Effects of addition of hydrophobic sucrose fatty acid oligoesters on crystallization rates of n-hexadecane in oil-in-water emulsions

Ultrasonic velocity measurements were made on crystallization rates of n-hexadecane dispersed in an oil-in-water (O/W) emulsion (20 wt.% oil and 80 wt.% water) in which Tween 20 was employed for emulsification. Highly hydrophobic emulsifiers, sucrose fatty acid oligoesters involving stearic acid (S-170), lauric acid (L-195) and oleic acid (O-170) moieties, were added to n-hexadecane in an attempt to modify the crystallization rate of n-hexadecane. The crystallization process of n-hexadecane was monitored by variations in the ultrasonic velocity values, which increase with increasing amount of crystal fractions in the oil phase of the emulsion. In comparison with the results of the O/W emulsion systems with the additive P-170 (a sucrose palmitate) (N.Kaneko et al., J. Crystal Growth 197 (1999) 263), the following results were obtained: (a) the addition of S-170 accelerated the nucleation in the emulsion system in the same manner as P-170, no acceleration was revealed with the additive O-170, and L-195 showed moderate effects; (b) the rate of crystal growth was retarded by S-170 and L-195, but not by O-170; (c) the effects of acceleration of nucleation occurred singly in the emulsion system, but not in the bulk system; and (d) the acceleration of nucleation was exhibited through two stages with increasing concentrations of the additives. These results showed the remarkable influence of the fatty acid chain structures of sucrose oligoesters on the acceleration of heterogeneous nucleation of n-hexadecane in the O/W emulsions. The heterogeneous nucleation effected by the addition of S-170 and P-170 was discussed taking into account the adsorption at the oil-water interface and the formation of reversed micelles of the sucrose oligoesters added in the oil phase.     

Particle tracking using confocal microscopy to probe the microrheology in a phase-separating emulsion containing nonadsorbing polysaccharide

Brownian diffusion of fluorescent microspheres (0.21, 0.5, and 0.89 microm diameter) in conjunction with confocal microscopy has been used to monitor the microrheology of phase-separated regions in a protein-stabilized oil-in-water emulsion containing various low concentrations of a nonadsorbing polysaccharide, xanthan gum. The sensitivity and reliability of the technique has been demonstrated in test experiments on (i) aqueous glycerol solutions and (ii) concentrated surfactant-stabilized emulsions (30-60 vol % oil, 1-2 wt % Tween 20). From particle tracking measurements on the caseinate-stabilized emulsions (30 vol % oil, 1.4 wt % sodium caseinate, pH 7) containing xanthan (0.03-0.07 wt %), the apparent viscosity in the oil-droplet-rich regions has been estimated to be up to 10(3) times higher than that in the phase-separated xanthan-rich regions. This means that our previously determined shape relaxation times for xanthan-containing blobs in the same systems can be attributed to the dominant viscoelasticity of the surrounding regions of concentrated oil droplets and not to the rheology of the xanthan-rich blobs themselves. These data provide clear and unequivocal evidence for the dominant role of the interconnected depletion-flocculated network of oil droplets in the physicochemical mechanism by which hydrocolloid thickeners control the creaming instability of concentrated oil-in-water emulsions.     

Fractional crystallization of oil droplets in O/W emulsions dispersed by Synperonic F127

The aim of this works is to study an oil-in-water emulsion stabilized with a triblock copolymer Synperonic F127 which presents a double size distribution of oil droplets. The emulsions were studied experimentally by means of differential scanning calorimetry (DSC) and dynamic light scattering (DLS). The DSC analysis was carried out focusing on the cooling behavior of the emulsion. The cooling thermograms of the oil-in-water emulsion revealed two crystallization peaks with Gaussian profile; the interesting characteristic is that both peaks are separated in temperature. In accordance to previous works for a single oil dispersed within an aqueous phase, the DSC technique must show a single Gaussian peak of crystallization attributable to a size distribution of droplets. In the present case of emulsions stabilized with 1 g/L of Synperonic F127, the aggregation behavior of triblock as a function of temperature allows to produce an emulsion with a double size droplet distribution. Comparison with emulsions stabilized with 2 and 4 wt% of non-ionic Tween 20 are also presented.     

