The Maillard reaction and food allergies: is there a link?

Molecular Profiling of Peanut under Raw, Roasting, and Autoclaving Conditions Using High-Resolution Magic Angle Spinning and Solution 1H NMR Spectroscopy

Higher rates of peanut allergy have been observed in countries that commonly roast peanuts prior to consumption. Despite the importance of understanding the role of thermal processing in allergy and on peanut composition, studies toward generating signatures that identify molecular contents following processing are scant. Here, we identified spectral signatures to track changes and differences in the molecular composition of peanuts under raw, roasted, and high-pressure and high-temperature autoclaved conditions. We analyzed both the solid flesh of the seed and solutions derived from soaking peanuts using High-Resolution Magic Angle Spinning (HR-MAS) and solution 1H Nuclear Magnetic Resonance (NMR) spectroscopy, respectively. The NMR spectra of intact peanuts revealed triglycerides as the dominant species, assigned on the basis of multiplets at 4.1 and 4.3 ppm, and corresponding defatted flours revealed the presence of sugars. Sucrose assigned based on a doublet at 5.4 ppm (anomeric proton), and triglycerides were the most abundant small molecules observed, with little variation between conditions. Soaked peanut solutions were devoid of lipids, and their resulting spectra matched the profiles of defatted peanuts. Spectral signatures resulting from autoclaving differed strikingly between those from raw and roasted peanuts, with considerable line-broadening in regions corresponding to proteins and amino-acid side chains, from 0.5 to 2.0 ppm and 6.5 to 8.5 ppm. Taken together, by using complementary NMR methods to obtain a fingerprint of the molecular components in peanuts, we demonstrated that autoclaving led to a distinct composition, likely resulting from the hydrolytic cleavage of proteins, the most important molecule of the allergic reaction.

Investigation of the allergenicity alterations of shrimp tropomyosin as glycated by glucose and maltotriose containing advanced glycation end products

Tropomyosin (TM) is the major allergen in shrimp that is known to be the primary trigger for shrimp-induced food allergy. Our previous reports suggest that glycation could reduce the allergenicity of TM and the reduction of allergenicity is largely dependent on the sources of saccharides. This investigation aimed to investigate the glycation of TM by glucose and maltotriose as well as the effects of glycation on the allergenicity of TM. Compared to TM, the IgG-binding capacity and IgE-binding capacity of tropomyosin glycated by glucose (TM-G) was greatly reduced with a longer glycation time, the release of allergic mediators from RBL-2H3 mast cells was reduced in a time-dependent manner, and weaker allergic reactions were induced in BALB/c mice. Conversely, tropomyosin glycated by maltotriose (TM-MTS) exhibited a stronger allergenicity after 48 hours of glycation due to the generation of neoallergens that were derived from the advanced glycation end products (AGEs). In conclusion, glucose could be used to desensitize the shrimp TM-induced food allergy via glycation, which could significantly reduce the allergenicity and alleviate allergic symptoms. This work could provide a novel approach to reduce the allergenicity of shrimp tropomyosin and prevent the shrimp tropomyosin-induced food allergy.

Pollen Sensitization Can Increase the Allergic Reaction to Non-Cross-Reactive Allergens in a Soy-Allergic Patient

During and after the pollen season, an increase in food-triggered allergic symptoms has been observed in pollen-food syndrome patients, possibly due to seasonal boosting of pollen-IgE levels. It has been suggested that consumption of birch-pollen-related foods plays a role in seasonal allergenic inflammation. However, whether this increased pollen sensitization during the pollen season can also affect the allergenicity of allergens that are non-cross-reactive with birch pollen remains in question. This study presents the case of a patient with soy allergy and pollinosis, who experiences worsening of gastrointestinal (GI) symptoms during the birch pollen season even though the eliciting food factor does not cross-react with birch pollen allergens and their homologs (e.g., Bet v 1 and Gly m 4). The results showed a notable increase in sIgE for Gly m 4 (3.3 fold) and Bet v 1 (2.6 fold) during the birch pollen season compared to outside the birch pollen season, while Gly m 5 and Gly m 6 showed only a slight increase (1.5 fold). The basophil activation test (BAT) showed that in this patient Gly m 5 and Gly m 6 are clinically relevant soy allergens, which correlates with the reported clinical symptoms to processed soy. Moreover, the BAT against raw soy shows an increase in basophil activation during the birch pollen season and a negative basophil activation result outside the birch pollen season. Thus, the worsening of GI symptoms could possibly be due to an increase in IgE receptors, an over-reactive immune system, and/or significant intestinal allergic inflammation. This case highlights the importance of including allergens that do not cross-react with birch pollen and using a functional assay such as the BAT to evaluate clinical relevance when assessing birch pollen seasonal influence on soy allergenicity.

Do advanced glycation end products contribute to food allergy?

