High internal phase Pickering emulsions

Biopolymer-based emulsion gels as fat replacers: A review of their design, fabrication, and applications

Excessive intake of fat has been linked to a variety of diet-related chronic diseases, such as diabetes, obesity, cardiovascular disease, and cerebrovascular disease. At the same time, fat provides calories and nutrients to the human body, as well as impacting the appearance, taste, texture, and palatability of foods. Consequently, it is not feasible to simply remove fats from food, without adversely affecting their nutritional, functional, and sensory properties. Emulsion gels are colloidal viscoelastic materials that can be used to mimic the appearance, taste, texture, and other properties of fats, while still providing valuable fat-soluble nutrients, like vitamins and nutraceuticals. In this article, we review the design and preparation of emulsion gels based on different food-grade biopolymers, including proteins, polysaccharides, and their complexes. In addition, we discuss how structural design principles can be used to create emulsion gels that exhibit a diverse range of different properties. The potential applications of emulsion gels as fat replacers in different kinds of foods are briefly summarized. When properly designed, emulsion gels can convert healthy plant-based liquid oils into semi-solid plastic fats that can mimic many of the rheological characteristics of animal fats. In conclusion, emulsion gels provide an effective approach for designing healthier and more nutritious low-fat foods.

High internal phase Pickering emulsions stabilized by surface-modified dialdehyde xylan nanoparticles

Polysaccharide-based particles have attracted considerable attention for stabilizing Pickering emulsions due to their sustainability and biocompatibility. In this study, we developed a novel approach utilizing hemicellulose-based nanoparticles for the stabilization of high internal phase Pickering emulsions (HIPPEs). Polyethylenimine-modified dialdehyde xylan nanoparticles (PEI-DAXNPs) were prepared through periodate oxidation of xylan nanoparticles obtained from esparto pulp, followed by a Schiff base reaction with polyethylenimine (PEI). Oil-in-water HIPPEs were fabricated using PEI-DAXNPs as the sole stabilizer through a one-time homogenization method and exhibited long-term stability after 180 days of storage. Furthermore, gel-like HIPPEs were obtained with a minimum concentration of 0.1 wt% PEI-DAXNPs in the continuous phase and exhibited shear-thinning behavior and promising viscoelastic properties, indicating good processability in the fabrication of soft materials and porous scaffolds. Therefore, the produced PEI-DAXNPs demonstrated significant potential as HIPPE stabilizers, providing inspiration for the valorization of hemicellulose-based nanoparticles.

Photothermal Miniemulsion Polymerization by Amphiphilic Gold Nanoclusters

Gold nanoclusters (AuNCs), which are approximately 2 nm in size, exhibit distinctive photophysical and catalytic properties, but their performance is often compromised by environmental factors. To mitigate these challenges, attempts have been made to incorporate AuNCs into polymer matrices to enhance their stability. Miniemulsion polymerization has proven to be an effective method for fabricating organic-inorganic composites. Here, we present a facile photothermal-assisted method for miniemulsion polymerization utilizing AuNCs, which serve as co-stabilizers of the emulsion and photothermal conversion agents. By grafting tryptamine onto hydrophilic AuNCs, the amphiphilic AuNCs were spontaneously adsorbed at the styrene/water interfaces, resulting in stable nanoemulsions. Taking advantage of the photothermal properties of surface-bounded AuNCs, rapid polymerization of styrene within the nanoemulsion was successfully initiated by external laser irradiation. The prepared nanocomposites inherited the photothermal activity of AuNCs and exhibited good photothermal stability and repeatability. This approach not only facilitates remote control of chemical reactions, but also optimizes the distribution of AuNCs within the final polymer matrix, thereby enabling the efficient synthesis of nanocomposites while exploiting the unique photofunctionality of AuNCs.

Natural-Based Microparticles as Sole Stabilizers of High Internal Phase Pickering Emulsions

Designing a water-reduced emulsion is a technical approach to creating more sustainable cosmetic products and reducing the strain on global water resources. This study explores the structuration of highly concentrated O/W emulsions solely stabilized by particles, also known as "high internal phase Pickering emulsions" (HIPPEs). It focuses especially on particles from natural origins with a micrometric scale instead of the highly modified nanometric ones commonly used (which may raise health issues). Highly concentrated O/W emulsions were formulated with different lipid phases (regarding the chemical nature and polarity) of up to 80%. A comprehensive array of particle natural sources (plant, mineral, etc.), micrometric sizes (from 3 to 45 μm), and geometries were screened. Parameters such as droplet size distribution, microstructure, relative stability (backscatter level changes), and pH were systematically monitored over 2 weeks. An experimental design approach was carried out on three particles to determine their stability domains in various formulation combinations, dissecting complex parameter interactions that pilot emulsion characteristics. Micrometric particles demonstrated excellent efficacy in structuring HIPPEs. A wide spectrum of systems can be engineered, exhibiting a wide range of microstructures (droplets ranging from micrometers to several millimeters), stabilities, and intrinsic properties (with pH values extending from approximately 6 to 10). Emulsions displaying resistance to coalescence in W/O systems were also successfully formulated by using hydrophobic natural particles. Waterless emulsions (less than 20% (w/w) water) stabilized exclusively with naturally derived microparticles represent promising architectures for designing future clean-label cosmetic prototypes. By meticulously selecting particle parameters, including their chemical composition, size, or origin, we can tailor the architecture of HIPPEs to obtain the targeted characteristics and functionalities. Beyond particle constituents, other ingredients influence the structural arrangement such as the lipid phase chemistry.

