Influence of sodium dodecyl sulfate on the physicochemical properties of whey protein-stabilized emulsions

The influence of sodium dodecyl sulfate (SDS) on the flocculation of droplets in 20 wt.% soybean oil-in-water emulsions stabilized by whey protein isolate (WPI) was investigated by light scattering, rheology and creaming measurements. The SDS concentrations used were low enough to prevent depletion flocculation by surfactant micelles and extensive protein displacement. In the absence of SDS, emulsions were prone to droplet flocculation near the isoelectric point of the proteins (4<pH<6), but were stable at a higher and lower pH. Flocculation led to an increase in emulsion viscosity, pronounced shear thinning behavior and accelerated creaming. When the surfactant-to-protein molar ratio was increased from 0 to 10, the emulsion instability range shifted to lower pH values due to binding of the negatively charged SDS molecules to the droplets. Our results indicate that the physicochemical properties of protein-stabilized emulsions can be modified by utilizing surfactant–protein interactions.     

Influence of free protein on flocculation stability of beta-lactoglobulin stabilized oil-in-water emulsions at neutral pH and ambient temperature

The influence of protein concentration and order of addition relative to homogenization (before or after) on the extent of droplet flocculation in oil-in-water emulsions stabilized by a globular protein was examined using laser diffraction. n-Hexadecane (10 wt%) oil-in-water emulsions (pH 7, 150 mM NaCl) stabilized by beta-lactoglobulin (beta-Lg) were prepared by three methods: (1) 4 mg/mL beta-Lg added before homogenization; (2)10 mg/mL beta-Lg added before homogenization; (3) 4 mg/mL beta-Lg added before homogenization and 6 mg/mL beta-Lg added after homogenization. Emulsion 1 contained little nonadsorbed protein (<3%) and underwent extremely rapid and extensive droplet flocculation immediately after homogenization. Emulsion 2 contained a significant fraction of nonadsorbed beta-Lg and exhibited relatively slow droplet flocculation for some hours after homogenization. Measurements on Emulsion 3 showed that the extremely rapid particle growth observed in Emulsion 1 could be arrested by adding native beta-Lg immediately after homogenization. The extent of particle growth in the three types of emulsions was highly dependent on the time that the salt was added to the emulsions, i.e., after 0 or 24 h aging. We postulate that the observed differences are due to changes in droplet surface hydrophobicity caused by differences in the packing or conformation of adsorbed proteins. Our data suggest that history effects have a strong influence on the flocculation stability of protein-stabilized emulsions, which has important implications for the formulation and production of protein stabilized oil-in-water emulsions.     

Comparison of droplet flocculation in hexadecane oil-in-water emulsions stabilized by beta-lactoglobulin at pH 3 and 7

The influence of surface and thermal denaturation of adsorbed beta-lactoglobulin (beta-Lg) on the flocculation of hydrocarbon oil droplets was measured at pH 3 and compared with that at pH 7. Oil-in-water emulsions (5 wt % n-hexadecane, 0.5 wt % beta-Lg, pH 3.0) were prepared that contained different levels of salt (0-150 mM NaCl) added immediately after homogenization. The mean particle diameter (d43) and particle size distribution of diluted emulsions were measured by laser diffraction when they were either (i) stored at 30 degrees C for 48 h or (ii) subjected to different thermal treatments (30-95 degrees C for 20 min). In the absence of salt, little droplet flocculation was observed at pH 3 or 7 because of the strong electrostatic repulsion between the droplets. In the presence of 150 mM NaCl, a progressive increase in mean particle size with time was observed in pH 7 emulsions during storage at 30 degrees C, but no significant change in mean particle diameter with time (d43 approximately 1.4 +/- 0.2 microm) was observed in the pH 3 emulsions. Droplet aggregation became more extensive in pH 7 emulsions containing salt (added before thermal processing) when they were heated above 70 degrees C, which was attributed to thermal denaturation of adsorbed beta-Lg leading to interdroplet disulfide bond formation. In contrast, the mean particle size decreased and the creaming stability improved when pH 3 emulsions were heated above 70 degrees C. These results suggest that the droplets in the pH 3 emulsions were weakly flocculated at temperatures below the thermal denaturation temperature of beta-Lg (T < 70 degrees C) but that flocs did not form so readily above this temperature, which was attributed to a reduction in droplet surface hydrophobicity due to protein conformational changes. The most likely explanation for the difference in behavior of the emulsions is that disulfide bond formation occurs much more readily at pH 7 than at pH 3.     

