Effect of crystalline emulsifier composition on structural transformations of water-in-oil emulsions: Emulsification and quiescent conditions

Influence of Manufacturing Process on the Microstructure, Stability, and Sensorial Properties of a Topical Ointment Formulation

The manufacturing process for ointments typically involves a series of heating, cooling, and mixing steps. Precise control of the level of mixing through homogenization and the cooling rate, as well as temperature at different stages, is important in delivering ointments with the desired quality attributes, stability, and performance. In this work, we investigated the influence of typical plant processing conditions on the microstructure, stability, and sensorial properties of a model ointment system through a Design of Experiments (DoE) approach. Homogenization speed at the cooling stage after the addition of the solvent (propylene glycol, PG) was found to be the critical processing parameter that affects stability and the rheological and sensorial properties of the ointment. A lower PG addition temperature was also found to be beneficial. The stabilization of the ointment at a lower PG addition temperature was hypothesized to be due to more effective encapsulation by crystallizing mono- and diglycerides at the lower temperature. The in vitro release profiles were found to be not influenced by the processing parameters, suggesting that for the ointment platform studied, processing affects the microstructure, but the effects do not translate into the release profile, a key performance indicator. Our systematic study represents a Quality-by-Design (QbD) approach to the design of a robust manufacturing process for delivering stable ointments with the desired performance attributes and properties.

Future of Structured Lipids: Enzymatic Synthesis and Their New Applications in Food Systems

Structured lipids (SLs) refer to a new type of functional lipid obtained by modifying natural triacylglycerol (TAG) through the restructuring of fatty acids, thereby altering the composition, structure, and distribution of fatty acids attached to the glycerol backbones. Due to the unique functional characteristics of SLs (easy to absorb, low in calories, reduced serum TAG, etc.), there is increasing interest in the research and application of SLs. SLs were initially prepared using chemical methods. With the wide application of enzymes in industries and the advantages of enzymatic synthesis (mild reaction conditions, high catalytic efficiency, environmental friendliness, etc.), synthesis of SLs using lipase has aroused great interest. This review summarizes the reaction system of SL production and introduces the enzymatic synthesis and application of some of the latest SLs discussed/developed in recent years, including medium- to long-chain triacylglycerol (MLCT), diacylglycerol (DAG), EPA- and DHA-enriched TAG, human milk fat substitutes, and esterified propoxylated glycerol (EPG). Lastly, several new ways of applying SLs (powdered oil, DAG plastic fat, inert gas spray oil, and emulsion) in the future food industry are also highlighted.

Effects of the Distribution Site of Crystallizable Emulsifiers on the Gastrointestinal Digestion Behavior of Double Emulsions

Double emulsions (DEs) are promising delivery vehicles for the protective and programmed release of bioactive compounds. Herein, DEs with monoglycerides crystallized at the internal- or external interface or oil phase were fabricated. The results suggested that the crystallization site of monoglycerides exerts a significant role in retarding the structural degradation and lipid digestion of DEs by affecting the available contact area of lipase. At the initial stage of intestinal digestion, compared with noncrystalline DEs (82.1%, 3.7 min), the burst release of internal markers in the internal interface crystallized emulsions was decreased by 42.4% and the lag time of free fatty acid (FFA) release was delayed by 5.8 min in the external interface crystallized emulsions. The structural integrity and digestion kinetics of the external interface crystallized DEs were synchronized with the retention time of the interfacial crystals. Therefore, crystallizable emulsifiers exhibit unique and fine regulatory effects on the digestive properties of emulsions.

Pickering nano-emulsions stabilized by solid lipid nanoparticles as a temperature sensitive drug delivery system

