Lipid oxidation in emulsions as affected by charge status of antioxidants and emulsion droplets

The influence of charge status of both lipid emulsion droplets and phenolic antioxidants on lipid oxidation rates was evaluated using anionic sodium dodecyl sulfate (SDS) and nonionic polyoxyethylene 10 lauryl ether (Brij)-stabilized emulsion droplets and the structurally similar phenolic antioxidants gallamide, methyl gallate, and gallic acid. In nonionic, Brij-stabilized salmon oil emulsions at pH 7.0, gallyol derivatives (5 and 500 microM) inhibited lipid oxidation with methyl gallate > gallamide > gallic acid. In the Brij-stabilized salmon oil emulsions at pH 3.0, low concentrations of the galloyl derivatives were prooxidative or ineffective while high concentrations were antioxidative. In SDS-stabilized salmon oil emulsions, oxidation rates were faster and the galloyl derivatives were less effective compared to the Brij-stabilized emulsions. Differences in antioxidant activity were related to differences in the ability of the galloyl derivatives to partition into emulsion droplets and to increase the prooxidant activity of iron at low pH.     

Ability of surfactant micelles to alter the physical location and reactivity of iron in oil-in-water emulsion

The purpose of this research was to determine how surfactant micelles influence iron partitioning and iron-promoted lipid oxidation in oil-in-water emulsions. Lipids containing ferric ions were used to produce oil-in-water emulsions, and continuous-phase iron concentrations in emulsions were measured as a function of varying continuous-phase polyoxyethylene 10-lauryl ether (Brij) concentrations. Continuous-phase iron concentrations increased with increasing surfactant micelle concentrations (0.1-2.0%) and storage time (1-7 days). At pH 3.0, the concentration of continuous-phase iron was higher than at pH 7.0. Similar trends in iron solubilization by Brij micelles were observed when either hexadecane or corn oil was used as the lipid phase. Lipid oxidation rates, as determined by the formation of lipid hydroperoxides and headspace hexanal, in corn oil-in-water emulsions containing iron decreased with increasing surfactant concentrations (0.5-2.0%). These results indicate that surfactant micelles could alter the physical location and prooxidant activity of iron in oil-in-water emulsions.     

Production and characterization of O/W emulsions containing droplets stabilized by lecithin-chitosan-pectin mutilayered membranes

The possibility of producing stable oil-in-water (O/W) emulsions containing oil droplets surrounded by multiple layer interfacial membranes from food grade ingredients has been demonstrated. These emulsions were produced using a three stage process that relies on the adsorption of charged biopolymers to oppositely charged surfaces. Emulsions (0.5 wt % corn oil, 0.1 wt % lecithin, 0.0078 wt % chitosan, 0.02 wt % pectin, and 100 mM acetic acid, pH 3.0) containing oil droplets stabilized by lecithin-chitosan-pectin membranes were formed using this interfacial layer-by-layer deposition process. The droplets in these emulsions had good stability to aggregation over a wide range of pH values and salt concentrations (pH 4-8 at 0 mM NaCl and pH 3-8 at 100 mM NaCl). This technology could be extremely useful to the food industry for the creation of O/W emulsions with improved properties or novel applications, e.g., improved stability to environmental stresses, protection of labile substances, controlled release, and triggered release.     

Metal-catalyzed oxidation of a structured lipid model emulsion

The effects of temperature, time, metal, citric acid, and tocopherol contents on the oxidation stability of a model oil-in-water emulsion prepared with enzymatically synthesized menhaden oil-caprylic acid structured lipid were evaluated by response surface methodology. The emulsions were stabilized by whey protein isolate. Oxidation was monitored by measuring lipid hydroperoxides and thiobarbituric acid reactive substances (TBARS). Cupric sulfate and ferrous sulfate were used to study the effect of metal concentration and type. A statistical model was developed to determine the relationships between all variables considered. The relationships differed depending on the type of metal catalyst used. For both metal types, the metal concentration had the highest positive effect on peroxide value. Citric acid had the highest negative effect on peroxide value for iron-containing emulsions, while tocopherol had the highest negative effects for copper-containing emulsions. Results from the TBARS test did not vary significantly enough to yield an acceptable model.     

