Optimization of lipid nanoparticle formation for beverage applications: Influence of oil type,cosolvents, and cosurfactants on nanoemulsion properties

The influence of flavor oil composition, cosolvents (glycerol and propylene glycol), and cosurfactant (lysolecithin) on the formation and stability of lemon oil nanoemulsions stabilized by sucrose monoesters was examined. At ambient temperature, nanoemulsions containing 1-, 3-, and 5-fold lemon oils were stable to droplet growth, whereas those containing 10-fold lemon oil were unstable. For 10-fold lemon oil nanoemulsions, the droplet growth rate increased with increasing temperature, cosolvent addition, and decreasing lysolecithin concentration, which was attributed to the influence of these factors on the phase inversion temperature. Clear nanoemulsions could be formulated that maintained small mean particle diameters (d ≈ 81 nm) during storage at ambient temperature for 1 month. The information generated in this study is useful for designing stable flavor nanoemulsions for applications in functional foods and beverages.     

Food-grade microemulsions and nanoemulsions: Role of oil phase composition on formation and stability

Lemon oil is widely used as a flavoring component in beverages, foods, cosmetics, and household products. Lemon oil comes in a variety of chemical compositions depending on its biological origin, extraction methods, and purification procedures. At present, there is a relatively poor understanding of the influence of lemon oil composition on its functional properties. In this study, we examined the influence of lemon oil fold (1×, 3×, 5× and 10×) on the formation and properties of oil-in-water microemulsions and nanoemulsions. The concentration of both polar (high water solubility and low log P) and non-polar (low-water solubility and high log P) components increased with increasing oil fold. The nature of the colloid dispersions formed was established using an emulsion titration method that involved titrating lemon oil droplets into a surfactant micelle solution (1% Tween 80). Oil fold affected the rate and extent of solubilization, as well as the stability of lemon oil droplets to growth. The maximum amount of lemon oil that could be solubilized within the micelles increased with increasing oil fold, as did the stability of lemon oil droplets to growth. The results were interpreted in terms of the ability of different lemon oil molecules to be incorporated within water or surfactant micelles, and the influence of lemon oil polarity on Ostwald ripening. This study provides valuable information about the relationship between lemon oil composition and its performance in colloidal delivery systems suitable for use in the food and beverage industries.     

Inhibition of Ostwald ripening in model beverage emulsions by addition of poorly water soluble triglyceride oils

Beverage emulsions containing flavor oils that have a relatively high water-solubility are unstable to droplet growth due to Ostwald ripening. The aim of this study was to improve the stability of model beverage emulsions to this kind of droplet growth by incorporating poorly water-soluble triglyceride oils. High pressure homogenization was used to prepare a series of 5 wt% oil-in-water emulsions stabilized by modified starch that had different lipid phase compositions (orange oil : corn oil). Emulsions prepared using only orange oil as the lipid phase were highly unstable to droplet growth during storage, which was attributed to Ostwald ripening resulting from the relatively high water-solubility of orange oil. Droplet growth could be effectively inhibited by incorporating ≥ 10% corn oil into the lipid phase prior to homogenization. In addition, creaming was also retarded because the lipid phase density was closer to that of the aqueous phase density. These results illustrate a simple method of improving the physical stability of orange oil emulsions for utilization in the food, beverage, and fragrance industries.     

Influence of chitosan on stability and lipase digestibility of lecithin-stabilized tuna oil-in-water emulsions

The influence of chitosan concentration (0–0.3 wt%) and molecular weight (120, 250 and 342.5 kDa) on the physical stability and lipase digestibility of lecithin-stabilized tuna oil-in-water emulsions was studied. The ζ-potential, droplet size, creaming stability, free fatty acids and glucosamine released was measured for the emulsions when they were subjected to an in vitro digestion model. The ζ-potential of the oil droplets in lecithin-chitosan stabilized emulsions changed from positive (≈+53 mV) to negative and the emulsions were unstable to droplet aggregation for all chitosan concentrations and molecular weights used after being subjected to the digestion model. The amount of free fatty acid and glucosamine released per unit amount of emulsion was higher when pancreatic lipase was included in the digestion model. These results suggest that lecithin-chitosan coated droplets can be degraded by lipase under simulated gastrointestinal conditions. Consequently, chitosan coated lipid droplets may serve as useful carriers for the delivery of bioactive lipophilic nutraceuticals.     