Effect of molecular weight and degree of deacetylation of chitosan on the formation of oil-in-water emulsions stabilized by surfactant-chitosan membranes

The objective of this study was to establish the influence of polyelectrolyte characteristics (molecular weight and charge density) on the properties of oil-in-water emulsions containing oil droplets surrounded by surfactant-polyelectrolyte layers. A surfactant-stabilized emulsion containing small droplets (d32 approximately 0.3 microm) was prepared by homogenizing 20 wt% corn oil with 80 wt% emulsifier solution (20 mM SDS or 2.5 wt% Tween 20, 100 mM acetate buffer, pH 3) using a high-pressure valve homogenizer. This primary emulsion was then diluted with various chitosan solutions to produce secondary emulsions with a range of chitosan concentrations (3 wt% corn oil, 0-1 wt% chitosan). The influence of the molecular characteristics of chitosan on the properties of these emulsions was examined by using chitosan ingredients with different molecular weights (MW approximately 15, 145, and 200 kDa) and degree of deacetylation (DDA approximately 40, 77, and 92%). The electrical charge and particle size of the secondary emulsions were then measured. Extensive droplet aggregation occurred when the chitosan concentration was below the amount required to saturate the droplet surfaces, but stable emulsions could be formed at higher chitosan concentrations. The zeta-potential and mean diameter (d32) of the particles in the secondary emulsions was not strongly influenced by chitosan MW, however the chitosan with the lowest DDA (40%) produced droplets with smaller mean diameters and zeta-potentials than the other two DDA samples examined. Interestingly, we found that stable multilayer emulsions could be formed by mixing medium or high MW chitosan with an emulsion stabilized by a non-ionic surfactant (Tween 20) due to the fact the initial droplets had some negative charge. The information obtained from this study is useful for preparing emulsions stabilized by multilayer interfacial layers.     

Influence of droplet characteristics on the formation of oil-in-water emulsions stabilized by surfactant-chitosan layers

The objective of this study was to establish the optimum conditions for preparing stable oil-in-water emulsions containing droplets surrounded by surfactant-chitosan layers. A primary emulsion containing small droplets (d32 approximately = 0.3 microm) was prepared by homogenizing 20 wt% corn oil with 80 wt% emulsifier solution (20 mM SDS, 100 mM acetate buffer, pH 3) using a high-pressure valve homogenizer. The primary emulsion was diluted with chitosan solutions to produce secondary emulsions with a range of oil and chitosan concentrations (0.5-10 wt% corn oil, 0-1 wt% chitosan, pH 3). The secondary emulsions were sonicated to help disrupt any droplet aggregates formed during the mixing process. The electrical charge, particle size, and amount of free chitosan in the emulsions were then measured. The droplet charge changed from negative to positive as the amount of chitosan in the emulsions was increased, reaching a relatively constant value (approximately +50 mV) above a critical chitosan concentration (C(Sat)), which indicated that saturation of the droplet surfaces with chitosan occurred. Extremely large droplet aggregates were formed at chitosan concentrations below C(Sat), but stable emulsions could be formed above C(Sat) provided the droplet concentration was not high enough for depletion flocculation to occur. Interestingly, we found that stable multilayer emulsions could also be formed by mixing chitosan with an emulsion stabilized by a nonionic surfactant (Tween 20) due to the fact the initial droplets had some negative charge. The information obtained from this study is useful for preparing emulsions stabilized by multilayer interfacial layers.     

Effect of lateral heterogeneity in mixed surfactant-stabilized interfaces on the oxidation of unsaturated lipids in oil-in-water emulsions

The development of lipid oxidation in oil-in-water (O/W) emulsions is widely influenced by the properties of the interfacial layer, which separates the oil and water phases. In this work, the effect of the structure of the interface on the oxidative stability of surfactant stabilized O/W emulsions was investigated. Emulsions were prepared with either single Tween 20 or Tween 20/co-surfactant mixtures in limiting amounts. The co-surfactants, Span 20 and monolauroyl glycerol have the same hydrophobic tail as Tween 20 but differ by the size and composition of their polar headgroup. Metal-initiated lipid oxidation, monitored through the measurement of oxygen uptake, formation of conjugated dienes and volatile compounds, developed more rapidly in the emulsions stabilized by the surfactant mixture than in the single Tween 20-stabilized emulsion. The reconstitution of Tween 20/co-surfactant films at the air-water interface and their surface-pressure isotherms highlighted that, contrary to single Tween 20 molecules, Tween 20/co-surfactant mixtures exhibited an heterogeneous distribution within the interfacial layer, offering probably easier access of water-soluble pro-oxidants to the oil phase. These observations provide direct information about the link between the homogeneity of the interface layer and the oxidative stability of emulsions.     