Impact of lipid physical state on the oxidation of methyl linolenate in oil-in-water emulsions

The purpose of this research was to examine the influence of the physical state of lipids on iron-promoted oxidation of methyl linolenate in octadecane oil-in-water emulsions. Octadecane and methyl linolenate oil-in-water emulsions were prepared that contained droplets having the octadecane as either liquid or solid. The physical state of the octadecane was confirmed by a differential scanning calorimeter (DSC). The effect of the physical state of the lipid on oxidation rates was determined as a function of iron concentration (80 and 160 microM), pH (3.0 or 7.0), emulsifier type, and cooling rate. Oxidation of methyl linolenate was determined by lipid hydroperoxides and thiobarbituric acid reactive substances (TBARS). Emulsions containing solid octadecane had higher rates of lipid hydroperoxide and TBARS formation than those containing liquid octadecane. The rate at which the emulsions were cooled had no influence on oxidation rates. Oxidation rates in both emulsions increased with increasing iron concentration and decreasing pH. Oxidation rates were lowest in emulsions with cationic droplet membranes (dodecyl trimethylammonium bromide-stabilized), presumably due to the repulsion of iron from the oxidizable methyl linolenate in the emulsion droplet core. These results suggest that upon crystallization of octadecane, the liquid methyl linolenate migrated to the emulsion droplet surface, where it was more prone to oxidation because it was in closer contact with the iron ions in the aqueous phase.     

Effects of alpha-tocopherol, beta-carotene, and soy isoflavones on lipid oxidation of structured lipid-based emulsions

Structured lipids (SLs) are triacylglycerols that have been modified to change the fatty acid composition and/or positional distribution in the glycerol backbone by chemically and/or enzymatically catalyzed reactions and/or genetic engineering. Ten percent oil-in-water emulsions were formulated with a canola oil/caprylic acid SL and stabilized with 0.5% whey protein isolate (WPI) or sucrose fatty acid ester (SFE). The effects of alpha-tocopherol, beta-carotene, genistein, and daidzein (added at 0.02 wt % of oil) on lipid oxidation were evaluated over a 15-day period in emulsion samples. Significantly (p < 0.05) less total oxidation (calculated from peroxide value and anisidine value measurements) occurred in the WPI emulsions compared to their SFE counterparts. In this study, alpha-tocopherol, beta-carotene, and both soy isoflavones exhibited prooxidant activities in SFE emulsions. Because of their ability to exhibit prooxidant activity under certain conditions, manufacturers must experiment with these compounds before adding them to SL-based products as functional ingredients.     

Chemical and antioxidant properties of casein peptide and its glucose Maillard reaction products in fish oil-in-water emulsions

Maillard reaction products (MRPs) were prepared by reacting casein peptides with different concentrations of glucose at 80 °C for up to 12 h. The chemical properties of MRPs and their effects on lipid oxidation in fish oil-in-water emulsions were investigated. Increasing browning development and absorbance in 294 nm in the MRPs caused an increase in DPPH radical scavenging, but a decrease in iron chelation, which could be related to the loss of free amino groups in the peptides. The MRPs produced with longer reaction time or higher glucose concentrations were less effective in inhibiting lipid oxidation in emulsions at pH 7.0 compared to casein peptides alone. However, the antioxidant activity of MRPs in emulsions at pH 3.0 was not decreased by prolonged heating. The bitterness of MRPs was less than that of the original casein peptides, and bitterness decreased with increasing heating time and glucose concentrations. Therefore, the Maillard reaction was a potential method to reduce the bitterness of casein peptides while not strongly decreasing their antioxidant activity.     

Effect of emulsifier on oxidation properties of fish oil-based structured lipid emulsions

The effects of the emulsifiers lecithin, Tween 20, whey protein isolate, mono-/diacylglycerols, and sucrose fatty acid ester on oxidation stability of a model oil-in-water emulsion prepared with enzymatically synthesized menhaden oil-caprylic acid structured lipid were evaluated. Oxidation was monitored by measuring lipid hydroperoxides, thiobarbituric acid reactive substances, and the ratio of combined docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) contents to palmitic acid in the emulsion. After high-pressure homogenization, all emulsions, except those prepared with lecithin, had similar droplet size distributions. All structured lipid emulsions, except for the lecithin-stabilized emulsions, were stable to creaming over the 48-day period studied. Emulsifier type and concentration affected oxidation rate, with 0.25% emulsifier concentration generally having a higher oxidation rate than 1% emulsifier concentration. Overall, oxidation did not progress significantly enough in 48 days of storage to affect DHA and EPA levels in the emulsion.     

