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Journal of Food, Agriculture & Environment, Vol.7 (3&4), July-October 2009 79

www.world-food.netJournal of Food, Agriculture & Environment Vol.7 (3&4) : 79-85. 2009

WFL PublisherScience and Technology

Meri-Rastilantie 3 B, FI-00980 Helsinki, Finland e-mail: [email protected]

Physicochemical properties of beverage emulsion as function of glycerol andvegetable oil contents

Hamed Mirhosseini * and Chin Ping TanDepartment of Food Technology, Faculty of Food Science and Technology, Universiti Putra Malaysia (UPM), 43400 UPM

Serdang, Selangor, Malaysia. *e-mail:[email protected]

Received 20 July 2009, accepted 27 September 2009.

AbstractThe main objective of present study was to investigate the effect of type and concentration of two emulsion components, namely glycerol (0.5, 1 and 1.5% w/w) and vegetable oil (2, 3 and 4% w/w), on average droplet size, polydispersity index, electrophoretic mobility, pH, cloudiness, density and stability of beverage emulsion. The results indicated that the physicochemical properties of beverage emulsions were significantly (p< 0.05) influenced by the addition of different concentration levels of supplementary emulsion components. The magnitude of all physicochemical properties significantly (p < 0.05) increased with increasing the concentration of glycerol from 0.5 to 1.5% (w/w). On the other hand, the increase in vegetable oil content resulted in significant (p < 0.05) increase in polydispersity index, cloudiness and stability of beverage emulsion; while a significant (p < 0.05) reduction in average droplet size and density was observed with increasing the proportion of vegetable oil in basic emulsion formulation. The addition of glycerol resulted in significant (p < 0.05) increase in average droplet size as compared to the control sample and vegetable oil-contained beverage emulsions. The present observation could be due to the positive effect of glycerol on the viscosity of beverage emulsion, thereby reducing the efficiency of homogenization and emulsification processes. The addition of both supplementary components led to undesirable effect on the homogeneity (i.e. higher PDI) of beverage emulsions. Electrophoretic mobility significantly (p < 0.05) increased as the concentration of glycerol or vegetable oil was increased. The significant (p < 0.05) effect of glycerol or vegetable oil on electrophoretic mobility was found to be pH dependent. The results showed that pH value was significantly increased with increasing glycerol or vegetable oil content, thus increasing the degree of electrophoretic mobility.

Key words: Glycerol, vegetable oil, emulsion component, average droplet size, polydispersity index, electrophoretic mobility, cloudiness, emulsion stability, beverage emulsion, emulsification process.

IntroductionMany food products appear in the form of oil-in-water (o/w) emulsions where the oil phase is in a fluid state (milk, coffee whiteners, dressings) or in (partially) crystalline state (ice cream mixes, whipping cream) 1. The term ‘beverage emulsion’ is used to describe a group of products that have similar composition, preparation and physiochemical properties, for example fruit drinks, punches and sodas. Beverage emulsions are o/w emulsions that are normally prepared as a concentrate that is diluted into finished products 2. This unique class of emulsions is usually stabilized by amphiphilic polysaccharides, such as Arabic gum or hydrophobically modified starch 3, 4. Among sugar alcohols (e.g. monolauroyl and monomyristoyl esters of glycerol, erythritol, arabitol, ribitol, xylitol and sorbitol), glycerol is a small water-soluble co-solvent which is used as a multifunctional component for the modification of physicochemical properties (appearance, stability and rheological properties) of the emulsion systems. Glycerol is a small water- soluble co-solvent that can modify the physicochemical properties of an emulsion. It is also used as a plasticizer and/or emulsifier to improve the formation, stability and rheological properties of emulsion and dispersion systems. Vegetable oil is one of most important emulsion components that can also alter the physicochemical properties of an emulsion. Rheological

behaviors, physical stability and optical properties (i.e. turbidity, cloudiness, refractive index and appearance) of emulsion and dispersion systems can be affected by the interaction between vegetable oil and other emulsion components. In beverage emulsions, vegetable oil is usually added to the emulsion formulation to induce the cloudy appearance in the finished product. Emulsion stability is a measure of the rate at which an emulsion creams, flocculates or coalesces. The specific gravity of an emulsion that is one of the main factors responsible for gravitational separation in food emulsions depends on the refractive index. When vegetable oil is uniformly dispersed in the emulsion system, the large difference in the specific gravity between the oil and aqueous phases can cause the deterioration of beverage emulsion and gives rise to ‘‘ringing’’ and ‘‘oiling- off’’ in the neck of the container. The physicochemical characteristics of oil-in-water emulsions such as beverage emulsion are important for designing of relevant equipment and apparatus, process control, handling, storage and shelf life. Many researchers 2, 5, 6 have studied the physicochemical characteristics of beverage emulsion. However, there is a lack of information regarding the effect of glycerol and vegetable oil on beverage emulsion properties.

