Interfacial and emulsion characterisation of chemically modified polysaccharides through a multiscale approach

Characteristics of Pickering emulsions stabilized by microgel particles of five different plant proteins and their application

Pickering emulsions stabilized by protein particles are of great interest for use in real food systems. This study was to investigate the properties of microgel particles prepared from different plant proteins, i.e., soybean protein isolate (SPI), pea protein isolate (PPI), mung bean protein isolate (MPI), chia seed protein isolate (CSPI), and chickpea protein isolate (CPI). MPI protein particles had most desirable Pickering emulsion forming ability. The particles of SPI and PPI had similar particle size (316.23 nm and 294.80 nm) and surface hydrophobicity (2238.40 and 2001.13) and emulsion forming ability, while the CSPI and CPI particle stabilized emulsions had the least desirable properties. The MPI and PPI particle stabilized Pickering emulsions produced better quality ice cream than the one produced by SPI particle-stabilized emulsions. These findings provide insight into the properties of Pickering emulsions stabilized by different plant protein particles and help expand their application in emulsions and ice cream.

Soy protein particles as stabilizers of heat-stable O/W emulsions with 20% protein content

In response to the increasing demand for nutritionally rich foods, consumer preference for protein-enriched beverages has grown. However, heat-induced protein aggregation and gelation significantly hinders the production of high-protein drinks. In this study, oil-in-water (O/W) emulsions with exceptional thermal stability were formulated using modified soy protein particles (MSPs). These MSPs effectively resisted gel formation, even at a protein concentration of up to 20% (w/v). In contrast, emulsions prepared with untreated soy proteins (SPs) experienced pronounced gelation under identical conditions. The compact structure of MSPs, in comparison to SPs, imparted resistance to heat-induced denaturation and aggregation. Additionally, the emulsion displayed heightened heat processing insensitivity, due to the enhanced hydrophobicity of MSPs and their rapid adsorption at the oil-water interface, resulting in a denser, more elastic, and resilient interfacial film. These findings provide practical insights for the formulation of protein-rich milk alternatives, meeting the evolving market demands.

Rheology and stability mechanism of pH-responsive high internal phase emulsion constructed gel by pea protein and hydroxypropyl starch

There is an increasing demand for stable, highly viscoelastic, and printable emulsion gels based on pea protein (PeaP) as a substitute for animal fat. In this article, a simple pH modulation strategy was applied to regulate high internal phase (HIPE) gels prepared from PeaP and hydroxypropyl starch (HPS). The results showed that the interfacial tension of PeaP decreased from 11.9 to 7.1 mN/m at 5% PeaP and from 9.9 to 6.3 mN/m at 10% PeaP with increasing pH from 7 to 11. The incorporation of HPS improved the strength and physical stability of the HIPE gel. HIPE gels showed the best three-dimensional printing ability at pH 11. The main mechanism of HIPE gels at pH 3 was hydrophobic interaction, while electrostatic interaction dominated at pH 7, 9, and 11. This study may provide insights into the development of PeaP-based HIPE gels as a printable fat alternative.

Structural and interfacial properties of acetylated Millettia speciosa Champ polysaccharide and stability evaluation of the resultant O/W emulsion containing β-carotene

The aim of this study was to investigate the effects of acetylation modification on the structural, interfacial and emulsifying properties of Millettia speciosa Champ polysaccharide (MSCP). Besides, the influence of acetylation modification on the encapsulation properties of polysaccharide-based emulsion was also explored. Results indicated that modification resulted in a prominent reduction in molecular weight of MSCP and the interfacial layer thickness formed by acetylated MSCP (AC-MSCP) was also decreased, but the adsorption rate and ability of AC-MSCP to reduce interfacial tension were improved. AC-MSCP formulated emulsion possessed smaller droplet size (6.8 μm) and exhibited better physical stability under stressful conditions. The chemical stability of β-carotene was also profoundly enhanced by AC-MSCP fabricated emulsion. Moreover, AC-MSCP improved lipids digestion extent, thus facilitating the formation of micelle and increasing bioaccessibility of β-carotene. This study provided insights for rational modification of polysaccharide-based emulsifier and designing delivery system for chemically labile hydrophobic bioactive components.

