The mechanism of the reduction in allergenic reactivity of bovine α-lactalbumin induced by glycation, phosphorylation and acetylation

Glycation of β-Lactoglobulin with different lengths sugar chains: Impacts on structure, allergenicity and flavor profile

This study aims to perform a comparative study on the structure, allergenicity and flavor profile of β-lactoglobulin (BLG)-galacto-oligosaccharides, maltose, maltotriose and maltopentaose conjugates formed by glycation. Glycation increased BLG's molecular weight, altered the conformational structures and secondary structure from α-helix and β-sheet to β-turn and unordered forms. K47, K83, K91, K135, K138 and K141 of BLG were glycated, destructing the antigen epitopes, leading to reducing the IgE/IgG binding capacity and the release of histamine and interleukin-6 in KU812 cells, with BLG-galacto-oligosaccharides and BLG-maltose showed the lowest allergenicity. Meanwhile, 36 volatile organic compounds (VOCs) were identified in the conjugates, among which 11 were key VOCs, including 2,3-Butanedione and 2-propanol-M, which were the most abundant in BLG-galacto-oligosaccharides and BLG-maltose and positively correlated with glycation levels. Overall, glycation of proteins by different lengths sugar chains influenced the epitope structures and glycation levels, altering allergenicity and the release of flavor compounds.

Ultrasound assisted glycation decreased the potential allergenicity through changing epitope and structures of Ses i 3

Ses i 3 is one of the major allergens in sesame, and this study aimed to investigate the effect and mechanism of ultrasound-assisted glycation on the potential allergenicity of Ses i 3. Results showed that the IgG and IgE binding of Ses i 3 was significantly reduced after ultrasound-assisted glycation, and the KU812 cell degranulation results showed a significantly decrease of degranulation in the ultrasound-assisted glycation group, suggesting a reduction in the allergenicity of Ses i 3. Subsequently, results from the contents of free amino groups and available lysine showed that ultrasound pretreatment facilitated the glycation reaction. Moreover, five linear epitopes were predicted, with S-5 (AA 571-582) being identified as the effective B cell linear epitope through solid-phase peptide synthesis and serological experiments. Its spatial location was also determined using a AlphaFold 3 model. Besides, inhibited competitive ELISA results indicated that the addition of inhibitor (S-5) didn't reduce the IgE binding of Ses i 3 in the ultrasound-assisted glycation group, suggesting that ultrasound-assisted glycation might have masked or destroyed the S-5 epitope. Ultraviolet (UV) spectra and intrinsic fluorescence emission spectrum results revealed a blue shift in the maximum absorption peaks, along with a significant reduction in surface hydrophobicity, indicating substantial changes in both secondary and tertiary structures. In conclusion, this study demonstrated that ultrasound-assisted glycation effectively reduced the allergenicity of Ses i 3, with the reduction being closely linked to changes in the S-5 epitope and structures. These findings will provide a basis for the development of hypoallergenic sesame products.

Effect of superheated steam on Maillard reaction products, digestibility, and antioxidant activity in β-Lactoglobulin-glucose system

This study analyzes the interactions among Maillard reaction products (MRPs), digestibility and antioxidant activity in a β-lactoglobulin-glucose (βlg-Glu) model system during superheated steam treatment at 120 °C for 1 to 5 min. With an increase in treatment duration, there were significant increases in glucose loss, grafting degree, browning, and the formation of intermediate products in βlg-Glu. Characteristic MRPs, including α-dicarbonyl compounds, 5-hydroxymethylfurfural, and advanced glycation end products (AGEs), were formed through the degradation of sugars and condensation reactions between carbonyls and amines, accompanied by an increase in oxidative products. These changes impacted the molecular weight distribution and conformational structure of βlg-Glu, resulting in decreased digestibility. βLg-Glu with the highest level of glycation exhibited superior antioxidant activity after in vitro digestion, which was closely associated with the increase in AGEs and oxidation products. Therefore, the protein-sugar system treated by superheated steam with different heating time can significantly affect the formation and activity of the products, providing theoretical basis for superheated steam processing nutritious and healthy food.

