Gel properties of soy protein isolate-potato protein-egg white composite gel: Study on rheological properties, microstructure, and digestibility

Effect of resonance acoustic mixing treatment on the gelation properties of pea protein isolate and the gel in vitro digestibility

This study aimed to investigate the effect of different durations (0, 5, 10, 15, 20, and 30 min) of resonance acoustic mixing (RAM) treatment on the gel properties and digestibility of pea protein isolate (PPI). Results indicated that RAM treatment enhanced the water holding capacity (WHC) of PPI gels, with the highest WHC of 94.79 % achieved after RAM treatment for 20 min. A 15-20 min RAM treatment altered the secondary structure of proteins in PPI gels, reducing α-helix content while increasing β-sheet content. This treatment also refined the microstructure of PPI gels, changing the surfaces from rough to smooth and the pores from large to small. RAM treatment for 5-20 min decreased the shear viscosity and gel strength of heat-induced PPI gels, although these properties slightly recovered when the treatment was extended to 30 min. Additionally, RAM treatment improved the in vitro digestibility of PPI gels. In conclusion, RAM treatment significantly influenced the structural, mechanical and digestive properties of PPI gels, and this effect can be regulated by adjusting the treatment duration, making it suitable for various practical applications.

Ultrasound-mediated soybean-egg white protein acid-induced emulsion gels: A multi-design approach integrating techno-functional properties, digestibility, and nutritional value

This study investigated the effects of formulation and ultrasound on the processing properties and nutrient digestion of soy protein isolate (SPI)-egg white protein (EWP) emulsion gels. The incorporation of EWP significantly improved the texture properties and freeze-thaw stability through disulfide bonds and homogeneous networks in comparison to SPI emulsion gels. However, swelling ratio of emulsion gels at SPI:EWP ratios of 3:1 and 2:1 decreased due to disruption of SPI network continuity. After ultrasound, SPI-EWP emulsion gels exhibited higher gel strength, freeze-thaw stability, and swelling ratio. Digestion kinetics showed an increased half-life time of SPI-EWP emulsion gels with no significant difference in PCmax. Flexible proteins could adsorb around small droplets, forming tight interfacial layers and a dense and uniform network according to particle size and Cryo-SEM. This work elucidated the mechanism of performance stabilization and digestion kinetics of SPI-EWP emulsion gels, supporting the design of animal and plant protein complex products.

Exploring the gelation potentials of chicken heart batter: From by-product to product

Chicken heart is the by-product of great amount in poultry industry owing to concentrated slaughter development, however, whose potential in food application is unclear. The gelation of chicken heart has great difficulties due to the muscle structure and protein structure of the heart. Therefore, different levels of sodium alginate (SA) were added into chicken heart batter (CHB) to investigate the gelation strategies. The results showed that the cooking loss of chicken heart gel (CHG) decreased by increasing SA level (0.12 %-0.48 %)，along with improved hardness, gumminess and chewiness. The G' and G" of CHB increased along with the SA addition, which mainly relates to hydrophobic interactions and disulfide bonds, followed by ionic bond and hydrogen bond. SA induced increased percentage of immobilized water and bound water. Moreover, the protein-SA interpenetrating network became denser and more uniform along with increased SA in CLSM and SEM images until CHG of 0.48 % SA. To the best of our knowledge, this is the first time that chicken heart is processed into gelation food, which endeavors to promote feed to food by a sustainable proposal.

How chloride salt mixtures affect the final gel properties of low-sodium myofibrillar protein: Underlining the perspective of gelation process

This study aimed to investigate the performance differences of low-sodium myofibrillar protein (MP) gels substituted by different chloride salt mixtures from the perspective of gelation process. The results revealed that low-sodium MP substituted by KCl/CaCl2 exhibited higher turbidity and particle size at 40 % substitution, and formed protein aggregates earlier at 53 °C. During the gelation process, KCl/CaCl2 increased the extent of cross-linking as the substitution level increased from 10 % to 40 %, which was prone to forming final gels with poor palatability. Microstructural and binarization results visually indicated that an irregular reticular structure composed of partial clusters formed when the temperature heated over 53 °C, and the cross-linked cluster blocks further shrunk from 53 °C to 73 °C. Rheological amplitude sweeps revealed that KCl/CaCl2-substitued MP displayed a faster fracture of the ductile structure, and this influenced the distribution of cluster blocks inside the network. The introduction of salt mixtures altered protein conformation, and more unordered structures were found in low-sodium MP containing CaCl2, rather than MP containing MgCl2. Additionally, Ca2+ ions increased the thermo-denatured temperature of MP, and extended the relaxation time of bound water at 53 °C, and Mg2+ ions slowed down the degree of liquid loss at 53 °C. As a result, the low-sodium MP containing CaCl2 exhibited a lower expansion of protein structure accompanied by the involvement of less proteins in gel formation and more liquid loss in the final gel.