Recent advances in understanding the interfacial activity of antioxidants in association colloids in bulk oil

The chemical stability of edible oils rich in polyunsaturated fatty acids (PUFAs) is a major challenge within the food and supplement industries, as lipid oxidation reduces oil quality and safety. Despite appearing homogeneous to the human eye, bulk oils are actually multiphase heterogeneous systems at the nanoscale level. Association colloids, such as reverse micelles, are spontaneously formed within bulk oils due to the self-assembly of amphiphilic molecules that are present, like phospholipids, free fatty acids, and/or surfactants. In bulk oil, lipid oxidation often occurs at the oil-water interface of these association colloids because this is where different reactants accumulate, such as PUFAs, hydroperoxides, transition metals, and antioxidants. Consequently, the efficiency of antioxidants in bulk oils is governed by their chemical reactivity, but also by their ability to be located close to the site of oxidation. This review describes the impact of minor constituents in bulk oils on the nature of the association colloids formed. And then the formation of mixed reverse micelles (LOOH, (co)surfactants, or antioxidations) during the peroxidation of bulk oils, as well as changes in their composition and structure over time are also discussed. The critical importance of selecting appropriate antioxidants and surfactants for the changes of interface and colloid, as well as the inhibition of lipid oxidation is emphasized. The knowledge presented in this review article may facilitate the design of bulk oil products with improved resistance to oxidation, thereby reducing food waste and improving food quality and safety.

Deciphering the thick filaments assembly behavior of myosin as affected by enzymatic deamidation

Enzymatic deamidation is a promising approach in enhancing the solubility of myofibrillar proteins (MPs) in water paving the way of tailor manufacturing muscle protein-based beverages. This work aimed to clarify the solubilization mechanism by deciphering myosin thick filaments assembly as affected by protein-glutaminase deamidation. With the extension of deamidation, filamentous structures in MPs shortened continuously. Dynamic monitoring of quartz crystal microbalance-dissipated showed the adsorption capacity of the deaminated MPs was reduced from 3.66 ng/cm2 to 2.03 ng/cm2, indicating that the ability to assemble myosin thick filaments was significantly weakened. By simulating the surface charge, it was found that deamidation may neutralize the positive charged clusters distanced at 14-29 nm from rod C-terminus. Since this region confers myosin electrostatic property to initiate staggered dimerization, deamidation in this region, which severely affected the electrostatic balance between residues, impaired ordered thick filament growing and elongating, thus promoting the solubilization of MPs in water.

A multi-scale approach to arabinoxylan-based emulsions: From molecular features, interfacial properties to emulsion behaviors

Arabinoxylan (AX) is well-known for its emulsification and beneficial biological activity, but the roles of AX's molecular features and interfacial properties in AX-based emulsion behaviors were unknown. We first used a multi-scale approach to correlate molecular, interfacial, droplet characteristics, and bulk emulsion of AXs from corn and wheat bran (CAXs and WAXs). Our results showed that among CAXs and WAXs solution (1 %, 2 % and 3 %, w/v), 0.25 M NaOH-treated CAX and WAX showed smaller particle sizes (493 nm and 8621 nm), lower interfacial tension and stronger interfacial layer, whose emulsion exhibited smaller initial droplets (541 nm and 660 nm) and better stability. Moreover, WAXs had bigger particle sizes, lower interfacial tension and stronger interfacial layer than CAXs, but CAXs exhibited better emulsifying and emulsion-stabilizing properties than WAXs. There is a satisfactory correlation among CAXs' or WAXs' molecular features, interfacial properties and emulsion behaviors. However, a good correlation from different grains AXs cannot be established.

Soy protein isolate-guar gum-goose liver oil O/W Pickering emulsions that remain stable under accelerated oxidation at high temperatures

BACKGROUND

Goose liver oil (GLO) is a solid-liquid mixture, rich in polyunsaturated fatty acids and high in nutritional value, but poor in fluidity and easily oxidized. Therefore, oil-in-water (O/W) Pickering emulsions of three polysaccharides and soy protein isolate (SPI) with GLO were prepared to improve the stability of it.

RESULTS

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), Fourier-transform infrared spectroscopy, and zeta potential revealed that the SPI and complexes with konjac glucomannan, pectin, and guar gum (GG) ranged from 17 to 75 kDa, with the site of action being the -OH stretch and the amide group, and bound by hydrogen bonding. Adding konjac glucomannan and GG significantly increased the water contact angle of the SPI to 74.1° and 59.0°, respectively. Therefore, the protein-polysaccharide complexes could enhance the emulsion stability. In addition, the O/W Pickering emulsions with GLO had near-Newtonian fluid rheological properties with a significant increase in apparent viscosity and viscoelasticity, forming a dual network structure consisting of a ductile and flexible protein network and a rigid and brittle polysaccharide network. The microstructure observation indicated that the O/W emulsions were spherical and homogeneous. The highest emulsification activity was observed for the SPI-GG-GLO emulsions, without significant delamination or flocculation and high oxidative stability after 7 days in storage.

CONCLUSION

These results demonstrate that the construction of SPI-GG-GLO O/W Pickering emulsions can stabilize GLO even at high temperatures that promote oxidation. © 2023 Society of Chemical Industry.

