Regulation mechanism of ionic strength on the ultra-high freeze-thaw stability of myofibrillar protein microgel emulsions

Magnetic fields improve the gel properties of myofibrillar proteins in low-salt myofibrillar protein emulsion systems

The effect of magnetic field on the properties of emulsified gels containing myofibrillar protein (MP-emulsified gels) with different salt concentration (0, 0.2, 0.4, 0.6 mol/L) were investigated. The results demonstrated that the magnetic field treatment (4 °C, 3.8 mT, 3 h) made the emulsion droplets smaller and more uniform. At the same time, the magnetic field treatment improved the gel strength and WHC (water holding capacity) of MP-emulsified gels by 88.89 % and 3.5 % at 0.2 mol/L NaCl, and it also ameliorated the network structure of emulsified gel. Raman spectra showed that magnetic field treatment induced the transformation of β-structure into α-helix structure in MP-emulsified gel. Under high salt conditions (0.4 mol/L ∼ 0.6 mol/L), the magnetic field promoted the exposure of aliphatic residues in the tertiary structure and influences the hydrophobic interaction between molecules. In conclusion, Magnetic field treatment (4 °C, 3.8 mT, 3 h) improved MP-emulsified gels properties, offering a promising strategy for low-salt meat products.

Collaborative stabilizing effect of trehalose and myofibrillar protein on high internal phase emulsions: Improved freeze-thaw stability and 3D printability

This study investigated the improvement of adding trehalose (Tre) on freeze-thaw (F-T) stability and 3D printability of myofibrillar protein (MP)-based high internal phase emulsions (HIPEs), also the underlying mechanism. Appropriate Tre addition formed thicker shell-like structure around MP by hydrogen bonds, and induced protein unfolding to ameliorate amphiphilicity. Additionally, Tre promoted the MP diffusion to interface to reduce interfacial tension. After interface saturation, Tre inducing MP rearrangement contributed more to form compact interface layer. Larger interface coverage increased hydrophobic interactions between droplets, constructing stronger MP-Tre-HIPEs gel network, inhibiting more free water to form ice crystals, confirmed by reduced destabilization index and freezing point. Such gel network enhanced their own viscoelasticity and thixotropic recovery, exhibiting superior printing accuracy. Conversely, excessive Tre aggregates (15 %-20 %) competed with MP for interfacial adsorption and filled between interfacial layer of adjacent droplets, weakening gel network. These findings expanded MP-HIPEs high-value application in frozen-foods and 3D printing.

Structure-property relationship of pea protein microgels as fat analogues in Pickering oil-in-water emulsions: effect of salt addition

BACKGROUND

The design of plant-based microgels provides a platform for food ingredients to enhance palatability and functionality. This work aimed to explore the modifying effect of salt addition (KCl) on the structure of pea protein microgel particles (PPI MPs), on the interfacial adsorption and characteristics of formed emulsions as fat analogues.

RESULTS

Salt addition (0-200 mmol L-1) promoted a structural transformation from α-helix to β-sheet, increased the surface hydrophobicity (from 1160.8 to 2280.7), and increased the contact angle (from 56.73° to 96.47°) of PPI MPs. The electrostatic shielding effect led to the tighter packing of MPs with irregular structures and lowered the adsorption energy barrier. Notably, salt-treated PPI MPs could adjust their adsorption state at the interface. The discernible adsorption of PPI MPs with 200 mmol L-1 salt addition that possessed enhanced anti-deformation ability dominated the interfacial stabilization, whereas a relatively rougher stretched continuous interfacial film formed after spreading and deformation of 0 mmol L-1 MPs. A tribological test suggested that emulsion stabilized by MPs at 0 (0.0053) and 80 mmol L-1 (0.0068) had similar friction coefficients to commercial mayonnaise (0.0058), whereas a higher salt concentration (200 mmol L-1) lowered its oral sensation due to the adsorption layer and enhanced the resistance to droplet coalescence during oral processing.

