modification of inducers or surfactants on metal surfaces for oil analysis. Here, we develop a quantitative SERS analyzer on two-liquid interfacial plasmonic arrays for direct quality classification of edible oils by a portable Raman device. The interfacial plasmonic array is self-assembled through mixing the gold nanoparticle (GNP) sols and oil sample dissolved in chloroform without any surfactants or pretreatments. Different kinds of edible oils dissolved in chloroform directly participate in self-assembly of plasmonic arrays that finally localizes onto a three-dimensional (3D) oil/water interface. The 3D plasmonic array is self-healing, shape adaptive, and can be transferred to any glass containers as a substrate-free SERS analyzer for direct Raman measurements. It produces sensitive responses of SERS on different kinds of edible oils. By virtue of principal component analysis (PCA), this analyzer is able to quickly distinguish six edible oils, oxidized oils, and adulterated oils. Moreover, the solvent chloroform generates unique and stable SERS bands that can utilized as an inherent internal standard (IIS) to calibrate SERS fluctuation and greatly improve quantitation accuracy. Compared to conventional lab methods, this analyzer avoids complex and time-consuming preprocessing and provides significant advantages in cost, speed, and utility. Our study illuminates a facile way to determine edible oil quality and promises great potential in food quality and safety analysis.

Analysis of Edible Oil Oxidation Based on Changes in the Electrical Conductivity of the Extracted Aqueous Phase

A novel and rapid method is developed to analyze oxidation in edible oils by using electrical conductivity (EC). The extent of edible oil oxidation is confirmed using the American Oil Chemists’ Society (AOCS) standard method as a reference. Analytical conditions, including temperature, oscillating time, and water–oil (v/v) ratio, are optimized to determine ECs. A model is established based on EC changes in the aqueous phase extracted from several water–oil mixtures. This model is used to predict the oxidation degree of the samples, and its results are validated by the AOCS standard methods. Results show that the analytical conditions exert no significant effects on EC determination. The model is developed using a water–oil (v/v) ratio of 5. Three regions are classified according to the ECs of the samples. Oils with ECs less than 6.9 µS cm−1 are found to be non‐oxidized oils, samples with ECs within 6.9–8.9 µS cm−1 are suspected oils, and samples with ECs exceeding 8.9 µS cm−1 correspond to oxidized oils. The total identification rate of the model in validation samples is 94.1%. The results of the present study clearly indicate that the proposed method can be used as an alternative to conduct qualitative discrimination of the oxidation degree of edible oils. Practical applications: A method based on EC changes in the aqueous phase is used to determine the extent of edible oil oxidation. A total of 151 oil samples are used and assigned to two groups for calibration (n = 83) and validation (n = 68) oil samples. In the EC method, determination of ECs is independent of analytical conditions, which provides great flexibility in the selection process. The method requires no spectral pre‐treatments or data processing methods, which simplifies the experiment process. Furthermore, the EC instrument is less than 40 $ USD, which is more affordable and portable in a small scale. These characteristics make the proposed method convenient for inspection departments to accomplish on‐site testing of edible oils. The EC method can be applied to determine edible oil oxidation.A method based on EC changes in the aqueous phase extracted from water–oil mixture is used to determine the extent of edible oil oxidation. At a water–oil (v/v) ratio of 5, the EC model can be divided into three regions: ECs of less than 6.9 µS cm−1 representing non‐oxidized oils, ECs within 6.9–8.9 µS cm−1 representing suspected oils, and ECs of over 8.9 µS cm−1 representing oxidized oils. The total identification rate of the model in validation samples is 94.1%.

Evaluation of Stability against Oxidation in Edible Fats and Oils

There is a lipid oxidation problem in edible oils and fats due to the fact that they are continuously exposed to various storage conditions or overheating. Therefore, investigation of the stabilization of edible oil products is an area worth researching due to consumer-related health concerns. Consequently, thermal oxidative deterioration might be prevented if the stability of the product is comprehended fairly. Thus, food formulations can be regulated depending on the findings of the stability measurements. In this review article, the mechanism and structure of lipid oxidation process have been explained. Furthermore, the significance of prediction of shelf-life has been mentioned as well as kinetic and thermodynamic comprehension in oxidation process. Additionally, all the mentioned stability measuring methods have been discussed, respectively.

