Underlying mechanism for the differences in heat-induced gel properties between thick egg whites and thin egg whites: Gel properties, structure and quantitative proteome analysis

Improving gelation properties of low concentration peanut protein isolate by phosphorylation

Low concentration (10 %) peanut protein isolate (PPI) could not form an ideal gel structure. However, phosphorylation is a convenient and cost-effective method to enhance gelation properties of proteins. Therefore, this paper aimed to improve gelation properties of low concentration PPI using sodium tripolyphosphate (STP). Gelation and structural properties of phosphorylated peanut protein isolate gel (P-PPIG) were analyzed by SEM, analysis of texture and rheology, water holding capacity (WHC), LF-NMR, intermolecular forces, surface hydrophobicity, FTIR, etc. Surface hydrophobicity of P-PPIG increased, but total content of α-helix and β-sheet decreased as STP concentration increased. The results of intermolecular forces manifested STP boosted hydrophobic interactions and disulfide bonds, which were crucial forces for forming P-PPIG. P-PPIG with 3 % STP had the most ordered network structure, the largest hardness (175.75 g), chewiness (132.71 g), final storage modulus (678,000 Pa) with temperature scanning, and the highest storage modulus and loss modulus with frequency scanning among all samples. Moreover, the analysis of LF-NMR indicated 3 % STP caused the lowest mobility of water with the highest WHC (97.51 %) of P-PPIG among all samples. The findings exhibited STP could promote gelation properties of P-PPIG, especially 3 % STP, providing data references for application of STP in protein gelation.

Proteomic Analysis of the Differences in Heat-Induced Gel Properties of Egg White between Two Chinese Indigenous Duck Breeds

The gel properties of egg white are important functional traits of poultry eggs, yet limited research exists on the utilization of egg whites from local Chinese duck breeds. This study systematically investigated gel properties, ultrastructure, and proteomics of Putian Black Duck (PTEW) and Liancheng White Duck egg whites (LCEW). Results showed that PTEW gels exhibited superior texture properties (hardness, 20.6% higher than LCEW; gumminess, 11.3% higher; chewiness, 11.1% higher; cohesiveness, 7.1% higher) and water holding capacity (7.7% higher). In contrast, LCEW gels were lighter (9.6% higher than PTEW) and whiter (7.3% higher than PTEW). Moreover, LCEW (78 °C) gelation occurred at a higher temperature than PTEW (74 °C). PTEW gels demonstrated a higher relative content of ordered secondary structures (α-helix, 8.6%; β-sheet, 77.3%; 3.7% and 6.2% higher than those of LCEW, respectively) and hydrophobic interactions (56.8%, 9.4% higher than LCEW), enhancing hardness and stability. SEM imaging revealed a denser, more uniform protein network in PTEW. Proteomic analysis identified key proteins, including ovalbumin, ovomucoid, ovalbumin-related protein Y, and ovostatin, as primary contributors to gelation differences. This study offers a comprehensive "properties-structure-substance" understanding of thermal gelation differences between PTEW and LCEW, providing a theoretical basis for utilizing Chinese native duck eggs.

Investigation on appearance, texture, and molecular structure of heat-alkali synergistically induced egg white gel

To investigate the effect of heat-alkali synergistical induction on egg white gels, the gels formed from fresh duck egg whites were induced by heating in a water bath at 50 °C, 55 °C, 60 °C and 65 °C for 10 min, followed by the addition of NaOH at concentrations of 4.5 %, 5.0 %, 5.5 %, and 6 % were investigated at the level of appearance, texture, and molecular structure in this study. The appearance, physical and chemical character, textural properties, and molecular structure comprehensive investigation concluded that alkali induction caused heat-induced egg white protein to continue to be denatured, the degree of transparency was increased, part of the free water was converted to bound water, the intermolecular repulsion increased, the microscopic pores increased. The proteins in egg white continued to be crosslinked to form a three-dimensional network structure, creating a stable gel structure.

Preparation and characterization of chickpea protein isolate-grape seed proanthocyanidin-konjac gum ternary complex: Focusing on structure, gel properties, stability and functional properties

The ternary complex effectively prevents droplet aggregation, Ostwald ripening, and phase separation through its gel network, thereby demonstrating its capability in bioactive compound delivery. In this work, the influence of varying chickpea protein isolate (CPI) levels on the microstructure, gel characteristics, stability and functional properties of grape seed proanthocyanidin (GSP) and konjac gum (KGM) stabilized ternary complexes was investigated. Visual appearance indicated the formation of a non-stratified ternary complex as the CPI enhanced to 3-4 %. Ternary complexes containing 4 % CPI exhibited the highest encapsulation efficiency (94.75 %), which was attributed to the formation of the smallest droplets, as confirmed by particle size analysis and microscopy. At the same time, the inclusion of CPI enhanced the color, pH, texture characteristics and water holding capacity (WHC) of ternary complexes. Moreover, rheological analysis further demonstrated that the ternary complexes exhibited solid-like behavior, with the storage modulus (G') exceeding the loss modulus (G"). Meanwhile, thermal stability improved from 77.97 % to 93.54 %, while the thawing loss rate decreased from 20.13 % to 15.03 %. The incorporation of 3 %-4 % CPI also enhanced the hydrogen bonding and hydrophobic interactions within the ternary complexes, resulting in more compact gel network structures. In addition, CPI increased the antioxidant properties of the ternary complex, with 4 % CPI increasing the 1,1-diphenyl-2-trinitrohydrazide (DPPH) radical scavenging rate by 18.69 % compared to the ternary complex containing 1 % CPI. The results demonstrated that CPI improved the stability and functional characterizations of ternary complexes, positioning it as a promising additive and fat substitute. Additionally, CPI showed potential as an effective carrier for functional bioactive compounds.

