Research Article Received: 28 October 2014,
Revised: 5 February 2015,
Accepted: 7 February 2015
Published online in Wiley Online Library: 26 March 2015
(wileyonlinelibrary.com) DOI 10.1002/ffj.3244
Preparation and characterization of nanoemulsions stabilized by food biopolymers using microfluidization Jian Zhang,a* Terry L. Peppardb and Gary A. Reinecciusa ABSTRACT: Emulsions are widely used in beverage products and typically impart cloudiness to the beverage. Nanoemulsions have the potential to provide a transparent appearance to the beverage. The objective of the present study was to investigate the formation of nanoemulsions using food biopolymers and its potential for clear beverage applications. The biopolymers chosen for study were Gum Arabic (GA), modified gum arabic (MGA), whey protein isolate (WPI) and modified starch (Purity Gum 2000, MS). Weighted orange oil terpenes (OT) and medium chain triglycerides (MCT) were used as the dispersed phase. Nanoemulsions were characterized by dynamic light scattering (DLS), cryogenic scanning electron microscopy (Cryo-SEM) and turbidimeter. Except for the WPI stabilized nanoemulsions, higher homogenization pressures (up to 22 000 psi) and a greater number of passes (up to 7) through a MicrofluidizerW produced nanoemulsions with a smaller mean droplet diameter in volume (MDD, dV). MS showed the best performance of the food biopolymers resulting in a MDD as small as 77 nm and a corresponding turbidity of 72 NTU (Nephelometric Turbidity Units) at 0.05% of the dispersed phase, whereas GA produced emulsions with the largest MDD. The MDD of MS stabilized nanoemulsions decreased with increasing MS concentrations (from 5 to 25 wt %). The effect of oil types on MDD was complex being dependent on the emulsifier and homogenization pressure. Turbidity of diluted nanoemulsions increases with MDD within the range of 70–300 nm. This study shows food biopolymers can be used to produce nanoemulsions using microfluidization under a high pressure. It was also demonstrated that nanoemulsions with a MDD < 100 nm can provide a clear appearance in beverage applications. The results provide an understanding of how manufacturing parameters and formulation influence the formation of nanoemulsions. Copyright © 2015 John Wiley & Sons, Ltd. Keywords: nanoemulsion; food biopolymers; microfluidization; high pressure; dynamic light scattering
Introduction
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Emulsions with droplet sizes in the range of 20–200 nm are typically referred to as nanoemulsions.[1–3] There is considerable confusion about the definition of naoemulsions versus microemulsions in the scientific literature. Recently, McClements[4] provided a thorough review of the terminology, difference and similarities of nanoemulsions and microemulsions. It is emphasized in this review that the key difference between microemulsion and nanoemulsion is thermodynamic stability: microemulsions are thermodynamically stable whereas nanoemulsion is not. It is challenging to distinguish nanoemulsions from microemulsions based on their composition, droplet size and preparation methods. Nanoemulsions can be fabricated by both high-energy and lowenergy homogenization methods.[4,5] As a low-energy approach, spontaneous emulsification has been reported to prepare food-grade nanoemulsions.[5,6] In this method, oil droplets are formed via an interfacial budding mechanism when an oil phase containing a water-dispersible substance mixed with an aqueous phase.[6] Yang et al.[5] compared the two approaches to produce nanoemulsions with the same materials and it was found that the low-energy method requires higher surfactant-to-oil ratios to produce droplets of < 100 nm. Lowenergy approaches are more effective at producing a small droplet size; however, they are largely limited by the type of surfactant and high surfactant-to-oil ratio. The high usage levels of surfactant are always associated with concerns of ingredient cost, off flavour and safety in beverage and food applications.
