Monomodal Droplet Size Distribution Research Articles

An original continuous process for double emulsions preparation using static mixers: Focus on the viscosity

A novel method for the preparation of water-in-oil-in-water (W/O/W) double emulsions is proposed and evaluated in this work. It is based on the classical two-step method in which the inner water-in-oil (W/O) emulsion is prepared using a high shear device (first batch step). This inner emulsion is then dispersed continuously in an aqueous phase using in line static mixers as second emulsification step for the formation of double emulsions. This somehow semi-continuous preparation method is evaluated when varying the viscosity of the three phases (from 1 to 100 mPa s) and the internal aqueous phase fraction (from 1 to 40 wt %). Under the investigated conditions, the use of static mixers is shown to be efficient for the formation of double emulsions with monomodal droplet size distributions and high encapsulation efficiency despite the shear thinning behavior of the inner emulsions. A correlation was established to relate the viscosity of the inner (W/O) emulsion with the fraction of the inner phase, that was found to be independent of the viscosity of the inner water phase. Moreover, it was possible to control the range of variation of the droplets size of the double emulsion from some tens to hundreds of micrometers while the residence time is less than a second. This fast and efficient double emulsion preparation process constitutes a promising alternative to classical batch processes.

Using cellulose nanofibers isolated from waste hop stems to stabilize dodecane or olive oil-in-water Pickering emulsions

TEMPO-oxidized cellulose nanofibers (TOCNF) were isolated from agricultural waste hop stems and used as stabilizers of oil-in-water Pickering emulsions. The TOCNF-stabilized emulsions were prepared using two types of oils (dodecane and olive oil), different TOCNF concentrations (0.5%, 0.8%, and 1.0% in the continuous phase), and multiple oil/water ratios (10–30% oil by weight). The stability of dodecane/TOCNF (d-CNF) and olive oil/TOCNF (o-CNF) emulsions were investigated over one month at ambient temperature. While the instability behavior in d-CNF and o-CNF emulsions was different, their stabilities were enhanced with TOCNF concentrations and/or the lower oil ratios. The addition of TOCNF above 0.8% prevented separation for one month by sufficiently covering the oil/water interface and forming the entangled structure in the continuous phase. The mean diameter of oil droplets (dv) in d-CNF emulsions was 5–14 µm, depending on the initial TOCNF loading. As for o-CNF emulsions, dv was relatively smaller than that of d-CNF (3–8 µm), and flocculation and Ostwald ripening were considered to dominate the destabilization at o/w 10/90 showing a monomodal droplet size distribution, while coalescence also contributed at o/w 20/80, showing a bimodal distribution.

A systematic approach to calibrate spray and break-up models for the simulation of high-pressure fuel injections

A novel calibration methodology is presented to accurately predict the fundamental characteristics of high-pressure fuel sprays for Gasoline Direct Injection (GDI) applications. The model was developed within the Siemens Simcenter STAR-CD 3D CFD software environment and used the Lagrangian–Eulerian solution scheme. The simulations were carried out based on a quiescent, constant volume, computational vessel to reproduce the real spray testing environment. A combination of statistic and optimisation methods was used for spray model selection and calibration and the process was supported by a wide range of experimental data. A comparative study was conducted between the two most commonly used models for fuel atomisation: Kelvin–Helmholtz/Rayleigh–Taylor (KH–RT) and Reitz–Diwakar (RD) break-up models. The Rosin–Rammler (RR) mono-modal droplet size distribution was tuned to assign initial spray characteristics at the critical nozzle exit location. A half factorial design was used to reveal how the various model calibration factors influence the spray properties, leading to the selection of the dominant ones. Numerical simulations of the injection process were carried out based on space-filling Design of Experiment (DoE) schedules, which used the dominant factors as input variables. Statistical regression and nested optimisation procedures were then applied to define the optimal levels of the model calibration factors. The method aims to give an alternative to the widely used trial-and-error approach and unveils the correlation between calibration factors and spray characteristics. The results show the importance of the initial droplet size distribution and secondary break-up coefficients to accurately calibrate the entire spray process. RD outperformed KH–RT in terms of prediction when comparing numerical spray tip penetration and droplet size characteristics to the experimental counterparts. The calibrated spray model was able to correctly predict the spray properties over a wide range of injection pressure. The work presented in this paper is part of the APC6 DYNAMO project led by Ford Motor Company.