80 Journal of Food, Agriculture & Environment, Vol.7 (3&4), July-October 2009

Molecular electrostatics plays an important role in determining the structure and stability of emulsion and dispersion systems. Analysis for electrostatics of emulsion droplets requires accurate information on the distribution of charged residues, their charging behavior and velocity of emulsion droplets. The velocity of a particle in an electric field is commonly referred to as its electrophoretic mobility. Among various theoretical and experimental methods available for probing emulsion droplet charges, an electrophoresis experiment using a Laser Doppler Velocimetry (LDV) method is one of the widely used techniques. Electrophoresis is the migration of an ion in a homogeneous electric field, the migration rate being proportional to the field applied. In fact, the electrophoretic mobility, which is defined by the molecular velocity divided by the external electric field, is a function of molecular shape, charge distribution, and other physicochemical properties of the system.

The main objective of present study was to investigate the influence of two emulsion components, namely glycerol (0.5, 1 and 1.5% w/w) and vegetable oil (2, 3 and 4% w/w), on physicochemical properties of beverage emulsion. Our previous study 7 indicated that the addition of glycerol and vegetable oil over the concentration levels studied to the emulsion formulation resulted in undesirable changes in some of the physicochemical properties of beverage emulsion. Thus, the influence of proposed concentration levels of glycerol and vegetable oils on the physicochemical properties of beverage emulsion was investigated in present study.

Materials and MethodsMaterials: Arabic gum (instant gum AS IRX, 40830 CNI) was provided by Colloides Naturels International Co. (Rouen, France). Xanthan gum was donated by CP Kelco (San Diego, CA, USA). Glycerol (98.5%) was purchased from BDH Ltd. (Poole, Dorset). Citric acid, sodium benzoate and potassium sorbate (p.a. > 95%) were provided by Fisher Scientific (Pittsburgh, PA, USA). Valencia cold pressed orange oil was provided by Danisco (Aarhus, Denmark). RBD palm olein was purchased from a local retailer.

Beverage emulsion preparation: A representative beverage emulsion with basic formulation composed of Arabic gum (20% w/w), xanthan gum (0.3% w/w), orange oil (14% w/w), sodium benzoate (0.1% w/w), potassium sorbate (0.1% w/w), citric acid (0.4% w/w) and deionized water was prepared as a control sample. The other beverage emulsions were also formulated based on the basic formulation but containing either different concentration of glycerol (0.5, 1 and 1.5% w/w) or vegetable oil (2, 3 and 4% w/w) depending on the target emulsion formulation. It should be noted that as glycerol or vegetable oil was added, the percentage of water was reduced in the formulation to accommodate the added components. To prepare the continuous phase of beverage emulsion, sodium benzoate, potassium sorbate and citric acid were sequentially dispersed in deionized water (60ºC) using a high shear mixer (Waring blender 32BL80, Torrington, CT, USA). While mixing the mixture, Arabic gum was gradually added to the deionized water (60ºC) and mixed for 3 min to facilitate hydration. The Arabic gum solution was kept overnight at room temperature to fully hydrate 6. Xanthan gum solution was also prepared separately by dissolving xanthan gum in deionized water and then mixed with Arabic gum solution to

prepare the continuous phase. For glycerol-contained beverage emulsions, glycerol was also

added to the continuous phase. While mixing the continuous phase, the cold pressed orange oil was gradually added as dispersed phase into the continuous phase to provide a coarse emulsion. For vegetable oil-contained beverage emulsions, dispersed phase was prepared by mixing cold pressed orange oil and vegetable oil, and then the mixture was added to the continuous phase. Fine emulsification was achieved by subjecting the pre-emulsions to pre-homogenization using a high shear homogenizer (Silverson L4R, Buckinghamshire, UK) for 1 min and then passed through a high-pressure homogenizer (APV, Crawley, UK) for three passes (30, 28 and 25 MPa) 7. In this study, the preparation of beverage emulsion was performed in duplicate for each emulsion formulation.

