Effect of Processing on the Structure and Allergenicity of Peanut Allergen Ara h 2 Roasted in a Matrix

Identification of digestion-resistant peptides in various processed peanut reveals their distinct allergenicity

Peanut protein is a significant food allergen that can trigger severe reactions. The allergenicity of peanut protein may be affected by the thermal processing method and matrices, and its anti-digestibility may also change accordingly. This study investigated how three heat treatment techniques affect the allergenicity and digestibility of peanut proteins and compared the differences in anti-digestive peptide segments by Mass spectrometry. Results showed that boiling and frying reduced sensitization, while roasting potentially increased it. After gastric digestion, allergenicity of Ara h 1 decreases due to breakdown of allergenic peptide segments. Hydrophobic regions of Ara h 1 where monomers interact resist degradation. Compared to boiling and frying, roasting can retain more allergenic peptides containing PGQFEDFF, YLQGFSRN, QEERGQRR, HRIFLAGDKD, and KDLAFPGSGE allergenic epitopes even after prolonged digestion. Meanwhile, digestion-resistant epitopes were affected by matrix and thermal treatments. These findings underscore the potential implications for food processing and allergy management strategies.

Employing conductive porous hydrogen-bonded organic framework for ultrasensitive detection of peanut allergen Ara h1

Peanut allergy has garnered worldwide attention due to its high incidence rate and severe symptoms, stimulating the demand for the ultrasensitive detection method of peanut allergen. Herein, we successfully developed a novel electrochemical aptasensor for ultrasensitive detection Ara h1, a major allergenic protein present in peanuts. A conductive nickel atoms Anchored Hydrogen-Bonded Organic Frameworks (PFC-73-Ni) were utilized as excellent electrocatalysts toward hydroquinone (HQ) oxidation to generate a readable current signal. The developed electrochemical aptasensor offers wide linear range (1-120 nM) and low detection limit (0.26 nM) for Ara h1. This method demonstrated a recovery rate ranging from 95.00% to 107.42% in standard addition detection of non-peanut food samples. Additionally, the developed electrochemical method was validated with actual samples and demonstrated good consistency with the results obtained from a commercial ELISA kit. This indicates that the established Ara h1 detection method is a promising tool for peanut allergy prevention.

Recent advance in sesame allergens: Influence of food processing and their detection methods

Sesame (Sesamum indicum L.) is a valuable oilseed crop with numerous nutritional benefits containing a diverse range of bioactive compounds. However, sesame is also considered an allergenic food that triggers various mild to severe adverse reactions (e.g., anaphylaxis). Strict dietary avoidance of sesame components is the best option to protect the sensitized consumers. Sesame or sesame-derived foods are always consumed after certain food processing operations, which would cause a considerable impact on the structure of sesame proteins, changing their sensitization capacity and detectability. In the review, the molecular structure properties, and immunological characteristics of the sesame allergens were described. Meanwhile, the influence of food processing techniques on sesame proteins and the relevant detection techniques used for the sesame allergens quantification are also emphasized critically. Hopefully, this review could provide valuable insight into the development and management for the new "Big Eight" sesame allergen in food industry.

The structure and potential allergenicity of peanut allergen monomers after roasting

Given that roasted peanut (Ro) products are commonly used in daily life, peanut allergenicity is a foremost concern. Analyzing the changes in the structure and potential allergenicity of individual allergens can promote the exploration of the structural basis of the alterations in the potential allergenicity of Ro. This work focused on four major allergens in raw peanut (Ra) and Ro. Structural changes were analyzed on the basis of circular dichroism, ultraviolet and fluorescence spectroscopy, and molecular dynamic simulation. The IgE recognition capability of allergens was assessed via western blot analysis. The IgE binding capacity of allergens was detected by conducting enzyme-linked immunosorbent assay. The potential allergenicity of allergens was evaluated using the KU812 cell degranulation model. The results showed that roasting induced different changes in the overall structures of allergens and altered the structures and electrostatic potential of IgE epitopes, especially Ara h 1 and Ara h 6. These alterations affected the potential allergenicity of allergens. Ara h 1 and Ara h 6 in Ro showed significantly enhanced IgE binding capacities and abilities to elicit KU812 cell degranulation, while Ara h 2 and Ara h 3 did not change significantly. For total protein, the roasted peanut protein showed decreased abilities to elicit KU812 cell degranulation. The results indicated that different allergens in Ro showed different changes of structures and potential allergenicity and that the conformational structure plays a crucial role in potential allergenicity of allergens.

