Parent Emulsion Research Articles

Effect of Continuous and Discontinuous Droplet-Size Distributions on the Viscosity of Concentrated Emulsions in Premix Membrane Emulsification

The dispersed phase volume fraction of concentrated emulsions can be substantially increased without a considerable increase in viscosity by optimizing the droplet-size distribution (DSD) of emulsion mixtures. However, due to the limitations of the traditional methods to control the DSD, the study of its effect on the viscosity of emulsion mixtures is usually limited. The premix membrane emulsification method was used to prepare a droplet-size-controlled concentrated emulsion, and the DSD’s effect on the viscous behavior of emulsion mixtures was investigated. It was observed that widening the DSD led to a decrease of the viscosity at lower shear rates, while at higher shear rates, a shear-thickening behavior was observed. In a discontinuous DSD, there was a tendency for the viscosity to decrease to a minimum value at about 75% mixing fraction of larger-droplet-size emulsions beyond which the viscosity increased until the monomodal packing limit. The viscosity could be decreased by more than 20-fold in bimodal emulsions depending on the droplet-size ratio. Mixing emulsions of different DSDs enabled attaining a viscosity lower than that of the monodispersed parent emulsions.

Novel methods to induce complex coacervation using dual fluid nozzle and metal membranes: Part I – Use of metal membranes for emulsification

This study is part I of two parts where the use of metal membranes was evaluated to produce emulsions and to induce complex coacervation. In this work, we aimed to produce emulsion droplets using metal membranes to be used in complex coacervation in batch stirring and by a new method in which coacervation is induced using a two-fluid nozzle. Investigation on the optimum membrane morphology, dispersed phase injection rate and emulsification shear stress was carried out. Emulsions of gelatin and ginger oil (4% and 10% w/w) were produced by membrane emulsification in a dispersion cell, with droplet sizes varying from 32 to 128 µm; gelatin concentration had great influence on droplet size and size distribution. Complex coacervation between gelatin and gum Arabic without the use of crosslinking agents was carried out by atomization and batch stirring, and the size of the parent emulsion droplets, coacervation shear stress and emulsion formulation influenced the size of the capsules produced, which varied from 35 to 151 µm. Batch stirring complex coacervation produced single core capsules and atomization coacervation produced multicore capsules, both with spherical morphology. Encapsulation yield of dried capsules varied from 37% to 99% and encapsulation efficiency 5–66%. Formulation had a greater effect on the encapsulation efficiency than on the encapsulation yield.

Macroporous Ceramic Monolith from Nanoparticle-Polyelectrolyte-Stabilized Pickering Emulsions.

In this work, we present a simple and scalable approach for fabricating porous ceramic from emulsions stabilized by a binary mixture of oppositely charged nanoparticles and a polyelectrolyte. The electrostatic heteroaggregation is exploited to form weakly charged particle-polyelectrolyte complexes (PPCs) that readily stabilize oil-in-water emulsions. The concentration of surface-active PPCs is varied to obtain Pickering emulsion gels that can be processed and converted into the macroporous ceramic structure. The polyelectrolyte in the binary mixture not only enables the adsorption of particles to the oil-water interface and renders processability of the emulsions but also acts as a binder. Nearly one-to-one correspondence between the microstructure of the green ceramic obtained after the evaporation of solvents from the gel-like emulsions and the parent emulsions is observed. The green ceramic is further sintered under controlled conditions to obtain a porous ceramic monolith. We demonstrate that the microstructure and the pore size distribution in the final ceramic can be altered by tuning the composition of the individual species used in the emulsion formulation, i.e., by optimization of the particle-polyelectrolyte ratio used in the processing route.

