Manipulating interfacial behavior and emulsifying properties of myosin through alkali-heat treatment

The influence of pH-ultrasonic-induced myofibrillar protein conformation of Penaeus vannamei (Litopenaeus vannamei) on emulsification and digestion characteristics of fish oil oleogel-based emulsions

pH-induced and ultrasound treatment can both adjust spatial conformation to improve the interfacial stability, and fish oil oleogel could be used to enhance oil binding capacity. The relationship between stabilization mechanism and lipid digestion was revealed, considering the protein conformation and interfacial characteristics. The results showed that pH-ultrasonic-induced myofibrillar proteins (MPs) at pH 7.0 had higher interfacial adsorption capacity and surface hydrophobicity as well as more stable secondary structures, which lowered the particle size and enhanced the interfacial stability. In the stomach, the particle size increased along with the decrease in electrostatic repulsion, and β-sheets significantly increased, which promoted aggregation and flocculation. In the small intestine, the reduction of β-sheets favored the interfacial replacement and facilitated the lipid digestion. Therefore, pH-ultrasonic-modified method improved the structure and function of MPs, facilitated the interfacial stability and intestinal digestion.

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.

Advances of protein-based emulsion gels as fat analogues: Systematic classification, formation mechanism, and food application

Fat plays a pivotal role in the appearance, flavor, texture, and palatability of food. However, excessive fat consumption poses a significant risk for chronic ailments such as obesity, hypercholesterolemia, and cardiovascular disease. Therefore, the development of green, healthy, and stable protein-based emulsion gel as an alternative to traditional fats represents a novel approach to designing low-fat food. This paper reviews the emulsification behavior of proteins from different sources to gain a comprehensive understanding of their potential in the development of emulsion gels with fat-analog properties. It further investigates the emulsifying potential of protein combined with diverse substances. Then, the mechanisms of protein-stabilized emulsion gels with fat-analog properties are discussed, mainly involving single proteins, proteins-polysaccharides, as well as proteins-polyphenols. Moreover, the potential applications of protein emulsion gels as fat analogues in the food industry are also encompassed. By combining natural proteins with other components such as polysaccharides, polyphenols, or biopolymers, it is possible to enhance the stability of the emulsion gels and improve its fat-analog texture properties. In addition to their advantages in protecting oil oxidation, limiting hydrogenated oil intake, and delivering bioactive substances, protein-based emulsion gels have potential in food 3D printing and the development of specialty fats for plant-based meat.

Combined effects of high-intensity ultrasound treatment and hydrogen peroxide addition on the thermal stabilities of myofibrillar protein emulsions at low ionic strengths

In this study, the effects of high-intensity ultrasound (HIU) treatment combined with hydrogen peroxide (H2O2) addition on the thermal stability of myofibrillar protein (MP)-stabilized emulsions in low-salt conditions were investigated. Results showed that compared to using either HIU or H2O2 treatment alone, HIU treatment combined with H2O2 was most effective in enhancing the physical stability of emulsions. Moreover, the emulsion stabilized by MPs co-treated with HIU and H2O2 exhibited the most uniform distribution, highest absolute zeta potential, and optimal rheological properties upon heating. This combination effect during heating was caused by the inhibition of disulfide bond cross-linking of myosin heads by H2O2 and the dissociation of filamentous myosin structures using the HIU treatment. In addition, the results of oxidative stability analysis indicated that the addition of H2O2 increased the content of oxidation products; however, the overall influence on the oxidative stability of emulsions was not significant. In conclusion, the combination of HIU and H2O2 treatment is a promising approach to suppress heat-induced MP aggregation and improve the thermal stability of corresponding emulsions.