Pickering polymerized high internal phase emulsions: Fundamentals to advanced applications

Pickering-polymerized high internal phase emulsions have attracted attention since their successful first preparation 15 years ago, primarily due to their large pores and potential for functionalization during production. This review elucidates the fundamental principles of Pickering emulsions, Pickering HIPEs, and Pickering PolyHIPEs while comparing them to conventional surfactant-stabilized counterparts. The morphology of Pickering PolyHIPEs, with particular emphasis on methods for achieving interconnected structures, is explored and critically assessed. Lastly, the mechanical properties and diverse applications of these materials are reviewed, highlighting their use as catalytic supports and sorbent materials. The study aims to guide both new and experienced researchers in the field by comprehensively addressing the current potential and challenges of Pickering PolyHIPEs. Once the mystery behind the closed cellular pores of Pickering PolyHIPEs is resolved, these materials are expected to become more popular, particularly in applications where mass transfer is critical, such as tissue engineering.

Fiber complex-stabilized high-internal-phase emulsion for allicin encapsulation: microstructure, stability, and thermal-responsive properties

BACKGROUND

Stimuli-responsive emulsions have garnered significant attention for their ability to enhance sensory qualities and control the release of encapsulated nutrient in emulsion-based products. However, the characteristics of synthetic materials of fabricating stimuli-responsive emulsions have been a crucial limitation in the food industry. Regulating the behavior of molecules at the interface could potentially achieve the desired stimuli-responsive behavior, but currently there is limited information available.

RESULTS

High-internal-phase emulsions (HIPEs) were fabricated for the encapsulation of allicin, stabilized by a complex of 20 g kg-1 whey protein amyloid fibrils (WPF) and 20 g kg-1 glycyrrhizin fibers (GA). The intermolecular interactions between WPF and GA in the fiber complexes were predominantly governed by hydrophobic and electrostatic forces. These complexes adsorbed and stacked around the oil droplets, forming a protective interfacial film that enhanced droplet stability. An increased proportion of WPF (WPF = 3:1 or 4:1) surrounding the oil droplets enhanced the accelerated storage stability of HIPEs, with instability indexes approaching 0.2. Additionally, HIPEs displayed a temperature-dependent modulus, with the emulsion stabilized by a WPF ratio of 3:1 showing the highest modulus at 85 °C. The encapsulation efficiency of allicin in HIPEs ranged from 88.69 ± 6.62% to 101 ± 1.37% at 25 °C, and from 31.95 ± 1.92% to 78.69 ± 4.63% after incubation at 85 °C for 8 h. The release profile of allicin from the HIPEs exhibited thermal responsiveness, depending on the interfacial content of GA.

CONCLUSION

These findings indicated that the thermal-responsive properties of HIPEs can be strategically engineered by manipulating their interfacial characteristics. © 2024 Society of Chemical Industry.

A Montmorillonite-Based Pickering Nanoemulsion for the Integration of Photothermal Therapy and NIR-Responsive Drug Delivery

Chemo/photothermal combination therapy is a promising and practical approach for cancer treatment which calls for certain nanovehicles to achieve the spatiotemporal co-occurrence of photothermal conversion and drug delivery. Herein, we developed a montmorillonite-based Pickering emulsion equipped with a near-infrared photothermal agent (indocyanine green, ICG) and anticarcinogen (paclitaxel, PTX). With both montmorillonite and ICG functioning as interfacial stabilizers, the Pickering emulsion showed good stability and nanoscale droplet size, which were favored for cellular applications. Due to the vast oil-water interface, where the majority of amphiphilic ICG was prone to distribute, the Pickering nanoemulsion could achieve a higher local concentration of ICG than the aqueous solution, therefore leading to a higher local photothermal performance under near-infrared irradiation. The Pickering nanoemulsion exhibited fast cell penetration, which promoted the photothermal therapeutic effect of ICG. Moreover, the inner phase of the Pickering nanoemulsion also facilitated the loading of PTX, further improving its killing efficacy against cancer cells under near-infrared irradiation, because the photothermal conversion of the Pickering nanoemulsion could not only cause heat damage by itself but also promote the loaded PTX to diffuse out and induce cell death. Therefore, this clay-based Pickering nanoemulsion as a nanovehicle could realize the synergy of chemo- and photothermal therapy.

Formation of self-assembled fibril aggregates of trypsin-controllably hydrolyzed soy protein and its regulation on stability of high internal phase Pickering emulsions

The mechanisms of trypsin hydrolysis time on the structure of soy protein hydrolysate fibril aggregates (SPHFAs) and the stability of SPHFAs-high internal phase Pickering emulsions (HIPPEs) were investigated. SPHFAs were prepared using soy protein hydrolysate (SPH) with different trypsin hydrolysis time (0 min-120 min) to stabilize SPHFAs-HIPPEs. The results showed that moderate trypsin hydrolysis (30 min, hydrolysis degree of 2.31 %) induced SPH unfolding and increased the surface hydrophobicity of SPH, thereby promoting the formation of flexible SPHFAs with maximal thioflavin T intensity and ζ-potential. Moreover, moderate trypsin hydrolysis improved the viscoelasticity of SPHFAs-HIPPEs, and SPHFAs-HIPPEs remained stable after storage at 25 °C for 80 d and heating at 100 °C for 1 h. Excessive trypsin hydrolysis (> 30 min) decreased the stability of SPHFAs-HIPPEs. In conclusion, moderate trypsin hydrolysis promoted the formation of flexible SPHFAs with high surface charge by inducing SPH unfolding, thereby promoting the stability of SPHFAs-HIPPEs.