A novel IgE epitope-specific antibodies-based sandwich ELISA for sensitive measurement of immunoreactivity changes of peanut allergen Ara h 2 in processed foods

Background

Peanut is an important source of dietary protein for human beings, but it is also recognized as one of the eight major food allergens. Binding of IgE antibodies to specific epitopes in peanut allergens plays important roles in initiating peanut-allergic reactions, and Ara h 2 is widely considered as the most potent peanut allergen and the best predictor of peanut allergy. Therefore, Ara h 2 IgE epitopes can serve as useful biomarkers for prediction of IgE-binding variations of Ara h 2 and peanut in foods. This study aimed to develop and validate an IgE epitope-specific antibodies (IgE-EsAbs)-based sandwich ELISA (sELISA) for detection of Ara h 2 and measurement of Ara h 2 IgE-immunoreactivity changes in foods.

Methods

DEAE-Sepharose Fast Flow anion-exchange chromatography combining with SDS-PAGE gel extraction were applied to purify Ara h 2 from raw peanut. Hybridoma and epitope vaccine techniques were employed to generate a monoclonal antibody against a major IgE epitope of Ara h 2 and a polyclonal antibody against 12 IgE epitopes of Ara h 2, respectively. ELISA was carried out to evaluate the target binding and specificity of the generated IgE-EsAbs. Subsequently, IgE-EsAbs-based sELISA was developed to detect Ara h 2 and its allergenic residues in food samples. The IgE-binding capacity of Ara h 2 and peanut in foods was determined by competitive ELISA. The dose-effect relationship between the Ara h 2 IgE epitope content and Ara h 2 (or peanut) IgE-binding ability was further established to validate the reliability of the developed sELISA in measuring IgE-binding variations of Ara h 2 and peanut in foods.

Results

The obtained Ara h 2 had a purity of 94.44%. Antibody characterization revealed that the IgE-EsAbs recognized the target IgE epitope(s) of Ara h 2 and exhibited high specificity. Accordingly, an IgE-EsAbs-based sELISA using these antibodies was able to detect Ara h 2 and its allergenic residues in food samples, with high sensitivity (a limit of detection of 0.98 ng/mL), accuracy (a mean bias of 0.88%), precision (relative standard deviation < 16.50%), specificity, and recovery (an average recovery of 98.28%). Moreover, the developed sELISA could predict IgE-binding variations of Ara h 2 and peanut in foods, as verified by using sera IgE derived from peanut-allergic individuals.

Conclusion

This novel immunoassay could be a user-friendly method to monitor low level of Ara h 2 and to preliminary predict in vitro potential allergenicity of Ara h 2 and peanut in processed foods.

Mass Spectrometry Analysis on the Breakage of Allergens in High-Molecular-Mass Polymer of Roasted Peanuts

Peanut allergy is a prevalent and concerning food allergy. Roasting can introduce structural changes to peanut allergens, affecting their allergenicity, but the structure on the primary structure is unclear. Here, the breakage sites were identified by mass spectrometry and software tools, and structural changes were simulated by molecular dynamics and displayed by PyMOL software. Results revealed that the appearance frequencies of L, Q, F, and E were high at the N-terminal of the breakage site, while S and E were dominant at the C-terminal. In the conformational structure, breakage sites were found close to disulfide bonds and the Cupin domains of Ara h 1 and Ara h 3. The breakage of allergens destroyed linear epitopes and might change the conformation of epitopes, which could influence peanuts' potential allergenicity.

Investigation of peanut allergen-procyanidin non-covalent interactions: Impact on protein structure and in vitro allergenicity

Interactions between plant polyphenols and food allergens may be a new way to alleviate food allergies. The non-covalent interactions between the major allergen from peanut (Ara h 2) with procyanidin dimer (PA2) were therefore characterized using spectroscopic, thermodynamic, and molecular simulation analyses. The main interaction between the Ara h 2 and PA2 was hydrogen bonding. PA2 statically quenched the intrinsic fluorescence intensity and altered the conformation of the Ara h 2, leading to a more disordered polypeptide structure with a lower surface hydrophobicity. In addition, the in vitro allergenicity of the Ara h 2-PA2 complex was investigated using enzyme-linked immunosorbent assay (ELISA) kits. The immunoglobulin E (IgE) binding capacity of Ara h 2, as well as the release of allergenic cytokines, decreased after interacting with PA2. When the ratio of Ara h 2-to-PA2 was 1:50, the IgE binding capacity was reduced by around 43 %. This study provides valuable insights into the non-covalent interactions between Ara h 2 and PA2, as well as the potential mechanism of action of the anti-allergic reaction caused by binding of the polyphenols to the allergens.

