Ability of surfactant micelles to alter the partitioning of phenolic antioxidants in oil-in-water emulsions

In oil-in-water emulsions, the physical location of antioxidants can be an important determinant in their activity. Surfactants can potentially influence the physical location of antioxidants in oil-in-water emulsions by causing solubilization of lipid-soluble antioxidants into the aqueous phase. Excess Brij micelles in an oil-in-water emulsion were found to increase the partitioning of phenolics into the continuous phase with polar antioxidants (propyl gallate) partitioning more than nonpolar antioxidants (butylated hydroxyltoluene). Solubilization of propyl gallate was rapid coming to equilibrium in less than 5 min. Increasing surfactant micelle concentrations from 0.3 to 2.8% increased the solubilization of propyl gallate by 2.3-fold. Solubilization of phenolic antioxidants into the aqueous phase by Brij micelles did not alter the oxidative stability of salmon oil-in-water emulsions, suggesting that surfactant micelles influenced oxidation rates by mechanisms other than antioxidant solubilization.     

Ability of surfactant headgroup size to alter lipid and antioxidant oxidation in oil-in-water emulsions

Oxidation of oil-in-water emulsion droplets is influenced by the properties of the interfacial membrane surrounding the lipid core. To evaluate how surfactant headgroup size influences lipid oxidation rates, emulsions were prepared with polyoxyethylene 10 stearyl ether (Brij 76) or polyoxyethylene 100 stearyl ether (Brij 700), which are structurally identical except for their hydrophilic headgroups, with Brij 700 containing 10 times more polyoxyethylene groups than Brij 76. Fe(2+)-promoted decomposition of cumene hydroperoxide was lower in Brij 700-stabilized than in Brij 76-stabilized hexadecane emulsions. Fe(2+)-promoted alpha-tocopherol oxidation rates were similar in hexadecane emulsion regardless of surfactant type. Brij 700 decreased production of hexanal from methyl linoleate and the formation of lipid peroxides and propanal from salmon oil compared to emulsions stabilized by Brij 76. These results indicate that emulsion droplet interfacial thickness could be an important determinant in the oxidative stability of food emulsions.     

Ability of surfactant hydrophobic tail group size to alter lipid oxidation in oil-in-water emulsions

Oxidation of oil-in-water emulsion droplets is influenced by the properties of the interfacial membrane surrounding the lipid core. Previous work has shown that an important factor in the oxidation of oil-in-water emulsions is surfactant properties that impact interactions between water-soluble prooxidants and lipids in the emulsion droplet. The purpose of this research was to study the impact of surfactant hydrophobic tail group size on lipid oxidation in oil-in-water emulsions stabilized by polyoxyethylene 10 lauryl ether (Brij-lauryl) or polyoxyethylene 10 stearyl ether (Brij-stearyl). The ability of iron to decompose cumene peroxide was similar in hexadecane emulsions stabilized by Brij-stearyl and Brij-lauryl. Oxidation of methyl linoleate in hexadecane emulsions containing cumene peroxide was greater in droplets stabilized by Brij-lauryl than in those stabilized by Brij-stearyl at pH 3 with no differences observed at pH 7.0. Oxidation of salmon oil was greater in emulsions stabilized by Brij-lauryl than in those stabilized by Brij-stearyl as determined by both lipid peroxides and headspace propanal. These results suggest that surfactant hydrophobic tail group size may play a minor role in lipid oxidation in oil-in-water 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.     

Ability of surface-active antioxidants to inhibit lipid oxidation in oil-in-water emulsion

Lipid oxidation in dispersed lipids is prevalent at the oil-water interface where lipid hydroperoxides are decomposed into free radicals by transition metals. Free radical scavenging antioxidants are believed to be most effective in lipid dispersions when they accumulate at the oil-water interface. The surface activity of antioxidants could be increased by their conjugation to hydrocarbon chains. In this study, p-hydroxyphenylacetic acid (HPA) was conjugated with either a butyl or dodecyl group. The HPA conjugates were more effective at decreasing interfacial tension than unconjugated HPA, indicating that they were able to adsorb at lipid-water interfaces. However, free HPA was a more effective antioxidant than butyl and dodecyl conjugates in Menhaden oil-in-water emulsions as determined by both lipid hydroperoxides and thiobarbituric acid reactive substances. The increased antioxidant activity of free HPA could be due to its more effective free radical scavenging activity and its higher concentration in the lipid phase of oil-in-water emulsions in the presence of surfactant micelles where it can act as a chain-breaking antioxidant.     

