The self-assembly, aggregation and phase transitions of food protein systems in one, two and three dimensions

Stabilizing interactions of casein microparticles after a thermal post-treatment

Casein microparticles from milk are important carrier materials for bioactive substances with stability and swelling properties that can be influenced by heat treatment. Microparticles produced by depletion flocculation and film drying remain stable in acidic media but swell and disintegrate under slightly alkaline conditions. Heat treatment after formation can stabilize the microparticles via a disulfide bridge network and newly formed hydrophobic contacts. Temperatures >60 °C are required so that denatured whey protein initiate formation of disulfide bridges via thiol exchange reactions. The particles then swell in a two-step process and exhibit an overshooting effect. If formation of disulphide bridges is prevented during heat treatment by adding N-methylmaleimide, overshooting swelling disappears and microparticles continue to expand instead. The analysis with parallel system dynamics models is based on the swelling of uncross-linked caseins, which is limited by the expansion capacity of cross-linked caseins.

Casein-based hydrogels: Advances and prospects

Casein-based hydrogels (Casein Gels) possess advantageous properties, including mechanical strength, stability, biocompatibility, and even adhesion, conductivity, sensing capabilities, as well as controlled-releasing behavior of drugs. These features are attributed to their gelation methods and functionalization with various polymers. Casein Gels is an important protein-based material in the food industry, in terms of dairy and functional foods, biological and medicine, in terms of carrier for bioactive and sensitive drugs, wound healing, and flexible sensors and wearable devices. Herein, this review aims to highlight the importance of the features mentioned above via a comprehensive investigation of Casein Gels through multiple directions and dimensional applications. Firstly, the composition, structure, and properties of casein, along with the gelation methods employed to create Casein Gels are elaborated, which serves as a foundation for further exploration. Then, the application progresses of Casein Gels in dairy products, functional foods, medicine, flexible sensors and wearable devices, are thoroughly discussed to provide insights into the diverse fields where Casein Gels have shown promise and utility. Lastly, the existing challenges and future research trends are highlighted from an interdisciplinary perspective. We present the latest research advances of Casein Gels and provide references for the development of multifunctional biomass-based hydrogels.

Interfacial mechanics of β-casein and albumin mixed protein assemblies at liquid-liquid interfaces

Protein emulsifiers play an important role in formulation science, from food product development to emerging applications in biotechnologies. The impact of mixed protein assemblies on surface composition and interfacial shear mechanics remains broadly unexplored, in comparison to the impact that formulation has on dilatational mechanics and surface tension or pressure. In this report, we use interfacial shear rheology to quantify the evolution of interfacial shear moduli as a function of composition in bovine serum albumin (BSA)/β-casein mixed assemblies. We present the pronounced difference in mechanics of these two protein, at oil interfaces, and observe the dominance of β-casein in regulating interfacial shear mechanics. This observation correlates well with the strong asymmetry of adsorption of these two proteins, characterised by fluorescence microscopy. Using neutron reflectometry and fluorescence recovery after photobleaching, we examine the architecture of corresponding protein assemblies and their surface diffusion, providing evidence for distinct morphologies, but surprisingly comparable diffusion profiles. Finally, we explore the impact of crosslinking and sequential protein adsorption on the interfacial shear mechanics of corresponding assemblies. Overall, this work indicates that, despite comparable surface densities, BSA and β-casein assemblies at liquid-liquid interfaces display almost 2 orders of magnitude difference in interfacial shear storage modulus and markedly different viscoelastic profiles. In addition, co-adsorption and sequential adsorption processes are found to further modulate interfacial shear mechanics. Beyond formulation science, the understanding of complex mixed protein assemblies and mechanics may have implications for the stability of emulsions and may underpin changes in the mechanical strength of corresponding interfaces, for example in tissue culture or in physiological conditions.

Platelet Membrane-Coated r-SAK Improves Thrombolytic Efficacy by Targeting Thrombus

Thrombolytic therapy is one of the most effective treatments for thrombus dissolution and recanalization of blocked vessels in thrombotic diseases. However, the application of the thrombolytic strategy has been limited due to unsatisfactory thrombolytic efficacy, relatively higher bleeding complications, and consequently restricted indications. Recombinant staphylokinase (r-SAK) is a third-generation thrombolytic agent produced by genetic engineering technology, which exhibits a better thrombolytic efficacy than urokinase and recombinant streptokinase. Inspired by the natural affinity of platelets in hemostasis and pathological thrombosis, we developed a platelet membrane (PM)-coated r-SAK (PM-r-SAK). Results from animal experiments and human in vitro studies showed that the PM-r-SAK had a thrombolytic efficacy equal to or better than its 4-fold dose of r-SAK. In a totally occluded rabbit femoral artery thrombosis model, the PM-r-SAK significantly shortened the initial recanalization time compared to the same dose and 4-fold dose of r-SAK. Regarding the recanalized vessels, the PM-r-SAK prolonged the time of reperfusion compared to the same dose and 4-fold dose of r-SAK, though the differences were not significant. An in vitro thrombolytic experiment demonstrated that the thrombolytic efficacy of PM-r-SAK could be inhibited by platelet-poor plasma from patients taking aspirin and ticagrelor. PM coating significantly improves the thrombolytic efficacy of r-SAK, which is related to the thrombus-targeting activity of the PM-r-SAK and can be inhibited by aspirin- and ticagrelor-treated plasma.