The development of biomaterials with low environmental impact has seen increased interest in recent years. In this field, lipid nanoparticles have found a privileged place in research and industry. The purpose of this study was to develop Pickering O/W nano-emulsions only stabilized by solid lipid nanoparticles (SLNs), as a new generation of safe, non-toxic, biocompatible, and temperature-sensitive lipid nano-carriers. The first part is dedicated to understanding the interfacial behavior of SLNs and their related stabilization mechanisms onto nano-emulsions formulated by ultrasonication. Investigations were focused on the surface coverage as a function of the SLN size and volume fraction of dispersed oil, in order to prove that the droplet stabilization is effectively performed by the nanoparticles, and to disclose the limitations of this formulation. Characterization is performed by dynamic light scattering and transmission electron microscopy. The second part of the study investigated SLN adsorption on a model oil/water interface (surface tension and rheology) through an axisymmetrical drop shape analysis (drop tensiometer), following the interfacial tension and the rheological behavior. The objective of this part is to characterize the phenomenon governing the droplet/interface interactions, and disclose the rheological behavior of the interfacial SLN monolayer. The effect of temperature was also investigated, proving a real destabilization of the nano-suspension when the sample is heated above a temperature threshold, impacting on the integrity of the SLNs, which partially melt, and strongly enhancing the release of a model drug (ketoprofen) encapsulated in the nano-emulsion oil core. To conclude, Pickering nano-emulsions only stabilized by SLNs appear to be a very efficient innovative drug nano-carrier, opening new doors as a potential temperature-sensitive drug delivery system.

Ultrastable Water-in-Oil High Internal Phase Emulsions Featuring Interfacial and Biphasic Network Stabilization

In this work, we present gel-in-gel water-in-oil (W/O) high internal phase emulsions (HIPEs) that feature high stability by structuring both phases of the emulsion. Compared to significant advances made in oil-in-water (O/W) HIPEs, W/O HIPEs are extremely unstable and difficult to generate without introducing high concentrations of surfactants. Another main challenge is the low viscosity of both water and oil phases which promotes the instability of W/O HIPEs. Here, we demonstrate ultrastable W/O HIPEs that feature biphasic structuring, in which hydrogels are dispersed in oleogels, and self-forming, low-concentration interfacial Pickering crystals provide added stability. These W/O HIPEs exhibit high tolerance toward pH shock and destabilizing environments. In addition, this novel ultrastable gel-in-gel W/O HIPE is sustainable and made solely with natural ingredients without the addition of any synthetic stabilizers. By applying phase structuring within the HIPEs through the addition of various carrageenans and beeswax as structurants, we can increase the emulsion's stability and viscoelastic rheological properties. The performance of these gel-in-gel W/O HIPEs holds promise for a wide range of applications. As a proof of concept, we demonstrated herein the application as a gelled delivery system that enables the co-delivery of hydrophilic and hydrophobic materials at maximized loads, demonstrating high resistance to gastrointestinal pHs and a controlled-release profile.

Particle-Stabilized Fluid-Fluid Interfaces: The Impact of Core Composition on Interfacial Structure

The encapsulation of small molecule drugs in nanomaterials has become an increasingly popular approach to the delivery of therapeutics. The use of emulsions as templates for the synthesis of drug impregnated nanomaterials is an exciting area of research, and a great deal of progress has been made in understanding the interfacial chemistry that is critical to controlling the physicochemical properties of both the encapsulated material and the templated material. For example, control of the interfacial tension between an oil and aqueous phase is a fundamental concern when designing drug delivery vehicles that are stabilized by particulate surfactants at the fluid interface. Particles in general are capable of self-assembly at a fluid interface, with a preference for one or the other of the phases, and much work has focussed on modification of the particle properties to optimize formation and stability of the emulsion. An issue arises however when a model, single oil system is translated into more complex, real-world scenarios, which are often multi-component, with the incorporation of charged active ingredients and other excipients. The result is potentially a huge change in the properties of the dispersed phase which can lead to a failure in the capability of particles to continue to stabilize the interface. In this mini-review, we will focus on two encapsulation strategies based on the selective deposition of particles or proteins on a fluid-fluid interface: virus-like particles and polymer microcapsules formed from particle-stabilized emulsion templates. The similarity between these colloidal systems lies in the fact that particulate entities are used to stabilize fluid cores. We will focus on those studies that have described the effect of subtle changes in core composition on the self-assembly of particles at the fluid-fluid interface and how this influences the resulting capsule structure.

Physical compatibility between wax esters and triglycerides in hybrid shortenings and margarines prepared in rice bran oil

BACKGROUND

Wax esters contribute to the transformation of liquid oils into solid-like oleogel systems, which can act as alternatives for trans- and/or saturated fats in food products. The use of solely waxes reduces the solid content, consistency and sensory quality in the final products. Therefore, a combination of sunflower wax and palm fat in rice bran oil was created to accomplish the hybrid low-saturated shortenings and margarines with a compatible structure and lower amounts of saturated fats.