Ability of iron to promote surfactant peroxide decomposition and oxidize alpha-tocopherol.

Peroxides are an important factor in oxidative reactions in foods because their decomposition can result in formation of highly reactive free radicals. Emulsifiers such as the Brijs, Tweens, and lecithin were found to contain 4-35 micromol of peroxides/g of surfactant. Peroxide concentrations in Tween 20 micelles increased in the presence of low iron concentrations but decreased when iron concentrations were high, suggesting that iron was capable of promoting both peroxide formation and decomposition. Oxidation of alpha-tocopherol was observed in micelles high in peroxides (Tween 20) but not in micelles where peroxide concentrations were low (Brij). Transition metals accelerated the oxidation of alpha-tocopherol in Tween 20 micelles, whereas EDTA stabilized alpha-tocopherol in the presence of added Fe(2+). These results suggest that surfactant peroxides could decrease the oxidative stability of food emulsions by acting as a source of free radicals, especially in the presence of transition metals.     

Effects of droplet crystallization and melting on the aroma release properties of a model oil-in-water emulsion

Aroma compounds partition between the dispersed and the continuous phases in emulsions, and phase transitions in the lipid droplets profoundly affect the position of the equilibrium. In the present study, the release of ethyl butyrate, ethyl pentanoate, ethyl heptanoate, and ethyl octanoate from a series of sodium caseinate-stabilized, n-eicosane emulsions was investigated as a function of solid and liquid lipid droplet concentration. For all compounds, headspace volatile concentrations above the solid droplet emulsions were higher than those above the liquid droplet emulsions. The interaction with liquid droplets could be modeled in terms of volume-weighted bulk partition coefficients while the more nonpolar volatiles bound to the surface of solid lipid droplets. The amount of volatiles bound to solid surfaces increased with aqueous concentration up to a critical point and then rapidly increased. The critical point corresponds to the dissolution of the solid lipid in a phase of adsorbed volatile. The binding of volatiles to both solid and liquid eicosane droplets is reversible.     

Effects of lecithin and pectin on riboflavin-photosensitized oxidation of orange oil in a multilayered oil-in-water emulsion

The effects of lecithin and pectin on riboflavin-photosensitized oxidation of orange oil in a multilayered oil-in-water emulsion are studied by response surface methodology. Lecithin and pectin contents are two variables studied. Mean oil droplet size, viscosity, and ζ-potential are investigated for evaluation of emulsion stability. Headspace oxygen depletion, increase of conjugated diene value, and released amounts of limonene and carvone are used as responses to evaluate the oxidative stability of orange oil in this emulsion. The results show that both lecithin and pectin contents have significant effects (p < 0.05) on the oxidative stability of orange oil in the multilayered emulsion during photosensitized oxidation. No interactive effect (p < 0.05) is found between the lecithin and pectin contents. To achieve optimal oxidative stability, the suggested values in ratio for lecithin and pectin contents are 14.1 ± 0.5 and 19 ± 0.7, respectively.     

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.     

The effects of surfactant type, pH, and chelators on the oxidation of salmon oil-in-water emulsions.

