Hydrogel microspheres for encapsulation of lipophilic components: Optimization of fabrication & performance

Filled hydrogel microspheres consisting of small oil droplets trapped within biopolymer matrices are useful for encapsulating and delivering lipophilic bioactive agents. The aim of this study was to improve the current method of microsphere fabrication by increasing lipid loading capacity and microsphere yields, reducing the number of processing steps involved in fabrication, and creating microspheres that resist gravitational separation during storage. Filled hydrogel microspheres were fabricated from a phase separated mixture of pectin, caseinate, and emulsified oil to form an oil-in-water-in-water (O/W₁/W₂) emulsion. This system was then acidified and the resulting microspheres were cross-linked with transglutaminase. The order in which the biopolymer phases (W₁ and W₂) and oil droplets (O) were mixed together did not impact the lipid loading capacity. Decreasing the proportion of the continuous biopolymer phase (W₂) used in the preparation procedure increased microsphere yields; however too low proportions (60–70%) caused excessive foaming and protein coagulation. Alternative methods of fabricating filled hydrogel particles using free oil (rather than emulsified oil) proved unsuccessful, resulting in the formation of large non-encapsulated oil droplets (d ∼ 10 μm). Hydrogel microspheres (d₃₂ ∼ 3 μm) with high stability to gravitational separation could be produced by fabricating microspheres with an oil-to-biopolymer ratio of ∼2.6, since this ratio formed particles with a density that nearly matched the surrounding aqueous phase.     

Encapsulation,protection, and release of polyunsaturated lipids using biopolymer-based hydrogel particles

Delivery systems are needed to encapsulate polyunsaturated lipids, protect them within food products, and ensure their bioavailability within the gastrointestinal tract. Hydrogel particles assembled from food-grade biopolymers are particularly suitable for this purpose. In this study, hydrogel microspheres were fabricated by electrostatic complexation of low methoxy pectin and caseinate by decreasing the solution pH from 7 to 4.5. After hydrogel particle formation, the caseinate was enzymatically cross-linked using transglutaminase to improve the stability of the biopolymer matrix. The effect of hydrogel particle encapsulation on the physical location, chemical stability, and lipase digestibility of emulsified polyunsaturated lipids (fish oil) was investigated. The cross-linked hydrogel particles formed using this process were relatively small (D₄₃ = 4.6 μm), negatively charged (ζ = − 37 mV), and evenly distributed within the system. Confocal microscopy confirmed that the fish oil droplets were trapped within casein-rich hydrogel microspheres. Encapsulation of the fish oil droplets improved their stability to lipid oxidation compared to conventional emulsions, which was attributed to a high local concentration of antioxidant protein around the emulsified lipids. The rate and extent of digestion of the encapsulated lipid droplets within a simulated small intestine were similar to those of non-encapsulated ones. These results suggest that casein-rich hydrogel microspheres may protect polyunsaturated lipids in foods and beverages, but release them after ingestion.     

Ferrous bisglycinate content and release in W1/O/W2 multiple emulsions stabilized by protein–polysaccharide complexes

Ferrous bisglycinate aqueous solution was entrapped in the inner phase (W₁) of water-in-oil-in-water (W₁/O/W₂) multiple emulsions. The primary ferrous bisglycinate aqueous solution-in-mineral oil (W₁/O) emulsion contained 15% (w/w) ferrous bisglycinate, had a dispersed phase mass fraction of 0.5, and was stabilized with a mixture of Grindsted PGPR 90:Panodan SDK (6:4 ratio) with a total emulsifiers concentration of 5% (w/w). This primary emulsion was re-emulsified in order to prepare W₁/O/W₂ multiple emulsions, with a dispersed mass fraction of 0.2, and stabilized using protein (whey protein concentrate (WPC)):polysaccharide (gum arabic (GA) or mesquite gum (MG) or low methoxyl pectin (LMP)) complexes (2:1 ratio) in the W₂ aqueous phase. The W₁/O/W₂ multiple emulsion stabilized with WPC:MG (5% w/w total biopolymers concentration) provided smaller droplet sizes (2.05 μm), lower rate of droplet coalescence (7.09 × 10⁻⁷ s⁻¹), better protection against ferrous bisglycinate oxidation (29.75% Fe³⁺) and slower rate of ferrous bisglycinate release from W₁ to W₂ (K_H = 0.69 mg mL⁻¹ min^−0.5 in the first 24 h and 0.07 mg mL⁻¹ min^−0.5 for the next 19 days of storage time). Better encapsulation efficiencies, enhanced protection against oxidation and slower release rates of ferrous bisglycinate were achieved as the molecular weight of the polysaccharide making up protein:polysaccharide complex was higher. Thus, the factor that probably affected most the overall functionality of multiple emulsions was the thickness of the complex adsorbed around the multiple emulsion oil droplets. These thicknesses determined indirectly by measuring the z-average diameter of the complexes, and that of the WPC:MG (529.4 nm) was the largest.     

