摘要 :
Double emulsions are very promising for various applications in pharmaceutics, cosmetics, and food. Despite lots of published research, only a few products have successfully been marketed due to immense stability problems. This re...
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Double emulsions are very promising for various applications in pharmaceutics, cosmetics, and food. Despite lots of published research, only a few products have successfully been marketed due to immense stability problems. This review describes approaches on how to characterize the stability of double emulsions. The measurement methods are used to investigate the influence of the ingredients or the process on the stability, as well as of the environmental conditions during storage. The described techniques are applied either to double emulsions themselves or to model systems. The presented analysis methods are based on microscopy, rheology, light scattering, marker detection, and differential scanning calorimetry. Many methods for the characterization of double emulsions focus only on the release of the inner water phase or of a marker encapsulated therein. Analysis methods for a specific application rarely give information on the actual mechanism, leading to double emulsion breakage. In contrast, model systems such as simple emulsions, microfluidic emulsions, or single-drop experiments allow for a systematic investigation of diffusion and coalescence between the individual phases. They also give information on the order of magnitude in which they contribute to the failure of the overall system. This review gives an overview of various methods for the characterization of double emulsion stability, describing the underlying assumptions and the information gained. With this review, we intend to assist in the development of stable double emulsion-based products.
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Water-in-oil-in-water (W1/O/W2) double emulsions must resist W1–W1, O–O and W1–W2 coalescence to be suitable for applications. This work isolates the stability of the oil droplets in a double emulsion, focusing on the impact of...
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Water-in-oil-in-water (W1/O/W2) double emulsions must resist W1–W1, O–O and W1–W2 coalescence to be suitable for applications. This work isolates the stability of the oil droplets in a double emulsion, focusing on the impact of the concentration of the hydrophilic surfactant. The stability against coalescence was measured on droplets ranging in size from millimeters to micrometers, evaluating three different measurement methods. The time between the contact and coalescence of millimeter-sized droplets at a planar interface was compared to the number of coalescence events in a microfluidic emulsion and to the change in the droplet size distributions of micrometer-sized single and double emulsions. For the examined formulations, the same stability trends were found in all three droplet sizes. When the concentration of the hydrophilic surfactant is reduced drastically, lipophilic surfactants can help to increase the oil droplets’ stability against coalescence. This article also provides recommendations as to which purpose each of the model experiments is suited and discusses advantages and limitations compared to previous research carried out directly on double emulsions.
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In water-in-oil-in-water (W1/O/W2) double emulsions several irreversible instability phenomena lead to changes. Besides diffusive processes, coalescence of droplets is the main cause of structural changes. In double emulsions, inn...
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In water-in-oil-in-water (W1/O/W2) double emulsions several irreversible instability phenomena lead to changes. Besides diffusive processes, coalescence of droplets is the main cause of structural changes. In double emulsions, inner droplets can coalesce with each other (W1-W1 coalescence), inner droplets can be released via coalescence (W1-W2 coalescence) and oil droplets can coalesce with each other (O-O coalescence). Which of the coalescence pathways contributes most to the failure of the double emulsion structure cannot be determined by common measurement techniques. With monodisperse double emulsions produced with microfluidic techniques, each coalescence path can be observed and quantified simultaneously. By comparing the occurrence of all possible coalescence events, different hydrophilic surfactants in combination with PGPR are evaluated and discussed with regard to their applicability in double emulsion formulations. When variating the hydrophilic surfactant, the stability against all three coalescence mechanisms changes. This shows that measuring only one of the coalescence mechanisms is not sufficient to describe the stability of a double emulsion. While some surfactants are able to stabilize against all three possible coalescence mechanisms, some display mainly one of the coalescence mechanisms or in some cases all three mechanisms are observed simultaneously.
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We report a Lego-inspired glass capillary micro-fluidic device capable of encapsulating both organic and aqueous phase change materials (PCMs) with high reproducibility and 100% PCM yield. Oil-in-oil-in-water (O/O/W) and water-in-...
