Pickering emulsions for food and drinks

Stimuli-Responsive Pickering Emulsions Regulated via Polymerization-Induced Self-Assembly Nanoparticles

With the development of reversible deactivated radical polymerization techniques, polymerization-induced self-assembly (PISA) is emerging as a facile method to prepare block copolymer nanoparticles in situ with high concentrations, providing wide potential applications in different fields, including nanomedicine, coatings, nanomanufacture, and Pickering emulsions. Polymeric emulsifiers synthesized by PISA have many advantages comparing with conventional nanoparticle emulsifiers. The morphologies, size, and amphiphilicity can be readily regulated via the synthetic process, post-modification, and external stimuli. By introducing stimulus responsiveness into PISA nanoparticles, Pickering emulsions stabilized with these nanoparticles can be endowed with "smart" behaviors. The emulsions can be regulated in reversible emulsification and demulsification. In this review, the authors focus on recent progress on Pickering emulsions stabilized by PISA nanoparticles with stimuli-responsiveness. The factors affecting the stability of emulsions during emulsification and demulsification are discussed in details. Furthermore, some viewpoints for preparing stimuli-responsive emulsions and their applications in antibacterial agents, diphase reaction platforms, and multi-emulsions are discussed as well. Finally, the future developments and applications of stimuli-responsive Pickering emulsions stabilized by PISA nanoparticles are highlighted.

Soft Colloidal Particles at Fluid Interfaces

The assembly of soft colloidal particles at fluid interfaces is reviewed in the present paper, with emphasis on the particular case of microgels formed by cross-linked polymer networks. The dual polymer/colloid character as well as the stimulus responsiveness of microgel particles pose a challenge in their experimental characterization and theoretical description when adsorbed to fluid interfaces. This has led to a controversial and, in some cases, contradictory picture that cannot be rationalized by considering microgels as simple colloids. Therefore, it is necessary to take into consideration the microgel polymer/colloid duality for a physically reliable description of the behavior of the microgel-laden interface. In fact, different aspects related to the above-mentioned duality control the organization of microgels at the fluid interface, and the properties and responsiveness of the obtained microgel-laden interfaces. This works present a critical revision of different physicochemical aspects involving the behavior of individual microgels confined at fluid interfaces, as well as the collective behaviors emerging in dense microgel assemblies.

The fabrication, characterization, and application of chitosan-NaOH modified casein nanoparticles and their stabilized long-term stable high internal phase Pickering emulsions

The demand for facile delivery systems from natural biopolymers with long-term storage stability to deliver liposoluble nutraceuticals such as β-carotene (BC) is increasing. In this work, a facile and reliable emulsifier of chitosan (CS)-NaOH-modified casein (CA) nanoparticles (NPs) was fabricated for the stabilization of high internal phase Pickering emulsions (HIPPEs) with versatile stability. Dynamic light scattering, TEM, FTIR, and interface tension results indicated that CS-CA NPs exhibited nanoscale (109-373 nm), positive charge (22-38 mV), pH-response, spherical in shape, assembled spontaneously by non-covalent interactions, and high surface activity. Optical microscopy, confocal laser scanning microscopy (CLSM), and rheometer results demonstrated that HIPPEs were emulsified by a dense and compact 3D network between the continuous phase and the interfacial region. Hence, the CS-CA NP-stabilized HIPPEs showed long-term storage stability (over 18 months at ambient temperature) and thermostabilization (1 month at 80 °C). The robust and compact CS-CA NPs dramatically declined the contents of primary and secondary oxidation production in HIPPEs than that by corn oil. Moreover, CS-CA NPs stabilized HIPPEs appreciably enhanced the bioaccessibility (2.56 times) and chemical stability (thermal, UV-light, and storage) of BC. This research evidenced that CS-protein or polysaccharide-CA-based systems could be an encouraging formulation to commercially construct tunable HIPPEs with adorable stability for liposoluble nutraceuticals with enhanced attributes.