Lipid oxidation in emulsions is influenced by the ability of transition metals to associate with emulsion droplets. The oxidative stability of 5% salmon oil-in-water emulsion was influenced by surfactant type, with oxidation rates being greatest in emulsions stabilized by anionic sodium dodecyl sulfate (SDS) followed by nonionic Tween 20 and cationic dodecyltrimethylammonium bromide (DTAB). EDTA inhibited lipid oxidation in all the emulsions, and apo-transferrin inhibited oxidation in the Tween 20-stabilized emulsions at pH 7.0, suggesting that continuous-phase iron was an active prooxidant. Iron associated with Tween-20 stabilized hexadecane emulsion droplets could be partitioned into the continuous phase by lowering the pH to 相似文献   

Effects of metal chelator, sodium azide, and superoxide dismutase on the oxidative stability in riboflavin-photosensitized oil-in-water emulsion systems

The effects of riboflavin photosensitization on the oxidative stability of oil-in-water (O/W) emulsions were determined using lipid hydroperoxides and headspace volatile analyses. The influences of a metal chelator, sodium azide, and superoxide dismutase (SOD) on oxidation pathways were tested to gain a better understanding of the role of transition metals, singlet oxygen, and superoxide anion, respectively. Emulsions with riboflavin and visible light irradiation had significantly higher lipid hydroperoxides and volatiles (p < 0.05) as compared to samples without light irradiation or riboflavin. The addition of ethylenediammetetraacetic acid (EDTA) decreased the formation of lipid hydroperoxides, hexanal, 2-heptenal, and 1-octen-3-ol in a concentration-dependent manner. Sodium azide, a singlet oxygen physical quencher, only inhibited the formation of 2-heptenal and 1-octen-3-ol. Overall, photosensitized riboflavin participated in both type I and type II pathways in O/W emulsions, and these pathways enhance the prooxidant activity of metals through their ability to produce lipid hydroperoxides and superoxide anion.     

Chemical and physical stability of citral and limonene in sodium dodecyl sulfate-chitosan and gum arabic-stabilized oil-in-water emulsions

Citral and limonene are the major flavor components of citrus oils. Both of these compounds can undergo chemical degradation leading to loss of flavor and the formation of undesirable off-flavors. Engineering the interface of emulsion droplets with emulsifiers that inhibit chemical reactions could provide a novel technique to stabilize citral and limonene. At present, emulsified flavor oils are usually stabilized by gum arabic (GA), which is a naturally occurring polysaccharide-protein complex. The objective of this study was to examine if citral and limonene were more stable in emulsions stabilized with a sodium dodecyl sulfate (SDS)-chitosan complex than GA. Citral degraded less in GA-stabilized than in SDS-chitosan-stabilized emulsions at pH 3.0. However, SDS-chitosan-stabilized emulsions were more effective at retarding the formation of the citral oxidation product, p-cymene, than GA-stabilized emulsions. Limonene degradation and the formation of limonene oxidation products, limonene oxide and carvone, were lower in the SDS-chitosan- than GA-stabilized emulsions at pH 3.0. The ability of an SDS-chitosan multilayer emulsifier system to inhibit the oxidative deterioration of citral and limonene could be due to the formation of a cationic and thick emulsion droplet interface that could repel prooxidative metals, thus decreasing prooxidant-lipid interactions.     

Effect of the simultaneous interaction among ascorbic acid, iron and pH on the oxidative stability of oil-in-water emulsions

The objective of this study was to demonstrate how different factors can simultaneously influence the oxidative stability of an oil-in-water emulsion, and how these factors can be used to enlarge the variation range of oxidation markers, expressed as peroxide value (PV) and TBARS. Initially, a Plackett-Burman design was used to screen seven factors (temperature, pH, and iron, copper, ascorbyl palmitate, ascorbic acid, and sodium chloride concentrations). A temperature elevation of 30 to 60 °C reduced PV and TBARS, a pH change from 3.0 to 7.0 increased PV and reduced TBARS, and the presence of ascorbic acid (1 mmol/L) had no significant effect on PV but increased TBARS (p < 0.05). Thus, the temperature was fixed at 30 °C, and an emulsion was formulated with different combinations of ascorbic acid, iron, and pH according to a central composite rotatable design. Regression models were fitted to PV and TBARs responses and optimized to get the higher values of both markers of oxidation. The optimized emulsion contained 1.70 mmol/L AH (ascorbic acid) and 0.885 mmol/L FeSO(4) · 7H(2)O (1.0 mmol/L Fe(2+)) at pH 5.51 and 30 °C. The range of variation observed for oxidation markers in the optimized emulsion model (PV, 0-4.27 mequiv/L; TBARS, 0-13.55 mmol/L) was larger than the variation observed in the nonoptimized model (PV, 0-1.05 mequiv/L; TBARS, 0-1.00 mmol/L). The antioxidant activity of six compounds (Trolox, α-tocopherol, caffeic acid, gallic acid, catechin, and TBHQ) was evaluated using the optimized emulsion conditions. After application of the Tukey HSD post hoc statistical test, the samples that were not different (p < 0.05) in the nonoptimized emulsions showed a significant difference in the optimized emulsions. Considering the importance of the interactions on oxidation studies, our model represents a significant improvement in a direct methodology that can be applied to evaluate natural compounds under different combination of factors.     

