Comparison of the Digestibility of the Major Peanut Allergens in Thermally Processed Peanuts and in Pure Form

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.

Mitigating the allergenicity of peanut allergen Ara h 1 by cold atmospheric pressure argon plasma jet

BACKGROUND

Peanut allergy is recognized as a major food allergy that triggers severe and even fatal symptoms. Avoidance of peanuts in the diet is the main option for current safety management. Processing techniques reducing peanut allergenicity are required to develop other options. Cold plasma is currently considered as a novel non-thermal approach to alter protein structure and has the potential to alleviate immunoreactivity of protein allergen.

RESULTS

The application of a cold argon plasma jet to peanut protein extract could reduce the amount of a 64 kDa protein band corresponding to a major peanut allergen Ara h 1 using sodium dodecyl sulfate-polyacrylamide gel electrophoresis, but the overall protein size distribution did not change significantly. A decrease in peanut protein solubility was a possible cause that led to the loss of protein content in the soluble fraction. Immunoblotting and enzyme-linked immunosorbent assay elucidated that the immunoreactivity of Ara h 1 was significantly decreased with the time treated with plasma. Ara h 1 antigenicity reduced by 38% after five scans (approximately 3 min) of cold argon plasma jet treatment, and the reduction was up to 66% after approximately 15 min of treatment.

CONCLUSION

The results indicate that cold argon plasma jet treatment could be a suitable platform for alleviating the immunoreactivity of peanut protein. This work demonstrates an efficient, compact, and rapid platform for mitigating the allergenicity of peanuts, and shows great potential for the plasma platform as a non-thermal technique in the food industry. © 2023 Society of Chemical Industry.

Effect of high-moisture extrusion and addition of transglutaminase on major peanut allergens content extracted by three step sequential method

The effect of high-moisture extrusion (HME) with or without transglutaminase (TGase) on peanut allergen levels and their extractability was studied. A three-stage sequential protein extraction significantly improved the protein recovery in processed samples (extrudate meat analogue); from 5.56 to 18.75 mg/100 mg without TGase, and from 4.59 to 20.82 mg/100 mg with 0.3% TGase. The total major allergen content was reduced by 91% (Ara h 1), 61% (Ara h 2), 60% (Ara h 6), and 55% (Ara h 3). Western-blot analysis of soluble extracts reflected the presence of Ara h 1 and Ara h 2 in significantly lower, indicating a potential reduction in IgE binding. During different processing zones, the most significant reduction in allergenic proteins was in the melting zone. The significant alteration in secondary and tertiary structures as a result of crosslinking shearing and degradation of proteins is likely to lead to allergen reduction.

Ranking of 10 legumes according to the prevalence of sensitization as a parameter to characterize allergenic proteins

•

10 different legumes extracts could be ranked based on the variations in the prevalence of sensitization.

•

Variations in the prevalence of sensitization allowed for ranking of 18 different individual legume proteins.

•

Ranking can be used to select reference proteins to develop predictive assays for the assessment of the sensitizing potential of novel proteins.

Predicting the allergenicity of novel proteins is challenging due to the absence of validated predictive methods and a well-defined reference set of proteins. The prevalence of sensitization could be a parameter to select reference proteins to characterize allergenic proteins. This study investigated whether the prevalence of sensitization of legume extracts and proteins can indeed be used for this purpose. A random sample of suspected food-allergic patients (n=106) was therefore selected. 10 extracts (processed and non-processed) and 18 individual proteins (2S albumins, 7S and 11S globulins) from black lentil, blue and white lupine, chickpea, faba bean, green lentil, pea, peanut, soybean, and white bean were isolated and the prevalence of sensitization and the intensity of IgE binding were evaluated. The prevalence of sensitization ranged from 5.7 % (faba bean and green lentil) to 14.2 % (peanut). The prevalence of sensitization for individual legume proteins ranged from 0.0 % for albumin 1 (pea) to 15.1 %–17.9 % for Ara h 1, 2, 3, and 6 (peanut). The prevalence of sensitization correlated strongly with the intensity of IgE binding for individual proteins (p < 0.05, ρ = 0.894), for extracts no correlation was found. The discovered ranking can be used to select reference proteins for the development and validation of predictive in vitro or in vivo assays for the assessment of the sensitizing potential.