Improvement of the Oxidative Stability of Sesame Oil Using Spirulina as a Natural Antioxidant

Background: Nowadays, natural antioxidants are used to replace synthetic antioxidants for delaying or preventing the oxidation of edible oils. In this study, phenolic compounds and antioxidant properties of methanol extracts of Spirulina microalgae (Arthrospira platensis) were measured. Methods: Phenolic content was measured by Folin–Ciocalteau method and antioxidant activity was measured by the 2, 2-diphenyl-1-picrylhydrazyl (DPPH) method. Also, spirulina microalgae as natural antioxidant, was added to sesame oil for improving its oxidative stability. The effects of methanol extract of these microalgae in four concentrations (0, 500, 1000 and 2000 ppm) and synthetic antioxidants of butylated hydroxyl anyzole (BHA) and butylated hydroxytoluene (BHT) in two levels (100 and 200 ppm) in retarding the sesame oil oxidation were examined. Results: The results showed that spirulina extract had 50.54 mg gallic acid/g samples total phenols and antiradical activity (84.38%). By increasing the concentration of the extracts, the oxidation process decreased. Methanol extract at 1000 ppm concentration had the highest antiradical activity than other concentrations and its antiradical activity was alike the synthesis antioxidant of BHA. By Increasing of storage period, peroxide values in 500 and 1000 ppm of spirulina extracts first increased then decreased and in other treatment increased. During storage time thiobarbituric acid index increased. However, this increase was higher in control treatment than others. Conclusion: According to the stated content, it can be said that methanol extracts of spirulina have appropriate antioxidant properties and spirulina can be used as a natural antioxidant to improve the oxidative stability of sesame oil.

Synergistic effect of 3,4-dihydroxyphenylglycol with hydroxytyrosol and α-tocopherol on the Rancimat oxidative stability of vegetable oils

Abstract The current work evaluated the ability of pure 3,4-dihydroxyphenylglycol (DHPG) and hydroxytyrosol (HT) in combination with a commercial phenolic extract from Olea europaea rich in HT to prevent the oxidation of edible vegetable oils. The commercial phenolic extract was highly soluble in all matrices and significantly improved the oxidation stability and delayed the onset of rancidity of oils compared to a control (with no antioxidant). The combinations of DHPG with other natural antioxidants, such as HT and α-tocopherol, showed that it can be a useful supplement to increase the shelf life of sunflower oil. Synergism was observed when DHPG and HT were added in combination. The synergistic effect was directly related to the concentration ratio between both antioxidants. The mixtures containing DHPG/α-tocopherol and DHPG/HT/α-tocopherol also showed effectiveness in delaying oxidation.

Coating of Sol–Gel Film on Silver Nanodendrite as a Novel Solid-Phase Microextraction Fiber for Determination of Volatile Aldehydes in Edible Oils

In this work, a novel solid-phase microextraction fiber was fabricated by a new substrate applied for quantitative analysis of trace volatile aldehydes emitted during thermal oxidation of edible oils, analyzed by GC–MS. Ag nanodendrites as a porous substrate, spontaneously coated on a Cu wire, and polydimethylsiloxane/polyethylene glycol (PDMS/PEG) were deposited onto the substrate by sol–gel dip-coating. Parameters affecting the extraction efficiency, such as the substrate porosity, extraction time and temperature, and desorption time and temperature were investigated and optimized. The desorption temperature was chosen as 260 °C, and desorption time was set at 3 min. Results shows that extraction efficiency of sol–gel coating deposited on Ag nanodendrite substrate is meaningfully higher than that of deposited on bare Cu wire. Under the optimum conditions, the limits of detection (LODs) ranged between 0.5 to 0.2 μg/L. The relative standard deviations including repeatability (within fibers) and reproducibility (between fibers) varied between 7.5–11.2 and 9.3–16.2%, respectively.