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High-pressure homogenization allows more flexibility of nanoemulsion formulation. Typically, energy input, generally from a mechanical device, is required to manufacture nanoemulsions stabilized with biopolymers. Nanoemulsions have many interesting physical properties that are different from those of larger microscale emulsions. For instance, microscale emulsions exhibit scattering of visible light and have an appearance ranging from bluish to grey.[2,4,6] By contrast, nanoemulsion droplets are much smaller than a visible wavelength, so most nanoemulsions appear optically transparent when diluted at low volume fractions of the dispersed phase. Likewise, nanoemulsions exhibit enhanced shelf stability against gravitationally driven creaming as the Brownian motion keeps the droplets suspended homogenously over long periods of time.[2,6] Nanoemulsions have been receiving more attention in recent years in the beverage industry owing to potential applications in clear beverages, alcohol-free mouthwashes and fortified drinks. However, few successful nanoemulsion-based beverages are on the market primarily because of a lack of functional edible and permissible emulsifiers. * Correspondence to: Jian Zhang, University of Minnesota, Department of Food Science and Nutrition, 1334 Eckles Avenue, St Paul, MN 55108, USA. E-mail:
[email protected] a
University of Minnesota, Department of Food Science and Nutrition, 1334 Eckles Avenue, St Paul, MN 55108, USA
b
Robertet Flavors, Inc. 10 Colonial Drive, Piscataway, NJ 08854, USA
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Nanoemulsions stabilized by food biopolymers Many of the factors that influence the formation of conventional emulsions also apply to nanoemulsions. These factors include homogenization pressure, volume fraction of the dispersed phase, emulsifiers and emulsifier concentrations.[7–10] Emulsifier is one of the most important parameters in determining the ability to form and stabilize a nanoemulsion.[11–13] Emulsifiers also vary considerably in cost, ease of utilization, ingredient compatibility and environmental sensitivity.[14–16] There is a growing trend in the food industry to replace synthetic emulsifiers with more natural, label-friendly ones, such as phospholipids, proteins or polysaccharides. Proteins and phospholipids are good at producing small droplets but have relatively poor stability to environmental stresses, e.g. pH, salt and heating.[17–20] In contrast, polysaccharides provide good stability to environmental stresses but are relatively poor at producing small droplets.[21,22] The objective of the present study was to investigate the formation of nanoemulsions and optical properties of diluted nanoemulsions relevant to clear beverage applications. High-pressure microfluidization was used to produce nanoemulsions with food biopolymers as emulsifiers. Manufacturing parameters including homogenization pressure and the number of passes through a MicrofluidizerW and emulsion formulation, such as emulsifiers, oil phases and concentration of emulsifiers, were evaluated. Dynamic light scattering (DLS), cryogenic scanning electron microscopy (Cryo-SEM) and a turbidity metre were used to characterize the prepared nanoemulsions.
Materials and Methods Materials TIC Gums, Inc. (Belcamp, MD, USA) donated samples of PreHydratedW Gum Arabic Spray Dry Powder (GA) and OSAn modified gum arabic (TicamulsionWA-2010, MGA). Modified starch (Purity Gum 2000, MS) was donated by Ingredion (Westchester, IL, USA). Whey protein isolate (WPI) was provided by Davisco (Eden Prairie, MN, USA). Orange oil terpenes were obtained from Citrus and Allied Essences Ltd. (Lake Success, NY, USA) and MiglyolW812, an MCT, was purchased from Sasol Germany GmbH (Witten, Germany); ester gum was obtained from J.H. Calo Co. (Westbury, NY, USA). MiglyolW812 is a combination of triglycerides based on the following fatty acid composition: C6:0 max. 2%, C8:0 50% to 65%, C10:0 30% to 45%, C12:0 max. 2% and C14:0 max. 1%. The orange oil terpenes used were comprised primarily of limonene (95.6%), myrcene (2.8%), sabinene (2.8%), α-pinene (0.9%) and octanal (0.2%).
