Effect of transglutaminase cross-linking on the allergenicity of tofu based on a BALB/c mouse model

Effect of transglutaminase crosslinking combined with lactic fermentation on the potential allergenicity and conformational structure of soy protein

BACKGROUND

Food allergies are a growing concern worldwide, with soy proteins being important allergens that are widely used in various food products. This study investigated the potential of transglutaminase (TGase) and lactic acid bacteria (LAB) treatments to modify the allergenicity and structural properties of soy protein isolate (SPI), aiming to develop safer soy-based food products.

RESULTS

Treatment with TGase, LAB or their combination significantly reduced the antibody reactivity of β-conglycinin and the immunoglobulin E (IgE) binding capacity of soy protein, indicating a decrease in allergenicity. TGase treatment led to the formation of high-molecular-weight aggregates, suggesting protein crosslinking, while LAB treatment resulted in partial protein hydrolysis. These structural changes were confirmed by Fourier transform infrared spectroscopy, which showed a decrease in β-sheet content and an increase in random coil and β-turn contents. In addition, changes in intrinsic fluorescence and ultraviolet spectroscopy were also observed. The alterations in protein interaction and the reduction in free sulfhydryl groups highlighted the extensive structural modifications induced by these treatments.

CONCLUSION

The synergistic application of TGase and LAB treatments effectively reduced the allergenicity of SPI through significant structural modifications. This approach not only diminished antibody reactivity of β-conglycinin and IgE binding capacity of soy protein but also altered the protein's primary, secondary and tertiary structures, suggesting a comprehensive alteration of SPI's allergenic potential. These findings provide a promising strategy for mitigating food allergy concerns and lay the foundation for future research on food-processing techniques aimed at allergen reduction. © 2024 Society of Chemical Industry.

Characterization of the potential allergenicity of enzymatically hydrolyzed casein in Balb/c mouse model

Bovine casein is a major allergen present in cow milk to induce anaphylaxis. In this study, the potential allergenicity of enzymatically hydrolyzed casein (HC) was evaluated based on in vitro and in vivo. The results showed that Alcalase and Protamex treatment (AT, PT) reduced the potential allergenicity of CN, with the greatest reductions of 68.25% and 50.75%, respectively. In addition, in vivo results showed that HC effectively alleviated allergic response symptoms of Balb/c mice; a significant tendency toward decreased serum IgG1 and mast cell tryptase levels was observed, accompanied by a decrease of Th2-associated IL-4, IL-5, and IL-13 and an increase of IFN-γ levels in spleen. Moreover, the inflammation of the lung, jejunum, and ileum was remarkably ameliorated. The findings indicated that HC induced a shift toward Th1 response and maintained the Th1/Th2 immune balance. Importantly, our results provide the basis for the production of hypoallergenic dairy products.

Oral administration of egg ovalbumin allergen induces dysregulation of tryptophan metabolism in sensitized BALB/c mice

Food allergy (FA), triggered by specific dietary allergens, has emerged as a substantial global concern for food safety and public health. While studies have elucidated changes in immune cells and cytokines associated with allergen exposure, a comprehensive analysis of the host's metabolic features and the interaction between metabolites and the gut microbiota has not been conducted. In this study, egg allergen ovalbumin (OVA) was administered by the oral route to sensitized BALB/c mice to faithfully replicate key aspects of human FA, including severe allergic diarrhea, mast cell infiltration, and elevated levels of serum IgE, mMCPT-1, and Th2 cell hallmark cytokines (such as IL-4, IL-5, and IL-13). Furthermore, the untargeted and targeted metabolomic analyses indicated that FA in mice precipitated a substantial decrease in the tryptophan metabolites indole-3-acrylic acid (IA) and indole-3-lactic acid (ILA). The integration of shotgun metagenome and metabolome data further unveiled that the dysregulation of indole metabolism is related to a decline in the abundance of beneficial bacteria such as Lactobacillus and Bifidobacterium. Additionally, disruption of the tryptophan indole derivative pathway compromises the maintenance of intestinal mucosal function through the AHR signaling pathway, manifested by decreased expression of Reg3g and IL22. Taken together, this study demonstrated that the anaphylaxis triggered by oral ingestion of food allergens can lead to disruptions in tryptophan metabolism, consequently impairing intestinal immune homeostasis.