Role of the pea protein aggregation state on their interfacial properties

HYPOTHESIS

Plant protein ingredients from similar sources can vary in functionality not only because of compositional differences, but also because of differences in their structure depending on their processing history. It is essential to understand these distinctions to develop novel food emulsion using plant proteins. It is hypothesized that differing interfacial properties can be attributed to their structures, aggregation, and colloidal states.

EXPERIMENTS

The adsorption behavior of a commercial protein isolate, homogenized or non-homogenized, was compared to a mildly extracted isolate to evaluate the effect of aggregation state and structural differences. After characterization of the particle size and protein composition, the interfacial properties were compared.

FINDINGS

Atomic force microscopy provided evidence of interfaces packed with protein oligomers regardless of the treatment. Differences in adsorption kinetics and interfacial shear rheology depending on oil polarity suggested different interfacial structures. A polydisperse mixture of protein oligomers resulted in increased rearrangements and protein-protein interactions at the interface. Homogenization of commercial proteins resulted in a lower interfacial tension and less elastic interfaces compared to those of native proteins due to the presence of larger aggregates. This study highlights how the interfacial properties can be related to the protein aggregation state resulting from differences in processing history.

Food emulsions stabilized by proteins and emulsifiers: A review of the mechanistic explorations

The stability of food emulsions is the basis for other properties. During their production and processing, emulsions tend to become unstable due to their thermodynamic instability, and it is usually necessary to add emulsifiers and proteins to stabilize emulsions. It becomes crucial to study the intrinsic mechanisms of emulsifiers and proteins and their joint stabilization of food emulsions. This paper summarizes the research on intrinsic mechanisms of food emulsions stabilized by emulsifiers and proteins in recent years. The destabilization and stabilization of emulsions are related to the added surfactants. The properties, type, and concentration of emulsifiers determine the stability of emulsions, and the emulsifiers can be classified into different types (e.g., ionic or nonionic, solid or liquid) according to their properties and sources. The physicochemical properties of proteins (e.g., spatial conformation, hydrophobicity) and the composition of proteins can also determine the stability of emulsions, and emulsions stabilized by emulsifiers and proteins together not only depend on these factors but also have a great relationship with the mutual combination and competition between the two. The instability and stability of emulsions are related to factors such as interfacial interaction forces, the rheological nature of the interface, and the added surfactant.

Insights into the emulsification mechanism of the surfactant-like protein oleosin

Oleosins are proteins with a unique central hydrophobic hairpin designed to stabilize lipid droplets (oleosomes) in plant seeds. For efficient droplet stabilization, the hydrophobic hairpin with a strong affinity for the apolar droplet core is flanked by hydrophilic arms on each side. This gives oleosins a unique surfactant-like shape making them a very interesting protein. In this study, we tested if isolated oleosins retain their ability to stabilize oil-in-water emulsions, and investigated the underlying stabilization mechanism. Due to their surfactant-like shape, oleosins when dispersed in aqueous buffers associated to micelle-like nanoparticles with a size of ∼33 nm. These micelles, in turn, clustered into larger aggregates of up to 20 µm. Micelle aggregation was more extensive when oleosins lacked charge. During emulsification, oleosin micelles and micelle aggregates dissociated and mostly individual oleosins adsorbed on the oil droplet interface. Oleosins prevented the coalescence of the oil droplets and if sufficiently charged, droplet flocculation as well.

A Unified Description of Salt Effects on the Liquid-Liquid Phase Separation of Proteins

Protein aggregation via liquid-liquid phase separation (LLPS) is ubiquitous in nature and is intimately connected to many human diseases. Although it is widely known that the addition of salt has crucial impacts on the LLPS of proteins, full understanding of the salt effects remains an outstanding challenge. Here, we develop a molecular theory that systematically incorporates the self-consistent field theory for charged macromolecules into the solution thermodynamics. The electrostatic interaction, hydrophobicity, ion solvation, and translational entropy are included in a unified framework. Our theory fully captures the long-standing puzzles of the nonmonotonic salt concentration dependence and the specific ion effect. We find that proteins show salting-out at low salt concentrations due to ionic screening. The solubility follows the inverse Hofmeister series. In the high salt concentration regime, protein continues salting-out for small ions but turns to salting-in for larger ions, accompanied by the reversal of the Hofmeister series. We reveal that the solubility at high salt concentrations is determined by the competition between the solvation energy and translational entropy of the ion. Furthermore, we derive an analytical criterion for determining the boundary between the salting-in and salting-out regimes, which is in good agreement with experimental results for various proteins and salt ions.