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We report a Lego-inspired glass capillary micro-fluidic device capable of encapsulating both organic and aqueous phase change materials (PCMs) with high reproducibility and 100% PCM yield. Oil-in-oil-in-water (O/O/W) and water-in-oil-in-water (W/O/W) core—shell double emulsion droplets were formed to encapsulate hexadecane (HD, an organic PCM) and salt hydrate SP21EK (an aqueous PCM) in a UV-curable polymeric shell, Norland Optical Adhesive (NOA). The double emulsions were consolidated through on-the-fly polymerization, which followed thiol-ene click chemistry for photoinitiation. The particle diameters and shell thicknesses of the microcapsules were controlled by manipulating the geometry of glass capillaries and fluid flow rates. The microcapsules were monodispersed and exhibited the highest encapsulation efficiencies of 65.4 and 44.3% for HD and SP21EK-based materials, respectively, as determined using differential scanning calorimetry (DSC). The thermogravimetric (TGA) analysis confirmed much higher thermal stability of both encapsulated PCMs compared to pure PCMs. Polarization microscopy revealed that microcapsules could sustain over 100 melting—crystallization cycles without any structural changes. Bifunctional microcapsules with remarkable photocatalytic activity along with thermal energy storage performance were produced after the addition of 1 wt % titanium dioxide (Ti02) nanoparticles (NPs) into the polymeric shell. The presence of Ti02 NPs in the shell was confirmed by higher opacity and whiteness of these microcapsules and was quantified by energy dispersive X-ray (EDX) spectroscopy. Young's modulus of HD-based microcapsules estimated using micromanipulation analysis increased from 58.5 to 224 MPa after Ti02 incorporation in the shell.
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Successfully replacing meat with plant-based options will require not only replicating the texture of muscular fibres, but also imitating the taste, aroma, and juiciness of meat as closely and realistically as possible. This study...
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Successfully replacing meat with plant-based options will require not only replicating the texture of muscular fibres, but also imitating the taste, aroma, and juiciness of meat as closely and realistically as possible. This study examines the impact of rapeseed oil on the textural properties of meat analogues. Pea protein and soy protein are chosen as model systems to assess the effect of rapeseed oil. Optical, mechanical, and rheological characterisation tests are conducted to investigate the oil droplet distribution, the gel strength, Young's modulus, and the length of the LVE region. The hypothesis is that oil droplets will act as active fillers in the protein matrix, and thus, diminish the strength of the protein gel network. The results of this study show that rapeseed oil droplets act as inactive fillers, as they are not bound to both examined protein matrices. Soy protein extrudates display minimal changes, while pea protein extrudates are significantly affected by the addition of oil. For example, oil addition decreased the G′ in the LVE region of pea protein meat analogues by 50%, while soy protein samples showed no significant changes. Despite the similar interfacial activities of the investigated proteins, the decreased encapsulation efficiency of pea protein was confirmed by the higher amount of extracted oil from the respective extrudates.
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Due to their nested structure, double emulsions have the potential to encapsulate value-adding substances until their application, making them of interest to various industries. However, the complex, nested structure negatively af...
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Due to their nested structure, double emulsions have the potential to encapsulate value-adding substances until their application, making them of interest to various industries. However, the complex, nested structure negatively affects the stability of double emulsions. Still, there is a lack of suitable measurement technology to fundamentally understand the cause of the instability mechanisms taking place. This study presents a novel measurement method to continuously track filling degree changes due to water diffusion in a water-in-oil-in-water (W1/O/W2) double emulsion droplet. The measurement method is based on the Raman effect and provides both photometric and spectrometric data. No sample preparation is required, and the measurement does not affect the double emulsion droplet.
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Double emulsions are a promising formulation for encapsulation and targeted release in pharmaceutics, cosmetics and food. An inner water phase is dispersed in an oil phase, which is again emulsified in a second water phase. The en...
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Double emulsions are a promising formulation for encapsulation and targeted release in pharmaceutics, cosmetics and food. An inner water phase is dispersed in an oil phase, which is again emulsified in a second water phase. The encapsulated inner water phase can be released via diffusion or via coalescence, neither of which is desired during storage but might be intended during application. The two interfaces in a double emulsion are stabilized by a hydrophilic and a lipophilic surfactant, to prevent the coalescence of the outer and the inner emulsion, respectively. This study focuses on the influence of the hydrophilic surfactant on the release of inner water or actives encapsulated therein via coalescence of the inner water droplet with the outer O–W2 interface. Since coalescence and diffusion are difficult to distinguish in double emulsions, single-droplet experiments were used to quantify differences in the stability of inner droplets. Different lipophilic (PGPH and PEG-30 dipolyhydroxylstearate) and hydrophilic surfactants (ethoxylates, SDS and polymeric) were used and resulted in huge differences in stability. A drastic decrease in stability was found for some combinations, while other combinations resulted in inner droplets that could withstand coalescence longer. The destabilization effect of some hydrophilic surfactants depended on their concentration, but was still present at very low concentrations. A huge spread of the coalescence time for multiple determinations was observed for all formulations and the necessary statistical analysis is discussed in this work. The measured stabilities of single droplets are in good accordance with the stability of double emulsions for similar surfactant combinations found in literature. Therefore, single droplet experiments are suggested for a fast evaluation of potentially suitable surfactant combinations for future studies on double-emulsion stability.