Pickering Emulsions and Antibubbles Stabilized by PLA/PLGA Nanoparticles

Micrometer-sized double emulsions and antibubbles were produced and stabilized via the Pickering mechanism by colloidal interfacial layers of polymeric nanoparticles (NPs). Two types of nanoparticles, consisting either of polylactic acid (PLA) or polylactic-co-glycolic acid (PLGA), were synthesized by the antisolvent technique without requiring any surfactant. PLA nanoparticles were able to stabilize water-in-oil (W/O) emulsions only after tuning the hydrophobicity by means of a thermal treatment. A water-in-oil-in-water (W/O/W) emulsion was realized by emulsifying the previous W/O emulsion in a continuous water phase containing hydrophilic PLGA nanoparticles. Both inner and outer water phases contained a sugar capable of forming a glassy phase, while the oil was crystallizable upon freezing. Freeze drying the double emulsion allowed removing the oil and water and replacing them with air without losing the three-dimensional (3D) structure of the original emulsion owing to the sugar glassy phase. Reconstitution of the freeze-dried double emulsion in water yielded a dispersion of antibubbles, i.e., micrometric bubbles containing aqueous droplets, with the interfaces of the antibubbles being stabilized by a layer of adsorbed polymeric nanoparticles. Remarkably, it was possible to achieve controlled release of a flourescent probe (calcein) from the antibubbles through heating to 37 °C leading to bursting of the antibubbles.

Edible mayonnaise-like Pickering emulsion stabilized by pea protein isolate microgels: Effect of food ingredients in commercial mayonnaise recipe

Particle stabilized O/W Pickering emulsion has great potential for making egg-free mayonnaise. In this study, we fabricated pea protein isolate (PPI) microgels by gel-breaking method and applied in mayonnaise-like Pickering emulsion. The effects of acetic acid (pH), sodium chloride (NaCl), and sucrose, which are typically used in commercial mayonnaise were studied. The minimum droplet size (47.0 μm) was found below isoelectric point. The NaCl decreased ζ-potential to almost 0 and risen droplet size to 75.9 μm. The sucrose enhanced the emulsion's viscosity while lowering thixotropic recovery rate. Based on droplet size, viscosity, thixotropic recovery, and microstructure; 350 mmol NaCl and 4 wt% sucrose was finally used to make egg-free mayonnaise-like Pickering emulsion, and showed similar properties compared with commercial mayonnaise, and the thixotropy recovery rate was near 100%. A plant-scale test further confirmed the feasibility. The results showed the PPI microgels had a strong application prospect to form egg-free mayonnaise.

Recent progress in Pickering emulsions stabilised by bioderived particles

In recent years, the demand for non-surfactant based Pickering emulsions in many industrial applications has grown significantly because of the option to select biodegradable and sustainable materials with low toxicity as emulsion stabilisers. Usually, emulsions are a dispersion system, where synthetic surfactants or macromolecules stabilise two immiscible phases (typically water and oil phases) to prevent coalescence. However, synthetic surfactants are not always a suitable choice in some applications, especially in pharmaceuticals, food and cosmetics, due to toxicity and lack of compatibility and biodegradability. Therefore, this review reports recent literature (2018-2021) on the use of comparatively safer biodegradable polysaccharide particles, proteins, lipids and combinations of these species in various Pickering emulsion formulations. Also, an overview of the various tuneable factors associated with the functionalisation or surface modification of these solid particles, that govern the stability of the Pickering emulsions is provided.

Exploring water in oil emulsions simultaneously stabilized by solid hydrophobic silica nanospheres and hydrophilic soft PNIPAM microgel

A general drawback of microgels is that they do not stabilize water-in-oil (w/o) emulsions of non-polar oils. Simultaneous stabilization with solid hydrophobic nanoparticles and soft hydrophilic microgels overcomes this problem. For a fundamental understanding of this synergistic effect the use of well defined particle systems is crucial. Therefore, the present study investigates the stabilization of water droplets in a highly non-polar oil phase using temperature responsive, soft and hydrophilic PNIPAM microgel particles (MGs) and solid and hydrophobic silica nanospheres (SNs) simultaneously. The SNs are about 20 times smaller than the MGs. In a multiscale approach the resulting emulsions are studied from the nanoscale particle properties over microscale droplet sizes to macroscopic observations. The synergy of the particles allows the stabilization of water-in-oil (w/o) emulsions, which was not possible with MGs alone, and offers a larger internal interface than the stabilization with SNs alone. Furthermore, the incorporation of hydrophilic MGs into a hydrophobic particle layer accelerates the emulsions sedimentation speed. Nevertheless, the droplets are still sufficiently protected against coalescence even in the sediment and can be redispersed by gentle shaking. Based on droplet size measurements and cryo-SEM studies we elaborate a model, which explains the found phenomena.