Development and characterization of medium and high internal phase novel multiple Pickering emulsions stabilized by hordein nanoparticles

Medium and high internal phase W1/O/W2 multiple Pickering emulsions (MPEs) were fabricated by physically-modified hordein nanoparticles. A triphasic system was developed at dispersed phase volume fraction (Φ) of 0.5 with an overrun value of ∼40%. No overrun was detected in high internal phase MPEs (Φ 0.8). Optical and confocal laser scanning microscopy confirmed the formation of MPEs. Monomodal droplet size distribution with a mean diameter of 32.90 and 21.48 μm was observed for MPEs at Φ 0.5 and Φ 0.8, respectively. Static multiple light scattering confirmed that creaming was the main mechanism behind the instability of MPEs. Both MPEs revealed pseudo-plastic behavior and predominant storage modulus (G′) over the applied frequency range. The encapsulation efficiency of vitamin B12 in MPEs was 98.3% and remained relatively constant during 28 d. These results suggested the excellent potential of hordein nanoparticles as appropriate candidate for designing multi-structural colloidal systems using plant proteins.

Protein isolates from Cajanus cajan L. as surfactant for o:w emulsions: pH and ionic strength influence on protein structure and emulsion stability

This work has focused on the study of the influence of pH (2.1, 3.9, 6.3, 8.3) and ionic strength (μ) (0.10 and 0.54) on the formation and stability of oil in water (o:w) emulsions using a protein isolate of Cajanus cajan (PPI8) as emulsifier. Also, the influence of protein concentration was evaluated. Interfacial tension was better at pH2.1 and pH8.3, and it was improved at pH6.3 with the increase in ionic strength. Most emulsions showed a monomodal droplet size distribution, except at pH8.3 (μ: 0.54) where a bimodal distribution was observed. The critical concentration range of proteins was between 1.5 and 2.0% (μ: 0.10) and 1.0–1.5% (μ: 0.54). At pH6.3, the surface average diameter was independent of ionic strength (0.5%, 1.0%, and 2.0%). At low ionic strength, stable emulsions (protein concentration ≥1.0%) were obtained (up to 7 days) at pH2.1, pH6.3, and pH8.3, despite the differences in flocculation index (FI) observed. FI of emulsions remained constant up to 7 days of storage, except at pH2.1 (1.0%) and pH8.3 (2.0%). The emulsion stability at high ionic strength was pH dependent, at pH3.9 was improved even at low protein concentration due to the increase in protein solubility and apparent viscosity of emulsion. Because of their techno-functional properties, PPI8 could lead to the development of innovative products suitable for those consumers that demands for alternative plant-based protein sources.

Addition of a mushroom by-product in oil-in-water emulsions for the microencapsulation of sunflower oil by spray drying

The by-product generated after ergosterol extraction from mushrooms (A. bisporus) is rich in polysaccharides (β-glucans) and proteins. The usefulness of this mushroom’s by-product (MC) in oil microencapsulation by spray drying was evaluated partially replacing maltodextrin (13.5% w/w dry matter) and totally substituting Tween®20 with MC. Ergosterol was investigated as antioxidant. Non-Newtonian stable emulsions with mono-modal droplet size distributions were obtained with MC. Oil encapsulation efficiency was high (≥89%) and oil within microcapsules containing MC exhibited higher (p < 0.05) oxidative stability during spray drying. Powders containing MC exhibited larger particles (d5027% larger), 12% lower solubility in water and perceptible color changes. During storage (35 °C 50% RH), conjugated dienes increased more slowly in microcapsules containing MC. Reductions up to 28% in linoleic acid were observed after 150 days. Ergosterol was 95% degraded after 150 days in powders with MC and totally degraded after 2 days in powders without MC.