Effects of glycation method on the emulsifying performance and interfacial behavior of coconut globulins-fucoidan complexes

Coconut globulins (CG) possesses potential as an emulsifier but has not been utilized well. In this study, the emulsifying performance of glycated CG-fucoidan (CGF) complexes, and the relationship between emulsifying stability and interfacial behavior were investigated. The results showed that the grafting of fucoidan increased the molecular weight of CG, and decreased the zeta potential and fluorescence intensity. With the higher glycosylation degree, the fucoidan modified CG exhibited better emulsifying stability and higher viscosity. Moreover, the result of adsorption kinetics revealed that elasticity was the main property of the interface layer. Compared to CG, CGF complexes with high degree of glycosylation had thicker interfacial layer on the oil-water interface. A thicker elastic interfacial layer may be beneficial to the emulsion stability, owing to the strong interaction of electrostatic repulsion and steric hindrance between oil droplets. These findings may provide useful information for glycated CGF complexes as emulsifiers in functional food.

Aggregate Size Modulates the Oil/Water Interfacial Behavior of Myofibrillar Proteins: Toward the Thicker Interface Film and Disulfide Bond

Myofibrillar protein (MP) aggregate models have been established to elucidate the correlation between their aggregate sizes and interfacial properties. The interfacial layer thickness was measured by the polystyrene latex method and quartz crystal microbalance with dissipation measurement. Interfacial conformations were then characterized in situ (front-surface fluorescence spectroscopy) and ex situ (reactive sulfhydryl group and secondary structure measurement following MP displacement). The viscoelasticity of the interfacial film and its resistance to surfactant-induced competitive displacement were reflected by the dilatational rheology and dynamic interfacial tension with the bulk phase exchange. Finally, we compared the findings of competitive displacement before/after adding a sulfhydryl-blocking agent, N-ethylmaleimide, to highlight the role of S-S linkage on interfacial film formation and stability. We substantiated that the aggregate size of the MP governed their interfacial properties. Small-sized aggregates exhibited more ordered secondary structures on the oil-water interface, which was conducive to the adsorption ratio of the protein and the adsorption dynamics. Although larger aggregates lowered the diffusion rate during interfacial film formation, they allowed the thicker and more viscoelastic interfacial film to be constructed afterward through more disulfide bond formation, resulting in greater resistance to surfactant-induced competitive displacement.

Quality characteristics of peanut protein-based patties produced with pre-emulsified olive oil as a fat replacer: Influence of acylglycerol type

The emulsion (O/W) may be used as a fat replacer to develop healthier meat analogs. The purpose of this work was to evaluate the effects of oil incorporation methods (direct oil addition and emulsion addition) and oil types [triacylglycerol (TAG) and diacylglycerol (DAG)] on the quality characteristics of peanut protein-based patties crosslinked by transglutaminase (TGase). The patties formulated with emulsions showed larger texture parameters (springiness, cohesiveness and gumminess), lower cooking loss and higher acceptability compared with directly adding oil. The rheological results confirmed that the presence of emulsions strengthened the gel structure in patties, which allowed the patties containing emulsions to stabilize free water. Whereas, TAG-based emulsion was more effective than DAG-based emulsion in improving quality of products, possibly because the competitive adsorption at oil-water interface of DAG reduced the crosslinking between the interfacial protein and adjacent protein molecules. This study revealed the relationship between the acylglycerol type in emulsion and the patty quality, providing a reference for the development of plant-based patties.

Structural and emulsion-stabilizing properties of the alkali-extracted arabinoxylans from corn and wheat brans

This study investigated the structural and emulsion-stabilizing capacities of alkali-extracted arabinoxylans from corn and wheat bran (CAXs and WAXs). The results demonstrated that all AXs were mainly composed of arabinose and xylose. WAXs had a higher weight-average molecular weight (Mw, 375-473 KDa) and protein content (3.09-8.68 %) but lower total phenolic acid content (TPC, 1.18-1.91 mg gallic acid equivalents/g) than CAXs; however, CAX stabilized emulsions exhibited smaller and more regular oil droplet size (524-589 nm) and higher absolute value of ζ potential (48-52 mV) compared with WAX stabilized emulsions during storage. Moreover, the increment of NaOH concentration caused a decrease in Mw, protein content, and TPC of CAXs or WAXs and the corresponding CAXs or WAXs emulsions showed bigger and more unstable oil droplets during 14 d storage. The Mw, protein, and TPC were well correlated with their emulsion stability. Furthermore, emulsions stabilized by AXs with low-concentration NaOH could resist better various temperatures, pH, and NaCl. In conclusion, the structural properties of AXs derived from different cereal sources and treated with different concentrations of NaOH varied, leading to differences in their ability to stabilize emulsions. CAXs or WAXs obtained from low-concentration NaOH treatment demonstrated significant potential as highly effective natural emulsifiers.

