Simultaneous separation of the four major allergens of hen egg white

Shedding light on the interaction of ovalbumin and resveratrol: structure, digestibility, transport, and allergenicity assessment of OVA-RES complexes

BACKGROUND

The interaction between food allergens and plant polyphenols has become a safe and effective management strategy to prevent food allergies. Ovalbumin (OVA) is the most abundant allergen in egg whites. Resveratrol (RES) is a plant polyphenol that is abundant in red grapes, berries, and peanuts, and has an anti-allergic effect on allergy-related immune cells. However, there is little information about the effect of RES on the allergenicity of OVA. In this study, the effect of RES on the allergenicity of OVA was investigated.

RESULTS

Molecular docking and spectroscopic studies indicated that the addition of RES changed the structure of OVA. The digestion and transfer rate of OVA-RES were effectively improved with an in vitro gastrointestinal digestion model and Caco-2 cell model, especially when the molar ratio of OVA-RES was 1:20. Meanwhile, the KU812 cell degranulation assay proved that the potential allergenicity was remarkably decreased while the molar ratios of OVA-RES were increased to 1:20. Furthermore, hydrogen bonds and van der Waals forces were the dominating forces to stabilize the OVA-RES complexes.

CONCLUSION

All the findings demonstrated that the potential allergenicity of OVA was reduced when interacting with RES, and RES can be a potential food material for preparing a hypoallergenic protein, especially for egg allergy. © 2023 Society of Chemical Industry.

Effects of unfolding treatment assisted glycation on the IgE/IgG binding capacity and antioxidant activity of ovomucoid

Ovomucoid is the immune-dominant allergen in the egg white of hens. Due to its structure based on nine disulfide bonds as well as its resistance to heat and enzymatic hydrolysis, the allergenicity of this food protein is difficult to decrease by technological processes. We sought to reduce its allergenicity through the Maillard reaction. The unfolding of ovomucoid with L-cysteine-mediated reduction was used to increase accessibility to conformational and linear epitopes by modifying the secondary and tertiary structures of the allergen. Glycation with different saccharides revealed the beneficial effect of maltose glycation on the IgG-binding capacity reduction. By determining the better glycation conditions of unfolded ovomucoid, we produced ovomucoid with reduced IgE binding capacity due to the glycation sites (K17, K112, K129, and K164) on epitopes. Moreover, after simulated infant and adult gastrointestinal digestion, the unfolded plus glycated ovomucoid showed higher ABTS˙+ scavenging activity, O2˙- scavenging activity, ˙OH scavenging activity, Fe2+ chelating activity, and a FRAP value; in particular, for ˙OH scavenging activity, there was a sharp increase of more than 100%.

Imidazole-octyl mixed-mode stationary phase based on macroporous silica for the purification of ovomucoid and ovotransferrin

A process-simplified hard template approach was established to synthesize the monodisperse macroporous silica microspheres with homogeneous structures by twice alkali-thermal treatment and calcination routes. Porous vinyl-functionalized polysesquioxane microspheres (V-PMSQ) were synthesized through a hydrolyzation-polycondensation method and used as templates. The template particles with large aperture and high pore volume were obtained by adjusting the pH value and reaction time of the twice alkali-thermal reaction. After calcination, monodisperse silica microspheres with an average pore size of 30 nm, homogeneous pore structures, and narrow particle size distribution were fabricated, which can be directly used as chromatographic matrices without classification. After that, a new reversed-phase/strong anion-exchange (RP/SAX) mixed-mode stationary phase Sil-S-VOIM was prepared by bonding the 1-vinyl-3-octyl-imidazole ligands to the above silica microspheres through a "thiol-ene" click reaction. The performance of the Sil-S-VOIM column was evaluated by one acidic protein (transferrin) and two basic proteins (lysozyme, α-chymotrypsin) and compared to a single imidazole-modified Sil-S-VIM column and an octyl-modified Sil-C8 column, respectively. Due to the synergistic effect of electrostatic repulsion and hydrophobic interactions, baseline separations of the above proteins were observed only on the Sil-S-VOIM column, with resolutions of 2.55 and 2.01 between lysozyme and transferrin, and between transferrin and α-chymotrypsin, respectively, indicating good selectivity and separation ability compared with single-mode stationary phases. It was applied to the isolation of egg white samples with peaks identified by SDS-PAGE and MALDI-TOF-MS. The results showed that the selective retention and isolation of ovomucoid and ovotransferrin were successfully achieved, with yields of 78.8% and 67.2%, respectively. The protocol described in this work is simpler, faster, and has higher protein recovery. Overall, this new mixed-mode stationary phase provided a promising potential for the separation and determination of intact proteins.

Epitope Mapping of Lysozyme Using the Chinese Egg-Allergic Sera at Both Pooled and Individual Levels

To accurately map the B-cell linear epitopes of lysozyme (LYS) in eggs, five bioinformatics tools were first used to obtain the mimotopes. Afterward, based on the Chinese egg-allergic sera samples screened by the indirect enzyme-linked immunosorbent, the epitopes possessing the capability of binding to IgG/IgE were mapped at both pooled and individual levels by using overlapping peptides covering the complete amino acid sequence of LYS. Six B-cell linear epitopes and two dominant B-cell linear epitopes that could bind to LYS-sIgG were mapped for the first time. Seven IgE-binding epitopes and three dominant IgE-binding epitopes were also obtained. Furthermore, AA31-34 and AA88-91 were the shared dominant epitopes of LYS-sIgG and LYS-sIgE at pooled and individual levels. Overall, the mapped B-cell linear epitopes filled in the gaps in the study of LYS epitopes, and the results may provide theoretical support for the following immunotherapy of egg allergy.

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.

Functional Properties and Extraction Techniques of Chicken Egg White Proteins

Chicken egg whites contain hundreds of proteins, and are widely used in the food, biological and pharmaceutical industries. It is highly significant to study the separation and purification of egg white proteins. This review first describes the structures and functional properties of several major active proteins in egg whites, including ovalbumin, ovotransferrin, ovomucoid, lysozyme, ovomucin, ovomacroglobulin and avidin. Then, the common techniques (including precipitation, chromatography and membrane separation) and some novel approaches (including electrophoresis, membrane chromatography, aqueous two-phase system and molecular imprinting technology) for the separation and purification of egg white proteins broadly reported in the current research are introduced. In addition, several co-purification methods for simultaneous separation of multiple proteins from egg whites have been developed to improve raw material utilization and reduce costs. In this paper, the reported techniques in the last decade for the separation and purification of chicken egg white proteins are reviewed, discussed and prospected, aiming to provide a reference for further research on egg proteins in the future.

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.