Flammulina velutipes protein-Flammulina velutipes soluble polysaccharide-tea polyphenols particles stabilized Pickering emulsions for the delivery of β-carotene

The delivery vehicles based on protein-polysaccharide-polyphenol are promising methods to encapsulate bioactive components with the aim of improving their solubility and bioavailability. In this study, we used Flammulina velutipes protein (FVP) and Flammulina velutipes soluble polysaccharides (FVSP) as raw materials and prepared FVP-FVSP and FVP-FVSP-TP composite particles loaded with tea polyphenols (TP), the high internal phase Pickering emulsions stabilized by FVP-FVSP and FVP-FVSP-TP for the delivery of β-carotene (BC) were created. FVP-FVSP-TP has more promise as Pickering emulsion stabilizer than FVP-FVSP because of the smaller particle size, proper contact angle, and lower surface tension. The optimal preparation conditions of the emulsion were 4 % particle concentration and 80 % oil phase volume fraction. The emulsions stabilized by FVP-FVSP and FVP-FVSP-TP were o/w emulsions. Compared to the emulsion stabilized by FVP-FVSP, the FVP-FVSP-TP stabilized emulsion had higher G', G″ values and viscosity and showed better thermal, centrifugal, storage and oil oxidation stability. Moreover, FVP-FVSP-TP stabilized emulsions could further enhance the retention rate and bioaccessibility of TP and β-carotene. This study provides a theoretical basis for the application of FVP and FVSP in Pickering emulsions, and a reference for the fabrication of delivery vehicles to improve the stability and bioaccessibility of bioactive substances.

Development and Application of High-Internal-Phase Water-in-Oil Emulsions Using Amphiphilic Nanoparticle-Based Emulsifiers

High-internal-phase water-in-oil (W/O) emulsions generated in situ have garnered considerable attention as novel profile control systems. However, conventional emulsifiers are unreactive and poorly dispersed in water, necessitating large dosages and resulting in poor injectivity. In this study, we synthesized amphiphilic nanoparticles (SiO2-NH2-DAC NPs) containing amine and long-chain alkyl groups using a one-pot method and investigated the stabilized emulsion properties. Our results indicated that W/O emulsions with a water-to-oil ratio (WOR) of 7:3 to 8:2 could be prepared with just 0.1 wt% of SiO2-NH2-DAC NPs under neutral and basic conditions, with demulsification occurring under acidic conditions (pH = 2.1), demonstrating the pH-responsiveness of the W/O emulsions. The emulsion viscosity increased from 150 to 2555 mPa·s at different WORs. An additional 18.7% oil recovery was achieved using SiO2-NH2-DAC NPs in a heterogeneous core, highlighting their potential as a promising profile control candidate.

Pickering emulsions stabilized by prolamin-based proteins as innovative carriers of bioactive compounds

Pickering emulsions (PEs) can be used as efficient carriers for encapsulation and controlled release of different bioactive compounds. Recent research has revealed the potential of prolamins in development of nanoparticle- and emulsion-based carriers which can improve the stability and bioavailability of bioactive compounds. Prolamin-based particles have been effectively used as stabilizers of various PEs including single PEs, high internal phase PEs, multiple PEs, novel triphasic PEs, and PE gels due to their tunable self-assembly behaviors. Prolamin particles can be fabricated via different techniques including anti-solvent precipitation, dissolution followed by pH adjustment, heating, and ion induced aggregation. Particles fabricated from prolamins alone or in combination with other hydrocolloids or polyphenols have also been used for stabilization of different PEs which were shown to be effective carriers for food bioactives, providing improved stability and functionality. This article covers the recent advances in various PEs stabilized by prolamin particles as innovative carriers for bioactive ingredients. Strategies applied for fabrication of prolamin particles and prolamin-based carriers are discussed. Emerging techno-functional applications of prolamin-based PEs and possible challenges are also highlighted.

Influence of flaxseed-derived diglyceride-based high internal phase Pickering emulsions on the rheological and physicochemical properties of myofibrillar protein gels

The study aimed to investigate the influence of flaxseed-derived diglyceride-based high internal phase Pickering emulsions (HIPPE) at different levels (0%, 10%, 20%, 30%, 40%, and 50%) on the rheological and physicochemical properties of myofibrillar protein (MPs) gels. The study indicated that with increasing HIPPE levels, there was a significant increase in whiteness while a decrease in water-holding capacity. The gels with 10% HIPPE levels had higher ionic bonds, while those with 40% and 50% HIPPE levels showed higher hydrogen bonds. By increasing HIPPE levels in the formation of MP gels, the T2 relaxation time was found to decrease. Additionally, in all MP gels, G' values were significantly higher than G" values over time. Adding lower contents of HIPPE levels resulted in a more compact microstructure. These findings indicate that flaxseed-derived diglyceride-based HIPPEs could be utilized as fat substitutes in meat products to enhance their nutritional quality.

Production of Monodisperse Large Drop Emulsions by Means of High Internal Phase Pickering Emulsions-Processing and Formulation

High internal phase Pickering emulsions (HIPPE) have received significant research attention in the last two decades due to their potential for a wide range of applications. The appropriate processing of such high-viscosity emulsions, hundreds of times more viscous than that of the continuous phase, and the control of the final droplet size remain challenges to be tackled. Our research targeted this knowledge gap by examining the influence of the emulsion formulation and the processing conditions on the final droplet size. The dispersed phase fraction (100 cSt silicon oil) ranged between 75 and 80%. The emulsions were produced in a regular mixing tank equipped with a helical ribbon impeller rotating at a low speed (100-150 rpm). The effective viscosity of the continuous phase was obtained from the experimental torque measurements. The droplet size distributions were measured after emulsification and dilution in the continuous phases. It is shown that the capillary number obtained from the observed emulsification performance can help predict the final droplet size. Our approach provides a straightforward methodology to generate concentrated Pickering emulsions with controlled and predictable droplet size.