Concentrated Pickering emulsions stabilised by hemp globulin-caseinate nanoparticles: tuning the rheological properties by adjusting the hemp globulin : caseinate ratio

Industrial hemp (Cannabis sativa L.) is an underutilised novel protein source. However, the utilisation of hemp seed protein is limited by its low solubility in water. Soluble nanoparticles were made by complexing hemp globulin (HG) with sodium caseinate (SC) via a pH-cycling method. Oil-in-water Pickering emulsions were made with these co-assembled protein nanoparticles. The emulsions were composed of 70% oil phase and 30% water phase (v/v), and contained 2% protein (w/v, pure SC or HG-SC nanoparticles with an HG : SC ratio of 1 : 2 or 1 : 1). All emulsions were stable during 21 days of storage, as there was no phase separation, coalescence or flocculation. At day 0, all emulsions were solid-like (G' > G'') regardless of the protein composition. The rheological properties of the emulsions during storage could be tuned by controlling the HG : SC ratio in the HG-SC nanoparticles, i.e. the emulsions became more solid-like over time when there was more HG in the nanoparticles. In contrast, emulsions stabilised by pure SC became more liquid-like during storage. The internal structure and interactions within the emulsions were evaluated by fitting frequency sweep test data according to a co-operative theory of flow. The result suggested that the solid-like emulsion resulted from stronger short-range interactions between flocs of oil droplets, which developed during storage when there was more HG in the HG-SC nanoparticles, and not from the formation of a three-dimensional network. These HG-SC nanoparticles can be used to control the rheological properties of an emulsion during its shelf life.

Nanostarch: Preparation, Modification, and Application in Pickering Emulsions

Nanostarch, as a food-grade Pickering emulsion stabilizer, has attracted wide attention owing to its biodegradability, nontoxicity, small size, and large specific surface area. In this review, the preparation, modification, and application of Pickering emulsions incorporating nanostarch are described. At present, methods for nanostarch preparation mainly include acid hydrolysis, acid hydrolysis combined with other treatments, nanoprecipitation, ultrasonication, ball milling, and cross-linking. Nanostarch is a promising Pickering emulsion stabilizer, and its emulsifying ability of nanostarch is significantly improved by hydrophobic modification. The hydrophobicity, charge, size, and content of nanostarch affect the emulsion stability. Future developments in this area of research include the efficient and environmentally friendly preparation of nanostarch as well as the control of its hydrophobicity via modification. Future studies should focus on the digestibility and storage stability of Pickering emulsions stabilized by nanostarch under different conditions.

Limonene-in-water Pickering emulsion and on-demand separation using thermo-responsive biodegradable nanoparticles

In the last few decades, Pickering emulsions have regained attention due to the possibility of forming stable oil-in-water emulsions with interesting interfacial properties. As an example, the more and more stringent regulations on the products for home and personal care are pushing the market towards the use of biodegradable materials in order to reduce their environmental impact. In this scenario, an appealing opportunity is offered by the use of biodegradable polymeric nanoparticles (NPs) for the stabilization of fragrance oils in water. In this work, modular biodegradable NPs have been synthesized through a combination of ring opening polymerization and reversible addition-fragmentation chain transfer emulsion polymerization and used to produce limonene-in-water Pickering emulsions. This strategy allowed controlling independently the NP size, polymer molecular weight, and hydrophobicity acting on the microstructure of the constituting copolymers. Stable limonene-in-water Pickering emulsions could be obtained, with the size of the oil phase and the wetting by limonene that can be strictly controlled by tuning the NP physico-chemical properties. Finally, the adoption of thermo-responsive polymer chains within the shell of the Pickering emulsifiers enabled the on-demand destabilization of the emulsions and hence the selective dispensing of limonene by simply increasing the temperature.

