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Sulfated polysaccharides exhibit great potential for regulating protein-protein interactions. In the present study, three sulfated microcrystalline cellulose (MCS) with different degrees of sulfate substitution (DS S : 0.33, 0.51, 0.61) were synthesized and the effects of DS S on the regulation of egg white protein (EWP) aggregation and gelation properties were investigated. The results found that the improvement of protein mechanical properties by MCS is closely related to the level of sulfate substitution. The higher the DS S , the more ordered protein aggregates and compact gel network formed during heating as compared to that of pure EWP. Lower DS S (0.33) shows little effect on the mechanical properties of EWP. Furthermore, all the MCSs could significantly destroy the tertiary structure of protein molecules during heating, while for the secondary structure, MCS with higher DS S (0.51 and 0.61) could effectively control the decreasing tendency of α-helix and increasing tendency of β-sheet. Hydrophobic interactions were recognized as the major intermolecular force in the compact mixed gels (EWP/MCS2 and EWP/MCS3 gels, DS S was 0.51 and 0.61, respectively). These findings provide a vital understanding of the gelling mechanism of the protein-polysaccharide system and the application of sulfated polysaccharides in protein-based food products., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Ovalbumin (OVA) is a model protein with extensive research on structure and function, however, the application of OVA in food processing is limited due to its low gelation properties. In this study, thermally-induced highly transparent and elastic hydrogels from OVA pretreated by succinylation combined with pH-shifting method were reported. Transmission electron microscope (TEM) and free sulfhydryl groups determination revealed that the pretreatment induced the stretching of the protein structure and promoted the formation of preliminary aggregates. Further heating the pretreated OVA suspension resulted in a homogeneous and macroporous gel network with thin connecting walls. Such homogeneous gel network structures may be related to the effective modulation of the thermal aggregation efficiency of proteins by succinylation and the high level of protein unfolding by pH-shifting treatments, which synergistically allowed for more active sites to be created during heating to facilitate intermolecular interactions, including hydrogen bonding and hydrophobic interactions. Notably, the method resulted in a 507.14% increase in elasticity, a 60.74% increase in water holding capacity of the OVA hydrogels compared to the native OVA hydrogels without pretreatment. Also, the hydrogels were transparent with 73.11% light transmittance. In conclusion, succinylation and pH-shifting combined treatment could be an effective method for the preparation of OVA hydrogels with superior gelation properties., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

A comprehensive investigation was conducted regarding the molecular forces involved in the formation of dry heated egg white protein (DEWP) gels. From the preparation of DEWP powders to the formation of DEWP gels, multiple interactions are involved: the aggregation of DEWP powders in the dry state, the aggregation of DEWP solutions in the water state, and the subsequent gelling process of DEWP gels. The methods included analyses of zeta-potentials, surface hydrophobicity, reducing and nonreducing SDS-PAGE, sulfhydryl (SH) group content, molecular forces, particle size, and critical gel concentration. The results indicated that dry heat promoted the electrostatic and hydrophobic interactions in DEWP and DEWP aggregates. Disulfide (SS) bonds dominated the aggregation process of DEWP solutions in the water state, while hydrophobic and electrostatic interactions dominated the gel forming process. This phenomenon became even more obvious with a longer dry heat time. Furthermore, the intensified molecular interactions induced by dry heat resulted in the formation of smaller gel particles, and a relatively lower protein concentration was required for gel formation. All these factors contributed to the ultimate linear and fine-stranded DEWP gel network, which is more favorable in food processing and application., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

