pH and heat induced structural changes of chicken ovalbumin in relation with antigenic properties

Rheological and physicochemical properties of heat-induced ovalbumin gels in presence of sodium carboxymethyl cellulose

In this study, the effect of sodium carboxymethylcellulose (CMC-Na) on the rheological and physicochemical properties of heat-induced ovalbumin (OVA) gels was evaluated. The OVA/CMC-Na composite gels were prepared by heat-induced (85 °C, pH 7.0) a mixture of CMC-Na (0, 0.2, 0.4, 0.8 and 1%) and OVA. The results revealed that the addition of CMC-Na dramatically reduced the springiness and hardness of the composite gels, while slightly enhancing the intermolecular hydrogen bonding interactions, which facilitated the improvement of the softness of the gels. It can be observed by SEM that the added CMC-Na was stacked on the surface of the OVA, resulting in visible "linear bumps". All gel samples exhibited shear-thinning behavior. The apparent viscosity of the composite gels increased with the addition of CMC-Na, and the OVA gel with 1% CMC-Na showed the highest apparent viscosity and the lowest storage modulus (G'). Additionally, low field nuclear magnetic resonance (LF-NMR) measurements indicated that the increasing CMC-Na boosted the water mobility of the composite gel. This study offers a novel approach to the development of ovalbumin-based soft gel foods, especially for certain populations with swallowing difficulties.

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.

Pasteurization induced protein interaction decreased the potential allergenicity of ovalbumin and ovomucoid in egg white

BACKGROUND

Approximately 9.9% of young children in China suffer from egg allergies. Ovalbumin (OVA) and ovomucoid (OVM) are both the main allergens with higher allergenicity in egg white. The previous studies mainly focused on the effects of pasteurization on the structure and allergenicity of the isolated protein itself. The effects of the interaction between OVA and OVM on their spatial structure and allergenicity under pasteurization are still unclear. Therefore, in this study, the spectroscopic, immunological, and cytological methods were used to investigate the effects on OVA and OVM by their interactions which were induced by the following pasteurization, heating for 10 min at 60, 65, and 70 °C, respectively.

RESULTS

Results indicated that OVA and OVM could form macromolecular aggregates by their interaction at 70 °C, and their solubility was decreased while turbidity was increased. The spatial structures of OVA and OVM were both changed by their interaction, when pasteurization temperature was at 70 °C the exposure of their hydrophobic groups and α-helix content were decreased while their β-sheet was increased. The potential allergenicity of OVA and OVM was also changed, which showed that the immunoglobulin G (IgG)-binding ability of OVA and OVM could be increased, and their IgE-binding ability was decreased a bit. The releases of interleukin 4 (IL-4), IL-6, β-HEX, histamine and tumor necrosis factor alpha (TNF-α) from OVA-OVM-induced KU812 cells were all decreased at 70 °C.

CONCLUSION

Therefore, according to the results, if the liquid egg products were pasteurized for 10 min, the temperature of 70 °C should be carefully considered. © 2022 Society of Chemical Industry.

The Effects of Phosphorylation and Microwave Treatment on the Functional Characteristics of Freeze-Dried Egg White Powder

The effects of phosphorylation pre-treatments at 1.5, 2.5, and 3.5% levels, as well as microwave application at 200, 400, and 700 watts levels for 2 min, on the functional parameters of egg white powder obtained by the freeze dryer procedure were investigated. P1.5-M200 had the highest oil-holding capacity, emulsion stability, and emulsion activity, while P2.5-M200 had the highest foam capacity. The P2.5-M400 had the largest particle size, and P3.5-M200 had the highest degree of phosphorylation and protein solubility. On the other hand, P3.5-M200 had the highest solution viscosity by 1% (w/v), water-holding capacity, and foam stability, in the treatments that used phosphorylation and microwave treatment simultaneously. FTIR spectroscopy of the unfolding structure of egg white protein revealed changes in the protein’s secondary structure, such as the development of β-sheets and β-turns, as well as the binding of negatively charged phosphate groups on the serine, threonine, and tyrosine side chains. The phosphorylation and microwave treatments reduced the particle size of the egg white protein powder while increasing the surface area of the protein molecules, according to SEM analyses.