SYNERGETIC EFFECT OF SUCROSE AND ETHANOL ON FORMATION OF TRIGLYCERIDE MICROEMULSIONS

The phase behavior of soybean oil, a nonionic surfactant (ethoxylated monodiglycerides) and an aqueous phase of water containing ethanol, and sucrose was investigated at 35 and 40°C. A minimum concentration of 20 wt% ethanol was required for the formation of isotropic solutions. Addition of sucrose to the aqueous phase decreased the amount of ethanol required to form these solutions. The solubilization mechanism of the oil was investigated by small angle x-ray diffraction and polarized light microscopy. A stable lamellar liquid crystalline phase was formed for a mixture of 75/25 surfactant/sucrose solution (2.5 wt% sucrose). This phase was destabilized with increased concentrations of sucrose and liquid crystalline phases having hexagonal structures were favored at 8.75 wt% sucrose. At a ratio of 55/45 wt% of surfactant/sucrose solution (9 wt% sucrose) hexagonal structures were formed and could be destabilized or destroyed by addition of ethanol. The concept of stabilization and destabilization of liquid crystalline mesophases was applied to the solubilization of triglycerides in aqueous solutions. Two microemulsion regions were identified; oil-in-water (L₁) and water-in-oil (L₂) in systems containing soybean oil, ethoxylated monodiglycerides, and 20 wt% ethanol solution. At 55/45 wt% surfactant/20 wt% ethanol solution,7.5 wt% of soybean oil was solubilized. Addition of 10, 20, and 30 wt% sucrose, at the same ratio of surfactant to ethanol solution, increased the solubility of the oil to 9, 13.5, and 18 wt% respectively. In addition, the size of the L₁ phase increased and moved to the aqueous corner of the phase diagram and the size of the L₂ phase decreased.     

Influence of oil polarity on droplet growth in oil-in-water emulsions stabilized by a weakly adsorbing biopolymer or a nonionic surfactant

The influence of oil type (n-hexadecane, 1-decanol, n-decane), droplet composition (hexadecane:decanol), and emulsifier type (Tween 20, gum arabic) on droplet growth in oil-in-water emulsions was studied. Droplet size distributions of emulsions were measured over time (0-120 h) by laser diffraction and ultrasonic spectroscopy. Emulsions containing oil molecules of low polarity and low water solubility (hexadecane) were stable to droplet growth, irrespective of the emulsifier used to stabilize the droplets. Emulsions containing oil molecules of low polarity and relatively high water solubility (decane) were stable to coalescence, but unstable to Ostwald ripening, irrespective of emulsifier. Droplet growth in emulsions containing oil molecules of relatively high polarity and high water solubility (decanol) depended on emulsifier type. Decanol droplets stabilized by Tween 20 were stable to droplet growth in concentrated emulsions but unstable when the emulsions were diluted. Decanol droplets stabilized by gum arabic exhibited rapid and extensive droplet growth, probably due to a combination of Ostwald ripening and coalescence. We proposed that coalescence was caused by the relatively low interfacial tension at the decanol-water boundary, which meant that the gum arabic did not absorb strongly to the droplet surfaces and therefore did not prevent the droplets from coming into close proximity.     