Influence of oil droplet size on the oxidative stability of the free and encapsulated fractions of freeze‐dried microencapsulated sunflower oil

SummaryThe effect of oil droplet size (ODS) on the oxidative stability (OS) of dried microencapsulated oils has been scarcely studied, and results are contradictory. A few studies have shown increased OS when the ODS was reduced and this was attributed to a decrease in the surface oil content (SOC). Yet, in such studies, only the total oil fraction was evaluated. In the present work, the free (FO) and encapsulated oil (EO) fractions of freeze‐dried microencapsulated sunflower oil were analysed to study the effect of changes in the ODS by using different homogenisation pressure (15 or 70 MPa) in the emulsification step. The OS of both the free and encapsulated fractions increased when the ODS was significantly reduced in two samples with different encapsulation matrix, namely caseinate/lactose and maltodextrin/sucrose/gelatine. A reduction in the SOC would explain the increased stability of the FO, but not that of the EO. An additional protective role of the interfacial film could have been involved. In conclusion, if the encapsulation matrix and the interfacial region are effective as oxygen barriers, a reduction in the ODS of the parent emulsion by an increase in the homogenisation pressure will result in capsules more stable against lipid oxidation.

INFLUENCE OF EMULSIFICATION METHODS AND SPRAY DRYING PARAMETERS ON THE MICROENCAPSULATION OF TURMERIC OLEORESIN

Turmeric (Curcuma longa L.) oleoresin possess valuable phenolic compounds that are susceptible to degradation, and microencapsulation is a powerful technique to increase its stability. Emulsification is a preponderant step in microencapsulation of hydrophobic compounds and physical-chemical properties of the parent emulsion affects effectiveness of spray-drying process and functional properties of the produced microcapsules. The present work aimed to evaluate the influence of emulsion formulation, emulsification methods, and spray-drying operational conditions on the encapsulation efficiency of turmeric oleoresin using maltodextrin/gelatin blends as wall material. The effects of different concentrations of maltodextrin (12 - 31.7 wt %) and gelatin (0.6 - 6 wt %), combined with three methods of emulsification - high shear homogenization with and without emulsifier addition, and sonication – were evaluated regarding emulsion droplet mean diameter and stability. Based on the results, an emulsion formulated with 26 g of maltodextrin and 0.6 g of gelatin per 100 g of emulsion was selected to study the influence of spray drying conditions - drying-air temperature (124 – 190 oC), atomization airflow (275 – 536 L h-1), and emulsion feeding flow (1.4 – 8.6 mL min-1) - on encapsulation efficiency, water content, and solubility of turmeric oleoresin microcapsules. Sonication resulted in higher emulsion stability and, although drying-air temperature did not affect significantly the microcapsule properties, the best set of spray drying conditions was drying-air at 160 ºC, atomization airflow of 420 L h-1, and emulsion feeding flow of 6 mL min-1. Combinations of higher atomization airflow and lower emulsion feeding flow resulted in lower values of curcumin encapsulation efficiency.

Enhanced Thermal Conductivity of High Internal Phase Emulsions with Ultra-Low Volume Fraction of Graphene Oxide

Thermal conductivity enhancement in a multiphase fluid such as water-in-oil emulsion can substantially improve efficacies in a broad range of applications. However, nanoparticle additives that are often used to do so can catastrophically destabilize a delicate emulsion system, in our case, a high internal phase emulsion (HIPE), whereas large concentration of additives can adversely impact practical processing aspects. Therefore, means to enhance the thermal conductivity of emulsions with a minute concentration of additives (<1 wt %) is a major scientific challenge. We report the enhancement in thermal conductivity of HIPE, by consigning either lipophilic GO (fGO) in the oil phase or hydrophilic GO in the water phase in combination with a well-known emulsifier. The rheological properties of fGO-HIPE showed non-Newtonian viscoelastic behavior similar to that of the original emulsion but with lower elastic modulus and viscosity, indicating that GO incorporation has enhanced processability. The thermal conductivity enhancements can be predicted by thermal circuit models, and the HIPEs with fGO and GO demonstrated 21 and 13% enhancements over the parent emulsion with a minor 0.1 w/w addition, respectively. A possible role of ordered colloidal structures of GO and fGO underlining this prepercolation behavior is inferred from comprehensive imaging and thermal studies.

Encapsulation of EPA and DHA concentrate from Kilka fish oil by milk proteins and evaluation of its oxidative stability.