Concurrent phase separation and gelation in mixed oat β-glucans/sodium caseinate and oat β-glucans/pullulan aqueous dispersions

The phase separation behavior of mixed oat β-glucans/sodium caseinate and oat β-glucans/pullulan aqueous dispersions at 20 °C has been studied. The concentration of β-glucans required for induction of phase separation and the physical state of the separated phases, as revealed by visual observations and dynamic rheometry, depended on the molecular weight of β-glucans and the initial polymeric composition. For β-glucans with apparent molecular weights (M_w) 35 and 65 × 10³ the β-glucan concentration at which thermodynamic incompatibility occurred decreased from about 2–2.5% (w/w) at low concentrations (∼0.2%) of sodium caseinate or pullulan to about 1–1.5% (w/w) β-glucans at high levels (up to 7.5% w/w) of the second biopolymer; these bi-phasic systems consisted of an upper liquid phase and a lower gel-like phase. For β-glucans with M_w of 110 × 10³, a bi-phasic system with two liquid phases appeared above a certain β-glucan concentration, which decreased from approximately 4% to 1% (w/w) with increasing sodium caseinate levels in the range of 0.2–7.5% (w/w). With further increase in β-glucan concentration, the lower phase turned into a gel, and at even higher β-glucan concentrations, the polymer demixing process was ‘arrested’ by chain aggregation events, leading to a macroscopically single gel phase. Generally, the aggregation of β-glucans seemed to interfere with the phase separation phenomenon resulting in an increase of β-glucan concentration in the lower phase between 5% and 110% and only a slight increase of sodium caseinate or pullulan concentration in the upper phase (<10%), due to kinetic entrapment of the polymeric components into a highly viscous medium.     

Inhibition of lipid oxidation by encapsulation of emulsion droplets within hydrogel microspheres

The purpose of this study was to assess whether the oxidation of polyunsaturated lipids could be inhibited by encapsulating them within protein-rich hydrogel microspheres (size range 1-100 μm). Filled hydrogel microspheres were fabricated as follows: (i) high methoxy pectin, sodium caseinate, and casein-coated lipid droplets were mixed at pH 7, (ii) the mixture was acidified (pH 5), (iii) casein was cross-linked using transglutaminase, (iv) the pH was adjusted to pH 7. Samples were stored in the dark at 55 °C and were monitored for lipid hydroperoxide formation and headspace propanal. Oxidation of fish oil (1% vol/vol) in the microspheres was compared with that in oil-in-water emulsions stabilised by either sodium caseinate or Tween 20. Emulsions stabilised by Tween 20 oxidised faster than either microspheres or emulsions stabilised by casein, while microspheres and the casein stabilised emulsion showed similar oxidation rates. Results highlight the natural antioxidant properties of food proteins.     