Methods Preparation of nanoemulsions
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Measurement of refractive index Refractive indices of the dispersed phase were measured at 589 nm using an Abbe refractometer (Carl Zeiss, Jena, Germany) at room temperature. Distilled water was used as a standard for calibration check. Measurements were conducted in triplicates. Droplet size characterization Droplet size and distribution were determined by dynamic light scattering (DLS) using ZetaPALS (BIC 90Plus; Brookhaven Instrument Corporation, NY, USA). The DLS instrument was equipped with a photometer, Lexel 95–2 Ar+ laser operating at a wavelength of 659 nm, a photomultiplier and Brookhaven BI-9000AT correlator. The refractive indices of the dispersed phase were measured as 1.5045 for the OT-based oil phase and 1.4619 for the MCT-based oil phase. Water was selected as a solvent as all samples were diluted before measurement with distilled water to about 0.05% of the dispersed phase. The protocol for measurement and data acquisition was detailed elsewhere using the same instrument.[23,24] A brief summary is provided here. The light intensity correlation function was obtained at 25 °C with scattering angle of 90°, solvent refractive index of 1.3330 and solvent viscosity of 0.89 mPa•s. The correlation function is a combination of the diffusion coefficient (Dί) of each droplet that is converted to droplet diameter (dί) using the Stokes–Einstein equation Eqn (1), di ¼
kbT 3πηDi
(1)
where kb is the Boltzmann constant, T is the absolute temperature and η is viscosity. Correlation functions were downloaded from the ZetaPALS and fitted using the regularized positive exponential sum (REPES) program. REPES yields a series of discrete particle diameters to represent the particle size distribution. The software, GENDIST, was used to solve the REPES algorithm[25,26] and provided the intensity weighted size distribution as defined in Eqn (2), X ni d i 6 dI ¼ X (2) ni d i 5 where ni is the number of droplets with a diameter of di. The averaged diameter in mass, dm, is defined in Eqn (3), X ni di 4 dm ¼ X (3) ni di 3 Each sample was run for six cycles and mass average mean droplet diameter (MDD) was reported in present study. Size span was expressed below Eqn (4) to define the polydispersity of prepared nanoemulsions Span ¼
dðv; 90Þ d ðv; 10Þ d ðv; 50Þ
(4)
where d(V,10), d(V,50) and d(V,90) are diameters at which the cumulative mass of the droplets is under 10%, 50% and 90%, respectively.
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Dispersions of MS, GA and MGA were prepared with distilled water by mixing for 2 h using an overhead mixer (CarterW 1L.81; Carter Motor, IL, USA) at room temperature. The WPI was solubilized by mixing with a magnetic stir bar for 2 h. A coarse emulsion was prepared by blending 5 wt % oil phase (orange oil terpenes with ester gum at a 1:1 ratio, or Miglyol oil with ester gum at a 4:1 ratio) and 95 wt % of an aqueous phase containing WPI, GA, MS or MGA using a high shear mixer (Greerco Corp., Hudson, NH, USA) at about 6000 rpm for 2 min. The resulting pre-emulsion was passed through a MicrofluidizerW (Model M-110Y with F20Y & H30Z Chambers; Microfluidics Corporation, Newton, MA, USA) at different
pressures and number of passes. A cooling coil immersed in ice water was used to control the temperature of the emulsions exiting from the Microfluidizer. Orange terpenes (OT) and Miglyol oil (MCT) were mixed with ester gum at different ratios to have the same density of dispersed phases. In following text, OT and MCT nanoemulsions stand for weighted orange oil terpenes and Miglyol oil nanoemulsions, respectively. Emulsions were prepared in duplicate.
J. Zhang et al. Cryo-SEM (Philips CM12; Philips, Eindhoven, The Netherland) was used to characterize the droplet size of nanoemulsions qualitatively. One drop of emulsion was placed on a copper grid, which was quickly transferred to a liquid nitrogen bath for solidification. The copper grid was then transferred to the SEM cold stage using a cryo-holder. The stage was kept under 170 °C with liquid nitrogen cooling. Nanoemulsion samples were also diluted to 0.05% w/w dispersed phase with distilled water for better imaging of microstructure. Measurement of viscosity Viscosities of dispersed and continuous phases were measured using a Brookfield rotational rheometer (Brookfield, RVIII model; Stoughton, MA, USA) with cone and plate geometries at a rotation speed of 60 rpm. A series of standard solutions were used for calibration. A water bath was used for temperature control of 25 °C. The data were acquired using Rheocalc Software. Samples were prepared in duplicate for viscosity measurement. Measurement of turbidity A Turbidimeter (Hach 2100AN; Geotech Environmental Equipment, Denver, CO, USA) with a range of 0–8000 NTU (Nephelometric Turbidity Units) was used to determine the turbidity of the nanoemulsions prepared in this study. The turbidimeter consists of a colour filter module for 455-nm wavelength and a 90 °C angle detector. The turbidimeter was calibrated using a series of turbidity standards ranging from 0 to 2000 NTU. Emulsions were diluted to 0.05% w/w of the dispersed phase for turbidity measurement. Dilutions were prepared in triplicates. Two readings were taken for each sample.