Double network emulsion gel prepared with different polyphenol modified egg white protein: A promising fat substitute for oral processing and fatty taste supplement

This study investigated the effects of differential modification of the structural flexibility of egg white protein (EWP) by different polyphenols, which in turn enhanced the oral processing properties and fat perception of EWP-based double network emulsion gel (DNEG). After modification with polyphenols, the skeleton of gel became more delicate, which improved the hardness and cohesion of DNEG. This transformation was attributed to the shift from hydrophobic interactions to hydrogen and covalent bonds. Notably, proanthocyanidins (PC) effect was better, which resulted in a 58.5 % increase in oral wettability and a more appropriate oral tribological performance (0.53). Besides, DNEG increased fatty taste perception via the "ball bearing" effect as a fat substitute in sausage. In summary, this study could enhance the refined design of gels and provide ideas for improving the fatty taste of low-fat, healthy foods.

Understanding the anti-browning mechanism and physicochemical properties in potato pulp during the magnetic field processing

To reduce the detrimental effects of enzymatic-browning on potato pulp quality, this study investigated the anti-browning potential of magnetic field at varying intensities. The magnetic field (4 mT) enhanced the structural integrity of potato pulp cells, with the highest hardness (119.37 g). Furthermore, the potato pulp subjected to a magnetic field treatment of 4 mT for 60 min at a temperature of 32 °C (PP-MF-4) shown an orderly macromolecular aggregation, increased viscoelastic properties of potato pulp. The PP-MF-4 demonstrated excellent anti-browning capability, as evidenced by the highest L⁎ value (59.18), reduced browning index, and lower accumulation of browning-products. Furthermore, the PP-MF-4 exhibited a significant reduction in oxidative damage, attributed to enhanced antioxidant activity and total phenolic content. Besides, the PP-MF-4 inhibited browning enzymes and improved the molecular structure orderliness. Consequently, magnetic field presents a viable approach for mitigating enzymatic-browning in potato pulp, offering a promising methods for preserving its quality.

Gelation properties and swallowing characteristics of heat-induced whey protein isolate/chia seed gum composite gels as dysphagia food

Soft gels based on protein-polysaccharide composite systems play a crucial role in the dietary management of people with dysphagia. The effect of chia seed gum (CSG) on the gelling and swallowing properties of heat-induced whey protein isolate (WPI) gels (3.125-75 mg/mL) was investigated. The results showed that adding CSG reduced the gelation concentration of WPI and weak gels could form at 12.5 mg/mL WPI concentration. In addition, the viscoelasticity and water-binding capacity of the WPI/CSG composite gels were gradually enhanced with increasing WPI concentrations. The WPI/CSG composite systems can be classified as level 2-5 dysphagia-oriented foods according to the International Dysphagia Diet Standardization Initiative (IDDSI) framework. The incorporation of CSG promoted the cross-linking of protein aggregates and the formation of compact and continuous network structures, resulting in improved gelling properties of composite systems. This study contributes to the development of novel soft gel-type dysphagia foods with better textural characteristics.

Ozone treatment increase the whiteness of soy protein isolate through the degradation of isoflavone

The color of soy protein isolate (SPI) influences the appearance of products such as tofu and soymilk, consequently impacting consumer preferences. Typically, whiter-colored SPIs were more favorite. However, products currently manufactured in the industry predominantly exhibit a yellowish hue. In our study, the incorporation of gaseous ozone into the production process of SPI notably improved its appearance on color. Simultaneously, a reduction in the isoflavone content enriched in SPI due to ozone treatment was observed, suggesting a potential mechanism for improving the whiteness of SPI. In addition, we discovered that the introduction of ozone for different times oxidized ozone-sensitive sulfhydryl groups, tryptophan, and tyrosine in proteins, thereby affecting the protein structure. This finding was determined through the analysis of free sulfhydryl groups, disulfide bonds, SDS-PAGE electrophoresis, FTIR, and endogenous fluorescence spectroscopy of SPIs. Meanwhile, the ozone treatment did not induce protein aggregation or alter its functional properties.