Characteristics of insoluble soybean fiber (ISF) concentrated emulsions: Effects of pretreatment on ISF and freeze-thaw stability of emulsions

The properties of emulsions could be affected by the interactions between the components and network stabilization effect, which are commonly adjusted by changes in pH, ionic strength and temperature. In this work, insoluble soybean fiber (ISF) obtained via homogenization after alkaline treatment was pretreated firstly and then resultant emulsions were freeze-thawed. Heating pretreatment reduced droplet size, enhanced viscosity and viscoelasticity as well as subsequent stability of ISF concentrated emulsions, while both acidic pretreatment and salinized pretreatment decreased the viscosity and weakened the stability. Furthermore, ISF emulsions exhibited a good freeze-thaw performance which was further improved by secondary emulsification. Heating promoted the swelling of ISF and strengthened the gel-like structure of emulsions while salinization and acidization weakened the electrostatic interactions and caused the destabilization. These results indicated that pretreatment of ISF significantly influenced the concentrated emulsion properties, providing guidance for the fabrication of concentrated emulsions and related food with designed characteristics.

Ultrasound treated fish myofibrillar protein: Physicochemical properties and its stabilizing effect on shrimp oil-in-water emulsion

Effects of ultrasonication at different amplitudes (40% and 60%) and time (5, 10, and 15 min) on the physicochemical and emulsifying properties of the fish myofibrillar protein (FMP) were investigated. Solubility, surface hydrophobicity, and emulsifying properties were augmented when FMP was subjected to ultrasonication at 40% amplitude for 15 min (p < 0.05). Protein pattern study revealed that augmenting amplitude and duration of ultrasound treatment reduced band intensity of myosin heavy chain. Ultrasound treatment facilitated the adsorption of FMP on oil droplets as indicated by the increases in both adsorbed and interfacial protein contents (p < 0.05). Ultrasound-treated FMP (UFMP) sample showed the alteration in chemical bonds as depicted by Fourier transform infrared (FTIR) spectra. Ultrasound treatment altered the β-sheet and random coil of FMP. During storage for 30 days at 30 °C, UFMP stabilized shrimp oil (SO)-in-water emulsion had higher turbidity but lower d₃₂, d₄₃, and polydispersity index than emulsion stabilized by untreated FMP (p < 0.05). Furthermore, emulsion stabilized by UFMP had lower flocculation and coalescence indices (p < 0.05). Microstructure observation revealed smaller droplet sizes and higher stability of droplets in emulsion stabilized by UFMP. Confocal laser scanning microscopic images demonstrated a monodisperse emulsion stabilized by UFMP. This coincided with higher viscosity and modulus values (G' and G″ ). Emulsion stabilized by UFMP exhibited viscous, shear-thinning, and non-Newtonian behavior and no phase separation occurred during storage. Therefore, ultrasonication was proven to be a potential method for enhancing the emulsifying properties of FMP and improving the stability of SO-in-water emulsion during prolonged storage.

Differentiating the effects of hydrophobic interaction and disulfide bond on the myofibrillar protein emulsion gels at the high temperature and the protein interfacial properties

The study presented the effects of modulating the hydrophobic interaction and disulfide bond on the properties of myofibrillar protein (MP) emulsion gels at high temperature (95 °C) and the differentiation on the contribution of non-covalent (hydrophobic interaction) and covalent intermolecular interactions (disulfide bond) to the properties of interfacial protein films were also determined. The hydrophobic interactions among MP were modulated by the addition of octenyl succinic anhydride (OSA), and the disulfide bonds were modulated by the SH/SS exchange reactions mediated by GSH. The results showed that the MP emulsion gel properties at 95 °C were improved by modulating the hydrophobic interaction or disulfide bonds, and the dynamic interfacial adsorption of MP and dissipation quartz crystal microbalance experiments showed the interfacial adsorption pattens of protein were also changed. In addition, the hydrophobic interactions putted emphasis on improving the gel matrix, whereas the disulfide bonds focused on increasing the stiffness of interfacial protein films.

