Structure of adsorbed layers of mixtures of proteins and surfactants

Enzymatic Hydrolysis of Triglycerides at the Water-Oil Interface Studied via Interfacial Rheology Analysis of Lipase Adsorption Layers

The enzymatic hydrolysis of sunflower oil occurs at the water-oil interface. Therefore, the characterization of dynamic interfacial phenomena is essential for understanding the related mechanisms for process optimizations. Most of the available studies for this purpose deal with averaged interfacial properties determined via reaction kinetics and dynamic surface tension measurements. In addition to the classical approach for dynamic surface tension measurements, here, the evolution of the dilational viscoelasticity of the lipase adsorbed layer at the water-oil interface is characterized using profile analysis tensiometry. It is observed that lipase exhibits nonlinear dilational rheology depending on the concentration and age of the adsorbed layer. For reactive water-oil interfaces, the response of the interfacial tension to the sinusoidal area perturbations becomes more asymmetric with time. Surface-active products of the enzymatic hydrolysis of triglycerides render the interface less elastic during compression compared to the expansion path. The lipolysis products can facilitate desorption upon compression while inhibiting adsorption upon expansion of the interface. Lissajous plots provide an insight into how the hysteresis effect leads to different interfacial tensions along the expansion and compression routes. Also, the droplet shape increasingly deviates from a Laplacian shape, demonstrating an irreversible film formation during aging and ongoing hydrolysis reaction, which supports our findings via interfacial elasticity analysis.

Nucleation of melt: From fundamentals to dispersed systems

The most evident aspects of a first order transition of a system from an old to a new phase, are the presence of a discontinuity at the interface between both phases and the thermal effects related to the latent heat exchanged with the surrounding environment. These effects are the result of a sequence of events promoted by thermodynamic conditions persisting over the equilibrium in a metastable state. The breakdown of metastability is promoted by infinitesimal energy fluctuations resulting in the germination of clusters of the new phase that can grow to a critical size (nucleus) and then develop or vanish. Examples of these sequences are common in various technological fields such as combustion, food processing, pharmaceutical manufacturing, condensation, and phase change heat transfer, etc. This work aims to highlight a logical path that leads the readers from the fundamental phenomenology to the most intricated aspects of the nucleation within dispersed systems such as oil-in-water emulsions. Differences between the homogeneous and heterogeneous mechanisms are, under the light of the Classical Nucleation Theory (CNT), presented in bulk and confined systems until defining a minimum confinement size. By collecting insights coming from a rich scientific literature mostly focused on the stability of emulsified systems, the discussion is then on the aspects related to the surface related mechanisms. Two main aspects are then considered: a) the wettability of the nucleating cluster by the surrounding melt; b) the affinity between the adsorbed layer, where a surfactant is located, and the oil melt phase (mainly n-alkanes and triacylglycerols with different moieties). In cases where nucleation is dominating over the dewetting of the nucleus, the contact angle can be considered as a constant value. The affinity in terms of molecular features between the surfactant and the oil phase can promote the template effect. Several factors seem to play a role in this interaction such as the thermal characteristics of the surfactant and comparable dimensions between the molecule (or fractions) of the dispersed compound and the tail of the surfactant.

Corn Oil-Water Separation: Interactions of Proteins and Surfactants at Corn Oil/Water Interfaces

Purification and collection of industrial products from oil-water mixtures are commonly implemented processes. However, the efficiencies of such processes can be severely influenced by the presence of emulsifiers that induce the formation of small oil droplets dispersed in the mixtures. Understanding of this emulsifying effect and its counteractions which occur at the oil/water interface is therefore necessary for the improvement of designs of these processes. In this paper, we investigated the interfacial mechanisms of protein-induced emulsification and the opposing surfactant-induced demulsification related to corn oil refinement. At corn oil/water interfaces, the pH-dependent emulsifying function of zein protein, which is the major storage protein of corn, was elucidated by the surface/interface-sensitive sum frequency generation (SFG) vibrational spectroscopy technique. The effective stabilization of corn oil droplets by zein protein was illustrated and correlated to its ordered amide I group at the oil/water interface. Substantial decrease of this ordering with the addition of three industrial surfactants to corn oil-zein solution mixtures was also observed using SFG, which explains the surfactant-induced destabilization and coalescence of small oil droplets. Surfactant-protein interaction was then demonstrated to be the driving force for the disordering of interfacial proteins, either by disrupting protein layers or partially excluding protein molecules from the interface. The ordered zein proteins at the interface were therefore revealed to be the critical factor for the formation of corn oil-water emulsion.