Allergenicity assessment of β-lactoglobulin ferulic acid-glucose conjugates

We prepared the β-lactoglobulin (BLG)-ferulic acid (FA)-glucose (Glu) conjugates by alkaline method and Maillard reaction to assess the allergenicity. FA and Glu can form a ternary covalent conjugate with BLG, as evidenced by the shortening of SEC retention time, upward migration of SDS-PAGE protein bands, considerable decrease in free amino and sulfhydryl content, and changes in multistructure. BLG-Glu-FA conjugates weakly bound to immunoglobulin E in allergic sera was weak, reduced interleukin 4 and tumor necrosis factor α levels in RBL-2H3 cells and histamin and interleukin 6 secretion levels in KU812 cells, and inhibited the nuclear factor-κB signaling pathway. In vivo experiments showed that the conjugates regulated T-cell homeostasis in mouse splenic and mesenteric lymphocytes and attenuated splenic and duodenal immune injury. Therefore, the conjugates of BLG with FA combined with Glu altered the epitope structure and exhibited low allergenicity.

Dietary glycation compounds - implications for human health

The term "glycation compounds" comprises a wide range of structurally diverse compounds that are formed endogenously and in food via the Maillard reaction, a chemical reaction between reducing sugars and amino acids. Glycation compounds produced endogenously are considered to contribute to a range of diseases. This has led to the hypothesis that glycation compounds present in food may also cause adverse effects and thus pose a nutritional risk to human health. In this work, the Senate Commission on Food Safety (SKLM) of the German Research Foundation (DFG) summarized data on formation, occurrence, exposure and toxicity of glycation compounds (Part A) and systematically assessed potential associations between dietary intake of defined glycation compounds and disease, including allergy, diabetes, cardiovascular and renal disease, gut/gastrotoxicity, brain/cognitive impairment and cancer (Part B). A systematic search in Pubmed (Medline), Scopus and Web of Science using a combination of keywords defining individual glycation compounds and relevant disease patterns linked to the subject area of food, nutrition and diet retrieved 253 original publications relevant to the research question. Of these, only 192 were found to comply with previously defined quality criteria and were thus considered suitable to assess potential health risks of dietary glycation compounds. For each adverse health effect considered in this assessment, however, only limited numbers of human, animal and in vitro studies were identified. While studies in humans were often limited due to small cohort size, short study duration, and confounders, experimental studies in animals that allow for controlled exposure to individual glycation compounds provided some evidence for impaired glucose tolerance, insulin resistance, cardiovascular effects and renal injury in response to oral exposure to dicarbonyl compounds, albeit at dose levels by far exceeding estimated human exposures. The overall database was generally inconsistent or inconclusive. Based on this systematic review, the SKLM concludes that there is at present no convincing evidence for a causal association between dietary intake of glycation compounds and adverse health effects.

Effects of Glycosylation Combined with Phosphate Treatment on the Allergenicity and Structure of Tropomyosin in Litopenaeus vannamei

Tropomyosin (TM) is the main allergen in shrimp (Litopenaeus vannamei). In this study, the effects of allergenicity and structure of TM by glycosylation (GOS-TM), phosphate treatment (SP-TM), and glycosylation combined with phosphate treatment (GOS-SP-TM) were investigated. Compared to GOS-TM and SP-TM, the IgG/IgE binding capacity of GOS-SP-TM was significantly decreased with 63.9 ± 2.0 and 49.7 ± 2.7%, respectively. Meanwhile, the α-helix content reduced, surface hydrophobicity increased, and 10 specific amino acids (K30, K38, S39, K48, K66, K74, K128, K161, S210, and K251) were modified by glycosylation on six IgE linear epitopes of GOS-SP-TM. In the BALB/c mice allergy model, GOS-SP-TM could significantly reduce the levels of specific IgE, IgG1, and CD4+IL-4+, while the levels of IgG2a, CD4+CD25+Foxp3+, and CD4+IFN-γ+ were increased, which equilibrated Th1 and Th2 cells, thus alleviating allergic symptoms. These results indicated that glycosylation combined with phosphate treatment can provide a new insight into developing hypoallergenic shrimp food.