Effects of guar gum or xanthan gum addition in conjunction with pasteurization on liquid egg white

In this study, effects of varying levels of xanthan or guar gum (XG/GG, 0.05%, 0.1%, 0.2%, 0.4% and 0.8%, w/v) on the spatial structure and functional properties of egg white (EW) proteins under different pasteurization conditions of the liquid egg was evaluated. Results showed that XG could bury the aromatic ring residues and reduce the hydrophobicity of protein in EW, whereas GG could only increase the hydrophobicity. With 0.8% GG addition and pasteurization under 60℃/3.5 min, the emulsifying stability of EW was improved by nearly 100%, while with 0.8% XG addition the gel structure of EWwould become porousandloosen under each pasteurization condition. The hardness of EW gels was decreased by 90% when the concentration of XG was 0.4% or 0.8%. According to the results, the concentration of gums and the pasteurization parameters should be considered together when adding gums into the liquid egg products for pasteurization simultaneously.

Encapsulation of Curcumin in a Ternary Nanocomplex Prepared with Carboxymethyl Short Linear Glucan-Sodium-Caseinate-Pectin Via Electrostatic Interactions

This work chemically modified short linear glucan (SLG) by introducing a surface carboxymethyl group to obtain carboxymethylated SLG (CMSLG), then prepared CMSLG-based ternary nanocomplex particles based on electrostatic interactions with sodium-caseinate (NaCas) and pectin. These nanocomplex particles are homogeneous, generally exhibiting sizes of <200 nm with spherical shape and negative surface charge. In addition, the results showed the increase in both the mass ratio of CMSLG and NaCas and the synthesis temperature can improve the colloidal stability of nanocomplex particles when they are exposed to simulated gastrointestinal fluids containing digestive enzymes. Moreover, nanocomplex particles have an exceptional capability to encapsulate curcumin, and this encapsulation efficiency increased as the mass ratios of CMSLG and NaCas were increased. The study also investigated the antioxidant activity and in vitro release properties of curcumin encapsulated by nanocomplex particles and found that CMSLG/NaCas/pectin had improved higher ABTS radical scavenging capacity and allowed for the controlled, sustained release of curcumin in simulated gastrointestinal fluid within 6 hours. Thus, this study provides new insights into the design of a CMSLG-based ternary nanocomplex and its use as a potential oral delivery system for lipophilic bioactive compounds. PRACTICAL APPLICATION: Curcumin, as a sort of natural polyphenolic compound, has many physiologic functions such as anti-oxidation, anticancer, and prevention of Alzheimer's disease. However, the application of the curcumin has been limited by its poor water solubility and unstable physicochemical property. To solve this problem, the nanotechnology has been used to prepare the nano-delivery carriers for curcumin. This work prepared a ternary nanoparticle based on the carboxymethyl short linear glucan, sodium-caseinate, and pectin. The ternary nanoparticle can achieve a higher encapsulation efficiency for curcumin. In addition, the ternary nanoparticle can enhance the ABTS radical scavenging capacity and provided control and sustained release of curcumin in the simulated gastrointestinal fluid.

Preparation of hypoallergenic ovalbumin by high-temperature water treatment

The high-temperature water treatment is one of the methods used to reduce the molecular weight of proteins. In this study, in order to establish a practical method for preparing hypoallergenic materials using the high-temperature water treatment, we investigated the effects of processing temperature on the antigenicity and allergenicity of a food allergen. Additionally, the foaming ability of the samples was also evaluated as a function desired in the food industry. We used ovalbumin as a model allergen. As a result, although there was no significant difference among the samples treated with different processing temperatures, all the antigens treated with high-temperature water showed a decrease in antigenicity and allergenicity. In addition, when ovalbumin was treated at a temperature of 130 °C or higher, there was a significant improvement in foaming properties. These findings indicate that high-temperature water treatment is a potential strategy for preparing practical hypoallergenic materials.