Research note: Study on liquid-liquid phase separation of thick and thin egg white

"Gel-like" thick egg white (TKEW) and "solution-like" thin egg white (TNEW) are not mutually soluble in fresh egg white, showing a natural liquid-liquid phase separation phenomenon. The effects of storage temperature, storage time, ultrasonic force, mechanical stirring and chemical ions on the stability of liquid-liquid phase of TKEW and TNEW were systematically analyzed in this paper. It was found that the collapse of TKEW gel structure was the key to cause two phase separation. Room temperature storage was easier to cause the structure of TKEW collapsed and the viscosity decreased, which led to the phase separation interface between TKEW and TNEW began to lose stability. Besides, ultrasonic treatment, stirring and phosphate-buffered saline (20 mmol/L) in acidic environment also reduced the proportion of TKEW, and result in the disappearance of the two-phase interface. While, the salt at physiological concentration was found to contribute to the stability of TKEW. The rule of liquid-liquid phase separation of TKEW and TNEW provided an important basis for egg white storage and diversified utilization.

Anti-colorectal cancer activity of constructed oleogels based on encapsulated bioactive canola extract in lecithin for edible semisolid applications

Globally, colorectal cancer ranks second in women and third in men. Hydrophilic anticancer agents have limited use in lipid systems due to their weak solubility. Therefore, this study aimed to develop oleogels based on pumpkin seed oil (R1) and hydrophilic bioactive canola extract (BCE or R2) that were extracted from canola meal by-products. BCE was effectively dispersed in oleogels through the encapsulation of BCE with various concentrations (0.08, 0.2, and 0.4%) in soy lecithin to form BCE gelling agents. Four formulations (F1 as plain, F2-F4 with different concentrations of BCE) were produced using two gelators (BCE gelling agent and beeswax). The oxidative stability, microstructure, FTIR, antioxidant activity, and time-dependent experiment were investigated. The cytotoxicity against colorectal HCT116 and Caco-2 cancer cell lines in vitro was evaluated. The anti-apoptotic PI3k and COX-2 protein expressions were also assessed. The peroxide, p-anisidine, and total oxidation values of F4 were 7.85, 26.66, and 42.35, respectively, during 60 days at 60 ± 2 °C. The antioxidant activity values of F4 were 74.40% for DPPH, 54.28% for ABTS, and 5.77 mg/g for FRAP. F4 demonstrated the highest significant cytotoxic effects on cancerous cells, particularly in the Caco-2 cells with 1.40- and 1.41-fold increases compared to R2 and the positive control doxorubicin, respectively. PI3k and COX-2 expression levels were down-regulated while iNOS activity was up-regulated in both cells, with very high down-regulation recorded for F4 in Caco-2 cells. This study developed a method for producing stable lipid products loaded with hydrophilic antioxidants that may be used as an anti-colorectal platform.

Research note: Proteomics profiling reveal key proteins in egg white emulsification

Egg white proteins are widely recognized as excellent natural emulsifiers, yet the molecular mechanisms underlying their emulsification properties remain incompletely understood, particularly regarding the roles of individual proteins in complex natural systems. Using 4D-label-free quantitative proteomics, we systematically investigated protein dynamics during egg white emulsification by comparing egg white (EW) and the aqueous phases of egg white emulsions (EWE-W). Proteomic analysis identified 96 distinct proteins, with 64 showing significant abundance changes during emulsification. Among them, lysozyme, ovomucin and Protein TENP were heavily involved in the formation of the oil-water interface during the emulsification process, leading to a significant decrease in their abundance in EWE-W. In particular, Protein TENP showed the most significant reduction in abundance among all differential proteins. These findings provide new insights for optimizing egg white functionality in food applications and understanding protein-based emulsion systems.

Duckweed protein: Extraction, modification, and potential application

Discovering alternative protein sources that are both nutritious and environmentally friendly is essential to meet the growing global population's needs. Duckweed offers promise due to its cosmopolitan distribution, rapid growth, high protein content, and scalability from household tanks to large lagoons without requiring arable land that competes for the major crops. Rich in essential amino acids, particularly branched-chain amino acids, duckweed supports human health. Extraction methods, such as ultrasound and enzymatic techniques, enhance protein yield compared to traditional methods. However, low protein solubility remains a challenge, addressed by protein modification techniques (physical, chemical, and biological) to broaden its applications. Duckweed proteins hold potential as functional food ingredients due to their unique physicochemical properties. This review also includes patents and regulations related to duckweed protein, filling a gap in current literature. Overall, duckweed presents a sustainable protein source with a lower environmental impact compared to conventional crops.

Design and test of steam-injected continuous scrambled egg device

To solve the existing problems of low yield, uneven quality, and single form of industrially scrambled eggs, we have developed a continuous high-output steam scrambled egg device based on the principle of steam injected. By establishing calibration curves for egg, oil, and steam flow rates, determining the key parameters of the equipment, and simulating the heat transfer process between steam and egg by Computational Fluid Dynamics (CFD), we created the device and verified its production performance. The results show that the capacity of this device can reach 104.4 kg/h, which greatly improves production efficiency. By precisely adjusting the steam flow, this device can produce scrambled eggs in the form of blocks, thick slices, thin slices, and broken. Moreover, the differences between the scrambled eggs produced by this device and the traditional frying pan were not significant in terms of color, taste and sensory evaluation (p > 0.05). Most importantly, this device produces scrambled eggs with better elasticity, softer texture, and better overall uniformity of maturity to achieve consumer satisfaction. This study provides technical support for the industrialized continuous production of Chinese egg dishes.

