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Walnut allergy in context
Walnuts are among the most common causes of tree nut allergy, a condition that affects 0.6-1.14% of North Americans and can be associated with life threatening allergic reactions. While the prevalence and severity of walnut allergy make this condition a concern for both clinicians and the food industry, relatively little is known about the properties and behavior of walnut allergens. The objective of this work was to evaluate walnut allergens in terms of their molecular characteristics, clinical importance, and behavior in the context of complex food systems. Mass spectrometry (MS) analyses revealed greater levels of diversity in walnut allergens than previously understood. The observed variation in native walnut proteins appears to arise from both sequence isoforms and posttranslational modifications, including proteolysis. An example of the latter was demonstrated with the identification of a series of stable peptide fragments, which originated from the N-terminal region of the 7S vicilin-like globulin sequence and showed IgE binding in approximately 27% of sera from walnut-allergic individuals. Greater knowledge of the genomes and proteomes of plant foods is needed in order to fully utilize advanced molecular analysis techniques, including mass spectrometry. Walnut proteins were also shown to have unique solubility requirements that could impact the efficacy of existing clinical diagnostic tools. IgE immunoblotting indicated that 76% of blot-reactive sera from individuals with reported walnut allergy demonstrated IgE binding with the walnut 11S legumin, an allergen particularly insoluble in the types of aqueous solutions traditionally used for diagnostic materials. The development of new diagnostic tools that accommodate the solubility requirements of all of the walnut allergens may be necessary. Lastly, individual walnut allergens were shown to respond differently to thermal processing. Under more intense roasting conditions, the level of total soluble walnut protein decreases dramatically, but the high molecular weight proteins are particularly affected. The insoluble protein fraction does, however, retain at least some of its IgE binding capacity. In addition, MS detection of walnut proteins can be dramatically affected by thermal processing due to changes in solubility and digestibility.
Downs, Melanie L, "Walnut allergy in context" (2013). ETD collection for University of Nebraska - Lincoln. AAI3603815.