Effect of high-methoxy pectin on properties of casein-stabilized emulsions

We report on the effect of high-methoxy pectin on the stability and rheological properties of fine sunflower oil-in-water emulsions prepared with α_s1-casein, β-casein or sodium caseinate. The aqueous phase was buffered at pH 7.0 or 5.5 and the ionic strength was adjusted with sodium chloride in the range 0.01–0.2 M. Average emulsion droplet sizes were found to be slightly larger at the lower pH and/or with pectin present during emulsification. Analysis of the serum phase after centrifugation indicated that some pectin becomes incorporated into the interfacial layer at pH 5.5 but not at pH 7.0. This was also supported by electrophoretic mobility measurements on protein-coated emulsion droplets and surface shear viscometry of adsorbed layers at the planar oil–water interface. A low pectin concentration (0.1 wt%) was found to give rapid serum separation of moderately dilute emulsions (11 vol% oil, 0.6 wt% protein) and highly pseudoplastic rheological behaviour of concentrated emulsions (40 vol% oil, 2 wt% protein). We attribute this to reversible depletion flocculation of protein-coated droplets by non-adsorbed pectin. At ionic strength below 0.1 M, the initial average droplet sizes, the creaming behaviour, and the rheology were found to be similar for emulsions made with either of the individual caseins (α_s1 and β) or with sodium caseinate. At higher ionic strength, however, whereas emulsions containing β-casein or sodium caseinate were stable, the corresponding α_s1-casein emulsions exhibited irreversible salt-induced flocculation which was not inhibited by the presence of the pectin.     

Crosslinking of interfacial layers in multilayered oil-in-water emulsions using laccase: Characterization and pH-stability

The enzymatic crosslinking of polymer layers adsorbed at the interface of oil-in-water emulsions was investigated. A sequential two step process, based on the electrostatic deposition of pectin onto a fish gelatin interfacial membrane was used to prepare emulsions containing oil droplets stabilized by fish gelatin-beet pectin membranes (citrate buffer, 10 mM, pH 3.5). First, a fine dispersed primary emulsion (5% soybean oil (w/v), 1% (w/w) gelatin solution) (citrate buffer, 10 mM, pH 3.5) was produced using a high pressure homogenizer. Second, a series of secondary emulsions were formed by diluting the primary emulsion into pectin solutions (0 - 0.4% (w/w)) to coat the droplets. Oil droplets of stable emulsions with different oil droplet concentrations (0.1%, 0.5%, 1.0% (w/v)) were subjected to enzymatic crosslinking. Laccase was added to the fish gelatin-beet pectin emulsions and emulsions were incubated for 15 min at room temperature. The pH- and storage stability of primary, secondary and secondary, laccase-treated emulsions was determined. Results indicated that crosslinking occurred exclusively in the layers and not between droplets, since no aggregates were formed. Droplet size increased from 350 to 400 nm regardless of oil droplet concentrations within a matter of minutes after addition of laccase suggesting formation of covalent bonds between pectin adsorbed at interfaces and pectin in the aqueous phase in the vicinity of droplets. During storage, size of enzymatically treated emulsions decreased, which was found to be due to enzymatic hydrolysis. Results suggest that biopolymer-crosslinking enzymes could be used to enhance stability of multilayered emulsions.     

Food-grade filled hydrogels for oral delivery of lipophilic active ingredients: Temperature-triggered release microgels

Delivery systems are often needed to encapsulate lipophilic active agents, protect them during storage, and then release them within the mouth. In this study, gelatin and caseinate were used to fabricate temperature-sensitive filled hydrogel particles. Filled hydrogel microspheres were formed by electrostatic complexation of caseinate and gelatin in the presence of caseinate-coated lipid droplets. This was achieved by mixing aqueous 1% sodium caseinate and 1% gelatin solutions (volume ratio 1:2) at pH 5.8 with an oil-in-water emulsion. The majority of lipid droplets were trapped within the hydrogel microspheres. Turbidity and viscosity measurements of the hydrogels indicated that hydrogel particles dissociated upon heating because of gelatin melting (around 35 °C). Light scattering and confocal fluorescence microscopy indicated that lipid droplets were released from the gelatin-based hydrogel particles after oral processing, which was attributed to hydrogel melting under simulated mouth conditions. Our results suggest that hydrogel particles based on electrostatic complexation of sodium caseinate and gelatin could be useful as oral delivery systems for lipophilic active agents.     