Influence of different β-glucans on the physical and rheological properties of egg yolk stabilized oil-in-water emulsions

The objective of this study was to obtain additional information on the influence of different β-glucan preparations, i.e. curdlan (CL), barley (BG), oat (OG), and yeast (YG) β-glucans, on the physical and rheological properties of egg yolk stabilized oil-in-water emulsions containing 20% oil. The emulsion without β-glucan (REF) was also prepared as a reference. Addition of CL and OG increased emulsion oil droplet sizes, whereas BG and YG showed no effect. Emulsion microstructures revealed that β-glucans induced flocculation of the oil droplet in the following order: CL > BG ≈ OG > YG. Dynamic oscillatory shear tests indicated that all emulsions exhibited weak gel-like characteristics which were enhanced by β-glucans addition as evidenced by an increase in G′ and a decrease in tan δ values. Flow tests showed that β-glucans enhanced thixotropy and yield stress of the emulsions. Stability tests demonstrated that β-glucans addition improved creaming stability of the emulsions during storage possibly due to an increase in viscosity of the continuous phase and/or a formation of a three-dimensional droplet network. CL exhibited the most pronounced effects on the aforementioned properties of emulsions compared to the other β-glucans tested. YG gave emulsion with higher viscoelastic properties and yield stress but lower stability than those made with BG or OG, indicating complex relationship between rheology and stability of these emulsion systems.     

Influence of chitosan and NaCl on physicochemical properties of low-acid tuna oil-in-water emulsions stabilized by non-ionic surfactant

An influence of low molecular weight (LMW) chitosan on physicochemical properties and stability of low-acid (pH 6) tuna oil-in-water emulsion stabilized by non-ionic surfactant (Tween 80) was studied. The mean droplet diameter, droplet charge (ζ-potential), creaming stability and microstructure of emulsions (5 wt% oil) were evaluated. The added chitosan was adsorbed on the surface of oil droplets stabilized by Tween 80 through electrostatic interactions. Such addition of chitosan at different concentrations (0–10 wt%) to emulsions showed slight effect on the mean droplet diameter. However, the degree of flocculation was a function of chitosan concentration assessed by emulsions' microstructure and creaming index. The impact of chitosan on the strength of the colloidal interaction between the emulsion droplets increased with increasing chitosan concentration. The mean diameter of droplet in emulsions increased with increasing NaCl because of the electrostatic screening effect. The addition of LMW chitosan could be performed to create tuna oil emulsions with low-acid to neutral character, as well as various physicochemical and stability properties suitable for health food products.     

Influence of particle size on lipid digestion and β-carotene bioaccessibility in emulsions and nanoemulsions

The interest in incorporating carotenoids, such as β-carotene, into foods and beverages is growing due to their potential health benefits. However, the poor water-solubility and low bioavailability of carotenoids is currently a challenge to their incorporation into many foods. The aim of this work was to study the influence of particle size on lipid digestion and β-carotene bioaccessibility using corn oil-in-water emulsions with different initial droplet diameters: large (d₄₃ ≈ 23 μm); medium (d₄₃ ≈ 0.4 μm); and small (d₄₃ ≈ 0.2 μm). There was a progressive increase in the mean particle size of all the emulsions as they passed through a simulated gastrointestinal tract (GIT) consisting of mouth, stomach, and small intestine phases, which was attributed to droplet coalescence, flocculation, and digestion. The electrical charge on all the lipid particles became highly negative after passage through the GIT due to accumulation of anionic bile salts, phospholipids, and free fatty acids at their surfaces. The rate and extent of lipid digestion increased with decreasing mean droplet diameter (small ≈ medium ? large), which was attributed to the increase in lipid surface area exposed to pancreatic lipase with decreasing droplet size. There was also an appreciable increase in β-carotene bioaccessibility with decreasing droplet diameter (small > medium > large). These results provide useful information for designing emulsion-based delivery systems for carotenoids for food and pharmaceutical uses.     

