Chantal Brossard

Sweetness–texture interactions in model dairy desserts: effect of sucrose concentration and the carrageenan type

Sweetness–texture interactions were investigated in model dairy desserts varying in both sucrose concentration and carrageenan composition (κ-, ι-, λ-carrageenans or an equal-weight mixture of the three). Nineteen panellists evaluated sweetness and five oral texture attributes while instrumental texture was characterised by penetrometry. For each carrageenan composition, sweetness significantly increased with sucrose. Rheological profiles or oral texture attributes allowed to distinguish four matrices. Sweetness–texture interactions were observed but no common rule was applied. On the one hand, firmness of κ-carrageenan desserts, springiness and firmness of ι-carrageenan desserts, unctuousness of λ-carrageenan desserts and brittleness and unctuousness of mix-carrageenan ones increased with sucrose concentration. These changes can be partly attributed to changes in the mechanical profiles. On the other hand, variation of carrageenan composition modified sweetness assessment at higher concentrations, λ-carrageenan desserts being the sweetest and ι-carrageenan desserts the least sweet. A model, which considered carrageenan composition, sucrose concentration and their interactions, was established to relate sweetness and composition of the desserts.

Allergy to deamidated gluten in patients tolerant to wheat: specific epitopes linked to deamidation

Gluten proteins can be modified by deamidation to enhance their solubility and technological applications. However, severe allergic reactions have been reported after the consumption of food products containing deamidated gluten (DG) in subjects tolerant to wheat. This work aimed to characterize allergen profiles for these patients in comparison with those of patients allergic to wheat and to identify IgE‐binding epitopes.

Assessment of allergenicity of diploid and hexaploid wheat genotypes: Identification of allergens in the albumin/globulin fraction

Wheat is an important part of the daily diet of millions of people. However, this staple food is also responsible for food allergies. Ancient cultivars of wheat are gaining interest today but nothing is known about their allergenicity. Many wheat proteins have been reported as causative food allergens, including some prolamin-type gluten proteins, and salt soluble proteins of the albumin/globulin (A/G) type. The objective of this work is to obtain information about the allergenicity of the salt soluble A/G fraction of an ancient diploid cultivar compared with a standard hexaploid bread wheat cultivar using 20 sera from patients with wheat allergy. Differences in the IgE reactivity of sera towards the two genotypes were quantified by ELISA. Qualitative differences in IgE-binding proteins were searched after 1D or 2D electrophoresis. For most of the sera, the concentration in A/G specific IgE was higher for the hexaploid T. aestivum (cv Récital) than for the diploid T. monococcum (cv Engrain). The analysis of 2D spots revealed by immunoblotting leads to the identification by mass spectrometry of 39 IgE-binding proteins, some of them unknown until now as wheat allergens. Numerous allergens were identified, differences observed between Engrain and Récital will be discussed.

Wheat gliadins modified by deamidation are more efficient than native gliadins in inducing a Th2 response in Balb/c mice experimentally sensitized to wheat allergens.

SCOPE Wheat gluten proteins such as gliadins constitute major food allergens. Gluten can be modified industrially by deamidation which increases its solubility and enhances its use as a food ingredient. Sensitization to deamidated gluten has been reported to cause severe allergic reactions with anaphylaxis. The aim of this study was therefore to compare the sensitization and elicitation potentials of native (NG) and deamidated (DG) gliadins. The reactivity pattern of mice IgE was also compared with that of DG-allergic patients. METHODS AND RESULTS The ability of DG to sensitize Balb/c mice using intra-peritoneal administration with aluminium hydroxide as an adjuvant, and to elicit an allergic response after a challenge, was tested in comparison with NG. Mice sensitized with DG secreted higher levels of total IgE, IL-4, gliadin-specific IgE and IgG1 than mice sensitized with NG. By contrast, mice sensitized with NG produced higher levels of gliadin-specific IgG2a and INFγ. After a challenge, histamine levels were higher in mice sensitised with DG. CONCLUSIONS DG can sensitize mice much more efficiently than NG. Moreover, this mouse model of allergy to DG revealed an IgE reactivity pattern against purified gliadins which was very similar to that of DG-allergic patients.

The thermal aggregation of ovalbumin as large particles decreases its allergenicity for egg allergic patients and in a murine model.

Most egg-allergic children can tolerate extensively cooked eggs. Ovalbumin, a major allergen in egg whites, is prone to aggregate upon heating. This study compares ovalbumins allergenicity when it is aggregated as large particles to ovalbumin in its native form. Immunoglobulins (Ig)-binding and the degranulation capacities of native and aggregated ovalbumin were measured with sera from egg-allergic children and from mice sensitized to native or aggregated ovalbumin. The influence of ovalbumin structure on Ig production upon sensitization and elicitation potency by challenge was also studied. We showed that heat aggregation of ovalbumin as large particles enhances IgG production and promotes IgG2a production (a shift toward the T helper 1 profile). Aggregated ovalbumin displayed lower Ig-binding and basophil-activation capacities for sera from both allergic patients and mice. This work illustrates the links between ovalbumin structure after heating and allergenicity potential using parameters from both the sensitization and elicitation phases of the allergic reaction.