Molar mass effect in food and health

It is demanded to supply foods with good quality for all the humans. With the advent of aging society, palatable and healthy foods are required to improve the quality of life and reduce the burden of finance for medical expenditure. Food hydrocolloids can contribute to this demand by versatile functions such as thickening, gelling, stabilising, and emulsifying, controlling texture and flavour release in food processing. Molar mass effects on viscosity and diffusion in liquid foods, and on mechanical and other physical properties of solid and semi-solid foods and films are overviewed. In these functions, the molar mass is one of the key factors, and therefore, the effects of molar mass on various health problems related to noncommunicable diseases or symptoms such as cancer, hyperlipidemia, hyperglycemia, constipation, high blood pressure, knee pain, osteoporosis, cystic fibrosis and dysphagia are described. Understanding these problems only from the viewpoint of molar mass is limited since other structural characteristics, conformation, branching, blockiness in copolymers such as pectin and alginate, degree of substitution as well as the position of the substituents are sometimes the determining factor rather than the molar mass. Nevertheless, comparison of different behaviours and functions in different polymers from the viewpoint of molar mass is expected to be useful to find a common characteristics, which may be helpful to understand the mechanism in other problems.

Main Applications of Cyclodextrins in the Food Industry as the Compounds of Choice to Form Host-Guest Complexes

Cyclodextrins (CDs) are cyclic oligomers broadly used in food manufacturing as food additives for different purposes, e.g., to improve sensorial qualities, shelf life, and sequestration of components. In this review, the latest advancements of their applications along with the characteristics of the uses of the different CDs (α, β, γ and their derivatives) were reviewed. Their beneficial effects can be achieved by mixing small amounts of CDs with the target material to be stabilized. Essentially, they have the capacity to form stable inclusion complexes with sensitive lipophilic nutrients and constituents of flavor and taste. Their toxicity has been also studied, showing that CDs are innocuous in oral administration. A review of the current legislation was also carried out, showing a general trend towards a wider acceptance of CDs as food additives. Suitable and cost-effective procedures for the manufacture of CDs have progressed, and nowadays it is possible to obtain realistic prices and used them in foods. Therefore, CDs have a promising future due to consumer demand for healthy and functional products.

The quantitative impact of fluid vs. solid interfaces on the catalytic performance of pickering emulsions

Pickering emulsions (PEs), i.e. particle stabilized emulsions, are used as reaction environments in biphasic catalysis for the hydroformylation of 1-dodecene into tridecanal using the catalyst rhodium (Rh)-sulfoxantphos (SX). The present study connects the knowledge about particle-catalyst interactions and PE structure with the reaction results. It quantifies the efficiency of the catalytic performance of the catalyst localized in the voids between the particles (liquid-liquid interface) and the catalyst adsorbed on the particle surface (liquid-solid interface) using a new numerical approach. First, it is ensured that the overall packing density and geometry at the droplet interface and the size of the water droplets of the resulting w/o PEs are predictable. Second, it is shown that approximately all particles assemble at the droplet surface after emulsion preparation and neither the packing parameter nor the droplet size change with the particle surface charge or size when the total particle cross section is kept constant. Third, studies on the influence of the catalyst on the emulsion structure reveal that irrespective of the particle charge the surface active and negatively charged catalyst Rh-SX reduces the PE droplet size significantly and decreases the particle packing parameter from s = 0.91 (hexagonal packing in 2D) to s = 0.69 (shattered structure). In this latter case, large voids of the free w/o interface form and become covered with the catalyst. With a deep knowledge about the PE structure the reaction efficiencies of the liquid-liquid vs. the solid-liquid interface are quantified. By excluding any other influence factors, it is shown that the activity of the catalyst is the same at the fluid and solid interface and the performance of the reaction is explained by the geometry of the system. After the reaction, the catalyst retention via membrane filtration is shown to be successfully achieved without damaging the emulsions. This enables the continuous recovery of the catalyst, i.e. the most expensive compound in PE-based catalytic reactions, being a crucial criterion for industrial applications.