Preparation and characterisation of a novel emulsifier system based on glycerol monooleate by spray-drying

Glycerol monooleate (GMO) improves creaming stability in protein-stabilised emulsions but is unsuitable for direct aqueous applications due to its low solubility in water. Encapsulation could transform waxy solid GMO into a water-dispersible powder. This study assessed spray-drying to produce instantised GMO powders, and investigated emulsion formulation (GMO concentration (33.6%, 47.0%); dextrose equivalent (DE) values of maltodextrin (DE 10, 18)) on emulsion and powder properties. Results showed that all homogenised emulsions were suitable for spray-drying due to their high emulsion stability, monomodal droplet size distributions (150–180 nm) and low viscosity (20–65 mPa s). All instantised powders exhibited good dispersibility (65–90%) in water. The instantised powder with low GMO levels showed high encapsulation efficiencies (93–94%) with low surface oils (3%) and uniform droplet size distributions when reconstituted. Results demonstrated that spray-drying can successfully produce instantised powders for food applications to improve product quality.

Low-energy membrane-based processes to concentrate and encapsulate polyphenols from carob pulp

Forward osmosis (FO) and emulsification with dynamic membranes of tunable pore size (DMTS) were assessed to concentrate and encapsulate polyphenol extracts from carob pulp. In the FO step, a feed solution temperature of 40 °C resulted in the fastest concentration and the highest polyphenol yield. Moreover, FO at 35 °C enabled to concentrate up to about 20 times in 3 h using a pilot scale unit of 0.5 m2 of membrane area. Phenolic compounds were subsequently encapsulated in the inner water phase (W1) of water-in-oil-in-water (W1/O/W2) emulsions produced with DMTS, which enabled to obtain emulsions with a monomodal droplet size distribution (span<1, d3,2 ≤20 μm), and polyphenol encapsulation efficiencies ranging between 87.0 ± 0.2% and 77.4 ± 0.4%. To extend the shelf-life of the encapsulated polyphenols, solid microcapsules were produced by spray drying. After rehydrating the solid microcapsules, the structure of the W1/O/W2 emulsion was partially recovered.

Freeze-drying of black chokeberry pomace extract-loaded double emulsions to obtain dispersible powders.

Black chokeberry pomace extract is rich in polyphenolic antioxidants, including anthocyanins. Added to foods, bioactive compounds of the extract can undergo undesirable changes both during food handling and digestion. In this study, we examined the possibility of encapsulating a considerable amount of black chokeberry pomace extract in the inner water phase of double emulsion (water-in-oil-in-water), for intended use in food applications. Furthermore, this study investigated the feasibility of double emulsions loaded with the extract for freeze-drying to obtain dispersible powders. A substantial amount (2.1%) of black chokeberry pomace extract was efficiently encapsulated in the inner water phase of double emulsion and remained entrapped during 60 days of storage (<97%) as well as during the freeze-drying of emulsions. Reconstituted emulsions obtained after the rehydration process were found to show monomodal droplet size distribution, decent creaming stability (approximately 97%), and good encapsulation efficiency (95.36%). Such characteristics of powdered double emulsions loaded by black chokeberry pomace extract make them suitable for food application as retainer and preservative of bioactive polyphenolic-rich extracts. PRACTICAL APPLICATION: Powders of double emulsions loaded by black chokeberry pomace extract could be used as a source of bioactive polyphenolic compounds.

Pea flour as stabilizer of oil-in-water emulsions: Protein purification unnecessary

Plant proteins have recently gained considerable attention as stabilizers of food-grade oil-in-water emulsions. However, the separation of plant proteins from their native matrix can be cumbersome due to the molecular complexity of plants. This issue could be alleviated by avoiding the protein purification step. In this work, we show that native pea flour containing 50 wt% starch and 20 wt% protein has similar interfacial properties compared to concentrated pea protein systems (~55 wt% protein). Interfacial tension profile of pea flour was similar to that of concentrated pea protein, indicating that proteins are the primary stabilizing agents of the interface. The fabricated oil-in-water emulsions (10.0 wt% oil) made with pea flour or pea protein concentrate containing 0.2 and 0.3 wt% protein showed a similar monomodal droplet size distribution. Moreover, both emulsions stabilized by the pea flour and the pea protein concentrate had similar rheological properties, showing that starch granules did not have any impact on the physical properties. This work clearly showed that stable oil-in-water emulsions can be produced with pea flour and further purification of pea proteins is not necessary.