Chain reactions of temperature-induced egg white protein amorphous aggregates: Formation, structure and material composition of thermal gels

Egg white protein is widely used in food, chemical, medical and other fields due to its excellent thermal gel properties. However, the regularity of egg white thermal gel (EWTG) by temperature influence is still unknown. In this study, we investigated the potential mechanism of temperature (75-95 °C, 15 min) gradient changes inducing thermal aggregation and gel formation of EWTG. The results showed that changes in textural characteristics and water holding capacity (WHC) of EWTGs depended on switching in protein aggregation morphology (spherical shape - chain shape - regiment shape) and gel network structure differences ("irregular bead-like" - "regular lamellar structure"). In addition, proteomics indicated that the generation of amorphous protein aggregates at 95 °C might be related to Mucin 5B as the aggregation core. The research revealed the EWTG formation from "whole egg white protein" to "single molecules", aiming to provide a reference for quality control in gel food processing.

Ultrasonic-microwave technique promotes the physicochemical structure of hydrogel and its release characterization of curcumin in vitro

In this study, soybean protein isolate and hawthorn pectin were mixed to prepare binary hydrogels using ultrasound and microwave techniques. Moderate treatment can not only significantly improve the mechanical strength of the hydrogel, but also increase the tightness of the internal cross-linking. The strengthening of interactions (hydrogen bonds, hydrophobic interactions, and disulfide bonds) was the main reason for this trend. Especially, the ultrasonic-microwave (80 s) treatment hydrogel possessed excellent hardness (33.426 N), water-holding capacity (98.26%), elasticity (G' = 1205 Pa), and a more homogeneous and denser microstructure. In addition, the hydrogel minimized the extent of curcumin loss (21.23%) after 5 weeks of storage. In general, the ultrasonic-microwave technique could significantly promote the physicochemical structure and curcumin bioaccessibility of hydrogels, which showed excellent market prospects in the food industry.

Moderation-excess interactions of epigallocatechin gallate and CaCl2 modulate the gelation performance of egg white transparent gels

In this study, the moderation-excess interaction of epigallocatechin gallate (EGCG) and calcium ions (Ca2+) to the gelation performance of transparent egg white protein (EWP) gel (EWG) was explored. The oxidation of EGCG introduced a yellowish-brown EWG, whereas the weakening of Ca2+ ionic bonds caused a notable reduction in the hardness of EWG, from 120.67 g to 73.57 g. Achieving the optimal EGCG-to-Ca2+ ratio in EWG conferred enhanced water-holding capacity to 86.98%, while an excess of EGCG attributed to the creation of a three-dimensional structure within the void "walls". The elevated presence of EGCG influenced the ionic bonds and hydrophobic interactions, thereby presenting a moderate-excess relationship with sulfhydryl and disulfide bonds, β-sheet, and α-helical structures. Notably, EGCG reduced the digestibility of EWG to 50.06%, while concurrently fostering the creation of smaller particle sizes. This study provides a scientific basis for the controllable preparation and quality regulation of transparent EWG.

Dynamic changes in the aggregation-depolymerization behavior of Ovomucin-Complex and its binding to urease during in vitro simulated gastric digestion

Ovomucin-Complex extracted from egg white is expected to have a barrier function similar to gastric mucin. In this study, the dynamic changes in structure, rheological properties and binding ability of Ovomucin-Complex during in vitro simulated gastric digestion were investigated. The results from HPLC and CLSM showed that extremely acidic pH (pH = 2.0) promoted Ovomucin-Complex to form aggregation. Acid-induced aggregation may hinder its binding to pepsin, thus rendering Ovomucin-Complex resistant to pepsin. Consequently, most of the polymer structure and weak gel properties of Ovomucin-Complex retained after simulated gastric digestion as verified by HPLC, CLSM and rheological measurement, although there was a small breakdown of the glycosidic bond as confirmed by the increased content of reducing sugar. The significantly reduced hydrophobic interactions of Ovomucin-Complex were observed under extremely acidic conditions and simulated gastric digestion compared with the native. Noticeably, the undigested Ovomucin-Complex after simulated gastric digestion showed a higher affinity (KD = 5.0 ± 3.2 nm) for urease - the key surface antigen of Helicobacter pylori. The interaction mechanism between Ovomucin-Complex and urease during gastric digestion deserves further studies. This finding provides a new insight to develop an artificial physical mucus barrier to reduce Helicobacter pylori infection.

Histological and molecular difference in albumen quality between post-adolescent hens and aged hens

The decline in albumen quality resulting from aging hens poses a threat to the financial benefits of the egg industry. Exploring the underlying mechanisms from the perspective of cell molecules of albumen formation is significant for the efficient regulation of albumen quality. Two individual groups of Hy-Line Brown layers with ages of 40 (W40) and 100 (W100) wk old were used in the present study. Each group contained over 2,000 birds. This study assessed the egg quality, biochemical indicators and physiological status of hens between W40 and W100. Subsequently, a quantitative proteomic analysis was conducted to identify differences in protein abundance in magnum tissues between W40 and W100. In the W40 group, significant increases (P < 0.05) were notable for albumen quality (thick albumen solid content, albumen height, Haugh unit), serum indices (calcium, estrogen, and progesterone levels), magnum histomorphology (myosin light-chain kinase content, secretory capacity, mucosal fold, goblet cell count and proportion) as well as the total antioxidant capacity of the liver. However, the luminal diameter of the magnum, albumen gel properties and random coil of the albumen were increased (P < 0.05) in the W100 group. The activity of glutathione, superoxidase dismutase, and malondialdehyde in the liver, magnum, and serum did not vary (P > 0.05) among the groups. Proteomic analysis revealed the identification of 118 differentially expressed proteins between the groups, which comprised proteins associated with protein secretion, DNA damage and repair, cell proliferation, growth, antioxidants, and apoptosis. Furthermore, Kyoto Encyclopedia of Genes pathway analysis revealed that BRCA2 and FBN1 were significantly downregulated in Fanconi anemia (FA) and TGF-β signaling pathways in W100, validated through quantitative real-time PCR (qRT-PCR). In conclusion, significant age-related variations in albumen quality, and magnum morphology are regulated by proteins involved in antioxidant capacity.