Peanut de-oiling at room temperature by micro-aqueous hydration: Co-destabilization driven by oleosome coalescence and protein aggregation

The peanut de-oiling industry currently lacks efficient processing technologies for de-oiling at low or room temperatures. A novel method, micro-aqueous extraction (MAE), offers over 93 % de-oiling efficiency at room temperature and is also effective for other oilseeds like sesame, camellia, and rapeseed. Despite its effectiveness, the exact mechanism behind oleosomes destabilization at a critical hydration level or oil volume fraction (φ ∼ 0.75) is not fully understood. This study investigates how MAE affects peanut oleosome size, paste stability, and the interfacial properties of surfactant proteins. Results showed that micro-aqueous hydration and agitation caused small droplets (85.6 vol% < 10 μm) to coalesce into larger droplets (90.0 vol% > 30 μm) due to press-induced rupture of the liquid film. Simultaneously, agitation decreased water mobility and protein intrinsic fluorescence, while increasing paste viscosity, leading to protein aggregation. This aggregation further promoted oleosome coalescence. Additionally, hydration and agitation weakened the ability of membrane proteins to stabilize oleosomes by increasing interfacial tension and decreasing dilatational storage modulus. The insights into the peanut oleosome destabilization mechanism for MAE provide a foundation for scaling up the process, with the potential to replace current hot and cold pressing techniques.

Spatially selective catalysis of OSA starch for preparation of Pickering emulsions with high emulsification properties

The traditional strategies of chemical catalysis and biocatalysis for producing octenyl succinic anhydride modified starch can only randomly graft hydrophobic groups on the surface of starch, resulting in unsatisfactory emulsification performance. In this work, a lipase-inorganic hybrid catalytic system with multi-scale flower like structure is designed and applied to spatially selective catalytic preparation of ocenyl succinic anhydride modified starch. With the appropriate floral morphology and petal density, lipases distributed in the "flower center" can selectively catalyze the grafting of hydrophobic groups in a spatial manner, the hydrophobic groups are concentrated on one side of starch particles. The obtaining OSA starch exhibits excellent emulsifying property, and the pickering emulsion has good protective effect on the embedded curcumin. This work provides a direction for the development of high-performance starch-based emulsifiers for the food and pharmaceutical industries, which is of great significance for improving the preparation and emulsification theory research of modified starch.

High internal phase pickering emulsions stabilized by zein/whey protein nanofibril complexes: Preparation and lycopene loading

High internal phase Pickering emulsions (HIPPEs) prepared from natural polymers have attracted much attention in the food manufactures. However, single zein-stabilized HIPPEs are poorly stable and prone to flocculation near the isoelectric point. To address this issue, in this study, zein and whey protein nanofibrils (WPN) complex nanoparticles (ZWNPs) were successfully prepared using a pH-driven method, and ZWNPs were further used as HIPPEs stabilizers. The results showed that zein and WPN were combined together through hydrogen bonding and hydrophobic interaction to form ZWNPs, and the HIPPEs stabilized by ZWNPs had excellent stability, which could effectively protect the internally encapsulated lycopene and improve the bioaccessibility of lycopene. In conclusion, this study provides a new strategy for the preparation of stable hydrophobic protein-based HIPPEs, represented by zein.

Critical Review of Food Colloidal Delivery System for Bioactive Compounds: Physical Characterization and Application

Bioactive compounds (BACs) have attracted much attention due to their potential health benefits. However, such substances have problems such as difficulty dissolving in water, poor stability, and low intestinal absorption, leading to serious limitations in practical applications. Nowadays, food colloidal delivery carriers have become a highly promising solution due to their safety, controllability, and efficiency. The use of natural macromolecules to construct delivery carriers can not only regulate the solubility, stability, and intestinal absorption of BACs but also effectively enhance the nutritional added value of functional foods, improve sensory properties, and extend shelf life. Moreover, smart-responsive colloidal delivery carriers can control the release characteristics of BACs, thus improving their absorption rate in the human body. This review describes the characteristics of several typical food colloid delivery carriers, focuses on their physical properties from static structure to dynamic release, summarizes their applications in delivery systems, and provides an outlook on the future development of food colloid delivery carriers. The different compositions and structures of food colloids tend to affect their stability and release behaviors, and the different surface properties and rheological characteristics of the carriers predestine their different application scenarios. The control of in vivo release properties and the effect on food media should be emphasized in the future exploration of safer and more controllable carrier systems.

New discovery of the coalescence kinetics of sesame oil droplets under a high internal phase: A highly efficient oil extraction technique

Traditional pressing is of low efficiency (< 80 %). A highly efficient sesame oil extraction technique was discovered via micro-hydration of sesame paste (φ = ∼ 75 %) and then agitation with a yield of ∼ 95 %. However, the extraction mechanism is still unknown. To uncover this, microscopic imaging was used, and it found that agitation progressively increased the droplet size of micro-hydrated paste (φ = 74.5 %) from an initial size of < 4 μm. As agitated for 20 min, almost 85 % (v/v) of oil was over 20 μm, which was linearly and positively correlated (R2 > 0.96) with oil yield. Increase in droplet size was due to droplet compression, film rupture, and droplet coalescence. The coalescence frequency based on agitation time followed an exponent curve (R2 > 0.97). This coalescence might be related to the decreased water relaxation time and increased paste viscosity. This study, for the first time, found the oil droplet coalescence in hydrated sesame paste (φ = 74.5 %) during agitation, thereby successfully extracting oil at room temperature. The findings of this work can be a starting point for research on micro-hydration extraction for oil-containing materials from a packing density of oil droplets point view.

Influence of carboxymethyl cellulose on the stability, rheology, and curcumin bioaccessibility of high internal phase Pickering emulsions

Recently, there has been a focus on using biopolymer-based particles to stabilize high internal phase Pickering emulsions (HIPPEs) due to the notable advances in biocompatibility and biodegradability. In this work, the complex particles of peanut protein isolate and carboxymethyl cellulose (CMC) with various substitution degrees (DS; 0.7 and 0.9) and weight average molecular weights (Mw; 90, 250, and 700 kDa) were prepared and characterized as novel stabilizers. For the obtained four types of morphologically distinct particles, the complex particles formed by CMC (0.9 DS and 250 kDa) showed cluster structures with an average size of 1.271 μm, equally biphasic wettability with three-phase contact angles of 91.5°, and the highest diffusion rate at the oil-water interface. HIPPEs stabilized by these particles exhibited more elastic behavior due to the smaller tanδ and higher viscosity, as well as excellent thixotropic recovery properties and stability against heating, storage, and freeze-thawing. Furthermore, confocal laser scanning microscopy verified that these particles formed a dense interfacial layer around the oil droplets, which could resist flocculation and coalescence between oil droplets during in vitro digestion. The improved bioaccessibility of curcumin-loaded HIPPEs made these delivery systems potentially apply in functional foods.