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Spray drying of whey protein-based emulsions is a common task in food engineering.Lipophilic, low molecular weight emulsifiers including lecithin, citrem, and mono- and diglycerides,are commonly added to the formulations, as they ...
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Spray drying of whey protein-based emulsions is a common task in food engineering.Lipophilic, low molecular weight emulsifiers including lecithin, citrem, and mono- and diglycerides,are commonly added to the formulations, as they are expected to improve the processing and shelflife stability of the products. During the atomization step of spray drying, the emulsions are subjectedto high stresses, which can lead to breakup and subsequent coalescence of the oil droplets. The extentof these phenomena is expected to be greatly influenced by the emulsifiers in the system. The focusof this study was therefore set on the changes in the oil droplet size of whey protein-based emulsionsduring atomization, as affected by the addition of low molecular weight emulsifiers. Atomizationexperiments were performed with emulsions stabilized either with whey protein isolate (WPI),or with combinations of WPI and lecithin, WPI and citrem, and WPI and mono- and diglycerides.The addition of lecithin promoted oil droplet breakup during atomization and improved dropletstabilization against coalescence. The addition of citrem and of mono- and diglycerides did notaffect oil droplet breakup, but greatly promoted coalescence of the oil droplets. In order to elucidatethe underlying mechanisms, measurements of interfacial tensions and coalescence times in singledroplets experiments were performed and correlated to the atomization experiments. The results onoil droplet breakup were in good accordance with the observed differences in the interfacial tensionmeasurements. The results on oil droplet coalescence correlated only to a limited extent with theresults of coalescence times of single droplet experiments.
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Abstract Double emulsions of the water‐in‐oil‐in‐water type are promising encapsulation and delivery systems containing at least one hydrophilic and one lipophilic surfactant. Currently, there are still very few implementation...
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Abstract Double emulsions of the water‐in‐oil‐in‐water type are promising encapsulation and delivery systems containing at least one hydrophilic and one lipophilic surfactant. Currently, there are still very few implementations on the market, as these systems are subject to extreme stability problems. This study focuses on stability problems induced by the transport of hydrophilic surfactant molecules through the lipophilic phase to the encapsulated inner water droplets. In particular, a model system was developed to quantify surfactant transport and resulting effects on the coalescence of encapsulated water droplets. Changes in stability of the inner water droplets are demonstrated for different surfactants and compared to the stability of the inner water‐in‐oil emulsions and corresponding double emulsions.
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摘要 :
Double emulsions are very promising for various applications in pharmaceutics, cosmetics, and food. Despite lots of published research, only a few products have successfully been marketed due to immense stability problems. This re...
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Double emulsions are very promising for various applications in pharmaceutics, cosmetics, and food. Despite lots of published research, only a few products have successfully been marketed due to immense stability problems. This review describes approaches on how to characterize the stability of double emulsions. The measurement methods are used to investigate the influence of the ingredients or the process on the stability, as well as of the environmental conditions during storage. The described techniques are applied either to double emulsions themselves or to model systems. The presented analysis methods are based on microscopy, rheology, light scattering, marker detection, and differential scanning calorimetry. Many methods for the characterization of double emulsions focus only on the release of the inner water phase or of a marker encapsulated therein. Analysis methods for a specific application rarely give information on the actual mechanism, leading to double emulsion breakage. In contrast, model systems such as simple emulsions, microfluidic emulsions, or single-drop experiments allow for a systematic investigation of diffusion and coalescence between the individual phases. They also give information on the order of magnitude in which they contribute to the failure of the overall system. This review gives an overview of various methods for the characterization of double emulsion stability, describing the underlying assumptions and the information gained. With this review, we intend to assist in the development of stable double emulsion-based products.
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