Enriching Eggs with Bioactive Compounds through the Inclusion of Grape Pomace in Laying Hens Diet: Effect on Internal and External Egg Quality Parameters

(1) Background: Grapes and their associated by-products (such as grape pomace, GP) stand out for their polyphenol content, which makes them a source of bioactive compounds with antioxidant capacity. The aim of this research was to determine if the inclusion of 50 g/kg of GP in the diet of hens could enrich eggs with antioxidants and to study its effect on internal and external egg quality parameters. (2) Methods: A trial was conducted with two genetic lines of hens, which were fed either a control diet or a diet containing 50 g/kg of GP. Performance, internal and external egg quality, and egg yolk content of vitamins E and A and gallic acid were determined. (3) Results: In eggs laid by hens fed a GP diet, Haugh units and yolk color scores were enhanced, and eggshells became thinner, but without affecting the breaking strength. No dietary effect was observed on the vitamin contents of the yolk. A higher gallic acid content was observed in the yolks of eggs laid by hens fed the GP diet, suggesting that some dietary phenolic compounds could be transferred to the eggs. Hen genetics influenced egg weight, albumen Haugh units, shell thickness, and α- and γ-tocopherol concentration in yolks. (4) Conclusions: Dietary inclusion of GP improved the internal quality of eggs, enriching yolks with a phenolic compound but reducing shell thickness.

Integrated landscape of chicken egg chalaza proteomics

Chicken egg chalaza (CLZ) is a natural colloidal structure in eggs that exists as an egg yolk stabilizer and is similar in composition to egg white. In this study, the proteome, phosphoproteome, and N-glycoproteome of CLZ were characterized in depth. We hydrolyzed the CLZ proteins and enriched the phosphopeptides and glycopeptides. We identified 45 phosphoproteins and 80 N-glycoproteins, containing 59 phosphosites and 203 N-glycosylation sites, respectively. Typically, the ovalbumin in CLZ was both phosphorylated and N-glycosylated, with 4 phosphosites and 4 N-glycosylation sites. Moreover, we identified 2 N-glycosylated subunits of ovomucin, mucin-5B and mucin-6, with 32 and nine N- glycosylation sites, respectively. Analysis of the phosphorylation and N-glycosylation status of CLZ proteins could provide novel insights into the structural and functional characteristics of CLZ.

Irradiation-Assisted Enhancement of Foaming and Thermal Gelation Functionality of Liquid Egg White

Ionizing radiation has its unique popularity as a non-thermal decontamination technique treating with protein-rich foodstuffs to ensure the microbial and sensory quality, particularly for shell eggs. However, the changes in the functional properties of egg protein fractions such as liquid egg white (LEW) with macro/microstructural information are still controversial. Hence, this study was designed to elaborate the foaming and heat-set gelation functionality of LEW following different γ-ray irradiation dose treatments (0, 1, 3 or 5 kGy). For such, the physicochemical properties (active sulfhydryl and the hydrophobicity of protein moieties), structural characteristics (through X-ray diffraction, Fourier-transform infrared spectroscopy and differential scanning calorimetry) and interfacial activities (rheological viscosity, interfacial tension, microrheological performance) were investigated. Then, the thermal gelation of LEW in relation to the texture profile and microstructure (by means of a scanning electron microscope) was evaluated followed by the swelling potency analysis of LEW gel in enzyme-free simulated gastric juice. The results indicated that irradiation significantly increased the hydrophobicity of liquid egg white proteins (LEWPs) (p < 0.05) by exposing non-polar groups and the interfacial rearrangement from a β-sheet to linear and smaller crystal structure, leading to an enhanced foaming capacity. Microstructural analysis revealed that the higher dose irradiation (up to 5 kGy) could promote the proteins' oxidation of LEW alongside protein aggregates formed in the amorphous region, which favored heat-set gelation. As evidenced in microrheology, ≤3 kGy irradiation provided an improved viscoelastic interface film of LEW during gelatinization. Particularly, the LEW gel treated with 1 kGy irradiation had evident swelling resistance during the times of acidification at pH 1.2. These results gave new insight into the irradiation-assisted enhancement of foaming and heat-set gelation properties of LEW.

Heat-induced gelation of egg white proteins depending on heating temperature: Insights into protein structure and digestive behaviors in the elderly in vitro digestion model

This study investigated the effects of heating temperature of egg white gels (EWGs) on the digestive characteristics by heating egg white (EW) to reach 75 °C (EWG-75) and 95 °C (EWG-95). The gel protein structure showed a decrease in the maximum tryptophan fluorescence intensity and a significant increase in the surface hydrophobicity of EWGs compared to EW (P < 0.05). The total and reactive free sulfhydryl groups were higher in the EWGs than in the EW (P < 0.05). While the proportions of α-helical and β-sheet structures remained similar in EW and EWG-75 (P > 0.05), EWG-95 exhibited a notable decrease in α-helix content (P < 0.05) and an increase in β-sheet content (P < 0.05). Furthermore, EWG-95 displayed higher hardness and cohesiveness than EWG-75 (P < 0.05). In the adult and elderly in vitro digestion models, EWG-95 exhibited the highest protein digestibility (50.44 % and 54.65 % in the models of elderly and adult subjects, respectively) after GI digestion (P < 0.05), followed by EWG-75 and EW. The electrophoretogram of the digesta revealed more intense protein bands in the elderly digestion model, particularly in the gastric digesta of EW, indicating slower digestion compared to the adult model. Therefore, EW should be appropriately heated before consumption, especially for elderly individuals, to facilitate efficient protein digestion and absorption.

