Impact of Free Fatty Acids and Phospholipids on Reverse Micelles Formation and Lipid Oxidation in Bulk Oil

Association colloids such as phospholipid reverse micelles could increase the rate of lipid oxidation in bulk oils. In addition to phospholipids, other surface active minor components in commercial oils such as free fatty acids may impact lipid oxidation rates and the physical properties of reverse micelles. In this study, the effects of free fatty acids on changes in the critical micelle concentration (CMC) of 1,2-Dioleoyl-sn-glycero-3-phosphocholine (DOPC) in stripped corn oil (SCO) were determined by using the 7,7,8,8-tetracyanoquinodimethane solubilization technique. Different free fatty acids including myristoleic, oleic, elaidic, linoleic and eicosenoic were added at 0.5 % by wt along with the DOPC into the bulk oils. There was no significant effect of free fatty acids with different chain length, configuration and number of double bonds on the CMC value for DOPC in bulk oil. However, increasing concentrations of oleic acid (0.5 to 5 % by wt) caused the CMC value for DOPC in bulk oils to increase from 400 to 1,000 μmol/kg oil. Physical properties of DOPC reverse micelles in the presence of free fatty acids in bulk oils were also investigated by the small angle X-ray scattering technique. Results showed that free fatty acids could impact on the reverse micelle structure of DOPC in bulk oils. Moreover, free fatty acid decreased pH inside reverse micelle as confirmed by the NMR studies. The oxidation studies done by monitoring the lipid hydroperoxide and hexanal formation revealed that free fatty acids exhibited pro-oxidative activity in the presence and absence of DOPC. Different types of free fatty acids had similar pro-oxidative activity in bulk oil.     

Plasma Polymerization Modified Polyvinylidene Fluoride (PVDF) Membrane Development and Characterization for Degumming of Soybean Oil

Unmodified and surface‐modified polyvinylidene fluoride (PVDF) membranes were tested for their ability to degum soybean crude oil and crude oil miscellas. The membrane was modified with 1,1,1,3,3,3‐hexafluoro‐2‐propanol or hexamethyldisiloxane (HMDSO) by radio‐frequency plasma polymerization at 10–100 W glow discharge power and 1–30 min contact time. The membranes were characterized by contact angle measurements, attenuated total reflectance Fourier transform infrared spectroscopy, atomic force microscopy, and scanning electron microscopy. Modification of the PVDF membrane with HMDSO at 60 W power for 5 min increased the interfacial free energy between water and solid surface from 30 ± 2 to 64 ± 2 mJ/m². This membrane was tested for permeate flux and phospholipid rejection with crude oil and different concentrations of miscella. Although formation of the polymer film on the membrane tended to decrease membrane pore size, the modified membrane had an oil flux as good as the unmodified membrane did. In addition, the modified‐membrane improved the phospholipid rejection and removed 76 % of the phospholipids from the crude oil and 81–90 % of the phospholipids from crude oil miscellas.     

Impact of Phosphoethanolamine Reverse Micelles on Lipid Oxidation in Bulk Oils

Phospholipids are important minor components in edible oil that play a role in lipid oxidation. Surface active phospholipids have an intermediate hydrophilic–lipophilic balance value, which allows them to form association colloids such as reverse micelles in bulk oil. These association colloids can influence lipid oxidation since they create lipid–water interfaces where prooxidants and antioxidants can interact with triacylglycerols. In this study, we examined the formation of reverse micelles in a stripped oil system by dioleoyl phosphoethanolamine (DOPE) and the effect of these physical structures on lipid oxidation kinetics. The critical micelle concentration (CMC) of DOPE was approximately 200 µmol/kg oil at 45 °C. Oxidation kinetics studies showed that DOPE was prooxidative when it was above its CMC (400 and 1,000 µM), reducing the lag phase from 14 days (control) to 8 days. The addition of combinations of DOPE and dioleoyl phosphocholine (DOPC) resulted in formation of mixed micelles with a CMC of 80 µmol/kg oil at 45 °C. These mixed micelles were also prooxidative when concentrations (100 and 500 µM) were above the CMC, decreasing the lag phase from 14 to 8 days. These findings provide a better understanding of the role of phospholipids in lipid oxidation of edible oil and could contribute to better antioxidant solutions.     