CONCLUSION

Salt could be a modifier to tune the structure of microgels, and further promote the formation and attributes of emulsions. This study would improve application attributes of PPI MPs in the design of realistic fat analogues. © 2024 Society of Chemical Industry.

Freeze-thaw stability of high-internal-phase emulsion stabilized by chickpea protein microgel particles and its application in surimi

BACKGROUND

Future applications of high-internal-phase emulsions (HIPEs) are highly regarded, but poor freeze-thaw stability limits their utilization in frozen products. This study aimed to characterize the structure of chickpea protein microgel particles (HCPI) induced by NaCl and to assess its impact on the freeze-thaw stability of HIPEs.

RESULTS

The results showed that NaCl induction (0-400 mmol L-1) increased the surface hydrophobicity (175.9-278.9) and interfacial adsorbed protein content (84.9%-91.3%) of HCPI. HIPEs prepared with HCPI induced by high concentration of NaCl exhibited superior flocculation index and centrifugal stability, and their freeze-thaw stability was better than that of natural chickpea protein. The increase in NaCl concentration reduced the droplet aggregation and coalescence index of the freeze-thaw emulsions, diminishing the precipitation of oil from the emulsion. Linear and nonlinear rheology showed that the strengthened gel structure (higher G' values) restricted water flow and counteracted the damage to the interfacial film by ice crystals at 100-400 mmol L-1 NaCl, thus improving the viscoelasticity of the freeze-thaw emulsions. Finally, the thawing loss of surimi gel with HCPI-200 HIPE was reduced by 2.04% compared to directly adding oil.

CONCLUSION

This study provided a promising strategy to improve the freeze-thaw stability of HIPEs and reduce the thawing loss of frozen products. © 2024 Society of Chemical Industry.

Characteristics and stabilization of Pickering emulsions constructed using myosin from bighead carp (Aristichthys nobilis)

Myosin from bighead carp (Aristichthys nobilis) as a main type of fish protein possesses a good emulsifying ability. However, whether bighead carp myosin (BCM) could construct stable Pickering emulsions is still unclear. Therefore, myosin particles and Pickering emulsions stabilized by bighead carp myosin (BCMPEs) were analyzed. The surface structure of BCM particles at 0.6 mol/L NaCl treatment was uniform and compact with a contact angle of 86.4 ± 2.7°, exhibiting the potential ability to construct O/W Pickering emulsions. The size and flocculation index (FI) of BCMPEs decreased with the increase in BCM concentrations of 1%-4% (w/v). Reversely, the size of BCMPEs increased with the increase in oil-water ratios. BCM particles could uniformly distribute at the oil-water interface to stabilize BCMPEs at a BCM concentration of 4% (w/v) and an oil-water ratio of 6:4 (v/v). This study could help explore fish proteins to construct Pickering emulsions for the deep processing of fish products.

A novel Pickering emulsion gels stabilized by cellulose nanofiber/dihydromyricetin composite particles: Microstructure, rheological behavior and oxidative stability

Particle concentrations (w) and oil content (Φ) are crucial factors influencing the gel stability of Pickering emulsions. To understand the stabilization mechanism comprehensively, we prepared emulsion gels stabilized by CNF/DMY composite particles at various w (0.5-1.5 wt%) and Φ (0.2-0.6, v/v). The microstructure revealed the adsorption of these particles at the oil-water interface, with excess particles forming a three-dimensional network structure in the continuous phase. Rheological studies showed that the network structure of Pickering emulsions was significantly influenced by w and Φ, resulting in improved emulsion gel strength that hindered the movement of oil droplets and oxygen in the continuous phase, thereby enhancing emulsion stability. Three scenarios for the critical strain (γco) were observed: at Φ = 0.2, γco decreased with increasing w, while at Φ = 0.4, γco increased with increasing w. At Φ = 0.6, γco remained relatively constant regardless of w. In conclusion, adjusting particle concentration and oil content enabled the control of microstructure, rheological properties, and antioxidant capacity of emulsion gels. These findings could be a valuable resource for formulating and ensuring the quality of emulsion gel-based products in the food industry.