Sugars can bind non-enzymatically to proteins, nucleic acids or lipids and form compounds called Advanced Glycation End Products (AGEs). Although AGEs can form in vivo, factors in the Western diet such as high amounts of added sugars, processing methods such as dehydration of proteins, high temperature sterilisation to extend shelf life, and cooking methods such as frying and microwaving (and reheating), can lead to inordinate levels of dietary AGEs. Dietary AGEs (dAGEs) have the capacity to bind to the Receptor for Advanced Glycation End Products (RAGE) which is part of the endogenous threat detection network. There are persuasive epidemiological and biochemical arguments that correlate the rise in food allergy in several Western countries with increases in dAGEs. The increased consumption of dAGEs is enmeshed in current theories of the aetiology of food allergy which will be discussed.

Changing the IgE Binding Capacity of Tropomyosin in Shrimp through Structural Modification Induced by Cold Plasma and Glycation Treatment

Tropomyosin (TM) is the major allergen of shrimp (Penaeus chinensis). Previous studies showed that separate cold plasma or glycation have their drawback in reducing allergenicity of TM, including effectiveness and reliability. In the current study, a new processing combining cold plasma (CP) and glycation was proposed and its effect on changing IgE binding capacity of TM from shrimp was investigated. Obtained results showed the IgE binding capacity of TM was reduced by up to 40% after CP (dielectric barrier discharge, 60 kV, 1.0 A) combined with glycation treatment (4 h, 80 °C), compared with the less than 5% reduction after single CP or glycation treatment. Notably, in contrast to the general way of CP prompting glycation, this study devised a new mode of glycation with ribose after CP pretreatment. The structural changes of TM were explored to explain the decreased IgE binding reactivity. The results of multi-spectroscopies showed that the secondary and tertiary structures of TM were further destroyed after combined treatment, including the transformation of 50% α-helix to β-sheet and random coils, the modification and exposure of aromatic amino acids, and the increase of surface hydrophobicity. The morphology analysis using atomic force microscope revealed that the combined processing made the distribution of TM particles tend to disperse circularly, while it would aggregate after either processing treatment alone. These findings confirmed the unfolding and reaggregation of TM during combined processing treatment, which may result in the remarkable reduction of IgE binding ability. Therefore, the processing of CP pretreatment combined with glycation has the potential to reduce or even eliminate the allergenicity of seafood.

Inhibitory effect of LSOPC on AGEs formation and sensory quality in cookies

At the conclusion of the Maillard reaction (MR), free amino groups of proteins, amino acids, or lipids with the carboxyl groups of reducing sugars to form stable molecules known as advanced glycation end products (AGEs), which hasten aging and may potentially be the root cause of a number of chronic degenerative diseases. According to researches, lotus seedpod oligomeric procyanidins (LSOPC), a premium natural antioxidant produced from lotus waste, can be included in cookies to improve flavor and lower the risk of illnesses linked to AGEs. In this work, we used cookies without LSOPC as a control to examine the effects of adding various concentrations of LSOPC (0, 0.05, 0.1, 0.2, and 0.4%) on the AGEs formation and the sensory quality in cookies. The amounts of AGEs and N-ε-carboxymethyl lysine (CML) decreased with the increase of LSOPC concentration, indicating that the concentration of LSOPC was positively correlated with the ability to inhibit AGEs formation. It was also demonstrated that the amount of antioxidant capacity of the cookies increased significantly with the increase of LSOPC concentration. On the other hand, the chromaticity, texture, electronic nose, and other aspects of the cookies' sensory attributes were also evaluated. The color of the cookies deepened and the flavor varied as LSOPC added content increased. The sensory quality of the cookies was examined, and the findings indicated that LSOPC would somewhat improve that quality. These findings implied that AGEs formation could be decreased in cookies while also enhancing their sensory quality by adding LSOPC.

Investigation of the Structure and Allergic Potential of Whey Protein by Both Heating Sterilization and Simulation with Molecular Dynamics

As the main allergens in milk, whey proteins are heat-sensitive proteins and are widespread in dairy products and items in which milk proteins are involved as food additives. The present work sought to investigate the effect of heating sterilization on the allergenicity of α-lactalbumin (α-LA) and β-lactoglobulin (β-LG), the main composite and allergen in whey protein isolate (WPI), by combining molecular dynamics with experimental techniques for detecting the spatial structure and IgE binding capacity. The structure of WPI was basically destroyed at heat sterilization conditions of 95 °C for 5 min and 65 °C for 30 min by SDS-PAGE analysis and spectroscopic analysis. In addition, α-lactalbumin (α-LA) may be more sensitive to temperature, resulting in exposure to allergic epitopes and increasing the allergic potential, while the binding capacity of β-lactoglobulin (β-LG) to IgE was reduced under 65 °C for 30 min. By the radius of gyration (Rg) and root-mean-square deviation (RMSD) plots calculated in molecular dynamics simulations, α-LA was less structurally stable at 368 K, while β-LG remained stable at higher temperatures, indicating that α-LA was more thermally sensitive. In addition, we observed that the regions significantly affected by temperatures were associated with the capacity of allergic epitopes (α-LA 80-101 and β-LG 82-93, 105-121) to bind IgE through root-mean-standard fluctuation (RMSF) plots, which may influence the two major allergens. We inferred that these regions are susceptible to structural changes after sterilization, thus affecting the allergenicity of allergens.