Vegetable oil degumming with polyimide and polyvinylidenefluoride ultrafiltration membranes

The removal of phospholipids (‘degumming’) is the first step in the process of refining crude vegetable oil. Membrane separation has been often proposed as an alternative to the conventional procedure (water degumming). Until now, the instability of polymeric membranes in organic solvents has been the major obstacle in applying this technique. In this work, a local synthesized polyvinylidenefluoride (PVDF) and a commercial polyimide (PI) membrane were evaluated for their flux and rejection properties during degumming of soybean oil in a laboratory‐scale cross‐flow ultrafiltration cell. Degumming experiments were done at different temperatures and feed flows, keeping constant both the feed concentration and the transmembrane pressure. PVDF and PI membranes gave selectivity values and permeate color that did not differ significantly from each other. Retention coefficients larger than 98% were obtained in all cases. In every experiment, a decline in permeate flux with time occurred at the beginning of the degumming process. By increasing the feed rate, a higher permeate flux was obtained. The results show that the PVDF membrane had a higher productivity than the PI one. Copyright © 2003 Society of Chemical Industry     

Membrane degumming of crude rice bran oil: Pilot plant study

The procedure for the classical chemical refining of vegetable oils consists of degumming, alkali neutralization, bleaching, and deodorization. Conventional refining of rice bran oil using alkali gives oil of acceptable quality, but the refining losses are very high. A critical work has been carried out to study the application of membrane technology in the pretreatment of crude rice bran oil. Oils intended for physical refining should have a low phosphorus content, and this is not readily achievable by the conventional acid/water degumming process. The application of membrane technology for the pretreatment of rice bran oil has been investigated. The process has already been successfully applied to other vegetable oils. Ceramic membranes, which are important from the commercial point of view, were examined for this purpose. The results showed that the membrane‐filtered oils met the requirements of physical refining, with a substantial reduction in color. It was observed that most of the waxy material was also rejected. Experiments were carried out to establish the relationship between permeate flux and rejection with membrane pore size, trans‐membrane pressure and micellar solute concentration.     

Formation of Phospholipid Association Colloids in Rapeseed Oil and Their Effect on Lipid Autoxidation in the Presence of Sinapic and Ferulic Acid

This study describes the formation of 1,2‐dioleoyl‐sn‐glycero‐3‐phosphocholine (DOPC) association colloids (reverse micelles) in rapeseed oil and interactions of sinapic and ferulic acids with these structures. Furthermore, the process of oil autoxidation in the presence of DOPC is characterized and the antioxidant efficiency of phenolic acids in the oil containing reverse micelles is determined. Formation of DOPC reverse micelles above the phospholipid critical micelle concentration (51.13 µmol kg^–1) is observed. The fluorescence probe emission parameters confirm the interactions of sinapic and ferulic acids with reverse micelles and changes of their structure (reduced rigidity) as a result of phenolic acid incorporation. In the analyzed rapeseed oil, an evident prooxidative effect of DOPC reverse micelles is found, as their presence accelerates decomposition of hydroperoxides to hexanal. The antioxidant effect of sinapic acid is strongly influenced by the presence of DOPC reverse micelles. Ferulic acid shows a concentration‐dependent antioxidant effect in relation to the formation of hexanal. Practical Applications: Understanding the influence of sinapic and ferulic acids on the structure of association colloids and rapeseed oil autoxidation in the presence of reverse micelles should facilitate extension of shelf life and reduce oil quality deterioration during storage. This knowledge may also be used to optimize industrial oil refining to provide the desired amount of amphiphilic minor components and native antioxidants. Thus, developed refining using mild conditions or even minimizing the degree of refining is attractive in view of greater retention of health‐promoting compounds in vegetable oil, reduction of processing costs, and increased sustainability of the oil‐refining process.     