Focusing on the mechanism of glycinin-soybean lipophilic protein hybrid gels: Effect of ultrasonic, subunit interactions, and formation process analysis

Heat facilitates aggregation and gel formation of soybean proteins. Ultrasonic reduces the size of protein aggregates. This study examined the impact of glycinin (11S) subunits on soybean lipophilic proteins (SLPs) gel formation and underlying mechanisms. Effects of protein dispersion pretreatment with 400 W ultrasonic and associated mechanisms were assessed. Addition of the A- and B-subunits before and after ultrasonic minimally affected SLP secondary structure. A-subunit addition before ultrasonic negligibly affected SLP tertiary structure. Addition of the B-subunit after ultrasonic reduced hydrophobic thermal aggregation. However, the small B-subunit size was unfavorable for the formation of a gel matrix, which led to poor gel properties. In contrast, solubility of the A-subunit after ultrasonic was increased to 31.06 ± 1.62 %). Particle size was decreased to 43.33 ± 1.36 nm for A:SLP (1:2). Endogenous fluorescence spectroscopy demonstrated increased protein unfolding after ultrasonic and decreased disulfide bonds. These changes improved the gel state. Rheological and microstructural analyses revealed increased energy storage modulus and yield strain, accompanied by a more homogeneous microstructure following ultrasonic. Microscopic improvement resulted in increased encapsulated water within interstitial spaces of the A-SLP gel matrix. This enhanced water mobility in B-SLP gels, in turn weakening gel stability. The changes observed in B-SLP were primarily due to reduced hydrophobic interactions between the proteins. The findings clarify the effect of ultrasonic treatment on the formation of soybean globulin-SLP hybrid gels at the subunit level. The data provide a theoretical basis for the synergistic utilization of soybean proteins among different components.

A novel strategy of dysphagia-oriented matrices bovine tendon collagen-cassava starch composite gels

Dysphagia foods are designed for individuals with swallowing difficulties to consume safely. Texture-modified diets have become essential in dysphagia management. This study aimed to assess the safety and effectiveness of bovine tendon collagen (BTC) as a texture modifier to alter the starch gel network through a synergistic effect with cassava starch (CS), enhancing its application in dysphagia foods. The results indicated that BTC addition initially reduced gel water retention then increased, with a minimum observed at 2 % BTC. However, all gels demonstrated excellent WHC. The viscoelasticity, hardness, adhesion, gumminess, and thermal stability of composite gels improved with rising BTC concentrations. Secondary structure analysis revealed BTC altered the ordered structures of CS, with hydrogen bonds playing a key role. The microstructure showed that BTC disrupted and attached to the gel network, forming a more compact structure. Additionally, BTC inhibited CS digestion, increasing resistant starch content and decreasing rapidly digestible starch content. Furthermore, International Dysphagia Diet Standardization Initiative tests indicated that 2 % BTC gels could be categorized as level 4 (pureed or extremely thick), while gels with 4-6 % BTC could be classified as level 5 (minced and moist). These findings highlight the potential of BTC-CS composite gels for innovative dysphagia food development.

Exploring Sustainable Future Protein Sources

With the exponential growth of the world population and the decline in agricultural production due to global warming, it is predicted that there will be an inevitable shortage of food and meat resources in the future. The global meat consumption, which reached 328 million tons in 2021, is expected to increase by about 70% by 2050, and the existing livestock industry, which utilizes limited resources, is having difficulty meeting the demand. Accordingly, cultured meat produced by culturing cells in the laboratory, edible insects consumed after cooking or processing, and plant-based meat processed by extracting proteins from plants have been proposed as sustainable food alternatives. These future protein sources are gaining popularity among consumers who prefer a healthy diet due to their nutritional benefits, and they are receiving attention for their potential to reduce environmental impact. This review describes the types and characteristics of protein sources such as cultured meat, antiserum media, edible insects, soy protein, wheat protein, and other mushroom mycelia, processing processes and technologies, market status, institutional challenges and prospects, and mushroom cultured meat.