Transglutaminase-Cross-Linked Tofu Suppressed Soybean-Induced Allergic Reactions by Enhancing Intestinal Mucosa Immune Tolerance

Currently, food allergies are closely related to intestinal health, and ensuring the integrity and health of intestinal mucosa could reduce the incidence of food allergies. In this study, a soybean-allergic mouse model was used to explore the mechanism of intestinal mucosa immune response induced by enzyme-cross-linked tofu. The effects of enzyme-cross-linked tofu on intestinal mucosal immunity in mice were determined by hematoxylin-eosin (HE) staining and flow cytometry. Our results reveled that the MTG-cross-linked tofu reduced the reactivity of the intestinal mucosal immune system, which mainly manifested as a decrease in the dendritic cell (DC) levels of mesenteric lymph nodes (MLNs), increasing the Th1 cells and Tregs in Peyer's patch (PP) nodes and MLNs, and inhibiting the Th2 cells. Compared with soy protein, enzyme-cross-linked tofu had less damage to the small intestinal tract of mice. Therefore, the above-mentioned results fully revealed that the enzyme-cross-linked tofu promoted the transformation of intestinal mucosal immune cells, shifted the Th1/Th2 balance toward Th1, and reduced its sensitization effect.

Heat/non-heat treatment alleviates β-conglycinin-triggered food allergy reactions by modulating the Th1/Th2 immune balance in a BALB/c mouse model

BACKGROUND

With the increasing popularity of plant protein-based diets, soy proteins are favored as the most important source of plant protein worldwide. However, potential food allergy risks limit their use in the food industry. This work aims to reveal the mechanism of β-conglycinin-induced food allergy, and to explore the regulatory mechanism of heat treatment and high hydrostatic pressure (HHP) treatment in a BALB/c mouse model.

RESULTS

Our results showed that oral administration of β-conglycinin induced severe allergic symptoms in BALB/c mice, but these symptoms were effectively alleviated through heat treatment and HHP treatment. Moreover, β-conglycinin stimulated lymphocyte proliferation and differentiation; a large number of cytokines interleukin (IL)-4, IL-5, IL-10, IL-12 and IL-13 were released and interferon γ secretion was inhibited, which disrupted the Th1/Th2 immune balance and promoted the differentiation and proliferation of naive T cells into Th2-type cells.

CONCLUSION

Heat/non-heat treatment altered the conformation of soybean protein, which significantly reduced allergic reactions in mice. This regulatory mechanism may be associated with Th1/Th2 immune balance. Our results provide data support for understanding the changes in allergenicity of soybean protein within the food industry. © 2024 Society of Chemical Industry.

Covalent conjugation with quercetin mitigates allergenicity of the bee pollen allergen Bra c p in a murine model

Profilin family members are highly conserved food allergens that can cause widespread cross-allergic reactions. Our previous research has demonstrated that the covalent conjunction with quercetin can disrupt the conformational epitopes of a profilin allergen, Bra c p. In this study, we further investigated the intrinsic molecular mechanisms using molecular dynamics simulations. Moreover, the allergenic potential of Bra c p and its conjugate with quercetin was assessed in BALB/c mice. The results showed that continuous interaction with quercetin increased the molecular motion of Bra c p, causing changes to its α-helices and exposing hydrophobic residues which altered antigenic epitopes. Additionally, mice treated with Bra c p-quercetin conjugate showed reduced allergic reactions compared to those treated with Bra c p alone by regulating purine metabolism, calcium signaling, and CD4+CD25+ Tregs proportion. Quercetin conjugation decreases the allergenicity of Bra c p, providing a scientific foundation for reducing the profilin allergens in food.

Immunoglobulin E Epitope Mapping and Structure-Allergenicity Relationship Analysis of Crab Allergen Scy p 9

Filamin C is an allergen of Scylla paramamosain (Scy p 9), and six IgE linear epitopes of the allergenic predominant region had previously been validated. However, the IgE epitope and structure-allergenicity relationship of Scy p 9 are unclear. In this study, a hydrophobic bond was found to be an important factor of conformation maintaining. The critical amino acids in the six predicted conformational epitopes were mutated, and the IgE-binding capacity and surface hydrophobicity of four mutants (E216A, T270A, Y699A, and V704A) were reduced compared to Scy p 9. Ten linear epitopes were verified with synthetic peptides, among which L-AA187-205 had the strongest IgE-binding capacity. In addition, IgE epitopes were mapped in the protruding surface of the tertiary structure, which were conducive to binding with IgE and exhibited high conservation among filamin genes. Overall, these data provided a basis for IgE epitope mapping and structure-allergenicity relationship of Scy p 9.