Glycosylation reduces the allergenicity of turbot (Scophthalmus maximus) parvalbumin by regulating digestibility, cellular mediators release and Th1/Th2 immunobalance

With turbot being increasingly consumed, turbot parvalbumin (TPV) allergy has become a pressing problem requiring immediate resolution. Glycosylation treatment not only resulted in cross-link formation but also caused changes in the simulated gastric fluid and simulated intestinal fluid digestion stability of TPV. In addition, KU812 experimentation revealed lower levels of β-hexosaminidase, histamine, tryptase, interleukin 4 (IL-4)/IL-13 in glycated protein-treated mice compared with native PV-treated ones. Glycated TPV exhibited a weaker allergic reaction compared with native TPV. Systemic anaphylaxis resulted in mild anaphylactic responses and reduced temperature, along with significantly increased levels of immunoglobulin E and histamine. Furthermore, glycosylation treatment reduced the release of cellular mediators and cytokines (IL-4/IL-13). Glycation to T-PV decreased allergic responses by downregulating Th2 cytokines, regulated the Th1/Th2 balance and effectively reduce the allergenicity and sensitisation ability of T-PV.

Receptor Mediated Effects of Advanced Glycation End Products (AGEs) on Innate and Adaptative Immunity: Relevance for Food Allergy

As of late, evidence has been emerging that the Maillard reaction (MR, also referred to as glycation) affects the structure and function of food proteins. MR induces the conformational and chemical modification of food proteins, not only on the level of IgG/IgE recognition, but also by increasing the interaction and recognition of these modified proteins by antigen-presenting cells (APCs). This affects their biological properties, including digestibility, bioavailability, immunogenicity, and ultimately their allergenicity. APCs possess various receptors that recognize glycation structures, which include receptor for advanced glycation end products (RAGE), scavenger receptors (SRs), galectin-3 and CD36. Through these receptors, glycation structures may influence the recognition, uptake and antigen-processing of food allergens by dendritic cells (DCs) and monocytes. This may lead to enhanced cytokine production and maturation of DCs, and may also induce adaptive immune responses to the antigens/allergens as a result of antigen uptake, processing and presentation to T cells. Here, we aim to review the current literature on the immunogenicity of AGEs originating from food (exogenous or dietary AGEs) in relation to AGEs that are formed within the body (endogenous AGEs), their interactions with receptors present on immune cells, and their effects on the activation of the innate as well as the adaptive immune system. Finally, we review the clinical relevance of AGEs in food allergies.

Epitope mapping and the effects of various factors on the immunoreactivity of main allergens in egg white

Egg white has high protein content and numerous biological/functional properties. However, reported allergenicity for some of the proteins in egg white is an issue that needs to be paid exclusive attention. A consideration of the structure of IgE epitopes and their sequences, as well as a comprehensive understanding of the effects of various processes on epitopes and the impact of the gastrointestinal tract on them, can help target such issues. The current study focuses on the identified IgE epitopes in egg white proteins and evaluation of the effects of the gastrointestinal digestion, carbohydrate moiety, food matrix, microbial fermentation, recombinant allergen, heat treatment, Maillard reaction and combination of various processes and gastrointestinal digestion on egg white allergenicity. Although the gastrointestinal tract reduces the immunoreactivity of native egg white proteins, some of the IgE epitope-containing fragments remain intact during the digestion process. It has been found that the gastrointestinal tract can have both positive and negative impacts on the IgE binding activities of egg white proteins. Elimination of the carbohydrate moiety leads to a reduction in the immunoreactivity of ovalbumin. But, such effects from the carbohydrate parts in the IgE binding activity need to be explored further. In addition, the interaction between the egg white proteins and the food matrix leads to various effects from the gastrointestinal tract on the digestion of egg white proteins and their subsequent immunoreactivity. Further on this matter, studies have shown that both microbial fermentation and Maillard reaction can reduce the IgE binding activities of egg white proteins. Also, as an alternate approach, the thermal process can be used to treat the egg white proteins, which may result in the reduction or increase in their IgE binding activities depending on the conditions used in the process. Overall, based on the reported data, the allergenicity levels of egg white proteins can be mitigated or escalated depending on the conditions applied in the processing of the food products containing egg white. So far, no practical solutions have been reported to eliminate such allergenicity.

Reducing the Allergenicity of Shrimp Tropomyosin and Allergy Desensitization Based on Glycation Modification

Shrimp is a major allergic food that could trigger severe food allergy, with the most significant and potent allergen of shrimp referred to as tropomyosin (TM). Glycation modification (Maillard reaction) could reportedly weaken the allergenicity of TM and generate hypoallergenic TM, while up to now, there is still a lack of investigations on the hypoallergenic glycated tropomyosin (GTM) as a candidate immunotherapy for desensitizing the shrimp TM-induced allergy. This study analyzed the effects of glycation modification on decreasing the allergenicity of TM and generated hypoallergenic GTM and how GTM absorbed to the Al(OH)₃ function as a candidate immunotherapy for desensitizing allergy. As the results, in comparison to TM, the saccharides of smaller molecular sizes could lead to more advanced glycation end products in GTMs than saccharides of greater molecular sizes, and TM glycated by saccharides of different molecular sizes (glucose, maltose, maltotriose, maltopentaose, and maltoheptaose) exhibited lower allergenicity as a hypoallergen upon activating the allergic reactions of the mast cell and mouse model, while TM glycated by maltose had insignificant allergenicity changes upon activating the allergic reactions of the mast cell and mouse model. In addition, the hypoallergenic GTM + Al(OH)₃ was efficient as a candidate immunotherapy; this work intended to offer preclinical data to promote GTM + Al(OH)₃ as a candidate allergen-specific immunotherapy for desensitizing the allergy reactions for patients allergic to shrimp food.