Pectin extraction from common fig skin by different methods: The physicochemical, rheological, functional, and structural evaluations

Four extraction methods of hot-water (HWE), ultrasound-assisted (UAE), microwave-assisted (MAE), and ultrasound-microwave assisted (UMAE) were utilized to determine the best technique to extract pectin from the common fig (Ficus carica L.) skin. UMAE (11.71%) significantly showed a more extraction yield than MAE (9.26%), UAE (8.74%), and HWE (6.05%). A significant dose-dependent antioxidant capacity for pectins 1,1-diphenyl-2-picryl-hydrazyl (DPPH), and 2,2′-azinobis (3-ethylbenzothiazoline-6-sulphonicacid) (ABTS) radical scavenging activity was found. The UMAE-pectin with the maximum galacturonic acid content (76.85%) and molecular weight (6.91 × 103 kDa) presented the highest emulsifying activity (61.2–61.3%) and emulsion stability (94.3–95.2%) with a monomodal droplet size distribution at cold and ambient storage temperatures. A non-Newtonian shear-thinning behavior was detected at 1.5–3.0% pectic-solutions. X-ray diffraction (XRD) analysis showed a non-crystalline nature for pectins extracted by UMAE. FTIR spectroscopy and HPLC photodiode array detector revealed that conventional and novel extraction technologies do not change the chemical structure and monosaccharide composition of pectin significantly.

Formulation and stability evaluation of water-in-fat and water-in-oil emulsions loaded with short-chain fatty acid

This study sought to formulate water-in-fat (W/F) and water-in-oil (W/O) emulsions loaded with a short-chain fatty acid and to evaluate storage stability of these emulsions. Premixtures comprising a dispersed aqueous phase loaded with 5 wt% butyric acid and a continuous phase with a hydrophobic emulsifier were subjected to a single-pass, temperature-controlled, high-pressure homogenization at 100 MPa to formulate W/F and W/O emulsions. Submicron W/F and W/O emulsions with Sauter mean diameters d3,2 < 0.5 μm and monomodal droplet size distributions were obtained at different weight fractions of the dispersed phase (Wd) in the range of 1–5 wt%. At a Wd of 5 wt%, the W/F emulsions maintained a consistent distribution after 4 weeks of storage and following consecutive melting–solidification cycles. The results demonstrated formulation of stable submicron W/F emulsions loaded with a short-chain fatty acid, with potential for possible applications as nutrient delivery systems to the large bowel.

Food grade microemulsion systems: Sunflower oil/castor oil derivative-ethanol/water. Rheological and physicochemical analysis

Microemulsions are thermodynamically stable systems that have attracted considerable attention in the food industry as delivery systems for many hydrophobic nutrients. These spontaneous systems are highly dependent on ingredients and composition. In this work phase diagrams were constructed using two surfactants (Kolliphor RH40 and ELP), water, sunflower oil, and ethanol as cosurfactant, evaluating their physicochemical properties. Stability of the systems was studied at 25 and 60 °C, monitoring turbidity at 550 nm for over a month to identify the microemulsion region. Conductivity was measured to classify between water-in-oil and oil-in-water microemulsions. The phase diagram constructed with Kolliphor RH40 exhibited a larger microemulsion area than that formulated with Kolliphor ELP.All formulations showed a monomodal droplet size distribution with low polydispersity index (<0.30) and a mean droplet size below 20 nm. Systems with higher water content presented a Newtonian behavior; increasing the dispersed phase content produced a weak gel-like structure with pseudoplastic behavior under flow conditions that was satisfactorily modeled to obtain structural parameters.