Synergistic effect of microfluidization and transglutaminase cross-linking on the structural and oil-water interface functional properties of whey protein concentrate for improving the thermal stability of nanoemulsions

Generally, whey protein concentrate (WPC) undergoes high-temperature denaturation and aggregation, which reduces its emulsifying properties and is not conducive to as an emulsifier to maintain the thermal stability of emulsions. In this study, dynamic high-pressure microfluidization technology (DHPM) combined with TGase (TG) cross-linking was applied to prepare DHPM-TG-WPC, and the thermal stabilization mechanism of nanoemulsions prepared with DHPM-TG-WPC was explored. Results showed DHPM treatment could promote the formation of TG-crosslinked WPC polymers. Compared to WPC, the free sulfhydryl and free amino group content of DHPM-TG-WPC was significantly decreased (P < 0.05), the surface hydrophobicity and interfacial tension of DHPM-TG-WPC were increased by 45.23 % and 62.34 %, respectively. And its emulsifying stability index and interface protein adsorption was significantly enhanced (P < 0.05). Furthermore, compared to WPC, DHPM-WPC and TG-WPC, DHPM-TG-WPC-stabilized nanoemulsions showed the best 15 days of storage stability after thermal sterilization. This study provides a theoretical basis for the application of modified-WPC emulsion.

A review of oil and water retention in emulsified meat products: The mechanisms of gelation and emulsification, the application of multi-layer hydrogels

Emulsified meat products are key deep-processing products due to unique flavor and high nutritional value. Myosin dissolves, and protein aggregation and heat-induced gelation occur after myosin unfolds and hydrophobic groups are exposed. Myosin could form interfacial protein membranes and wrap fat globules. Emulsified fat globules may be filled in heat-induced gel networks. Therefore, this review intends to discuss the influences of heat-induced gelation and interfacial adsorption behavior on oil and water retention. Firstly, the mechanism of heat-induced gelation was clarified from the perspective of protein conformation and micro-structure. Secondly, the mechanism of emulsification stability and its factors affecting interfacial adsorption were demonstrated as well as limitations and challenges. Finally, the structure characteristics and application of multi-layer hydrogels in the gelation and emulsification were clarified. It could conclude that the characteristic morphology, spatial conformation and structure adjustment affected heat-induced gelation and interfacial adsorption behavior. Spatial conformation and microstructure were adjusted to improve the oil and water retention by pH, ionic strength, amino acid, oil phase characteristic and protein interaction. Multi-layer hydrogels facilitated oil and water retention. The comprehensive review of gelation and emulsification mechanisms could promote the development of meat products and improvement of meat processing technology.

Soy protein nanoparticles prepared by enzymatic cross-linking with enhanced emulsion stability

Particle-stabilized emulsions have shown increasing potential application in food emulsion systems. Here, soy protein, an abundant and inexpensive plant-based protein, was used to develop nanoparticles for emulsion stabilizer applications. An enzymatic cross-linking method based on microbial transglutaminase (mTG) was developed for the fabrication of soy protein nanoparticles (SPNPs). The emulsion stability was compared between soy protein isolate (SPI) and three different nanoparticles. The size of SPNPs ranged from 10 nm to 40 nm, depending on the production conditions. The emulsions stabilized by SPNPs were stable for at least 20 days at room temperature, whereas the emulsion that was stabilized by SPI showed a significant creaming and phase separation phenomenon. The SPNPs also showed a higher antioxidant and reducing effect compared to SPI. The use of mTG induced cross-linking resulted in the formation of covalent bonding between protein molecules, and led to the formation of nanoparticles with higher stability. The approaches support the utilization of inexpensive and abundant plant-based resources as emulsion stabilizers in food applications.