Influence of environmental stresses on stability of oil-in-water emulsions containing droplets stabilized by beta-lactoglobulin-iota-carrageenan membranes

An oil-in-water emulsion (5 wt% corn oil, 0.5 wt% beta-lactoglobulin (beta-Lg), 0.1 wt% iota-carrageenan, 5 mM phosphate buffer, pH 6.0) containing anionic droplets stabilized by interfacial membranes comprising of beta-lactoglobulin and iota-carrageenan was produced using a two-stage process. A primary emulsion containing anionic beta-Lg coated droplets was prepared by homogenizing oil and emulsifier solution together using a high-pressure valve homogenizer. A secondary emulsion containing beta-Lg-iota-carrageenan coated droplets was formed by mixing the primary emulsion with an aqueous iota-carrageenan solution. The stability of primary and secondary emulsions to sodium chloride (0-500 mM), calcium chloride (0-12 mM), and thermal processing (30-90 degrees C) were analyzed using zeta-potential, particle size and creaming stability measurements. The secondary emulsion had better stability to droplet aggregation than the primary emulsion at NaCl 相似文献   

Oil and Water Separation Using a Glass Microfiber Coalescing Bed

A vertical sleeve separator using glass microfiber with a mean diameter of 4 µm as coalescence medium was explored to remove oil from the oil-in-water (O/W) emulsions. The artificial emulsions were prepared by mixing diesel oil and water to obtain oil droplets with a mean diameter about 7 µm. A series of experiments were performed to investigate the effect of such parameters as bed porosity (0.850–0.925), bed height (2.0–20.0 mm), flow velocity (1.0–20.0 mL/s), and influent oil concentration (200.0–3000.0 mg/L) on the effluent oil concentration and oil removal efficiency. The obtained effluent oil concentration was from 4.98 to 53.04 mg/L, and the oil removal efficiency was 96.4–99.8%. In addition, the article identifies the interaction between bed porosity and height, explains the mutual influences between the emulsion velocity and concentration, and quantitatively derives the appropriate ranges of bed characteristics and operating conditions.     

Preparation of finely dispersed O/W emulsion from fatty acid solubilized in subcritical water

A novel method for preparing a finely dispersed oil-in-water emulsion is proposed. Octanoic acid dissolved in water at a high temperature of 220 or 230 degrees C at 15 MPa was combined with an aqueous solution of a surfactant and then the mixture was cooled. When a nonionic surfactant, decaglycerol monolaurate (ML-750) or polyoxyethylene sorbitan monolaurate (Tween 20), was used, fine emulsions with a median oil droplet diameter of 100 nm or less were successfully prepared at ML-750 and Tween 20 concentrations of 0.083% (w/v) and 0.042%, respectively, or higher. The diameters were much smaller than those of oil droplets prepared by the conventional homogenization method using a rotor/stator homogenizer. However, an anionic surfactant, sodium dodecyl sulfate, was not adequate for the preparation of such fine emulsions by the proposed method. Although the interfacial tensions between octanoic acid and the surfactant solutions were measured at different temperatures, they were not an indication for selecting a surfactant for the successful preparation of the fine emulsion by the proposed method.     

Texture and Stability of Emulsions: Role of Oscillatory Structural Forces

A digitized optical imaging technique was used to obtain the droplet size distribution, texture, and the radial distribution function which determines the inter-droplet interactions in emulsion systems. The effects of sucrose ester and polyglycerin stearic acid ester as emulsifiers on the stability (i.e., creaming) of oil-in-water food emulsions were investigated, ft was observed that as the concentration of the emulsifier was increased, the droplet size decreased, and the emulsion became more monodispersed and the stability increased. This was confirmed by the experimentally determined radial distributions and the structure factors. It was found that the emulsion made with the fatty acid ester was more stable than that with sucrose ester, and was less polydisperse with better texture. A statistical thermodynamic model was applied which accounts for the droplet-droplet interaction forces, i.e., oscillatory structural forces, and the polydispersity effect to predict the creaming velocity of an oil-in-water emulsion. Good agreement was found between the experimentally determined creaming velocity and the model predictions.     

Formation and Physical Stability of Zanthoxylum bungeanum Essential Oil Based Nanoemulsions Co-Stabilized with Tea Saponin and Synthetic Surfactant