Structural dependence of concentrated skim milk curd on micellar restructuring

This study was conducted to establish an understanding of how milk concentration modulates the rennet curd structure. Rennet-induced gelation and renneting under slow acidification achieved using glucono-δ-lactone (GDL) and structural properties of reconstituted skim milk gels at two concentration levels (9 and 25 % total solids) were studied by measuring variations in (a) viscoelastic behaviour, (b) micellar size, charge density, diffusivity, and (c) hydrophobicity using dynamic rheometry, dynamic light scattering and fluorimetry, respectively. Concentrated milk showed a greater estimated hydrodynamic radius of casein micelles, lower zeta (ζ)-potential, ratio of serum to total Calcium (Ca) and charge density and increased surface hydrophobicity, all supporting the view that micellar restructuring particularly sub-particle transfer takes place and contributes to rapid gelation. Moreover, hydrophobic interactions occurred very quickly (within 5 min in combined gels, 10 min for renneting only), demonstrating their pivotal role during the flocculation stage. All gels exhibited a solid viscoelastic character as the elastic modulus (G') was greater than loss modulus (G″) while both G' and tan δ (G''/G') were frequency-dependent. Frequency sweeps classified the concentrated gels into three stiffness categories caused by the level of rennet or GDL as rigid, hard and soft, whereas an increased flow-like behaviour (high tan δ), restricted diffusion and excessive water retention revealed limited structural rearrangements (contraction & macrosyneresis) during curd ageing. Acidification increased the diffusion rate in control curd, thus, enhanced contractive rearrangements, macrosyneresis and curd strength. Findings suggest that micellar restructuring induced by milk concentration is the principal modulator of the curd structure.

Characterizations of emulsion gel formed with the mixture of whey and soy protein and its protein digestion under in vitro gastric conditions

Partially replacing animal proteins with plant proteins to develop new products has much attention. To get knowledge of their application in emulsion gels, heat-induced composite protein emulsion gels were fabricated using the mixtures of whey protein isolate (WPI) and soy protein isolate (SPI) with the final total protein concentration of 10% (w/w). The water holding capacity (WHC), mechanical and rheological properties and microstructure of mixed protein emulsion gels prepared at different WPI to SPI ratios (100:0, 90:10, 70:30, 50:50, 30:70, 10:90, 0:100, w/w) were investigated. The ratios of WPI to SPI showed little effect on the WHC of the mixed protein emulsion gels (p > 0.05). Increasing the ratio of SPI decreased the hardness and storage modulus (G') of mixed protein emulsion gels, whereas the porosity of mixed protein emulsion gels in the microstructure increased, as shown by CLSM. Both β-lactoglobulin and α-lactalbumin from WPI and 7 S and 11 S from SPI participated in forming the gel matrix of mixed protein emulsion gels. More protein aggregates existed as the gel matrix filler at the high soy protein levels. Interestingly, the G' of mixed protein emulsion gels at the WPI to SPI ratio of 50:50 was higher than the sum of G' of individual WPI and SPI emulsion gels. The whey protein network predominated the gel matrix, while soy protein predominated in the active filling effect. When subjected to an in vitro dynamic gastric digestion model, soy protein in the gels (WPI:SPI = 50:50) degraded faster than whey protein during gastric digestion. This study provided new information on the characteristics of composite protein emulsion gel fabricated with the WPI and SPI mixture.

Stress-independent delay time in yielding of dilute colloidal gels

We investigate the yielding under shear for dilute poly(N-isopropyl acrylamide-co-fumaric acid) (PNIPAM-FAc) colloidal gels obtained above the volume phase transition temperature. In this temperature range, the microgel suspensions form colloidal gels due to hydrophobic interparticle interactions under appropriate pH and ionic strength conditions. Step-strain tests revealed that yielding occurs when the applied strain exceeds a specific threshold, requiring a finite, stress-independent delay time (tD). This is distinct from previous findings on delayed yielding in other colloidal gels, where tD decreases with increasing stress. In the start-up shear tests, yield strain (γy) at a higher strain rate () increases with escalating , while γy at lower  remains constant. This characteristic γy- relationship is successfully explained by a simple model using the stress-independent tD value without an adjustable fitting parameter. The distinctive yielding behavior, underscored by a stress-independent tD, is expected to originate from strain-induced macroscopic phase separation into a dense colloidal gel and water, observable separately from rheological measurements.

Interface-mediated protein aggregation

The aggregation of proteins at interfaces has significant roles and can also lead to dysfunction of different physiological processes. The interfacial effects on the assembly and aggregation of biopolymers are not only crucial for a comprehensive understanding of protein biological functions, but also hold great potential for advancing the state-of-the-art applications of biopolymer materials. Recently, there has been remarkable progress in a collaborative context, as we strive to gain control over complex interfacial assembly structures of biopolymers. These biopolymer structures range from the nanoscale to mesoscale and even macroscale, and are attained through the rational design of interactions between biological building blocks and surfaces/interfaces. This review spotlights the recent advancements in interface-mediated assembly and properties of biopolymer materials. Initially, we introduce the solid-liquid interface (SIL)-mediated biopolymer assembly that includes the inorganic crystalline template effect and protein self-adoptive deposition through phase transition. Next, we display the advancement of biopolymer assembly instigated by the air-water interface (AWI) that acts as an energy conversion station. Lastly, we discuss succinctly the assembly of biopolymers at the liquid-liquid interface (LLI) along with their applications. It is our hope that this overview will stimulate the integration and progression of the science of interfacial assembled biopolymer materials and surfaces/interfaces.