Effects of chitosan oligosaccharide and hyriopsis cumingii polysaccharide on the quality of wheat flour and extruded flour products

Abstract

Effects of chitosan oligosaccharide (COS) and hyriopsis cumingii polysaccharide (HCP) on the quality of wheat flour and corresponding extruded flour products were investigated in this work. The results showed that both COS and HCP are conducive to the improvement of dough quality. Moreover, compared to control group samples, the moisture content, expansion ratio and oil absorption rate of the samples were increased and the hardness were decreased with the addition of COS. These phenomena indicate the quality of extruded flour products became better in the presence of COS as well. However, HCP has little or no effect on the quality of extruded flour products may be due to its degradation under high temperature and pressure extrusion. COS with higher stability exhibited better improvement effects on the quality of extruded flour products and showed a promising prospect for application in extruded food industry.

Graphical Abstract

Effects of deglycosylation and the Maillard reaction on conformation and allergenicity of the egg ovomucoid

Ovomucoid (OVM), known as the major allergen in egg white, has gained increasing concerns in industrialized countries. Here, we found the deglycosylation and Maillard reaction with galactooligosaccharide (GOS) and fructooligosaccharide (FOS) can induce conformational transformation of OVM from other structures (β-turn, strang, and random coils) to α-helix. We also introduced an approach to reduce the allergenicity of Gallus domesticus OVM by Maillard reaction with GOS and FOS. However, the OVM glycated by mannosan (MOS) and deglycosylated OVM exhibited higher allergenicity than native OVM. Therefore, GOS and FOS, especially GOS, could be applied in the reduction of the potential allergenicity of OVM through glycation. Furthermore, these findings may provide new insights into the development of hypoallergenic egg products. PRACTICAL APPLICATION: In this study, the allergenicity and conformation of OVM treated with deglycosylation and glycation (GOS, FOS, and MOS) were investigated. The results would provide a better understanding of the effects of deglycosylation and Maillard reaction with different reducing sugars on the molecular characteristics of OVM and further provide new insights into the development of hypoallergenic egg products.

Investigation of glycated shrimp tropomyosin as a hypoallergen for potential immunotherapy

Tropomyosin (TM) is the most important allergen in shrimps that could cause food allergy. Glycation is reported to be effective in reducing TM allergenicity and produce hypoallergen; however, up to now, there are very few reports on the potential of hypoallergenic glycated TM (GTM) as allergen immunotherapy for shrimp TM-induced food allergy. This study investigated the glycation of TM-produced hypoallergen and the immunotherapeutic efficacy of GTM + Al(OH)₃ as potential allergen immunotherapy. Compared to TM, the TM glycated by glucose (TM-G), maltotriose (TM-MTS), maltopentaose (TM-MPS) and maltoheptaose (TM-MHS) had weaker allergy activation on mast cells and mouse model as a hypoallergen. However, the TM glycated by maltose (TM-M) insignificantly affected the allergenicity. In addition, the GTM absorbed into Al(OH)₃ could be efficacious as potential allergen immunotherapy, particularly for the TM glycated by the saccharides having larger molecular size (e.g., TM-MHS), which could provide preclinical data to develop GTM + Al(OH)₃ as a candidate immunotherapy for shrimp allergic patients.

In vitro gastroduodenal and jejunal brush border membrane digestion of raw and roasted tree nuts

Heat treatments induce chemical/physical modifications, which may affect the stability to enzymatic digestion and consequently the allergenicity of food proteins to a varying extent, depending on the time/temperature regimen. Herein, we evaluated the stability to digestion of whole tree nut (walnuts, hazelnuts and almonds) allergens in a food digestion model reflecting the real one by, taking into consideration the allergen-containing processed (roasted) food. To this aim, whole raw and roasted tree nuts were subjected to in vitro digestion combining the harmonized oral-gastric-duodenal digestion models with brush border membrane enzymes (BBM) to simulate the jejunal degradation of peptides. The degradation of allergens was monitored by integrated proteomic/peptidomic and bio-informatic tools. Roasting increased digestibility of tree nuts, since very few peptides were detected in digested samples (<6.5 kDa fraction). After BBM digestion step, the degradation of peptides was enhanced in roasted walnuts and hazelnuts compared to the raw counterpart. Conversely, almond allergens showed a different behaviour, since the presence of resistant peptides was more evident for roasted almonds, probably because of the hydrolysis of high molecular weight aggregates generated during roasting. Our results provide new insight into the relationship between thermal processing and metabolic fate of tree nut allergens, highlighting the importance of investigating the digestion stability of whole allergenic food, rather than purified proteins.