Herbal small molecule-based low/medium internal phase supramolecular gel emulsion for diabetic wound healing

It remains a big challenge to fabricate low / medium internal phase gel emulsion for the safe wound dressing with low stimulation to the skin. Herein, utilizing the self-assembly and gelation of amphiphilic herbal small molecule-glycyrrhizic acid (GA) derived from traditional Chinese medicine, a new type of supramolecular gel emulsion (SGE) with antibacterial activity and low / medium internal phase was proposed. In the SGE, the oil droplets were stabilized by the nanofibers self-assembled from GA, and the SGE was formed by the supramolecular assembly of GA nanofibers in the presence of Pickering emulsions. As a result, under low / medium internal phase (φ = 30-50 %), SGEs could be readily prepared. Antibacterial tests demonstrated that the growth of gram-positive Staphylococcus aureus (S. aureus) and gram-negative Escherichia coli (E. coli) could be effectively inhibited by the SGE. Additionally, compared to high internal phase SGE, SGE with φ = 50 % displayed lower cytotoxicity and a positive impact on the healing process of infectious diabetic wounds. This work provided a novel approach for constructing low / medium internal phase gel emulsion via herbal small molecule-based supramolecular assembly.

Carrageenan-induced conjugated oat protein isolate microgel particles as structure modulators in fat analogues and their digestion behaviors

HYPOTHESIS

Engineering plant-based microgel particles (MPs) at a molecular scale is meaningful to prepare functional fat analogues. We hypothesize that oat protein isolate (OPI) and κ-carrageenan (CA) have synergy in MPs formation, using MPs with controllable structure, and further to fabricate fat analogues with adjustable characteristics is feasible. Their digestion fate will also be possibly modulated by interfacial coatings.

EXPERIMENTS

OPI-based conjugated MPs with tunable rigidities by changing crosslinking densities were designed. The relationship between microgel structures, and emulsion gel properties was explored through spectroscopy, microstructure, rheology and tribology. The delivery to lycopene, as well as inhibiting digestion behaviors of fat analogues was evaluated in a simulated gastro-intestinal tract.

FINDINGS

The rigidity of conjugated MPs could be tailored to optimize the performance of fat analogues. OPI-1 %CA MPs could stabilize emulsions up to 95 % oil fraction with fine texture. Tribological behaviors had a dependence on microgel elasticity and interfacial coatings, medium hard MP-stabilized emulsion was less disrupted without coalescence after oral processing. Digestion was delayed by denser and harder MPs by softening the interfacial particle layer or limiting lipase accessibility. Softer conjugated MPs possessed better flexibility and were broken down more easily leading to a higher rate of lipid digestion.

Influences of carboxymethyl chitosan upon stabilization and gelation of O/W Pickering emulsions in the presence of inorganic salts

The objective of this study was to investigate the effects of carboxymethyl chitosan (CMCS) on the stabilization and gelation of oil-in-water (O/W) Pickering emulsions (PEs) with polyphenol-amino acid particles in the presence of inorganic salts. The results revealed that the CMCS-induced depletion interactions contributed to improving the emulsification ability and interfacial adsorption efficiency of polyphenol-amino acid particles as well as constructing the network structures in the continuous phase. These relevant changes collectively resulted in elevating stability, viscosity and moduli of PEs. The additional effects of different inorganic salts with varying additions were further investigated, and the addition-dependent phenomena were observed. At low additions of inorganic salts, the occurrence of the chelation of inorganic salts with CMCS consolidated the constructed network structure, favorable to the gelation of PEs. With increasing additions, this chelation effect became stronger which compromised the CMCS-induced depletion, gradually leading to destabilization of PEs. In terms of ion species, the more pronounced effect on emulsion stability was achieved with calcium ions than with potassium and iron ions. This study expects to provide a new perspective on the extending application of cationic CMCS for improving the stability of O/W PEs in the food industry.