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.     

Conjugated linoleic acids alter the fatty acid composition and physical properties of egg yolk and albumen

Effects of dietary conjugated linoleic acids (CLAs) and docosahexaenoic acid (DHA) on the fatty acid composition of different egg compartments after storage were studied. Four dietary treatments [supplemented with safflower oil (SAFF, control group), DHA, CLAs plus DHA (CAD), and CLAs alone] were administered to Single Comb White Leghorn (SCWL) laying hens. Eggs from the different treatment groups were collected and stored for 10 weeks at 4 degrees C before analysis. Fatty acids from the yolk (yolk granules and plasma), egg albumen, and vitelline membrane were analyzed by gas chromatography. The yolk of eggs from hens given CLAs had significantly higher amounts of saturated fatty acids, typically 16:0 and 18:0, but lower amounts of polyunsaturated fatty acids (PUFAs) compared to eggs from the control group (SAFF). CLA content was highest in the yolk and present in both neutral and polar lipids, with the greatest concentrations in neutral lipids. DHA was incorporated mainly into yolk polar lipids. Lipids in yolk plasma and granules contained similar amounts of CLAs. The fatty acid compositions of vitelline membrane and egg albumen mirrored that of the egg yolk. CLA supplementation resulted in hard and rubbery yolks when compared to hard-cooked eggs from the control group. This study showed that feeding CLAs to hens led to accumulation of the isomers in polar and neutral lipids of the egg yolk and that these isomers migrated into egg albumen. Because the sensory properties of hard-cooked eggs were negatively affected by the enrichment of a mixture of CLA isomers in this study, further research should be conducted to evaluate how the different isomers alter the properties of egg yolk and albumen so that the quality of designed eggs containing CLAs and DHA can be improved.     

New insights into the role of iron in the promotion of lipid oxidation in bulk oils containing reverse micelles

Formation of physical structures, known as association colloids, in bulk oils can promote lipid oxidation. However, the cause of this accelerated lipid oxidation is unknown. Therefore, the aim of this study was to investigate whether transition metals were important prooxidants in bulk oils containing reverse micelles produced from 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and water. The Fe(III) chelator deferoxamine (DFO) increased the oxidative stability of stripped soybean oil (SSO) containing reverse micelles from 2 to 7 days. Because phosphatidylcholine (1,2-dibutyl-sn-glycero-3-phosphocholine) that does not form reverse micelles is not prooxidative, these results suggest that the prooxidant activity of DOPC reverse micelles could be due to their ability to concentrate both endogenous iron and lipid hydroperoxides at the water-lipid interface, thereby increasing the ability of iron to decompose lipid hydroperoxides. DFO was also able to improve the activity of α-tocopherol and Trolox in SSO containing DOPC reverse micelles increasing the lag phase from 2 to 11 and 13 days, respectively. DOPC reverse micelles decreased iron-promoted α-tocopherol and Trolox decomposition and decreased the ability of α-tocopherol and Trolox to decrease Fe(III) concentrations. Overall, these results suggest that iron is an important prooxidant in bulk oils containing reverse micelles; therefore, finding ways to control iron reactivity in association colloids could provide new technologies to increase the oxidative stability of oils.     

