Effect of processing on aggregation mechanism of egg white proteins

Divalent metal ions under low concentration environment improved the thermal gel properties of egg yolk

To improve the thermal gel properties of egg yolk, the effect of several valence metal ions (K+, Ca2+, Mg2+ and Fe3+) with different concentrations (0-0.72%) on the rheological, gel, and structural properties of egg yolk were investigated. Results showed that monovalent and divalent ions were beneficial to the formation of uniform and dense gel network, especially with the addition of 0.72% magnesium ion, which further improved gel hardness, water holding capacity (WHC) and viscoelastic properties, the properties of egg yolk gel increased with the increase of the concentration of mono-bivalent metal ions. Adding ferric ion remarkably increased the average particle size (d4,3) and apparent viscosity of egg yolk, destroying the disulfide bonds and the hydrophobic interactions in gel. Fourier transform infrared spectroscopy (FT-IR) and fluorescence spectra analysis revealed that metal ions promoted the hydrophobic aggregation among egg yolk proteins and induced the transition of protein secondary structure from ordered to disordered. This work will provide a theoretical reference for the development of low salt and nutrient fortified egg yolk products.

Electron beam irradiation induced aggregation, structural and functional changes of soybean 11S globulin

This study investigated the effects of different irradiation doses of an electron beam (e-beam) (0, 2, 4, 6, 8, and 10 kGy) on the structure, emulsification, foaming, and rheological and gel properties of soybean 11S globulin. The irradiation treatment at 4 and 6 kGy significantly increased the solubility, surface hydrophobicity, disulfide bonding, and ζ-potential of 11S globulin, decreased the particle size of the protein solution, and effectively improved the emulsifying activity and foaming stability of the protein solution. Moreover, irradiation induced moderate cross-linking and aggregation of the proteins, thereby increasing the apparent viscosity and shear stress of the protein solution. In addition, the low-field NMR and microstructure analysis results revealed that protein gels formed a dense and homogeneous three-dimensional mesh structure after irradiation (6 kGy), along with increased content of bound water (T2b) and water not readily flowable (T21) and a decrease content of free water (T22). Overall, our results confirmed that e-beam irradiation could significantly improve the physicochemical properties of soybean 11S globulin. Our study thus provides a new technical means for the application of electron beam irradiation technology toward protein modification and broadens the high-value utilization of soybean 11S globulin in the food processing industry.

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.

Inhibition of water-diluted precipitate formation from egg whites by ultrasonic pretreatment: Insights from quantitative proteomics analysis

The formation of the egg white precipitate (EWP) during dilution poses challenges in food processing. In this paper, the effects of 90 W and 360 W ultrasonic intensities on the inhibition of EWP formation were investigated. The findings revealed that 360 W sonication effectively disrupted protein aggregates, decreasing the dry matter of EWP by 5.24 %, particle size by 57.86 %, and viscosity by 82.28 %. Furthermore, the ultrasonic pretreatment unfolded protein structures and increased the content of β-sheet structures. Combined with quantitative proteomics and intermolecular forces analysis, the mechanism by which ultrasonic pretreatment inhibited water-diluted EWP formation by altering protein interactions was proposed: ultrasonic pretreatment disrupted electrostatic interactions centered on lysozyme, as well as hydrogen-bonding interactions between ovomucin and water. In conclusion, our research provides valuable insights into the application of ultrasonic pretreatment as a means to control and improve the quality of egg white-based products.

Magnesium ions regulated ovalbumin-lysozyme heteroprotein complex: Aggregation kinetics, thermodynamics and morphologic structure