Oesophageal eosinophilia accompanies food allergy to hen egg white protein in young pigs

BACKGROUND

Esophagitis with eosinophilia, inflammation, and fibrosis represent a chronic condition in humans with food allergies.

OBJECTIVE

In this investigation, we asked whether esophagitis with an eosinophilic component is observed in young pigs rendered allergic to hen egg white protein (HEWP).

METHODS

Food allergy was induced in young pigs using two protocols. In one protocol, sensitized pigs were challenged by gavage with a single dose of HEWP. Clinical signs were monitored for 24 hours, and then, gastrointestinal (GI) tissues were collected for histological examination. The phenotype of circulating, ovalbumin (OVA)-specific T cells also was examined in HEWP challenged animals. In the second protocol, sensitized animals were fed HEWP for 28 days. Animals were then examined by endoscopy and gastrointestinal tissues collected for histological examination.

RESULTS

In pigs challenged by gavage with HEWP, clinical signs were noted in 5/6 pigs including diarrhoea, emesis, and skin rash. Clinical signs were not seen in any control group. Histological analysis revealed significant levels of oesophageal eosinophilic infiltration (P < .05) in 4/6 of these animals, with two also displaying eosinophilic infiltration in the stomach. Eosinophils were not increased in ileum or colon samples. Increased numbers of circulating, OVA-specific CD4⁺ T cells also were observed in pigs that received HEWP by gavage. In the group of animals fed HEWP, endoscopy revealed clinical signs of esophagitis including oedema, granularity, white spots, and furrowing, while histology revealed oedema, immune cell infiltration, and basal zone hyperplasia.

CONCLUSIONS AND CLINICAL RELEVANCE

Food allergy in the pig can be associated with esophagitis based on histological and endoscopic findings, including eosinophilic infiltration. The young pig may, therefore, be a useful large animal model for the study of eosinophilic esophagitis in humans.

Glycation by saccharides of different molecular sizes affected the allergenicity of shrimp tropomyosin via epitope loss and the generation of advanced glycation end products

Tropomyosin is the most potent allergen of shrimp that can cause severe food allergy. However, to date, an effective approach to eliminate this allergenicity is still lacking. Glycation is a promising approach that can reduce the allergenicity of shrimp tropomyosin by destroying the epitopes; however, advanced glycation end products (AGEs) are also generated during glycation, which can function as neoallergens to strengthen the allergenicity; therefore, it is hard to tell how the glycation of an allergen with different saccharides affects the allergenicity via epitope loss and neoallergen generation. This study was aimed at the elucidation of how the glycation of tropomyosin (TM) with saccharides of different molecular sizes (glucose, maltose, and maltotriose) affected the allergenicity through epitope loss and the generation of neoallergns that belonged to advanced glycation end products (AGEs). Saccharides of higher molecular sizes (maltotriose) could lead to higher glycated TM than saccharides of smaller molecular sizes (glucose and maltose). Compared with TM, the TM glycated by glucose (TM-G) and maltotriose (TM-MTS) had lower allergenicity and contributed to weaker mouse allergy symptoms; on the other hand, the TM glycated by maltose (TM-M) had no significant impact on the allergenicity due to the generation of AGE-related neoallergens, which might offset the glycation-induced epitope loss. The glycation of TM by maltotriose led to lower generation of AGE neoallergens (e.g. CML) than that in the cases of glucose and maltose; therefore, maltotriose could be applied to desensitize TM-induced food allergy through glycation, and this could be a potential immunotherapy for shrimp allergy patients.

Immune Effects of the Nitrated Food Allergen Beta-Lactoglobulin in an Experimental Food Allergy Model

Food proteins may get nitrated by various exogenous or endogenous mechanisms. As individuals might get recurrently exposed to nitrated proteins via daily diet, we aimed to investigate the effect of repeatedly ingested nitrated food proteins on the subsequent immune response in non-allergic and allergic mice using the milk allergen beta-lactoglobulin (BLG) as model food protein in a mouse model. Evaluating the presence of nitrated proteins in food, we could detect 3-nitrotyrosine (3-NT) in extracts of different foods and in stomach content extracts of non-allergic mice under physiological conditions. Chemically nitrated BLG (BLGn) exhibited enhanced susceptibility to degradation in simulated gastric fluid experiments compared to untreated BLG (BLGu). Gavage of BLGn to non-allergic animals increased interferon-γ and interleukin-10 release of stimulated spleen cells and led to the formation of BLG-specific serum IgA. Allergic mice receiving three oral gavages of BLGn had higher levels of mouse mast cell protease-1 (mMCP-1) compared to allergic mice receiving BLGu. Regardless of the preceding immune status, non-allergic or allergic, repeatedly ingested nitrated food proteins seem to considerably influence the subsequent immune response.

Influence of the Maillard Reaction on the Allergenicity of Food Proteins and the Development of Allergic Inflammation

PURPOSE OF REVIEW

The Maillard reaction (MR) is a non-enzymatic reaction between reducing sugars and compounds with free amino groups such as proteins and takes place during thermal processing and storage of foods. This review aims to discuss potential effects of dietary MR products on the pathological mechanisms of allergic diseases.