Porous Hydrogels for Immunomodulatory Applications

Cancer immunotherapy relies on the insight that the immune system can be used to defend against malignant cells. The aim of cancer immunotherapy is to utilize, modulate, activate, and train the immune system to amplify antitumor T-cell immunity. In parallel, the immune system response to damaged tissue is also crucial in determining the success or failure of an implant. Due to their extracellular matrix mimetics and tunable chemical or physical performance, hydrogels are promising platforms for building immunomodulatory microenvironments for realizing cancer therapy and tissue regeneration. However, submicron or nanosized pore structures within hydrogels are not favorable for modulating immune cell function, such as cell invasion, migration, and immunophenotype. In contrast, hydrogels with a porous structure not only allow for nutrient transportation and metabolite discharge but also offer more space for realizing cell function. In this review, the design strategies and influencing factors of porous hydrogels for cancer therapy and tissue regeneration are first discussed. Second, the immunomodulatory effects and therapeutic outcomes of different porous hydrogels for cancer immunotherapy and tissue regeneration are highlighted. Beyond that, this review highlights the effects of pore size on immune function and potential signal transduction. Finally, the remaining challenges and perspectives of immunomodulatory porous hydrogels are discussed.

Preparation of a Porous Protein-Based Composite Material by In Situ Polymerization of Pickering High Internal Phase Emulsion for Adsorption of Lead Ions

The preparation of complex porous materials using a small molecular surfactant as the stabilizer of a high internal phase emulsion can result in harm to the environment. In this study, porous composites based on soy protein isolate with poly(acrylic acid) were prepared by in situ polymerization of a high internal phase monomer emulsion with an internal phase volume fraction of 80%. The material was prepared from acrylic acid and an N,N-methyl diacrylic acid monomer solution as the continuous phase, peanut oil as the dispersed phase, and soy protein isolate as the composite stabilizer. Scanning electron microscopy showed that porous composites exhibited a concave/convex three-dimensional interpenetrating pore structure. Fourier-transform infrared spectra revealed the existence of many active groups such as carboxyl, amino, hydroxyl, and sulfhydryl. The composite had a high adsorption capacity for lead ions, even at low concentration, with a removal rate of up to 95.7%. The adsorption process conformed to a two-stage model involving internal diffusion and Langmuir isothermal adsorption. The maximum saturated adsorption capacity was 36.71 mg/g when the initial solution concentration was 150 mg/L, the adsorbent concentration was 7.0 g/L, and the adsorption mechanism involved chemical interactions between the lead ions and the composite groups -COOH, -OH, and -SH.

Bovine serum albumin-liposome stabilized high oil-phase emulsion: Effect of liposome ratio on interface properties and stability

This study aimed to solve the issue of poor lipophilicity of natural bovine serum albumin (BSA) by combining with liposomes (Lips) to stabilize high oil-phase emulsions (HOPEs). The interaction between BSA and Lips was mainly driven by hydrophobic forces, followed by hydrogen bonding. The secondary structure and tertiary structure of BSA were characterized and indicated that the addition of Lips promoted the structural expansion of BSA exposing the hydrophobic groups inside. Interfacial adsorption behaviours were assessed through dynamic interfacial tension, three-phase contact angle, and quartz crystal microbalance with dissipation. These results indicated that BSA-Lips crosslinking improved wettability, promoting adsorption and rearrangement at the oil-water interface, thereby resulting in a dense interfacial layer. The emulsifying efficacy of BSA-stabilized HOPEs also displayed a distinct Lips dependency. Varying the BSA-to-Lips ratio transformed their consistency from flowing to semi-solid, reinforcing the gel network. Under optimal conditions (BSA: Lips = 1:1), the droplet size of BSA-Lips stabilized HOPEs reached a minimum with a highly uniform distribution. Moreover, a 1:1 BSA to Lips ensured outstanding storage, thermal, and centrifugal stability for the HOPEs. This work provides valuable references for the interaction between protein and Lips, guiding the development of highly stable HOPEs stabilizers.

High Internal Phase Emulsions Stabilized with Ultrasound-Modified Spirulina Protein for Curcumin Delivery

Spirulina protein (SP) is recognized as a nutritious edible microbial protein and holds potential as a natural emulsifier. Due to the inherent challenges SP faces in stabilizing high internal phase emulsions (HIPEs), ultrasonic techniques were utilized for modification. Noticeable alterations in the structural and functional properties of SP were observed following ultrasonic treatment at various power levels (0, 100, 300, and 500 W). Ultrasound treatment disrupted non-covalent interactions within the protein polymer structure, leading to the unfolding of molecular structures and the exposure of hydrophobic groups. Importantly, the particle size of SP was reduced the most at an ultrasonic power of 300 W, and the three-phase contact angle reached its peak at 84.3°. The HIPEs stabilized by SP modified with 300 W ultrasonication have high apparent viscosity and modulus values and strong storage stability under different environmental conditions. Additionally, the encapsulation of curcumin in HIPEs led to improved retention of curcumin across various settings. The bioavailability increased to 35.36, which is 2.8 times higher than the pure oil. These findings suggest that ultrasound-modified SP is a promising emulsifier for HIPEs, and is expected to encapsulate hydrophobic nutrients such as curcumin more effectively.

