Loading...
6 results
Search Results
Now showing 1 - 6 of 6
- Phenolic compounds: a novel approach to reduce egg allergenicity?Publication . Vapor, Alcides; Tomaz, Cândida T.; Mendonça, AntónioHen's egg allergy has been climbing in all countries due to eggs ubiquity in foodstuffs. This allergy is an IgE mediated reaction that affects mainly infants and young children. So far, the processes used to decrease the allergenicity of egg proteins, such as cooking, thermal processing, storage and enzymatic digestion have not been totally effective. Previous studies demonstrated that proteins form complexes with phenolic compounds, so the aim of this work was to analyze the effect of these compounds in ovalbumin (OVA) conformation and its possible application to reduce eggs allergenicity. OVA was incubated at different temperatures with phenolic compounds (caffeic, chlorogenic, ferulic, gallic and tannic acids; resveratrol and quercetin) and was analyzed by circular dichroism (CD), Attenuated Total Reflection–Fourier Transform Infra-Red (ATRFTIR) spectroscopy and fluorescence. Changes in the secondary structure of OVA were evidenced by CD and ATR-FTIR. Also, protein fluorescence decreased with increasing concentrations of phenolic compounds. The thermodynamic analysis suggested that electrostatic interactions are important in the binding process, and the quenching mechanism occur by contact. This was confirmed by docking where the phenolic compounds bind specifically to some regions of the protein, including those with the allergenic epitopes.
- Interactions of Phenolic Compounds with OvalbuminPublication . Vapor, Alcides; Tomaz, Cândida T.; Mendonça, AntónioOvalbumin (OVA) is the major protein in egg white and can cause allergy mainly in infants and young children [1]. Egg allergy is an IgE mediated reaction and is one the most common food allergies. So far, the avoidance of the egg has been the unique way to prevent this allergy [2]. It is well known that phenolic compounds can bind to proteins promoting structural and functional changes. In this work, the interactions between OVA and the phenolic compounds were studied through spectroscopic techniques (fluorescence, circular dichroism (CD), Fourier transform infrared spectroscopy (FTIR)) and docking. OVA solutions were incubated at different temperatures and times, with different phenolic compounds prepared with the same buffer solution (Gallic, Caffeic, Ferulic, Chlorogenic and Tannic Acids, Resveratrol and Quercetin). Results indicate that OVA's structure was affected by the binding of phenolic compounds. CD and FTIR experiments showed changes in the secondary structure of OVA, originated by the conversion of α-helix into β-sheets [1]. Fluorescence spectra demonstrated that phenolics are quenchers of fluorescent aminoacids (Tyrosine, Phenylalanine and Tryptophan) meaning that interactions occur directly or near these aminoacids. Fluorescence results also suggest that these interactions are electrostatic and thermodynamically favorable (∆G<0). Docking studies showed that the tested phenolic compounds can interact directly with OVA epitopes, or with its neighbors, thus avoiding the IgE binding. Therefore, the phenolic compounds can be used as a strategy for reducing egg allergy in foods.
- Ovalbumin Structural Changes by Phenolic Compounds InteractionsPublication . Vapor, Alcides; Tomaz, Cândida T.; Mendonça, AntónioOvalbumin (OVA) is the most prevalent protein in egg white and, represents the major allergen from avian egg white that causes IgE-mediated food allergic reactions particularly in children. It has been shown that phenolic compounds interact with proteins by a single or multipoint mechanism, promoting structural and functional changes. Moreover, the interaction of some allergens with polyphenols, led to permanent modification of the tertiary structure of the allergen, which can result in a reduction in its IgE-binding capacity. This work aimed to analyse the effect of phenolic compounds (Gallic, Caffeic, Ferulic, Chlorogenic and Tannic Acids, Resveratrol and Quercetin) on the native structure of OVA, using Circular Dichroism (CD), fluorescence and Fourier transform infrared spectroscopy (FTIR). The phenolic compounds were incubated with OVA at different times, concentrations and temperatures. Changes in OVA secondary and tertiary structures were increasingly induced with increasing temperatures by the phenolic compound. Also, for a constant temperature, the changes found in OVA structure increased with the phenolic compounds concentration. The results show that the interactions between phenolic compounds and OVA result in complexes (phenolics – OVA) where OVA native structure is changed. This is likely to affect epitopes and hence OVA allergenicity.