Determination of average droplet size and polydispersity index(PDI): In the present study, average droplet size and polydispersity index (PDI) of beverage emulsions were determined by integrated light scattering using a Malvern zeta sizer (Malvern series ZEN 3500, Malvern Instruments Ltd., Worcester, UK). The measurement of droplet size was performed immediately after sample preparation. To avoid multiple scattering effects, the emulsions were diluted (1:100) with deionized water prior to analysis; then directly placed into the module. A laser beam was directed through the diluted samples, scattered by the droplets in a characteristic pattern dependent on their size and detected by an array of photodiodes located behind the cuvette 6. The droplet size measurement ranges of a Malvern zeta sizer appears in the units of nm. All measurements were repeated in triplicates for each prepared beverage emulsion. Average of three injections with four readings made per injection of each prepared emulsion was recorded. For duplicate samples, the mean of these average droplet size was used for data analysis.

Determination of electrophoretic mobility: As described in our previous study 8, the beverage emulsions were diluted (1:100) for the measurement of electrophoretic mobility using a Malvern zeta sizer (Malvern series ZEN 3500, Malvern Instruments Ltd., Worcester, UK). The measurement of electrophoretic mobility is calculated based on the Henry equation as follows:

UE = 2γεƒ(K

a) / 3η (1)

where UE is electrophoretic mobility calculating from the ζ-potential

(γ), viscosity (η), dielectric constant ε and Henry function (ƒ(Ka)).

The velocity is calculated from the measured frequency then expressed as mobility by dividing by the applied field. The measurement of electrophoretic mobility was carried out immediately after emulsion preparation using a maintenance-free capillary cell. In order to avoid the presence of air bubbles, the filling was done using a 1 ml syringe. The capillary cell was filled with diluted beverage emulsion (1:100) then fully inserted into the module. The measurement range of a Malvern zeta sizer appears in the unit of µm cm/Vs for electrophoretic mobility. The measurements were reported as average of three individual injections, with four readings made per injection of each prepared emulsion.


Determination of emulsion pH, cloudiness, density and stability:The pH values of beverage emulsions were measured by means of a glass pH electrode (Mettler Toledo, Schwerzenbach, Switzerland). The measurement of pH was carried out in duplicate for each prepared emulsion.

The beverage emulsions were diluted to 1:1000 for the measurement of cloudiness. The absorbance readings were carried out by using a UV-visible spectrophotometer (Spectronic Genesys™ 10, GENEQ inc., Montreal, Canada). For the measurement of cloudiness, the diluted beverage emulsions were contained in quartz cuvettes with a 1 cm path length. Cloudiness was calculated from the absorbance at 660 nm 9. High absorbance values correspond to high cloudiness. Distilled water was used as a reference. The measurements were made using a standard single-beam arrangement, grating-based, double detectors. Wavelength accuracy of the instrument was found to be approximately ± 1.0 nm with wavelength repeatability equal to ± 0.5 nm. The measurement of cloudiness was carried out in triplicate and average of three measurements was used for data analysis.

The density of beverage emulsion concentrates was measured at room temperature using hydrometers (CMS Hydrometers, Curtis Matheson Scientific, NY, USA) of appropriate range 6. The measurement was carried out in duplicates and then average of three individual measurements was taken as a response value for data analysis.

Emulsion stability was studied by measuring the extent of gravitational phase separation. The beverage emulsions were diluted to 1:1000 for the measurement of cloudiness, respectively. For this test, 15 ml of a prepared beverage emulsion was transferred into 20 ml test tube and stored for 2 weeks at room temperature (25± 1°C). As described in previous studies 10, 11, emulsion stability index (ESI) can be calculated as percentage of the initial emulsion height (HE), height of the cream layer (HC) and height of the sedimentation phase (HS): ESI (%) = 100 × (HE – (HS + HC)) / HE. The higher emulsion stability was demonstrated by the larger ESI. The measurement was performed in triplicate samples. In the present study, emulsion stability index (ESI) was only shown to clarify the stability of beverage emulsions.

Statistical analysis: The data obtained from the measurements were subjected to univariate analysis of variance (ANOVA) and least significant difference tests (LSD) to determine the significant differences among the samples. All measurements were carried out in duplicate or triplicate for each sample. The experimental data were reported as the mean ± SD of independent trials. Significant differences among mean values were determined by the Fisher’s test significance defined at p < 0.05. The data analysis was performed using the Minitab software v. 13.2 statistical package (Minitab Inc., PA, USA).