Quantitative proteomics provides new insights into the mechanism of improving rehydration of egg white powder by ultrasonic pretreatment

Poor rehydration is one of the key factors affecting the functional properties of egg white powder (EWP). Reducing rehydrated precipitates is important for the processing and application of EWP. In this study, effects of ultrasonic pretreatment on the physicochemical and functional properties of EWP rehydration solutions were studied with the aim of revealing the mechanism of ultrasonic pretreatment to improve rehydration. Compared with freeze-dried EWP (FD) and spray-dried EWP (SD), the percentage of ultrasonic pretreated FD (UFD) and ultrasonic pretreated SD (USD) rehydrated precipitates decreased by 13.0 % and 5.6 %, respectively, after ultrasonic pretreatment (0.25 W/mL for 10 min); and the average particle sizes of UFD and USD solutions decreased by 22.5 % and 15.5 %, respectively. Fourier transform infrared spectroscopy showed that ultrasonic pretreatment caused higher β-sheet content in the protein secondary structure of UFD rehydrated precipitates (49.2 %). Quantitative proteomic analysis revealed a decrease in the abundance of major egg white proteins (ovalbumin, ovotransferrin, ovomucoid and ovomucin) in the rehydrated precipitates of UFD, except for lysozyme. It was also shown that lysozyme-centered aggregates were disrupted in the rehydrated precipitates of UFD. Our research suggests that ultrasonic pretreatment improves EWP rehydration by reducing the interactions between high abundance proteins as well as improving the solubility of high abundance proteins.

Translucency mechanism of heat-induced pigeon egg white gel

In this study, the properties of pigeon egg white (PEW) and chicken egg white (CEW) thermal gels were compared, with the aim of revealing the mechanisms involved in the high transparency of PEW thermal gels. Results demonstrated that PEW gels exhibited higher transparency than CEW gels. Scanning electron microscope (SEM) and transmission electron microscope (TEM) analysis revealed that PEW gels formed a fine chain gel network structure with an average diameter of thermal aggregates (89.84 ± 7.13 nm). The molecular properties of PEW proteins, such as higher content of β-sheet structures (32.73 %), reactive groups (free sulfhydryl groups, hydrophobic groups), and absolute zeta potential (-3.563 mV), were found to contribute to the formation of smaller thermal aggregates during thermal denaturation. The microrheology measurements showed that these features allowed PEW proteins to interact less with each other and form smaller thermal aggregates during thermal denaturation, which facilitated the formation of fine chain gel networks and thus improved the transparency of the gels. The present study initially reveals the molecular basis of the high transparency of PEW thermal gels and provides a theoretical reference for the development of new highly transparent protein materials.

Underlying mechanisms of egg white thinning in hot spring eggs during storage: Weak gel properties and quantitative proteome analysis

As a weakly gelling protein, hot spring egg white underwent thinning during storage. This study explored the mechanism of thinning in hot spring egg white from the perspective of "gel structure and protein composition" using quantitative proteomics, SEM, SDS-PAGE, and other techniques. Quantitative proteomics analysis showed that there were 81 (44 up-regulated and 21 down-regulated) key proteins related to thinning of hot spring egg white. The changes in the relative abundance of proteins such as ovalbumin-related Y, mucin-6, lysozyme, ovomucoid, and ovotransferrin might be important reasons for thinning in hot spring egg white. SEM results indicated that the gel network gradually became regular and uniform, with large pores appearing on the cross-section and being pierced. Along with the decrease in intermolecular electrostatic repulsion, protein molecules gradually aggregated. The particle size gradually increased from 139.1 nm to 422.5 nm. Meanwhile, the surface hydrophobicity, and disulfide bond content gradually increased. These changes might be the reasons for thinning in hot spring egg white during storage. It can provide a new perspective for studying the thinning mechanism of weakly gelling egg whites.

Quantitative proteomic analysis of chicken egg white and its components

The protein profiles and properties of chicken egg white and its three components (thick egg white, TKEW; thin egg white, TNEW; and chalaza, CLZ) were comprehensively compared. The proteomes of TNEW and TKEW are relatively similar, but the abundance of mucin-5B and mucin-6 (the two subunits of ovomucin) is significantly higher in TKEW than in TNEW (42.97% and 870.04%, respectively), while the lysozymes in TKEW are 32.57% higher (p < 0.05) than those in TNEW. Meanwhile, the properties (including the spectroscopy, viscosity, and turbidity) of TKEW and TNEW are significantly different. Comprehensively, it is speculated that the electrostatic interactions between lysozyme and ovomucin are the main reason for the high viscosity and turbidity of TKEW. Compared with egg white sample (EW), CLZ has a higher abundance of insoluble proteins (mucin-5B, 4.23-fold; mucin-6, 6.89-fold) and a lower abundance of soluble proteins (ovalbumin-related protein X, 89.35% lower than EW; ovalbumin-related protein Y, 78.51% lower; ovoinhibitor, 62.08% lower; riboflavin-binding protein, 93.67% lower). These compositional differences should explain the insolubility of CLZ. These findings are important references for deepening the research and development of egg white in the future, such as the thinning of egg white, the molecular basis of changes in egg white properties, and the differential application of TKEW and TNEW.

Formation mechanism of salted egg yolk mudding during storage: Protein oxidation, gel structure, and conformation

The aim of this study was to investigate the formation mechanism of salted egg yolk (SEY) mudding during storage. Results showed that the soluble protein, hardness, and intrinsic fluorescence intensity of SEY decreased significantly during storage, while total volatile basic nitrogen, sulfhydryl group, dityrosine, adhesiveness, and surface hydrophobicity increased significantly, and the intrinsic fluorescence peak position red-shifted at first and then blue-shifted. In addition, from the results of infrared and microstructure analyses, there was an obvious oxidation reaction between protein and lipid in the late storage stage; the structure of SEY was destroyed, many random coils were formed, and the degree of protein-lipid binding and the crystallinity of SEY protein decreased during storage. Finally, the heatmap analysis revealed that the protein and lipid oxidation and conformational changes might be the main reasons for SEY mudding. This study can provide theoretical guidance for the control of SEY mudding.