Effects of Lactobacillus on the Differentiation of Intestinal Mucosa Immune Cells and the Composition of Gut Microbiota in Soybean-Sensitized Mice

In the early stage of this study, three strains of Lactobacillus with anti-soybean allergy potential were screened: Lactobacillus acidophilus CICC 6081, Lactobacillus delbrueckii subsp. Bulgaricus CICC 6103 and Lactobacillus plantarum subsp. Plantarum CICC 20988. The aim of this study was to analyze the desensitization effect of three strains of Lactobacillus administered by gavage to soybean-allergic mice through the differentiation of immune cells in intestinal lymph nodes and the changes to gut microbiota. The results showed that the three strains of Lactobacillus could stimulate the proliferation of dendritic cells (DCs) and regulate the balance of Th1/Th2 differentiation in the MLNs and PPs of soybean-allergic mice. Furthermore, the Th17/Tregs cell-differentiation ratio in the MLNs of the Lactobacillus-treated mice was significantly lower than that of the allergic mice (p < 0.05). Compared to the control group, the Shannon, Sobs and Ace indexes of intestinal microbiota in the allergic mice were significantly increased (p < 0.05), and the proportion of Clostridiales was significantly higher (p < 0.05), which was reversed by Lactobacillus gavage. In conclusion, the three strains of Lactobacillus can inhibit the intestinal mucosal immune response and regulate gut microbiota balance in soybean-allergic mice.

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.

IgE-Binding and Immunostimulating Properties of Enzymatic Crosslinked Milk Proteins as Influenced by Food Matrix and Digestibility

Dairy foods are essential in the diet, although in some susceptible individuals they may cause allergy to cow's milk proteins. Therefore, alternative methods are sought to reduce their allergenicity. Transglutaminase (TG) is widely used in dairy products mainly to improve texture. Although it has been claimed that TG can be used to modify the digestibility and allergenicity of foods, its impact within a real matrix has been rarely studied. The aim of this work was to assess the allergenic potential of crosslinked skim milk (SM), milk casein fraction (CN), and whey protein (WP). To this purpose, inhibition ELISA with sera from milk allergic patients, in vitro activation tests of mouse mast cells and splenocytes, and simulated gastrointestinal digestion assays were performed. The results showed that cross-linking increased the binding of IgE to WP, but decreased IgE-binding to SM and CN. However, no differences were observed in the ability of cross-linked proteins to induce mast cell degranulation compared to native proteins. The cross-linking of SM and CN reduced Th2 cytokine release from the splenocytes of sensitized mice. All TG-treated samples exhibited more resistance to in vitro digestion than the untreated proteins and the human IgE binding capacity after digestion was higher. In conclusion, TG treatment of milk proteins does not reduce the risk of eliciting allergic symptoms in cow's milk allergic patients.

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.

Effect of sea cucumber peptides on the immune response and gut microbiota composition in ovalbumin-induced allergic mice

The prevalence of food allergies has increased in Asian countries. The aim of this study was to determine the potential value of sea cucumber peptide (SCP) for anti-allergic therapeutics in terms of their effect on immune response and gut microbiota composition. Results exhibited that SCP could significantly improve the allergy symptoms caused by ovalbumin and could reduce the risk of IgE mediated allergic disorders, as well as repair the morphological damage in the colon. Flow cytometry analysis indicated that SCP could improve the ratio of CD4+/CD8+ T lymphocytes. 16S rRNA results indicated that SCP could differently impact the composition of microbiota. The relative abundances of Bacteroidetes and Firmicutes and the Bacteroidetes/Firmicutes ratio were altered in normal mice. When compared with the OVA treated group, the SCP treated groups showed an increase in the relative abundance of Lachnospiraceae, Muribaculaceae and Ruminococcaceae, and a decrease in Bacteroidaceae, Prevotellaceae, and Lactobacillaceae. These results demonstrate that SCP exhibits potential antiallergic activities in a mouse model of ovalbumin allergy by regulating intestinal microbiota diversity and upregulating the immune response of T lymphocyte subpopulations, which might provide important evidence that SCP can be developed into a novel functional food for inhibiting ovalbumin allergy.