Improve the fiber structure and texture properties of plant-based meat analogues by adjusting the ratio of soy protein isolate (SPI) to wheat gluten (WG)

The effects of the ratio change of SPI and WG (11: 1, 10: 2, 9: 3, 8: 4, 7: 5, 6: 6 and 5: 7) on the product characteristics of plant-based meat analogues (PBMAs) were investigated. The results show that the addition of WG significantly reduces the hardness and chewiness of PBMAs, but significantly improves the springiness and brightness of PBMAs. When the ratio of SPI to WG is 9: 3, PBMAs has the best fiber structure, storage modulus and apparent viscosity. Fourier transform infrared spectroscopy (FT-IR) results showed that the transition from α-helix to β-fold was an important reason for PBMAs fibers reinforcement. The intermolecular interaction of protein shows that the enhancement of fiber structure of PBMAs is related to the increase of disulfide bonds. In this study, low cost and high simulation degree PBMAs are provided as a reference for developing PBMAs.

Ultrasonic treatment of emulsion gels with different soy protein-hemp protein composite ratios: Changes in structural and physicochemical properties

To improve the emulsion gel system of single soybean isolate protein (SPI) and to broaden the application field of hemp protein isolate (HPI), ultrasonic treatment and HPI were introduced to improve the properties of SPI emulsion gel and to explore the mechanism. The results showed that the gel strength (218.6 g) and water-holding capacity (86.24 %) of the emulsion gels were improved under ultrasonic treatments when the ratio of SPI:HPI was >6:4, and the reticulation structure of the gels was enhanced. When the ratio of SPI:HPI was <6:4, the gel structure was loose and formless. Ultrasonic treatment has a significant effect on the emulsion gel with the ratio of SPI:HPI was >6:4. Appropriate ultrasonic treatment (400 W) changed the protein structure, improved the rheological properties of emulsion gels to form the protein-oil-coated network structure. However, excessive ultrasonic treatment (600 W) will destroy the conformation of the protein, reducing the stability of the structure. The effect of ultrasonic treatment on emulsion gels with the ratio of SPI:HPI was <6:4 is low, but improved the gel protein digestibility. This study provides a theoretical basis for the application of ultrasonic in composite protein emulsion gels systems and the development and application of HPI.

Deacetylation enhances the structure and gelation properties of konjac glucomannan/soy protein isolate cold-set gels

This study aimed to investigate the effect of the deacetylated konjac glucomannan (DKGM), with varying degree of deacetylation (DD), on the physicochemical and structural properties of transglutaminase-induced soy protein isolate (SPI) cold-set gels. Compared with native konjac glucomannan (KGM), DKGM significantly enhanced the gel strength, water-holding capacity, and thermal stability of the composite gels, with DK3 (DKGM with 65.85 % deacetylation) showing the most significant improvement. The secondary and tertiary structures of SPI in the DK3 group were the most stable. Compared with the KGM group, the DK3 group showed a 58.32 % increase in hydrophobic interaction and a 37.98 % decrease in free sulfhydryl content. The microstructure results demonstrated that DK3 was uniformly dispersed within the SPI network, promoting the formation of a continuous and dense network structure. This was mainly due to DK3 having a moderate particle size and low viscosity. Therefore, DKGM with a moderate DD is conducive to forming a more ordered and dense gel network structure, imparting optimal gel performance to the SPI cold-set gel.

Impact of pH on the fabrication of egg white reinforced soy protein composite microgels for gastrointestinal delivery purposes

Protein molecules such as soy protein isolate (SPI) and egg white (EW) are highly promising materials for developing hydrogels (especially micro/nanogels) for the encapsulation, protection and controlled release of bioactive substances. However, there are limited numbers of studies on the formulation and behavior of these two gelling materials as microgels. In our study, composite microgels of SPI and EW at various component ratios and pH conditions have been successfully prepared; the rheological behavior and structural properties of these composite microgels before, during and after in vitro digestion have been analyzed; and their performance in curcumin encapsulation and gastrointestinal delivery has also been investigated. It was concluded that the SPI-EW composites at a mass ratio of 50 : 50 showed the best gelling properties in terms of storage modulus. Composite microgels prepared at pH 4 had larger particle sizes with more compact structures than those prepared at pH 7, due to their acidic complex coacervation, and therefore were more resistant to gastrointestinal digestion. The results suggest that the SPI-EW composite microgel particles prepared at pH 4 could achieve better sustained-release of curcumin in the in vitro gastrointestinal tract, with preserved antioxidant activity. Our study shows promise for the utilization of protein-based composite micro/nanogels for oral delivery applications.