2D foam film coating of antimicrobial lysozyme amyloid fibrils onto cellulose nanopapers

Amyloid fibrils made from inexpensive hen egg white lysozyme (HEWL) are bio-based, bio-degradable and bio-compatible colloids with broad-spectrum antimicrobial activity, making them an attractive alternative to existing small-molecule antibiotics. Their surface activity leads to the formation of 2D foam films within a loop, similar to soap films when blowing bubbles. The stability of the foam was optimized by screening concentration and pH, which also revealed that the HEWL amyloid foams were actually stabilized by unconverted peptides unable to undergo amyloid self-assembly rather than the fibrils themselves. The 2D foam film was successfully deposited on different substrates to produce a homogenous coating layer with a thickness of roughly 30 nm. This was thick enough to shield the negative charge of dry cellulose nanopaper substrates, leading to a positively charged HEWL amyloid coating. The coating exhibited a broad-spectrum antimicrobial effect based on the interactions with the negatively charged cell walls and membranes of clinically relevant pathogens (Staphylococcus aureus, Escherichia coli and Candida albicans). The coating method presented here offers an alternative to existing techniques, such as dip and spray coating, in particular when optimized for continuous production. Based on the facile preparation and broad spectrum antimicrobial performance, we anticipate that these biohybrid materials could potentially be used in the biomedical sector as wound dressings.

Helicity degree of carrageenan conformation determines the polysaccharide and water interactions

The polysaccharide in solution at critical concentration, Cc (g/L), is assimilated to a nano hydrogel (nHG) made of a single polysaccharide chain. Taking as reference the characteristic temperature of 20 ± 2 °C at which kappa-carrageenan (κ-Car) nHG swelling is greater with a Cc = 0.55 ± 0.05 g/L, the temperature of the minimum deswelling in the presence of KCl was found at 30 ± 2 °C for 5 mM with a Cc = 1.15 ± 0.05 g/L but not measurable above 100 °C for 10 mM of which Cc = 1.3 ± 0.05 g/L. Lowering the temperature to 5 °C, contraction of the nHG and further coil-helix transition with self-assembly increases the sample's viscosity, which steadily evolves with time in a logarithmic scale. Accordingly, the relative increment of the viscosity per unit of concentration, R_v (L/g), should increase in agreement with increasing polysaccharide concentration. But the R_v decreases for κ-Car samples above 3.5 ± 0.5 g/L in the presence of 10 mM KCl under steady shear 15 s^-1. This reflects a decrease of κ-Car helicity degree knowing that the polysaccharide is rather hydrophilic when its helicity degree is the lowest.

Protein-Stabilized Emulsion Gels with Improved Emulsifying and Gelling Properties for the Delivery of Bioactive Ingredients: A Review

In today's food industry, the potential of bioactive compounds in preventing many chronic diseases has garnered significant attention. Many delivery systems have been developed to encapsulate these unstable bioactive compounds. Emulsion gels, as colloidal soft-solid materials, with their unique three-dimensional network structure and strong mechanical properties, are believed to provide excellent protection for bioactive substances. In the context of constructing carriers for bioactive materials, proteins are frequently employed as emulsifiers or gelling agents in emulsions or protein gels. However, in emulsion gels, when protein is used as an emulsifier to stabilize the oil/water interface, the gelling properties of proteins can also have a great influence on the functionality of the emulsion gels. Therefore, this paper aims to focus on the role of proteins' emulsifying and gelling properties in emulsion gels, providing a comprehensive review of the formation and modification of protein-based emulsion gels to build high-quality emulsion gel systems, thereby improving the stability and bioavailability of embedded bioactive substances.

The Characteristics of Whey Protein and Blueberry Juice Mixed Fermentation Gels Formed by Lactic Acid Bacteria

The properties of blueberry juice and whey protein gels formed by the mixed fermentation of L. plantarum 67 and L. paracasei W125 were investigated. The state of the gels, including the colour and surface morphology of the microspheres, showed significant changes with different fermentation times. The polyphenolic, flavonoid, and protein release of whey protein or combined blueberry juice fermented gels under in vitro digestion were investigated. The whey protein and blueberry juice fermented gels had more small pores, with a honeycomb structure, compared to whey protein fermented gels. The hardness of the gels was increased after fermentation for 7 h for the whey protein gels and whey protein mixture blueberry juice gels. The storage modulus and water-holding capacity of the gels were increased between fermentation times of 6 h and 8 h. The swelling rates of the whey protein gels fermented for 7 h and whey protein mixed blueberry juice gels fermented for 8 h and kept in pepsin-free simulated gastric fluid for 1 h had higher values. The release of polyphenols, flavonoids, and protein for the fermented gels was higher at fermentation of 7 h in the in vitro digestion experiment. We found that the chewiness of the whey protein gels, or whey protein mixed fermentation gels, was higher at a fermentation time of 7.5 h and 8 h. However, the cohesiveness values were not significantly different. Therefore, whey protein fermented gels and whey protein mixed blueberry juice fermented gels should be fermented for more than 7 h. This facilitates the release of polyphenols, flavonoids, and protein in the gastric juices.