The application of encapsulation technology in the food Industry: Classifications, recent Advances, and perspectives

Encapsulation technology has been extensively used to enhance the stability, specificity, and bioavailability of essential food ingredients. Additionally, it plays a vital role in improving product quality and reducing production costs. This study presents a comprehensive classification of encapsulation techniques based on the state of different cores (solid, liquid, and gaseous) and offers a detailed description and analysis of these encapsulation methods. Specifically, it introduces the diverse applications of encapsulation technology in food, encompassing areas such as antioxidant, protein activity, physical stability, controlled release, delivery, antibacterial, and probiotics. The potential impact of encapsulation technology is expected to make encapsulation technology a major process and research hotspot in the food industry. Future research directions include applications of encapsulation for enzymes, microencapsulation of biosensors, and novel technologies such as self-assembly. This study provides a valuable theoretical reference for the in-depth research and wide application of encapsulation technology in the food industry.

Aminopoly(carboxylic acid)-Functionalized PolyHIPE Beads toward Eliminating Trace Heavy Metal Ions from Water

Many advanced materials are designed for the removal of heavy metal ions from water. However, materials for eliminating trace heavy metal ions from wastewater to meet drinking water standards remain a major challenge. Herein, epoxy group-functionalized open-cellular beads are synthesized by UV polymerization of a water-in-oil-in-water system. The epoxy groups are further transformed into diethylenetriaminepentaacetic acid (DTPA) with hexamethylene diamine as a bridging agent. The resulting material (DTPA@polyHIPE beads) can eliminate trace Cu(II), Cr(III), Pb(II), Fe(III), or Cd(II) from water. When 0.15 g of DTPA@polyHIPE beads are used to adsorb metal ions of 20 mg in 100 mL of water, the residue concentrations of Cu(II), Cr(III), Pb(II), Fe(III), and Cd(II) are reduced to 0.08, 0.06, 0.02, 0.09, and 0.07 mg/L, respectively. The adsorption efficiencies of the beads for these ions are all higher than 99.55%. The adsorbent is durable and exhibits good recyclability by retaining an adsorption capacity of ≥91% after 5 cycles. The negative values of ΔG in the adsorption process indicate that the adsorption is feasible and spontaneous. The chemical adsorption follows the Freundlich adsorption model, indicating a multilayer heterogeneous adsorption. The DTPA@polyHIPE beads have a great potential application in dealing with trace heavy metal ion polluted water.

Zr-Based MOF-Stabilized CO2-Responsive Pickering Emulsions for Efficient Reduction of Nitroarenes

A Pickering emulsion is a natural microreactor for interfacial catalysis in which an emulsifier is critical. Recently, a metal-organic framework (MOF) has attracted attention to emulsify water-organic mixtures for constructing a Pickering emulsion. However, a few stimuli-responsive Pickering emulsions based on MOFs have been reported, and the MOF emulsifiers cannot be regenerated at room temperature. Herein, the Zr-MOF with a rodlike morphology is synthesized using ionic liquid as a modulator and then modified with n-(trimethoxysilylpropyl)imidazole (C3im) to prepare a series of functionalized Zr-MOFs (MOF-C3im). It is found that MOF-C3im is an excellent emulsifier to construct stable and CO2-responsive Pickering emulsions even at low content (>0.20 wt %). Notably, the emulsification and demulsification of the emulsions can be easily and reversibly switched by bubbling of CO2 and N2 alternatively at room temperature because CO2 and imidazole molecules anchored on the Zr-MOF underwent a reversible acid-base reaction, resulting in an obvious change in the wettability of the emulsifier. As a proof of concept, the reduction reactions of nitrobenzene have been successfully carried out in these Pickering emulsions, demonstrating the efficient integration as a microreactor for chemical reaction, product separation, and emulsifier recycling under ambient conditions. This strategy provides an innovative option to develop stimulus-responsive Pickering emulsions for sustainable chemical processes.

Tunable rheological properties of high internal phase emulsions stabilized by phosphorylated walnut protein/pectin complexes: The effects of pH conditions, mass ratios, and concentrations

The current study reported high internal phase emulsions (HIPEs) stabilized by phosphorylated walnut protein/pectin complexes (PWPI/Pec) and elucidated how their rheological properties were modulated by pH conditions, mass ratios, and concentrations of the complexes. At pH 3.0, the HIPEs stabilized by PWPI/Pec exhibited smaller oil droplet sizes, as well as higher storage modulus (G') and flow stress, in comparison to those stabilized by the complexes formed at pH 4.0-6.0. These observations can be directly linked to pH-dependent changes in particle size, surface hydrophobicity, and wettability of the PWPI/Pec complexes. Rheological analysis revealed that all generated HIPEs displayed weak strain overshoot behavior, irrespective of pH conditions. Notably, HIPEs stabilized by PWPI/Pec at mass ratios of 2:1 and 4:1 showed enlarged oil droplet sizes, lower G' and flow stress but higher flow strain with unaffected loss factor compared to those stabilized by PWPI/Pec 1:1. However, reducing the concentration of PWPI/Pec led to a simultaneous decrease in G', flow stress, and flow strain, along with a significant increase in the loss factor of the HIPEs. Furthermore, the HIPEs formed with 1% PWPI/Pec 1:1 at pH 3.0 demonstrated excellent stability against heat treatment and long-term storage. These results provide valuable insights into the modulation of rheological characteristics of HIPEs and offer guidance for the application of walnut protein-based stabilizers in HIPE systems.