A comprehensive review on glycation and its potential application to reduce food allergenicity

Food allergens are a major concern for individuals who are susceptible to food allergies and may experience various health issues due to allergens in their food. Most allergenic foods are subjected to heat treatment before being consumed. However, thermal processing and prolonged storage can cause glycation reactions to occur in food. The glycation reaction is a common processing method requiring no special chemicals or equipment. It may affect the allergenicity of proteins by altering the structure of the epitope, revealing hidden epitopes, concealing linear epitopes, or creating new ones. Changes in food allergenicity following glycation processing depend on several factors, including the allergen's characteristics, processing parameters, and matrix, and are therefore hard to predict. This review examines how glycation reactions affect the allergenicity of different allergen groups in allergenic foods.

Food Allergens: When Friends Become Foes-Caveats and Opportunities for Oral Immunotherapy Based on Deactivation Methods

Food allergies represent a serious health concern and, since the 1990s, they have risen gradually in high-income countries. Unfortunately, the problem is complex because genetic, epigenetic, and environmental factors may be collectively involved. Prevention and diagnoses have not yet evolved into efficacious therapies. Identification and control of allergens present in edible substances hold promise for multi-purpose biomedical approaches, including oral immunotherapy. This review highlights recent studies and methods to modify the otherwise innocuous native proteins in most subjects, and how oral treatments targeting immune responses could help cancel out the potential risks in hypersensitive individuals, especially children. We have focused on some physical methods that can easily be conducted, along with chemo-enzymatic modifications of allergens by means of peptides and phytochemicals in particular. The latter, accessible from naturally-occurring substances, provide an added value to hypoallergenic matrices employing vegetal wastes, a point where food chemistry meets sustainable goals as well.

Molecular structure, IgE binding capacity and gut microbiota of ovalbumin conjugated to fructose and galactose:A comparative study

Ovalbumin (OVA) was modified by fructose (Fru) and galactose (Gal) to study the structure, IgG/IgE binding capacity and effects on human intestinal microbiota of the conjugated products. Compared with OVA-Fru, OVA-Gal has a lower IgG/IgE binding capacity. The reduction of OVA is not only associated with the glycation of R84, K92, K206, K263, K322 and R381 in the linear epitopes, but also with conformational epitope changes, manifested as secondary and tertiary structural changes caused by Gal glycation. In addition, OVA-Gal could alter the structure and abundance of gut microbiota at phylum, family, and genus levels and restore the abundance of bacteria associated with allergenicity, such as Barnesiella, Christensenellaceae_R-7_group, and Collinsela, thereby reducing allergic reactions. These results indicate that OVA-Gal glycation can reduce the IgE binding capacity of OVA and change the structure of human intestinal microbiota. Therefore, Gal glycation may be a potential method to reduce protein allergenicity.