High-level production of patatin in Pichia pastoris and characterization of N-glycosylation modification in food processing properties

Patatin is an acidic protein found in potatoes that is commonly used in food and pharmaceutical industries due to its excellent emulsifying and gelation abilities. Pichia pastoris is widely used as a host for recombinant protein production because it can incorporate post-translational modifications. In this study, a patatin titre of 2189.8 mg/L was achieved in a 5 L bioreactor using P. pastoris GS115 with signal peptide mutation, dual promoter construction, co-expression of chaperone proteins and optimised fermentation. To enhance the application of recombinant patatin in the food processing field, the level of N-glycosylation was elevated by genetic engineering. Properties of natural patatin, recombinant patatin and patatinL109T (N-glycosylated modified patatin) were investigated including foaming, hydrophobicity and emulsifying abilities. The functional properties of recombinant patatin were enhanced by introducing N-glycosylation, which also improved the water-holding capacity of its gel. The patatinL109T gel exhibited superior elasticity and water retention properties. The findings provide valuable insight and serve as a reference for the utilisation of recombinant patatin. The established enhancement strategy could be applied to other recombinant proteins.

A straight-forward fabrication of yuba films with controllable mechanical properties by oil-in-water emulsion model system rather than soymilk

The traditional process of producing yuba films from soybeans strictly limits the development of its industrial production due to the numerous processes and intricate procedures involved. In this study, a straight-forward and effective strategy was proposed to substitute soymilk with an emulsion made from soybean protein isolate and soybean oil for the formation of yuba films. It was found that the mechanical properties of yuba films formed through this method were controlled by the concentrations of proteins and oils. As the protein concentrations increased, a higher ratio of adsorbed proteins adhered to the surface of oil droplets, which in turn facilitated the recombination of proteins and the formation of larger aggregates during heat incubation. The rheological properties and interfacial adsorption behavior suggested that larger protein aggregates exhibited a greater diffusion rate and were more prone to unfolding and re-crosslinking at the interface through heat induction, resulting in the formation of stronger protein networks. Confocal laser scanning microscope images revealed a notable increase in the density of oil distribution within the yuba films as the oil concentrations in the pre-emulsion rose. Combined with the dense protein network formed at high protein concentrations, the elongation of yuba films was significantly increased.

Effects of eggshell powder emulsion gel on the oxidative stability and sustained-release effect of lavender essential oil

This study aimed to develop a new type of eggshell powder (EP) emulsion gels for improving the antioxidant ability and sustained release effect of lavender essential oil (LEO). The effects of EP addition on the physicochemical, structural properties, oxidative stability, and sustained-release performance of the emulsion gels were investigated. The results showed that with the increase of EP addition (0-1 %), the gel strength initially increased and then decreased. The emulsion gel with 1 % EP had better freeze-thaw stability (36.77 %), thermal stability (78.63 °C), and water holding capacity (96.57 %). Moreover, the micromorphology results indicated that the EP-ovalbumin (OVA)-konjac glucomannan (KGM) complex showed a connected filamentous network structure, and the emulsion gel with 1 % EP addition had the most uniform and densest network structure. Furthermore, the EP emulsion gel had the highest free sulfhydryl content and hydrophobic interaction, and LEO exhibited the best antioxidant and sustained-release properties at this time. In conclusion, the findings demonstrated the potential of eggshell powder to enhance emulsion gel stability, which could improve the high-value utilization of egg by-products.