Results and DiscussionEffect of glycerol and vegetable oil on average droplet sizeand PDI: In this study, the beverage emulsions containing 4% (w/w) vegetable oil showed the smallest average droplet size (~1075 nm). As clearly shown in Fig. 1, the average droplet size of glycerol-contained beverage emulsions appeared to be larger (p < 0.05) than the control sample and vegetable oil-contained beverage emulsions. The results indicated that the addition of 0.5% (w/w) glycerol led to the significant (p < 0.05) increase in

average droplet size as compared to the control sample. Subsequently, the average droplet size significantly (p < 0.05) became larger as the proportion of glycerol in the emulsion formulation was increased up to 4.5% (w/w). The present observation may be explained by the positive effect of glycerol on the viscosity of beverage emulsion. This phenomenon can reduce the efficiency of homogenization and emulsification processes thereby increasing the average droplet size.

The results indicated that the presence of 2% (w/w) of vegetable oil in the basic emulsion formulation significantly (p < 0.05) decreased the average droplet size (Fig. 1). A slight reduction in average droplet size was observed with the increase of vegetable oil content (up to 4% w/w) in the basic emulsion formulation. This observation was unexpected as the increase of oil phase content in the emulsion formulation would to increase average droplet size. However, Raymundo et al. 12 also reported that the increase in oil content decreased the average droplet size. In general, it was found that the PDI was significantly (p < 0.05) influenced by the type and concentration of the independent variables studied (Fig. 2). The beverage emulsion with narrow droplet size distribution would be considered as the desirable beverage emulsion. Thus, the results showed that the optimum PDI (the least value) was provided by the control sample (Fig. 2). In fact, the addition of both supplementary emulsion components had an undesirable effect on the homogeneity of final product. Thus, the present results suggested that the more intense homogenization condition should be considered for the preparation of glycerol-contained beverage emulsion. The results indicated that the beverage emulsions containing vegetable oil was more homogenous (or uniform) than the glycerol-contained beverage emulsion. As shown in Fig. 2, the addition of 0.5% (w/w) glycerol to the basic emulsion formulation significantly (p < 0.05) increased PDI as compared with the control sample. Subsequently, an increase in glycerol content up to 1.5% (w/w) significantly (p < 0.05) increased PDI compared to the control sample. This observation may also be due to the strong positive effect of glycerol on the viscosity of beverage emulsion.

Effect of glycerol and vegetable oil on electrophoretic mobilityand pH: As shown in Fig. 3, the electrophoretic mobility of beverage emulsions was significantly (p < 0.05) influenced with adding different concentrations of glycerol or vegetable oil. As demonstrated in the Henry equation (1), the direct relationship between the magnitude of electrophoretic mobility and zeta potential is observed. Therefore, the beverage emulsion with high electrophoretic mobility value would be considered as desirable beverage emulsion. In the present study, the beverage emulsion containing the highest glycerol content (1.5% w/w) showed the largest electrophoretic mobility, thereby the highest zeta potential among all prepared beverage emulsions. As also illustrated by D’Errico et al. 13, the main effect of glycerol on dispersion system is a lowering of the medium dielectric constant, thereby enhancing the electrostatic interaction in solution. In comparison with the control sample, the electrophoretic mobility increased with the addition of glycerol or vegetable oil to the basic emulsion formulation. Subsequently, the increase in the glycerol or vegetable oil concentration resulted in significant (p < 0.05) increase in electrophoretic mobility (Fig. 3). The significant (p < 0.05) effect of glycerol or vegetable oil on electrophoretic


mobility appeared to be pH dependent (Fig. 3). In fact, the pH value was significantly (p < 0.05) increased with increasing glycerol or vegetable oil content (Fig. 3). As a rule, a positive close correlation is shown between the magnitude of zeta potential and electrophoretic mobility (Eq. 1). Therefore, the increase in pH value induced by glycerol or vegetable oil resulted in significant (p < 0.05) increase in zeta potential thereby increasing electrophoretic mobility. As stated by previous researchers 14, the electrophoretic mobility of oil droplets is pH-dependent and changes sign at low pH. Clearly ions do also play a role in this system. This behavior is often explained by hydroxyl (OH–) or hydronium ions (H