RECENT FINDINGS

Since the MR leads to modification of proteins with various types of glycation structures, the impact of the MR on the immunogenicity and potential allergenicity of food proteins in many allergenic foods has been assessed. In addition, recent studies have suggested that the MR products, in particular "advanced glycation end products (AGEs)," contained in the diet may be involved in the development of chronic inflammation by acting as inflammatory components and affecting the gut microbiome. This review found that the biological, immunological, and allergic properties of dietary MR products are diverse due to the complexity of the MR.

Glycated proteins in nutrition: Friend or foe?

Advanced glycation end products (AGEs) are formed in in vivo, and accumulate in tissues and body fluids during ageing. Endogenous AGE-modified proteins show altered structure and function, and may interact with receptor for AGEs (RAGE) resulting in production of reactive oxygen species, inflammatory, atherogenic and diabetogenic responses. AGEs are also formed in thermally processed foods. Studies in rodents document that dietary AGEs are partially absorbed into circulation, and accumulate in different tissues. Knowledge on the health effects of high dietary intake of AGEs is incomplete and contradictory. In this overview we discuss the data from experimental and clinical studies, either those supporting the assumption that restriction of dietary AGEs associated with health benefits, or data suggesting that dietary intake of AGEs associates with positive health outcomes. We polemicize whether the effects of exaggerated intake or restriction of highly thermally processed foods might be straightforward interpreted as the effects of AGEs-rich vs. AGEs-restricted diets. We also underline the lack of studies, and thus a poor knowledge, on the effects of different single chemically defined AGEs administration, concurrent intake of different dietary AGEs, of load with dietary AGEs corresponding to the habitual diet in humans, and on those of dietary AGEs in vulnerable populations, such as infants and particularly elderly.

Impacts of glycation and transglutaminase-catalyzed glycosylation with glucosamine on the conformational structure and allergenicity of bovine β-lactoglobulin

β-Lactoglobulin (β-LG) is recognized as the major milk allergen. In this study, the effects of transglutaminase (TGase) and glucosamine (GlcN)-catalyzed glycosylation and glycation on the conformational structure and allergenicity of β-LG were investigated. The formations of cross-linked peptides were demonstrated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and GlcN-conjugated modification was identified using matrix-assisted laser desorption ionization-time of flight-mass spectrometry (MALDI-TOF-MS). Structural analysis revealed that glycosylation and glycation of β-LG induced unfolding of the primary protein structure followed by a loss of the secondary structure. As revealed by circular dichroism (CD) spectroscopy, glycosylated β-LG exhibited the highest increase in the β-sheets from 32.6% to 40.4% (25 °C) and 44.2% (37 °C), and the percentage of α-helices decreased from 17.7% to 14.4% (25 °C) and 12.3% (37 °C), respectively. The tertiary and quaternary structures of β-LG also changed significantly during glycosylation and glycation, along with reduced free amino groups and variation in surface hydrophobicity. Immunoblotting and indirect enzyme-linked immuno sorbent assay (ELISA) analyses demonstrated that the lowest IgG- and IgE-binding capacities of β-LG were obtained following glycosylation at 37 °C, which were 52.7% and 56.3% lower than that of the native protein, respectively. The reduction in the antigenicity and potential allergenicity of glycosylated β-LG was more pronounced compared to TGase treated- and glycated β-LG, which correlated well with the structural changes. These results suggest that TGase-catalyzed glycosylation has more potential compared to glycation for mitigating the allergenic potential of milk products.

Immunomodulation by Processed Animal Feed: The Role of Maillard Reaction Products and Advanced Glycation End-Products (AGEs)

The immune system provides host protection to infection with pathogenic organisms, while at the same time providing tolerance upon exposure to harmless antigens. Thus, an impaired immune function is associated with increased susceptibility to infections with increased disease severity and thereby necessitating the therapeutic use of antibiotics. Livestock performance and feed efficiency, in addition to their health status, are dependent on the microbial load of their gut, the barrier function of the intestinal epithelium and the activity of the mucosal immune system, all of which can be modulated by dietary components. The majority of feeds that are consumed in pets and livestock have been processed. Processing promotes a non-enzymatic reaction between proteins and sugars called Maillard reaction (MR). Maillard reaction products (MRPs) and advanced Maillard reaction products (AGEs) determine taste, smell, and color of many food products therefore the MR is highly relevant for the feed industry. MRPs interact with different types of immune receptors, including the receptor for advanced glycation end products (RAGE) and immunomodulatory potential of feed proteins can be modified by Maillard reaction. This MR has become an important concern since MRPs/AGEs have been shown to contribute to increasing prevalence of diet-related chronic inflammatory states in the gut with negative health consequences and performance. The immunomodulatory effects of dietary MRPs and AGEs in livestock and pet animals are far less well-described, but widely considered to be similar to the relevant concepts and mechanisms obtained in the human field. This review will highlight immunological mechanisms underlying initiation of the innate and adaptive immune responses by MRPs/AGEs present in animal feeds, which are currently not completely understood. Bridging this knowledge gap, and taking advantage of progress in the human field, will significantly improve nutritional quality of feed and increase the prevention of diet-mediated inflammation in animals.