Physical stability of R-(+)-Limonene emulsions stabilized by Ulva fasciata algae polysaccharide

The physical stability of R-(+)-Limonene emulsions stabilized by Ulva fasciata polysaccharide (UFP) was investigated in this study. Emulsion physical stability was evaluated under different polysaccharide concentrations (1%–5%, wt/wt) and pH values (3.0–11.0). The stability of R-(+)-Limonene emulsions was demonstrated by droplet size distribution, rheological properties, zeta potential and visual phase separation. R-(+)-Limonene emulsions displayed monomodal droplet size distributions, high absolute values of zeta potential and good storage stability when 3% (wt/wt) UFP was used. The rheological properties and stability of R-(+)-Limonene emulsions appeared to be dependent on polysaccharide concentration. The emulsion stability was impacted by pH. Higher zeta potential (−52.6mV) and smaller mean droplet diameter (2.45μm) were achieved in neutral liquid environment (pH 7.0). Extreme acidity caused the flocculation of emulsions, which was manifested as phase separation, while emulsions were quite stable in an alkaline environment. Through comparing the stabilities of emulsions stabilized by different emulsifiers (i.e. UFP, GA and Gelatin), the result suggested that UFP was the best emulsifying agent among them.

Effect of emulsifier type on physicochemical properties of water‐in‐oil emulsions for confectionery applications

SummaryIn a first step of designing tailored confectionery masses using water‐in‐oil emulsions, a parameter screening on emulsion rheology and stability was carried out. The experimental set‐up included cocoa butter as continuous phase and the variation of the disperse phase (water, or 50% sucrose in water), two volume fraction levels and the type of emulsifier (lecithin, polyglycerol polyricinoleate (PGPR), ammonium phosphatide (YN) and blends of lecithin or YN with PGPR). Emulsions were characterised by microscopy, laser diffraction, analytical centrifugation and shear rheology. Results show multimodal droplet size distributions in lecithin‐ or YN‐stabilised emulsions, and droplets which tend to form aggregates and an internal network responsible for shear thinning. PGPR emulsions are characterised by monomodal droplet size distributions and smaller droplets without networking tendency. They exhibit Newtonian flow behaviour and a much higher stability against phase separation. In emulsifier blends, PGPR is mainly responsible for the modulation of physical properties of the emulsions.

Influences of Ulva fasciata polysaccharide on the rheology and stabilization of cinnamaldehyde emulsions

Emulsifying properties of water soluble polysaccharides from Ulva fasciata (UFP) were evaluated in cinnamaldehyde/water emulsions in terms of droplet size distribution, rheological properties, visual phase separation, and zeta-potential. The cinnamaldehyde/water (10%, wt/wt) emulsions were formulated and stabilized by different concentrations of UFP (0.1–4%, wt/wt). The obtained emulsions showed monomodal droplet size distributions with average droplet size (D[3,2]) below 1.0μm, when 3% (wt/wt) UFP was added as the emulsifying agent under a homogenization pressure of 75MPa. The rheological properties and zeta-potential of the emulsions appeared to be dependent on the UFP concentration. Furthermore, the UFP exhibited better emulsifying and stabilizing properties in the investigated system when compared to other commercial polysaccharides of gum Arabic and gum Ghatti. The results also suggested that the emulsifying and stabilizing mechanism of the UFP may not only be ascribed to its surface-active protein moiety, but also to the hydrophobicity of the polysaccharide itself. These findings provided a theoretical basis for potential utilization of UFP as a novel hydrocolloid emulsifying agent.

Role of the phases composition on the incorporation of gallic acid in O/W and W/O emulsions

This work aimed to study the incorporation and preservation of gallic acid (GA) in emulsions formulated using soybean oil as oil phase, polyoxyethylene sorbitan (Tween 20) and polyglycerol polyricinoleate (PGPR) as surfactants. The systems evaluated were oil-in-water (O/W) and water-in-oil (W/O) emulsions prepared using the same aqueous to oily phases weight ratio (3:1). The volume fraction of surfactant was 0.01, 0.02 or 0.04 and gallic acid concentration in the final emulsions was 0 or 0.5% w/w. Increasing GA concentration did not show any effect on the initial or equilibrium interfacial tension (22mN/m) in GA solution/soybean oil systems but reduced the average diameter of the droplets in both emulsions. The W/O emulsions showed bimodal droplet size distribution, pseudoplastic behavior and the presence of GA decreased the phase separation. The O/W emulsions exhibited kinetic stability, monomodal droplet size distribution and Newtonian fluid behavior. Results showed that the emulsification process was an efficient method to protect the bioactive against oxidation. Fresh O/W emulsions showed higher GA retention but during the storage time, the W/O emulsions showed a better capacity to retain the gallic acid. However, both emulsions exhibited high retention of bioactive (>86.61%) after 7days of storage showing that this strategy could be used in different emulsified food products.