Formation of dispersed particles composed of soybean oil and phosphatidyl choline

The purpose of this study was to investigate the dispersal mechanism of soybean oil (SO) in phospholipids to form a fat emulsion. SO was dispersed with soybean phosphatidyl choline (PC) using sonication. The dispersal mechanism was evaluated by characterizing the dispersed particles using dynamic light scattering, fluorescence spectroscopy and surface monolayer techniques. The dispersions in SO fractions being in the range of 0.1‐0.7 were stable at room temperature for 3 d. A limited amount of SO was incorporated into PC bilayer membranes. The excess SO separating from the PC bilayers was stabilized as emulsion particles by the PC surface monolayer. When the PC content was lower (SO more than 0.8 mol‐%), the PC monolayer did not completely cover the hydrophobic SO particle surfaces. In this case, the particle size increased drastically and the separation into oil and water occurred. Therefore, the solubility between SO and PC and the coexistence of emulsion and liposomal particles are critical parameters for the stabilization of the particles in water.     

Activity of horseradish peroxidase in aqueous and reverse micelles and back‐extraction from reverse‐micellar phases

Studies on the activity of the enzyme horseradish peroxidase (HRP) have been carried out in micellar as well as reverse‐micellar media. The activity of the enzyme was studied in the presence of different classes of surfactants – ionic as well as non‐ionic. In aqueous media, the activity of the enzyme varied depending on whether the concentration of the surfactant used was above or below the critical micellar concentration (CMC). The enzyme was also studied in reverse‐micellar systems. HRP was introduced into the reverse micellar phase by the injection method and its activity within the reverse micelles was determined. The effect of water to surfactant ratio (W_o) on activity within reverse micelles was studied, and an almost two‐fold increase in activity was seen when the enzyme was encapsulated within reverse micelles of aqueous phase fractional hold‐up (?) of 0.0072 (v/v) consisting of sodium bis‐(2‐ethylhexyl) sulfosuccinate (AOT) in isooctane at a W_o of 20. The activity of HRP was measured over a wide range of AOT concentrations having different W_o values. Back‐extraction of HRP from these reverse micelles was carried out at varying ionic strengths of phosphate buffer. Back extraction was found to be highest at pH 7.0 in 40 mol m^?3 phosphate buffer and 100 mol m^?3 sodium chloride. © 2001 Society of Chemical Industry     

Determination of Mineral Oil-Saturated Hydrocarbons (MOSH) in Vegetable Oils by Large Scale Off-Line SPE Combined with GC-FID

A method based on an off-line large-scale solid phase extraction (SPE) approach combined with conventional gas chromatographic-flame ionization detection (GC-FID) was developed to determine the mineral oil-saturated hydrocarbons (MOSH) in vegetable oils. A large-scale SPE column loaded with 10 g of activated silica gel impregnated with 1% silver nitrate which was used to retain lipids and olefins in vegetable oils and the MOSH in the oil samples was eluted with hexane. Then 2 μL concentrated solution was splitlessly injected into a common GC-FID instrument. The quantification limit reached 2.5 mg/kg when the MOSH fraction was concentrated to 0.1 mL. The accuracy of this procedure, as assessed by measuring the recoveries from spiked oil samples, was higher than 80%. This procedure was applied to analyze the MOSH in 38 commercial vegetable oils from Chinese market, which was the first survey of mineral oil contaminant in Chinese edible oils. The oil samples contaminated with different levels of MOSH, among which, 15 samples contained no mineral oils and 3 samples were contaminated with more than 50 mg/kg of MOSH. The highest contamination level was found in one of rice oils, in which the concentration of MOSH was up to 713.36 mg/kg. Of the 9 types of oils analyzed, camellia oil contained MOSH ranging between 6.76 and 78.49 mg/kg, averaging 46.72 mg/kg, indicating a higher contamination level than other types of oils. The results suggested that it is necessary to routinely detect mineral oil contamination in vegetable oils for food safety.     

新型药物载体聚乙烯-聚丙交酯载药颗粒的制备及表征

Methoxy poly （ethylene glycol） -poly （D, L-lactide） block copolymers （PEG-PLA） were prepared through ring-opening polymerization. The oil in water suspension method was used to prepare block copolymer micelles. The critical micelle concentration （CMC） by fluorescence spectroscopy was 0. 0056 mg· ml^- 1. The physical state of the inner core region of micelles was characterized with ^1 HNMR. The size of indomethacin （IMC） loaded micelles measured by dynamic light scattering （DLS） showed narrow monodisperse size distribution and the average diameters were less than 50 nm. In addition, the nanoparticles with relatively high drug loading content （DLC） were obtained.     

