Effects of droplet size on the oxidative stability of oil-in-water emulsions

Interfacial structural role of pH-shifting processed pea protein in the oxidative stability of oil/water emulsions

Understanding the behavior of protein surfactants at the oil-water interface is essential to the design of physicochemically stable emulsions. The objective of the study was to investigate the steric role of an interfacial membrane made of structurally modified pea protein with alkaline pH treatment (APP) in the oxidative stability of oil-in-water emulsions. Confocal laser scanning microscopy depicted more uniform and smaller oil droplets that had a reduced tendency to coalesce for emulsions prepared with APP than with native pea protein (NPP). Correspondingly, the APP emulsions were less prone to oxidation (malonaldehyde, peroxide) during storage. Similarly, cryo-transmission electron microscopy revealed more uniform air pockets with smoother undersurface that were surrounded by partially coalesced emulsions in whipped creams prepared with APP than with NPP. The improved interfacial properties and steric hindrance played a crucial role in the inhibition of oxidation in emulsions by alkaline pH-modified pea protein.

Composition, properties and potential food applications of natural emulsions and cream materials based on oil bodies

Oil bodies are micron- or submicron-sized organelles found mainly in parts of plants such as seeds, nuts or some fruits and their main role is to function as energy stores.

Effect of droplet size on autoxidation rates of methyl linoleate and α-linolenate in an oil-in-water emulsion

Methyl linoleate and α-linolenate were used as representative n-6 and n-3 polyunsaturated fatty acid esters, respectively, to examine the effect of oil droplet size on autoxidative stability in oil-in-water systems. The emulsions, which were prepared via membrane emulsification and had a mean oil droplet size of approximately 1-30 μm, and had a stable size during the autoxidation of each substrate at 55°C. The autoxidation of methyl linoleate did not depend on oil droplet size during the entire process and that of methyl α-linolenate was independent of oil droplet size during the first half of the autoxidation process. However, the autoxidation rate of methyl α-linolenate proceeded faster in the emulsion with smaller oil droplet size during the last half of the autoxidation process.

Characterization of an antioxidant surfactant-free topical formulation containing Castanea sativa leaf extract

CONTEXT

Inclusion of antioxidants in topical formulations can contribute to minimize oxidative stress in the skin, which has been associated with photoaging, several dermatosis and cancer.

OBJECTIVE

A Castanea sativa leaf extract with established antioxidant activity was incorporated into a semisolid surfactant-free formulation. The objective of this study was to perform a comprehensive characterization of this formulation.

MATERIALS AND METHODS

Physical, microbiological and functional stability were evaluated during 6 months storage at 20 °C and 40 °C. Microstructure elucidation (cryo-SEM), in vitro release and in vivo moisturizing effect (Corneometer® CM 825) were also assessed.

RESULTS AND DISCUSSION

Minor changes were observed in the textural and rheological properties of the formulation when stored at 20 °C for 6 months and the antioxidant activity of the plant extract remained constant throughout the storage period. Microbiological quality was confirmed at the end of the study. Under accelerated conditions, higher modifications of the evaluated parameters were observed. Cryo-SEM analysis revealed the presence of oil droplets dispersed into a gelified external phase. The release rate of the antioxidant compounds (610 ± 70 µgh(-0.5)) followed Higuchi model. A significant in vivo moisturizing effect was demonstrated, that lasted at least 4 h after product's application.

CONCLUSION

The physical, functional and microbiological stability of the antioxidant formulation was established. Specific storage conditions should be recommended considering the influence of temperature on the stability. A skin hydration effect and good skin tolerance were also found which suggests that this preparation can be useful in the prevention or treatment of oxidative stress-mediated dysfunctions.

Structure and oxidative stability of oil in water emulsions as affected by rutin and homogenization procedure

The structural properties of oil-in-water (O/W) emulsions, as well as their oxidative stability upon storage at 50 °C, were studied. Eight different formulations were prepared, with the aim of studying the effect of three variables: the composition of the oil phase, the presence of the flavonoid rutin and the homogenization procedure on the structure and the oxidative stability. It was found that high pressure homogenization, through droplet size reduction, stabilized the emulsions both against creaming and oil oxidation. The interfacial protein was also partially replaced by rutin, further improving the stability of the emulsions, whereas purification of the oil phase had hardly any effect. Thus, the structural and oxidative stability of emulsions was controlled by the size of the droplets and improved by the addition of rutin.