Impact of surface deposition of lactoferrin on physical and chemical stability of omega-3 rich lipid droplets stabilised by caseinate

There is considerable interest in developing delivery systems to encapsulate and protect chemically labile lipophilic food components, such as omega-3 rich oils. In this study, multilayer emulsion-based delivery systems were prepared consisting of omega-3 rich oil droplets coated by either caseinate (Cas) or lactoferrin–caseinate (LF–Cas). Surface deposition of LF onto Cas-coated oil droplets was confirmed by ζ-potential measurements. Emulsions containing lactoferrin and caseinate had better physical stability to pH changes and salt addition (pH 3–7, 0–50 mM CaCl₂ at pH 7) than those containing only caseinate (pH 5–7, 0–2 mM CaCl₂ at pH 7). The addition of LF also retarded the formation of lipid oxidation markers (hydroperoxides and thiobarbituric acid reactive substances) in the emulsions. The ability of LF to enhance both the physical and chemical stability of protein-stabilised emulsions is useful for the fabrication of delivery systems designed for utilisation within the drug and food industries.     

Stability and release properties of double-emulsions stabilised by caseinate–dextran conjugates

The subject of the present paper was to investigate the possibility of stabilising water-in-oil-in-water emulsions (W/O/W) by using sodium caseinate (SC)–dextran (Dex) conjugates in order to influence the release of vitamin B₁₂ from the inner water phase (W₁) to the outer aqueous phase (W₂).To prepare the conjugate the SC was combined with Dex (M_r 250,000 or 500,000 g/mol) and incubated at 60 °C and a humidity of 79% for 8 h.The double emulsions, with encapsulated vitamin B₁₂, were prepared using a two-step emulsification technique. Whereas different amounts of polyglycerin polyricinoleate (PGPR, E476) were the hydrophobic emulsifier, the conjugate and the SC alone were used as the hydrophilic emulsifiers. The investigations comprised the determination of the particle size distribution of the W/O/W emulsion and measurement of the amount of vitamin B₁₂ migration from W₁- to the W₂-phase during the second stage of emulsion preparation and after heating or pH changing of emulsion.The water-containing oil droplets of the W/O/W emulsions were smaller and distributed more narrowly using SC–Dex conjugate as emulsifier instead of pure protein. Under acidic conditions, the conjugate-containing emulsions were more coalescence stable than the emulsions with SC, and the vitamin B₁₂ release from the inner W₁-phase was significantly decreased.     

Sustainable production of pectin from lime peel by high hydrostatic pressure treatment

The application of high hydrostatic pressure technology for enzymatic extraction of pectin was evaluated. Cellulase and xylanase under five different combinations (cellulase/xylanase: 50/0, 50/25, 50/50, 25/50, and 0/50 U/g lime peel) at ambient pressure, 100 and 200 MPa were used to extract pectin from dried lime peel. Extraction yield, galacturonic acid (GalA) content, average molecular weight (M_w,ave), intrinsic viscosity [η]_w, and degree of esterification (DE) were compared to those parameters obtained for pectins extracted using acid and aqueous processes. Pressure level, type and concentration of enzyme significantly (p < 0.05) influenced yield and DE of pectin. Enzyme and high pressure extraction resulted in yields which were significantly (p < 0.05) higher than those using acid and aqueous extraction. Although pressure-induced enzymatic treatment improves pectin yield, it does not have any significant effect on M_w,ave and [η]_w of pectin extracts indicating the potential of high pressure treatment for enzymatic pectin production as a novel and sustainable process.     

Development of multiple emulsions based on the repulsive interaction between sodium caseinate and LBG

The stability of oil-in-water, water-in-water and multiple emulsions containing sodium caseinate (Na-CN) and/or locust bean gum (LBG) at pH 5.5 was investigated with different compositions using a visual analysis (creaming and/or phase separation), optical microscopy and rheological measurements. Oil-in-water emulsions (O/W) were produced by high pressure homogenization, which promoted the formation of very small droplets (∼0.4 μm) and hindered the destabilization process. In the second step of this study, a visual phase diagram was constructed in order to identify the concentrations of sodium caseinate (Na-CN) and locust bean gum (LBG) that led to phase separation at pH 5.5. A mixed solution composed of 3% (w/v) Na-CN and 0.3% (w/v) LBG was chosen to produce the water-in-water and multiple emulsions. After centrifugation, the solution was separated into an upper phase rich in polysaccharide (PS) and a bottom phase rich in protein (PR), which were mixed in different proportions (1:3, 1:1, 3:1), forming the water-in-water (W/W) emulsions. The stability, microstructure and rheological properties of the W/W emulsions depended strongly on the composition of the biopolymers. An increase in the polysaccharide concentration in the W/W emulsions led to the production of more viscous and stable systems. Multiple emulsions with different characteristics were prepared and also depended on the biopolymer composition. The system with the highest polysaccharide content was the only one that showed an O/W/W structure, while the others presented the microstructure of an O/W-W/W emulsion.     