Structural Basis of IgE Binding to α- and γ-Gliadins: Contribution of Disulfide Bonds and Repetitive and Nonrepetitive Domains.

Wheat products cause IgE-mediated allergies. The present study aimed to decipher the molecular basis of α- and γ-gliadin allergenicity. Gliadins and their domains, the repetitive N-terminal and the nonrepetitive C-terminal domains, were cloned and expressed in Escherichia coli. Their secondary structures and their IgE binding capacity were compared with those of natural proteins before and after reduction/alkylation. Allergenicity was evaluated with sera from patients who had a wheat food allergy or bakers asthma. The secondary structures of natural and recombinant proteins were slightly different. Compared with natural gliadins, recombinant proteins retained IgE binding but with reduced reactivity. Reduction/alkylation decreased IgE binding for both natural and recombinant gliadins. Although more continuous epitopes were identified in the N-terminal domains of α- and γ-gliadins, both the N-terminal and C-terminal domains contributed to IgE binding. As for other members of the prolamin superfamily, disulfide bonds appear to be of high importance for IgE binding.

Meta-analysis of IgE-binding allergen epitopes.

IgE-binding epitopes are related to allergic symptoms by eliciting degranulation of special cells and release of molecules that trigger the hypersensitivity reaction. Little is known about what characterises allergen IgE-binding epitopes, although advances in analytical methods have led to the identification of a large number of them. To assess if a binary classification of allergen regions into epitopes or non-epitopes may accurately reflect biological reality, we computed the fraction of allergen amino acids that are involved in epitopes. A relationship between this fraction and the increasing number of literature references was modelled. Due to the wide variety of methods that are used in the literature, a peak in the number of matches between an allergen sequence and its epitopes confirms their validity. Accordingly, our graphical representation of positive assays along sequences provides an overview of epitope localisation, which should help to highlight major positions for IgE binding to allergens.

How Proteins Aggregate Can Reduce Allergenicity: Comparison of Ovalbumins Heated under Opposite Electrostatic Conditions

Heated foods are recommended for avoiding sensitization to food proteins, but depending on the physicochemical conditions during heating, more or less unfolded proteins aggregate differently. Whether the aggregation process could modulate allergenicity was investigated. Heating ovalbumin in opposite electrostatic conditions led to small (A-s, about 50 nm) and large (A-L, about 65 μm) aggregates that were used to sensitize mice. The symptoms upon oral challenge and rat basophil leukemia degranulation with native ovalbumin differed on the basis of which aggregates were used during the sensitization. Immunoglobulin-E (IgE) production was significantly lower with A-s than with A-L. Although two common linear IgE-epitopes were found, the aggregates bound and cross-linked IgE similarly or differently, depending on the sensitizing aggregate. The ovalbumin aggregates thus displayed a lower allergenic potential when formed under repulsive rather than nonrepulsive electrostatic conditions. This further demonstrates that food structure modulates the immune response during the sensitization phase with some effects on the elicitation phase of an allergic reaction and argues for the need to characterize the aggregation state of allergens.

Revisiting egg yolk involvement in children’s food allergy to egg

Background Food allergy to egg is commonly diagnosed in childhood with good prognosis. Egg white is considered as the main culprit with major 4 identified allergens (Gal d 1 to Gal d 4). Egg yolk (with two identified allergens Gal d 5 and Gal d 6 in the livetin fraction) retained less attention and its clinical involvement remains unclear. This study revisits sensitization to both egg fractions in a cohort of children allergic to egg and investigates IgE reactivity toward the main egg yolk fractions.

Acid-Hydrolyzed Gliadins Worsen Food Allergies through Early Sensitization

SCOPE Food allergies result from a complex immune response involving both innate and adaptive immune cells. Major proteins of wheat flour, gliadins, appear to be important allergens, and their characteristics can influence the allergic response. This study investigates the immune reaction when developing a food allergy to gliadins in native, deamidated, or hydrolyzed forms. METHODS The immune response after one or two intraperitoneal sensitizations and after oral challenge with each gliadin form is analyzed. RESULTS Results demonstrate that deamidated gliadins induce a stronger allergic reaction compared to native gliadins. Moreover, deamidation induces an earlier increase in intestinal permeability associated with more pronounced Th2 and Th17 polarizations together with an influx of antigen-presenting cells, especially cDC2. CONCLUSION Altogether, Results indicate that industrial processes such as deamidation or hydrolysis influences food allergenicity through immune modulation and helps us to develop tools to determine how these processes can influence this reaction and encourage or decrease allergic reactions.