Digestion and Transport across the Intestinal Epithelium Affects the Allergenicity of Ara h 1 and 3 but Not of Ara h 2 and 6

Scope

No accepted and validated methods are currently available which can accurately predict protein allergenicity. In this study, the role of digestion and transport on protein allergenicity is investigated.

Methods and results

Peanut allergens (Ara h 1, 2, 3, and 6) and a milk allergen (β‐lactoglobulin) are transported across pig intestinal epithelium using the InTESTine model and afterward basophil activation is measured to assess the (remaining) functional properties. Additionally, allergens are digested by pepsin prior to epithelial transport and their allergenicity is assessed in a human mast cell activation assay. Remarkably, transported Ara h 1 and 3 are not able to activate basophils, in contrast to Ara h 2 and 6. Digestion prior to transport results in a significant increase in mast cell activation of Ara h 1 and 3 dependent on the length of digestion time. Activation of mast cells by Ara h 2 and 6 is unaffected by digestion prior to transport.

Conclusions

Digestion and transport influences the allergenicity of Ara h 1 and 3, but not of Ara h 2 and 6. The influence of digestion and transport on protein allergenicity may explain why current in vitro assays are not predictive for allergenicity.

Multivariate Chemometrics as a Strategy to Predict the Allergenic Nature of Food Proteins

The purpose of the present study is to develop a simple method for the classification of food proteins with respect to their allerginicity. The methods applied to solve the problem are well-known multivariate statistical approaches (hierarchical and non-hierarchical cluster analysis, two-way clustering, principal components and factor analysis) being a substantial part of modern exploratory data analysis (chemometrics). The methods were applied to a data set consisting of 18 food proteins (allergenic and non-allergenic). The results obtained convincingly showed that a successful separation of the two types of food proteins could be easily achieved with the selection of simple and accessible physicochemical and structural descriptors. The results from the present study could be of significant importance for distinguishing allergenic from non-allergenic food proteins without engaging complicated software methods and resources. The present study corresponds entirely to the concept of the journal and of the Special issue for searching of advanced chemometric strategies in solving structural problems of biomolecules.

Epitopes with similar physicochemical properties contribute to cross reactivity between peanut and tree nuts

Many individuals with peanut (PN) allergy have severe reactions to tree nuts (TN) such as walnuts or cashews. Although allergenic proteins in TN and PN have overall low identity, they share discrete sequences similar in physicochemical properties (PCP) to known IgE epitopes. Here, PCP-consensus peptides (cp, 13 aa and 31 aa) were identified from an alignment of epitope rich regions of walnut vicilin, Jug r 2, leader sequence (J2LS) and cross-reactive epitopes in the 2S albumins of peanut and synthesized. A peptide similarity search in the Structural Database of Allergenic Proteins (SDAP) revealed a network of peptides similar (low property distance, PD) to the 13 aa cp (13cp) in many different plant allergens. Peptides similar to the 13cp in PN and TN allergens bound IgE from sera of patients allergic to PN and TN in peptide microarray analysis. The 13cp was used to produce a rabbit consensus peptide antibody (cpAB) that detected proteins containing repeats similar to the 13cp in western blots of various nut extracts, in which reactive proteins were identified by mass spectrometry. The cpAB bound more specifically to allergens and nut extracts containing multiple repeats similar to the 13 cp, such as almond (Pru du 6), peanut (Ara h 2) and walnut (Jug r 2). IgE binding to various nut extracts is inhibited by recombinant J2LS sequence and synthetic 31cp. Thus, several repeated sequences similar to the 13cp are bound by IgE. Multiple similar repeats in several allergens could account for reaction severity and clinically relevant cross-reactivity to PN and TN. These findings may help improve detection, diagnostic, and therapeutic tools.