Denatured pre-treatment assisted polyphenol oxidase-catalyzed cross-linking: effects on the cross-linking potential, structure, allergenicity and functional properties of OVA

To evaluate the impacts of denatured pre-treatments (heating and denaturants) on cross-linking and the combined effect of pre-treatment and cross-linking on the structure, allergenicity and functional properties of OVA, OVA was pre-treated in different ways and then cross-linked. Results showed that the cross-linking reaction was obviously promoted with heating at 100 °C for 5 min or 0.5% of SDS as the pretreatment. Due to the coordinated process of pre-treatments and cross-linking, the secondary structure was changed and the gastrointestinal digestion of OVA was promoted. Meanwhile, the emulsifying properties, foaming properties, and antioxidant properties of OVA were remarkably improved. Furthermore, the IgG and IgE binding capacities of OVA, as well as the OVA-induced degranulation capacity of KU812 were all significantly decreased. However, upon comparing the cross-linking assisted by two different pre-treatments, it was seen that heating at 100 °C for 5 min was better than being treated with 0.5% of SDS in reducing the potential allergenicity of OVA. Therefore, we concluded that heat denaturation (at 100 °C for 5 min) assisted enzymatic cross-linking may provide a new cross-linking method to develop hypoallergenic foods with good functional properties.

Irradiation technology: An effective and promising strategy for eliminating food allergens

Food allergies are one of the major health concerns worldwide and have been increasing at an alarming rate in recent times. The elimination of food allergenicity has been an important issue in current research on food. Irradiation is a typical nonthermal treatment technology that can effectively reduce the allergenicity of food, showing great application prospects in improving the quality and safety of foods. In this review, the mechanism and remarkable features of irradiation in the elimination of food allergens are mainly introduced, and the research progress on reducing the allergenicity of animal foods (milk, egg, fish and shrimp) and plant foods (soybean, peanut, wheat and nuts) using irradiation is summarized. Furthermore, the influencing factors for irradiation in the elimination of food allergens are analyzed and further research directions of irradiation desensitization technology are also discussed. This article aims to provide a reference for promoting the application of irradiation technology in improving the safety of foods.

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.

Stability of Engineered Ferritin Nanovaccines Investigated by Combined Molecular Simulation and Experiments

Human ferritin is regarded as an attractive and promising vaccine platform because of its uniform structure, good plasticity, and desirable thermal and chemical stabilities. Besides, it is biocompatible and presumed safe when used as a vaccine carrier. However, there is a lack of knowledge of how different antigen insertion sites on the ferritin nanocage impact the resulting protein stability and performance. To address this question, we selected Epstein-Barr nuclear antigen 1 as a model epitope and fused it at the DNA level with different insertion sites, namely, the N- and C-termini of ferritin, to engineer proteins E1F1 and F1E1, respectively. Protein properties including hydrophobicity and thermal, pH, and chemical stability were investigated both by molecular dynamics (MD) simulation and by experiments. Both methods demonstrate that the insertion site plays an important role in protein properties. The C-terminus insertion (F1E1) leads to a less hydrophobic surface and more tolerance to the external influence of high temperature, pH, and high concentration of chemical denaturants compared to N-terminus insertion (E1F1). Simulated protein hydrophobicity and thermal stability by MD were in high accordance with experimental results. Thus, MD simulation can be used as a valuable tool to engineer nanovaccine candidates, cutting down costs by reducing the experimental effort and accelerating vaccine design.

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.