RESULTS

During cooling of the hybrid shortenings, sunflower wax crystallized first and acted as nucleation sites for the crystallisation of palm fat. At 5 °C, a mixture of different crystal morphologies (α, β', and β crystals) existed in the hybrid shortening. In margarine processing, the hybrid samples were subjected to a simultaneous cooling-emulsification, in which sunflower wax crystallised first at the interface and adsorbed onto the water droplets. Based on the hardness measurements, the maximum amount of palm fat replaceable by 1.0%wt sunflower wax was up to 40% in shortenings and 25% in margarines. A higher amount of sunflower wax (2.5%wt) reduced up to 40% of saturated fats in the hybrid emulsions.

CONCLUSION

The addition of 1.0%wt sunflower wax enhanced the solid content and network strength of hybrid palm-based shortenings. Sunflower wax helped to stabilise the water droplets inside the wax-based crystalline network without flocculation during shear-cooling. This research provides fundamental insight into the structuring of hybrid systems containing waxes, which could be interesting for the production of low-saturated fat products in the food industry. © 2017 Society of Chemical Industry.

Comparison of Pickering and network stabilization in water-in-oil emulsions

We compared the efficacy of Pickering crystals, a continuous phase crystal network, and a combination thereof against sedimentation and dispersed phase coalescence in water-in-oil (W/O) emulsions. Using 20 wt % water-in-canola oil emulsions as our model, glycerol monostearate (GMS) permitted Pickering-type stabilization, whereas simultaneous usage of hydrogenated canola oil (HCO) and glycerol monooleate (GMO) primarily led to network-stabilized emulsions. A minimum of 4 wt % GMS or 10 wt % HCO was required for long-term sedimentation stability. Although there were no significant differences between the two in mean droplet size with time, the free water content of the network-stabilized emulsions was higher than Pickering-stabilized emulsions, suggesting higher instability. Microscopy revealed the presence of crystal shells around the dispersed phase in the GMS-stabilized emulsions, whereas in the HCO-stabilized emulsion, spherulitic growth in the continuous phase and on the droplet surface occurred. The displacement energy (E(disp)) to detach crystals from the oil-water interface was ∼10(4) kT, and was highest for GMS crystals. Thermal cycling to induce dispersed phase coalescence of the emulsions resulted in desorption of both GMS and GMO from the interface, which we ascribed to solute-solvent hydrogen bonding between the emulsifier molecules and the solvent oil, based on IR spectra. Overall, Pickering crystals were more effective than network crystals for emulsion stabilization. However, the thermal stability of all emulsions was hampered by the diffusion of the molten emulsifiers from the interface.

Cationic ester-containing gemini surfactants: physical-chemical properties

Three ester-containing cationic gemini surfactants, two with decanoyl chains and either a three-carbon or a six-carbon spacer unit and one with dodecanoyl chains and a three-carbon spacer, were synthesized and evaluated. A corresponding monomeric cationic ester surfactant was used for comparison. This type of amphiphile, a so-called esterquat, is known to undergo rapid hydrolysis above the critical micelle concentration because of micellar catalysis. The esterquat geminis of this work were found to be much more susceptible to hydrolysis than the esterquat monomer. This difference is believed to be caused by anchimeric assistance by the second cationic headgroup in the gemini amphiphiles. However, there is no correlation between the rate of chemical hydrolysis and the rate of biodegradation. The monomeric esterquat, which is the most stable in the chemical hydrolysis experiments, was the only surfactant that passed the test for "readily biodegradable". We also observed a considerable difference in the hydrolysis rate within the small series of gemini surfactants. The amphiphile with two decanoyl chains and a three-carbon spacer, N,N'-bis(2-(decanoyloxy)ethyl)-N,N,N',N'-tetramethyl-1,3-propanediammonium dibromide, had the fastest rate of hydrolysis. This surfactant also exhibited a considerably lower degree of micelle ionization than the other surfactants, which is believed to be due to the closer proximity of the charged groups on the micelle surface. A small distance between headgroups will give more pronounced neighboring group participation, accounting for the increased rate of hydrolysis. An interesting property of the surfactant that is the most susceptible to hydrolysis is that it gives rise to an extremly stable foam. We propose that the foam stability is a result of the partial hydrolysis of the surfactant generating sodium decanoate, an anionic surfactant, that forms a mixed film with the starting cationic gemini surfactant. It is known that mixed monolayers in which there is a strong attractive interaction between surfactant headgroups can lead to stable foams.