Stability and release properties of double emulsions for food applications

Water-in-oil-in-water (W₁/O/W₂) double emulsions (DEs) containing gelatin and sodium chloride (NaCl) in the inner aqueous phase were developed for controlled release applications. Emulsions were prepared with water and canola oil, as well as with polyglycerol polyricinoleate and polysorbate 80 as emulsifiers for the primary water-in-oil (W₁/O) emulsion and secondary W₁/O/W₂ emulsions, respectively. All DEs containing both NaCl and gelatin were stable against sedimentation for the month-long study whereas control emulsions (with either no NaCl or gelatin) showed visual phase separation. The average oil globule size in freshly-prepared DEs grew from ∼45 to 70 μm with an increase in salt load from 2 to 8% (w/w), and changed little after 1 month. Besides its role in stabilization, NaCl was also used as a marker to evaluate DE release behaviour. The salt diffusion coefficient obtained using Fujita’s model rose from 4.7 to 6.0 × 10⁻¹¹ cm²/s with increasing NaCl concentration in the DEs from 2 to 8% (w/w). All stable DEs showed a high salt retention in the inner aqueous phase (>94%) after 1 month of storage at 4 °C. These results demonstrated the synergistic action of a gelling agent and electrolyte in stabilizing and modulating the release behaviour of NaCl from W₁/O/W₂ DEs.     

Controlling lipid digestion by encapsulation of protein-stabilized lipid droplets within alginate–chitosan complex coacervates

The control of lipid digestibility within the human gastrointestinal tract is important for the development of many functional food and pharmaceutical products. This article describes the preparation, characterization, and in vitro digestibility of lipid droplets encapsulated within hydrogel beads. Protein-stabilized lipid droplets were first coated with an alginate layer, and then they were trapped within chitosan/calcium alginate coacervates. The filled hydrogel beads were formed using two methods: “direct method” – add a suspension of alginate-coated lipid droplets to a calcium/chitosan solution; “indirect method” – add chitosan solution to a suspension of alginate-coated lipid droplets and calcium. The in vitro digestibility of the encapsulated lipid droplets was then monitored using a pH-stat method to simulate the small intestine. For both methods, the filled hydrogel beads were relatively stable to aggregation/dissociation from pH 1 to 6, but underwent extensive aggregation and sedimentation at higher pH values. Relatively small hydrogel beads (d < 50 μm) caused a moderate delay in the rate of lipid digestion, while large hydrogel beads (d > 100 μm) could delay the digestion rate appreciably. This study has important implications for designing delivery systems that control lipid digestion by encapsulating lipid droplets within hydrogel beads.     

Formation of biopolymer particles by thermal treatment of β-lactoglobulin–pectin complexes

The purpose of this study was to prepare and characterize biopolymer particles based on thermal treatment of protein–polysaccharide electrostatic complexes formed from a globular protein (β-lactoglobulin) and an anionic polysaccharide (beet pectin). Initially, the optimum pH and pectin concentration for forming protein–polysaccharide complexes were established by mixing 0.5 wt% β-lactoglobulin solutions with beet pectin (0–0.5 wt%) at different pH values (3–7). Biopolymer complexes in the sub-micron size range (d = 100–300 nm) were formed at pH 5.0 and 0.1 wt% pectin. These particles were then subjected to a thermal treatment (30–90 °C at 0.8 °C min⁻¹). The presence of pectin increased the thermal aggregation temperature of the protein, although aggregate formation was still observed when the protein–polysaccharide systems were heated above about 70 °C. The impact of pH (3–7) on the properties of heat-treated biopolymer particles (83 °C, 15 min, pH 5) was then established. The biopolymer particles were stable to aggregation over a range of pH values, which increased as the amount of pectin was increased. The biopolymer particles prepared in this study may be useful for encapsulation and delivery of bioactive food components, or as substitutes for lipid droplets.     