This study aims to investigate the mechanism of magnesium ions regulated ovalbumin-lysozyme (OVA-LYS) heteroprotein aggregation behavior via aggregation kinetics model, exploring the relationship between differential aggregation behavior and protein molecular structure, intermolecular interactions and thermal stability. Results showed that the aggregation rate (kapp) and maximum absorbance (Amax) of the OVA-LYS heteroprotein complex were located between OVA and LYS. Meanwhile, the thermal denaturation temperature (Td) and denaturation enthalpy (ΔH) were between the values of OVA and LYS as well. Compared with OVA, the thermal stability of the OVA-LYS heteroprotein complex increased owing to the electrostatic interactions between OVA and LYS, resulting in slower aggregation rate and lower aggregation degree. Molecular dynamics simulations revealed the molecular conformational changes during OVA-LYS binary protein binding and the stability of the complex conformation. Moreover, MgCl2 weakened the OVA-LYS interactions through Debye shielding while increasing thermal stability, allowing the two proteins to aggregate into amorphous precipitates rather than spherical coacervates. Overall, this study provides information to further understand the regulation mechanism of proteins differential aggregation behavior by ions.

Allergenicity, assembly and applications of ovalbumin in egg white: a review

Ovalbumin (OVA), the most abundant protein in egg whites, has been widely used in various industries. Currently, the structure of OVA has been clearly established, and the extraction of high-purified OVA has become feasible. However, the allergenicity of OVA is still a serious problem because it can cause severe allergic reactions and may even be life-threatening. The structure and allergenicity of the OVA can be altered by many processing methods. In this article, a detailed description on the structure and a comprehensive overview on the extraction protocols and the allergenicity of OVA was documented. Additionally, the information on assembly and potential applications of OVA was summarized and discussed in detail. Physical treatment, chemical modification, and microbial processing can be applied to alter the IgE-binding capacity of OVA by changing its structure and linear/sequential epitopes. Furthermore, research indicated that OVA could assemble with itself or other biomolecules into various forms (particles, fibers, gels, and nanosheets), which expanded its application in the food field. OVA also shows excellent application prospects, including food preservation, functional food ingredients and nutrient delivery. Therefore, OVA demonstrates significant investigation value as a food grade ingredient.

Alteration of the allergenicity of cow's milk proteins using different food processing modifications

Milk is an essential source of protein for infants and young children. At the same time, cow's milk is also one of the most common allergenic foods causing food allergies in children. Recently, cow's milk allergy (CMA) has become a common public health issue worldwide. Modern food processing technologies have been developed to reduce the allergenicity of milk proteins and improve the quality of life of patients with CMA. In this review, we summarize the main allergens in cow's milk, and introduce the recent findings on CMA responses. Moreover, the reduced effects and underlying mechanisms of different food processing techniques (such as heating, high pressure, γ-ray irradiation, ultrasound irradiation, hydrolysis, glycosylation, etc.) on the allergenicity of cow's milk proteins, and the application of processed cow's milk in clinical studies, are discussed. In addition, we describe the changes of nutritional value in cow's milk treated by different food processing technologies. This review provides an in-depth understanding of the allergenicity reduction of cow's milk proteins by various food processing techniques.

Succinylation Modified Ovalbumin: Structural, Interfacial, and Functional Properties

In this study, ovalbumin (OVA) was succinylated with the addition of different levels of succinic anhydride, and the structural and functional properties of succinylated OVA (SOVA) were investigated. SDS−PAGE and FTIR spectrum confirmed the covalent attachment of the succinyl group to OVA. Thermal stability and the absolute value of zeta potential (pH 6.0) of SOVA were enhanced by 14.90% and 76.77% higher than that of the native OVA (NOVA), respectively. Circular dichroism (CD) spectra demonstrated that the succinylation decreased the α−helix and increased β−sheet content to 21.31% and 43.28%, respectively. The content of free sulfhydryl groups increased and intrinsic fluorescence spectra suggested the SOVA became more unfolded and flexible as the degree of succinylation enhanced. Furthermore, succinylation effectively enhanced the solubility and decreased the interface tension (oil−water and air−water interface) of OVA. Compared to NOVA, the emulsifying activity and stability of SOVA were increased by 1.6 times and 1.2 times, respectively, and foaming capacity and stability were enhanced by 2.7 times and 1.5 times, respectively.