In this study, succinic anhydride (SA) and octenyl succinic anhydride (OSA) were used to modify the egg white protein (EWP), and acylated EWP was further prepared as a gel by adding NaOH and heat modification. The results showed that the acylation degree for the SA- and OSA-added groups reached 57.68% and 26.95%, respectively, and the average size, the absolute value of ζ-potential, increased significantly with SA and OSA addition, indicating that acylation improved the stability of EWP solution. Furthermore, the surface hydrophobicity increased for the SA-added group while decreasing for the OSA-added group, and the acylation process exposed the flexibility part of the protein molecule. Acylated EWP prepared gel (EWG) showed a translucent and slightly yellow appearance (except for the sol state of the OSA-added 1:50 group), the gel strength, water-holding capacity and rheological properties for SA-added EWG were remarkably reduced while OSA-added EWG improved apparently. Intermolecular forces analysis indicated that the addition of SA promoted the formation of disulfide bonds and strengthened proteins interactions while adding OSA weakened the interactions. Microstructural observations revealed a rougher gel network structure and weaker protein cross-linking in the gel prepared after the acylation of proteins. However, the high efficiency of SA and promotion of protein-molecule interactions were unable to counteract the negative effect of SA on the extension of the gel network structure, and the interaction between OSA expanded the formation of the gel network structure., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Edible films based on egg white protein (EWP) were prepared, and it were modified by high-intensity ultrasound (HIUS) to improve the functional properties. The findings indicated the properties of EWP films were improved at the appropriate time of HIUS treatment. With the increase of ultrasonic time, water vapor permeability (WVP) and tensile strength (TS) of EWP films ascended and then declined, and the best performance (3.30 g·mm/ m 2 ·h·KPa for WVP, and 7.28 MPa for TS) was achieved when ultrasonic time was 10 min. Thermogravimetric analysis exhibited ultrasound could enhance the thermal stability of EWP films. The SEM reflected moderate ultrasonic treatment could make the EWP films smoother. The FTIR spectroscopy and X-ray diffraction patterns of EWP films were changed by HIUS, which illustrated the secondary structure of the protein was altered. The transverse relaxation curve obtained by LF-NMR analysis showed the tightness between water and the films., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Edible alginate microgels are widely used to encapsulate, retain, protect, and release bioactive molecules in foods. Encapsulation of food proteins within alginate microgels may be advantageous for certain applications, such as creating controlled release delivery systems or for protection of other co-encapsulated bioactive components. Egg white protein-loaded alginate microgels were fabricated in this study using a simple injection-gelation method. The impact of pH (pH 3, 5 and 7) and thermal treatment (25 to 85 °C) on the encapsulation efficiency, retention, and physicochemical properties of the microgels was measured. Protein encapsulation efficiency and retention was highest at the lowest pH, which was attributed to the strong electrostatic attraction between the cationic egg white proteins and anionic alginate. Thermal treatment of the egg white proteins before microgel formation enhanced their encapsulation and retention, which was attributed to an increase in their physical dimensions due to unfolding and aggregation. As a result, it was more difficult for them to diffuse through the pores in the alginate microgels. The information obtained in this study may facilitate the design of more effective protein-loaded alginate microgels for food and other applications., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

To investigate the potential of glycation and/or heat modified egg white protein (EWP) as stabilizer for oil-in-water emulsions, glycated EWP (GEWP) was prepared by a dry-heated Maillard reaction using EWP and isomalto-oligosaccharide. Heat-induced GEWP nanoparticles (HGN) were then fabricated by heating GEWP at 90 °C for 30 min at pH 6.0-9.0. The physicochemical characteristics (particle diameter, ζ-potential and surface hydrophobicity) and emulsifying capacity of GEWP and HGN were investigated. In addition, the storage, oxidation, thermal treatment and salt stabilities of emulsions prepared with GEWP and HGN were evaluated. The results indicated that the emulsions prepared with modified EWPs exhibited higher protein adsorption on the oil-water interface and smaller particle size. The GEWP- and HGN-stabilized emulsions were stable against droplet aggregation during storage and exhibited better oxidation stability, which may be related to the enhanced antioxidant activity and absorption ability of the modified EWPs. Additionally, the emulsions prepared with GEWP and HGN exhibited higher heat and salt stabilities due to the increase in surface hydrophobicity and net charge. The thermostable structure of the proteins induced by glycation and heat treatment also contributed to the improvement in heat stability. Overall, the HGN-stabilized emulsions exhibited the best physicochemical stability among the modified EWPs., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Protein susceptibility to in vitro gastrointestinal digestion of ovomucin-depleted egg white (OdEW) adjusted to pH 4, 5, 7 and 9 and processed by heat (60 and 80 °C for 10 min) or pulsed electric fields (PEF) (1.4-1.8 kV/cm, 259-695 kJ/kg) was studied by assessing peptide production, proteolytic pattern, and the final peptide profile. Ovotransferrin was more susceptible to pepsin hydrolysis than lysozyme, with ovalbumin showing the highest proteolytic resistance. Ovalbumin was, however, hydrolyzed by pancreatin to produce a stable fragment. Heat treatment of OdEW solutions at 60 °C had little impact on protein susceptibility with the ovalbumin dimers formed having a comparable resistance to pepsinolysis as ovalbumin. Heating at 80 °C significantly enhanced protein susceptibility, as ovalbumin and protein aggregates formed were completely hydrolyzed within 30 min of pepsinolysis. Adjusting OdEW solution to pH 4 and treating with PEF at 695 kJ/kg enhanced protein susceptibility, similar to heat treatment at 80 °C, mainly owing to the enhanced enzymatic hydrolysis of ovalbumin. PEF processing can, therefore, increase protein digestion while minimizing protein aggregation, which will enhance protein functionality in egg whites., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The aim of the present study was to fabricate catechin-egg white protein (CT-EWP) conjugates as novel food-grade antioxidant emulsifiers designed to improve the physicochemical stability of β-carotene (BC) emulsions. CT-EWP conjugates were synthesized using free radical grafting, and the formation of conjugates was confirmed by electrophoresis and liquid chromatography-mass spectrometry. The physicochemical stability of BC emulsions was characterized by measuring alterations in particle size, ζ-potential and BC retention. The particle size and ζ-potential changed more rapidly at 37°C than at 4 or 25°C, however no creaming or oiling-off were observed at any of the storage temperatures, suggesting all emulsions were physically stable throughout the 30-day storage period. Compared to emulsions stabilized by EWP or CT+EWP physical mixtures (no conjugation), CT-EWP conjugate-stabilized emulsions had better resistance to environmental stresses, such as thermal processing and high ionic strengths, which was attributed to a stronger steric repulsion between the oil droplets. CT-EWP conjugates also significantly reduced the degradation rate of BC in emulsions during storage (p<0.05), which was attributed to their strong antioxidant and interfacial activities. These results indicate that CT-EWP conjugates can be utilized to develop food-grade delivery systems to protect chemically labile lipophilic bioactive compounds., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

The effect of either pulsed electric fields (PEF) or thermal processing on protein aggregation of ovomucin-depleted egg white (OdEW) solutions at different pH was assessed by solution turbidity and SDS-PAGE. Heating to 60°C for 10min caused marked protein aggregation of OdEW at pH5, 7, and 9. At constant electric field strength (E=1.4-1.8kV/cm), PEF processing under high specific energy input (W spec =260-700kJ/kg) induced some protein aggregation at pH5 and 7, but not at either pH4 or 9. Similar effects of pH on protein aggregation were observed upon PEF processing at varied E (from 0.7 to 1.7kV/cm) but with constant W spec (713kJ/kg). Analysis by SDS-PAGE revealed that proteins in the OdEW solution at pH5 were most susceptible to both PEF- and heat-induced protein aggregation and lysozyme was only involved in the formation of insoluble aggregates under PEF. The present study shows that PEF treatment has considerable potential for minimizing protein aggregation in the processing of heat-labile egg white proteins. Retaining the OdEW proteins in solution during processing has potential industry application, for example, protein fortification of drinks with OdEW, where minimizing solution turbidity would be advantageous., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Egg white protein (EWP) was phosphorylated by dry heating in the presence of pyrophosphate. The antioxidant activity of phosphorylated EWP (PP-EWP) was then investigated before and after conjugation of epigallocatechin gallate (EGCG). The binding interaction between EWPs and EGCG was investigated by UV and FTIR, which indicated that more EGCG bound to PP-EWP than to native EWP and dry-heated EWP. The antioxidant activities including ABTS + free-radical scavenging capacity, oxygen radical antioxidant capacity, reducing power, chelating capacity, and superoxide anion scavenging activity of EWP were remarkably improved by phosphorylation before and after conjugation of EGCG. The improved antioxidant property of PP-EWP can be attributed to the introduced phosphate group, more exposed hydrophobic group, increased surface thiol group of protein, and more EGCG bound to EWP. The secondary structure of PP-EWP decreased with more bound EGCG. This study is the first to describe an improvement in the antioxidant property of EWP by phosphorylation and conjugation of EGCG, thereby providing insight into the design of food protein antioxidant., (Copyright © 2014 Elsevier Ltd. All rights reserved.)