Acoustic and electroacoustic spectroscopy of water-in-diluted-bitumen emulsions

Water-in-oil emulsions of Athabasca bitumen diluted with toluene have been studied using the latest advances in acoustic and electroacoustic spectroscopy. From the sound attenuation spectra of emulsions, the water droplet size distribution is measured. The electrical surface charge density of the water droplets is obtained from the colloid vibration current. In the case of freshly prepared water-in-oil emulsions, the droplet size increased while the surface charge density decreased with time. The time-dependent relaxation of the surface charge ranges from several hours to 3 days, and it is probably due to the slow adsorption/desorption kinetics of bituminous components at the water-oil interface. This study illuminates the contribution of the electrostatic interactions to the stability of water-in-oil emulsions.     

Influence of iota-carrageenan on droplet flocculation of beta-lactoglobulin-stabilized oil-in-water emulsions during thermal processing

The influence of thermal processing on droplet flocculation in oil-in-water emulsions stabilized by either beta-lactoglobulin (primary emulsions) or beta-lactoglobulin-iota-carrageenan (secondary emulsions) at pH 6 has been investigated. In the absence of salt, the zeta-potential of the primary emulsion was less negative (-40 mV) than that of the secondary emulsion (-55 mV) due to adsorption of anionic iota-carrageenan to the anionic beta-Lg-coated droplet surfaces. The zeta-potential and mean diameter (d(43) approximately 0.3 microm) of droplets in primary and secondary emulsions did not change after storage at temperatures ranging from 30 to 90 degrees C. In the presence of 150 mM NaCl, the zeta-potential of the primary emulsion was much less negative (-27 mV) than that of the secondary emulsion (-50 mV), suggesting that the latter was less influenced by electrostatic screening effects. The zeta-potential of the primary emulsions did not change after storage at elevated temperatures (30-90 degrees C). The zeta-potential of the secondary emulsions became less negative, and the aqueous phase iota-carrageenan concentration increased at storage temperatures exceeding 50 degrees C, indicating iota-carrageenan desorbed from the beta-Lg-coated droplets. In the primary emulsions, appreciable droplet flocculation (d(43) approximately 8 microm) occurred at temperatures below the thermal denaturation temperature (T(m)) of the adsorbed proteins due to surface denaturation, while more extensive flocculation (d(43) > 20 microm) occurred above T(m) due to thermal denaturation. In the secondary emulsions, the extent of droplet flocculation below T(m) was reduced substantially (d(43) approximately 0.8 microm), which was attributed to the ability of adsorbed carrageenan to increase droplet-droplet repulsion. However, extensive droplet flocculation was observed above T(m) because carrageenan desorbed from the droplet surfaces. Differential scanning calorimetry showed that iota-carrageenan and beta-Lg interacted strongly in aqueous solutions containing 0 mM NaCl, but not in those containing 150 mM NaCl, presumably because salt weakened the electrostatic attraction between the molecules.     

Influence of protein concentration and order of addition on thermal stability of beta-lactoglobulin stabilized n-hexadecane oil-in-water emulsions at neutral pH