Heat-induced amorphous aggregates assembly of soy protein modulate in vitro digestibility of potato starch

This research focused on the characteristics of amorphous aggregates derived from soy protein (SPAA), and their effects on the structural, physicochemical, and digestive properties of potato starch (PS). The SPAA induced by different heating temperatures at pH 7.0 formed an inhomogeneous spherical structure. The presence of SPAA could improve the degree of short-range order of starch, increase thermal stability, reduce pasting viscosity and breakdown, and setback viscosity values of PS. For the PS complexed with SPAAs under simulated cooking conditions, the fraction of digested starch at 300 min (C₃₀₀) decreased by 6-14 %, and rapid digestible starch content (RDS) decreased by 18-25 %, while the slowly digestible starch (SDS) and resistant starch (RS) increased by 0.4-3 % and 15-23 %, respectively. The SPAA at higher temperature treatment (SPAA₁₃₀) reduced digestive rate coefficient (k) values more significantly than SPAA at a lower temperature (SPAA₇₀, SPAA₉₀, SPAA₁₁₀). And the SPAA had no inhibitory effect on α-amylase. The results of this study would significantly contribute to expanding the theoretical information about protein regulation in starch digestion and promoting the development of healthy foods with digestion-resistant properties.

Dual improvement in curcumin encapsulation efficiency and lyophilized complex dispersibility through ultrasound regulation of curcumin-protein assembly

Ultrasound has a recognized ability to modulate the structure and function of proteins. Discovering the influential mechanism of ultrasound on the intramolecular interactions of egg-white protein isolate-curcumin (EPI-Cur) nanoparticles and their intermolecular interaction during freeze drying and redispersion is meaningful. In this study, under the extension of pre-sonication time, the protein solubility, surface hydrophobicity, and curcumin encapsulation rate showed an increasing trend, reaching the highest value at 12 min of treatment. However, the values decreased under the followed extension of ultrasound time. After freeze drying and redispersion were applied, the EPI-Cur sample under 12 min of ultrasound treatment exhibited minimal aggregation degree and loss of curcumin. The retention and loading rates of curcumin in the lyophilized powder reached 96 % and 33.60 mg/g EPI, respectively. However, under excessive ultrasound of >12 min, scanning electron microscopy showed distinct blocky aggregates. Overexposure of the hydrophobic region of the protein triggered protein-mediated hydrophobic aggregation after freeze drying. X-ray diffraction patterns showed the highest crystallinity, indicating that the free curcumin-mediated hydrophobic aggregation during freeze drying was enhanced by the concentration effect and intensified the formation of larger aggregates. This work has practical significance for developing the delivery of hydrophobic active substances. It provides theoretical value for the dynamic dispersity change in protein-hydrophobic active substances during freeze drying and redissolving.

Improvement of Storage Stability of Zein-Based Pickering Emulsions by the Combination of Konjac Glucomannan and L-Lysine

In this work, L-lysine (Lys) was employed together with konjac glucomannan (KGM) to fabricate zein colloidal particles (ZCPs) aimed at enhancing the storage stability of Pickering emulsions. With the addition of Lys, zein-Lys colloidal particles (ZLCPs) and zein-Lys-KGM (ZLKCPs) exhibited smaller particle size (133.64 ± 1.43, 162.54 ± 3.51 nm), polydispersity index (PDI) (0.10 ± 0.029, 0.13 ± 0.022), π value, and more adsorbed protein. Meanwhile, KGM underwent deamidation in an alkaline solution, so the emulsions stabilized by ZLKCPs exhibited a solid gel-like structure with higher storage modulus (G′) and loss modulus (G′′), leading to lower fluidity and better stability. The synergistic effects of Lys and KGM improved the stability of the emulsion. Hydrophobic interactions and hydrogen bonds were the main driving forces forming colloidal particles, which were determined by driving force analysis.