Interactions between iron, phenolic compounds, emulsifiers, and pH in omega-3-enriched oil-in-water emulsions

The behavior of antioxidants in emulsions is influenced by several factors such as pH and emulsifier type. This study aimed to evaluate the interaction between selected food emulsifiers, phenolic compounds, iron, and pH and their effect on the oxidative stability of n-3 polyunsaturated lipids in a 10% oil-in-water emulsion. The emulsifiers tested were Tween 80 and Citrem, and the phenolic compounds were naringenin, rutin, caffeic acid, and coumaric acid. Lipid oxidation was evaluated at all levels, that is, formation of radicals (ESR), hydroperoxides (PV), and secondary volatile oxidation products. When iron was present, the pH was crucial for the formation of lipid oxidation products. At pH 3 some phenolic compounds, especially caffeic acid, reduced Fe(3+) to Fe(2+), and Fe(2+) increased lipid oxidation at this pH compared to pH 6. Among the evaluated phenols, caffeic acid had the most significant effects, as caffeic acid was found to be prooxidative irrespective of pH, emulsifier type, and presence of iron, although the degrees of lipid oxidation were different at the different experimental conditions. The other evaluated phenols were prooxidative at pH 3 in Citrem-stabilized emulsions and had no significant effect at pH 6 in Citrem- or Tween-stabilized emulsions on the basis of the formation of volatiles. The results indicated that phenol-iron complexes/nanoparticles were formed at pH 6.     

Lipid oxidation in corn oil-in-water emulsions stabilized by casein,whey protein isolate,and soy protein isolate

Proteins can be used to produce cationic oil-in-water emulsion droplets at pH 3.0 that have high oxidative stability. This research investigated differences in the physical properties and oxidative stability of corn oil-in-water emulsions stabilized by casein, whey protein isolate (WPI), or soy protein isolate (SPI) at pH 3.0. Emulsions were prepared with 5% corn oil and 0.2-1.5% protein. Physically stable, monomodal emulsions were prepared with 1.5% casein, 1.0 or 1.5% SPI, and > or =0.5% WPI. The oxidative stability of the different protein-stabilized emulsions was in the order of casein > WPI > SPI as determined by monitoring both lipid hydroperoxide and headspace hexanal formation. The degree of positive charge on the protein-stabilized emulsion droplets was not the only factor involved in the inhibition of lipid oxidation because the charge of the emulsion droplets (WPI > casein > or = SPI) did not parallel oxidative stability. Other potential reasons for differences in oxidative stability of the protein-stabilized emulsions include differences in interfacial film thickness, protein chelating properties, and differences in free radical scavenging amino acids. This research shows that differences can be seen in the oxidative stability of protein-stabilized emulsions; however, further research is needed to determine the mechanisms for these differences.     

Antioxidant activity of a proanthocyanidin-rich extract from grape seed in whey protein isolate stabilized algae oil-in-water emulsions

Algae oil-in-water emulsions stabilized with 0.2% whey protein isolate (WPI) at pH 3.0 and 7.0 were chosen to evaluate antioxidant activity of a proanthocyanidin-rich extract from grape seed. In this emulsion system, (+)-catechin and ascorbic acid (620 microM) were found to be prooxidative at pH 3.0 and ineffective at pH 7.0. Grape seed extract was not able to effectively inhibit both lipid hydroperoxides and propanal formation when added to the emulsion at 124 microM. However, increasing the concentration of the grape seed extract to 620 microM resulted in inhibition of both lipid hydroperoxide and propanal formation at pH 3.0 and 7.0. None of the antioxidants tested had any effect on the physical stability of the WPI-stabilized emulsion. The superior antioxidant activity of the grape seed extract is likely due to the presence of oligomeric procyanidins which are better antioxidants compared to their monomeric counterparts.     

Impact of whey protein emulsifiers on the oxidative stability of salmon oil-in-water emulsions

To obtain a better understanding of how the interfacial region of emulsion droplets influences lipid oxidation, the oxidative stability of salmon oil-in-water emulsions stabilized by whey protein isolate (WPI), sweet whey (SW), beta-lactoglobulin (beta-Lg), or alpha-lactalbumin (alpha-La) was evaluated. Studies on the influence of pH on lipid oxidation in WPI-stabilized emulsions showed that formation of lipid hydroperoxides and headspace propanal was much lower at pH values below the protein's isoelectric point (pI), at which the emulsion droplets were positively charged, compared to that at pH values above the pI, at which the emulsion droplets were negatively charged. This effect was likely due to the ability of positively charged emulsion droplets to repel cationic iron. In a comparison of lipid oxidation rates of WPI-, SW-, beta-Lg-, and alpha-La-stabilized emulsions at pH 3, the oxidative stability was in the order of beta-Lg > or = SW > alpha-La > or = WPI. The result indicated that it was possible to engineer emulsions with greater oxidative stability by using proteins as emulsifier, thereby reducing or eliminating the need for exogenous food antioxidants.     