The influence of protein concentration and order of addition relative to homogenization (before or after) on the extent of droplet flocculation in heat-treated oil-in-water emulsions stabilized by a globular protein were examined using laser diffraction. n-Hexadecane (10 wt%) oil-in-water emulsions (pH 7, 150 mM NaCl) stabilized by beta-lactoglobulin (beta-Lg) were prepared by three methods: (1) 4 mg/mL beta-Lg added before homogenization; (2) 4 mg/mL beta-Lg added before homogenization and 6 mg/mL beta-Lg added after homogenization; (3) 10 mg/mL beta-Lg added before homogenization. The emulsions were then subjected to various isothermal heat treatments (30-95 degrees C for 20 min), with the 150 mM NaCl being added either before or after heating. Emulsion 1 contained little nonadsorbed protein and exhibited extensive droplet aggregation at all temperatures, which was attributed to the fact that the droplets had a high surface hydrophobicity, e.g., due to exposed oil or extensive protein surface denaturation. Emulsions 2 and 3 contained a significant fraction of nonadsorbed beta-Lg. When the NaCl was added before heating, these emulsions were relatively stable to droplet flocculation below a critical holding temperature (75 and 60 degrees C, respectively) but showed extensive flocculation above this temperature. The stability at low temperatures was attributed to the droplets having a relatively low surface hydrophobicity, e.g., due to complete saturation of the droplet surface with protein or due to more limited surface denaturation. The instability at high temperatures was attributed to thermal denaturation of the adsorbed and nonadsorbed proteins leading to increased hydrophobic interactions between droplets. When the salt was added to Emulsions 2 and 3 after heating, little droplet flocculation was observed at high temperatures, which was attributed to the dominance of intra-membrane over inter-membrane protein-protein interactions. Our data suggests that protein concentration and order of addition have a strong influence on the flocculation stability of protein-stabilized emulsions, which has important implications for the formulation and production of many emulsion-based products.     

Flocculation and coalescence of droplets in oil-in-water emulsions formed with highly hydrolysed whey proteins as influenced by starch

The effects of added unmodified amylopectin starch, modified amylopectin starch and amylose starch on the formation and properties of emulsions (4 wt.% corn oil) made with an extensively hydrolysed commercial whey protein (WPH) product under a range of conditions were examined. The rate of coalescence was calculated based on the changes in the droplet size of the emulsions during storage at 20 degrees C. The rates of creaming and coalescence in emulsions containing amylopectin starches were enhanced with increasing concentration of the starches during storage for up to 7 days. At a given starch concentration, the rate of coalescence was higher in the emulsions containing modified amylopectin starch than in those containing unmodified amylopectin starch, whereas it was lowest in the emulsions containing amylose starch. All emulsions containing unmodified and modified amylopectin starches showed flocculation of oil droplets by a depletion mechanism. However, flocculation was not observed in the emulsions containing amylose starch. The extent of flocculation was considered to correlate with the rate of coalescence of oil droplets. The different rates of coalescence could be explained on the basis of the strength of the depletion potential, which was dependent on the molecular weight and the radius of gyration of the starches. At high levels of starch addition (>1.5%), the rate of coalescence decreased gradually, apparently because of the high viscosity of the aqueous phase caused by the starch.     

Enhancement of Ostwald ripening by depletion flocculation

The time dependence of the dynamic mobility and the ultrasonic attenuation of octane and decane oil-in-water emulsions stabilized by sodium dodecyl sulfate (SDS) was measured. The emulsions grew to larger droplets due to Ostwald ripening. The growth rate measured by attenuation depends on the surfactant concentration and the polydispersity of the emulsion. At surfactant concentrations below the critical micelle concentration (cmc) of SDS, the growth was linear with time and the rate was dependent on the polydispersity of the drops; the rate was several times faster than that predicted on the basis of a diffusion growth mechanism. Above the cmc, however, as the droplets grew in size there was a point at which the rate of growth increased, which corresponds to the droplet size at which depletion forces due to the surfactant micelles become significant. Under these conditions both the electroacoustic dynamic mobility and the acoustic attenuation spectra displayed characteristics of flocs: a large decrease in the phase lag at higher frequencies in the dynamic mobility spectrum and a decrease in the attenuation coefficient at low-megahertz frequencies with an increase at higher frequencies. This depletion flocculation enhancement in ripening rates in the presence of SDS micelles provides another, alternative, and self-consistent mechanism for the effect of surfactant micelles on Ostwald ripening.     