Assessment of the effect of glycation on the allergenicity of sesame proteins

Sesame allergy is a growing concern worldwide. In this study, sesame proteins was glycated with glucose, galactose, lactose and sucrose respectively, and the allergenicity of different glycated sesame proteins were assessed by a comprehensive strategy, including simulated gastrointestinal digestion in vitro, a BALB/c mice model, a rat basophilic leukemia (RBL)-2H3 cell degranulation model and a serological experiment. Firstly, simulated gastrointestinal digestion in vitro showed that glycated sesame proteins were more easily to digest than raw sesame. Subsequently, the allergenicity of sesame proteins was assessed in vivo by detecting the allergic indexes of mice, and results showed that the levels of total immunoglobulin E (IgE) and histamine were reduced in glycated sesame proteins treated mice. Meanwhile, the Th2 cytokines (IL-4, IL-5, and IL-13) were downregulated significantly, demonstrating that sesame allergy was relieved in glycated sesame treated mice. Thirdly, the RBL-2H3 cell degranulation model results showed that the release of β-hexosaminidase and histamine were decreased to different degrees in glycated sesame proteins treated groups. Notably, the monosaccharide glycated sesame proteins exhibited lower allergenicity both in vivo and in vitro. Furthermore, the study also analyzed the structure alteration of sesame proteins, and the results showed that the secondary structure of glycated sesame proteins were changed (the content of α-helix and β-sheet were reduced), and the tertiary structure of sesame proteins after glycation modification was also changed (microenvironment around aromatic amino acids was altered). Besides, the surface hydrophobicity of glycated sesame proteins was also reduced except sucrose glycated sesame proteins. In conclusion, this study demonstrated that glycation reduced the allergenicity of sesame proteins effectively, especially glycation with monosaccharides, and the allergenicity reduction might be related to structural changes. The results will provide a new reference for developing hypoallergenic sesame products.

Alteration of the allergenicity of cow's milk proteins using different food processing modifications

Milk is an essential source of protein for infants and young children. At the same time, cow's milk is also one of the most common allergenic foods causing food allergies in children. Recently, cow's milk allergy (CMA) has become a common public health issue worldwide. Modern food processing technologies have been developed to reduce the allergenicity of milk proteins and improve the quality of life of patients with CMA. In this review, we summarize the main allergens in cow's milk, and introduce the recent findings on CMA responses. Moreover, the reduced effects and underlying mechanisms of different food processing techniques (such as heating, high pressure, γ-ray irradiation, ultrasound irradiation, hydrolysis, glycosylation, etc.) on the allergenicity of cow's milk proteins, and the application of processed cow's milk in clinical studies, are discussed. In addition, we describe the changes of nutritional value in cow's milk treated by different food processing technologies. This review provides an in-depth understanding of the allergenicity reduction of cow's milk proteins by various food processing techniques.

New Mechanistic Advances in FcεRI-Mast Cell-Mediated Allergic Signaling

Mast cells originate from the CD34⁺/CD117⁺ hematopoietic progenitors in the bone marrow, migrate into circulation, and ultimately mature and reside in peripheral tissues. Microbiota/metabolites and certain immune cells (e.g., Treg cells) play a key role in maintaining immune tolerance. Cross-linking of allergen-specific IgE on mast cells activates the high-affinity membrane-bound receptor FcεRI, thereby initiating an intracellular signal cascade, leading to degranulation and release of pro-inflammatory mediators. The intracellular signal transduction is intricately regulated by various kinases, transcription factors, and cytokines. Importantly, multiple signal components in the FcεRI-mast cell–mediated allergic cascade can be targeted for therapeutic purposes. Pharmacological interventions that include therapeutic antibodies against IgE, FcεRI, and cytokines as well as inhibitors/activators of several key intracellular signaling molecues have been used to inhibit allergic reactions. Other factors that are not part of the signal pathway but can enhance an individual’s susceptibility to allergen stimulation are referred to as cofactors. Herein, we provide a mechanistic overview of the FcεRI-mast cell–mediated allergic signaling. This will broaden our scope and visions on specific preventive and therapeutic strategies for the clinical management of mast cell–associated hypersensitivity reactions.

Phosphorylation of ovalbumin after pulsed electric fields pretreatment: Effects on conformation and immunoglobulin G/immunoglobulin E-binding ability

Ovalbumin (OVA) is one of major allergens of hen egg white with excellent nutritional and processing properties. Previous research exhibits that pulsed electric field (PEF) treatment could partially unfold OVA. This may contribute to the improvement of OVA phosphorylation. In this study, the effect of PEF pretreatment combined with phosphorylation on the structure and immunoglobulin (Ig) G/IgE-binding ability of OVA was investigated. The structural changes were measured by circular dichroism (CD), ultraviolet absorption, and fluorescence spectroscopy. The IgG- and IgE-binding abilities were determined by inhibition enzyme-linked immunosorbent assay (ELISA) using rabbit polyclonal antibodies and egg-allergy patients’ sera, respectively. The results showed that PEF pretreatment combined with phosphorylation markedly reduced the IgG- and IgE-binding abilities. It was attributed to the changes in secondary and tertiary structure, which was reflected in the increase of ultraviolet (UV) absorbance, α-helix content, and the increase the molecular weight. Moreover, it suggested PEF pretreatment improved the phosphorylation of OVA and enhanced the reduction of IgG/IgE-binding capacity of phosphorylated OVA. Therefore, PEF pretreatment combined with phosphorylation has the potential for developing a method for OVA desensitization.