Double emulsion (W/O/W) gel stabilised by polyglycerol polyricinoleate and calcium caseinate as mangiferin carrier: insights on formulation and stability properties

Mangiferin (MGF) is a phenolic compound isolated from mango, but its poor solubility significantly limits its use. In this study, MGF was embedded into the inner aqueous phase of W₁/O/W₂ emulsions. Firstly, the dissolution method of MGF was determined. MGF remained stable in solution with pH 13 at 30 min, and its solubility reached 10 mg mL⁻¹. When the pH of MGF solutions was adjusted from pH 13 to pH 6, MGF did not immediately crystallise, providing sufficient time to construct the MGF-loaded W₁/O/W₂ emulsions. Subsequently, the MGF-loaded W₁/O/W₂ emulsions were constructed using polyglycerol polyricinoleate (PGPR) and calcium caseinate (CAS). The formation and stability of the W₁/O/W₂ emulsions were investigated. The MGF-loaded W₁/O/W₂ emulsions stabilised with 1% PGPR and 1% – 3% CAS exhibited a low viscosity, limited loading capacity, and poor stability. Conversely, the MGF-loaded W₁/O/W₂ emulsions stabilised by 3%PGPR–3%CAS exhibited optimal loading capacity (encapsulation efficiency = 95.31% and loading efficiency = 0.91%) and stability, which was attributed to the fact that high viscosity and gel state retarded the migration of inner aqueous phase. These results indicated that the W₁/O/W₂ emulsions stabilised by PGPR and CAS may be a potential alternative for encapsulating mangiferin.     

Water soluble inner aqueous phase markers as indicators of the encapsulation properties of water-in-oil-in-water emulsions stabilized with sodium caseinate

The aim of this study was to evaluate the suitability of Methylene Blue (MB) and Vitamin B₁₂ (Vit-B₁₂) as water soluble inner aqueous phase (W₁) markers for measuring the encapsulation efficiency and stability of water-in-oil-in-water (W₁/O/W₂) double emulsions stabilized by sodium caseinate (NaCN). The encapsulation efficiency and stability were determined by centrifugation of the double emulsion to separate the cream phase (W₁/O) and the outer aqueous phase (W₂) and measuring the concentration of marker in W₂ by absorbance spectrophotometry. To validate this method the marker concentration measurable and the stability of the marker in W₂ were measured. Both markers could be accurately measured in W₂ and there was no change in the concentration of marker on storage of a W₂ solution for 7 days at 45 °C. The recovery yields of MB and Vit-B₁₂ in the recovered W₂ of an oil-in-water (O/W₂) emulsion, determined using the procedure normally used for measuring encapsulation efficiency and stability, were 78% and 99%, respectively, and 52 and 100%, respectively. Double emulsions had encapsulation efficiency of 61.9 ± 21.4% and 16.6 ± 1.1% and encapsulation stability of 62.0 ± 22.6% and 10.7 ± 0.7% for MB and Vit-B₁₂, respectively. Recovery yield and encapsulation efficiency/stability data for MB indicate that it is not a suitable marker for measuring the encapsulation properties of NaCN stabilized double emulsions while similar data for Vit-B₁₂ indicate that it is a suitable marker for studying the encapsulation properties of double emulsions stabilized with NaCN. Methods used in other studies to measure encapsulation properties of double emulsions are discussed in light of the results obtained in this study.     

Sodium caseinate–maltodextrin conjugate stabilized double emulsions: Encapsulation and stability

The potential food applications of water-in-oil-in-water (W₁/O/W₂) double emulsions are great, including the encapsulation of flavours or active ingredients. However, the stability of these emulsions restricts their applications in food systems. Sodium caseinate (NaCN)–maltodextrin (Md40 or Md100) conjugates were investigated for their potential to improve the stability of W₁/O/W₂ double emulsions compared to NaCN. NaCN–Md40 and NaCN–Md100 conjugates were prepared by a Maillard-type reaction by dry heat treatment of mixtures of NaCN–Md40 or NaCN–Md100 at 60 °C and 79% relative humidity for 4 days. Water-in-oil-in-water (W₁/O/W₂) double emulsions with NaCN, NaCN–Md40 or NaCN–Md100 as outer aqueous phase containing emulsifier were prepared using a two-step emulsification process. General emulsion stability was characterised by determining the droplet size distribution, viscosity characteristics and by confocal microscopy of the W₁/O/W₂ double emulsions on formation and after their storage under accelerated shelf life testing conditions at 45 °C for up to 7 days. Inner phase encapsulation and stability were characterised by monitoring the level of entrapped Vitamin B₁₂ in the inner aqueous phase on formation of the double emulsions and after storage at 45 °C for up to 7 days. Conjugate stabilized emulsions were more generally stable than NaCN stabilized emulsions. In comparison to NaCN stabilized emulsions, conjugate stabilized emulsions showed improved Vitamin B₁₂ encapsulation efficiency in the inner aqueous phase on emulsion formation and improved encapsulation stability following storage of the emulsions.     