Comparison of the interfacial properties of native and refolded myofibrillar proteins subjected to pH-shifting

The emulsion abilities of pale, soft, exudative (PSE)-like chicken breast protein are unsatisfied, which are urgently needed to be ameliorated. This study evaluated the improvement of pH-shifting (11.0-, 11.5- and 12.0-7.0) on emulsion properties of the PSE-like chicken breast myofibrillar proteins (MPs) and the underlined structure-driven interfacial mechanism. It was found pH-shifting promoted the exposure of buried hydrophobic groups and free sulfhydryl groups, and changed secondary structures. Emulsions stabilized by refolded MPs exhibited more uniform and dispersed distributions with more adsorbed proteins at the interface. Electrophorogram showed both disulfide and non-disulfide covalent bonds were involved during interfacial protein-protein interaction. The results from circular dichroism and front-surface fluorescence spectroscopy revealed interfacial MPs were exposed to a more hydrophobic environment and increased β-sheets enhanced their molecular interactions. In addition, interfacial proteins after pH-shifting was less likely to be replaced by Tween 20.

The Emulsion Properties of Chicken Liver Protein Recovered through Isoelectric Solubilization/Precipitation Processes

This study investigated the feasibility to improve the emulsifying capacity of chicken liver (CL) protein using different isoelectric solubilization/precipitation (ISP) processes. The CL proteins were first solubilized at alkaline pH 10.5, 11.0, 11.5, and 12.0, followed by precipitation at pH 5.0, 5.5, and 6.0, respectively. Fresh CL paste was set as the control (raw). With the increase in solubilization pH, the protein recovery yield increased under the same precipitation pH, and the pH 12.0, 5.5 treatment obtained the highest recovery yield of 82% (p < 0.05), followed by the pH 5.0 precipitation treatments and the pH 12.0, 6.0 treatment. The particle size distribution of D3,2 and D4,3 was smaller for the pH 10.5 (except for the D4,3 of pH 10.5, 5.0) and pH 11.0 solubilization treatments than those of the other treatments (p < 0.05), regardless of precipitation pH. Compared with that of the raw control, the emulsions of the pH 10.5 and pH 11.0 solubilization treatments, and pH 12.0, 6.0 treatment showed good stability. The pH 10.5, 6.0 treatment showed the best emulsification activity, followed by the pH 10.5, 5.5, pH 11.0, 6.0, pH 12.0, 6.0, pH 10.5, 5.0, pH 11.0, 5.5, and pH 11.0, 5.0 treatments, which were uniformly distributed and were stable without the stratification of emulsions. It was concluded that CL protein recovered through suitable ISP showed potential as an emulsifier, and thus expanded the application of CL protein for human consumption.

Effects of Tea Polyphenol Palmitate Existing in the Oil Phase on the Stability of Myofibrillar Protein O/W Emulsion

This study aimed to explore the effect of adding different concentrations (0, 0.01%, 0.03%, and 0.05% (w/w)) of tea polyphenol palmitate (TPP) in the oil phase on the emulsifying properties of 5 and 10 mg/mL myofibrillar protein (MP). Particle size results revealed that the flocculation of droplets increased as TPP concentration increased and that droplets in 5 mg/mL MP emulsions (25−34 μm) were larger than in 10 mg/mL MP emulsions (14−22 μm). The emulsifying activity index of 5 mg/mL MP emulsions decreased with increasing TPP concentration. The micrographs showed that the droplets of MP emulsions exhibited extensive flocculation at TPP concentrations >0.03%. Compared with 5 mg/mL MP emulsions, 10 mg/mL MP emulsions showed better physical stability and reduced flocculation degree, which coincided with lower delta backscattering intensity (ΔBS) and Turbiscan stability index values. The flow properties of emulsions can be successfully depicted by Ostwald−de Waele models (R2 > 0.99). The concentrations of TPP and protein affect the K values of emulsions (p < 0.05). Altogether, increased protein concentration in the continuous phase could improve emulsion stability by increasing viscosity, offsetting the adverse effects of TPP to a certain extent. This study is expected to promote the rational application of TPP in protein emulsion products of high quality and acceptability.