Influence of interfacial composition on oxidative stability of oil-in-water emulsions stabilized by biopolymer emulsifiers

The objective of this research was to evaluate the influence of storage pH (3 and 7) and biopolymer emulsifier type (Whey protein isolate (WPI), Modified starch (MS) and Gum arabic (GA)) on the physical and oxidative stability of rice bran oil-in-water emulsions. All three emulsifiers formed small emulsion droplets (d₃₂ < 0.5 μm) when used at sufficiently high levels: 0.45%, 1% and 10% for WPI, MS and GA, respectively. The droplets were relatively stable to droplet growth throughout storage (d₃₂ < 0.6 μm after 20 days), although there was some evidence of droplet aggregation particularly in the MS-stabilized emulsions. The electrical charge on the biopolymer-coated lipid droplets depended on pH and biopolymer type: −13 and −27 mV at pH 3 and 7 for GA; −2 and −3 mV at pH 3 and 7 for MS; +37 and −38 mV at pH 3 and 7 for WPI. The oxidative stability of the emulsions was monitored by measuring peroxide (primary products) and hexanal (secondary products) formation during storage at 37 °C, for up to 20 days, in the presence of a pro-oxidant (iron/EDTA). Rice bran oil emulsions containing MS- and WPI-coated lipid droplets were relatively stable to lipid oxidation, but those containing GA-coated droplets were highly unstable to oxidation at both pH 3 and 7. The results are interpreted in terms of the impact of the electrical characteristics of the biopolymers on the ability of cationic iron ions to interact with emulsified lipids. These results have important implications for utilizing rice bran oil, and other oxidatively unstable oils, in commercial food and beverage products.     

Utilisation of pectin coating to enhance spray-dry stability of pea protein-stabilised oil-in-water emulsions

In this study, development of pea (Pisum sativum) protein stabilised dry and reconstituted emulsions is presented. Dry emulsions were prepared by spray-drying liquid emulsions in a laboratory spray-dryer. The effect of drying on the physical stability of oil-in-water emulsions containing pea protein-coated and pea protein/pectin-coated oil droplets has been studied. Oil-in-water emulsions (5 wt.% Miglyol 812 N, 0.25 wt.% pea protein, 11% maltodextrin, pH 2.4) were prepared that contained 0 (primary emulsion) or 0.2 wt.% pectin (secondary emulsion). The emulsions were then subjected to spray-drying and reconstitution (pH 2.4). The stability of the emulsions to dry processing was then analysed using oil droplet size, microstructure, Zeta potential, and creaming measurements. Obtained results showed that the secondary emulsions had better stability to droplet aggregation after drying than primary emulsions. To interpret these results, we propound that pectin, an anionic polysaccharide, formed a less charged protective layer around the protein interfacial film surrounding the oil droplets that improved their stability to spray-drying mainly by increasing steric effects.     

Influence of glycerol and sorbitol on thermally induced droplet aggregation in oil-in-water emulsions stabilized by β-lactoglobulin

The influence of polyol cosolvents (glycerol and sorbitol) on the flocculation stability of hydrocarbon oil-in-water emulsions stabilized by a globular protein was examined. Salt (150 mM NaCl) and polyols (0–40 wt%) were added to n-hexadecane oil-in-water emulsions stabilized by β-lactoglobulin (β-Lg, pH 7.0) either before or after isothermal heat treatments (30–90 °C for 20 min). When salt was added to emulsions before heat treatment, appreciable droplet flocculation was observed below the thermal-denaturation temperature of the adsorbed β-Lg (T_m∼70 °C), and more extensive flocculation was observed above T_m. On the other hand, when salt was added after heat treatment, appreciable droplet flocculation still occurred below T_m, but little flocculation was observed above T_m. Addition of cosolvents to the emulsions increased the temperature where extensive droplet flocculation was first observed when they were heated in the presence of salt, which was attributed to their ability to increase T_m and to reduce the droplet collision frequency, with sorbitol being more effective than glycerol. Our results are interpreted in terms of the influence of the cosolvents on protein conformational stability, protein-protein interactions and the physiochemical properties of aqueous solutions. This study has important implications for the formulation and production of protein stabilized oil-in-water emulsions for industrial applications, such as foods, pharmaceuticals and cosmetics.     