- Strategies for reducing the allergenicity of hen egg by treatment with natural antioxidantsPublication . Vapor, Alcides Walter; Tomaz, Cândida Ascensão Teixeira; Mendonça, António José Geraldes deFood allergies are caused by abnormal immune responses to food components (allergens), namely proteins. For this reason, eggs are one of the richest foods in the food chain and are therefore essential for a healthy diet. However, worldwide 6-9 % of the child population and 4 % of adults are allergic to eggs, which prevent their consumption or any derived products. Hen’s egg allergy has increased worldwide due to the ubiquitous of eggs in the diet. Ovalbumin (OVA) is the most abundant protein in the egg white and causes allergy, especially in children and young children, being one of the most common food allergies, mediated by IgE. Until now, the processes used to decrease the allergenicity of egg proteins, such as cooking, thermal processing, and enzymatic digestion have not been totally effective, because the allergens have high stability and resistance. Thus, there are no drugs to prevent allergic reactions, and avoiding the egg has been the only way to prevent this allergy. Phenolic compounds (PC) are recognized as having a potent antioxidant, anti-inflammatory, antibacterial, antiviral and antitumor activity. In addition, these compounds, present in fruits and vegetables, can bind to peptides and proteins to form complexes, being able to promote alteration of its native conformation and to contribute to the reduction of allergenicity. Therefore, the goal of this work was the development of a process to reduce the allergenicity of hen egg proteins through the action of natural antioxidants, such as PC, under different experimental conditions, in order to promote alterations of proteins native structure, and concomitantly, of its allergenic capacity. Spectroscopic techniques have stood out among the various methods, as they use small amounts of sample, do not cause damage of the sample and can be used in different experimental conditions to analyse the conformational changes that can occur during the chemical, physical and enzymatic modifications of proteins. Thus, the OVA changes promoted by the different PC were evaluated using techniques such as circular dichroism (CD), fluorescence and total attenuated reflection - infrared Fourier transform (ATR-FTIR). The OVA solutions were incubated at different temperatures, with different PC (gallic, caffeic, ferulic, chlorogenic and tannic acids, resveratrol and quercetin) prepared with the same buffer solution. The results showed that the structure of OVA was affected by the binding of these compounds. The fluorescence spectra demonstrated that the PC quenched the fluorescent amino acid tryptophan, which means that the interactions occurred directly or close to this amino acid residue. It was also observed that the fluorescence of OVA solutions decreased with increasing PC concentration. The quenching mechanism calculated from the Stern-Volmer constant (KSV) and the bimolecular quenching constant (Kq) suggests a static quenching mechanism. However, when considering the effect of temperature variation (298.15 to 318.15 K and 318.15 to 328.15 K) on fluorescence quenching, it was found that KSV and Kq decreased with the increase of temperature in some OVA-PC complexes, leading to a dynamic extinction mechanism. On the other hand, for other complexes, KSV and Kq increased with increasing temperature, or remained constant, suggesting, respectively, a static extinction mechanism and a mixed extinction mechanism (static and dynamic). The same effect was observed for the binding constant Kb, with temperature change. Furthermore, the thermodynamic analysis, according to the values found for ΔH and ΔS for all OVA-PC complexes tested, at both temperatures, suggested that the reactions occurred spontaneously (ΔG<0) with the participation of weak interactions, namely hydrophobic interactions and hydrogen. The experiments with CD and ATR-FTIR showed changes in the secondary structure of OVA, originated by the conversion of the α-helix into β- sheets. Molecular docking showed that the PC can interact directly with OVA epitopes or in its neighborhood, preventing IgE binding. Therefore, the application of natural antioxidants, such as PC, in the treatment of egg proteins appears to be a potential alternative to the current methods used in reducing the allergenicity of egg proteins. In fact, all PC bound to OVA, changing its secondary and tertiary structure. As future perspectives, in-depth studies will be carried out with the whole egg treated with selected PC, to evaluate the binding of the specific IgE, as a strategy to reduce allergy to eggs and to produce hypoallergenic eggs. The confirmation of the decrease of allergenicity will be carried out by immunoblotting and ELISA tests with sera from patients allergic to egg and comparing the levels of specific IgE that binds to treated and untreated OVA with PC. Subsequently, the reduction/elimination of allergenicity in vivo will be evaluated by skin prick tests in allergic patients using OVA and whole egg extracts, treated with PC. It is expected to produce an egg-derived product that allows the egg-allergic population to consume it.
- Interactions of phenolic compounds with ovalbumin: a spectroscopic approachPublication . Vapor, Alcides; Tomaz, Cândida T.; Mendonça, AntónioOvalbumin (OVA) is the major protein in egg white and can cause allergy mainly in infants and young children. Egg allergy is an IgE mediated reaction and is one the most common food allergies. So far, the avoidance of the egg has been the unique way to prevent this allergy. It is well known that phenolic compounds can bind to proteins promoting structural and functional changes and, phenolic compounds are been recognized as having a potent antioxidant, anti-inflammatory and antitumoral activity. In this work, the interactions between OVA and the phenolic compounds were studied through spectroscopic techniques (fluorescence, circular dichroism (CD), Fourier transform infrared spectroscopy (FTIR)) and docking. spectroscopy (FTIR)) and docking.
- Processes for reducing egg allergenicity: Advances and different approachesPublication . Vapor, Alcides; Mendonça, A.J.G. De; Tomaz, C.Egg is a versatile ingredient and ubiquitous food. Nevertheless, egg proteins are a common cause of allergy mainly in childhood. Until now, egg eviction has been the best way to prevent this disorder, however, processed food can contribute to mitigate allergies and to guarantee life quality of allergic individuals. This review focuses on discussing and highlighting recent advances in processes to reduce egg allergenicity as well as new approaches to egg allergy management. In recent times, different methods have been developed to reduce egg allergies, by hiding the epitopes or changing the native or conformational structure of the proteins. Despite processing food has not yet been a solution to completely remove the allergenic potential of egg proteins, innovative strategies, such as addition of phenolic compounds, have been developed with promising results.