Stability and radical‐scavenging activity of heated olive oil and other vegetable oils

The effect of heating at 180 °C on the antioxidant activity of virgin olive oil (VOO), refined olive oil (ROO) and other vegetable oil samples (sunflower, soybean, cottonseed oils, and a commercial blend specially produced for frying) was determined by measuring the radical‐scavenging activity (RSA) toward 1,1‐diphenyl‐2‐picrylhydrazyl radical (DPPH^?). The RSA of the soluble (polar) and insoluble (non‐polar) in methanol/water fractions of olive oil samples was also measured. The stability of heated oils was assessed by determining their total polar compound (TPC) content. VOO was the most thermostable oil. Total polar phenol content and the RSA of VOO heated for 2.5 h decreased by up to 70 and 78%, respectively, of their initial values; an up to 84% reduction in RSA of VOO polar and non‐polar fractions also occurred. Similar changes were observed in the RSA of ROO and its non‐polar fraction after 2.5 h of heating. The other oils retained their RSA to a relatively high extent (up to 40%) after 10 h of heating, but in the meantime they reached the rejection point (25–27% TPC). The results demonstrate that VOO has a remarkable thermal stability, but when a healthful effect is expected from the presence of phenolic compounds, heating has to be restricted as much as possible.     

Characterization of vegetable oils‐alumina membranes interactions by diffuse reflectance Fourier transform infrared spectroscopy

Adsorption of vegetable oil components, either as pure molecules or as mixtures, on alumina membranes was investigated by diffuse reflectance Fourier transform infrared spectroscopy. All tested compounds displayed very similar spectra. Triolein and diolein physically adsorb onto alumina by hydrogen bonding with the carbonyl groups of the carboxylic ester and surface hydroxyls. Monolein most likely interacts with glycerol hydroxyls, while phospholipids appear to adsorb either by the ester carbonyl or charged phosphate group. Due to the catalytic properties of alumina some hydrolysis takes place during treatments. The resulting oleic acid, most likely chemisorbs by ionic interactions with the carboxylic C=O bond of the alumina. The fact that no change in the symmetric and asymmetric CH₂ stretches is noticed in comparison with the free (unbound) form indicates that the molecules are not parallel, but at an angle to the surface. When alumina comes into contact with increasing amounts of crude vegetable oils a broadening of the band at 3280 cm^‐1 indicates an increasing adsorption of molecules with free hydroxyls, such as mono‐ and di‐acylglycerols or phospholipids. Among all oil components, sodium oleate seems to adsorb preferentially to alumina. However, a subsequent adsorption of a lipidic monolayer at the membrane surface or even inside the pores, is not consistent with the drastic flux reduction observed in previous studies during microfiltration, and could only initiate formation or/and deposition of macromolecular structures inside membrane pores.     

Ethanolamines used for degumming of rapeseed and sunflower oils as diesel fuels

Pure vegetable oils can be used as alternative fuel for standard unmodified diesel engines, provided the oil viscosity has been lowered by heating before they enter the fuel injection system. In its role as diesel fuel, a vegetable oil has to have, among other parameters, a low acidity and low contents of phosphorus and the alkali earth metals Ca + Mg. Such parameters can be achieved by appropriate partial refining of oil by degumming. In this article, three common ethanolamines, monoethanolamine (MEA), diethanolamine (DEA) and triethanolamine (TEA), were used as degumming agents for removing non‐hydratable phospholipids from crude rapeseed and sunflower oils. Among the studied ethanolamines, MEA is the most effective for the removal of phosphorus. After degumming with MEA (0.5 wt‐%), the phosphorus content in rapeseed oil was reduced from 445 to 3.5 ppm, and from 163 to 2.2 ppm in sunflower oil. After oil treatment with MEA (1.0 wt‐%), the residual content of Ca and Mg decreased from 136 to 4.2 ppm and from 55.4 to 1.1 ppm in rapeseed oil. In sunflower oil, the values of Ca and Mg decreased from 23.9 to 1.5 ppm and from 24.6 to 1.0 ppm. The acid value of the oils also decreased after degumming with ethanolamines. The advantage of this oil treatment process is that it takes place at ambient temperature, resulting in lower production costs and simpler technology.     