3O+)

adsorption onto a water–oil interface or to the hydrophobic surface induced by anisotropic water dipole orientation close to the surface, leading to an excess of hydroxyl ions at neutral or high pH or of hydronium ions at low pH 15. This phenomenon would be expected to change the contact potential between oil and water and hence the zeta potential of oil droplets. The effect of supplementary components on pH value and electrophoretic mobility was more pronounced by the significant (p < 0.05) effect of glycerol rather than vegetable oil (Fig. 3). The beverage emulsions containing glycerol exhibited significantly (p < 0.05) higher electrophoretic mobility and pH compared to the control sample and vegetable oil-contained beverage emulsions (Fig. 3). This observation may be explained by the presence of the higher negatively charged side groups (–OH) in the glycerol structure thereby more increasing pH value and zeta potential.

Effect of glycerol and vegetable oil on cloudiness:As a rule, the beverage emulsion may provide flavor, color and cloudy appearance for the beverage, or just simply the cloudiness 2. Thus, this unique class of emulsions would be considered as the desirable product when they can support a high degree of cloudiness in the diluted form. In the present study, the beverage emulsion containing 4% (w/w) vegetable oil exhibited the highest cloudiness value among all prepared beverage emulsions. In all cases, the presence of different concentration of vegetable oil in the basic emulsion formulation provided the significant (p < 0.05) higher cloudiness value as compared with the control sample and glycerol- contained beverage emulsions (Fig. 4). The positive relationship between opacity and oil phase concentration has been reported in other studies 10. As compared to the control sample, a slightly significant (p < 0.05) decrease in cloudiness of beverage emulsion was observed with the addition of 0.5% (w/w) glycerol to the basic emulsion formulation, whereas the increase in the proportion of glycerol from 0.5% to 1.5% (w/w) resulted in a significant (p < 0.05) increase in the cloudiness value as compared with the emulsion containing 0.5% (w/w) glycerol (Fig. 4). However, the beverage emulsion containing the highest glycerol content

(1.5% w/w) showed the lower cloudiness value as compared with the control sample. Increase in cloudiness value induced by increasing glycerol content could be explained by the fact that glycerol increases the refractive index and dielectric constant of aqueous solution 16 and hence decreases the scattering efficiency of emulsion droplets. As mentioned earlier, the beverage emulsion containing vegetable oils exhibited a significant (p < 0.05) higher cloudiness value than the glycerol-contained beverage emulsions. The emulsions containing glycerol had a larger average droplet size than the vegetable oil-contained beverage emulsions (data not shown), thus the coarser glycerol-contained beverage emulsions with larger mean particle size showed less turbidity, because

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Figure 1. The changes of average droplet size as function of glycerol (a) and vegetable oil (b) contents.


smaller mean particle size provides more surface area/unit mass of oil phase to scatter light, i.e. more turbidity. Chantrapornchai and McClements 17 also reported that the turbidity of the solution containing glycerol remained low for the first few minutes of heating, after which they increased rapidly. As compared with the control sample, the addition of 2% (w/w) vegetable oil increased the cloudiness value of beverage emulsion. Subsequently, the significant (p < 0.05) increase in the emulsion cloudiness was observed with the increase of vegetable oil content from 2% to 4% (w/w) (Fig. 4).

Effect of glycerol and vegetable oil on density: Theresults indicated that the density of beverage emulsions was significantly (p < 0.05) influenced by type and concentration of supplementary emulsion component (Fig. 5). The beverage emulsions containing glycerol showed a significantly (p < 0.05) higher density value than the vegetable oil-contained beverage emulsion (Fig. 5). This observation may be explained by the higher density (~1.26 g/cm3) of glycerol than that of vegetable oil (< 0.95 g/cm3). Thus, the presence of these supplementary emulsion components in the emulsion formulation can be useful to modulate the density of beverage emulsion. However, the present results suggest that the dosage of glycerol and vegetable oil in the emulsion formulation should be carefully considered for the pre-formulation of beverage emulsion due to their significant (p < 0.05) positive and negative effects on emulsion density. As compared with the control sample, the magnitude of density value significantly (p < 0.05) increased with the presence of 0.5% (w/w) glycerol in the beverage emulsion formulation (Fig. 5). Subsequently, the increase of glycerol content from 0.5% to 1.5% (w/w) significantly (p < 0.05) increased the density of beverage emulsion (Fig. 5). Conversely, a significant (p < 0.05) reduction in the density value was found when 2% (w/w) vegetable oil was added to the basic emulsion formulation. Consequently, the increase of vegetable oil concentration up to 4% (w/w) significantly (p < 0.05) decreased the density of beverage emulsion (Fig. 5). Previous researchers 10 also pointed out that the density of o/w emulsion decreased when the proportion of oil phase increased.