The physical and structural properties of acid-Ca2+ induced casein-alginate/Ca2+ double network gels

The design of protein or polysaccharide interpenetrating network gels according to their physicochemical properties is required to obtain the desired properties of hydrogels. In this study, a method was proposed to prepare casein-calcium alginate (CN-Alg/Ca²⁺) interpenetrating double-network gels by the release of calcium from a calcium retarder during acidification to form calcium-alginate (Alg/Ca²⁺) gel and casein (CN) acid gel. Compared with the casein-sodium alginate (CN-Alg) composite gel, the CN-Alg/Ca²⁺ dual gel network with an interpenetrating network gel structure has better water-holding capacity (WHC) and hardness. The rheology and microstructure results showed that the dual-network gels of CN and Alg/Ca²⁺ induced by gluconic acid-δ-sodium (GDL) and calcium ions were the network structure of the Alg/Ca²⁺ gel, which was the "first network", and the CN gel, which was the "second network". It was proven that the microstructure, texture characteristics, and WHC of the double-network gels could be regulated by changing the concentration of Alg in the double-network gels and that the 0.3 % CN-Alg/Ca²⁺ double gels showed the highest WHC and firmness values. The aim of this study was to provide useful information for the preparation of polysaccharide-protein mixed gels in the food industry or other fields.

Improvement of enzymatic cross-linking of ovalbumin and ovotransferrin induced by transglutaminase with heat and reducing agent pretreatment

The effects of transglutaminase (TGase, 1.0 unit/mL) with heat (95 °C, 5 min), 2-mercaptoethanol (2-ME, 0.83 %), and l-cysteine (l-Cys, 50 mM) pretreatment on the cross-linking of ovalbumin (OVA) and ovotransferrin (OVT) were investigated. SDS-PAGE revealed that although the polymerization of OVA and OVT did not occur after 3 h of incubation at 40 °C with TGase, OVA polymerized into high molecular weight polymers following TGase with 2-ME and heat pretreatment after 3 h of incubation. The surface hydrophobicity and reactive sulfhydryl (SH) groups of OVA samples significantly increased from 4065.7 ± 136.7 and 89.3 ± 1.2 SH groups (μmol/g) to 31483.6 ± 342.7 and 119.5 ± 3.7 SH groups (μmol/g), respectively. Similar results were obtained for OVT with TGase and l-Cys pretreatment and a 3-h incubation at 40 °C. The use of TGase, a reducing agent, and/or heat pretreatment can be used for the polymerization of OVA and OVT.

Quantitative proteomics study on the changes of egg white of yellow preserved primary chicken eggs soaked in alkali solution

In order to investigate the changes of egg white of primary chicken eggs after being soaked in alkali solution, the tandem mass tags (TMT)-labeled quantitative proteomic technology combined with bioinformatics was conducted in this study. The results indicated that 100 differentially expressed proteins (DEPs) in yellow preserved primary egg white (YPPEW), 75 of which were highly and significantly correlated with the quality traits of YPPEW (| r | ≥ 0.9000, P < 0.01). Most of DEPs were involved in cellular processes by binding in extracellular space. Six pathways revealed the potential anti-inflammatory, anti-virus, anti-cancer and neuromodulatory mechanism of YPPEW. The current research provided a theoretical basis for the further study on YPPEW.

Influence and effect mechanism of disulfide bonds linkages between protein-coated lipid droplets and the protein matrix on the physicochemical properties, microstructure, and protein structure of ovalbumin emulsion gels

In this study, disulfide bonds between the interfacial protein film formed on the lipid particles and the protein in ovalbumin emulsion gels were blocked with 0, 1, 3, 5 and 10 mM of the N-ethylmaleimide (NEM) to explore the influence and effect mechanism of disulfide bonds between the interfacial proteins on the physicochemical properties, microstructure, and protein structure of sunflower oil-ovalbumin emulsion gels. Ovalbumin emulsion gels with NEM-treated ovalbumin emulsion (N-OE) had lower hardness, free sulfhydryl content, water holding capacity (WHC), and surface hydrophobicity, but higher spin-spin relaxation time (T₂) than ovalbumin emulsion gels with NEM-treated ovalbumin substrate solution (N-OSS). In addition, N-OE and N-OSS had lower hardness, free sulfhydryl content, WHC and surface hydrophobicity, as well as a more coarse and disordered microstructure than non-NEM treated ovalbumin emulsion gel (control group). The free sulfhydryl content, hardness, WHC, and surface hydrophobicity of the ovalbumin emulsion gels all decreased as the NEM concentration rose (p < 0.05), whereas the amide A band changed to higher wave numbers. These results collectively indicated that the reduction of disulfide between the interfacial layer and the proteins inhibited the hydrophobic effect, the formation of hydrogen bonds, and prevented the formation of larger aggregates. Thus the disulfide bonds between the interfacial proteins contribute to the hardness enhancement and water stabilization of the ovalbumin gel.

Quantitative proteomics provides insights into the mechanism of the differences in heat-induced gel properties for egg white proteins with different interior quality during ageing in laying hens

The purpose of this study was to investigate the mechanism for the differences in heat-induced gel properties of egg white proteins with different interior quality during ageing in laying hens. Quantitative proteomic analysis revealed that the abundance of ovotransferrin, avidin, mucin 5B, and clusterin increased with decreasing Haugh units (HU), leading to the transition from disorder to order in the secondary and tertiary structure of egg white proteins, with the burial of hydrophobic groups and a reduction in the negative charge on the protein surface, rendering the egg white protein solution aggregated. These changes would accelerate the rate of aggregation of egg white proteins during heating, resulting in the loss of orientation of the molecular chains, forming coarse and porous gel structures and poor gel properties. This research provides a new idea for improving the gelling properties of egg whites from lower interior quality during ageing in laying hens.