Synergistic Interactions of Plant Protein Microgels and Cellulose Nanocrystals at the Interface and Their Inhibition of the Gastric Digestion of Pickering Emulsions

It is possible that Pickering emulsions can optimize the transport of nutraceuticals, pharmaceuticals, and other bioactive compounds in human physiology. So-called ultrastable Pickering emulsions are often destabilized in the gastric digestion regime if the particles are proteinaceous in nature. The present study seeks to test how the interfacial structure can be engineered via synergistic particle-particle interactions to impact the gastric coalescence of Pickering emulsions. In this study, we designed plant-based protein-particle-stabilized oil-in-water emulsions (PPM-E, with 20 wt % sunflower oil) via pea protein microgels (PPM at 1 wt %). The PPM hydrodynamic diameter is ∼250 nm. In vitro gastric digestion of PPM-E confirmed droplet coalescence within 30 min of pepsin addition. Supposedly surface-active cellulose nanocrystals (CNCs, 1-3 wt %) were added to PPM-E at pH 3.0 to determine if they could act as a barrier to interfacial pepsinolysis due to the CNC and PPM being oppositely charged at this gastric pH value. A combination of confocal microscopy, zeta potential, and Langmuir trough measurements suggested that CNCs and PPMs might form a combined layer at the O/W interface, owing to the electrostatic attraction between them. CNCs at >2 wt % inhibited the pepsinolyis of the adsorbed PPM film and thus droplet coalescence. However, increasing concentrations of CNC also increased the bulk viscosity of the PPM-E and eventually caused gelation of the emulsions, which would also delay their gastric breakdown. In conclusion, tuning the bulk and interfacial structure of Pickering emulsions via synergistic interactions between two types of particles could be an effective strategy to modify the enzymatic breakdown of such emulsions, which would have important applications in pharmaceuticals, foods, and other soft-matter applications.

Cellulose-based dispersants and flocculants

Natural dispersants and flocculants, often referred to as dispersion stabilizers and liquid-solid separators, respectively, have secured a promising role in the bioprocessing community. They have various applications, including in biomedicine and in environmental remediation. A large fraction of existing dispersants and flocculants are synthesized from non-safe chemical compounds such as polyacrylamide and surfactants. Despite numerous advantages of synthetic dispersants and flocculants, issues such as renewability, sustainability, biocompatibility, and cost efficiency have shifted attention towards natural homologues, in particular, cellulose-based ones. Within the past decade, cellulose derivatives, obtained via chemical and mechanical treatments of cellulose fibrils, have successfully been used for these purposes. In this review article, by dividing the functional cellulosic compounds into "polymeric" and "nanoscale" categories, we provide insight into the engineering pathways, the structural frameworks, and surface chemistry of these "green" types of dispersants and flocculants. A summary of their efficiency and the controlling parameters is also accompanied by recent advances in their applications in each section. We are confident that the emergence of cellulose-based dispersing and flocculating agents will extend the boundaries of sustainable green technology.

Displacement of interfacially-bound monoglyceride crystals in water-in-oil emulsions by a non-ionic surfactant

HYPOTHESIS

Micron and nano-scale particles are increasingly used to stabilize water-in-oil (W/O) emulsions. Though remarkably stable, the resulting emulsions can be broken by adding low molecular weight surfactants that modify the wettability of the interfacially-adsorbed particles.

EXPERIMENTS

W/O emulsions were prepared using lipophilic crystals of the monoglyceride glycerol monostearate (GMS), followed by addition of sorbitan monooleate (SMO) at concentrations below and above its critical micelle concentration (CMC). Systematic measurements of interfacial tension and three-phase contact angles, as well as characterization of emulsion sedimentation and microstructure, were used to assess GMS crystal wettability and emulsion destabilization.