Assessing and Predicting Physical Stability of Emulsion-Based Topical Semisolid Products: A Review

The emulsion-based topical semisolid dosage forms present a high degree of complexity due to their microstructures which is apparent from their compositions comprising at least two immiscible liquid phases, often times of high viscosity. These complex microstructures are thermodynamically unstable, and the physical stability of such preparations is governed by formulation parameters such as phase volume ratio, type of emulsifiers and their concentration, HLB value of the emulsifier, as well as by process parameters such as homogenizer speed, time, temperature etc. Therefore, a detailed understanding of the microstructure in the DP and critical factors that influence the stability of emulsions is essential to ensure the quality and shelf-life of emulsion-based topical semisolid products. This review aims to provide an overview of the main strategies used to stabilize pharmaceutical emulsions contained in semisolid products and various characterization techniques and tools that have been utilized so far to evaluate their long-term stability. Accelerated physical stability assessment using dispersion analyzer tools such as an analytical centrifuge to predict the product shelf-life has been discussed. In addition, mathematical modeling for phase separation rate for non-Newtonian systems like semisolid emulsion products has also been discussed to guide formulation scientists to predict a priori stability of these products.

Tuning interfacial microstructure of alginate-based amphiphile by dynamic bonding for stabilizing Pickering emulsion

Polysaccharide-based soft colloidal particles mediated by the dynamic bonding-engineered interfacial self-assembly can regulate the properties of oil-water interfacial films, availing the stability of emulsions under a wide pH range. The amphiphilic phenylboronic alginate soft colloidal particles (Alg-PBA) were designed to stabilize pH-responsive Pickering emulsions (PEs). Combining stability analysis with quartz crystal microbalance and dissipation monitoring (QCM-D), the microstructure and viscoelasticity of Alg-PBA at the oil-water interface were determined. The results showed that PEs stabilized by Alg-PBA due to a thicker and stronger viscoelastic interface film induced by BO bonds and hydrogen bonds. The structure-function relationship of the Alg-PBA emulsifier driven by dynamic bonds was further elaborated at multiple scales by laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). Meanwhile, the microstructure of aerogels templated by emulsion could be tuned by adjusting dynamic bonds, which provides a new idea for polysaccharide soft material engineering.

Sodium alginate emulsion loaded with linalool: Preparation, characterization and antibacterial mechanism against Shigella sonnei

This study aimed to prepare sodium alginate-linalool emulsion (SA-LE) to overcome the low solubility of linalool and explore its inhibitory activity against Shigella sonnei. The results indicated that linalool significantly reduced the interfacial tension between SA and oil phase (p < 0.05). Droplet sizes of fresh emulsions were uniform with sizes from 2.54 to 2.58 μm. The ζ-potential was between -23.94 and -25.03 mV, and the viscosity distribution was 973.62 to 981.03 mPa·s at pH 5-8 (near neutral pH) without significant difference. In addition, linalool could be effectively released from SA-LE in accordance with the Peppas-Sahlin model, mainly described by Fickian diffusion. In particular, SA-LE can inhibit S. sonnei with a minimum inhibitory concentration of 3 mL/L, which was lower than free linalool. The mechanism can be described as damaging the membrane structure and inhibiting respiratory metabolism accompanied by oxidative stress based on FESEM, SDH activity, ATP and ROS content. These results suggest that SA is an effective encapsulation strategy to enhance the stability of linalool and its inhibitory effect on S. sonnei at near neutral pH. Moreover, the prepared SA-LE has the potential to be developed as a natural antibacterial agent to address the growing food safety challenges.

Light-adjusted supramolecular host-guest interfacial recognition for reconfiguring soft colloidal aggregates

The soft interfacial template-assisted confined self-assembly of block copolymers (BCPs) guiding colloidal aggregates has been extensively investigated by interfacial instability. Whether the macromolecular polymer architectonics possessed stimulus-responsive self-regulated structural controllability more readily implement the morphological diversity of colloidal aggregates. Herein, we in-situ constructed the alginate-modified β-cyclodextrin/azobenzene-functionalized alkyl chains (Alg-β-CD/AzoC12) system by supramolecular host-guest interfacial recognition-engineered strategy, in which possessed photo-stimulated responsive structural reconfigurability by modulating assembly/disassembly behaviors between CD and Azo at oil/water interface. The host-guest droplet interfaces acted as soft templates managing interfacial instability by synergistically integrating supra-amphiphilic host-guest polymers with cosurfactants, further constructing various soft supracolloidal aggregates, including soft nanoaggregates, microspheres with tunable degrees of surface roughness. Additionally, the stimuli-altering structural reconfigurability of supramolecular host-guest polymers was regulated by ultraviolet/visible irradiation, endowing soft aggregates with structural diversity. It's highly anticipated that the supramolecular host-guest interfacial recognition self-assembly establishes great bridge between supramolecular host-guest chemistry and colloid interface science.