Glyceride product from lipase-catalyzed hydrolysis of fish oil (large-scale) is a rich source of n-3 PUFA (49.62%); but it is prone to oxidation. Our aim was to encapsulate this product by a mixture of whey powder and sodium caseinate (4:1) as a new wall material. The emulsification was done using ultrasonication in different powers (180-380W) and times (1-3min) and, then, the emulsions were freeze-dried to obtain the powders. Based on encapsulation efficiency, sonication (88-94%) could inhibit the presence of oil at the surface of powder particles in comparison with the samples prepared without sonication (control, 68%). The highest oxidation rate and the lowest L-value were found for the unencapsulated glyceride product stored in air atmosphere followed by the control powder, the powders from sonication treatment and the unencapsulated glyceride product under N2, respectively. In the case of oxidative stability of the samples, the sonication time was more significant than sonication power. According to our results, a sonication treatment of 380W for 3min was recommended to prepare parent emulsions during fish oil encapsulation.

Development and characterization of spray-dried chia oil microcapsules using by-products from chia as wall material

This research deals with the characteristics of spray-dried chia oil microcapsules formulated with different wall materials, including new encapsulant agents from chia seed (protein rich fraction, PRF; chia mucilage, Muc). The performance of six different wall materials combinations was studied: sodium caseinate and lactose (NaCas + L), NaCas and maltodextrin (NaCas + Mx), PRF and Mx (PRF + Mx), and each of the previous three with the addition of Muc. The particle size, rheology, and stability of the parent emulsions were analyzed. The characterization of the powders obtained by spray-drying the parent emulsions was carried out by their moisture content, water activity, microencapsulation efficiency, glass transition temperature, morphology, oxidative stability, and dispersibility. Emulsions were reconstituted from the powders at different storage times and analyzed by their particle size and stability. The encapsulation efficiencies were NaCas + L + Muc (96.23 ± 0.40%) ~NaCas + L (95.20 ± 0.42%) > NaCas + Mx + Muc (86.65 ± 0.27%) > NaCas + Mx (71.26 ± 0.06%) > PRF + Mx (57.74 ± 3.49%) ~PRF + Mx + Muc (53.37 ± 0.99%). The addition of Muc significantly improved the ME% in microcapsules with NaCas + Mx. The induction time values (ti) of NaCas + L, PRF + Mx and NaCas + Mx systems were about two, three, and five times higher than that of chia bulk oil, respectively. Thus, the studied wall materials were efficient to protect chia seed oil against the oxidation process.

Microstructure and long-term stability of spray dried emulsions with ultra-high oil content

The aim of this study was to investigate the microstructure and long-term mechanical as well oxidative stability of a new class of spray dried emulsion containing ultrahigh oil content. Emulsion (20 wt% oil) stabilized by whey protein (1 wt%) was thermally cross-linked at 82 °C for 10 min and spray dried without any additional wall materials using inlet/outlet air temperature of 105 ± 2/65 ± 2 °C, respectively at a pilot scale. Confocal micrograph showed cohesive cross-linked whey protein film present at the oil-water interface and at the powder surface stabilising the oil powder particles containing 95.3 wt% oil. The mean droplet size of parent emulsion (0.21, 0.38, 0.76, 2.31 μm) significantly influenced the mechanical stability of the resulting oil powder in terms of oil leakage (2.73, 0.93, 4.1, 7.54 wt%) upon compaction. Scanning electron microscopy revealed the level of surface oil and porous “sponge” like internal microstructure of the oil powder with polyhedral, closely packed droplets. Strong correlations existed between the mechanical properties of the oil powder and the oxidative stability over 5 months. The kinetics of oxidation of oil powder was higher than that of corresponding bulk oil with or without added antioxidants as evidenced by evolution of primary oxidation products (hydroperoxides) and secondary oxidation products (hexanal). This might be due to the multi-step processing (e.g. homogenization, thermal cross-linking, spray drying) as well as inability of the cohesive but permeable protein matrix to protect the ultra-high content of oil droplets from diffusion of oxygen and prooxidants.