Impact of konjac glucomannan with varied deacetylation degrees on plant-based meat analogue: Study on the gel properties, digestibility, and microstructure

Polysaccharides are widely used to improve the quality of plant-based meat analogue (PMA). In this study, four kinds of konjac glucomannan (KG) with different deacetylation degrees (DD) were prepared, namely KG1 (native KG, DD = 0.00 %), KG2 (DD = 41.40 %), KG3 (DD = 80.01 %) and KG4 (DD = 89.07 %), and their effects on the quality of PMA were studied. Results manifested that KG3 improved the hardness (from 3017.16 g to 3307.16 g) and protein digestibility (from 49.65 % to 53.01 %) of PMA without reducing the P21, KG2 and KG4 were less effective than KG3, while KG1 led to a significant decline in the hardness and protein digestibility of PMA. The rheological properties and intermolecular force analysis showed that the partially deacetylated KG was more conducive to improving the G' of the protein system during heating and the proportion of covalent bonds in PMA. These findings suggested that partially deacetylated KG was more promising than native or highly deacetylated KG in PMA. Furthermore, scanning electron microscopy revealed that the morphology of KG gradually changed from fine filaments, to coarse filaments, short filaments and granules as DD increased. This study provides a theoretical basis for the application of partially deacetylated KG in PMA.

Effect of tremella polysaccharides on the quality of collagen jelly: insight into the improvement of the gel properties and the antioxidant activity of yak skin gelatin

BACKGROUND

The present study aimed to investigate the effects of tremella polysaccharides on the gel properties and antioxidant activity of yak skin gelatin with a view to improving the quality of collagen jellies. The preparation of composite gels were performed by yak skin gelatin (66.7 mg mL-1) and tremella polysaccharides with different concentrations (0, 2, 4, 6, 8 mg mL-1), and finally the collagen jelly was prepared by composite gel (yak skin gelatin: 66.7 mg mL-1; tremella polysaccharides:6 mg mL-1) with the best performance.

RESULTS

Tremella polysaccharides not only improved the hardness, springiness, gel strength, water holding capacity and melting temperature of yak skin gelatin, but also enhanced the composite gel's scavenging activity against ABTS radicals, DPPH radicals, O2 and OH radicals. The filling of tremella polysaccharides into the gelatin network increased the number of crosslinking sites inside the gel, which resulted in the gel network structure becoming dense and orderly. The gel particles became finer and more uniform, and the thermal stability was improved. Furthermore, the sensory score of commercially available gelatin jelly decreased more rapidly during storage compared to the composite gel jelly.

CONCLUSION

The gel properties and antioxidant activity of yak skin gelatin were improved by adding tremella polysaccharides, and then the quality and storage properties of the jelly were improved, which also provided technical reference for the development of functional gel food. © 2024 Society of Chemical Industry.

Effect of salting and dehydration treatments on the physicochemical and gel properties of hen and duck egg yolks, plasma and granules

BACKGROUND

Salted hen egg yolks are less oily and less flavorful than salted duck egg yolks. However, hen eggs have a more adequate market supply and have a broader application prospect than duck eggs. In the present study, egg yolks, plasma, and granules were dehydrated by adding 1% NaCl to simulate traditional curing process of salted egg yolk. The changes in the pickling process of hen egg yolks (HEY) and duck egg yolks (DEY) plasma and granules were compared to reveal the gelation mechanism and the underlying causes of quality differences in salted HEY and DEY. Salted HEY can be compared with the changes in DEY during the pickling process to provide a theoretical basis for the quality improvement of salted HEY to salted DEY.

RESULTS

The results showed that both plasma and granules were involved in gel formation, but exhibited different aggregation behaviors. Based on the intermolecular forces, the HEY proteins achieved aggregation mainly through hydrophobic interactions and DEY proteins mainly through covalent binding. According to spin-spin relaxation time, HEY gels immobilized a large amount of lipid and interacted strongly with lipids. DEY gels showed much free lipid and had weak interaction with lipid. The microstructure showed that HEY proteins were easily unfolded to form a homogeneous three-dimensional gel network structure after salting, whereas heterogeneous aggregates were formed to hinder the gel development in DEY. Changes in protein secondary structure content showed that pickling can promote the transformation of the α-helices to β-sheets structure in HEY gels, whereas more α-helices structure was formed in DEY gels.

CONCLUSION

The present study has demonstrated that different gelation behaviors of hen and duck egg yolk proteins (especially in plasma) through salting treatment led to the difference in the quality of salted HEY and DEY. © 2024 Society of Chemical Industry.