Determination of phospholipids in vegetable oil by fourier transform infrared spectroscopy

A method was developed to determine the total phospholipid content in vegetable oil by Fourier transform infrared spectroscopy (FTIR). Calibration curves of I-α-phosphatidylcholine (PC), I-α-phosphatidylethanolamine (PE), and I-α-phosphatidylinositol (PI) in hexane were generated at different concentrations. The optimal phospholipid absorption bands between 1200–970 cm⁻¹ were identified and used for quantitative determination. High R ²≥0.968 were observed between band areas and phospholipid standard concentrations. Phospholipids from crude soybean oil were obtained by water degumming, and purification was performed on a silicic acid column. The phospholipid contents of purified phospholipid extract, degummed and crude soybean oil determined from calibration equations were >90, 0.0113, and 1.77%, respectively. High correlations of determination (R ²≥0.933) were observed between the FTIR method and thin-layer chromatography-imaging densitometry method for the determination of phospholipid content. FTIR was found to be a useful analytical tool for simple and rapid quantitative determination of phospholipids in vegetable oil.     

Plasticization effects of epoxidized vegetable oils on mechanical properties of poly(3‐hydroxybutyrate)

The effect of various epoxidized vegetable oils as potential plasticizers for poly(3‐hydroxybutyrate) (PHB) was evaluated in terms of changes in mechanical and thermal properties and morphology. PHB is a biodegradable aliphatic polyester obtained from bacterial fermentation. High stiffness and fragility are two of its main drawbacks. To overcome this behaviour, PHB was plasticized with various amounts of two different epoxidized vegetable oils: epoxidized linseed oil (ELO) and epoxidized soybean oil (ESBO). The total ELO and ESBO content varied in the range 5 phr (per hundred resin) to 20 phr and plasticized PHB materials were obtained by melt extrusion and compounding followed by injection moulding. The results show that the plasticizing effect provided by ELO is more efficient than that by ESBO with balanced properties at a concentration of 10 phr ELO. ELO addition leads to an improvement in mechanical ductile properties with a noticeable increase in elongation at break and impact absorbed energy. With regard to thermal properties, the addition of both ELO and ESBO leads to a marked increase in thermal stability of PHB. All these findings suggest that addition of 10 phr ELO leads to optimized PHB formulations with potential uses in technical applications. © 2016 Society of Chemical Industry     

A new analytical method to monitor lipid peroxidation during bleaching

Whereas solid phase microextraction (SPME) combined with gas chromatography is a wide‐spread technique in certain fields of food analysis this technique is quite new for the analysis of vegetable oils. The method is sensitive enough to follow changes in the oxidative state of vegetable oils by measuring the amount of volatile materials produced during storage and the refining process. In the present study degummed rapeseed oil was bleached using different activated bleaching earths applied in four dosages. Their effect on lipid degradation was determined both by traditional methods (e.g. UV absorbance, p‐anisidine value) and by the SPME‐HS method. Although the p‐anisidine value (p‐AV) gives only the concentration of β‐unsaturated aldehydes it correlates well to the amount of total volatile substances as determined by SPME at the headspace of the sample. The extracted volatile materials were separated and identified by gas chromatography combined with mass spectrometry. SPME gives more information about the stage of oxidation and the applied bleaching earth by quantifying the volatile compounds. Additionally SPME does not require any toxic reagent such as p‐methoxy aniline which is used to determine the p‐AV. Although bleaching is very important it was disregarded in recent years. Therefore one of the aims of the present study is to draw back more attention towards bleaching.     