Changes in structural and functional properties of whey protein cross-linked by polyphenol oxidase

The natural whey protein is unstable, to achieve more efficient utilization, the functional properties of whey protein were modified by changing its structure, and enzymatic cross-linking is one of the common methods in dairy products to change the functional characterization. This study was conducted with objective to evaluate the structural and functional of whey protein which was cross-linked by polyphenol oxidase from Agaricus bisporus. Whey protein was cross-linked by polyphenol oxidase, and the polymers and dimers were revealed by SDS-PAGE and LC-MS/MS, the structural alterations of the polymers were analyzed by UV-vis, fluorescence spectroscopy and SEM, and the effects of functional properties of whey protein after cross-linked were also explored. Results showed that dimer and high polymer of β-lactoglobulin were formed, the secondary structure of whey protein was exhibited a significant variation, and the microstructure changed obviously. Moreover, the foaming and antioxidant activity of whey protein was enhanced although the emulsifying was reduced after cross-linked. These findings emphasize the feasible application of enzymatic cross-linking in improving the functional properties of whey protein, and provide a new direction for changing the traditional processing technology of whey protein and developing high-quality products.

Application of definitive screening design to optimization of the protein extraction and functional properties of proteins in Auricularia auricula

BACKGROUND

Auricularia auricula (A. auricula) is one of the most abundant sources of plant protein in edible fungi. Problems of low protein yield exist in traditional methods of protein extraction such as alkali extraction and ultrasonic-assisted alkali after pretreatment with enzymes. Thus, the protein extraction process was investigated and optimized using a definitive screening design from A. auricula to improve the protein yield under practical operating conditions of temperature, the concentration of NaCl, meal/water ratio, extraction time and pH.

RESULTS

The yield of protein isolates of the isoelectric-ammonium sulfate precipitation (9.34% w/w) was obtained almost three times and the protein content (55.23% w/w) was approximately 1.6 times that of the traditional extraction method of isoelectric precipitation. Next, the optimized method was successfully applied to the analysis of the functional properties of the protein. A. auricula protein isolate (AAPI) had better solubility, emulsification and foaming capacity than soy protein isolate (SPI) and pea protein isolate (PPI), and the oil holding capacity of AAPI exhibited extremely well, which was approximately five times that of SPI and six times that of PPI. The texture properties of AAPI gel were similar to those of PPI gels.

CONCLUSION

AAPI extracted by the optimized method had a satisfactory yield and had the potential to substitute plant-originated proteins in food processing. © 2022 Society of Chemical Industry.

Lysozyme impacts gel properties of egg white protein via electrostatic interactions, polarity differences, local pH regulation, or as a filler

The effects of lysozyme on egg white gel properties and their underlying causes were investigated under comparison between lysozyme removed with ion exchange resin and three levels of commercial lysozyme powder (1/2, 2/2, 3/2 the natural concentration in egg white) re-added in the lysozyme-removed system. Results showed that a lysozyme-removed gel obtained the best water holding capacity (61.61 %), lowest cooking loss (11.85 %), and enhanced textural properties (hardness, 638.04 g; resilience, 0.57; and gumminess), which was attributed to lysozyme promoting protein aggregation and weakening electrostatic repulsion by charge neutralization and competition for water, and this could be eliminated by removing lysozyme. Besides, the stronger intermolecular interactions (enhanced ionic bonds, hydrogen bonds and inhibited hydrophobic interactions), the shorter transverse relaxation time (T₂₁ and T₂₂), as well as more uniform microstructure formed in the lysozyme-removed gel, allowing the gels to bind more water molecules. With return of lysozyme, the gel properties were weakened to varying degrees, which was also ascribed to the filling of lysozyme in gel matrix narrowed interspace for binding and storage of water. In sum, adjustment on the content of lysozyme can regulate the gel properties of egg white, so as to obtain gels with regulable gel quality and processing characteristics.

Non-destructive prediction of yak meat freshness indicator by hyperspectral techniques in the oxidation process

This study examined the potential of hyperspectral techniques for the rapid detection of characteristic indicators of yak meat freshness during the oxidation of yak meat. TVB-N values were determined by significance analysis as the characteristic index of yak meat freshness. Reflectance spectral information of yak meat samples (400-1000 nm) was collected by hyperspectral technology. The raw spectral information was processed by 5 methods and then principal component regression (PCR), support vector machine regression (SVR) and partial least squares regression (PLSR) were used to build regression models. The results indicated that the full-wavelength based on PCR, SVR, and PLSR models were shown greater performance in the prediction of TVB-N content. In order to improve the computational efficiency of the model, 9 and 11 characteristic wavelengths were selected from 128 wavelengths by successive projection algorithm (SPA) and competitive adaptive reweighted sampling (CARS), respectively. The CARS-PLSR model exhibited excellent predictive power and model stability.

Quantitative proteomic analysis provides insight into the survival mechanism of Salmonella typhimurium under high-intensity ultrasound treatment

The survival mechanism of Salmonella treated with high-intensity ultrasound (HIU) should be explored to further enhance the bactericidal efficacy of HIU. In this study, culturable Salmonella was reduced by applying HIU. Electron microscope imaging revealed that HIU caused the disintegration of cell structure and leakage of intracellular substances. For the Salmonella after the HIU treatment, key enzymes of the tricarboxylic acid [TCA] cycle were significantly downregulated, which led to a reduced ATP content (45.25%-75.00%), although ATPase activity was augmented by 33.82%-60.64% in the Salmonella. Accordingly, surviving Salmonella could have tolerated the stress of HIU by upregulating their environmental sensing (two-component system), chemotaxis (bacterial chemotaxis), substance uptake (ABC transporter), and ATP production (oxidative phosphorylation). Therefore, synergistically blocking the ATP production, signal transduction, or substance intake of Salmonella offer promising potential strategies to improve the bactericidal effect of HIU in industrial food processing.