Thermal Stability Improvement of Core Material via High Internal Phase Emulsion Gels

Biocompatible particle-stabilized emulsions have gained significant attention in the biomedical industry. In this study, we employed dynamic high-pressure microfluidization (HPM) to prepare a biocompatible particle emulsion, which effectively enhances the thermal stability of core materials without the addition of any chemical additives. The results demonstrate that the HPM-treated particle-stabilized emulsion forms an interface membrane with high expansion and viscoelastic properties, thus preventing core material agglomeration at elevated temperatures. Furthermore, the particle concentration used for constructing the emulsion gel network significantly impacts the overall strength and stability of the material while possessing the ability to inhibit oxidation of the thermosensitive core material. This investigation explores the influence of particle concentration on the stability of particle-stabilized emulsion gels, thereby providing valuable insights for the design, improvement, and practical applications of innovative clean label emulsions, particularly in the embedding and delivery of thermosensitive core materials.

Stabilization of High Internal Phase Oil-in-Water Emulsions Using "Whole" Gracilaria lemaneiformis Slurry

In this study, a Gracilaria lemaneiformis slurry (GLS) was prepared using low-energy mechanical shearing. The resulting GLS, which was rich in polysaccharides, was utilized as an effective stabilizer for oil-in-water emulsions. The microstructures and stability of the resulting emulsions were controlled by adjusting the emulsion formulations, including Gracilaria lemaneiformis (GL) mass concentration and oil volume fraction (φ). The optimized GL mass concentration and φ conditions yielded high internal phase emulsions (HIPEs) with gel-like textures. Moreover, the presence of exogenous Ca2+ resulted in bridging structures in the emulsions, enhancing their viscoelasticity and forming a robust physical barrier against droplet coalescence. Our findings highlight the effectiveness of the GLS as an emulsifier for stabilizing HIPEs. Notably, this method relies solely on physical processes, aligning with the desirability of avoiding chemical additives, particularly in the food industry.

High internal phase Pickering emulsions stabilised by ultrasound-induced soy protein-β-glucan-catechin complex nanoparticles to enhance the stability and bioaccessibility of curcumin

AIMS

To evaluate the potential applications of soy protein-glucan-catechin (SGC) complexes prepared with different ultrasound times in stabilising high internal phase Pickering emulsion (HIPPE) and delivering curcumin.

METHODS

The SGC complexes were characterised by particle size, morphology, zeta potential, Fourier transform infra-red, and fluorescence spectroscopy. Formation and stability of curcumin emulsions were monitored by droplet size, microstructure, rheological property, lipid oxidation, and in vitro digestion.

RESULTS

Short-time ultrasound-induced complexes (SGC-U15) exhibited a small size and wettability of ∼82.5°. The chemical stability and bioaccessibility of curcumin was greatly improved by SGC-U15-stabilised HIPPEs, even after 70 days of storage, heating at 100 °C for 30 min, ultraviolet irradiation for 120 min, and in vitro digestion, owing to the formation of elastic gel-like structure at the oil/water interfaces.

CONCLUSION

Our findings may contribute to the design of emulsion-based delivery systems using ultrasound-induced protein-polysaccharide-polyphenol complexes.

Stabilization of high internal phase Pickering emulsions with millimeter-scale droplets using silica particles

High internal phase emulsions stabilized with colloidal particles (Pickering HIPEs) have recently been studied intensively because of their great stability achieved by the irreversible adsorption of particles onto the oil-water interface and their usage as a template for synthesizing porous polymeric materials, called PolyHIPEs. In most cases, Pickering HIPEs with microscale droplets ranging from tens of micrometers to hundreds of micrometers have been successfully achieved, but the stabilization of Pickering HIPEs with millimeter-sized droplets is rarely reported. In this study, we report for the first time that, by using shape-anisotropic silica particle aggregates as a stabilizer, successful stabilization of Pickering HIPEs with millimeter-sized droplets can be achieved, and the size of droplets can be simply controlled. Additionally, we demonstrate that stable PolyHIPEs with large pores can be readily converted to PolyHIPEs with millimeter-scale pores, which have advantages in absorbent materials and biomedical engineering applications.

Covalent Bond Interfacial Recognition of Polysaccharides/Silica Reinforced High Internal Phase Pickering Emulsions for 3D Printing

Significant challenges remain in designing sufficient viscoelasticity polysaccharide-based high internal phase Pickering emulsions (HIPPEs) as soft materials for 3D printing. Herein, taking advantage of the interfacial covalent bond interaction between modified alginate (Ugi-OA) dissolved in the aqueous phase and aminated silica nanoparticles (ASNs) dispersed in oil, HIPPEs with printability were obtained. Using multitechniques coupling a conventional rheometer with a quartz crystal microbalance with dissipation monitoring, the correlation between interfacial recognition coassembly on the molecular scale and the stability of whole bulk HIPPEs on the macroscopic scale can be clarified. The results showed that Ugi-OA/ASNs assemblies (NPSs) were strongly retargeted into the oil-water interface due to the specific Schiff base-binding between ASNs and Ugi-OA, further forming thicker and more rigid interfacial films on the microscopic scale compared with that of the Ugi-OA/SNs (bared silica nanoparticles) system. Meanwhile, flexible polysaccharides also formed a 3D network that suppressed the motion of the droplets and particles in the continuous phase, endowing the emulsion with appropriately viscoelasticity to manufacture a sophisticated "snowflake" architecture. In addition, this study opens a novel pathway for the construction of structured all-liquid systems by introducing an interfacial covalent recognition-mediated coassembly strategy, showing promising applications.

High Internal Phase Emulsion Stabilization through Restricted Interdrop Fusion across Water Drainage Channels

This study introduces a promising approach to stabilize high internal phase emulsions (HIPEs) in which droplets are enveloped by octadecane (C18)-grafted bacterial cellulose nanofibers (BCNF_diC18), which are mainly surrounded by carboxylate anions and hydrophobically modified with C18 alkyl chains. For this purpose, BCNF_diC18, in which two octadecyl chains were grafted onto each of several cellulose unit rings on 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidized BCNFs, was fabricated using the Schiff base reaction. The wettability of BCNF_diC18 was adjusted by controlling the amount of the grafted C18 alkyl chain. Interfacial rheological analysis revealed that BCNF_diC18 enhanced the membrane modulus at the oil-water interface. We figured out that such a resilient interfacial membrane substantially prevented interdrop fusion across the water drainage channel formed between the jammed oil droplets, which was confirmed theoretically using the modified Stefan-Reynolds equation. These findings highlight that the use of surfactants in the form of nanofibers to form a rigid interfacial film plays a key role in hindering the interfusion of the internal phase and the collapse of the emulsion, which is essential for HIPE stabilization.