Production and characterization of oil-in-water emulsions containing droplets stabilized by multilayer membranes consisting of beta-lactoglobulin, iota-carrageenan and gelatin

The influence of environmental conditions (pH, NaCl, CaCl2, and temperature) on the properties and stability of oil-in-water (O/W) emulsions containing oil droplets surrounded by one-, two-, or three-layer interfacial membranes has been investigated. Three oil-in-water emulsions were prepared with the same droplet concentration and buffer (5 wt % corn oil, 5 mM phosphate buffer, pH 6) but with different biopolymers: (i) primary emulsion: 0.5 wt % beta-Lg; (ii) secondary emulsion: 0.5 wt % beta-Lg, 0.1 wt % iota-carrageenan; (iii) tertiary emulsion: 0.5 wt % beta-Lg, 0.1 wt % iota-carrageenan, 0-2 wt % gelatin. The secondary and tertiary emulsions were prepared by electrostatic deposition of the charged biopolymers onto the surfaces of the oil droplets so as to form two- and three-layer interfacial membranes, respectively. The stability of the emulsions to pH (3-8), sodium chloride (0-500 mM), calcium chloride (0-12 mM), and thermal processing (30-90 degrees C) was determined. We found that multilayer emulsions had better stability to droplet aggregation than single-layer emulsions under certain environmental conditions and that one or more of the biopolymer layers could be made to desorb from the droplet surfaces in response to specific environmental changes (e.g., high salt or high temperature). These results suggest that the interfacial engineering technology used in this study could lead to the creation of food emulsions with improved stability to environmental stresses or to emulsions with triggered release characteristics.     

A diffusing wave spectroscopy study of the dynamics of interactions between high methoxyl pectin and sodium caseinate emulsions during acidification

A non-invasive technique, diffusing wave spectroscopy (DWS), and traditional dynamic light scattering (DLS) were used to study the interactions of high methoxyl pectin (HMP) with sodium caseinate-stabilized emulsion droplets. At pH 6.8, the droplet size measured by DLS did not change as a function of HMP concentration (up to 0.3%). However, the droplet diameter measured by DWS kept relatively constant up to 0.07% HMP after which it showed drastic increases. The turbidity parameter 1/l* decreased with HMP concentration and levelled off at 0.07% HMP, indicating that the system underwent reorganization and reached equilibrium at 0.07% HMP. During acidification at pH 5.4, right before the pH of aggregation of control emulsions, all emulsions containing 0.05–0.2% HMP showed an increase of 1/l*. This increase indicated the interaction of HMP with sodium caseinate at the interface. Emulsions containing 0.05 and 0.1% HMP also showed destabilization, and the pH of destabilization depended on the concentration of HMP. Sufficient amounts of HMP (0.2%) stabilized the caseinate-coated oil droplets, and the mean square displacement slope was close to 1 throughout, indicating free diffusion of emulsion droplets.     

Flocculation and Coalescence of Oil-in-Water Poly(dimethylsiloxane) Emulsions

The stability of poly(dimethylsiloxane) (PDMS) oil-in-water emulsions has been investigated in the presence of added NaCl as well as in the presence of added surfactant. The emulsions were prepared using a combination of nonionic (C(x)E(y), x and y represent the number of methylene (C) and ethylene oxide (E) groups, respectively) and cationic (quarternary alkylammonium) surfactants. The droplets were observed to exhibit weak flocculation in the presence of high NaCl concentration (1 M). Phase separation and optical microscopic observations revealed that the principal mechanism for emulsion destabilization at high salt concentration was coalescence, which was accelerated at elevated temperature (50 degrees C). The effective coalescence rate for diluted emulsions was investigated using photon correlation spectroscopy. The small effective Hamaker constant for PDMS is the primary reason for the slow rate of coalescence observed for the emulsions at neutral pH in the presence of NaCl. The stability of PDMS emulsions to flocculation is qualitatively similar to that reported for low Hamaker constant dispersions (e.g., microgel particles). Addition of cationic surfactants (cetyltrimethylammonium chloride and dodecyl dimethylbenzylammonium chloride) to the negatively charged droplets after preparation was shown to decrease the emulsion stability once the surfactant concentration exceeded the CMC. Electrophoretic mobility measurements showed that added cationic surfactant changed the sign of the droplet charge from negative to positive at concentrations well below the CMC. Charged micelles of the same sign as the droplets are electrostatically excluded from close approach to the droplet surface within a distance (varepsilon) which results in depletion flocculation. Copyright 2000 Academic Press.     