Egg white protein-based delivery system for bioactive substances: a review

Some bioactive substances in food have problems such as poor solubility, unstable chemical properties and low bioavailability, which limits their application in functional food. Recently, many egg white protein-based delivery carriers have been developed to improve the chemical stability, biological activity and bioavailability of bioactive substances. This article reviewed the structure and properties of several major egg white proteins commonly used to construct bioactive substance delivery systems. Several common carrier types based on egg white proteins, including hydrogels, emulsions, micro/nanoparticles, aerogels and electrospinning were then introduced. The biological functions of common bioactive substances, the limitations, and the role of egg white protein-based delivery systems were also discussed. At present, whole egg white protein, ovalbumin and lysozyme are most widely used in delivery systems, while ovotransferrin, ovomucoid and ovomucin are less developed and applied. Egg white protein-based nanoparticles are currently the most commonly used delivery carriers. Egg white protein-based hydrogels, emulsions, and microparticles are also widely used. Future research on the application of various egg white proteins in developed new delivery systems will provide more choices for the delivery of various bioactive substances.

Gastrointestinal fate of food allergens and its relationship with allergenicity

Food allergens are closely related to their gastrointestinal digestion fate, but the changes in food allergens during digestion and related mechanisms are quite complicated. This review presents in detail digestion models for predicting allergenicity, the fates of food allergens in oral, gastric and duodenal digestion, and the applications of digestomics in mapping IgE-binding epitopes of digestion-resistant peptides. Moreover, this review highlights the structure-activity relationships of food allergens during gastrointestinal digestion. Digestion-labile allergens may share common structural characteristics, such as high flexibility, rendering them easier to be hydrolyzed into small fragments with decreased or eliminated allergenicity. In contrast, the presence of disulfide bonds, tightly wound α-helical structures, or hydrophobic domains in food allergens helps them resist gastrointestinal digestion, stabilizing IgE-binding epitopes, thus maintaining their sensitization. In rare cases, digestion leads to increased allergenicity due to exposure of new epitopes. Finally, the action of the food matrix and processing on the digestion and allergenicity of food allergens as well as the underlying mechanisms was overviewed. The food matrix can directly act on the allergen by forming complexes or new epitopes to affect its gastrointestinal digestibility and thereby alter its allergenicity or indirectly affect the allergenicity by competing for enzymatic cleavage or influencing gastrointestinal pH and microbial flora. Several processing techniques attenuate the allergenicity of food proteins by altering their conformation to improve susceptibility to degradation by digestive enzymes. Given the complexity of food components, the food itself rather than a single allergen should be used to obtain more accurate data for allergenicity assessment. PRACTICAL APPLICATION: The review article will help to understand the relationship between food protein digestion and allergenicity, and may provide fundamental information for evaluating and reducing the allergenicity of food proteins.

Gel Properties of Blue Round Scad (Decapterus Maruadsi) Mince as Influenced by the Addition of Egg White Powder

The use of egg white powder (EWP) to enhance the physicochemical properties, molecular structure, and thermal stability of Decapterus maruadsi mince gels was investigated. The thermal stability was analyzed by adding spray-dried EWP (0%, 0.2%, 0.4%, 0.6%, 0.8%, 1%) to the mince, and mince gels were prepared to study the changes in their fracture constant, water distribution, microstructure and protein conformation of mince gels. In addition, the stress-strain curve of the EWP-mince gel was measured to obtain its compressive modulus (E). The formation of the mince gel was promoted by EWP, and the whiteness, fracture constant, water-holding capacity, and immobilized water were all enhanced. At 0.8% addition of EWP, the fracture constant increased from 176.715±2.463 N/m to 348.631±3.144 N/m (p<0.05), which was a nearly twofold improvement. Additionally, the water-holding capacity increased from 75.21% to 79.99%, and the percentage of immobilized water increased from 94.03% to 94.91%. The EWP-mince gel network structure was the most uniform and dense, and there were increases in hydrogen bonds, disulfide bonds, β-sheets, and β-turns in mince gels, as well as the storage modulus (G') and enthalpy (ΔH). In contrast to the control group, the relative content of α-helixes decreased from 53.34% to 37.09% and transformed into other secondary structures, and the bulk water and cooking loss also decreased to 2.41% and 8.51%, respectively. Consequently, EWP effectively improved the quality of mince products, and the effect was most apparent when 0.8% was added.