Influence of protein concentration on the stability of oil-in-water emulsions formed with aggregated milk proteins during spray drying

The ability of aggregated milk proteins to stabilize oil-in-water emulsions during the spray drying process is not well understood and has been highlighted in this study. We investigated the behavior of oil droplets in emulsions (12.0%, w/w, maltodextrin; 20.0%, w/w, soya oil) stabilized with either milk protein concentrate (MPC) or calcium caseinate (CaCas) (0.5–5.0%, w/w) before and after spray drying. In comparison with the respective parent emulsions, spray drying and redispersion caused a shift in the droplet size distribution toward larger values for emulsions made using low concentrations (0.5–2.0%) of MPC or CaCas. However, the droplet size distribution was affected very slightly by spray drying when the protein concentration was between 3.0 and 5.0%. The average droplet diameters of redispersed CaCas emulsions were noticeably larger than those of redispersed MPC emulsions. The unadsorbed protein concentrations in the parent emulsions were comparable for emulsions containing CaCas and MPC, except at 5.0% (w/w) when emulsions containing MPC had a higher concentration of unadsorbed protein in the bulk phase. The amount of extractable oil in MPC-containing powders decreased with an increase in the protein concentration in the emulsions prior to spray drying. However, the amount of extractable oil in CaCas emulsion powders was nearly twice that in MPC emulsion powders even at 5.0% protein in the emulsion. The results obtained from this study clearly show that aggregated milk proteins are able to provide stability to oil droplets during the spray drying process, albeit a higher concentration of protein is required as compared to non-aggregated protein products.

Porous TiO2 Materials through Pickering High-Internal Phase Emulsion Templating

We report a facile method for preparing porous structured TiO2 materials by templating from Pickering high-internal phase emulsions (HIPEs). A Pickering HIPE with an internal phase of up to 80 vol %, stabilized by poly(N-isopropylacrylamide)-based microgels and TiO2 solid nanoparticles, was first formulated and employed as a template to prepare the porous TiO2 materials with an interconnected structure. The resultant materials were characterized by scanning electron microscopy, X-ray diffraction, and mercury intrusion. Our results showed that the parent emulsion droplets promoted the formation of macropores and interconnecting throats with sizes of ~50 and ~10 μm, respectively, while the interfacially adsorbed microgel stabilizers drove the formation of smaller pores (~100 nm) throughout the macroporous walls after drying and sintering. The interconnected structured network with the bimodal pores could be well preserved after calcinations at 800 °C. In addition, the photocatalytic activity of the fabricated TiO2 was evaluated by measuring the photodegradation of Rhodamine B in water. Our results revealed that the fabricated TiO2 materials are good photocatalysts, showing enhanced activity and stability in photodegrading organic molecules.

Microencapsulation of astaxanthin with blends of milk protein and fiber by spray drying

This study investigated the encapsulation of astaxanthin using spray drying method to enhance its stability and application in food systems. Blends of milk protein (either whey protein isolate, WPI or sodium caseinate, SC) and carbohydrate (soluble corn fiber, SCF 70) were applied as the wall materials. The results demonstrated that spray drying could be applied to transform the stable astaxanthin emulsions into powders with reasonably good properties, including water activity, surface morphology and oxidative stability. The reconstituted emulsions also showed good stability similar to the parent emulsions. The microencapsulation efficiency was high (∼95%) for both wall systems under investigation, indicating the suitability of these wall matrices for encapsulating the hydrophobic astaxanthin.

Dilute nanoemulsions via separation of satellite droplets

A facile method is suggested for fabrication of dilute nanoemulsions. In a typical emulsification process, drops are usually accompanied by off-grade satellite droplets. The size of these satellite droplets ranges from hundreds of nanometers to above microns. Experiments were carried out to assess the possibility of separation of nanodrops from macroemulsions made via a conventional method in order to produce nanoemulsions. A low-power homogenizer was used to produce parent emulsions which were then injected from the bottom to a glass column containing water and allowed to cream. By monitoring drops remaining in the bottom of the column, it is clearly shown how progressively smaller they become with time yielding eventually dilute nanoemulsions. The average diameter of drops reduced to 100nm when oil with high viscosity was used. The concentration of resulting nanoemulsions increased with increasing viscosity and ratio of the disperse phase of parent emulsions.