Improving emulsion formation, stability and performance using mixed emulsifiers: A review

The formation, stability, and performance of oil-in-water emulsions may be improved by using combinations of two or more different emulsifiers, rather than an individual type. This article provides a review of the physicochemical basis for the ability of mixed emulsifiers to enhance emulsion properties. Initially, an overview of the most important physicochemical properties of emulsifiers is given, and then the nature of emulsifier interactions in solution and at interfaces is discussed. The impact of using mixed emulsifiers on the formation and stability of emulsions is then reviewed. Finally, the impact of using mixed emulsifiers on the functional performance of emulsifiers is given, including gastrointestinal fate, oxidative stability, antimicrobial activity, and release characteristics. This information should facilitate the selection of combinations of emulsifiers that will have improved performance in emulsion-based products.

Formation of protein/surfactant adsorption layer as studied by dilational surface rheology

The review discusses the mechanism of formation of protein/surfactant adsorption layers at the liquid - gas interface. The complexes of globular proteins usually preserve their compact structure a low surfactant concentrations. Therefore a simple kinetic model of the adsorption of charged compact nanoparticles is discussed first and compared with experimental data. The increase of surfactant concentrations results in various conformational transitions in the surface layer. One can obtain information on the changes of the adsorption layer structure using the dilational surface rheology. The kinetic dependencies of the dynamic surface elasticity are strongly different for the adsorption of unfolded macromolecules and compact globules, and have local maxima in the former case corresponding to different steps of the adsorption. These distinctions allow tracing the changes of the tertiary structure of protein/surfactant complexes in the surface layer. The adsorption from mixed solutions of ionic surfactants with β-casein, β-lactoglobulin, bovine serum albumin and myoglobin is discussed with some details.

Effect of surfactants on surface activity and rheological properties of type I collagen at air/water interface

We describe the effect of three synthetic surfactants (anionic - sodium dodecyl sulfate (SDS), cationic - cetyltrimethylammonium bromide (CTAB) and nonionic - Triton X-100 (TX-100)) on surface properties of the type I calf skin collagen at the air/water interface in acidic solutions (pH 1.8). The protein concentration was fixed at 5×10^-6molL^-1 and the surfactant concentration was varied in the range 5×10^-6molL^-1-1×10^-4molL^-1, producing the protein/surfactant mixtures with molar ratios of 1:1, 1:2, 1:5, 1:10 and 1:20. An Axisymmetric Drop Shape Analysis (ADSA) method was used to determine the dynamic surface tension and surface dilatational moduli of the mixed adsorption layers. Two spectroscopic techniques: UV-vis spectroscopy and fluorimetry allowed us to determine the effect of the surfactants on the protein structure. The thermodynamic characteristic of the mixtures was studied using isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC). Modification of the collagen structure by SDS at low surfactant/protein ratios has a positive effect on the mixture's surface activity with only minor deterioration of the rheological properties of the adsorbed layers. The collagen/CTAB mixtures do not show that pronounced improvement in surface activity, while rheological properties are significantly deteriorated. The mixtures with non-ionic TX-100 do not show any synergistic effects in surface activity.

Thermodynamics, interfacial pressure isotherms and dilational rheology of mixed protein-surfactant adsorption layers

Proteins and their mixtures with surfactants are widely used in many applications. The knowledge of their solution bulk behavior and its impact on the properties of interfacial layers made great progress in the recent years. Different mechanisms apply to the formation process of protein/surfactant complexes for ionic and non-ionic surfactants, which are governed mainly by electrostatic and hydrophobic interactions. The surface activity of these complexes is often remarkably different from that of the individual protein and has to be considered in respective theoretical models. At very low protein concentration, small amounts of added surfactants can change the surface activity of proteins remarkably, even though no strongly interfacial active complexes are observed. Also small added amounts of non-ionic surfactants change the surface activity of proteins in the range of small bulk concentrations or surface coverages. The modeling of the equilibrium adsorption behavior of proteins and their mixtures with surfactants has reached a rather high level. These models are suitable also to describe the high frequency limits of the dilational viscoelasticity of the interfacial layers. Depending on the nature of the protein/surfactant interactions and the changes in the interfacial layer composition rather complex dilational viscoelasticities can be observed and described by the available models. The differences in the interfacial behavior, often observed in literature for studies using different experimental methods, are at least partially explained by a depletion of proteins, surfactants and their complexes in the range of low concentrations. A correction of these depletion effects typically provides good agreement between the data obtained with different methods, such as drop and bubble profile tensiometry.