Fabrication of food-grade Pickering high internal phase emulsions (HIPEs) stabilized by a dihydromyricetin and lysozyme mixture

This study evaluated the feasibility of fabricating food-grade HIPEs using a dihydromyricetin and lysozyme mixture. The effects of the oil phase volume fraction (φ), composition (lysozyme:dihydromyricetin, k), and addition amount (w) of the mixture on the formation and properties of the HIPEs were analyzed. Then, the interactions of dihydromyricetin and lysozyme were investigated. The results indicated that when w was 0.4%, HIPEs with φ value of 90% could be obtained. Furthermore, the k also affected the microstructure, mechanical properties, oil oxidation, and lutein protection ability of the HIPEs. However, the presence of dihydromyricetin did not affect lysozyme activity. Both isothermal titration calorimetry and molecular simulations proved that they did not form a typical host-guest complex. But, dihydromyricetin could absorb on the lysozyme surface. Therefore, we speculated that lysozyme and dihydromyricetin particles could overlap and form a 3D network structure to stabilize the HIPEs, which was consistent with the microstructure observations.

Inhibition of the liquefaction of alkali-induced egg white gel by sodium ascorbate

Effects of sodium ascorbate (1%, 2%, 3%) on the liquefaction of alkali-induced egg white gel (EWG) were investigated. Results showed hardness and water holding capacity (WHC) gradually decreased at 1%. However, hardness and WHC declined and then rose at 2% and 3%. Microstructural changes further confirmed the effects of sodium ascorbate on hardness and WHC. Electrophoresis showed sodium ascorbate caused the cross-linking between proteins, which was more resistant to degradation. Fourier transform infrared spectroscopy (FTIR) and surface hydrophobicity indicated sodium ascorbate significantly changed protein structure, especially at 2% and 3% resulted in protein reaggregation, increasing β-sheet, and decreasing surface hydrophobicity in the later stage. In general, sodium ascorbate didn't inhibit the liquefaction of alkali-induced EWG at 1%, but did effectively at 2% and 3%. Therefore, high concentrations of sodium ascorbate possess the potential to inhibit the "alkali injury liquefaction" of preserved egg whites without heavy metals.

Flavor impartment of mushroom on egg whites and sensory properties of egg whites with mushroom topping using quantitative descriptive analysis

BACKGROUND

Mushroom possesses desirable aroma, taste, texture, health-promoting and disease-preventing dietary components, making it an ideal ingredient, especially for animal-based food substitution. Nevertheless, no study has replaced egg whites partially with mushrooms and investigated their sensory quality. This study aimed to investigate flavor impartment of mushroom on egg whites and the sensory quality of roasting and steaming egg whites replaced by white and crimini mushrooms at 0%, 10%, 20% and 30%, respectively, using a panel trained with aroma chemical references for 31 sensory attributes with 0-10 line scales.

RESULTS

Roasted and steamed egg whites possessed major sensory attributes of sulfury and egg-like aroma and flavor (intensities > 3). After mushroom topping was added, the dominant sensory attributes shifted to mushroom-based flavor characteristics, including mushroom-like, earthy, dark meat, roasted, hay, soybean, potato, woody, umami, bitter, astringent and firmness texture. Mushroom variety showed significant (P ≤ 0.05) impacts on egg white sensory quality, with crimini introducing more intense flavor. The higher the mushroom proportion with egg whites, the more intense was the flavor associated with mushroom. Mushroom could enhance egg-like flavor in multiple dimensions, including aroma, taste and texture, according to partial least square regression.

CONCLUSION

White and crimini mushrooms enriched roasted and steamed egg white sensory quality with introduction of characteristic sensory attributes from mushrooms. Mushroom variety and proportion with egg whites displayed significant impacts on egg white sensory properties. The study contributed to understanding the impact of mushrooms on egg white sensory profile and served as a guide in incorporating mushroom in product development. © 2021 Society of Chemical Industry.