statistical data on MDD from SEM imaging, DSL was used to provide quantitative data on droplet size and size distribution. Figure 2 shows the droplet size distribution of the same sample as that in Figure 1. These data show the sample has a mono-modal distribution with a MDD of 182 nm and span of 0.62. The majority of droplets are in the range of 150–200 nm. It appears the DLS data agreed well with cryo-SEM data, so DLS was used as a main tool to character the size distribution of nanoemulsions prepared in this study. Effects of homogenization pressure and number of passes on MDD Homogenization pressures ranging from 6000 to 22 000 psi were evaluated to produce nanoemulsions stabilized by different emulsifiers. Figure 3 shows the effect of homogenization pressure on the MDD of MCT nanoemulsions. For GA stabilized emulsions, with increasing pressure from 6000 psi to 14 000 psi, MDD decreased after 1 pass but did not change significantly after 2 and 3 passes. When the pressure was further increased to 22 000 psi, MDD decreased dramatically compared with that at lower pressures. The smallest MDD obtained was about 350 nm when homogenized at 22 000 psi and passed through the system three times: this is still well above the size required to be considered a nanoemulsion. Increasing the number of passes from 1 to 3 did not lead to a great reduction in MDDs (17%, 10% and 10% reduction at 6000, 14 000 and 22 000 psi, respectively). These results suggest that GA is not an ideal candidate to produce nanoemulsions when using highpressure homogenization and using multiple passes.
Results and Discussion Characterization of Nanoemulsions Cryo-SEM was used qualitatively to characterize the droplet size of prepared nanoemulsions. Figure 1 shows a representative cryoSEM image of the MCT nanoemulsion stabilized by 5 wt% MS produced at 22 000 psi with three passes through a MicrofluidizerW. From the image, one would see the majority of droplets is within the size range of 100~200 nm and a few big droplets have a size around 300 nm. Aggregates of droplets were also observed which might be caused by droplet flocculation or insufficient sublimation of water during sample preparation. As it was challenging to obtain
Figure 2. Droplet size distribution of a 5 wt% modified starch (MS) stabilized nanoemulsions with 5 wt% Miglyol oil (MCT) as dispersed phase homogenized at 22,000 psi for 3 passes through a MicrofluidizerW
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Figure 1. Representative cryo-SEM image of 5 wt% modified starch (MS) stabilized nanoemulsions with 5 wt% Miglyol oil (MCT) as a dispersed phase homogenized at 22 000 psi for 3 passes through a MicrofluidizerW
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Nanoemulsions stabilized by food biopolymers
Figure 3. Effect of homogenization pressure and multiple passes on the mean droplet diameter (MDD) of Miglyol oil (MCT) nanoemulsions with a 5 wt% dispersed phase. Solid line, 10% Gum Arabic (GA); dotted line, 10% modified starch (MS); dashed line, 2% whey protein isolate (WPI)
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Effect of number of passes on particle size distribution The number of passes through a homogenizer affects not only MDD but particle size distribution. Figure 4 shows how the droplet size distribution of MS stabilized MCT nanoemulsions changes with an increasing number of passes. MDD decreased from 142 nm at 2 passes to 90 nm at 6 passes and the mass cumulative curves of size distribution shifted towards a smaller size with an increasing number of passes through the MicrofluidizerW. However, the span increased from 0.78 at 2 passes to 2.18 at 6 passes owing to a small fraction of larger droplets at a greater number of passes. The size distribution may have an impact on nanoemulsion stability which will be evaluated in future studies. Effect of emulsifier concentration on MDD As nanoemulsions have an extremely large specific surface area (Asp, surface area per unit of mass), higher concentrations of biopolymers may provide better coverage of the interface and further reduce interfacial tension to facilitate droplet rupture during homogenization. However, it was found that when emulsifier concentrations were increased from 2 to 4 wt % and from 5 to 10 wt % for WPI and MGA, respectively, MDDs decreased slightly but these were not statistically significant (data not shown). This suggests that the emulsifying property of WPI and MGA is determined by structure characteristics of the molecules instead of insufficient interfacial coverage of WPI or MGA during homogenization. Figure 5 shows how the MS concentration affected the MDD of nanoemulsions. There is a clear trend in that MDD decreased with increasing MS concentration (from 5 to 20 wt %). From Figure 6, one can see that 20% MS stabilized nanoemulsions shows less turbidity than those by 5% MS that suggest turbidity is closely related to MDD. No significant difference was found between samples stabilized by 20 and 25 wt% MS (Figure 5). The best performance was a MDD of 77 nm: the smallest MDD ever reported using food biopolymers. It is not a surprise that such a high MS concentration