High-intensity ultrasound improves the physical stability of myofibrillar protein emulsion at low ionic strength by destroying and suppressing myosin molecular assembly

The specific molecular behavior of myofibrillar proteins (MPs) in low-salt media limits the development of muscle protein-based emulsions. This study aimed to evaluate the potential of high-intensity ultrasound (HIU; 150, 300, 450, and 600 W) to improve the physical stability of MP emulsion at low ionic strength and decipher the underlying mechanism. According to the physical stability analysis, HIU pretreatment, especially at 450 W power, significantly improved the physical stability of MP emulsions, as evidenced by the reduced particle size, enhanced inter-droplet interactions, and increased uniformity of the droplet size distribution (p < 0.05). The results of interfacial protein composition, Fourier transform infrared spectroscopy analysis, and microscopic morphology observation of the aqueous MP suspension suggested that HIU induced the depolymerization of filamentous myosin polymers and inhibited the subsequent self-assembly behavior. These effects may facilitate protein adsorption and molecular rearrangement at the oil-water interface, forming a complete interfacial layer and, thus, droplet stabilization. Confocal laser scanning microscopy observations further confirmed these results. In conclusion, these findings provide direct evidence for the role of HIU in improving the physical stability of MP emulsions at low ionic strength.

Use of l-arginine-assisted ultrasonic treatment to change the molecular and interfacial characteristics of fish myosin and enhance the physical stability of the emulsion

The effects of l-arginine (Arg)-assisted ultrasonic treatment on the molecular and interfacial characteristics of myosin and emulsifying properties of the emulsion were evaluated to ascertain the underlying mechanism in improving the emulsion stability. Ultrasonication induced the exposure of residues of native myosin, which was increased by the addition of Arg (40 mM). Furthermore, in terms of emulsions containing Arg, the higher the ultrasonication intensity was, the greater the increase in adsorbed protein (from 15.43 ± 0.28% to 50.49 ± 1.65%) and π value, and the decrease in droplet sizes (from 4098 nm to 2324 nm) (P < 0.05). Moreover, the increase in the ordered structures of interfacial myosin induced by Arg and ultrasonication favoured the formation of a protein gelation network. In summary, Arg-assisted ultrasonic treatment improved the stability of the emulsion by inducing the exposure of native myosin and facilitating the formation of ordered structures of interfacial myosin.

Impact of methylglyoxal modification of chicken sarcoplasmic protein emulsions on emulsifying properties, rheological behavior and advanced glycation end products

BACKGROUND

Protein modification is used to improve emulsion properties. However, there are limited reports on the effect of methylglyoxal (MGO) modification on emulsifying properties and on the production of advanced glycation end-products (AGEs) in chicken sarcoplasmic protein emulsion (SPE). In this study, MGO solution was dispersed into prepared emulsion (17 mg mL^-1 sarcoplasmic-soybean oil (v/v 5:1)) at 0, 0.5, 5, 10, 30 and 50 mmol L^-1 concentrations. Emulsifying activity index (EAI), emulsifying stability index (ESI), Z-average diameter, polydispersity index (PDI), zeta potential, rheological behavior (thermal condensation characteristics and fluidity) and AGEs in different concentrations of MGO SPE were measured. In addition, the effect of MGO on the levels of AGEs, lipid and protein oxidation of the emulsion as well as their relationship has also been analyzed.

RESULTS

Our findings showed that ESI had the lowest value when MGO was added at a concentration of 10 mmol L^-1 , while Z-average, PDI, carbonyl and AGEs had the highest value at the same concentration. Also, 10 mmol L^-1 MGO played an important role in affecting the rheology of the emulsion. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) results showed that the presence of myofibrillar proteins (MPs) in SPE was the main reason for the crosslinking of polymers which could be damaged by high concentration of MGO (>10 mmol L^-1 ).

CONCLUSION

Different concentration of MGO showed varying effects on emulsion properties and on the formation of AGEs in chicken SPE. Pearson's correlation analysis concluded that protein oxidation played a significant positive role during MGO modification. © 2020 Society of Chemical Industry.