Insight into the solubilization mechanism of wheat gluten by protease modification from conformational change and molecular interaction perspective

The low solubility limits the utilization of other functional characteristics of wheat gluten (WG). This study effectively improved the solubility of WG through protease modification and explored the potential mechanism of protease modification to enhance the solubility of WG, further stimulating the potential application of WG in the food industry. Solubility of WG modified with alkaline protease, complex protease, and neutral protease was enhanced by 98.99%, 54.59%, and 51.68%, respectively. Notably, the content of β-sheet was reduced while the combined effect of hydrogen bond and ionic bond were increased after protease modification. Meanwhile, the reduced molecular size and viscoelasticity as well as the elevated surface hydrophobicity, thermostability, water absorption capacity, and crystallinity were observed in modified WG. Moreover, molecular docking indicated that protease was specifically bound to the amino acid residues of WG through hydrogen bonding, hydrophobic interaction, and salt bridge.

Mechanism of ultrasound-induced soybean/egg white composite gelation: Gel properties, morphological structure and co-aggregation kinetics

This study aims to develop ultrasound-assisted acid-induced egg white protein (EWP)-soy protein isolate (SPI) composite gels and to investigate the mechanistic relationship between the co-aggregation behavior of composite proteins and gel properties through aggregation kinetics monitored continuously by turbidity. The results showed that the inclusion of EWP caused the attenuation of gel properties and maximum aggregation (Amax) because EWP could aggregate with SPI at a higher rate (Kapp), which impeded the interaction between SPI and the formation of a continuous gelling network. In the EWP-dominated system, SPI with higher molecular weights also increased the fractal dimension of gels. Ultrasound improved properties of composite gels, especially the SPI-dominated system. After ultrasound treatment, the small, uniform size of co-aggregates and the decrease in potential led to an increase in the aggregation rate and formation of dense particles, consistent with an increase in gelation rate and texture properties. Excessively fast aggregation generated coarse chains and more pores. Still, the exposure of free sulfhydryl groups assisted the gel structure units to form a compact network through disulfide bonding. On the whole, the study could provide theoretical support for a deeper understanding on the interaction mechanism and gelation of composite proteins.

Investigating Texture and Freeze-Thaw Stability of Cold-Set Gel Prepared by Soy Protein Isolate and Carrageenan Compounding

In this study, the purpose was to investigate the effects with different concentrations of carrageenan (CG, 0-0.30%) on the gel properties and freeze-thaw stability of soy protein isolate (SPI, 8%) cold-set gels. LF-NMR, MRI, and rheology revealed that CG promoted the formation of SPI-CG cold-set gel dense three-dimensional network structures and increased gel network cross-linking sites. As visually demonstrated by microstructure observations, CG contributed to the formation of stable SPI-CG cold-set gels with uniform and compact network structures. The dense gel network formation was caused when the proportion of disulfide bonds in the intermolecular interaction of SPI-CG cold-set gels increased, and the particle size and zeta potential of SPI-CG aggregates increased. SG20 (0.20% CG) had the densest gel network in all samples. It effectively hindered the migration and flow of water, which decreased the damage of freezing to the gel network. Therefore, SG20 exhibited excellent gel strength, water holding capacity, freeze-thaw stability, and steaming stability. This was beneficial for the gel having a good quality after freeze-thaw, which provided a valuable reference for the development of freeze-thaw-resistant SPI cold-set gel products.

New insight into yolk sphere microgel structure impacted by lipid and protein distribution changing under heating processing

The gel structure of boiled, shelled egg yolk is formed by the accumulation of yolk spheres, which are rich in lipids and proteins, and investigating the properties of the lipid-protein complex gel structure of the yolk sphere under heating is important. In this study, we used SEM and CLSM to confirm lipid migration and protein aggregation. We observed that during the heating process, the thermal stability decreased, and there was an increase in the content of β-turns and the degrees of freedom of water and lipids. G' increased during the frequency sweep but decreased after heating for 120 min. The various yolk gel structures exhibited varying degrees of resistance to compression from external forces. Prolonged heating resulted in the presence of gaps and increased surface roughness of the spheres. In conclusion, heating induced lipid migration and protein aggregation in the sphere microgels, thereby altering the structural properties of the gels.