Wheat Amylase Trypsin Inhibitors Aggravate Intestinal Inflammation Associated with Celiac Disease Mediated by Gliadin in BALB/c Mice

Celiac disease (CD) is an autoimmune intestinal disorder caused by the ingestion of gluten in people who carry the susceptible gene. In current celiac disease research, wheat gluten is often the main target of attention, neglecting the role played by non-gluten proteins. This study aimed to describe the effects of wheat amylase trypsin inhibitors (ATI, non-gluten proteins) and gliadin in BALB/c mice while exploring the further role of relevant adjuvants (cholera toxin, polyinosinic: polycytidylic acid and dextran sulfate sodium) intervention. An ex vivo splenocyte and intestinal tissue were collected for analysis of the inflammatory profile. The consumption of gliadin and ATI caused intestinal inflammation in mice. Moreover, the histopathology staining of four intestinal sections (duodenum, jejunum, terminal ileum, and middle colon) indicated that adjuvants, especially polyinosinic: polycytidylic acid, enhanced the villi damage and crypt hyperplasia in co-stimulation with ATI and gliadin murine model. Immunohistochemical results showed that tissue transglutaminase and IL-15 expression were significantly increased in the jejunal tissue of mice treated with ATI and gliadin. Similarly, the expression of inflammatory factors (TNF-α, IL-1β, IL-4, IL-13) and Th1/Th2 balance also showed that the inflammation response was significantly increased after co-stimulation with ATI and gliadin. This study provided new evidence for the role of wheat amylase trypsin inhibitors in the pathogenesis of celiac disease.

Untargeted Metabolomic Profiling Reveals Changes in Gut Microbiota and Mechanisms of Its Regulation of Allergy in OVA-Sensitive BALB/c Mice

Gut microbiota plays an important role in the regulation of food allergy. However, the interactions between the gut flora and immune system are not well studied. Here, we obtained ovalbumin (OVA)-sensitive BALB/c mice, combined with serum untargeted metabolomics to investigate the mechanisms of the interactions. The serum metabolomics results showed that 17 serum metabolites were downregulated, enriched in the aminoacyl-tRNA biosynthesis pathway, whereas indole-3-propionic acid (IPA) was increased. Six operational taxonomic units (OTUs) at the family level were altered and correlated with immune endpoints. Combined metabolomic and microbiomic analyses revealed that IPA levels were correlated with differential bacterial OTUs and a positive correlation with Treg in splenic lymphocytes. These results suggest that the regulatory effects of intestinal flora on allergic responses may be achieved by metabolizing tryptophan to produce indole derivatives and the aminoacyl-tRNA biosynthesis pathway. The formation of OVA tolerance in mice may be related to the enrichment of Peptostreptococcaceae, Ruminococcaceae, and Lactobacillaceae.

Evaluation of allergenicity of cow milk treated with enzymatic hydrolysis through a mouse model of allergy

Cow milk (CM) allergy is a worldwide concern. Currently, few studies have been performed on the immunoreactivity of CM and fewer still on the antigenicity of CM in vivo and in vitro. In this study, we assessed the potential allergenicity of enzymatically hydrolyzed CM using in vitro ELISA and oral sensitization and challenge of BALB/c mice. Alcalase-, Protamex-, and Flavourzyme-treated CM (all from Novozymes) diminished IgE binding capacity, with greatest reductions of 56.31%, 50.62%, and 56.45%, respectively. Allergic symptoms and levels of total IgG1 were reduced, and allergic inflammation of the lung, jejunum, and spleen was relieved. Moreover, the numbers of CD8+ T and B220+ cells decreased, and the balance of CD4+ T/CD8+ T cells was effectively regulated. These findings suggest that the potential allergenicity of CM was reduced by enzymatic hydrolysis, and our research will lay a solid foundation for developing high-quality hypoallergenic CM products.

Enzymatic crosslinking and food allergenicity: A comprehensive review

Food allergy has become a major global public health concern. In the past decades, enzymatic crosslinking technique has been employed to mitigate the immunoreactivity of food allergens. It is an emerging non-thermal technique that can serve as a great alternative to conventional food processing approaches in developing hypoallergenic food products, owing to their benefits of high specificity and selectivity. Enzymatic crosslinking via tyrosinase (TYR), laccase (LAC), peroxidase (PO), and transglutaminase (TG) modifies the structural and biochemical properties of food allergens that subsequently cause denaturation and masking of the antigenic epitopes. LAC, TYR, and PO catalyze the oxidation of tyrosine side chains to initiate protein crosslinking, while TG initiates isopeptide bonding between lysine and glutamine residues. Enzymatic treatment produces a high molecular weight crosslinked polymer with reduced immunoreactivity and IgE-binding potential. Crosslinked allergens further inhibit mast cell degranulation due to the lower immunostimulatory potential that assists in the equilibration of T-helper (Th)1/Th2 immunobalance. This review provides an updated overview of the studies carried out in the last decade on the potential application of enzymatic crosslinking for mitigating food allergenicity that can be of importance in the context of developing hypoallergenic/non-allergenic food products.