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The failure of producing a GA stabilized nanoemulsion could be attributed to several reasons. First, GA is less surface active than other emulsifiers owing to the low proportion of surface active components, namely arabinogalactan protein.[27,28] The interfacial tension of GA solutions against oil at saturation coverage is 43 mN/m, which is much higher than that of other surfactants, e.g. 26 mN/m for Tween 20 solution.[29,30] According to Taylor’s equation more energy input is needed to produce GA stabilized nanoemulsions. Another reason for not achieving the desired particle size is that arabinogalactan protein is a relatively large molecule that exhibits slow adsorption kinetics during homogenization. It was reported that in a 0.5 w/v% GA solution, the surface tension decreased from 71 mN/m to 57.4 mN/m after 3 h of adsorption; the rate of surface tension decrease was slow and the induction time was high: the time to get 0.95 of the original surface tension was 3041 s.[31] The dramatic decrease in MDD when the homogenization pressure was increased from 14 000 psi to 22 000 psi was unexpected. There are two likely explanations for this phenomenon. First, highpressure homogenization, e.g. 22 000, changed the structure of the arabinogalactan protein, which favours emulsion formation owing to conformational changes that then makes the molecule better able to accumulate at the particle interface. It is a common phenomenon that high-pressure processes may change the protein structure and emulsifying capability.[32–34] Second, highpressure homogenization might fragment GA molecules resulting in smaller molecules and thus have higher adsorption kinetics. Floury et al.[35] reported that high-pressure homogenization had an impact on molecular weight (MW) and adsorption kinetics of methylcellulose. The MW of native methylcellulose decreased from about 300 000 to 80 000 g/mol when homogenized at 43 511 psi (1 pass) and the characteristic time of diffusion decreased from 14 to 4 s. Therefore, the smaller MDD at 22 000 psi might be attributed to modification of the GA structure during homogenization. For MS stabilized emulsions, increasing pressure and number of passes led to a decreasing MDD. The smallest MDD obtained was 169 nm at 22 000 psi (3 passes) which may be attributed to fast adsorption kinetics to the oil/water interface owing to the addition of hydrophobic groups on the hydrolyzed starch molecules. From the trend shown in Figure 3, one would expect that the MDD will further decrease at higher pressures (>22 000 psi) and a greater
number of passes (>3 passes). Chen et al.[36] reported that modified starch functioned well in producing vitamin E nanoemulsions. In the vitamin E emulsion systems, MDD decreased dramatically when the pressure was increased from 2900 to 43 500 psi. However, Jafari et al.[37] showed that the MDD of d-limonene emulsions stabilized by modified starch (Waxy corn starch modified; Hi-Cap) increased from 160 to 215 nm when the pressure increased from 3 045 to 12 200 psi using microfludization at 1 pass. The inconsistency of results could be attributed to the differences in the modified starch and oil phase used. Modified starches with different hydrophobic groups and degree of substitution have shown variable emulsifying properties in many studies.[38–40] For WPI stabilized emulsions, increasing pressure resulted in decreasing MDD. The smallest MDD obtained was 122 nm at 22 000 psi (2 passes). A complex relationship between pressure and MDD has been reported[41,42] for emulsions stabilized with whey protein concentrate. A substantial size reduction was observed when the pressure was increased from 7250 to 13 000 psi. However, when using pressures above 13 000 psi, the MDD of the sunflower oil emulsions increased with pressure. Significant structural changes in protein conformation were observed as the homogenization pressure was increased as indicated by microdifferential scanning calorimetry scans and polyacrylamide gel electrophoresis.[43–46] In the present study, the reduction in MDD with increasing pressure suggests WPI is not ’over processed‘ at 1 pass, but multiple passes may reduce the emulsifying properties as indicated by a slight increase in MDD above 2 passes.