Mechanical Properties, Microstructure, and In Vitro Digestion of Transglutaminase-Crosslinked Whey Protein and Potato Protein Hydrolysate Composite Gels

The production of animal protein usually leads to higher carbon emissions than that of plant protein. To reduce carbon emissions, the partial replacement of animal protein with plant protein has attracted extensive attention; however, little is known about using plant protein hydrolysates as a substitute. The potential application of 2 h-alcalase hydrolyzed potato protein hydrolysate (PPH) to displace whey protein isolate (WPI) during gel formation was demonstrated in this study. The effect of the ratios (8/5, 9/4, 10/3, 11/2, 12/1, and 13/0) of WPI to PPH on the mechanical properties, microstructure, and digestibility of composite WPI/PPH gels was investigated. Increasing the WPI ratio could improve the storage modulus (G') and loss modulus (G″) of composite gels. The springiness of gels with the WPH/PPH ratio of 10/3 and 8/5 was 0.82 and 0.36 times higher than that of the control (WPH/PPH ratio of 13/0) (p < 0.05). In contrast, the hardness of the control samples was 1.82 and 2.38 times higher than that of gels with the WPH/PPH ratio of 10/3 and 8/5 (p < 0.05). According to the International Organization for Standardization of Dysphagia Diet (IDDSI) testing, the composite gels belonged to food level 4 in the IDDSI framework. This suggested that composite gels could be acceptable to people with swallowing difficulties. Confocal laser scanning microscopy and scanning electron microscopy images illustrated that composite gels with a higher ratio of PPH displayed thicker gel skeletons and porous networks in the matrix. The water-holding capacity and swelling ratio of gels with the WPH/PPH ratio of 8/5 decreased by 12.4% and 40.8% when compared with the control (p < 0.05). Analysis of the swelling rate with the power law model indicated that water diffusion in composite gels belonged to non-Fickian transport. The results of amino acid release suggested that PPH improved the digestion of composite gels during the intestinal stage. The free amino group content of gels with the WPH/PPH ratio of 8/5 increased by 29.5% compared with the control (p < 0.05). Our results suggested that replacing WPI with PPH at the ratio of 8/5 could be the optimal selection for composite gels. The findings indicated that PPH could be used as a substitute for whey protein to develop new products for different consumers. Composite gels could deliver nutrients such as vitamins and minerals to develop snack foods for elders and children.

Photoactive Yellow Protein Adsorption at Hydrated Polyethyleneimine and Poly-l-Glutamic Acid Interfaces

Chiral and achiral vibrational sum-frequency generation (VSFG) spectroscopy was performed in the 1400-1700 and 2800-3800 cm^-1 range to study the interfacial structure of photoactive yellow protein (PYP) adsorbed on polyethyleneimine (PEI) and poly-l-glutamic acid (PGA) surfaces. Nanometer-thick polyelectrolyte layers served as the substrate for PYP adsorption, with 6.5-pair layers providing the most homogeneous surfaces. When the topmost material was PGA, it acquired a random coil structure with a small number of β₂-fibrils. Upon adsorption on oppositely charged surfaces, PYP yielded similar achiral spectra. However, the VSFG signal intensity increased for PGA surfaces with a concomitant redshift of the chiral C^α-H and N-H stretching bands, suggesting increased adsorption for PGA compared to PEI. At low wavenumbers, both the backbone and the side chains of PYP induced drastic changes to all measured chiral and achiral VSFG spectra. Decreasing ambient humidity led to the loss of tertiary structure with a re-orientation of α-helixes, evidenced by a strongly blue-shifted chiral amide I band of the β-sheet structure with a shoulder at 1654 cm^-1. Our observations indicate that chiral VSFG spectroscopy is not only capable of determining the main type of secondary structure of PYP, i.e., β-scaffold, but is also sensitive to tertiary protein structure.

Ultrathin Micellar Foam Films of Sodium Caseinate Protein Solutions

Sodium caseinates (NaCas), derived from milk proteins called caseins, are often added to food formulations as emulsifiers, foaming agents, and ingredients for producing dairy products. In this contribution, we contrast the drainage behavior of single foam films made with micellar NaCas solutions with well-established features of stratification observed for the micellar sodium dodecyl sulfate (SDS) foam films. In reflected light microscopy, the stratified SDS foam films display regions with distinct gray colors due to differences in interference intensity from coexisting thick-thin regions. Using IDIOM (interferometry digital imaging optical microscopy) protocols we pioneered for mapping nanotopography of foam films, we showed that drainage via stratification in SDS films proceeds by the expansion of flat domains that are thinner than surrounding by a concentration-dependent step-size, and nonflat features (nanoridges and mesas) form at the moving front. Furthermore, stratifying SDS foam films show stepwise thinning, such that the step-size and terminal film thickness decrease with concentration. Here we visualize the nanotopography in protein films with high spatiotemporal resolution using IDIOM protocols to address two long-standing questions. Do protein foam films formulated with NaCas undergo drainage via stratification? Are thickness transitions and variations in protein foam films determined by intermicellar interactions and supramolecular oscillatory disjoining pressure? In contrast with foam films containing micellar SDS, we find that micellar NaCas foam films display just one step, nonflat and noncircular domains that expand without forming nanoridges and a terminal thickness that increases with NaCas concentration. We infer that the differences in adsorbing and self-assembling unimers triumph over any similarities in the structure and interactions of their micelles.

Electrostatics-Induced Nucleated Conformational Transition of Protein Aggregation

Despite the wide existence of protein aggregation in nature and its intimate connection to many human diseases, the underlying mechanism remains unclear. Here, we develop a molecular theory by systematically incorporating the self-consistent field theory for charged macromolecules into the dilute solution thermodynamics. The kinetic pathway is tracked without any restriction on the morphology of the aggregates. We find that protein aggregation at low salt concentrations is via a two-step nucleated process involving a conformational transition from metastable spherical oligomer to elongated fibril. The scaling analysis elucidates the electrostatic origin of the conformational transition: the fibril enters the screening region much earlier than the spherical aggregate. As salt concentration increases, the classical mode of one-step nucleation corresponding to macroscopic liquid-liquid phase separation is recovered. Our results reveal that the screened electrostatic interaction is essential for the existence of the metastable oligomer and its subsequent conformational transition to fibril. The theoretical predictions of the kinetic pathway and the morphology of the aggregates are in good agreement with the experimental observations of real proteins.