Contribution of Chemical Modifications and Conformational Epitopes to IgE Binding by Ara h 3

Roasting is known to change the allergenic properties of peanuts. To study these observations at a molecular level, the relationship of IgE binding to the structure of Ara h 3 from raw and roasted peanuts was assessed. Ara h 3 (A3) was purified from raw (R), light roast (LR) and dark roast (DR) peanuts, the purity was assessed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and the secondary structures were compared with circular dichroism (CD) spectroscopy. In order to understand the contribution of structure to IgE binding, the R A3 was partially denatured (PD) by heat treatment (65 °C for 2 h), subjected to CD spectroscopy and IgE spot blot analysis with sera from peanut- allergic individuals. While we observed that the secondary structure of purified A3 from R and LR peanut in solution was affected by the reduction of disulfide bonds and heat treatment when purified from the peanut following the roasting process, only small alterations were seen in the secondary structure. The purified LR A3 bound higher levels of IgE than the RA3. CD spectroscopy of PD A3 revealed a reduction in the percentage of alpha helices, and serum IgE binding. Therefore, while A3 purified from roasted peanuts did not show significant changes in secondary structure, it showed higher IgE binding than R A3. Therefore, the higher IgE binding to LR A3 was more likely to be due to chemical modifications than structural changes. However, a decrease in the IgE binding was seen if R A3 was deliberately unfolded, indicating that the structure played an important role in IgE binding to A3.

The Effect of Digestion and Digestibility on Allergenicity of Food

Food allergy prevalence numbers are still on the rise. Apart from environmental influences, dietary habits, food availability and life-style factors, medication could also play a role. For immune tolerance of food, several contributing factors ensure that dietary compounds are immunologically ignored and serve only as source for energy and nutrient supply. Functional digestion along the gastrointestinal tract is essential for the molecular breakdown and a prerequisite for appropriate uptake in the intestine. Digestion and digestibility of carbohydrates and proteins thus critically affect the risk of food allergy development. In this review, we highlight the influence of amylases, gastric acid- and trypsin-inhibitors, as well as of food processing in the context of food allergenicity.

Effects of buffer additives and thermal processing methods on the solubility of shrimp (Penaeus monodon) proteins and the immunoreactivity of its major allergen

This study examines the potential of two buffer additives (Tween 20 and DTT) to improve the solubility of proteins from shrimp subjected to different heat treatments and the allergenicity of tropomyosin in the extracts. The concentration of soluble proteins extracted by all the buffers from processed shrimp was significantly reduced compared with untreated samples. The concentration of total soluble proteins from heat treated shrimp increased significantly when phosphate buffer containing both surfactant and reducing agent was used as the extraction buffer. However, the concentrations of heat-stable proteins in the buffers were mostly similar. The electrophoretic profile of extracted proteins showed that tropomyosin is very stable under the different heat treatment methods used in this study except for high pressure steaming where the intensity of tropomyosin band was reduced. Competitive inhibition ELISA showed that high pressure steaming reduced the allergenicity of tropomyosin compared with other heat treatments methods.

Food processing and allergenicity

Food processing can have many beneficial effects. However, processing may also alter the allergenic properties of food proteins. A wide variety of processing methods is available and their use depends largely on the food to be processed. In this review the impact of processing (heat and non-heat treatment) on the allergenic potential of proteins, and on the antigenic (IgG-binding) and allergenic (IgE-binding) properties of proteins has been considered. A variety of allergenic foods (peanuts, tree nuts, cows' milk, hens' eggs, soy, wheat and mustard) have been reviewed. The overall conclusion drawn is that processing does not completely abolish the allergenic potential of allergens. Currently, only fermentation and hydrolysis may have potential to reduce allergenicity to such an extent that symptoms will not be elicited, while other methods might be promising but need more data. Literature on the effect of processing on allergenic potential and the ability to induce sensitisation is scarce. This is an important issue since processing may impact on the ability of proteins to cause the acquisition of allergic sensitisation, and the subject should be a focus of future research. Also, there remains a need to develop robust and integrated methods for the risk assessment of food allergenicity.