Regulation of Protein Flexibility and Promoting the Cod Protein Gel Formation Using Ultrasound Treatment

In order to obtain a soft-textured protein gel suitable for the elderly, the cod protein gel was prepared by improving the protein flexibility under ultrasound treatment. It has been found that the increase in ultrasonic power, protein flexibility, particle size, ζ-potential, surface hydrophobicity, and α-helix content of preheated cod protein exhibited an increasing trend. The improvement of protein flexibility promoted uniformity and density of the gel network, water retention, and texture properties. The flexibility of preheated cod protein increased to 0.189, the water holding capacity of the gel reached up to 99.41%, and the hardness increased to 49.12 g, as the ultrasonic power level increased to 400 W. Protein flexibility was correlated well with the cohesiveness of the gel. The storage modulus (G') initially decreased and then increased during the heating-cooling process. The attractive forces forming between the flexible protein molecules during cooling in the ultrasound treatment groups promoted protein self-assembly aggregation and formed the cod protein gel. The gel obtained at 100-400 W could be categorized as Level 6─soft and bite-sized according to the International Dysphagia Diet Standardization Initiative (IDDSI) framework, indicating that the cod protein gel has potential as an easy-to-swallow diet for the elderly.

Changes in structural, rheological, and gel properties of egg white protein induced by preheating in the dry state

The knowledge of fundamental rheological concepts is essential to understand the gelling process of egg white proteins (EWP), which can be used to further manipulate the gel performance with desired sensorial attributes. In this study, the rheological and gel properties of EWP as influenced by heating in the dry state were investigated. The structural changes in dry heated EWP (DEWP) were also characterized in terms of morphology, protein stability, and protein microenvironment. The results showed that moderate dry heating induced linear aggregation of DEWP and decreased the denaturation temperature (Td) and enthalpy of denaturation (ΔH). Furthermore, the cross-linking on protein surface led to nonpolar microenvironment of hydrophobic groups, which lays the foundation of improved gel properties. The specific outcomes include the increase in the G'max and the G''max values, k'/k'' values of DEWP dispersions, gel hardness and gumminess of DEWP gels and a decrease in gelation temperature of DEWP dispersions. However, few changes were found in the springiness and cohesiveness of the DEWP gels with increasing dry heating time. Notably, gels prepared with DEWP also had better digestibility. Overall, these results can provide theoretical basis for quality control and sensory evaluation of DEWP in the food industry.

Effect of Ionic Strength on Heat-Induced Gelation Behavior of Soy Protein Isolates with Ultrasound Treatment

This study investigated the effect of ultrasound on gel properties of soy protein isolates (SPIs) at different salt concentrations. The results showed that ultrasound could significantly improve the gel hardness and the water holding capacity (WHC) of the salt-containing gel (p < 0.05). The gel presents a uniform and compact three-dimensional network structure. The combination of 200 mM NaCl with 20 min of ultrasound could significantly increase the gel hardness (four times) and the WHC (p < 0.05) compared with the SPI gel without treatment. With the increase in NaCl concentration, the ζ potential and surface hydrophobicity increased, and the solubility decreased. Ultrasound could improve the protein solubility, compensate for the loss of solubility caused by the addition of NaCl, and further increase the surface hydrophobicity. Ultrasound combined with NaCl allowed proteins to form aggregates of different sizes. In addition, the combined treatment increased the hydrophobic interactions and disulfide bond interactions in the gel. Overall, ultrasound could improve the thermal gel properties of SPI gels with salt addition.

Structural Analysis and Study of Gel Properties of Thermally-Induced Soybean Isolate-Potato Protein Gel System

Heat-induced composite gel systems consisting of different soybean protein isolate (SPI) and potato protein (PP) mixtures were studied to elucidate their "backbone" and property changes. This was achieved by comparing the ratio of non-network proteins, protein subunit composition, and aggregation of different gel samples. It was revealed that SPI was the "gel network backbone" and PP played the role of "filler" in the SPI-PP composite gel system. Compared with the composite gels at the same ratio, springiness and WHC decrease with PP addition. For hardness, PP addition showed a less linear trend. At the SPI-PP = 2/1 composite gel, hardness was more than doubled, while springiness and WHC did not decrease too much and increased the inter-protein binding. The hydrophobic interactions and electrostatic interactions and hydrogen bonding of the SPI gel system were enhanced. The scanning electron microscopy results showed that the SPI-based gel system was able to form a more compact and compatible gel network. This study demonstrates the use of PP as a potential filler that can effectively improve the gelling properties of SPI, thus providing a theoretical basis for the study of functional plant protein foods.