Glycation of the Major Milk Allergen β-Lactoglobulin Changes Its Allergenicity by Alterations in Cellular Uptake and Degradation

SCOPE

During food processing, the Maillard reaction (МR) may occur, resulting in the formation of glycated proteins. Glycated proteins are of particular importance in food allergies because glycation may influence interactions with the immune system. This study compared native and extensively glycated milk allergen β-lactoglobulin (BLG), in their interactions with cells crucially involved in allergy.

METHODS AND RESULTS

BLG was glycated in MR and characterized. Native and glycated BLG were tested in experiments of epithelial transport, uptake and degradation by DCs, T-cell cytokine responses, and basophil cell degranulation using ELISA and flow cytometry. Glycation of BLG induced partial unfolding and reduced its intestinal epithelial transfer over a Caco-2 monolayer. Uptake of glycated BLG by bone marrow-derived dendritic cells (BMDC) was increased, although both BLG forms entered BMDC via the same mechanism, receptor-mediated endocytosis. Once inside the BMDC, glycated BLG was degraded faster, which might have led to observed lower cytokine production in BMDC/CD4+ T-cells coculture. Finally, glycated BLG was less efficient in induction of degranulation of BLG-specific IgE sensitized basophil cells.

CONCLUSIONS

This study suggests that glycation of BLG by MR significantly alters its fate in processes involved in immunogenicity and allergenicity, pointing out the importance of food processing in food allergy.

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.

Differences in the Uptake of Ara h 3 from Raw and Roasted Peanut by Monocyte-Derived Dendritic Cells

Roasting has been implicated in the increase of peanut allergenicity due to the chemical reactions that occur during the process. However, this increase is not fully understood, and little information is available regarding the role of roasted peanut allergens in the initial phase of allergy, where dendritic cells (DCs) play a key role. We sought to analyze differences in the internalization of Ara h 3 from raw and roasted peanut by immature monocyte-derived DCs (MDDCs) and the implication of the mannose receptor in the uptake. Ara h 3 was purified from raw and roasted peanut (Ara h 3-raw and Ara h 3-roas) and labeled with a fluorescent dye. The labeled allergens were added to MDDCs obtained from 7 donors and internalization was analyzed after 10, 30, and 120 min by flow cytometry. In parallel, mannan, which blocks the mannose receptor, was added 30 min before adding the labeled allergens. Results showed that the internalization of Ara h 3-roas by MDDCs was significantly increased at every time point. However, the increase in the internalization of Ara h 3-raw was only significant after 2 h of incubation. Ara h 3-roas had an enhanced capacity to be internalized by MDDCs in comparison with Ara h 3-raw at every time point. Blocking the mannose receptor decreased the internalization of Ara h 3-roas but not Ara h 3-raw. In conclusion, the internalization of Ara h 3-roas by the MDDCs is enhanced when compared to Ara h 3-raw, and the mannose receptor might be implicated in this enhancement.

The Maillard Reaction Reduced the Sensitization of Tropomyosin and Arginine Kinase from Scylla paramamosain, Simultaneously

The Maillard reaction was established to reduce the sensitization of tropomyosin (TM) and arginine kinase (AK) from Scylla paramamosain, and the mechanism of the attenuated sensitization was investigated. In the present study, the Maillard reaction conditions were optimized for heating at 100 °C for 60 min (pH 8.5) with arabinose. A low level of allergenicity in mice was shown by the levels of allergen-specific antibodies, and more Th1 and less Th2 cells cytokines produced and associated transcription factors with the Maillard reacted allergen (mAllergen). The tolerance potency in mice was demonstrated by the increased ratio of Th1/Th2 cytokines. Moreover, mass spectrometry analysis showed that some key amino acids of IgE-binding epitopes (K₁₁₂, R₁₂₅, R₁₃₃ of TM; K₃₃, K₁₁₈, R₂₀₂ of AK) were modified by the Maillard reaction. The Maillard reaction with arabinose reduced the sensitization of TM and AK, which may be due to the masked epitopes.

Food Processing: The Influence of the Maillard Reaction on Immunogenicity and Allergenicity of Food Proteins

The majority of foods that are consumed in our developed society have been processed. Processing promotes a non-enzymatic reaction between proteins and sugars, the Maillard reaction (MR). Maillard reaction products (MRPs) contribute to the taste, smell and color of many food products, and thus influence consumers’ choices. However, in recent years, MRPs have been linked to the increasing prevalence of diet- and inflammation-related non-communicable diseases including food allergy. Although during the last years a better understanding of immunogenicity of MRPs has been achieved, still only little is known about the structural/chemical characteristics predisposing MRPs to interact with antigen presenting cells (APCs). This report provides a comprehensive review of recent studies on the influence of the Maillard reaction on the immunogenicity and allergenicity of food proteins.