Pickering emulsion with high freeze-thaw stability stabilized by xanthan gum/lysozyme nanoparticles and konjac glucomannan

In this study, freeze-thaw cycle experiments were conducted on food-grade Pickering emulsions co-stabilized with konjac glucomannan (KGM) and xanthan gum/lysozyme nanoparticles (XG/Ly NPs). The rheological properties, particle size, flocculation degree (FD), coalescence degree (CD), centrifugal stability, Differential scanning calorimetry (DSC), X-ray diffraction (XRD) and microstructure of Pickering emulsion stabilized by KGM before and after freeze-thaw were characterized. It was found that as the concentration of KGM increased, the flocculation degree (FD) and coalescence degree (CD) of the emulsion decreased after the freeze-thaw cycle compared to the control sample, and the microscopic images showed that the droplets became smaller and less affected by the freeze-thaw cycles. The rheological and water-holding properties also confirmed that the KGM-added emulsions still had a strong gel network structure and prevented the separation of the continuous and dispersed phases of the droplets after freezing and thawing. Freeze-thaw treatments had a negative effect on the stable emulsion of XG/Ly NPs, while the addition of KGM improved the freeze-thaw stability of the emulsion, which provided a theoretical basis for the development of emulsion products with high freeze-thaw stability.

Effect of NaCl concentration on the formation of high internal phase emulsion based on whey protein isolate microgel particles

At present, the effect of structural modification of microgel particles on high internal phase emulsions (HIPEs) is less studied. In this study, the structural modification effect of NaCl on whey protein isolate microgels (WPIMPs) was comprehensively characterized and applied to the construction of HIPEs. WPIMPs were prepared with NaCl (0-150 mM) and the structural changes were analyzed by measuring the particle size, Zeta-potential, and endogenous fluorescence spectra. The results showed that inducing WPIMPs by NaCl enhanced the surface hydrophobicity, decreased the Zeta potential, and elevated the degree of cross-linking. The interfacial behavior of WPIMPs was characterized by measuring interfacial tensions and adsorbed layer properties. The results showed that NaCl induction decreased the interfacial tension, increased the thickness of the adsorbed layer, and improved the viscoelasticity. The HIPEs were analyzed for micromorphology and particle sizes. The results indicated that NaCl-induced WPIMPs favored the formation of HIPEs with small particle sizes and provided HIPEs with superior environmental stability. This study provides a new idea for the structural modification of microgels and a new theoretical basis for the construction conditions of HIPE.

Evaluation of the Emulsifying Property and Oxidative Stability of Myofibrillar Protein-Diacylglycerol Emulsions Containing Catechin Subjected to Different pH Values

Myofibrillar protein-diacylglycerol emulsions containing catechin (MP-DAG-C) possess outstanding emulsifying property and oxidative stability. However, the effect of pH on MP-DAG-C emulsions should be revealed to provide possibilities for their application in practical meat products. Therefore, MP-DAG-C emulsions at different pH values were used in this study, in which lard, unpurified glycerolytic lard (UGL), and purified glycerolytic lard (PGL) were used as the oil phases. The results indicated that the emulsifying property of the UGL- and PGL-based emulsions increased compared to those of the lard-based emulsions (p < 0.05). The emulsifying activity and stability indices, absolute value of ζ-potential, and rheological characteristics increased with the increase in pH values (p < 0.05), with the droplets were smallest and distributed most uniformly at a pH of 6.5 compared to the other acidic environment (p < 0.05). The thiobarbituric acid substance and carbonyl content increased (p < 0.05), while the total sulfydryl content decreased (p < 0.05) during storage. However, there was no statistical difference between the oxidative stability of the MP-DAG-C emulsions with different pH values (p > 0.05). The results implied that the emulsifying property of MP-DAG-C emulsions increased with an increase in pH values. The oxidative stability of the MP-DAG-C emulsions at high pH values was improved by catechin.

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.