Formulation and stabilization of nano-/microdispersion systems using naturally occurring edible polyelectrolytes by electrostatic deposition and complexation

This review paper presents an overview of the formulation and functionalization of nano-/microdispersion systems composed of edible materials. We first summarized general aspects on the stability of colloidal systems and the roles of natural polyelectrolytes such as proteins and ionic polysaccharides for the formation and stabilization of colloidal systems. Then we introduced our research topics on (1) stabilization of emulsions by the electrostatic deposition using natural polyelectrolytes and (2) formulation of stable nanodispersion systems by complexation of natural polyelectrolytes. In both cases, the preparation procedures were relatively simple, without high energy input or harmful chemical addition. The properties of the nano-/microdispersion systems, such as particle size, surface charge and dispersion stability were significantly affected by the concerned materials and preparation conditions, including the type and concentration of used natural polyelectrolytes. These dispersion systems would be useful for developing novel foods having high functionality and good stability.

Adsorption of proteins at the solution/air interface influenced by added nonionic surfactants at very low concentrations for both components. 2. Effect of different surfactants and theoretical model

The influence of the addition of the nonionic surfactants dodecyl dimethyl phosphine oxide (C12DMPO), tetradecyl dimethyl phosphine oxide (C14DMPO), decyl alcohol (C10OH), and C10EO5 at concentrations between 10(-5) and 10(-1) mmol/L to solutions of β-casein (BCS) and β-lactoglobulin (BLG) at a fixed concentration of 10(-5) mmol/L on the surface tension is studied. It is shown that a significant decrease of the water/air surface tension occurs for all the surfactants studied at very low concentrations (10(-5)-10(-3) mmol/L). All measurements were performed with the buoyant bubble profile method. The dynamics of the surface tension was simulated using the Fick and Ward-Tordai equations. The calculation results agree well with the experimental data, indicating that the equilibration times in the system studied do not exceed 30 000 s, while the time required to attain the equilibrium on a plane surface is by one order of magnitude higher. To achieve agreement between theory and experiment for the mixtures, a supposition was made about the influence of the concentration of nonionic surfactant on the adsorption activity of the protein. The adsorption isotherm equation of the protein was modified accordingly, and this corrected model agrees well with all experimental data.

Interaction of Quillaja bark saponins with food-relevant proteins

The surface activity and aggregation behaviour of two Quillaja bark saponins (QBS) are compared using surface tension, conductometry and light scattering. Despite formally of the same origin (bark of the Quillaja saponaria Molina tree), the two QBS show markedly different ionic characters and critical micelle concentrations (7.7·10(-6) mol·dm(-3) and 1.2·10(-4) mol·dm(-3)). The new interpretation of the surface tension isotherms for both QBS allowed us to propose an explanation for the previous discrepancy concerning the orientation of the saponin molecules in the adsorbed layer. The effect of three food-related proteins (hen egg lysozyme, bovine β-lactoglobulin and β-casein) on surface tension of the saponins is also described. Dynamic surface tension was measured at fixed protein concentrations and QBS concentrations varying in the range 5·10(-7)-1·10(-3) mol·dm(-3). Both dynamic and extrapolated equilibrium surface tensions of the protein/QBS mixtures depend not only on the protein, but also on the QBS source. In general, the surface tension for mixtures of the QBS with lower CMC and less ionic character shows less pronounced synergistic effects. This is especially well visible for β-casein/QBS mixtures, where a characteristic maximum in the surface tension isotherm around the molar ratio of one can be noticed for one saponin product, but not for the other.

WITHDRAWN: Interfacial layers of complex-forming ionic surfactants with gelatin

The Publisher regrets that this article is an accidental duplication of an article that has already been published, http://dx.doi.org/ 10.1016/j.cis.2014.05.001. The duplicate article has therefore been withdrawn.