Behaviour of oil droplets during spray drying of milk-protein-stabilised oil-in-water emulsions

The effects of spray drying on the behaviour of oil droplets in oil-in-water emulsions (12.0%, w/w, maltodextrin; 20.0%, w/w, soya oil) stabilised with either sodium caseinate or whey protein isolate (WPI) were examined as a function of protein concentration (0.5–5.0%, w/w). Spray drying and redispersion caused a shift in the droplet size distribution to larger values for all emulsions made using low protein concentrations (0.5–2.0%, w/w), in comparison with their respective parent emulsions. However, the droplet size distribution was affected only very slightly by spray drying when the protein concentration was above 2.0% (w/w). The effects of maltodextrin concentration (1.0–25.0%, w/w) on the behaviour of WPI-stabilised emulsions (0.5–10.0%, w/w, WPI, 20.0%, w/w, soya oil) were also examined. Emulsions containing low levels of maltodextrin showed marked re-coalescence during spray drying and redispersion even at a WPI concentration of 10.0% (w/w).

Photopolymerised methacrylate-based emulsion-templated porous polymers

Highly porous and interconnected methacrylate-based porous materials were prepared by photopolymerisation of the continuous phase of high internal phase emulsion (HIPE) templates. The rapid cure afforded by photopolymerisation effectively ‘locks’ the emulsion morphology prior to emulsion destabilisation, in comparison to thermally-initiated HIPEs of similar compositions. Contrary to expectation, it was observed that fully cured photopolymerised polyHIPEs could be prepared with a thickness of up to 35mm, despite the severe opacity of the parent emulsions. This is attributed to a photofrontal polymerisation process, where radicals generated on the surface propagate rapidly through the bulk of the emulsion. Homogeneous, well-defined polyHIPE materials of up to 95% nominal porosity were obtained by photopolymerisation of HIPEs containing up to 30vol.% glycidyl methacrylate (GMA) in the monomer phase (the remaining monomers and crosslinker are acrylates). Surprisingly, poly(ethylene glycol) methacrylate (PEG-MA), a nonionic monomer that is miscible with both emulsion phases, could be added to such HIPEs after preparation. On polymerisation, hydrophilic, water-wettable porous materials were obtained. Finally, it was also demonstrated that all-methacrylate HIPEs could be prepared and cured to yield GMA-containing polyHIPEs. These findings demonstrate the versatility of photopolymerisation for the preparation of emulsion templated porous polymers.

Highly concentrated emulsions: 1. Average drop size determination by analysis of incoherent polarized steady light transport

The analysis of incoherent polarized steady light transport is reported as a convenient technique for the drop size determination in highly concentrated oil-in-water emulsions. The studied system consists in heptane-in-water emulsions stabilized with a copolymeric surfactant (Synperonic PE®/L64). Hundred grams of parent emulsions, at two volume fractions of dispersed phase ( φ = 0.958 and 0.937) were prepared using a semi-batch process. Then, they were diluted with the aqueous phase to obtain volume fractions ranging from 0.886 to 0.958. The use of a copolymeric surfactant allows the dilution of the highly concentrated emulsions without any change in the particle size distribution as confirmed by laser diffraction measurements. We found that the polarization technique allows the determination of the film thickness between water drops rather than their sizes. Consequently, we propose a geometrical relationship to determine an average drop size from the film thickness. The sensitivity of this alternative technique to detect changes in average drop size was studied by changing some process and formulation parameters. Drop size determination in highly concentrated emulsions via this method is useful since the measurement protocol neither involves dilution nor induces structural changes in the emulsion.