Stability in solution and reactivity with soils and soil components of iron and zinc complexes

Naturally derived complexes with the ability to complex (unidentate) or chelate (polydentate) metals are a cheaper alternative to synthetic chelates to correct micronutrient deficiencies, but despite their widespread use there is a lack of knowledge on their agronomic performance. The aim of this paper was to evaluate the stability of iron (Fe) and zinc (Zn) lignosulfonate, gluconate, amino acid, and humate complexes in solution over time and at different pH values. Also, their stability in a concentrated nutrient solution and their reactivity with soils and soil components was evaluated. In our experimental conditions, all the complexes (except Fe amino acid) remained stable in solution for an extended period of time. All Zn complexes and the Fe lignosulfonate were stable in solution up to pH 7.0–7.5, while Fe gluconate only maintained 20%–40% of the iron in solution in the pH range 5–11 and Fe amino acid and humate complexes barely maintained small concentrations of Fe in solution above pH 3. Most of the complexes maintained Fe and Zn in concentrated nutrient solutions for irrigation systems, but Fe amino acid only maintained around 70% of the iron added. In general, the interactions of complexes with soils and soil components produced a high retention. The interaction of Fe lignosulfonate with peat, illite, and ferrihydrite, and Fe gluconate with peat and illite resulted in significant amounts of Fe to remain in solution, while for the Fe amino acid and humate the Fe remaining in solution was low. All Zn complexes were highly retained in an acidic peat, illite, and montmorillonite clays and soils, while no retention was observed on ferrihydrite. In conclusion, the stability of complexes in different conditions is related to the percentage of complexed element in the products. While complexes can be used to maintain micronutrients in solution in aqueous media (foliar and fertigation), their application to soil should be considered as a measure to increase metal availabilities but not their solubility.     

Factors influencing the antioxidant and pro-oxidant activity of polyphenols in oil-in-water emulsions

The nonenzymatic oxidation of polyphenols bearing di- and trihydroxyphenol groups results in the generation of hydrogen peroxide (H?O?), a reactive oxygen species that can potentially compromise the oxidative stability of foods and beverages. An investigation of the factors that promote the oxidation of a model polyphenol, (-)-epigallocatechin-3-gallate (EGCG), was undertaken in a model lipid-based food system. Factors affecting oxidative stability, such as exogenous iron chelators (ethylenediaminetetraacetic acid; EDTA and 2,2-bipyridine; BPY) and pH (3 and 7) were evaluated in hexadecane and flaxseed oil-in-water (o/w) emulsions. At neutral pH, H?O? levels were observed to rise rapidly in hexadecane emulsions except for EDTA-containing treatments. However, EDTA-containing samples showed the highest rate of EGCG oxidation, suggesting that H?O? was rapidly reduced to hydroxyl radicals (HO?). Conversely, at pH 3, H?O? concentrations were lower across all treatments. EDTA conferred the highest degree of EGCG stability, with no loss of the catechin over the course of the study. In order to assess whether or not the H?O? production seen in oxidatively stable hexadecane emulsions translated to pro-oxidant activity in an oxidatively labile food lipid system, the effect of EGCG on the stability of flaxseed o/w emulsions was studied. EGCG displayed antioxidant activity at pH 7 throughout the study; however at pH 3, pro-oxidant activity was seen in EGCG-containing emulsions, with and without BPY. This study attempts to provide a mechanistic understanding of the conditions wherein polyphenols simultaneously exert pro-oxidant and antioxidant behavior in lipid dispersions.     

Potential of peroxynitrite to alter the color of myoglobin in muscle foods

Superoxide anion and nitric oxide can react to form the highly oxidizing species peroxynitrite. The objective of this research was to determine if peroxynitrite can promote the discoloration of myoglobin under conditions expected in muscle foods. Reagent peroxynitrite (25-100 microM) caused rapid and extensive formation of metmyoglobin from oxymyoglobin with the majority of metmyoglobin formation occurring during the first 5-10 min of incubation. Carbon dioxide caused a small decrease in the ability of peroxynitrite to oxidize oxymyoglobin, and peroxynitrite-promoted conversion of oxymyoglobin to metmyoglobin increased with decreasing pH (5.5-7.0). Differential scanning calorimetry suggested that peroxynitrite caused minimal changes in myoglobin structure. These results indicate that peroxynitrite can promote the conversion of oxymyoglobin to metmyoglobin under the conditions expected in muscle foods.