Effect of processing technologies on the digestibility of egg proteins

Egg and egg products are a rich source of highly bioavailable animal proteins. Several processing technologies can affect the structural and functional properties of these proteins differently and can influence their fate inside the gastrointestinal tract. The present review examines some of the processing technologies for improving egg protein digestibility and discusses how different processing conditions affect the digestibility of egg proteins under gastrointestinal digestion environments. To provide up-to-date information, most of the studies included in this review have been published in the last 5 years on different aspects of egg protein digestibility. Digestibility of egg proteins can be improved by employing some processing technologies that are able to improve the susceptibility of egg proteins to gastrointestinal proteases. Processing technologies, such as pulsed electric field, high-pressure, and ultrasound, can induce conformational and microstructural changes that lead to unfolding of the polypeptides and expose active sites for further interactions. These changes can enhance the accessibility of digestive proteases to cleavage sites. Some of these technologies may inactivate some egg proteins that are enzyme inhibitors, such as trypsin inhibitors. The underlying mechanisms of how different technologies mediate the egg protein digestibility have been discussed in detail. The proteolysis patterns and digestibility of the processed egg proteins are not always predictable and depends on the processing conditions. Empirical input is required to tailor the optimization of processing conditions for favorable effects on protein digestibility.

Proteins in Food Systems-Bionanomaterials, Conventional and Unconventional Sources, Functional Properties, and Development Opportunities

Recently, food companies from various European countries have observed increased interest in high-protein food and other products with specific functional properties. This review article intends to present proteins as an increasingly popular ingredient in various food products that frequently draw contemporary consumers’ attention. The study describes the role of conventional, unconventional, and alternative sources of protein in the human body. Furthermore, the study explores proteins’ nutritional value and functional properties, their use in the food industry, and the application of proteins in bionanomaterials. Due to the expected increase in demand for high-protein products, the paper also examines the health benefits and risks of consuming these products, current market trends, and consumer preferences.

Processes for reducing egg allergenicity: Advances and different approaches

Egg is a versatile ingredient and ubiquitous food. Nevertheless, egg proteins are a common cause of allergy mainly in childhood. Until now, egg eviction has been the best way to prevent this disorder, however, processed food can contribute to mitigate allergies and to guarantee life quality of allergic individuals. This review focuses on discussing and highlighting recent advances in processes to reduce egg allergenicity as well as new approaches to egg allergy management. In recent times, different methods have been developed to reduce egg allergies, by hiding the epitopes or changing the native or conformational structure of the proteins. Despite processing food has not yet been a solution to completely remove the allergenic potential of egg proteins, innovative strategies, such as addition of phenolic compounds, have been developed with promising results.

Whey allergens: Influence of nonthermal processing treatments and their detection methods

Whey and its components are recognized as value-added ingredients in infant formulas, beverages, sports nutritious foods, and other food products. Whey offers opportunities for the food industrial sector to develop functional foods with potential health benefits due to its unique physiological and functional attributes. Despite all the above importance, the consumption of whey protein (WP) can trigger hypersensitive reactions and is a constant threat for sensitive individuals. Although avoiding such food products is the most successful approach, there is still a chance of incorrect labeling and cross-contamination during food processing. As whey allergens in food products are cross-reactive, the phenomenon of homologous milk proteins of various species may escalate to a more serious problem. In this review, nonthermal processing technologies used to prevent and eliminate WP allergies are presented and discussed in detail. These processing technologies can either enhance or mitigate the impact of potential allergenicity. Therefore, the development of highly precise analytical technologies to detect and quantify the existence of whey allergens is of considerable importance. The present review is an attempt to cover all the updated approaches used for the detection of whey allergens in processed food products. Immunological and DNA-based assays are generally used for detecting allergenic proteins in processed food products. In addition, mass spectrometry is also employed as a preliminary technique for detection. We also highlighted the latest improvements in allergen detection toward biosensing strategies particularly immunosensors and aptasensors.