Discovery, verification, and validation of walnut protein marker peptides using LC-MS approaches

A key requirement of liquid chromatography-mass spectrometry (LC-MS)-based allergenic food protein analysis methods is to use protein marker peptides with good analytical performances in LC-MS analysis of commercial processed foods. In this study, we developed a multi-stage walnut protein marker peptide selection strategy involving marker peptide discovery and verification and LC-MS validation of chemically equivalent stable isotope-labeled peptides. This strategy proposed three walnut protein marker peptides, including two new marker peptides. Our LC-MS-based walnut protein analysis method using the three stable isotope-labeled peptides showed acceptable linearity (R2 >0.99), matrix effects (coefficient of variation <±15%), sensitivity (limit of detection >0.3 pg/μL, limit of quantification >0.8 pg/μL), recovery (85.1-103.4%), accuracy, and precision (coefficient of variation <10%). In conclusion, our multi-stage marker peptide selection strategy effectively selects specific protein marker peptides for sensitive detection and absolute quantification of walnut proteins in LC-MS analysis of commercial processed foods.

One-Step Purification of IgE Epitope-Specific Antibody Using Immunomagnetic Beads and Highly Sensitive Detection of Bovine β-Lactoglobulin for the Prediction of Milk Allergenicity in Foods

Bovine β-lactoglobulin (BLG) is a common allergen found in milk, and the immunoglobulin E (IgE) epitope plays a crucial role in cow milk allergy. Therefore, targeting the IgE epitope could be useful in accurately detecting BLG and assessing its allergenicity. However, producing an IgE epitope-specific antibody (IgE-EsAb) through traditional methods requires complex and time-consuming procedures. Here, IgE-EsAb was purified from rabbit anti-BLG sera by immunomagnetic beads in one step. Then, a sandwich ELISA (sELISA) based on the IgE-EsAb was developed to detect BLG and predict the potential milk allergenicity in foods. The obtained IgE-EsAb could specifically recognize the target IgE epitope of BLG and exhibited high affinity and specificity. The developed IgE-EsAb-based sELISA demonstrated an ultra-wide linear range of 3.9-1.28 × 105 ng/mL, with a limit of detection of 0.49 ng/mL for BLG. Additionally, the proposed immunoassay showed high specificity and recoveries (91.24-109.61%). The ability of the IgE-EsAb-based sELISA to evaluate the potential milk allergenicity in foods was validated using sera from cow milk allergy patients. These results suggest that immunomagnetic beads are an effective tool for rapidly obtaining the IgE-EsAb, and our proposed sELISA could be a reliable and user-friendly method for monitoring trace amounts of BLG and predicting the potential milk allergenicity of food samples.

IgE Recognition and Structural Analysis of Disulfide Bond Rearrangement and Chemical Modifications in Allergen Aggregations in Roasted Peanuts

Given that roasting changes the structure and allergenicity of peanut allergens, the structural information of peanut allergens must be expounded to explain the alteration in their allergenicity. This work focused on allergen aggregations (AAs) in roasted peanuts. IgE recognition capability was assessed via western blot analysis. The disulfide bond (DB) rearrangement and chemical modification in AAs were identified by combining mass spectroscopy and software tools, and structural changes induced by cross-links were displayed by molecular dynamics and PyMOL software. Results showed that AAs were strongly recognized by IgE and cross-linked mainly by DBs. The types of DB rearrangement in AAs included interprotein (98 peptide pairs), intraprotein (22 peptide pairs), and loop-linked (6 peptides) DBs. Among allergens, Ara h 2 and Ara h 6 presented the most cysteine residues to cross-linkf with others or themselves. DB rearrangement involved IgE epitopes and induced structural changes. Ara h 1 and Ara h 3 were predominantly chemically modified. Moreover, chemical modification altered the local structures of proteins, which may change the allergenic potential of allergens.

Reduced Allergenicity of Shrimp (Penaeus vannamei) by Altering the Protein Fold, Digestion Susceptibility, and Allergen Epitopes

The mechanism by which thermal/pressure processing influences the allergenicity of shrimp (Penaeus vannamei) was explored by anaphylaxis in mice, the protein structure, gastrointestinal digestion, and linear epitopes. Roasting induced the unfolding of the structure, which may reduce the allergenicity, but it made more linear epitopes to be exposed, causing mice to exhibit similar systemic anaphylaxis as mice fed with the raw shrimp protein (p > 0.05). However, the roasted + reverse-pressure-sterilized shrimp can significantly reduce specific antibodies, mast cell degranulation, vascular permeability, and histopathological morphology in mice compared with the raw and roasted shrimp (p < 0.05) because reverse-pressure sterilization causes protein to aggregate, hiding the heat/digested stable epitopes of arginine kinase (Glu59-Ser63, Asn112-Lys118, Leu131-Phe136, and Ser158-Glu162) and sarcoplasmic calcium-binding protein (Asn57-Phe67, Ser159-Cys165, and Glu126-Ala130) inside a 3D structure, while gastrointestinal digestion can destroy immunodominant, minor epitopes and the epitopes exposed by roasting. Meanwhile, the low binding frequency of IgE to troponin C was also responsible for maintaining the hypoallergenicity of shrimp.