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Figure 5. Effect of modified starch (MS) concentrations on the mean droplet diameter (MDD) of Miglyol oil (MCT) nanoemulsions produced at 22 000 psi
Figure 6. Diluted Miglyol oil (MCT) nanoemulsions with a 0.05% dispersed phase stabilized by modified starch (MS) and produced at 22 000 psi. Top, 5% MS stabilized nanoemulsions; bottom, 20% MS stabilized nanoemulsions. The number on the cap of vials stands for the number of passes (from 1 to 6) through a MicrofluidizerW Figure 4. Effect of the number of passes on the size distribution of 20 wt% modified starch (MS) stabilized Miglyol oil (MCT) nanoemulsions produced at 22 000 psi. Top, 2 passes with a mean droplet diameter (MDD) of 142 nm and span 0.78, middle, 4 passes with a MDD 98 nm and span 0.96, and bottom, 6 passes with a MDD 90 nm and span 2.18
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was needed to form a nanoemulsion. When the droplet size decreases from submicron to the nanoscale, the specific surface area increases immensely. The huge interface area of nanoemulsions requires a large number of polymers to cover and stabilize it. At optimal concentration of MS, the mass ratio of MS to oil phase is 4, which is comparable to 5.3 for vitamin E nanoemulsions stabilized by OSAn modified starch reported by Chen et al.[36] Another factor contributing to the decrease in MDDs observed with increasing MS concentrations is the change of phase viscosity. Continuous phase viscosity increased from 3.5 to 73.6 mPa•s when the MS concentration increased from 5 to 25 wt%. Dramatic changes in phase viscosity definitely affect the fluid properties of emulsions and thus affect the homogenization efficiency.[47–49] The influence of phase viscosity on formation of nanoemulsions is discussed in following text.
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Effect of the oil phase on MDD In practical applications, the oil phase composition of emulsions may vary greatly (e.g. vitamins, colorants, fish or vegetable oils and flavorings). Thus, it is necessary to evaluate the performance of different emulsifiers with different oil phases. Figure 7 shows the effects of two very different types of oils (terpene versus triglyceride) on the MDD of nanoemulsions stabilized by different emulsifiers. Interestingly the three emulsifiers behaved very differently. With MS as an emulsifier, at 1 pass the MCT nanoemulsion showed a smaller MDD than the OT nanoemulsions, whereas with an increase in number of passes, almost no difference in MDD was observed. With WPI as an emulsifier, no difference in MDD of MCT and OT nanoemulsions was observed at passes < 3, but with an increasing number of passes the OT nanoemulsions showed smaller MDD than the MCT nanoemulsions. With MGA as an emulsifier, OT produced nanoemulsions with smaller MDD than MCT regardless of the number of passes. These results suggest that the influence of oil type on MDD is complex depending on both emulsifier and homogenization parameters.
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Nanoemulsions stabilized by food biopolymers influence the efficiency of emulsifiers.[43–46] These interactions are influenced by homogenization conditions to a different extent depending on the nature of oils and emulsifiers. Effect of phase viscosity on MDD
Figure 7. Effect of the oil phase on the mean droplet diameter (MDD) of nanoemulsions produced at 22 000 psi and stabilized with 5% modified starch (MS), 2% whey protein isolate (WPI) and 5% modified gum arabic (MGA), respectively
Reiner et al.[11] reported that OT tended to form smaller MDD than MCT in emulsions stabilized by food biopolymer emulsifiers (e.g. modified starches and gum arabic) at 13 000 psi for 1 pass. Reiner explained the results using differences in solubility, polarity and viscosity between OT and MCT. It has been reported that the interfacial tension at the orange oil–water interface was about 5 mN/m at 30 °C[50] which is much lower than that of 25 mN/m at the MCT–water interface at 25 °C.[51] One would expect that the difference in interfacial tension at the OT–water and MCT–water interfaces partially contributed to the observed difference in MDDs. In practice, it is more complex because Ostwald ripening also affects droplet size that is governed by interfacial tension, oil solubility in a continuous phase, and size distribution. This complexity was reported previous in MS stabilized corn oil-orange oil nanoemulsions and a different Ostwald ripening rate was observed in nanoemulsions with different oil phase compositions (different ratio of orange oil to corn oil).[52] In order to investigate further, OT and MCT nanoemulsions stabilized by MS were produced at lower pressures, 6000 and 14 000 psi and the results are shown in Figure 8. Interestingly, at 6000 psi OT formed much smaller MDD than MCT, whereas at 14 000 psi no difference in MDD was observed. This clearly demonstrated that effects of oil type on emulsion formation are also pressure and number of passes dependent. The literature has shown that interactions of oil phase/emulsifier and emulsifier/emulsifier strongly
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Effect of MDD on turbidity For nanoemulsions, the dimensions of the particulate phase are much smaller than the wavelength of light (r