Recent progress in emulsion gels: from fundamentals to applications

Emulsion gels, also known as gelled emulsions or emulgels, have garnered great attention both in fundamental research and practical applications due to their superior stability, tunable morphology and microstructure, and promising mechanical and functional properties. From an application perspective, attention in this area has been, historically, mainly focused on food industries, e.g., engineering emulsion gels as fat substitutes or delivery systems for bioactive food ingredients. However, a growing body of studies has, in recent years, begun to demonstrate the full potential of emulsion gels as soft templates for designing advanced functional materials widely applied in a variety of fields, spanning chemical engineering, pharmaceutics, and materials science. Herein, a concise and comprehensive overview of emulsion gels is presented, from fundamentals to applications, highlighting significant recent progress and open questions, to scout for and deepen their potential applications in more fields.

High Internal Phase Pickering Emulsion Stabilized by Lipase-Coated ZIF-8 Nanoparticles towards Recyclable Biphasic Biocatalyst

High internal phase Pickering emulsion (Pickering HIPE) stabilized by enzyme-decorated metal-organic frameworks (MOFs) nanoparticles is developed for biphasic biocatalysts to enhance lipase catalysis and recycling. Specifically, enzyme decorated nanoparticles are prepared via ZIF-8 physisorption of a model lipase Candida antarctica Lipase B (CALB), named ZIF-8@CALB, to be both Pickering stabilizer and catalytic sites. An oil-in-water (o/w) Pickering HIPE with oil/water volume ratio of 3 could then be fabricated by homogenizing p-nitrophenyl palmitate (p-NPP) n-heptane solution into the ZIF-8@CALB aqueous dispersion. The biocatalytic hydrolysis of p-NPP is conducted by just standing the biphasic system at room temperature. The Pickering HIPE system achieves a product conversion of up to 48.9% within 0.5 h, whereas the p-NPP n-heptane solution system containing free CALB only achieves a stable product conversion of 6.8% for the same time. Moreover, the ZIF@CALB could be recovered by a simple centrifugation at 800 rpm, and then reused in the next cycle. The hydrolysis equilibrium conversion rate of p-NPP keeps over 40% for all 8 cycles, reflecting the high catalytic efficiency and recyclability of the Pickering HIPE. This study provides a new opportunity in designing Enzyme-MOFs-based Pickering interfacial biocatalyst for practical applications.

Protein-Based High Internal Phase Pickering Emulsions: A Review of Their Fabrication, Composition and Future Perspectives in the Food Industry

Protein-based high internal phase Pickering emulsions (HIPEs) are emulsions using protein particles as a stabilizer in which the volume fraction of the dispersed phase exceeds 74%. Stabilizers are irreversibly adsorbed at the interface of the oil phase and water phase to maintain the droplet structure. Protein-based HIPEs have shown great potential for a variety of fields, including foods, due to the wide range of materials, simple preparation, and good biocompatibility. This review introduces the preparation routes of protein-based HIPEs and summarizes and classifies the preparation methods of protein stabilizers according to their formation mechanism. Further outlined are the types and properties of protein stabilizers used in the present studies, the composition of the oil phase, the encapsulating substances, and the properties of the constituted protein-based HIPEs. Finally, future development of protein-based HIPEs was explored, such as the development of protein-based stabilizers, the improvement of emulsification technology, and the quality control of stabilizers and protein-based HIPEs.

Pickering Emulsion-Templated Nanocomposite Membranes for Excellent Demulsification and Oil-Water Separation

A worldwide steady increase in oily wastewater, due to oil spillage and various industrial discharges, requires immediate efforts toward development of an effective strategy and materials to preserve the natural water bodies. Designing a superwettable fibrous membrane of robust structure and anti-fouling property for efficient separation of oil-water mixtures and emulsions is therefore highly demanding. The electrospun fibrous membrane, which possesses porosity and flexibility and properties including superwettability and tunable functionality, can be considered as apposite materials for this cause. In this approach, we combined two strategies, viz., Pickering emulsion and near gel resin (nGR) emulsion electrospinning together to produce a fibrous nanocomposite membrane for efficient oil-water separation and demulsification. nGR Pickering emulsions were stabilized using hydrophilic SiO₂ nanoparticles and successfully optimized for fabricating the crosslinked core sheath-structured fibrous membrane. The prepared membrane provided twofold functionality due to the core sheath structure of the fibers. The crosslinked polystyrene core offered high oil adsorption capacity, whereas SiO₂-functionalized crosslinked polyvinyl alcohol sheath provided a rough, superhydrophilic surface with underwater oleophobic behavior to the membrane. The optimized SiO₂-Pickering emulsion-templated nanocomposite membrane demonstrated excellent underwater anti-oil adhesion behavior (UWOCA ∼148°) with efficient oil-water separation capacity of more than 99% and separation flux up to 3346 ± 91 L m^-2 h^-1. The membrane was evaluated against various oil-water emulsions and found to have a superior separation efficiency. Moreover, excellent anti-oil adhesion property provided the intact membrane, where consistent separation performance was achieved up to 10 separation cycles without any loss. The membrane was used for separation of hot oil-water emulsions and showed no structural disintegration or loss in separation performance when exposed to elevated temperatures. The developed nanocomposite membranes could efficiently be used for separation and demulsification, and their applications can be explored in various other fields including selective sorption, catalysis, and storage in future.