Bubble stability in the presence of oil-in-water emulsion droplets: Influence of surface shear versus dilatational rheology

We discuss the stability of bubbles to coalescence when undergoing a pressure drop and their stability to disproportionation under quiescent conditions, studied using previously established ‘single bubble layer experimental’ techniques, focussing on the effects on stability of the inclusion of a low volume fraction (0.25%) of stable oil droplets. Detailed measurements of the surface dilatational elasticity (?_s) and surface shear viscosity (η_s) of systems in the presence and absence of oil droplets have been performed. The surface rheology and stability have been measured as a function of adsorption time and pH, between pH 4.5 and 7, by including glucono-δ-lactone (GDL) as an acidification agent. Commercial sodium caseinate (SC) and purified β-lactoglobulin (β-L) were used at 1 wt% bulk concentration as bubble stabilizing agents. The emulsion oil droplet phase was n-tetradecane (TD) or 1-bromohexadecane (BHD), with a mean droplet size of (d₄₃) = 0.59 and 0.67 μm, respectively. The emulsion droplets were completely stable to coalescence and did not enter or spread at the air–water (A–W) interface. With SC at all pH values the values of η_s were markedly higher in the presence of TD droplets than in their absence, but particularly when the pH was lowered to pH ≤ 5.5 such that the SC started to aggregate. The increase in η_s correlated with the increase in coalescence stability under the same conditions. With neutrally buoyant BHD droplets the increase in η_s was not as great, but η_s was still significantly higher than in the absence of droplets, indicating that the rise to, and packing of, TD droplets at the A–W interface due to gravity was not solely responsible for their observed effects. The values of ?_s did not increase much at all for either β-L or SC as the pH was lowered and/or TD droplets were added, except at very low pH values, when the effects with SC were obscured by the tendency for the bulk SC to gel. In agreement with the relatively insignificant changes in ?_s as the pH was lowered or droplets were added, the resistance to disproportionation of bubbles did not change very much either.     

Formation of nanoemulsions stabilized by model food-grade emulsifiers using high-pressure homogenization: Factors affecting particle size

Nanoemulsions are finding increasing utilization in the food and beverage industries for certain applications because of their unique physicochemical and functional properties: high encapsulation efficiency; low turbidity; high bioavailability; high physical stability. In this study, we examined the impact of system composition and homogenization conditions on the formation of nanoemulsions using a high-pressure homogenizer (microfluidizer). The mean particle diameter decreased with increasing homogenization pressure and number of passes, with a linear log–log relationship between mean particle diameter and homogenization pressure. The minimum droplet diameter that could be produced after 6 passes at 14 kbar depended strongly on emulsifier type and concentration: SDS < Tween 20 < β-lactoglobulin < sodium caseinate. Small-molecule surfactants formed smaller droplets than proteins, which was attributed to their ability to rapidly adsorb to the droplet surfaces during homogenization. The impact of phase viscosity was examined by using different octadecane-to-corn oil ratios in the oil phase and different glycerol-to-water ratios in the aqueous phase. The minimum droplet size achievable decreased as the ratio of disperse phase to continuous phase viscosities (η_D/η_C) decreased for SDS-stabilized emulsions, but was relatively independent of η_D/η_C for β-lactoglobulin-stabilized emulsions. At low viscosity ratios, much smaller mean droplet diameters could be achieved for SDS (d ∼ 60 nm) than for β-lactoglobulin (d ∼ 150 nm). The information reported in this study will facilitate the rational design of food-grade nanoemulsions using high-pressure homogenization methods.