Influence of ionic calcium on stability of sodium caseinate emulsions

The stability of fine sodium caseinate emulsions (1 wt.% protein, 25 vol.% n-tetradecane, 20 mM imidazole, pH 7) containing various concentrations of calcium chloride has been investigated under perikinetic and orthokinetic conditions by measuring time-dependent changes in droplet-size distribution. Under quiescent storage conditions at 20°C, samples containing at least 10 mM ionic calcium added after emulsification were found to exhibit an increasing average droplet size with time and a developing bimodal droplet-size distribution. Under turbulent conditions of intense shearing, these same emulsions exhibited time-dependent flocculation and coalescence. This interpretation was confirmed by light microscopy. Emulsions prepared with up to 6 mM Ca²⁺ present during emulsification were stable in the presence or absence of flow, but satisfactory emulsions could not be prepared containing more than 6 mM ionic calcium. The results show that the emulsion stability is sensitive to whether the calcium ion content is adjusted before or after homogenization.     

Comparison of Pickering and network stabilization in water-in-oil emulsions

We compared the efficacy of Pickering crystals, a continuous phase crystal network, and a combination thereof against sedimentation and dispersed phase coalescence in water-in-oil (W/O) emulsions. Using 20 wt % water-in-canola oil emulsions as our model, glycerol monostearate (GMS) permitted Pickering-type stabilization, whereas simultaneous usage of hydrogenated canola oil (HCO) and glycerol monooleate (GMO) primarily led to network-stabilized emulsions. A minimum of 4 wt % GMS or 10 wt % HCO was required for long-term sedimentation stability. Although there were no significant differences between the two in mean droplet size with time, the free water content of the network-stabilized emulsions was higher than Pickering-stabilized emulsions, suggesting higher instability. Microscopy revealed the presence of crystal shells around the dispersed phase in the GMS-stabilized emulsions, whereas in the HCO-stabilized emulsion, spherulitic growth in the continuous phase and on the droplet surface occurred. The displacement energy (E(disp)) to detach crystals from the oil-water interface was ～10(4) kT, and was highest for GMS crystals. Thermal cycling to induce dispersed phase coalescence of the emulsions resulted in desorption of both GMS and GMO from the interface, which we ascribed to solute-solvent hydrogen bonding between the emulsifier molecules and the solvent oil, based on IR spectra. Overall, Pickering crystals were more effective than network crystals for emulsion stabilization. However, the thermal stability of all emulsions was hampered by the diffusion of the molten emulsifiers from the interface.     

Structural Effect and Composition of Anionic Copolymer on Protein Flocculation

Flocculation of lysozyme with anionic copolymers of acrylamide, acrylic acid, and sodium styrene sulfonate used as flocculants was performed in pursuit of high flocculation efficiency. Two major factors, pH and ionic strength, are used to investigate the relationship of the flocculation behavior of protein by copolymers and the functional group (–COOH, –NH₂, –SO₃H) compositions of these copolymers. The protein flocculation can be controlled by adjusting pH. In addition, the various copolymers exhibit differing effects on ionic strength induced protein flocculation. FT-Raman spectroscopy was applied to investigate the mechanism of interaction between protein and copolymer. An attempt was made to understand how the pH and ionic strength change the surface chemical characteristics of protein and copolymers, as well as the relationship between the structure of copolymer and the protein flocculation process.     

Poly(DEAEMa-co-PEGMa): a new pH-responsive comb copolymer stabilizer for emulsions and dispersions