Ovomucin may be the key protein involved in the early formation of egg-white thermal gel

Clarification of the mechanism of heat-induced gel formation by proteins under natural food systems could provide important references for the regulation of food texture. In the present study, the proteins involved in the early stage (heating at 72 °C for 8 min) of egg-white thermal gel (EWG) formation were studied quantitatively through comparative proteomic analysis. We discovered that the abundance of ovalbumin and ovomucoid increased significantly (p < 0.01), whereas that of ovotransferrin, lysozyme, ovomucin (mucin 5B and mucin 6) decreased significantly (p < 0.01), in the supernatant of EWG. If the initial interaction of egg white proteins was altered by ultrasonic pretreatment, the abundance of ovomucin and lysozyme in the supernatant of EWG increased, and was accompanied by the change from a solid gel to a fluid gel. Based on these results, we hypothesize that ovomucin has a key role in the formation and regulation of EWG properties.

Effect of sodium tripolyphosphate on the interaction and aggregation behavior of ovalbumin-lysozyme complex

The mechanism by which sodium tripolyphosphate affected the aggregation behavior of ovalbumin-lysozyme complexes was investigated in this work. The highest stability coefficients were detected for natural ovalbumin and lysozyme at pH 9.0 and pH 5.0, with values of 0.981 and 0.931, respectively. The turbidity of the phosphorylated ovalbumin-lysozyme complexes was 1.71-fold to the natural complexes at pH 7.0. This result was related to the fact that the phosphorylated sample had a lower isoelectric point. Besides, both intermolecular forces and SDS-PAGE analysis indicated that the disulfide bond was the most important interaction in the complex. Circular dichroism analysis showed that phosphorylation weakened the unfolding and stretching of the structure caused by heat treatment. Moreover, transmission electron microscopy pictures confirmed that the network structure of phosphorylated ovalbumin-lysozyme complex was broader than natural protein. This study provides information for further understanding the effect of phosphorylation on protein aggregation behavior.

Effects of pulsed electric fields on the conformation and gelation properties of myofibrillar proteins isolated from pale, soft, exudative (PSE)-like chicken breast meat: A molecular dynamics study

The potential of pulsed electric field (PEF) of different intensities (8, 18, and 28 kV/cm) on the conformation and gelation properties of myofibrillar proteins (MPs) extracted from pale, soft, and exudative-like (PSE-like) chicken meat was investigated. The results showed a positive correlation between gelation properties and PEF intensities in the range of 8-18 kV/cm; however, a further increase in intensity had a negative impact. Optimized PEF treatment (18 kV/cm) was capable of inducing MPs with a relatively small particle size, thus contributing to the production of a more homogeneous gel structure. The water distribution and mobility in the gel system significantly changed with increasing PEF intensities, the proportion of immobilized water (P₂₁) increased, and that of free water (P₂₂) decreased. Based on molecular dynamics simulations (MDS), an increasing trend in the number of hydrogen bonds and a reduction in the radius of gyration (Rg) after PEF treatment.

Construction expression and immunogenicity of a novel trivalent outer membrane protein (OmpU-A-II) from three bacterial pathogens in Japanese eels (Anguilla japonica)

Vibrio vulnificus, Edwardsiella anguillarum and Aeromonas hydrophila are three common bacterial pathogens in cultivated eels. To protect farming eels from infection by these pathogens, a trivalent outer membrane protein (OMP) containing partial sequences of OmpU from V. vulnificus, OmpA from E. anguillarum and OmpII from A. hydrophila was expressed and purified; then, the OMP was used as a vaccine to immunize Japanese eels (Anguilla japonica). Whole-blood cell proliferation, antibody titres and complement and lysozyme activities were detected at different days post-immunization (dpi), and the relative per cent survival (RPS) was determined after eels were infected with V. vulnificus, E. anguillarum or A. hydrophila at 28 dpi. The results showed that the OMP significantly stimulates the antibody titres. At 14 days after the challenge (i.e. at 28 dpi), the RPS of OMP against V. vulnificus, E. anguillarum and A. hydrophila was 20%, 70% and 11.1%, respectively. The construction, expression and immunogenicity of a trivalent Omp were reported for the first time, and this study will provide a valuable reference for the development of fish multiplex vaccines.