Determination of triacylglycerol oxidation mechanisms in canola oil using liquid chromatography\u2013tandem mass spectrometry

Triacylglycerol (TG), the main component of edible oil, is oxidized by thermal- or photo- oxidation to form TG hydroperoxide (TGOOH) as the primary oxidation product. Since TGOOH and its subsequent oxidation products cause not only the deterioration of oil quality but also various toxicities, preventing the oxidation of edible oils is essential. Therefore understanding oxidation mechanisms that cause the formation of TGOOH is necessary. Since isomeric information of lipid hydroperoxide provides insights about oil oxidation mechanisms, we focused on dioleoyl-(hydroperoxy octadecadienoyl)-TG (OO-HpODE-TG) isomers, which are the primary oxidation products of the most abundant TG molecular species (dioleoyl-linoleoyl-TG) in canola oil. To secure highly selective and sensitive analysis, authentic OO-HpODE-TG isomer references (i.e., hydroperoxide positional/geometrical isomers) were synthesized and analyzed with HPLC-MS/MS. With the use of the method, photo- or thermal- oxidized edible oils were analyzed. While dioleoyl-(10-hydroperoxy-8E,12Z-octadecadienoyl)-TG (OO-(10-HpODE)-TG) and dioleoyl-(12-hydroperoxy-9Z,13E-octadecadienoyl)-TG (OO-(12-HpODE)-TG) were characteristically detected in photo-oxidized oils, dioleoyl-(9-hydroperoxy-10E,12E-octadecadienoyl)-TG and dioleoyl-(13-hydroperoxy-9E,11E-octadecadienoyl)-TG were found to increase depending on temperature in thermal-oxidized oils. These results prove that our methods not only evaluate oil oxidation in levels that are unquantifiable with peroxide value, but also allows for the determination of oil oxidation mechanisms. From the analysis of marketed canola oils, photo-oxidized products (i.e., OO-(10-HpODE)-TG and OO-(12-HpODE)-TG) were characteristically accumulated compared to the oil analyzed immediately after production. The method described in this paper is valuable in the understanding of oil and food oxidation mechanisms, and may be applied to the development of preventive methods against food deterioration.

Combination of Gas Chromatography-Mass Spectrometry and Electron Spin Resonance Spectroscopy for Analysis of Oxidative Stability in Soybean Oil During Deep-Frying Process

Lipid oxidation of edible oil during frying process is a complex process and involves free radical chain reactions. Soybean oil with high amount of unsaturated fatty acids was used to investigate the impact of frying time on oxidative stability of oil. Electron spin resonance (ESR) spectroscopy technique was applied to identify and quantify the formed radicals, along with the assessment of physicochemical parameters including peroxide value, oxidative stability, fatty acid composition, and volatile profile. Results showed that the amount of formed free radicals determined by ESR in frying oil increased with the prolongation of frying time. The availability of this method was compared with physicochemical properties and the well correlation coefficients were obtained. Besides, main volatile aldehyde compounds produced by β-scission homolytic cleavage of peroxide group in frying oil during thermal oxidation were derived from oxidation of oleic and linoleic acid.

Thermal and oxidative stability of Sacha Inchi oil and capsules formed with biopolymers analyzed by DSC and 1H NMR

The oxidative stability of edible oils is an important feature to know due the undesirable changes that can occur in the storage. In this way, the oxidative induction time (OIT) value is an indicative to prevent this effect. The objectives of this study were to evaluate the omega-3 content and kinetic parameters of Sacha Inchi oil (SIO) and capsules that are formed with biopolymers, in addition, there were analyzed with differential scanning calorimetry (DSC) and proton nuclear magnetic resonance (1H NMR). The SIO and capsules, formed using an emulsion, were analyzed with DSC in an oxygen atmosphere to determine the OIT value in isothermal conditions at 100, 120 and 150 °C. The kinetic parameters (activation energy, pre-exponential factor and z value) of SIO were obtained, and the stability time was predicted at different temperatures. The 1H NMR spectra enabled us to assess the identification and percentage relative before and after the isothermal DSC oxidation of omega-3 concentration and formation of their oxidized compounds. (E-E)-2,4-Alkadienals were the primary oxidized compound and is strongly correlated with the decrease in omega-3 content. Isothermal DSC is a useful to determine the OIT (min) and kinetic parameters to predict the stability oxidation in different edible oils and thus prevent the inadequate consumption of edible oils oxidized.