Influence of the presence of monoglyceride on the interfacial properties of wheat gluten

BACKGROUND

The physical stability of several food systems depends strongly on their interfacial properties, which may be modified by adding proteins and low-molecular-weight surfactants to their formulation. This study deals with the possibility of using wheat gluten to alter the surface and interfacial properties of an aqueous system, considering the effects of protein concentration, pH and the presence of monostearin.

RESULTS

It was generally found that the surface tension decreased as the protein concentration increased, reaching a minimum value at 0.5 g kg(-1). The influence of protein concentration on surface tension was much greater than the effect of pH owing to the low ionic character of wheat gluten protein. At acidic and alkaline pH values the interfacial viscosity of the protein system underwent a significant increase with time. The addition of monostearin either promoted the displacement of protein molecules at the interface or generated an interfacial mixed film with surface tension values lower than those of both single components, depending on the pH.

CONCLUSION

The results obtained indicate that gluten can contribute to the stabilisation of air/water and oil/water interfaces in some food systems (emulsions, foams, etc.).

Probing the in situ competitive displacement of protein by nonionic surfactant using atomic force microscopy

Force-distance data obtained from an atomic force microscope have been used to follow the in situ displacement of beta-lactoglobulin from tetradecane droplets by Tween 20 (polyoxyethylenesorbitan monolaurate). Interpretation of the force-distance curves has shown that the slope of the region, traditionally termed the constant compliance region, is a useful indicator of droplet deformation within a given experiment. The magnitude of this slope can be used to monitor how the deformability of the droplet changes upon addition of surfactant. It has been found that, immediately after initial addition of surfactant, there is an increase in magnitude of this slope, indicating a stiffening of the droplet, attributed to a stiffening of the protein network formed at the surface of the droplet. Subsequent additions of Tween 20 reduce the magnitude of the slope until an equilibrium value is reached, where the interface becomes surfactant-dominated. These observations suggest that it is possible to monitor in situ the displacement of protein from individual oil droplets. The data have been interpreted in terms of the "orogenic" model of displacement, which is based on studies made on model interfaces. These data have been compared to those obtained using the more traditional techniques of dilatational rheology, surface loading, and surface potential measurements for analogous beta-lactoglobulin-stabilized droplets or emulsions.

Thermodynamics, adsorption kinetics and rheology of mixed protein-surfactant interfacial layers

Depending on the bulk composition, adsorption layers formed from mixed protein/surfactant solutions contain different amounts of protein. Clearly, increasing amounts of surfactant should decrease the amount of adsorbed proteins successively. However, due to the much larger adsorption energy, proteins are rather strongly bound to the interface and via competitive adsorption surfactants cannot easily displace proteins. A thermodynamic theory was developed recently which describes the composition of mixed protein/surfactant adsorption layers. This theory is based on models for the single compounds and allows a prognosis of the resulting mixed layers by using the characteristic parameters of the involved components. This thermodynamic theory serves also as the respective boundary condition for the dynamics of adsorption layers formed from mixed solutions and their dilational rheological behaviour. Based on experimental studies with milk proteins (beta-casein and beta-lactoglobulin) mixed with non-ionic (decyl and dodecyl dimethyl phosphine oxide) and ionic (sodium dodecyl sulphate and dodecyl trimethyl ammonium bromide) surfactants at the water/air and water/hexane interfaces, the potential of the theoretical tools is demonstrated. The displacement of pre-adsorbed proteins by subsequently added surfactant can be successfully studied by a special experimental technique based on a drop volume exchange. In this way the drop profile analysis can provide tensiometry and dilational rheology data (via drop oscillation experiments) for two adsorption routes--sequential adsorption of the single compounds in addition to the traditional simultaneous adsorption from a mixed solution. Complementary measurements of the surface shear rheology and the adsorption layer thickness via ellipsometry are added in order to support the proposed mechanisms drawn from tensiometry and dilational rheology, i.e. to show that the formation of mixed adsorption layer is based on a modification of the protein molecules via electrostatic (ionic) and/or hydrophobic interactions by the surfactant molecules and a competitive adsorption of the resulting complexes with the free, unbound surfactant. Under certain conditions, the properties of the sequentially formed layers differ from those formed simultaneously, which can be explained by the different locations of complex formation.