Effect of glycerol and vegetable oil on emulsionstability: The beverage emulsions must be stable in both diluted and concentrated forms 2. As shown in Fig. 6, the prepared emulsions except for the control sample and the emulsion containing 0.5% (w/w) glycerol exhibited the highest emulsion stability (100%). The results indicated that the addition of both supplementary emulsion components to the basic emulsion formulation resulted in the increased emulsion stability for the beverage emulsions (Fig. 6). Thus, the present study offered that the addition of supplementary emulsion components to the emulsion formulation could be useful in order to improve the emulsion stability. As shown in our previous study 7,

the addition of glycerol or vegetable oil significantly (p < 0.05) increased the zeta potential, thereby increasing the emulsion stability. In fact, the repulsive electrostatic interactions between similarly charged droplets do not allow them to get as close together as uncharged droplet. On the other hand, the cloud of counter ions surrounding a droplet moves less slowly than the droplet itself 18. The electrostatic contribution (or zeta potential) has a significant positive effect on the emulsion stability. Thus, the emulsion with higher magnitude of zeta potential containing the same charged droplets exhibits higher stability than the emulsion with lower

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Figure 4. The changes of cloudiness as function of glycerol (a) and vegetable oil (b) contents.


zeta potential containing opposite charged droplets. As compared with the control sample, the physical stability of beverage emulsion significantly (p < 0.05) improved with the addition of glycerol to the basic emulsion formulation (Fig. 6). Previous researcher 19

found that the concentration level of glycerol affects the magnitude of the repulsive and attractive forces governing the stability and rheological properties of an emulsion. As also demonstrated by previous researchers 20, 21, glycerol could be used as a plasticizer and emulsifier in order to improve the emulsion stability and rheological properties of o/w emulsions, dispersion systems and emulsion edible films. The stabilizing- effect of glycerol could be explained by the fact that the presence of glycerol alters the formation of the emulsions by increasing the viscosity of aqueous phase. According to the Stoke’s law, the increase of viscosity will reduce the phase separation in an emulsion. Previous researchers 22 described that the kinetics of gel formation could be altered by increasing the viscosity induced by glycerol and therefore retarding the rate of protein-protein encounters.

The presence of vegetable oil in the basic emulsion formulation also resulted in the significant (p < 0.05) increase in the emulsion stability. In a non-polar medium, the electrostatic self-energy required to create a charged surface is very high because of the low dielectric constant, and therefore it is unlikely that the particles acquire a surface charge sufficiently large to generate a stabilizing electrical double-layer force. Azzam and Omari 23 also reported that emulsion stability increased with increasing the oil volume. John et al. 24 also reported that the modified vegetable oil-in- water emulsions were stable. The increase of emulsion stability induced by the presence of glycerol and vegetable oil might be explained by their mobility enhancing effect. As a rule, when two identical colloidal particles interact across an aqueous solution, at distances much exceeding the sizes of the entities of the intervening medium (liquid molecules, polymer molecules), the interaction between identical particles and subsequently overall colloid stability are predominantly governed by the interplay of repulsive electrostatic double-layer forces and attractive Van der Waals forces as described by the DLVO theory. The double-layer force is due to the confinement of counter ions to the gap between two interacting charged surfaces. The elevated ion concentration in the gap between two identical surfaces gives rise to an osmotic pressure–the double-layer force. The electrostatic double-layer force is always repulsive force between identical surfaces, and its range decreases with the ionic strength of the solution; while attractive double-layer force can exist between unequal surfaces and its range decreases with increasing the electrophoretic mobility. In fact, the increase in the velocity of emulsion droplets (i.e. electrophoretic mobility) in the electrical field leads to increase the repulsive forces between emulsion droplets. Hence, the similarly charged droplets repel each other due to increase the repulsive forces between emulsion droplets thereby retarding the flocculation.

ConclusionsIn the present study, the effect of two supplementary emulsion components namely glycerol (0.5, 1 and 1.5% w/w) and vegetable oil (2, 3 and 4% w/w) on average droplet size, polydispersity index, electrophoretic mobility, cloudiness, density and physical

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