Development and Characterization of Multifunctional Gelatin-Lysozyme Films Via the Oligomeric Proanthocyanidins (OPCs) Crosslinking Approach

Herein, we report firstly the development of sustained antimicrobial and antioxidant gelatin-lysozyme films crosslinked by the oligomeric proanthocyanidins (OPCs), a duel-functional agent. Lysozyme release kinetic studies were performed at neutral and acidic pH, and they could be described as a biphasic process. OPCs crosslinking retarded lysozyme release at pH 7.0, in a dose dependent manner, and the inhibition zone tests confirmed that the sustained release of lysozyme was realized upon weak crosslinking with OPCs. OPCs crosslinking enhanced thermal stability of the gelatin films, and gave them the ability to barrier ultraviolet light. OPCs loadings endowed the films excellent antioxidant activities, the DPPH radical scavenging activity of the films increased linearly to 93.97% upon increasing OPCs loadings from 0 to 2.0%. Concomitantly, the reducing powder of the films increased linearly from 6.08 ± 0.09 to 45.53 ± 2.74 μmol Asc Acid/g film. Additionally, the antioxidant properties of gelatin films against lipid oxidation in edible oils were evaluated. Lipid hydroperoxides of algal oils in the gelatin bags were approximately a quarter of that in low-density polyethylene (LDPE)-based bags, and the malondialdehyde (MDA) values of algal oils were lower than that in LDPE-based bags by 1–2 orders of magnitude. Regrettably, the incorporation of OPCs did not enhance the antioxidant capability of gelatin films against lipid oxidation in wrapped edible oils, possibly due to the limited release toward algal oils in term of its oil-soluble attribute. This study opens a promising pathway for producing sustained antimicrobial and antioxidant gelatin films using a bi-functional agent.

Investigation of Phenols Activity in Early Stage Oxidation of Edible Oils by Electron Paramagnetic Resonance and 19F NMR Spectroscopies Using Novel Lipid Vanadium Complexes As Radical Initiators.

A novel dynamic method for the investigation of the phenols activity in early stage oxidation of edible oils based on the formation of α-tocopheryl radicals initiated by oil-soluble vanadium complexes is developed. Two new vanadium complexes in oxidation states V and IV were synthesized by reacting 2,2'-((2-hydroxyoctadecyl)azanediyl)bis(ethan-1-ol) (C18DEA) with [VO(acac)2] and 1-(bis(pyridin-2-ylmethyl)amino)octadecan-2-ol (C18DPA) with VOCl2. Addition of a solution of either complex in edible oils resulted in the formation of α-tocopheryl radical, which was monitored by electron paramagnetic resonance (EPR) spectroscopy. The intensity of the α-tocopheryl signal in the EPR spectra was measured versus time. It was found that the profile of the intensity of the α-tocopheryl signal versus time depends on the type of oil, the phenolic content, and the storage time of the oil. The time interval until the occurrence of maximum peak intensity be reached (tm), the height of the maximum intensity, and the rate of the quenching of the α-tocopheryl radical were used for the investigation of the mechanism of the edible oils oxidation. 19F NMR of the 19F labeled phenolic compounds (through trifluoroacetate esters) and radical trap experiments showed that the vanadium complexes in edible oil activate the one electron reduction of dioxygen to superperoxide radical. Superperoxide reacts with the lipids to form alkoperoxyl and alkoxyl lipid radicals, and all these radicals react with the phenols contained in oils.

Differences in antioxidant activity between two rice protein concentrates in an oil‐in‐water emulsion

Two formulations of rice protein concentrates (RPC) derived from brown rice were evaluated for their antioxidant activity in bulk oil and in oil‐in‐water emulsions. Bulk oils were mixed with RPC and heated to 180°C, and total polar compounds and triacylglycerol polymerization were measured. Minimal antioxidant activity was observed in the bulk oil phase. Rice protein concentrates were incorporated into soybean oil‐in‐water emulsions, which were oxidized at 50°C for 8 days. Lipid oxidation in emulsions was assessed via peroxide values (PV), headspace oxygen levels, headspace volatile oxidation products, and fatty acid analysis. One of the RPC treatments showed some antioxidant activity in emulsions, suggesting that RPC could potentially be used to extend shelf life and preserve product quality.Practical applications: Naturally derived antioxidants that can inhibit oxidation in edible oils are in high demand. As consumers become more label‐conscious, synthetic antioxidants are falling out of favor. Rice proteins offer a means of antioxidant capability in emulsions, which may have applications in improving shelf life and/or product quality in a variety of foods, including sauces, salad dressings, and dairy products. Rice protein concentrations show more promise in emulsions than in bulk oil.Protein concentrates derived from brown rice (left) were incorporated into oil‐in‐water emulsions (center) and showed differing abilities to suppress lipid oxidation (linolenic acid, shown right).