Application of nanofibrous protein for the purification of contaminated water as a next generational sorption technology: a review

Globally, wastes from agricultural and industrial activities cause water pollution. Pollutants such as microbes, pesticides, and heavy metals in contaminated water bodies beyond their threshold limits result in several diseases like mutagenicity, cancer, gastrointestinal problems, and skin or dermal issues when bioaccumulated via ingestion and dermal contacts. Several technologies have been used in modern times to treat wastes or pollutants such as membrane purification technologies and ionic exchange methods. However, these methods have been recounted to be capital intensive, non-eco-friendly, and need deep technical know-how to operate thus, contributing to their inefficiencies and non-efficacies. This review work evaluated the application of Nanofibrils-protein for the purification of contaminated water. Findings from the study indicated that Nanofibrils protein is economically viable, green, and sustainable when used for water pollutant management or removal because they have outstanding recyclability of wastes without resulting in a secondary phase-pollutant. It is recommended to use residues from dairy industries, agriculture, cattle guano, and wastes from a kitchen in conjunction with nanomaterials to develop nanofibrils protein which has been recounted for the effective removal of micro and micropollutants from wastewater and water. The commercialization of nanofibrils protein for the purification of wastewater and water against pollutants has been tied to novel methods in nanoengineering technology, which depends strongly on the environmental impact in the aqueous ecosystem. So, there is a need to establish a legal framework for the establishment of a nano-based material for the effective purification of water against pollutants.

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.

Binary Hydrogels: Induction Methods and Recent Application Progress as Food Matrices for Bioactive Compounds Delivery-A Bibliometric Review

Food hydrogels are biopolymeric materials made from food-grade biopolymers with gelling properties (proteins and polysaccharides) and a 3D network capable of incorporating large amounts of water. They have sparked considerable interest because of their potential and broad application range in the biomedical and pharmaceutical sectors. However, hydrogel research in the field of food science is still limited. This knowledge gap provides numerous opportunities for implementing their unique properties, such as high water-holding capacity, moderated texture, compatibility with other substances, cell biocompatibility, biodegradability, and high resemblance to living tissues, for the development of novel, functional food matrices. For that reason, this article includes a bibliometric analysis characterizing research trends in food protein-polysaccharide hydrogels (over the last ten years). Additionally, it characterizes the most recent developments in hydrogel induction methods and the most recent application progress of hydrogels as food matrices as carriers for the targeted delivery of bioactive compounds. Finally, this article provides a future perspective on the need to evaluate the feasibility of using plant-based proteins and polysaccharides to develop food matrices that protect nutrients, including bioactive substances, throughout processing, storage, and digestion until they reach the specific targeted area of the digestive system.

Polymorphic protein phase transitions driven by surface anisotropy

Phase transitions of proteins are strongly influenced by surface chemical modifications or mutations. Human γD-crystallin (HGD) single-mutants have been extensively studied because they are associated with the onset of juvenile cataract. However, they have also provided a rich library of molecules to examine how specific inter-protein interactions direct protein assembly, providing new insights and valuable experimental data for coarse-grained patchy-particle models. Here, we demonstrate that the addition of new inter-protein interactions by mutagenesis is additive and increases the number and variety of condensed phases formed by proteins. When double mutations incorporating two specific single point mutations are made, the properties of both single mutations are retained in addition to the formation of a new condensed phase. We find that the HGD double-mutant P23VC110M self-assembles into spherical particles with retrograde solubility, orthorhombic crystals, and needle/plate shape crystals, while retaining the ability to undergo liquid-liquid phase separation. This rich polymorphism is only partially predicted by the experimental data on the constituent single mutants. We also report a previously un-characterized amorphous protein particle, with unique properties that differ from those of protein spherulites, protein particulates previously described. The particles we observe are amorphous, reversible with temperature, tens of microns in size, and perfectly spherical. When they are grown on pristine surfaces, they appear to form by homogeneous nucleation, making them unique, and we believe a new form of protein condensate. This work highlights the challenges in predicting protein behavior, which has frustrated rational assembly and crystallization but also provides rich data to develop new coarse-grained models to explain the observed polymorphism.

Platelet Membrane Cloaked Nanotubes to Accelerate Thrombolysis by Thrombus Clot-Targeting and Penetration

Thrombotic diseases have a high rate of mortality and disability, and pose a serious threat to global public health. Currently, most thrombolytic drugs especially protein drugs have a short blood-circulation time, resulting in low thrombolytic efficiency. Therefore, a platelet membrane (Pm) cloaked nanotube (NT-RGD/Pm) biomimetic delivery system with enhanced thrombolytic efficiency is designed. Nanotubes (NT) with an excellent clot-penetration properties are used to load a protein thrombolytic drug urokinase (Uk). Platelet-targeting arginine glycine-aspartic peptide (RGD) is grafted onto the surface of the nanotubes (NT-RGD) prior to cloaking. Multiple particle tracking (MPT) technique and confocal laser scanning microscope (CLSM) analysis are applied and the results show that the nanotubes possess a strong penetration and diffusion capacity in thrombus clots. After the Pm cloaking on NT-RGD/Uk, it shows a thrombus microenvironmental responsive release property and the half-life of Uk is six times longer than that of free Uk. Most importantly, NT-RGD-Uk/Pm exhibits a 60% thrombolytic efficiency in the FeCl₃ -induced thrombosis mouse model, and it is able to significantly reduce the bleeding side effects of Uk. This Pm-cloaked nanotube system is an effective and promising platform for the controlled and targeted delivery of drugs for the thrombus treatment.