Impact of free fatty acid concentration and structure on lipid oxidation in oil-in-water emulsions

Free fatty acids are strong prooxidants in both bulk and emulsified oils. Addition of oleic acid to an oil-in-water emulsions increased lipid hydroperoxide and hexanal formation at free fatty acid concentrations as low as 0.1% of the lipid. The prooxidant effect of free fatty acids was dependent on fatty acid type with lipid oxidation rates being in the order of linolenic < linoleic < oleic. There were no significant differences in lipid oxidation rates when free fatty acid isomers with cis or trans double bonds were compared. The prooxidant activity of the free fatty acids was postulated to be due to their ability to attract prooxidant metals as well as co-oxidise the triacylglycerol in the oil. Overall, these results show that the oxidative stability of oil-in-water emulsions is strongly linked to both the concentration and type of free fatty acids present.     

Oxidative stability of olive oil–lemon juice salad dressings stabilized with polysaccharides

Lipid oxidation is a major cause of quality deterioration in food emulsions. Polysaccharides used to improve emulsion stability and texture may also affect lipid oxidation. In the present study, the oxidative stability of olive oil–lemon juice salad dressings, stabilized with gum arabic or propylene glycol alginate in admixture with xanthan, was investigated. Oil-in-water emulsions (50:50, v/v) were prepared with lemon juice and extra virgin olive oil and then homogenized at various homogenization rates to form different particle sizes. Keepability was followed by storing at room temperature for 6–8 months and measuring the formation of primary and secondary oxidation products. The shelf life was compared to that of the bulk olive oil. It was shown that the polysaccharides had the ability to inhibit lipid oxidation, probably due to their amphiphilic character (gum arabic and propylene glycol alginate) as well as their ability to induce viscosity increase. Olive oil–lemon juice emulsions were also assessed for consumer acceptance. The panellists were asked to smell the samples and rate them according to rancidity using a four-point (1 = no perception, 4 = extreme) intensity scale. The results were in accordance to those of chemical analysis. Lipid oxidation was not affected by the oil droplet size, as demonstrated by peroxide value measurements and sensory evaluation.     

Properties and antioxidant activity of fish skin gelatin film incorporated with citrus essential oils

Properties of protein-based film from fish skin gelatin incorporated with different citrus essential oils, including bergamot, kaffir lime, lemon and lime (50% based on protein) in the presence of 20% and 30% glycerol were investigated. Films containing 20% glycerol had higher tensile strength (TS) but lower elongation at break (EAB), compared with those prepared with 30% glycerol, regardless of essential oils incorporated (p < 0.05). Films incorporated with essential oils, especially from lime, at both glycerol levels showed the lower TS but higher EAB than the control films (without incorporated essential oil) (p < 0.05). Water vapour permeability (WVP) of films containing essential oils was lower than that of control films for both glycerol levels (p < 0.05). Films with essential oils had varying ΔE^* (total colour difference), where the highest value was observed in that added with bergamot essential oil (p < 0.05). Higher glycerol content increased EAB and WVP but decreased TS of films. Fourier transforms infrared (FTIR) spectra indicated that films added with essential oils exhibited higher hydrophobicity with higher amplitude at wavenumber of 2874–2926 cm⁻¹ and 1731–1742 cm⁻¹ than control film. Film incorporated with essential oils exhibited slightly lower thermal degradation resistance, compared to the control film. Varying effect of essential oil on thermal degradation temperature and weight loss was noticeable, but all films prepared using 20% glycerol had higher thermal degradation temperature with lower weight loss, compared with those containing 30% glycerol. Films added with all types of essential oils had rough cross-section, compared with control films, irrespective of glycerol levels. However, smooth surface was observed in all film samples. Film incorporated with lemon essential oil showed the highest ABTS radical scavenging activity and ferric reducing antioxidant power (FRAP) (p < 0.05), while the other films had lower activity. Thus, the incorporation of different essential oils and glycerol levels directly affected the properties of gelatin-based film from fish skin.     