Maillard reaction in food allergy: Pros and cons

Food allergens have a notable potential to induce various health concerns in susceptible individuals. The majority of allergenic foods are usually subjected to thermal processing prior to their consumption. However, during thermal processing and long storage of foods, Maillard reaction (MR) often takes place. The MR is a non-enzymatic glycation reaction between the carbonyl group of reducing sugars and compounds having free amino groups. MR may sometimes be beneficial by damaging epitope of allergens and reducing allergenic potential, while exacerbation in allergic reactions may also occur due to changes in the motifs of epitopes or neoallergen generation. Apart from these modulations, non-enzymatic glycation can also modify the food protein(s) with various type of advance glycation end products (AGEs) such as Nϵ-(carboxymethyl-)lysine (CML), pentosidine, pyrraline, and methylglyoxal-H1 derived from MR. These Maillard products may act as immunogen by inducing the activation and proliferation of various immune cells. Literature is available to understand pathogenesis of glycation in the context of various diseases but there is hardly any review that can provide a thorough insight on the impact of glycation in food allergy. Therefore, present review explores the pathogenesis with special reference to food allergy caused by non-enzymatic glycation as well as AGEs.

Control of Maillard Reactions in Foods: Strategies and Chemical Mechanisms

Maillard reactions lead to changes in food color, organoleptic properties, protein functionality, and protein digestibility. Numerous different strategies for controlling Maillard reactions in foods have been attempted during the past decades. In this paper, recent advances in strategies for controlling the Maillard reaction and subsequent downstream reaction products in food systems are critically reviewed. The underlying mechanisms at play are presented, strengths and weaknesses of each strategy are discussed, and reasonable reaction mechanisms are proposed to reinforce the evaluations. The review includes strategies involving addition of functional ingredients, such as plant polyphenols and vitamins, as well as enzymes. The resulting trapping or modification of Maillard targets, reactive intermediates, and advanced glycation endproducts (AGEs) are presented with their potential unwanted side effects. Finally, recent advances in processing for control of Maillard reactions are discussed.

Influence of storage and heating on protein glycation levels of processed lactose-free and regular bovine milk products

Thermal treatment preserves the microbiological safety of milk, but also induces Maillard reactions modifying for example proteins. The purpose of this study was evaluating the influence of consumer behaviors (storage and heating) on protein glycation degrees in bovine milk products. Lactosylation and hexosylation sites were identified in ultra-high temperature (UHT), lactose-free pasteurized, and lactose-free UHT milk (ULF) and infant formula (IF) using tandem mass spectrometry (electron transfer dissociation). Overall, 303 lactosylated and 199 hexosylated peptides were identified corresponding to 170 lactosylation (31 proteins) and 117 hexosylation sites (25 proteins). In quantitative terms, storage increased lactosylation up to fourfold in UHT and IF and hexosylation up to elevenfold in ULF and threefold in IF. These levels increased additionally twofold when the stored samples were heated (40°C). In conclusion, storage and heating appear to influence protein glycation levels in milk at similar or even higher degrees than industrial processing.

Identification and quantification of bovine protein lactosylation sites in different milk products

The microbiological safety of milk is typically guaranteed by thermal treatments, such as pasteurization and ultra high temperature (UHT) treatment, whereas infant formula (IF) is often produced at even harsher conditions including a drying process. Thermal treatments have raised concerns, as they may denature proteins and initiate protein modifications. Previous studies identified already many lactosylation sites in milk and showed that the lactosylation degree of some proteins correlates to thermal treatment conditions. Here, we studied the glycation degrees of 124 lactosylation sites in 28 bovine milk proteins in raw milk, three brands of pasteurized milk, three brands of UHT milk, and five brands of IF. Whereas, the glycation degree of many lactosylation sites increased from raw milk, to pasteurized milk, UHT milk, and IF, several modification sites showed a different behavior indicating that global measures do not correctly reflect the reactivity of distinct sites. Interestingly, the glycation degrees varied considerably among the brands of UHT milk and IF indicating that specific production processes of a company have to be considered and not only the classification of milk as pasteurized or UHT. Thus, proper adjustments of the technical processes should allow reducing the lactosylation levels in both UHT milk and IF.

SIGNIFICANCE

It is well established that thermal treatment of milk triggers protein modifications, such as lactosylation of lysine residues in several proteins, although the extent of lactosylation has not been quantitatively compared for a broad panel of protein lactosylation sites among different commercial products. The current study extends previous reports by relatively quantifying 124 confirmed lactosylation sites in 28 bovine milk proteins including several low abundant proteins. Whereas, glycation is generally assumed to be an unspecific chemical reaction with the modification degrees depending on the protein and sugar concentrations, we could show that each protein and even each lactosylation site in a given protein is differently affected by thermal processes indicating that the global lactosylation degrees will not allow predicting the influence of a technical process on individual proteins and lactosylation sites. Additionally, we could show that brands of each milk product differ significantly in their glycation degrees with UHT milk brands for example spanning the whole range from the relatively low lactosylation degree of pasteurized milk to the rather high lactosylation degree of IF. Similar differences were obtained for IF that generally showed the highest glycation degree. The targeted quantification approach established and validated here will be useful to reveal technical processing steps that trigger individual lactosylation sites and thus can help to prevent such unwanted reactions. Even slight changes of the technical processes might allow reducing the lactosylation degree of milk proteins significantly without challenging the microbiological safety or affecting consumer behavior.