The sol-gel-sol transformation behavior of egg white proteins induced by alkali

In the current study, we found an interesting phenomenon that fresh egg white (EW) undergo the sol-gel-sol transition with alkali treatment. The transformation behavior at different alkalinity (1.5%, 2.0%, and 2.5%) was investigated. As the gel formed, the hardness, lightness, surface hydrophobicity and the total number of identified peptides increased, and then, remarkable reduction when the gel collapsed. Rheological behavior indicated that the viscosity varied with shear rate. Fourier transform infrared spectroscopy (FTIR) showed that β-sheets gradually decreased as the α-helices increased during gel-sol transformation. The quantification of EW peptides analysis revealed that there was no dramatic correlation between the number of identified peptides and alkalinity. It was concluded that the sol-gel-sol transition was strongly dependent on alkali levels, moreover, high concentration promoted gel formation as well as liquefaction. The EW transformation behavior induced by alkali had a significant effect on protein aggregation and denaturation, and further changed physicochemical properties.

Critical reviews and recent advances of novel non-thermal processing techniques on the modification of food allergens

Nowadays, the increasing prevalence of food allergy has become a public concern related to human health worldwide. Thus, it is imperative and necessary to provide some efficient methods for the management of food allergy. Some conventional processing methods (e.g., boiling and steaming) have been applied in the reduction of food immunoreactivity, while these treatments significantly destroy nutritional components present in food sources. Several studies have shown that novel processing techniques generally have better performance in retaining original characteristics of food and improving the efficiency of eliminating allergens. This review has focused on the recent advances of novel non-thermal processing techniques including high-pressure processing, ultrasound, pulsed light, cold plasma, fermentation, pulsed electric field, enzymatic hydrolysis, and the combination processing of them. Meanwhile, general information on global food allergy prevalence and food allergy pathology are also described. Hopefully, these findings regarding the modifications on the food allergens through various novel food processing techniques can provide an in-depth understanding in the mechanism of food allergy, which in turn possibly provides a strategy to adapt in the reduction of food immunoreactivity for the food industries.

Immunization of a novel outer membrane protein from Aeromonas hydrophila simultaneously resisting A. hydrophila and Edwardsiella anguillarum infection in European eels (Angullia angullia)

In cultivated European eels, Aeromonas hydrophila, Edwardsiella anguillarum and Vibrio vulnificus are three important bacterial pathogens. In this study, an expressed recombinant Outer membrane proteinⅡ (rOmpⅡ) from A. hydrophila was intraperitoneally injected into European eels (Angullia angullia). All examined eels were equally divided into three groups. One group was injected with PBS only (PBS group), one group was injected with 1:1 mixture of PBS and Freund's incomplete adjuvant (PBS + F, adjuvant group), and the third group was injected with 1:1 mixture of 1 mg mL^-1 rOmpⅡ and Freund's incomplete adjuvant (rOmpⅡ+F, OmpⅡ group). The immunogenicity of OmpⅡ was studied by detecting the expression of 4 immune-related genes, stimulation index (SI) of the whole blood cell, serum antibody titer, lysozyme and Superoxide Dismutase (SOD) activity, and relative percent of survival (RPS) rate. The results showed that gene expression of MHC-Ⅱ, LysC, SOD and IgM in the OmpⅡ group significantly increased in liver, spleen, kidney and intestine. At 28 days post the immunization (dpi), the SI of whole blood cells in the OmpⅡ group increased significantly; at 14, 21, 28 and 42 dpi, the serum antibody titers against A. hydrophila and E. anguillarum in the OmpⅡ group were significantly higher than that of the PBS and the adjuvant group; the SOD in the OmpⅡ group was found increased significantly in liver, kidney, mucus and serum. On the 28 dpi, eels were challenged by A. hydrophila, E. anguillarum and V. vulnificus for cross protection study. The results showed that the RPS of the OmpⅡ group were 83.33%, 55.56% and 33.33% respectively. These results showed that the expressed OmpⅡ from A. hydrophila significantly improve the immune function of Europena eels and their resistance to the infection of A. hydrophila and E. anguillarum simultaneously.