Shear induced tuning and memory effects in colloidal gels of rods and spheres

Shear history plays an important role in determining the linear and nonlinear rheological response of colloidal gels and can be used for tuning their structure and flow properties. Increasing the colloidal particle aspect ratio lowers the critical volume fraction for gelation due to an increase in the particle excluded volume. Using a combination of rheology and confocal microscopy, we investigate the effect of steady and oscillatory preshear history on the structure and rheology of colloidal gels formed by silica spheres and rods of length L and diameter D (L/D = 10) dispersed in 11 M CsCl solution. We use a non-dimensional Mason number, Mn (=F_visc./F_attr.), to compare the effect of steady and oscillatory preshear on gel viscoelasticity. We show that after preshearing at intermediate Mn, attractive sphere gel exhibits strengthening, whereas attractive rod gel exhibits weakening. Rheo-imaging of gels of attractive rods shows that at intermediate Mn, oscillatory preshear induces large compact rod clusters in the gel microstructure, compared to steady preshear. Our study highlights the impact of particle shape on gel structuring under flow and viscoelasticity after shear cessation.

Functional Coating from Amyloid Superwetting Films

Tailoring the hydrophilicity of solid surfaces with a strong affinity to water has been extensively explored in the last 20 years, but studies have been limited to the single function of wettability. Here, the multifunctional properties of tailored surface films are extended from exhibiting superwettability to facilitating biological activities. It is shown that amyloid fibrils can be universally coated onto various substrates, such as fabrics (non-woven organic masks), metal meshes, polyethersulfone (PES), glass, and more, endowing the resulting surfaces with excellent performance in oil/water mixture and emulsion separation, antifouling, and antifogging. Moreover, the biocompatible crosslinked amyloid fibril coatings can serve as a platform for biocatalytic activities by immobilizing enzymes, as shown in the 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt (ABTS) oxidation and Reactive Black 5 (RB5) degradation by laccase from Trametes versicolor. The study provides a universal approach to modifying surface morphology and chemical properties via fibrous protein templates, opening the way to unexplored bio-based applications and functionalities.

Hydrogels as promising carriers for the delivery of food bioactive ingredients

The burden of public health challenges associated with the western dietary and living style is growing. Nutraceuticals have been paid increasing attentions due to their effects in promotion of health. However, in the gastrointestinal (GI) tract, the nutraceuticals suffer from not only the harsh acidic environment of the stomach and a variety of digestive enzymes, but also the antibacterial activity of intestinal bile salts and the action of protease from the gut microbiota. The amount of the nutraceuticals arriving at the sites in GI tract for absorption or exerting the bioactivities is always unfortunately limited, which puts forward high requirements for protection of nutraceuticals in a certain high contents during oral consumption. Hydrogels are three-dimensional polymeric porous networks formed by the cross-linking of polymer chains, which can hold huge amounts of water. Compared with other carries with the size in microscopic scale such as nanoparticle and microcapsules, hydrogels could be considered to be more suitable delivery systems in food due to their macroscopic bulk properties, adjustable viscoelasticity and large spatial structure for embedding nutraceuticals. Regarding to the applications in food, natural polymer-based hydrogels are commonly safe and popular due to their source with the appealing characteristics of affordability, biodegradability and biocompatibility. Although chemical crosslinking has been widely utilized in preparation of hydrogels, it prefers the physical crosslinking in the researches in food. The reasonable design for the structure of natural polymeric hydrogels is essential for seeking the favorable functionalities to apply in the delivery system, and it could be possible to obtain the enhanced adhesive property, acid stability, resistant to bile salt, and the controlled release behavior. The hydrogels prepared with proteins, polysaccharides or the mix of them to deliver the functional ingredients, mainly the phenolic components, vitamins, probiotics are discussed to obtain inspiration for the wide applications in delivery systems. Further efforts might be made in the in situ formation of hydrogels in GI tract through the interaction among food polymers and small-molecular ingredients, elevation of the loading contents of nutraceuticals in hydrogels, development of stomach adhesive hydrogels as well as targeting modification of gut microbiota by the hydrogels.

Association of two polyelectrolytes in salt solutions

The association of polyelectrolytes (PEs) in solution affects a wealth of structural and dynamic behaviors, and is also fundamentally important for an understanding of protein association and aggregation. Here, we theoretically study the association of two PE chains by addressing the stability and morphology of the non-spherical associates. Our theory predicts that an elongated pearl-necklace (PN) associate can be stable at high salt concentrations due to the screened electrostatic repulsion. This contradicts the implication of scaling theory. In addition, there is no one-to-one correspondence between the morphology of the associate and its constituting unimers, which is demonstrated by the existence of different association modes.