Controlled Assembly of Nanoparticle Structures: Spherical and Toroidal Superlattices and Nanoparticle-Coated Polymeric Beads

The emulsion droplet solvent evaporation method has been used to prepare nanoclusters of monodisperse magnetite nanoparticles of varying morphologies depending on the temperature and rate of solvent evaporation and on the composition (solvent, presence of polymer, nanoparticle concentration, etc.) of the emulsion droplets. In the absence of a polymer, and with increasing solvent evaporation temperatures, the nanoparticles formed single- or multidomain crystalline superlattices, amorphous spherical aggregates, or toroidal clusters, as determined by the energetics and dynamics of the solvent evaporation process. When polymers that are incompatible with the nanoparticle coatings were included in the emulsion formulation, monolayer- and multilayer-coated polymer beads and partially coated Janus beads were prepared; the nanoparticles were expelled by the polymer as its concentration increased on evaporation of the solvent and accumulated on the surfaces of the beads in a well-ordered structure. The precise number of nanoparticle layers depended on the polymer/magnetic nanoparticle ratio in the oil droplet phase parent emulsion. The magnetic nanoparticle superstructures responded to the application of a modest magnetic field by forming regular chains with alignment of nonuniform structures (e.g., toroids and Janus beads) that are in accord with theoretical predictions and with observations in other systems.

Control of the morphology and the size of complex coacervate microcapsules during scale‐up

AbstractScale‐up of complex coacervation, a fat encapsulation technology, is not trivial since the microcapsules morphology and size are highly affected by the processing conditions. So far it has been achieved empirically (trial and error approach). The goal of this study was to produce at various scale capsules with a single‐oil droplet as the core material and small enough to be below sensory threshold. The turbulence level was identified as the main scale‐up criterium and a master‐curve could be drafted showing the capsule mean diameter as function of the Reynolds number, independent of the level of production scale. From a parent emulsion with specific oil droplets size (12–15 μm), the Reynolds number had to be maintained above a critical value (15,000) to avoid capsules agglomeration with multiple oil cores and large particle sizes. To avoid aggregation, this turbulence level had to be kept until the temperature dropped below a critical value (14°C for a cooling rate of 35°C/2 h). Applying these learning led to a successful scale‐up from bench (2 L) to a pilot plant scale of 50 L. © 2009 American Institute of Chemical Engineers AIChE J, 2009

Impact of Physicochemical Characteristics on the Oxidative Stability of Fish Oil Microencapsulated by Spray-Drying

The aim of the present research was to identify principal parameters determining the oxidative stability of microencapsulated fish oil. Microcapsules were prepared by spray-drying using different types of n-octenylsuccinate-derivatized starch, gum Arabic, sugar beet pectin, sodium caseinate, and/or glucose syrup. Two principal components to classify the different microcapsules accounting for up to 79% of the variance were identified. The principal components were determined by physicochemical parameters reflecting the emulsifying ability of the encapsulant and the drying behavior of the parent emulsion. Microcapsules, which were identified by principal component analysis to be significantly different, exhibited a low stability upon storage, showing that the principal components and, thus, the underlying physicochemical parameters analyzed in the present study are correlated with core material stability.

Effect of the Interfacial Layer Composition on the Properties of Emulsion Creams

We have quantified observed differences in the microstructure and rheology of creaming emulsions stabilized by protein and low molecular weight surfactants. In this study, we made two sets of emulsions from a single parent emulsion, which differed only in their interfacial composition (i.e., either protein or surfactant). The protein studied was whey protein isolate. The zeta potential of the surfactant-stabilized emulsion was controlled by mixing anionic (SDS) and nonionic (Brij 35) surfactants to match the zeta potential of the protein-stabilized emulsion. Despite this, ultrasonic creaming measurements and confocal microscopy showed that the structures within the cream layers were different between the two sets of emulsions. The protein-stabilized emulsions appeared to slow or arrest the packing within the cream, leading to a lower density network of emulsion droplets, whereas the surfactant emulsion droplets rearranged more quickly into a well-packed, concentrated cream layer. Rheological analysis of the creams showed that despite the protein-stabilized emulsions having a lower dispersed phase volume fraction, their elastic modulus was approximately 30 times greater than that of a comparable surfactant-stabilized emulsion. These differences were caused by the ability of the protein to form a highly viscoelastic interfacial network around the droplets which may include intermolecular covalent cross-links. At close range the adhesive nature of the interaction between the layers contributes to the microstructure and rheology of concentrated emulsions. This is the first time that such well-defined emulsion systems have been studied in detail both noninvasively to look at the impact on creaming and also invasively to look at the impact on bulk rheological properties.