Changes in physicochemical properties, gel structure and in vitro digestion of marinated egg white gel during braising

In this paper, changes in physicochemical properties, gel structure and in vitro digestion of marinated egg with spice or tea during braising were investigated. Results indicated that the moisture content and surface hydrophobicity of marinated egg white showed an overall decreased trend. The springiness of marinated egg white showed an increased trend, and the hardness in the late stage showed an increased trend. Microstructure showed that compact gel structures formed many holes during the braising. Intermolecular forces showed that ionic bonds and disulfide bonds played a dominant role in the marinated egg white. Secondary structure showed that the β-turn showed a decreased trend, contrary to that of random coils and α-helices. Appropriate braising increased the digestibility of marinated egg white, but excessively long-time braising could reduce it. Both spice and tea braising could improve the gel strength of protein, and the tea braising was also slightly better than spice braising.

The Golden Egg: Nutritional Value, Bioactivities, and Emerging Benefits for Human Health

Egg is an encapsulated source of macro and micronutrients that meet all requirements to support embryonic development until hatching. The perfect balance and diversity in its nutrients along with its high digestibility and its affordable price has put the egg in the spotlight as a basic food for humans. However, egg still has to face many years of nutritionist recommendations aiming at restricting egg consumption to limit cardiovascular diseases incidence. Most experimental, clinical, and epidemiologic studies concluded that there was no evidence of a correlation between dietary cholesterol brought by eggs and an increase in plasma total-cholesterol. Egg remains a food product of high nutritional quality for adults including elderly people and children and is extensively consumed worldwide. In parallel, there is compelling evidence that egg also contains many and still-unexplored bioactive compounds, which may be of high interest in preventing/curing diseases. This review will give an overview of (1) the main nutritional characteristics of chicken egg, (2) emerging data related to egg bioactive compounds, and (3) some factors affecting egg composition including a comparison of nutritional value between eggs from various domestic species.

Eco-Innovation in Reusing Food By-Products: Separation of Ovalbumin from Salted Egg White Using Aqueous Two-Phase System of PEG 1000/(NH₄)₂SO₄

For the purpose of reducing pollution and the rational use of salted egg white, which is a byproduct of the manufacturing process of salted egg yolk, an aqueous two-phase system (ATPS) composed of polyethylene glycols (PEG 1000) and (NH₄)₂SO₄ was investigated to selectively separate ovalbumin (OVA) from salted egg white. With the aim of optimizing the selective separation of OVA using ATPS, a response surface method (RSM) experiment was carried out on the basis of a single-factor experiment. The OVA was characterized by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS⁻PAGE), reversed-phase high-performance liquid chromatography (RP-HPLC), liquid chromatography-nano electrospray ionization mass spectrometry (Nano LC-ESI-MS/MS), and Fourier transform infrared spectroscopy (FT-IR). Under the optimal conditions, the recovery yield of OVA through ATPS (Y) and the purity of OVA (P) could reach 89.25% and 96.28%, respectively. In conclusion, OVA was successfully separated from the salted egg white by PEG/(NH₄)₂SO₄ ATPS.

Low-pH induced structural changes, allergenicity and in vitro digestibility of lectin from black turtle bean (Phaseolus vulgaris L.)

Lectin was incubated in corresponding acidic buffers (pH 1.0-3.5) for a certain period (0.5, 1, 2, 4, 8, 12 and 24 h) at 25 °C. Low-pH induced changes in structure, allergenicity and in vitro digestibility of lectin from black turtle bean (Phaseolus vulgaris L.) were investigated in the present study. Results indicated that the alteration in structure was a progressive unfolding process mainly depending on pH environment, and the treated lectin attained a stable state at 8 h. Electrophoretic, dynamic light scattering (DLS) and size exclusion chromatography (SEC) analyses suggested that lectin monomers appeared in the solutions of pH < 2.0. Differential scanning calorimetry (DSC) confirmed that thermal stability of lectin weakened in low pH environments. Furthermore, ELISA and in vitro digestion assay showed allergenicity and digestibility significantly decreased with the structural alterations. These results showed low-pH treatments have great potential to reduce the damage of legumes protein consumption.

Can alternative epitope mapping approaches increase the impact of B-cell epitopes in food allergy diagnostics?