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.

Autoxidation of unsaturated lipids in food emulsion

Unsaturated lipids having various physiological roles are of significance in biochemistry, nutrition, medicine, and food. However, the susceptibility of lipids to oxidation is a major cause of quality deterioration in food emulsions. The reaction mechanism and factors that influence oxidation are appreciably different for emulsified lipids and bulk lipids. This article gives a brief overview of the current knowledge on autoxidation of oil-in-water food emulsions, especially those that contain unsaturated lipids, which are important in the food industry. Autoxidation of unsaturated lipids in oil-in-water emulsion is discussed, and so also their oxidation mechanism, the major factors influencing oxidation, determination measures, research status, and the problems encountered in recent years. Some effective strategies for controlling lipid oxidation in food emulsion have been presented in this review.

Food-grade nanoemulsions: formulation, fabrication, properties, performance, biological fate, and potential toxicity

Nanoemulsions fabricated from food-grade ingredients are being increasingly utilized in the food industry to encapsulate, protect, and deliver lipophilic functional components, such as biologically-active lipids (e.g., ω-3 fatty acids, conjugated linoleic acid) and oil-soluble flavors, vitamins, preservatives, and nutraceuticals. The small size of the particles in nanoemulsions (r<100 nm) means that they have a number of potential advantages over conventional emulsions-higher stability to droplet aggregation and gravitational separation, high optical clarity, ability to modulate product texture, and, increased bioavailability of lipophilic components. On the other hand, there may also be some risks associated with the oral ingestion of nanoemulsions, such as their ability to change the biological fate of bioactive components within the gastrointestinal tract and the potential toxicity of some of the components used in their fabrication. This review article provides an overview of the current status of nanoemulsion formulation, fabrication, properties, applications, biological fate, and potential toxicity with emphasis on systems suitable for utilization within the food and beverage industry.

Oxidative stability of egg and soy lecithin as affected by transition metal ions and pH in emulsion

Oxidative stability of egg and soy lecithin in emulsion was evaluated with two transition metal ions, cupric and ferric ion, at two concentration levels (50 and 500 microM). The effect of pH on lipid oxidation was also examined under these two concentrations for each ion. Egg lecithin (EL) had similar peroxide value (PV) development pattern as soy lecithin (SL) when treated with cupric ion under both acidic and neutral pH. Acidic pH of 3 accelerated oxidation of both EL and SL, especially under high concentration of copper. When treated with ferric ion, EL oxidized much faster than SL did. EL had higher value of thiobarbituric acid-reactive substances (TBARS) than SL, possibly because of its higher content of long-chain polyunsaturated fatty acids (PUFA). Acidic pH accelerated TBARS development for both EL and SL, but EL had more significantly increased values. Cupric ion was more powerful than ferric in catalyzing oxidation of both EL and SL under both acidic and neutral pH conditions as measured by PV and TBARS. Linoleic acid may contribute to higher PV production, however, arachidonic acid and docosahexaenoic acid may have contributed more to TBARS production. Overall, SL showed better oxidative stability than EL under the experimental conditions. This study also suggests that using multiple methods is necessary in properly evaluating lipid oxidative stability.

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.

Homogenization conditions affect the oxidative stability of fish oil enriched milk emulsions: oxidation linked to changes in protein composition at the oil-water interface

Fish oil was incorporated into milk under different homogenization temperatures (50 and 72 degrees C) and pressures (5, 15, and 22.5 MPa). Subsequently, the oxidative stability of the milk and changes in the protein composition of the milk fat globule membrane (MFGM) were examined. Results showed that high pressure and high temperature (72 degrees C and 22.5 MPa) resulted in less lipid oxidation, whereas low pressure and low temperature (50 degrees C and 5 MPa) resulted in faster lipid oxidation. Analysis of protein oxidation indicated that especially casein was prone to oxidation. The level of free thiol groups was increased by high temperature (72 degrees C) and with increasing pressure. Furthermore, SDS-PAGE and confocal laser scanning microscopy (CLSM) indicated that high temperature resulted in an increase in beta-lactoglobulin adsorbed at the oil-water interface. This was even more pronounced with higher pressure. Less casein seemed to be present at the oil-water interface with increasing pressure. Overall, the results indicated that a combination of more beta-lactoglobulin and less casein at the oil-water interface gave the most stable emulsions with respect to lipid oxidation.