Simulated in vitro digestion of α-lactalbumin modified by phosphorylation: Detection of digestive products and allergenicity

The effects of phosphorylation on the allergenicity of bovine α-lactalbumin (BLA) and digestive products were studied in vitro digestion. Two components with different molecular weight and conformation were obtained from natural and phosphorylated BLA. In vivo and in vitro assessment of allergenicity showed that phosphorylation prior to digestion significantly decreased the IgE/IgG binding capacity and allergic response in KU812 cells, and reduced the levels of IgG, IgE, IL-4 and histamine, with an increase in IFN-γ levels in mouse serum, depending on the changes in BLA structures, producing numerous small peptides. There were four phosphorylated sites (S22, T29, S47 and S70) in the high molecular weight components of phosphorylated BLA after digestion. These phosphorylated sites could mask the linear epitopes of digestive products, resulting in reduced allergic activity. Phosphorylation prior to digestion of dairy products can reduce the risk of anaphylaxis in patients with milk allergy to some extent.

Maillard Reaction Induced Changes in Allergenicity of Food

Food allergy is increasing in prevalence, posing aheavier social and financial burden. At present, there is still no widely accepted treatment for it. Methods to reduce or eliminate the allergenicity of trigger foods are urgently needed. Technological processing contributes to producing some hypoallergenic foods. Among the processing methods, the Maillard reaction (MR) is popular because neither special chemical materials nor sophisticated equipment is needed. MR may affect the allergenicity of proteins by disrupting the conformational epitope, disclosing the hidden epitope, masking the linear epitope, and/or forming a new epitope. Changes in the allergenicity of foods after processing are affected by various factors, such as the characteristics of the allergen, the processing parameters, and the processing matrix, and they are therefore variable and difficult to predict. This paper reviews the effects of MR on the allergenicity of each allergen group from common allergenic foods.

Bovine β-Lactoglobulin Covalent Modification by Flavonoids: Effect on the Allergenicity and Human Intestinal Microbiota

The present study aims to investigate the structure of covalent conjugates of bovine β-lactoglobulin (BLG) and flavonoids (luteolin, myricetin, and hyperoside), and their effect on the allergenicity and human intestinal microbiota. Covalent modification of amino acids in BLG by flavonoids was confirmed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and o-phthaldialdehyde assay. The secondary and conformational structures of BLG were changed by the covalent modification, which were determined by the circular dichroism, Fourier transform infrared spectroscopy, fluorescence spectroscopy, and UV spectroscopy. The enzyme-linked immunosorbent assay (ELISA) and cell experiments indicated that BLG covalent conjugates could reduce IgE/IgG binding capacities and suppress the allergy reactivity of RBL-2H3 cells, suggesting that the covalent modification modulated the balance of T cells. Meanwhile, covalent modification of BLG with these flavonoids can alter the diversity of human intestinal microbiota and the community abundance at phylum, family, and genus levels. The results revealed that covalent modification of BLG with flavonoids alters human intestinal microbiota, might result in the reduction of allergenicity, which could provide information for confirming the relationship between food allergy and the intestinal microbial ecosystem.