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.

Fabrication, characterization and emulsifying properties of agarose microgel

Agarose microgels were prepared with bottom-up approach, and the emulsifying properties of agarose microgels were investigated. Physical properties of microgels are varied with agarose concentration, and further affect the emulsifying performance of microgels. Enhanced surface hydrophobicity index and decreased particle size of microgels was recorded with the increasing of agarose concentration, which was conducive to emulsifying properties of microgels. Improved interfacial adsorption of microgels was evidenced by Dynamic surface tension and SEM. However, microscopic morphology of microgel at O/W interface indicated that increasing agarose concentration could weaken the deformability of microgels. The influence of external conditions (pH and NaCl) on the physical properties of microgels were investigated, and their effects on the emulsion stability were evaluated. Compared with acidification, NaCl was appeared to be more destructive to emulsion stability. Results indicated acidification and NaCl could decrease surface hydrophobicity index of microgels, but there was differentiation in the variation of particle size. It was inferred that deformability of microgels could make contribution to the stability of emulsion. This study verified that microgelation was a feasible scheme to improve the interfacial properties of agarose, and the influence of agarose concentration, pH, and NaCl on the emulsifying performance of microgels was investigated.

Quantitative analysis and interfacial properties of mixed pea protein isolate-phospholipid adsorption layer

Proteins and low-molecular-weight (LMW) surfactants are widely used for the physical stabilization of many emulsion-based food products. This study investigated the oil-water interfacial behavior between pea protein isolate (PPI) and phospholipid (PL). The emulsions prepared with different concentrations of PPI and PL were stabilized by their synergetic or competitive adsorption at the oil-water interface. In addition, the quantitative proteomics results could illustrate the displacements of proteins by PL. The result showed that the vicilin (7S) could be preferentially displaced by PL. Meanwhile, the results of quartz crystal microbalance with dissipation (QCM-D) indicated the high affinity of legumin (11S) with PL, suggesting that the legumin possessed higher interfacial affinity to prevent interfacial displacement. This research could help us to understand the interaction and competitive adsorption between plant proteins and LMW surfactants profoundly, which could promote the development of plant protein-based emulsion beverage with improved stability.

Coexistence of aggregates and flat states of hydrophobically modified sodium alginate at an oil/water interface: A molecular dynamics study

Hydrophobically modified sodium alginate stabilizes benzene in water emulsions. The stability of the emulsion is related to the interface properties at the mesoscopic scale, but the details of the polymer adsorption, conformation and organization at oil/water interfaces at the microscopic scale remain largely elusive. In this study, hydrophobically modified sodium alginate was used as a representative of amphiphilic polymers for prediction of distribution of HMSA at the oil/water interface by coarse-grained molecular dynamics simulation. The result showed that driven by the interaction energy between the hydrophobic segment and benzene, HMSA will actively accumulate at the oil/water interface. The HMSA molecules parallel to the oil/water interface prevent the hydrophobic segments in the micelles from approaching the oil/water interface, so that the micelles can exist stably by steric hindrance. This study would be helpful to understand the aggregation behavior of amphiphilic polymers at the oil/water interface, these results can have applications in diverse sectors such as drug, food industry, where polymers are used to stabilize emulsions.

Correlation between interfacial layer properties and physical stability of food emulsions: current trends, challenges, strategies, and further perspectives