Droplet characterization and stability of soybean oil/palm kernel olein O/W emulsions with the presence of selected polysaccharides

Droplet characteristics, flow properties and stability of egg yolk-stabilized oil-in-water (O/W) emulsions as affected by the presence of xanthan gum (XG), carboxymethyl cellulose (CMC), guar gum (GG), locust bean gum (LBG) and gum Arabic (AG) were studied. The dispersed phase (40%) of the emulsions was based on soybean oil/palm kernel olein blend (70:30) that partially crystallized during extended storage at 5 °C. In freshly prepared emulsions, the presence of XG, CMC, GG and LBG had significantly decreased the droplet mean diameters. XG, LBG, GG and CMC emulsions exhibited a shear-thinning behavior but AG emulsion exhibited a Bingham plastic behavior and control (without gum) emulsion almost exhibited a Newtonian behavior. Both control and AG emulsions exhibited a severe phase separation after storage (30 days, 5 °C). The microstructure of stored XG emulsion showed the presence of partially coalesced droplets, explaining a large increase in its droplet mean diameters. Increases in droplet mean diameters and decreases in flow properties found for stored GG and LBG emulsions were attributed to droplet coalescence. Nevertheless, the occurrence of droplet coalescence in these emulsions was considered to be small as no free oil could be separated under centrifugation force. Increases in flow properties and excellent stability towards phase separation found for stored CMC emulsion suggested that CMC could retard partial coalescence. Thus, the results support the ability of CMC, GG and LBG in reducing partial coalescence either by providing a sufficiently thick continuous phase or by acting as a protective coating for oil droplets.     

Structure and oxidative stability of oil in water emulsions as affected by rutin and homogenization procedure

The structural properties of oil-in-water (O/W) emulsions, as well as their oxidative stability upon storage at 50 °C, were studied. Eight different formulations were prepared, with the aim of studying the effect of three variables: the composition of the oil phase, the presence of the flavonoid rutin and the homogenization procedure on the structure and the oxidative stability. It was found that high pressure homogenization, through droplet size reduction, stabilized the emulsions both against creaming and oil oxidation. The interfacial protein was also partially replaced by rutin, further improving the stability of the emulsions, whereas purification of the oil phase had hardly any effect. Thus, the structural and oxidative stability of emulsions was controlled by the size of the droplets and improved by the addition of rutin.     

Rheology and microstructure of myofibrillar protein-plant lipid composite gels: Effect of emulsion droplet size and membrane type

Composite gels were prepared from 2% myofibrillar protein (MP) with 10% imbedded pre-emulsified plant oils (olive and peanut) of various particle sizes at 0.6 M NaCl, pH 6.2. Dynamic rheological testing upon temperature sweeping (20-70 °C at 2 °C/min) showed substantial increases in G′ (elastic modulus) of MP sols/gels with the addition of emulsions, and the G′ increases were inversely related to the emulsion droplet size. Furthermore, gels containing emulsified olive oil had a greater (P < 0.05) hardness than those containing emulsified peanut oil. Regardless of oil types, MP-coated oil droplets exhibited stronger reinforcement of MP gels than Tween 80-stablized oil droplets; the latter composite gels had considerable syneresis. Light microscopy with paraffin sectioning revealed a stable gel structure when filled with protein-coated oil droplets, compared to gels with Tween 80-treated emulsions that showed coalesced oil droplets. These results suggest that rheological characteristics, hardness, texture, and water-holding capacity of MP gels were influenced by type of oils, the nature of the interfacial membrane, and the size of emulsion droplets.     