The purpose of this work was to evaluate the possibility of adding tea saponin (TS) to reduce the synthetic surfactant concentration, and maintain or improve the shelf stability of nanoemulsions. The Zanthoxylum bungeanum essential oil (2.5 wt%) loaded oil-in-water nanoemulsions were co-stabilized by Tween 40 (0.5–2.5 wt%) and TS (0.1–5 wt%). A combination of several analytical techniques, such as dynamic laser scattering, interfacial tension, zeta potential, and transmission electron microscope, were used for the characterization of nanoemulsions. Low levels of TS (0.1–0.5 wt%) with Tween 40 had significant effects on the emulsification, and a nanoemulsion with the smallest droplet diameter of 89.63 ± 0.67 nm was obtained. However, in the presence of high TS concentration (0.5–5 wt%), micelles generated by the non-adsorbed surfactants in the aqueous lead to droplets growth. In addition, the combinations of Tween 40 and TS at the high level (>3.5 wt%) exerted a synergistic effect on stabilizing the nanoemulsions and preventing both Ostwald ripening and coalescence. The negative charged TS endowed the droplets with electrostatic repulsion and steric hinderance appeared to prevent flocculation and coalescence. These results would provide a potential application of natural TS in the preparation and stabilization of nanoemulsions containing essential oil.     

Investigations of the Effects of Xanthan and Sodium Caseinate on the Formation and Stability of an Oil-in-Water Emulsion Stabilized by a Nonionic Surfactant Using a Response Surface Method

Effects of xanthan and sodium caseinate concentrations on the rheological properties and stability of an oil-in water emulsion stabilized by a nonionic surfactant (Tween 20) were investigated. In order to evaluate the influence of component concentrations on the emulsion properties, a response surface method was applied. It was shown by polynomial simulation and modelization of responses of storage modulus and creaming index that in absence of Tween 20, the oily droplets were flocculated by bridging of sodium caseinate macromolecules, when those are insufficient to cover the entire interface. Additionally, it was noted that xanthan reinforces the polymeric network in the aqueous phase when the caseinate is not moved toward the phase. On the other hand, in presence of nonadsorbed caseinate, the polysaccharide develops segregative interactions by thermodynamic incompatibility. These nonadsorbed macromolecules can also flocculate the fatty globules by depletion.     

Behavior of soybean oil-in-water emulsion stabilized by nonionic surfactant

A soybean oil-in-water emulsion was prepared using nonionic Tween series surfactants. The effects of temperature, hydrophilic-lipophilic balance (HLB) value of the surfactant, and surfactant-to-oil ratio on the size of emulsion drops were investigated with an acoustic and electroacoustic devices. In the case of Tween 85, the influence of pH and electrolyte on the zeta potential of emulsion drops was examined. zeta potential appears to be strongly dependent on pH, varying in the case of high concentrations of NaCl from +60 to -90 mV. High concentrations of Na+ and K+ are capable of separating the oil phase from the emulsion. Divalent cations such as Ca2+ and Mg2+ lead to two points of zero charge at high concentrations, which is not observed for the case of hydrolyzable trivalent species like Al3+ and Fe3+.     

Flaxseed Oil-In-Water Emulsions Stabilized by Multilayer Membranes: Oxidative Stability and the Effects of pH

The investigation of the effect of multilayer membranes on the stability of flaxseed oil-in-water (o/w) emulsions was the main goal of this study. The primary emulsion was prepared by homogenizing the oil phase (10 wt%) with an aqueous sodium caseinate solution (90 wt% and a pH 6.8) using a high-pressure microfluidizer. This emulsion was mixed with a pectin solution to form a secondary emulsion at a pH 6.8 and then adjusted to a pH to 3 for the adsorption of anionic pectin molecules on the surface of the cationic droplet surfaces. The pH effect on the physical stability of the emulsions was evaluated by measuring the mean particle diameter, ζ-potential, creaming index, and visualization of the microstructure. Also, the oxidative stability was determined by monitoring the lipid hydroperoxides and thiobarbituric acid-reactive substances (TBARs) at 55°C. The results of this study indicate that a multilayer structure had a positive effect on the improvement of the physical and oxidative stability of the conventional emulsions under certain pH conditions and limited storage period.     

EFFECT OF DROPLET SIZE ON OXIDATION OF DOCOSAHEXAENOIC ACID IN EMULSION SYSTEM

We investigated the effect of oil droplet size on the oxidation rate of DHA monodispersed emulsion with xanthan. Xanthan-free emulsions creamed rapidly but no creaming was observed in the emulsions containing xanthan over 8 weeks. While the peroxide value (POV) of the xanthan-free emulsion reached 10meq/ kg at 20 days, that of both emulsion systems containing xanthan changed little during the first 20 days. The POV for the emulsion with small droplet was higher than that for the emulsion with large droplet.     