FINDINGS

GMS crystals formed shells around the dispersed droplets, resulting in emulsions stable against breakdown under quiescent conditions. With SMO concentrations added below CMC, emulsion stability was not significantly affected. At SMO concentrations above CMC, the integrity of the crystalline shell was markedly affected. Notably, the GMS crystals transitioned from preferential oil-wet to water-wet behavior, eventually leading to their diffusion into the droplets. Therefore, in-situ modification of particle wettability at the oil-water interface was responsible for emulsion breakdown. Findings from this study may provide a pathway for the design of particle-stabilized W/O emulsions with controllable breakdown properties for applications such as tailored release of aqueous bioactive compounds.

Nanotechnology in Food Systems: A Review

Recent developments of nanotechnology find its way into various fields of food production in our days. Nanotechnology could offer benefits in development of food products with enhanced functionality for health promotion, or modified texture convenient for elderly, and in quality and safety issues in the food supply chain. Nanoencapsulated bioactive components such as vitamins, antibacterial agents contribute to production of enriched food stuffs with the required appearance, flavour, taste, and texture. Nanomaterials can protect the sensitive compounds from environmental attack, release them in a programmed way, and provide favourable improvement in the bioavailability of nutraceuticals. The innovative approach in food packaging, including the detection, indication, and control of food products, serves the quality and safety improvements.

Self-assembled lipids for food applications: A review

Lipids play an important role in human nutrition. Several foodstuffs can be manufactured from the simple, compound and derived lipids. In particular, the use of self-assembled lipids (SLs, e.g. self-assembled L-α-lecithin) has brought great attention for the development of tailored, tuned and targeted colloidal structures loading degradation-sensitive substances with valuable antimicrobial, antioxidant and nutraceutical properties for food applications. For example, polyunsaturated fatty acids (PUFAs) and essential oils can be protected from degradation, thus improving their bioavailability in general terms in consumers. From a nanotechnological point of view, SLs allow the development of advanced and multifaceted architectures, in which each molecule of them are used as building blocks to obtain designed and ordered structures. It is important to note before beginning this review, that simple and compound lipids are the main SLs, while essential fatty acids and derived lipids in general have been considered by many research groups as the bulk loaded substances within several structures from self-assembled carbohydrates, proteins and lipids. However, this review paper is addressed on the analysis of the lipid-lipid self-assembly. Lipids can be self-assembled into various structures (micelles, vesicular systems, lyotropic liquid crystals, oleogels and films) to be used in different food applications: coatings, controlled and sustained release materials, emulsions, functional foods, etc. SLs can be obtained via non-covalent chemical interactions, primarily by hydrogen, hydrophilic and ionic bonding, which are influenced by the conditions of ionic strength, pH, temperature, among others. This manuscript aims to give an analysis of the specific state-of-the-art of SLs for food applications, based primarily on the literature reported in the past five years.

Interest of Pickering Emulsions for Sustainable Micro/Nanocellulose in Food and Cosmetic Applications

In the present review, natural and non-toxic particles made of micro/nanocellulose were specifically targeted as stabilizers of emulsions located at dispersed and continuous phases interfaces (called Pickering Emulsions, PEs). PEs are biphasic systems stabilized by solid particles with a recent interest in food and cosmetic domains. PEs have been more and more studied in the last ten years due to their advantages compared to conventional emulsions with surfactants. PEs have already been stabilized with various types of particles and particularly cellulose. Even if some studies showed that PEs were more stable when cellulose was chemically modified, numerous other recent studies showed that unmodified micro/nanocellulose is also promising biomaterial to stabilize PEs. Micro/nanocelluloses can be extracted by various green processes from numerous agricultural wastes and co-products, as banana peels, corncob, ginkgo seed shells, lime residues, mangosteen rind, oil palm empty fruit bunches, pistachio shells, as well as wheat straw. Main green processes used to treat cellulose are grinding, high pressure homogenization, microfluidization, enzymatic hydrolysis, subcritical water, extrusion, electron beam irradiation, cryocrushing, microwaves or sonication. PEs formulated with cellulose clearly participate to a global sustainable development but, additional studies will be necessary to better understand PEs stability and improve properties.