Formulation and properties of model beverage emulsions stabilized by sucrose monopalmitate: Influence of pH and lyso-lecithin addition

There is a growing trend toward utilizing more label friendly ingredients in foods and beverages. In this study, we focused on the utilization of sucrose monopalmitate (SMP) as a non-ionic surfactant for stabilizing acidic beverages. Orange oil-in-water emulsions (5% (w/w) oil) stabilized by SMP were prepared using high pressure homogenization (pH 7). The minimum droplet diameter was around 130 nm, while the minimum mass ratio of SMP-to-oil required to produce small droplets was 0.1-to-1. Extensive droplet aggregation occurred when the pH of the emulsions was reduced from pH 7 to 3, with the mean particle diameter increasing from around 0.13 to 7.25 μm. This effect was attributed to an appreciable reduction in droplet charge when the pH was reduced (ζ ≈− 35 mV at pH 3 and − 2 mV at pH 3) thereby decreasing the electrostatic repulsion between droplets. It was proposed that the negative charge on the SMP-coated droplets was due to the presence of anionic substances within the droplets, such as palmitic acid (pK_a ≈ 4.9). Palmitic acid may have been an impurity in the original ingredient or it may have been generated due to degradation of SMP during storage. The addition of anionic lyso-lecithin markedly improved the stability of the emulsions to droplet aggregation and phase separation at low pH, which was attributed to an increased electrostatic repulsion between the droplets. This study has important consequences for the formulation of acidic beverage emulsions with improved stability and physicochemical performance.     

Impact of iron encapsulation within the interior aqueous phase of water-in-oil-in-water emulsions on lipid oxidation

Iron (Fe³⁺) was encapsulated within the internal aqueous phase of water-in-oil-in-water (W/O/W) emulsions, and then the impact of this iron on the oxidative stability of fish oil droplets was examined. There was no significant change in lipid droplet diameter in the W/O/W emulsions during 7 days storage, suggesting that the emulsions were stable to lipid droplet flocculation and coalescence, and internal water diffusion/expulsion. The initial iron encapsulation (4 mg/100 g emulsion) within the internal aqueous phase of the water-in-oil (W/O) emulsions was high (>99.75%), although, a small amount leaked out over 7 days storage (≈10 μg/100 g emulsion). When W/O/W emulsions were mixed with fish oil droplets the thiobarbituric acid-reactive substances (TBARS) formed decreased (compared to fish oil droplets alone) by an amount that depended on iron concentration and location, i.e., no added iron < iron in external aqueous phase < iron in internal aqueous phase. These differences were attributed to the impact of W/O droplets on the concentration and location of iron and lipid oxidation reaction products within the system.     

Encapsulation of emulsified tuna oil in two-layered interfacial membranes prepared using electrostatic layer-by-layer deposition

Tuna oil-in-water emulsions (5 wt% tuna oil, 100 mM acetate buffer, pH 3.0) containing droplets stabilized either by lecithin membranes (primary emulsions) or by lecithin–chitosan membranes (secondary emulsions) were produced. The secondary emulsions were prepared using a layer-by-layer electrostatic deposition method that involved adsorbing cationic chitosan onto the surface of anionic lecithin-stabilized droplets. Primary and secondary emulsions were prepared in the absence and presence of corn syrup solids (a carbohydrate widely used in the micro-encapsulation of oils) and then their stability to environmental stresses was monitored. The secondary emulsions had better stability to droplet aggregation than primary emulsions exposed to thermal processing (30–90 °C for 30 min), freeze-thaw cycling (−18 °C for 22 h/30 °C for 2 h), high sodium chloride contents (200 mM NaCl) and freeze-drying. The addition of corn syrup solids decreased the stability of primary emulsions, but increased the stability of secondary emulsions. The interfacial engineering technology used in this study could lead to the creation of food emulsions with novel properties or improved stability to environmental stresses.