Viability and permeability across Caco-2 cells of CBZ solubilized in fully dilutable microemulsions

The purpose of this study was to evaluate the viability and permeability of carbamazepine (CBZ) solubilized in fully dilutable non-ionic microemulsions across Caco-2 cells used as a model for intestinal epithelium. Maximum solubilization capacity (SC) of CBZ was determined within water-in-oil (W/O), bicontinuous and oil-in-water (O/W) structures formed upon dilution. The effect of the nature of the oil phase, surfactant type, and the ratio between the oil phase and surfactant on the quantity of solubilized CBZ, droplets size, the viability of the cells and drug permeability was elucidated. We found that: (1) several fully dilutable microemulsions based on pharma-grade ingredients can be loaded with very significant amounts of CBZ, (2) W/O microemulsions (10wt% water) exhibit up to 3-fold higher solubilization capacity over the drug's solubility in oil (triacetin), (3) CBZ in the O/W microemulsions (80wt% water) exhibit up to 29-fold higher solubilization than in water, (4) the O/W droplets of the examined systems are 9-11nm in size, (5) the highest permeability was obtained in systems containing triacetin/alpha-tocopherol acetate/ethanol in 3/1/4wt% ratio as oil phase and Tween 60 as surfactant, (6) the replacement of alpha-tocopherol acetate by alpha-tocopherol inhibits CBZ release, (7) replacement of a saturated chain of Tween 60 by an unsaturated (Tween 80) or shorter chain (Tween 40) inhibited drug release, (8) the decrease in the oil phase to surfactant ratio leads to enhancement of drug release (dilution line 64>dilution line 73).     

Effect of surfactant sucrose ester on physical properties of dairy whipped emulsions in relation to those of O/W interfacial layers

Dairy foams were manufactured on a pilot plant with various sucrose ester contents. Oil-in-water emulsions were produced by high-pressure homogenisation of anhydrous milk fat (20 wt%) with an aqueous phase containing skim milk powder (6.5 wt%), sucrose (15 wt%), hydrocolloids (2 wt%), and sucrose esters. Sucrose ester content was varied from 0 to 0.35 wt%. Firmness and stability of dairy foams were determined. The fraction of protein associated with emulsion fat droplets and the compression isotherms of those droplets were determined as a function of sucrose ester content. With less than 0.1 wt% sucrose ester, no foam could be produced. The most firm and stable foams were obtained with ca. 0.1 wt% sucrose ester. The fraction of protein associated with emulsion droplets suddenly falls from 60% at a sucrose ester content lower than 0.1125% down to ca. 10-20% for higher surfactant content. Compression isotherms of emulsion droplets at the air-water interface show that, in the presence of surfactant, emulsion droplets disrupt and spread at the interface whilst without surfactant they become dispersed. This means that the presence of sucrose ester causes some destabilisation of fat droplet interfacial layers. There is hence an optimal sucrose ester content that allows some destabilisation of the oil-water interface without concomitant protein displacement from that interface. Consequently, with the recipe and manufacturing process used to produce dairy foams, there exists a compromise in sucrose ester content with regards to manufacture and shelf-life of dairy foams.     

Effect of Emulsifier Type on the Characterization of O/W Emulsions Using a Spectroscopy Technique

The droplet size distribution (DSD) of emulsions is the result of two competitive effects that take place during emulsification process, i.e., drop breakup and drop coalescence, and it is influenced by the formulation and composition variables, i.e., nature and amount of emulsifier, mixing characteristics, and emulsion preparation, all of which affect the emulsion stability. The aim of this study is to characterize oil-in-water (O/W) emulsions (droplet size and stability) in terms of surfactant concentration and surfactant composition (sodium dodecyl benzene sulphonate (SDBS)/Tween 80 mixture). Ultraviolet-visible (UV-vis) transmission spectroscopy has been applied to obtain droplet size and stability of the emulsions and the verification of emulsion stability with the relative cleared volume technique (time required for a certain amount of emulsion to separate as a cleared phase). It is demonstrated that the DSD of the emulsions is a function of the oil concentration and the surfactant composition with higher stability for emulsions prepared with higher SDBS ratio and lower relative cleared volume with the time. Results also show that smaller oil droplets are generated with increasing Tween 80 ratio and emulsifier concentration.