Stimulus responsive copolymers are an important class of surfactants that are attracting growing attention in the literature. When used to stabilize colloids, they confer responsiveness to an otherwise nonresponsive system. In this work, a new pH-responsive comb copolymer surfactant, poly(DEAEMa-co-PEGMa), where DEAEMa and PEGMa are diethylaminoethyl methacrylate and poly(ethylene glycol) methacrylate, is introduced and used to stabilize emulsions and particulate dispersions. The copolymer contained 70 mol % of DEAEMa. Turbidity versus pH measurements and photon correlation spectroscopy of the copolymer solutions revealed pH-triggered collapse of the chains above the pK(a). The surface activity of the copolymer increased with pH. The minimum surface tension measured was 33.6 mN/m at pH = 10. These data enabled identification of the pK(a) for poly(DEAEMa-co-PEGMa) as 6.8. The emulsions consisted of tetradecane-in-water and had a droplet size in the range 5-11 mum. They were slightly flocculated when the pH value was close to the isoelectric point. The emulsions phase separated at low pH values. The particulate dispersions were based on carbendazim, which is a fungacide, and had an average size of 1.8 mum. The data for the emulsions and carbendazim dispersions show that the extent of flocculation decreases with decreasing size of the dispersed phase. Analysis of the data suggest that optimum emulsion stability occurs in the pH region of 5.3-6.8 as judged by turbidity measurements. Electrophoretic mobility measurements as a function of pH for the emulsions and carbendazim dispersions reveal a similar isoelectric point in the range of 8.5-9.0, which is about two pH units higher than the pK(a) of the copolymer. A mechanism that explains the pH-responsive stability of the emulsions and dispersions is presented and discussed.     

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.     

Making Oil-in-Water Emulsions by Ultrasound and Stability Evaluation Using Taguchi Method

Oil-in-water emulsions containing 40% wt sunflower oil were prepared using ultrasound with the frequency of 30 kHz. The effect of sonication time, stabilizer concentration, NaCl, and pH of aqueous phase on the stability and particle size distribution of samples was investigated using Taguchi statistical method. The results showed that increasing sonication time decreased mean diameter of droplets and narrowed droplet size distribution curves. NaCl was found to have a positive effect on the stability of samples. More stable emulsions were prepared when using xanthan and pectin together at pH 4.     

Creaming Stability of Flocculated Monodisperse Oil-in-Water Emulsions

The influence of droplet flocculation on the creaming stability of monodisperse n-hexadecane oil-in-water emulsions was studied. The creaming velocity of emulsions with different droplet radii (0.43 and 0.86 μm), droplet concentrations (1-67 vol%), and sodium dodecyl sulfate (SDS) concentrations (7-80 mM) were measured. Depletion flocculation was observed in the emulsions when the aqueous phase SDS concentration exceeded a particular level ( approximately 40 mM for 0.43-μm droplets and approximately 15 mM for 0.86-μm droplets). Creaming was monitored by measuring the back-scattered light from an emulsion as a function of its height. The creaming velocity increased with increasing flocculation and decreased with increasing droplet concentration. These results have important implications for the formulation of emulsion-based materials. Copyright 2000 Academic Press.     

Modulation of emulsion rheology through electrostatic heteroaggregation of oppositely charged lipid droplets: influence of particle size and emulsifier content

The influence of electrostatically-induced heteroaggregation of oppositely charged lipid droplets on the rheology and stability of emulsions has been studied. 20 wt.% oil-in-water emulsions (pH 6) containing oppositely charged droplets were fabricated by mixing cationic lactoferrin-coated lipid droplets with anionic β-lactoglobulin-coated lipid droplets. Emulsions containing mixtures of droplets with different charges (positive or negative) and sizes (large or small) were prepared, and then their overall particle characteristics (ζ-potential and size) and rheology were measured. Emulsions formed by mixing positive droplets and negative droplets that were both relatively small (d(43) ≈ 0.3 μm) exhibited extensive flocculation and had paste-like properties at intermediate positive-to-negative particle ratios. On the other hand, emulsions formed by mixing positive droplets and negative droplets that were both relatively large (d(43) ≈ 3 μm) exhibited little aggregation and had relatively low viscosities at all particle ratios. Emulsions with small negative droplets and large positive droplets (or vice versa), exhibited some aggregation and viscosity enhancement at intermediate particle ratios. The presence of relatively high levels of protein in the aqueous phase of mixed emulsions reduced the level of droplet aggregation and viscosity enhancement observed, which was attributed to the ability of protein molecules to bind to droplet surfaces and neutralize their charges. Electrostatically-induced heteroaggregation of lipid droplets may be a useful means of controlling the physicochemical properties of emulsion-based products in the food, personal care, pharmaceutical and cosmetic industries.