Emulsions are thermodynamically unstable systems that tend to separate into two immiscible phases over time. The interfacial layer formed by the emulsifiers adsorbed at the oil-water interface plays an important role in the emulsion stability. The interfacial layer properties of emulsion droplets have been considered the cutting-in points that influence emulsion stability, a traditional motif of physical chemistry and colloid chemistry of particular significance in relation to the food science and technology sector. Although many attempts have shown that high interfacial viscoelasticity may contribute to long-term emulsion stability, a universal relationship for all cases between the interfacial layer features at the microscopic scale and the bulk physical stability of the emulsion at the macroscopic scale remains to be established. Not only that, but integrating the cognition from different scales of emulsions and establishing a unified single model to fill the gap in awareness between scales also remain challenging. In this review, we present a comprehensive overview of recent progress in the general science of emulsion stability with a peculiar focus on interfacial layer characteristics in relation to the formation and stabilization of food emulsions, where the natural origin and edible safety of emulsifiers and stabilizers are highly requested. This review begins with a general overview of the construction and destruction of interfacial layers in emulsions to highlight the most important physicochemical characteristics of interfacial layers (formation kinetics, surface load, interactions among adsorbed emulsifiers, thickness and structure, and shear and dilatational rheology), and their roles in controlling emulsion stability. Subsequently, the structural effects of a series of typically dietary emulsifiers (small-molecule surfactants,proteins, polysaccharides, protein-polysaccharide complexes, and particles) on oil-water interfaces in food emulsions are emphasized. Finally, the main protocols developed for modifying the structural characteristics of adsorbed emulsifiers at multiple scales and improving the stability of emulsions are highlighted. Overall, this paper aims to comprehensively study the literature findings in the past decade and find out the commonality of multi-scale structures of emulsifiers, so as to deeply understand the common characteristics and emulsification stability behaviour of adsorption emulsifiers with different interfacial layer structures. It is difficult to say that there has been significant progress in the underlying principles and technologies in the general science of emulsion stability over the last decade or two. However, the correlation between interfacial layer properties and physical stability of food emulsions promotes revealing the role of interfacial rheological properties in emulsion stability, providing guidance on controlling the bulk properties by tuning the interfacial layer functionality.

Determination of the Emulsion Stabilization Mechanisms of Quaternized Glucan of Curdlan via Rheological and Interfacial Characterization

Interfacial-active quaternized glucan of curdlan (QCD) with different degrees of substitution (DS) was prepared and used as stabilizers of oil-in-water (O/W) emulsions at different concentrations. The adsorption behavior of QCDs, rheology of bulk emulsions and interfacial films, emulsion morphology, and stability were investigated. The emulsifying capacity of QCD was essentially related to the viscoelastic features of the interfacial film and the continuous phase and the electrostatic repulsion among oil droplets. QCD molecules with different DS form structurally different interfacial films. The high-DS QCD formed a viscously predominant interfacial film with certain hydrophobicity, whereas the low-DS QCD molecules formed an elastically predominant film characterized by hydrogen bonds among adsorbed chains. The structuralization of low-DS QCD molecules through physical cross-linking in bulk and interfacial films at high concentrations was conducive to emulsion stability. Excess QCD chains in the bulk formed a weak gel-like network, further hindering the movement of droplets in the emulsions. Relevant emulsification and stability mechanisms were proposed. Finally, the stability of curcumin encapsulated in O/W emulsions was evaluated.

Adsorption and Assembly of Octenyl Succinic Anhydride Starch/Chitosan Electrostatic Complexes at Oil-Water Interface

Biopolymer electrostatic complexes are popular Pickering stabilizers whose structures greatly affect their interfacial properties. This study comprehensively demonstrated the interfacial adsorption and assembly of dissolved octenyl succinic anhydride (OSA) starch (OSA-D)/chitosan (CS) electrostatic complexes with different structures through complementary characterization methods. We found that compared with single-component systems, OSA-D/CS complexes exhibited significantly increased wetting stability and adsorption rate to the interface, which was reinforced by molecular dynamics simulations. Their soft structures and the entanglement of molecular chains led to the formation of thick and highly viscoelastic multilayer adsorbed films, which greatly resisted deformation against shearing forces. The adsorption and assembly of the complexes were strongly influenced by OSA-D/CS ratios and pH, which could be related to the different interfacial interaction strengths. Overall, the electrostatic complexation, structural characteristics, and interfacial properties of OSA-D/CS complexes were well related, thereby providing valuable information for the regulation of controlled interfaces and bulk system properties.

An "intelligent -responsive" bactericidal system based on OSA-starch Pickering emulsion

Pickering emulsion based on OSA-starch was developed in this study as an intelligent delivery system for the application of thymol against foodborne pathogens. Morphology and microstructure characterization showed that the Pickering emulsion was an O/W type emulsion and stayed stable at starch concentration of 200 mg/mL and oil fraction at 30 % with particle size of 10 μm and absolute Zeta potential of -12.5 mV. Low field nuclear magnetic resonance and rheology experiments indicated that a denser network structure was formed in this stable Pickering emulsion. Besides, the Pickering emulsion could endure long-time storage, low pH (3,5) and additional NaCl (50, 100, 200, 400 mM) and it showed enhanced bactericidal effects against Escherichia coli, Staphylococcus aureus (thymol =1.48 μmol/L) and Aspergillus flavus (thymol = 0.624 μmol/L) by inducing ROS eruption, membrane lipid peroxidation and cell shrink. Moreover, the bactericidal assay demonstrated that thymol could be intelligently released and a considerable 75 % timely bactericidal effect was detected after 9 days' intermittently exposing to E. coli, S. aureus and A. flavus in vitro, by comparison thymol alone showed only 20 % bactericidal effect due to its volatility. The results are of great importance to offer an intelligent delivery system of bio-actives defending foodborne pathogens.