Lipases at interfaces: a review

Lipases are acyl hydrolases that play a key role in fat digestion by cleaving long-chain triglycerides into polar lipids. Due to an opposite polarity between the enzyme (hydrophilic) and their substrates (lipophilic), lipase reaction occurs at the interface between the aqueous and the oil phases. Hence, interfaces are the key spots for lipase biocatalysis and an appropriate site for modulating lipolysis. Surprisingly enough, knowledge about the effects of the interfacial composition on lipase catalysis is still limited and only described by the term "interfacial quality". Recent systematic studies based on a biophysical approach allowed for the first time to show the effects of the interfacial microenvironment on lipase catalysis. These studies demonstrate that lipase activity as a function of interfacial composition is more attributed to substrate inaccessibility rather than to enzyme denaturation or inactivation, as it is often hypothesized. A detailed analysis of the interfacial properties of all compounds involved in triglyceride digestion revealed that lipolysis is a self-regulated reaction. This feedback mechanism can be explored as a new avenue to control lipase catalysis. To substantiate this hypothesis, oil hydrolysis in a model gastro-intestinal system was performed, which can be seen as an interfacial engineering approach to enzyme reactivity control. The presented characterization of the interfacial composition and its consequences provide a new approach for the understanding of lipase reactions at interfaces with direct impact on biotechnological and health care applications.

Implications of interfacial characteristics of food foaming agents in foam formulations

The manufacture of food dispersions (emulsions and foams) with specific quality attributes depends on the selection of the most appropriate raw materials and processing conditions. These dispersions being thermodynamically unstable require the use of emulsifiers (proteins, lipids, phospholipids, surfactants etc.). Emulsifiers typically coexist in the interfacial layer with specific functions in the processing and properties of the final product. The optimum use of emulsifiers depends on our knowledge of their interfacial physico-chemical characteristics - such as surface activity, amount adsorbed, structure, thickness, topography, ability to desorb (stability), lateral mobility, interactions between adsorbed molecules, ability to change conformation, interfacial rheological properties, etc. -, the kinetics of film formation and other associated physico-chemical properties at fluid interfaces. These monolayers constitute well defined systems for the analysis of food colloids at the micro- and nano-scale level, with several advantages for fundamental studies. In the present review we are concerned with the analysis of physico-chemical properties of emulsifier films at fluid interfaces in relation to foaming. Information about the above properties would be very helpful in the prediction of optimised formulations for food foams. We concluded that at surface pressures lower than that of monolayer saturation the foaming capacity is low, or even zero. A close relationship was observed between foaming capacity and the rate of diffusion of the foaming agent to the air-water interface. However, the foam stability correlates with the properties of the film at long-term adsorption.

Competition between lipases and monoglycerides at interfaces

Tensiometry (the pendant drop technique), interfacial shear rheology, and ellipsometry have been used to study the effect of polar lipids that are generated during fat digestion on the behavior of lipases at the oil-water interface. Both Sn-1,3 regiospecific and nonregiospecific lipases have been used, and a noncatalytically active protein, beta-lacloglobulin, has been used as reference in the interfacial shear rheology experiments. The results from the pendant drop measurements and the interfacial rheology studies were in agreement with each other and demonstrated that the Sn-2 monoglyceride, which is one of the lipolysis products generated when a Sn-1,3 regiospecific lipase catalyzes triglyceride hydrolysis, is very interfacially active and efficiently expels the enzyme from the interface. Ellipsometry conducted at the liquid-liquid interface showed that the lipase forms a sublayer in the aqueous phase, just beneath the monoglyceride-covered interface. Sn-1/3 monoglycerides do not behave this way because they are rapidly degraded to fatty acid and glycerol and the fatty acid (or the fatty acid salt) does not have enough interfacial activity to expel the lipase from the interface. Since the lipases present in the gastrointestinal tract are highly Sn-1,3 regiospecific, we believe that the results obtained can be transferred to the in vivo situation. The formation of stable and amphiphilic Sn-2 monoglycerides can be seen as a self-regulatory process for fat digestion.