Encapsulation and sustained release of curcumin by hawthorn pectin and Tenebrio Molitor protein composite hydrogel

In this study, the effects of pH value, mixing ratio and the Ca²⁺ concentration on the complex gelation of hawthorn pectin (HP) and Tenebrio Molitor protein (TMP) were investigated. The turbidity results showed that the composite gel had the maximum polymer concentration when the mixing ratio was 2:1 and the pH value was 3.35. The rheological measurement results showed that TMP/HP (15 mmol/L) hydrogel (THIH) had the highest storage modulus and loss modulus, indicating that the properties of the hydrogel at this Ca²⁺ concentration had been significantly improved. The results of scanning electron microscope and pore size also proved that the network structure prepared under this condition was compact and uniform, the pore size was small, which was beneficial to the entrapment of active components. Subsequently, in order to explore the storage stability and antioxidant activity of THIH-loaded curcumin in simulated gastrointestinal environment, in vitro simulated digestion experiment was carried out and satisfactory results were obtained. To sum up, THIH was a promising delivery system with broad application prospects, which was expected to provide a novel idea for the entrapment and delivery of active components.

Improving the gel properties of duck egg white by synergetic phosphorylation/ultrasound: Gel properties, crystalline structures, and protein structure

To improve the gel properties of duck egg white gel and increase the industrial value of duck egg white, the mechanisms of ultrasound and synergetic phosphorylation/ultrasound treatments were examined in this study. It was found that as the ultrasound power increased, the surface hydrophobicity, hardness, and cohesiveness of the gel system increased, and the ζ-potential and water mobility decreased. Of the two treatments, phosphorylation/ultrasound had the strongest impact on the conformation and crystallinity of the gel system and promoted the formation of high molecular polymers. Both gel systems displayed enhanced compactness, stability, and gel strength because of the enhanced protein-protein interactions via hydrogen bonds and protein aggregation, and increased the content of intramolecular β-sheets following ultrasound treatment, and synergetic phosphorylation/ultrasound further improved the stability, water binding and gel properties. This experiment showed that ultrasound and, particularly, phosphorylation/ultrasound are effective methods to improve the gel properties of duck egg white. This study enhanced our understanding of the interactions of sodium pyrophosphate and egg white under ultrasound treatment, and promote the potential application of sodium pyrophosphate and ultrasound treatment of novel food products.

Formulation and characterization of plant-based egg white analogs using RuBisCO protein

RuBisCO protein, which can be isolated from abundant and sustainable plant sources, can mimic some of the desirable functional attributes of egg white proteins. In this study, plant-based egg white analogs were successfully produced using 10 w% RuBisCO solutions (pH 8). These protein solutions had similar apparent viscosity-shear rate profiles, shear modulus-temperature profiles, gelling temperatures, and final gel strengths as egg white. However, there were some differences. RuBisCO protein gels were slightly darker than egg white, which was attributed to the presence of phenolic impurities. Moreover, RuBisCo proteins exhibited a single thermal transition temperature (∼66 °C) whereas egg white proteins exhibited two (∼66 and ∼81 °C). RuBisCO gels were more brittle but less chewy and resilient than egg white gels. This study provides valuable insights into the potential of RuBisCO protein for formulating plant-based egg white analogs.

Formation mechanism of high-viscosity gelatinous egg white among "Fenghuang Egg": Phenomenon, structure, and substance composition

"Fenghuang Egg" is a special egg product incubated for 12 days by fertilized hen eggs. Its egg white contains high-viscosity and excellent thermal gel strength. A comparative study on the differences in gel properties, structure, and substance composition between fresh egg white (FEW) and "Fenghuang egg" gelatinous egg white (GEW) was carried out. Experimental results showed GEW had better apparent viscosity, as well as the hardness, cohesiveness and water holding capacity (WHC) of thermal gel; the content and size of aggregate structure increased significantly in GEW, and a fibrous dense network composed of numerous spherical nanoparticles connected in series was formed after heating. In addition, it also discovered that more water molecules in GEW existed in the form of bound water. A total of 41 proteins changed significantly in FEW and GEW, Mucin 6 might be the main reason for the enhanced viscosity of GEW, and OVA might be the dominant protein differentiating the thermal gel properties between FEW and GEW. This study revealed that the differences in gel properties and structures between FEW and GEW were closely related to the content of highly glycosylated globular proteins, laying a theoretical foundation for the application of high-viscosity egg whites.

Modification methods and applications of egg protein gel properties: A review

Egg protein (EP) has a variety of functional properties, such as gelling, foaming, and emulsifying. The gel characteristics provide a foundation for applications in the food industry and research on EP. The proteins denature and aggregate to form a dense three-dimensional gel network structure, with a process influenced by protein concentration, pH, ion type, and strength. In addition, the gelation properties of EP can be altered to varying degrees by applying different treatment conditions to EP. Currently, modification methods for proteins include physical modification (heat-induced denaturation, freeze-thaw modification, high-pressure modification, and ultrasonic modification), chemical modification (glycosylation modification, phosphorylation modification, acylation modification, ethanol modification, polyphenol modification), and biological modification (enzyme modification). Pidan, salted eggs, egg tofu, and other egg products have unique sensory properties, due to the gel properties of EP. In accessions, EP has also been used as a new ingredient in food packaging and biopharmaceuticals due to its gel properties. This review will further promote EP gel research and provide guidance for its full application in many fields.