Effects of pH-shifting treatments on the emulsifying properties of rice protein isolates: Quantitative analysis of interfacial protein layer

For the limitation of poor solubility and interfacial adsorption capacity of rice protein isolates (RPI), in this work the effects of pH-shifting treatments on the emulsifying properties of RPI were investigated. The results showed that the particle size of the emulsion stabilized by alkaline pH-shifting treated RPI was smaller than that stabilized by acid pH-shifting treated RPI. In addition, the RPI-10 stabilized emulsion showed a more uniform particle size distribution, which was explained by its high emulsifying activity and stability (EAI: 49.5 m²/g, ESI: 59.5 min). The interface rheology results showed that the alkaline pH-shifting treatment could promote the protein rearrangement and subsequently formed interface film with higher rate of protein penetration and rearrangement. The quantitative analysis of adsorbed proteins in the RPI-10 stabilized emulsion showed that glutelin-type isoforms as major proteins in RPI were increased at the oil-water interface for their balanced distribution of the hydrophilic and hydrophobic amino acid group. These quantitative and interfacial rheology analysis could improve deep understanding of the interfacial properties of pH-shifting treated RPI, and promote the development of application in grain protein stabilized emulsion.

Multiscale combined techniques for evaluating emulsion stability: A critical review

Emulsions are multiscale and thermodynamically unstable systems which will undergo various unstable processes over time. The behavior of emulsifier molecules at the oil-water interface and the properties of the interfacial film are very important to the stability of the emulsion. In this paper, we mainly discussed the instability phenomena and mechanisms of emulsions, the effects of interfacial films on the long-term stability of emulsions and summarized a set of systematic multiscale combined methods for studying emulsion stability, including droplet size and distribution, zeta-potential, the continuous phase viscosity, adsorption mass and thickness of the interfacial film, interfacial dilatational rheology, interfacial shear rheology, particle tracking microrheology, visualization technologies of the interfacial film, molecular dynamics simulation and the quantitative evaluation methods of emulsion stability. This review provides the latest research progress and a set of systematic multiscale combined techniques and methods for researchers who are committed to the study of oil-water interface and emulsion stability. In addition, this review has important guiding significances for designing and customizing interfacial films with different properties, so as to obtain emulsion-based delivery systems with varying stability, oil digestibility and bioactive substance utilization.

Light-dimerization telechelic alginate-based amphiphiles reinforced Pickering emulsion for 3D printing

Functional Pickering emulsions that depend on the interparticle interactions hold promise for building template materials. A novel coumarin-grafting alginate-based amphiphilic telechelic macromolecules (ATMs) undergoing photo-dimerization enhanced particle-particle interactions and changed the self-assembly behavior in solutions. The influence of self-organization of polymeric particles on the droplet size, microtopography, interfacial adsorption and viscoelasticity of Pickering emulsions were further determined by multi-scale methodology. Results showed that stronger attractive interparticle interactions of ATMs (post-UV) endowed Pickering emulsion with small droplet size (16.8 μm), low interfacial tension (9.31 mN/m), thick interfacial film, high interfacial viscoelasticity and adsorption mass, and well stability. The high yield stress, outstanding extrudability (n₁ < 1), high structure maintainability, and well shape retention ability, makes them ideal inks for direct 3D printing without any additions. The ATMs provides an increased capacity to produce stable Pickering emulsions with tailoring their interfacial performances and, providing a platform for fabricating and developing alginate-based Pickering emulsion-templated materials.

Characterization of Physicochemical Properties of Oil-in-Water Emulsions Stabilized by Tremella fuciformis Polysaccharides

In this paper, emulsions stabilized by Tremella fuciformis polysaccharides (TFP) were prepared and the physiochemical properties were assessed. Results showed that the TFP emulsions illustrated the highest emulsifying activity (EAI) and emulsifying stability (ESI) when the concentration of TFP and oil were 0.8% and 10% (wt%). The higher pH value was in favor of the emulsifying properties, while the addition of NaCl impaired the stability, and the greater the concentration, the lower the EAI and ESI. Besides, the emulsifying and rheological properties and stability analysis were evaluated in comparison with gum arabic, pectin, and carboxymethyl cellulose emulsions. It was discovered that TFP illustrated better storage and freeze-thaw stability, which was proved by the result of zeta-potential and particle size. The rheological measurement revealed that all the emulsions behaved as pseudoplastic fluids, while TFP displayed a higher viscosity. Meanwhile, TFP emulsions tended to form a more stable network structure according to the analysis of the parameters obtained from the Herschel–Bulkley model. FTIR spectra suggested that the O-H bond could be destructed without the formation of new covalent bonds during the emulsion preparation. Therefore, this study would be of great importance for the research of emulsions stabilized by TFP as a natural food emulsifier.