Atomic force microscopy studies of functional and dysfunctional pulmonary surfactant films, II: albumin-inhibited pulmonary surfactant films and the effect of SP-A

Pulmonary surfactant (PS) dysfunction because of the leakage of serum proteins into the alveolar space could be an operative pathogenesis in acute respiratory distress syndrome. Albumin-inhibited PS is a commonly used in vitro model for studying surfactant abnormality in acute respiratory distress syndrome. However, the mechanism by which PS is inhibited by albumin remains controversial. This study investigated the film organization of albumin-inhibited bovine lipid extract surfactant (BLES) with and without surfactant protein A (SP-A), using atomic force microscopy. The BLES and albumin (1:4 w/w) were cospread at an air-water interface from aqueous media. Cospreading minimized the adsorption barrier for phospholipid vesicles imposed by preadsorbed albumin molecules, i.e., inhibition because of competitive adsorption. Atomic force microscopy revealed distinct variations in film organization, persisting up to 40 mN/m, compared with pure BLES monolayers. Fluorescence confocal microscopy confirmed that albumin remained within the liquid-expanded phase of the monolayer at surface pressures higher than the equilibrium surface pressure of albumin. The remaining albumin mixed with the BLES monolayer so as to increase film compressibility. Such an inhibitory effect could not be relieved by repeated compression-expansion cycles or by adding surfactant protein A. These experimental data indicate a new mechanism of surfactant inhibition by serum proteins, complementing the traditional competitive adsorption mechanism.

Thermodynamics and rheology of mixed protein-surfactant adsorption layers

The behaviour of mixed protein-surfactant surface layers at liquid interfaces has been described essentially qualitatively, until only very recently thermodynamic models were derived for interfacial layers formed by proteins and non-ionic or ionic surfactants, which represent the basis also for a quantitative understanding of the respective adsorption dynamics and dilational rheology of liquid interfaces. On the basis of experimental data obtained from single drop and bubble studies and optical methodologies like ellipsometry and BAM, a clear picture can be drawn now about liquid surface layers relevant for a broad field of applications.

Microstructure of β-lactoglobulin-stabilized emulsions containing non-ionic surfactant and excess free protein: Influence of heating

The influence of the non-ionic surfactant Tween 20 on the microstructure of beta-lactoglobulin-stabilized emulsions with substantial excess free protein present was investigated via confocal microscopy. The separate distributions of oil droplets and protein were determined using two different fluorescent dyes. In the emulsion at ambient temperature the excess protein and protein-coated oil droplets were associated together in a reversibly flocculated state. The pore-size distribution of the initial flocculated emulsion was found to depend on the surfactant/protein ratio R, and at higher values of R the system became more inhomogeneous due to areas of local phase separation. Evidence for competitive displacement of protein from the oil-water interface by surfactant was obtained only on heating (from 25 to 85 degrees C) during the process of formation of a heat-set emulsion gel. By measuring fluorescence intensities of the protein dye inside and outside of the oil-droplet-rich areas, we have been able to quantify the evolving protein distribution during the thermal processing. The results are discussed in relation to previous work on the competitive adsorption of proteins and surfactants in emulsions and the effect of emulsion droplets on the rheology of heat-set protein gels.

PFG-NMR analysis of intercompartment exchange and inner droplet size distribution of W/O/W emulsions

Presented is a novel application of pulsed field gradient (PFG)-NMR to the analysis of intercompartment exchange and the inner compartment droplet size distribution of a W/O/W multiple emulsion. The method involves monitoring the diffusional behavior of different components of the emulsion. Pfeuffer et al. [Pfeuffer, J.; Flogel, U.; Dreher, W.; Leibfritz, D. NMR Biomed. 1998, 11(1), 19-31.](1) and Price et al. [Price, W. S.; Barzykin, A. V.; Hayamizu, K.; Tachiya, M. Biophys. J. 1998, 74(5), 2259-2271.](2) proposed methods to extend Kärger's PFG-NMR model of exchange between two compartments to accommodate spherical inner compartments. Each model enables the prediction of the oil membrane permeability, the inner compartment volume fraction, and a representation of the inner compartment droplet size distribution. The models were fitted to PFG-NMR experimental data of W/O/W emulsions. The Pfeuffer et al. model provided the best description of the observed experimental data. Predicted values of permeability and swelling were consistent with those reported in the literature for W/O/W emulsions. The addition of sorbitol to either the inner or outer water compartment resulted in an increase in the oil membrane permeability. Inner compartment droplet size distribution measurements indicate that swelling, rupture, and coalescence are likely to have occurred during the secondary emulsification and emulsion ripening. In its present form, the method still constitutes a fast, noninvasive (no addition of a tracer), and in situ method for comparative analysis of the permeability, stability, and yield of different formulations of multiple emulsions with a single PFG-NMR experiment.