Allergenicity of peanut allergens and its dependence on the structure

Food allergies are a global food safety problem. Peanut allergies are common due, in part, to their popular utilization in the food industry. Peanut allergy is typically an immunoglobulin E-mediated reaction, and peanuts contain 17 allergens belonging to different families in peanut. In this review, we first introduce the mechanisms and management of peanut allergy, followed by the basic structures of associated allergens. Subsequently, we summarize methods of epitope localization for peanut allergens. These methods can be instrumental in speeding up the discovery of allergenicity-dependent structures. Many attempts have been made to decrease the allergenicity of peanuts. The structures of hypoallergens, which are manufactured during processing, were analyzed to strengthen the desensitization process and allergen immunotherapy. The identification of conformational epitopes is the bottleneck in both peanut and food allergies. Further, the identification and modification of such epitopes will lead to improved strategies for managing and preventing peanut allergy. Combining traditional wet chemistry research with structure simulation studies will help in the epitopes' localization.

Changes in Serum Protein-Peptide Patterns in Atopic Children Allergic to Plant Storage Proteins

Next to cow's milk and eggs, plant foods, i.e., legumes, tree nuts and cereal grains, most often sensitise atopic children. Storage proteins constitutes the most relevant protein fraction of plant foods, causing primary sensitisation. They exhibit strong allergenic properties and immunogenicity. Our goal was to analyse sensitisation to 26 plant storage proteins in a group of 76 children aged 0-5 years with chronic symptoms of atopic dermatitis using Allergy Explorer ALEX2 and to discover changes in serum protein-peptide patterns in allergic patients with the use of MALDI-TOF-MS. We reported that 25% of children were allergic to 2S albumins, 19.7% to 7S globulins, 13.2% to 11S globulins and 1.3% to cereal prolamins. The most common allergenic molecules were Ara h 1 (18.4%), Ara h 2 (17.1%), Ara h 6 (15.8%) and Ara h 3 (11.8%) from peanuts, and the mean serum sIgE concentrations in allergic patients were 10.93 kUA/L, 15.353 kUA/L, 15.359 kUA/L and 9.038 kUA/L, respectively. In children allergic to storage proteins compared to the other patients (both allergic and non-allergic), the cell cycle control protein 50A, testis-expressed sequence 13B, DENN domain-containing protein 5A and SKI family transcriptional corepressor 2 were altered. Our results indicate that the IgE-mediated allergy to storage proteins is a huge problem in a group of young, atopic children, and show the potential of proteomic analysis in the prediction of primary sensitisation to plant foods. It is the next crucial step for understanding the molecular consequences of allergy to storage proteins.

Effect of Structural Targeted Modifications on the Potential Allergenicity of Peanut Allergen Ara h 2

Protein structure affects allergenicity, and critical structural elements, especially conformational epitopes that determine allergenicity, have attracted a great deal of interest. In this study, we aimed to identify the localized structure that affects the potential allergenicity of protein by making targeted modifications of Ara h 2 and comparing the structure and allergenicity of mutants with those of the wide-type allergen. The structures of the allergen and its mutants were characterized by circular dichroism and ultraviolet absorption spectroscopy and simulated by molecular dynamics. The allergenicity was assessed by Western blotting, an indirect competitive enzyme-linked immunosorbent assay, a cell model, and a mouse model. Then, the structures that affect allergenicity were analyzed and screened. Our results showed that mutations in amino acids changed the nearby localized structure and the overall structures. The structural changes affected the IgE binding capacity of the allergen and reduced its potential allergenicity. The solvent accessible surface area (SASA) of aromatic residues was positively correlated with the IgE binding capacity. The integrity of the disulfide bond is also critical for the binding of IgE to allergens. Interestingly, different mutations induced similar electrostatic potential and allergenicity changes, such as localized structure R⁶²DPYSPSQDPYSPS⁷⁵. In conclusion, the disulfide bond and the SASA of aromatic residues are important for the allergenicity of Ara h 2. The localized structure R⁶²DPYSPSQDPYSPS⁷⁵ is also crucial for the allergenicity of Ara h 2.