Advances in Protein-Based Nanocarriers of Bioactive Compounds: From Microscopic Molecular Principles to Macroscopical Structural and Functional Attributes

Many proteins can be used to fabricate nanocarriers for encapsulation, protection, and controlled release of nutraceuticals. This review examined the protein-based nanocarriers from microscopic molecular characteristics to the macroscopical structural and functional attributes. Structural, physical, and chemical properties of protein-based nanocarriers were introduced in detail. The spatial size, shape, water dispersibility, colloidal stability, etc. of protein-based nanocarriers were largely determined by the molecular physicochemical principles of protein. Different preparative techniques, including antisolvent precipitation, pH-driven, electrospray, and gelation methods, among others, can be used to fabricate different protein-based nanocarriers. Various modifications based on physical, chemical, and enzymatic approaches can be used to improve the functional performance of these nanocarriers. Protein is a natural resource with a wide range of sources, including plant, animal, and microbial, which are usually used to fabricate the nanocarriers. Protein-based nanocarriers have many advantages in aid of the application of bioactive ingredients to the medical, food, and cosmetic industries.

Microgels as globular protein model systems

Understanding globular protein adsorption to fluid interfaces, their interfacial assembly, and structural reorganization is not only important in the food industry, but also in medicine and biology. However, due to their intrinsic structural complexity, a unifying description of these phenomena remains elusive. Herein, we propose N-isopropylacrylamide microgels as a promising model system to isolate different aspects of adsorption, dilatational rheology, and interfacial structure at fluid interfaces with a wide range of interfacial tensions, and compare the results with the ones of globular proteins. In particular, the steady-state spontaneously-adsorbed interfacial pressure of microgels correlates closely to that of globular proteins, following the same power-law behavior as a function of the initial surface tension. However, the dilatational rheology of spontaneously-adsorbed microgel layers is dominated by the presence of a loosely packed polymer corona spread at the interface, and it thus exhibits a similar mechanical response as flexible, unstructured proteins, which are significantly weaker than globular ones. Finally, structurally, microgels reveal a similar spreading and flattening upon adsorption as globular proteins do. In conclusion, microgels offer interesting opportunities to act as powerful model systems to unravel the complex behavior of proteins at fluid interfaces.

Nonlinear dilatational rheology of different protein aggregates at the oil-water interface

Proteins tend to self-assemble into different morphological aggregates such as nanoparticles or fibrils during heat treatment depending on the processing conditions. The protein aggregates exhibit excellent interfacial activity and even better ability to stabilize emulsions than native proteins. The interfacial rheological properties at the oil-water interface play a very important role in emulsion stability, among which the interfacial nonlinear rheology is closely related to their ability to resist large perturbation. However, there are very few studies reporting the nonlinear interfacial rheological behavior of protein aggregates at the oil-water interface. In this study, β-lactoglobulin fibrous aggregates (F) and nanoparticle aggregates (NP) were prepared, and the adsorption kinetics and dilatational nonlinear rheological behavior of β-lactoglobulin aggregates at the oil-water interface under large amplitude deformation were studied using a pendant drop tensiometer, and compared with those of native proteins. From the adsorption experiments, the adsorption of protein aggregates, especially fibrils, was faster than that of native proteins in the early stage, while in the late stage, the native proteins displayed a significantly higher degree of rearrangement than the fibrils. The surface hydrophobicity and the short fibrils present mainly determine the properties of the fibril interface, while the behavior of the nanoparticle interface was significantly influenced by the size and charge properties of the nanoparticles. From the dilatational experiment, the Lissajous plots revealed that the F interface at all pHs evaluated and the βlg interface at pH 5.8 displayed strain softening in both expansion and compression processes, while the NP interface at all pHs and βlg interface at pH 2 and pH 7 displayed strain softening in expansion and strain hardening in compression processes. The nonlinear response of the protein aggregates at the oil-water interface was more obvious at pH 5.8. The modulus change from frequency sweeps revealed that the fibril interface was strong but not very structured in contrast to that formed by the native proteins which displays high structuration although weak in strength, whereas the strength of the interface formed by protein nanoparticles is in between, but more sensitive to the surface charge.

Electric-field induced modulation of amorphous protein aggregates: polarization, deformation, and reorientation

Proteins in their native state are only marginally stable and tend to aggregate. However, protein misfolding and condensation are often associated with undesired processes, such as pathogenesis, or unwanted properties, such as reduced biological activity, immunogenicity, or uncontrolled materials properties. Therefore, controlling protein aggregation is very important, but still a major challenge in various fields, including medicine, pharmacology, food processing, and materials science. Here, flexible, amorphous, micron-sized protein aggregates composed of lysozyme molecules reduced by dithiothreitol are used as a model system. The preformed amorphous protein aggregates are exposed to a weak alternating current electric field. Their field response is followed in situ by time-resolved polarized optical microscopy, revealing field-induced deformation, reorientation and enhanced polarization as well as the disintegration of large clusters of aggregates. Small-angle dynamic light scattering was applied to probe the collective microscopic dynamics of amorphous aggregate suspensions. Field-enhanced local oscillations of the intensity auto-correlation function are observed and related to two distinguishable elastic moduli. Our results validate the prospects of electric fields for controlling protein aggregation processes.