Reducing the Allergenicity of α-Lactalbumin after Lipid Peroxidation

This study analyzed the effect of lipid peroxidation using 2,2'-azobis(2-amidinopropane)dihydrochloride (AAPH) and acrolein on the in vitro and in vivo allergenicity of α-lactalbumin (α-La). The structure of oxidized α-La was evaluated by sodium dodecyl sulfate polyacrylamide gel electrophoresis, fluorescence spectroscopy, and circular dichroism, whereas the changes in the allergenic properties were evaluated. Lipid peroxidation induced changes to the structural properties that might destroy and/or mask α-La epitopes. In comparison to native α-La, oxidation complexes caused a decrease in the immunoglobulin E (IgE) binding capacity, as observed via immunoblotting. Moreover, the capacity to release mediators and cytokines from KU812 cells was also greatly reduced. In vivo, oxidation with AAPH and acrolein caused a significant reduction in IgE, IgG, IgG1, mast cell protease 1, and plasma histamine, along with the reduction of mast surface c-Kit⁺ and FcεRI⁺ expression. Therefore, these results indicate that oxidation via AAPH and acrolein can potentially reduce the allergenicity of α-La, which can help with the better understanding of the changes in allergenicity of milk allergen by lipid peroxidation.

Two Faces of Milk Proteins Peptides with Both Allergenic and Multidimensional Health Beneficial Impact- Integrated In Vitro/In Silico Approach

The main food-origin antigens that the infant's body is in contact with are cow's milk proteins (CMP). Still, CMP are one of the main sources of beneficial biologically active peptides that play a role in treatment of non-communicable diseases. Safe methods to quickly predict the sensitizing potential of food proteins among their range of health-promoting properties are essential. The aim of study was to adapt an integrated approach combining several in silico (IS) studies and in vitro (IV) assays to screen the multifunctionality of CMP-derived peptides. Major histocompatability complex type II MHC II-binders, interleukin-4 and -10 inducers, interferon γ -inducers and immunobioactivity tools were used to predict the peptide-power of inducing allergies or tolerance. A comparison of the peptide profiless revealed the presence of one identical and one overlapping sequence in IS and IV hydrolysate. By IS analysis, four of 24 peptides were found to have high affinity and stimulate IL-4 expression, and by IV, one of seven peptides had this potential (Bos d9 peptide DIPNPIGSENSEK (195-208)). Three IV peptides may induce IL-10 expression. The IV/IS assessment seems promising agents for peptides' potential determination dedicated only to preliminary screening of peptides. The IV verification is still crucial in further steps of studies.

Improved antitumor activity and IgE/IgG-binding ability of α-Lactalbumin/β-lactoglobulin induced by ultrasonication prior to binding with oleic acid

Bovine α-lactalbumin (α-La)/β-lactoglobulin (β-Lg) was pretreated through ultrasonic treatment and subsequently binding with oleic acid (OA) by heat treatment. And, the antitumor activity, IgE/IgG-binding ability, and structural modifications were investigated. After α-La/β-Lg were treated by ultrasonic prior to binding with OA, the treated α-La/β-Lg showed high antitumor activity and IgE/IgG-binding ability, and significantly affected the structural modifications, which reflected by the reduction in α-helix content, the increase of molecular weight, intrinsic fluorescence intensity, and surface hydrophobicity. Molecular docking studies indicated that OA bound to α-La/β-Lg by hydrogen bonds and hydrophobic interaction. Therefore, ultrasonic prior to binding with OA could improve antitumor activity and IgE/IgG-binding ability of α-La/β-Lg as a result of structural modifications. And, ultrasonic prior to binding with fatty acid processing of milk products alone may increase the antitumor activity, this change may enhance the risk of an allergenic reaction in milk allergy patients to some extent. PRACTICAL APPLICATIONS: Fatty acids, natural ligands associated with the bovine milk proteins, and milk protein-fatty acid complex has a variety of functional applications in the food industry. This study revealed that antitumor activity, IgE/IgG-binding ability, and structural modifications of α-La/β-Lg induced by ultrasonic prior to binding with oleic acid. It will be beneficial to understand the mechanism of the functional changes of protein. Ultrasonic prior to binding with oleic acid will be more likely to develop a practical technology to improve the functional characteristics of milk protein and design the optimal nutritional performance of milk food.