Thermal insulation and antibacterial foam templated from bagasse nanocellulose /nisin complex stabilized Pickering emulsion

Foam packaging with good thermal insulation and antibacterial properties is promising for cold chain delivery to strengthen food safety. This study reports a novel antibacterial foam with thermal insulation templated from bagasse nanocellulose complex particle-stabilised acrylate epoxy soybean oil (AESO) Pickering emulsions. Nanocellulose/nisin complex particles (N-CNFs) were prepared by loading positively charged nisin onto negatively charged cellulose nanofibrils via electrostatic interactions, that highly enhanced the stability of nanocellulose at the AESO/water interface and imparted the corresponding foam with good antibacterial properties. The results show that the porosity of the foam prepared with N-CNFs increased from 10.9% to 29.9% compared with that of the foam corresponding with bare nanocellulose; the thermal conductivity of the N-CNF foam decreased substantially from 0.431 W/m·K to 0.197 W/m·K. Moreover, the prepared foam exhibited good antibacterial activity, and its bacteriostatic rate against Listeria monocytogenes was 91.33%. The incorporation of antibacterial peptides into nanocellulose has enriched the study of the Pickering emulsion templating method for preparing multifunctional foam materials and is expected to broaden the application of nanocellulose in the field of food packaging.

Interfacial characteristics and in vitro digestion of emulsion coated by single or mixed natural emulsifiers: lecithin and/or rice glutelin hydrolysates

BACKGROUND

The interfacial characteristics and in vitro digestion of emulsion were related to emulsifier type. The mean droplet diameter, ζ-potential, microstructure, interfacial tension, Quartz crystal microbalance with dissipation (QCM-D) and in vitro gastrointestinal fate of emulsions stabilized by soybean lecithin, hydrolyzed rice glutelin (HRG) and their mixture were researched.

RESULTS

The value of interfacial tension was much more dramatically declined for the sample containing 20 g kg^-1 of HRG. For QCM-D, a rigid layer was formed for all the samples after rinsing. The layer thickness was 0.87 ± 0.20, 2.11 ± 0.31 and 2.63 ± 0.22 nm, and adsorbed mass was 87.17 ± 10.31, 210.56 ± 20.12 and 263.09 ± 23.23 ng cm^-2 , for HRG, lecithin and HRG/lecithin, respectively, indicating both HRG and lecithin were adsorbed at the oil-water interface. Structural rearrangements at the interface occurred for HRG/lecithin. The kinetics and final amount of lipid digestion depended on emulsifier type: lecithin > HRG/lecithin > HRG. These differences in digestion rate were primarily due to differences in the aggregation state of the emulsifiers.

CONCLUSION

The incorporation of lecithin into HRG emulsions had better interfacial properties comparing with HRG emulsion and facilitated lipid digestibility. These results provide important information for the rational design of plant-based functional food. © 2021 Society of Chemical Industry.

Optimization and Rheological Study of an Exopolysaccharide Obtained from Fermented Mature Coconut Water with Lipomyces starkeyi

The current research aimed to solve the environmental pollution of mature coconut water by Lipomyces starkeyi and provide a study of its high value utilization. The innovation firstly investigated the rheological properties and interface behavior of a crude exopolysaccharide and provided a technical support for its application in food. A response surface methodology was performed to ameliorate the fermentation factors of the new exopolysaccharide with mature coconut water as a substrate, and the consequences suggested that the maximum yield was 7.76 g/L under optimal conditions. Rotary shear measurements were used to study the influence of four variables on the viscosity of the exopolysaccharide solution. The results illustrated that the exopolysaccharide solution demonstrated a shear-thinning behavior and satisfactory thermal stability within the test range. The viscosity of the exopolysaccharide solution was significantly affected by ionic strength and pH; it reached the peak viscosity when the concentration of NaCl was 0.1 mol/L and the pH was neutral. The adsorption behavior of the exopolysaccharide at the medium chain triglyceride–water interface was investigated by a quartz crystal microbalance with a dissipation detector. The results demonstrated that the exopolysaccharide might form a multilayer adsorption layer, and the thickness of the adsorption layer was at its maximum at a concentration of 1.0%, while the interfacial film was the most rigid at a concentration of 0.4%. Overall, these results suggest that the exopolysaccharide produced by Lipomyces starkeyi is an excellent biomaterial for usage in drink, makeup and drug fabrications as a thickening and stabilizing agent.