Iron-accelerated cumene hydroperoxide decomposition in hexadecane and trilaurin emulsions

Free radicals arising from lipid peroxides accelerate the oxidative deterioration of foods. To elucidate how lipid peroxides impact oxidative reactions in food emulsions, the stability of cumene hydroperoxide was studied in hexadecane or trilaurin emulsions stabilized by anionic (sodium dodecyl sulfate; SDS), nonionic (Tween 20), and cationic (dodecyltrimethylammonium bromide; DTAB) surfactants. Fe(2+) rapidly (within 10 min) decomposed between 10 and 31% of the cumene hydroperoxide in Tween 20- and DTAB-stabilized emulsions at pH 3.0 and 7.0 and in the SDS-stabilized emulsion at pH 7.0 with no further decomposition of peroxides occurring for up to 3 h. In SDS-stabilized emulsions at pH 3.0, Fe(2+) decreased peroxides by 90% after 3 h. Decomposition of peroxides in the absence of added iron and by Fe(3+) was observed only in SDS-stabilized emulsions at pH 3.0. These results suggest that peroxide decomposition by iron redox cycling occurs when iron emulsion droplet interactions are high.     

Volatile composition of sunflower oil-in-water emulsions during initial lipid oxidation: influence of pH.

The formation of odor active compounds resulting from initial lipid oxidation in sunflower oil-in-water emulsions was examined during storage at 60 degrees C. The emulsions differed in initial pH, that is, pH 3 and 6. The volatile compounds were isolated under mouth conditions and were analyzed by gas chromatography/sniffing port analysis. The lipid oxidation rate was followed by the formation of conjugated hydroperoxide dienes and headspace hexanal. The initial pH affected the lipid oxidation rate in the emulsions: the formation of conjugated diene hydroperoxides and the hexanal concentration in the static headspace were increased at pH 6. Pentanal, hexanal, 3-pentanol, and 1-octen-3-one showed odor activity in the emulsions after 6 days of storage, for both pH 3 and 6. Larger amounts of odor active compounds were released from the pH 6 emulsion with extended storage. It was shown that this increased release at pH 6 was not due to increased volatility because an increase in pH diminished the static headspace concentrations of added compounds in emulsions.     

Ability of lipid hydroperoxides to partition into surfactant micelles and alter lipid oxidation rates in emulsions

Lipid hydroperoxides are important factors in lipid oxidation due to their ability to decompose into free radicals. In oil-in-water emulsions, the physical location of lipid hydroperoxides could impact their ability to interact with prooxidants such as iron. Interfacial tension measurements show that linoleic acid, methyl linoleate, and trilinolein hydroperoxides are more surface-active than their non-peroxidized counterparts. In oil-in-water emulsion containing surfactant (Brij 76) micelles in the continuous phase, linoleic acid, methyl linoleate, and trilinolein hydroperoxides were solubilized out of the lipid droplets into the aqueous phase. Brij 76 solubilization of the different hydroperoxides was in the order of linoleic acid > trilinolein > or = methyl linoleate. Brij 76 micelles inhibited lipid oxidation of corn oil-in-water emulsions with greater inhibition of oxidation occurring in emulsions containing linoleic acid hydroperoxides. Surfactant solubilization of lipid hydroperoxides could be responsible for the ability of surfactant micelles to inhibit lipid oxidation in oil-in-water emulsions.     

Protein-stabilized nanoemulsions and emulsions: comparison of physicochemical stability, lipid oxidation, and lipase digestibility

The properties of whey protein isolate (WPI) stabilized oil-in-water (O/W) nanoemulsions (d(43) ≈ 66 nm; 0.5% oil, 0.9% WPI) and emulsions (d(43) ≈ 325 nm; 0.5% oil, 0.045% WPI) were compared. Emulsions were prepared by high-pressure homogenization, while nanoemulsions were prepared by high-pressure homogenization and solvent (ethyl acetate) evaporation. The effects of pH, ionic strength (0-500 mM NaCl), thermal treatment (30-90 °C), and freezing/thawing on the stability and properties of the nanoemulsions and emulsions were compared. In general, nanoemulsions had better stability to droplet aggregation and creaming than emulsions. The nanoemulsions were unstable to droplet flocculation near the isoelectric point of WPI but remained stable at higher or lower pH values. In addition, the nanoemulsions were stable to salt addition, thermal treatment, and freezing/thawing (pH 7). Lipid oxidation was faster in nanoemulsions than emulsions, which was attributed to the increased surface area. Lipase digestibility of lipids was slower in nanoemulsions than emulsions, which was attributed to changes in interfacial structure and protein content. These results have important consequences for the design and utilization of food-grade nanoemulsions.     