Preparation of Monodisperse Food-Grade Oleuropein-Loaded W/O/W Emulsions Using Microchannel Emulsification and Evaluation of Their Storage Stability

W/O/W emulsion is an emerging system in developing new functional and low-calorie food products. The aim of this study is to produce food-grade monodisperse water-in-oil-in-water (W/O/W) emulsions loaded with a hydrophilic bioactive oleuropein. W/O/W emulsions were prepared via high-pressure homogenization and subsequent microchannel (MC) emulsification. The internal aqueous phase was a 5-mM sodium phosphate buffer containing d(+)-glucose (5 wt.%) and oleuropein (0.1–0.7 wt.%). The oil phase consisted of soybean oil and tetraglycerin monolaurate condensed ricinoleic acid esters (TGCR; 3–8 wt.%). The external aqueous phase was a 5-mM sodium phosphate buffer containing d(+)-glucose (5 wt.%) and decaglycerol monolaurate (1 wt.%). Oleuropein-loaded submicron W/O emulsions with average droplet diameters as small as 0.15 μm and monomodal droplet size distributions were prepared by high-pressure homogenization when applying high TGCR concentrations of 5–8 wt.% and low oleuropein concentrations of 0.1–0.3 wt.%. Monodisperse oleuropein-loaded W/O/W emulsions with average W/O droplet diameters of around 27 μm and coefficients of variation of below 5 % were successfully prepared when using a silicon MC array plate with wide channels of 5-μm depth and 18-μm width. The monodisperse W/O/W emulsions prepared at high TGCR concentrations and low oleuropein concentrations were the most stable during 40 days of storage. The adsorption behavior of oleuropein at the internal aqueous–oil interface was relevant to W/O/W emulsions microstructure and stability. The results are believed to provide useful information for successfully preparing stable monodisperse W/O/W emulsions loaded with hydrophilic functional compounds. The surface activity of the loaded material seems to be a key parameter in optimizing the formulation of W/O/W food emulsion.

Synergistic effect of Laponite RD and oil soluble surfactant in stabilization of miniemulsions

Laponite RD was used in combination with the oil soluble surfactant dimethyl-di(hydrogenated tallow)ammonium iodide (2M2HT) for the stabilization of oil-in-water (o/w) miniemulsions. The 2M2HT promoted the adsorption of the Laponite RD at the oil–water interface. Either hexadecane or a mixture of hexadecane and heptane was used as the oil phase. Stable o/w miniemulsions were obtained with a droplet size of 225–300 nm, with mostly a monomodal droplet size distribution. Transmission electron microscopy (TEM) images showed that nanocapsules were formed and burst due to evaporation of hexadecane under the high vacuum conditions of TEM. This provided evidence of the robust nature of the Laponite discs that stabilized the droplets via both mechanical and electrostatic stabilization.

Freeze- or spray-dried gluten hydrolysates. 2.: Effect of emulsification process on droplet size and emulsion stability

Two gluten hydrolysates differing only in the drying process were studied: LS2 was freeze-dried and PS2 was spray-dried. The effect of emulsification procedure (turbo-mixer, valve-homogeniser) was determined as a function of the composition of the aqueous phase (hydrolysate dispersions, soluble fractions). With turbo-mixer, all emulsions presented a monomodal droplet size distribution but emulsions formed with hydrolysate dispersions were unstable whereas these formed with soluble fractions were very stable. With hydrolysate dispersions, the use of a valve-homogeniser decreased droplet size and improved considerably the resistance to coalescence. Nevertheless, the enhancement of emulsion stability was higher with LS2 dispersions than with PS2 dispersions. In contrast, with soluble fractions, emulsions formed with valve-homogeniser remained highly stable but the droplet distribution became polymodal. The higher energy input provided by a valve-homogeniser resulted in the insoluble fraction becoming involved in the emulsion formation. This led to a narrower droplet size distribution and more stable emulsions.