In vitro allergy diagnostics are currently based on the detection of specific IgE binding on intact allergens or a mixture thereof. This approach has drawbacks as it may yield false‐negative and/or false‐positive results. Thus, we reviewed the impact of known B‐cell epitopes of food allergens to predict transience or persistence, tolerance or allergy and the severity of an allergic reaction and to examine new epitope mapping strategies meant to improve serum‐based allergy diagnostics. Recent epitope mapping approaches have been worthwhile in epitope identification and may increase the specificity of allergy diagnostics by using epitopes predominately recognized by allergic patients in some cases. However, these approaches did not lead to discrimination between clinically relevant and irrelevant epitopes so far, since the polyclonal serum IgE‐binding epitope spectrum seems to be too individual, independent of the disease status of the patients. New epitope mapping strategies are necessary to overcome these obstacles. The use of patient‐derived monoclonal antibodies instead of patient sera for functional characterization of clinically relevant and irrelevant epitope combinations, distinguished by their ability to induce degranulation, might be a promising approach to gain more insight into the allergic reaction and to improve serum‐based allergy diagnostics.

Monitoring of Deamidation and Lanthionine Formation in Recombinant Mugwort Allergen by Capillary Zone Electrophoresis (CZE)-UV and Transient Capillary Isotachophoresis-CZE-Electrospray Ionization-TOF-MS

The response to thermal stress is an important parameter relevant for characterizing the biological activity and long-term stability of recombinant proteins, which may show irreversible, pH dependent structural changes under these conditions. We selected the recombinant pollen allergen of mugwort ( Artemisia vulgaris) rArt v 3.0201 as a relevant model to study structural changes due to thermal and pH stress by means of capillary zone electrophoresis (CZE)-UV and capillary zone electrophoresis (CZE)-electrospray ionization (ESI)-TOF-MS. Therefore, this recombinant protein was exposed to 95 °C under acidic (pH 3.4) and slightly alkaline (pH 7.3) conditions for up to 120 min. CZE-UV data showed a continuous degradation of the allergen accompanied by the gradual formation of several reaction products. Characterization of novel allergen variants occurring at longer migration times was done via CZE-ESI-TOF-MS using in-capillary transient capillary isotachophoresis (tCITP) preconcentration to facilitate the identification of minor variants. MS data revealed various modifications of rArt v 3.0201 in response to heating. Variants with deamidations and sulfur-related modifications including both yield and loss of sulfur were identified at increased migration times. Desulfurization produced allergen variants with up to four lanthionines that replaced initial disulfide bonds. In addition, mass spectra revealed shifts in the charge state distribution which indicate concomitant conformational alterations. Moreover, several low-abundant oxidized variants were identified. With extended thermal stress, the portfolio of variants increased and progressively shifted toward rArt v 3.0201 with high lanthionine content. The kinetics of conversion and the complexity of variant composition were pH dependent and increased under alkaline conditions.

Advances on the impact of thermal processing on structure and antigenicity of chicken ovomucoid

BACKGROUND

Ovomucoid (OVM) is the dominant allergen found in egg white. The heat-induced changes on chicken OVM structure and antigenic properties were assessed at acidic, neutral and alkaline pH values.

RESULTS

The fluorescence spectroscopy measurements indicated changes in the conformation of OVM caused by both pH and thermal treatment. The OVM molecule exhibited higher exposure of hydrophobic residues at 7.0, as indicated by the synchronous spectra, intrinsic fluorescence and quenching experiments. When heating the protein at pH 9.5, the molecular structure appeared more compact. The antigenic properties of OVM, estimated through the enzyme-linked immunosorbent assay, appeared not to be sensitive to heat at pH 7.0 and 4.5. Single molecule level investigations indicated that the secondary and tertiary structure of OVM was affected by the thermal treatment.

CONCLUSIONS

Experimental results indicated over 90% reduction of the antigenicity at pH 9.5 and temperature of 100 °C. Significant changes of the linear epitopes exposure and location of the conformational epitopes were highlighted after performing heating molecular dynamics simulations of OVM from 25 °C to 100 °C. © 2017 Society of Chemical Industry.