Influence of environmental conditions on the stability of oil in water emulsions containing droplets stabilized by lecithin-chitosan membranes

Oil-in-water emulsions containing cationic droplets stabilized by lecithin-chitosan membranes were produced using a two-stage process. A primary emulsion containing anionic lecithin-coated droplets was prepared by homogenizing oil and emulsifier solution using a high-pressure valve homogenizer (5 wt % corn oil, 1 wt % lecithin, 100 mM acetic acid, pH 3.0). A secondary emulsion containing cationic lecithin-chitosan-coated droplets was formed by diluting the primary emulsion with an aqueous chitosan solution (1 wt % corn oil, 0.2 wt % lecithin, 100 mM acetic acid, and 0.036 wt % chitosan). The stabilities of the primary and secondary emulsions with the same oil concentration to thermal processing, freeze-thaw cycling, high calcium chloride concentrations, and lipid oxidation were determined. The results showed that the secondary emulsions had better stability to droplet aggregation during thermal processing (30-90 degrees C for 30 min), freeze-thaw cycling (-10 degrees C for 22 h/30 degrees C for 2 h), and high calcium chloride contents (相似文献   

Influence of environmental stresses on stability of O/W emulsions containing cationic droplets stabilized by SDS-fish gelatin membranes

Oil-in-water (O/W) emulsions containing small oil droplets (d32 approximately 0.22 microm) stabilized by sodium dodecyl sulfate (SDS)-fish gelatin (FG) membranes were produced by an electrostatic deposition technique. A primary emulsion containing anionic SDS-coated droplets (zeta approximately -40 mV) was prepared by homogenizing oil and emulsifier solution using a high-pressure valve homogenizer (20 wt % corn oil, 0.46 wt % SDS, 100 mM acetic acid, pH 3.0). A secondary emulsion containing cationic SDS-FG-coated droplets (zeta approximately +30 mV) was formed by diluting the primary emulsion with an aqueous fish gelatin solution (10 wt % corn oil, 0.23 wt % SDS, 100 mM acetic acid, 2.00 wt % fish gelatin, pH 3.0). The stabilities of primary and secondary emulsions with the same oil concentration to thermal processing, ionic strength, and pH were assessed by measuring particle size distribution, zeta potential, microstructure, destabilized oil, and creaming stability. The droplets in secondary emulsions had good stability to droplet aggregation at holding temperatures from 30 to 90 degrees C for 30 min, [NaCl] < or = 100 mM, and pH values from 3 to 8. This study shows that the ability to generate emulsions containing droplets stabilized by multilayer interfacial membranes comprised of two or more types of emulsifiers, rather than a single interfacial layer comprised of one type of emulsifier, may lead to the development of food products with improved stability to environmental stresses.     

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.     

Stabilization of oil-in-water emulsions by cod protein extracts

The ability of two protein fractions extracted from cod to form and stabilize oil-in-water emulsions was examined: a high salt extracted fraction (HSE protein) and a pH 3 acid extracted fraction (AE protein). Both fractions consisted of a complex mixture of different proteins, with the predominant one being myosin (200 kDa). The two protein fractions were used to prepare 5 wt % corn oil-in-water emulsions at ambient temperature (pH 3.0, 10 mM citrate-imidazole buffer). Emulsions with relatively small mean droplet diameters (d(3,2) < 1 microm) and good creaming stability (> 9 days) could be produced at protein concentrations > or =0.2 wt % for both fractions. The isoelectric point of droplets stabilized by both protein fractions was pH approximately 5. The emulsions were stable to droplet flocculation and creaming at relatively low pH (< or =4) and NaCl concentrations (< or =150 mM) when stored at room temperature. In the absence of salt, the emulsions were also stable to thermal treatment (30-90 degrees C for 30 min), but in the presence of 100 mM NaCl droplet flocculation and creaming were observed in some of the emulsions, particularly those stabilized by the AE fraction. The results suggest that protein fractions extracted from cod can be used as emulsifiers to form and stabilize food emulsions.