Structure of Mixed Reverse Microemulsions Based on Sodium Bis (2-Ethylhexyl) Sulfosuccinate and Sodium Cholate

The microenvironment of water droplets of sodium bis (2-ethylhexyl) sulfosuccinate (AOT) and sodium cholate mixed reverse microemulsions was studied. Structural changes of water pockets in mixed reverse micelles were investigated by IR spectroscopy. The O-H stretching vibrational absorption spectra in the region of 3000–3800 cm⁻¹ were fit to three subpeaks with the Monte Carlo method. It was revealed that additives of sodium cholate suppress free water fraction in the water droplets of reverse micelles from 31% to 20% and support rising of bound fraction from 53% to 65%. The binding of optical probe ortho-nitroaniline to the mixed reverse micelles was determined by UV–visible spectroscopy. It was found that introducing of additives of sodium cholate below its critical micelle concentration (CMC) causes increasing of values of binding constant K_b twice compared with reverse micelles modified with pure water. However, values of the binding constant were reduced 4-fold at concentrations of sodium cholate higher than its CMC. Electrical conductivity of the reverse mixed micellar solutions (AOT + sodium cholate) was measured. Water-induced percolation in conductance of mixed reverse microemulsions occurs at a lower value of water/surfactant molar ratio (W) under the influence of sodium cholate, viz. electrical percolation threshold decreases from W = 32 to W = 15. The size of water droplets was estimated with the dynamic light scattering method. It was found that additives of sodium cholate below and higher than the CMC results in increasing and decreasing of hydrodynamic diameters of the water droplets, respectively, but sizes of water droplets decrease at concentrations of sodium cholate higher than its CMC.     

Micro‐reactor for transesterification of plant seed oils

The fatty acid compositions of vegetable or other plant seed oils are generally determined by gas chromatography (GC). Methyl esters (the most volatile derivatives) are the preferred derivatives for GC analysis. Esters of higher alcohols are good for the separation of volatile and positional isomers. All the esters of the C₁–C₈ alcohols of vegetable oils were silmilarly prepared by passing the reaction mixture containing the desired alcohol, oil and tetrahydrofuran through the micro‐reactor (a 3‐mL dispossible syringe packed with 0.5 g of NaOH powder). The reaction products were acidified with acetic acid and the mixture was analyzed by high‐performance size exclusion chromatography and GC. Transesterification was quantitative for primary alcohols, but an appreciable amount of free fatty acids was formed for secondary alcohols. Coriander seed oil was quantitatively esterified with 2‐ethyl 1‐hexanol with the micro‐reactor in less than 1 min. Oleic and petroselinic acid 2‐ethyl 1‐hexyl esters are baseline separated on an Rtx‐2330 capillary column (30 m×0.25 mm, 0.25 µm film thickness).     

Processing vegetable oils using nonporous denser polymeric composite membranes

Membrane processing offers several advantages over conventional processes for edible oil refining. In recent years, processing solvent-extracted, screw-pressed, and used frying oils using nonporous denser polymeric composite membranes without pretreatment and addition of chemicals has been extensively investigated. In the present review, results obtained with real and model systems have been summarized and a comprehensive explanation is provided on the mechanism of rejection and differential permeation of oil constituents. Phospholipid-TG and pigment-TG systems are construed as conventional solute-solvent systems, and tocopherol-TG and FFA-TG systems are treated as liquid mixtures exhibiting differential permeability. Dense membrane theory appears more applicable than the reverse osmosis theory in qualitatively explaining the differential permeability of liquid constituents of the oil. Membrane processing of oils appears to have the potential to be a one-step process, especially for screw-pressed oils, in producing a premium-quality product. However, the development of suitable membranes that enable higher fluxes is necessary for industrial adoption of this technology.     

Purity assessments of major vegetable oils based on δ13C values of individual fatty acids

The fatty acid compositions and δ¹³C values of the major fatty acids of more than 150 vegetable oils were determined to provide a database of isotopic information for use in the authentication of commercial maize oil. After extraction of oils from seeds, nuts or kernels, and methylation, fatty acid compositions were determined by capillary gas chromatography. All compositions were within the ranges specified by the Codex Alimentarius. Gas chromatography combustion-isotope ratio mass spectrometry was employed to determine the δ¹³C values of the major fatty acids of the oils. A large number of pure maize oils and potential adulterant oils from various parts of the world were studied to assess the sources of variability in δ¹³C values. Such information is vital to establishing the compound specific isotope technique as a reliable means of assessing vegetable oil purity. Variability in δ¹³C values was related to the geographical origin of the oil, year of harvest, and the particular variety of oil. This suggests that the ultimate δ¹³C values of fatty acids are determined by a combination of environmental and genetic factors.