Erroneous Belief that Digestive Stability Predicts Allergenicity May Lead to Greater Risk for Novel Food Proteins

Slow alignment of GMO allergenicity regulations with science on protein digestibility

The current science on food allergy supports the dual allergen exposure hypothesis where sensitization to allergenic proteins is favored by dermal and inhalation exposure, and tolerization against allergy is favored by exposure in the gut. This hypothesis is bolstered by the epidemiological evidence showing that regions where children are exposed early in life to allergenic foods have lower rates of allergy. This led medical experts to replace the previous recommendation to exclude commonly allergenic foods from the diets of young children with the current recommendation that such foods be introduced to children early in life. Past beliefs that lowering gut exposure would reduce the likelihood that a protein would be allergenic led regulators and risk assessors to consider digestively stable proteins to be of greater allergenic risk. This resulted in international guidance and government regulations for newly expressed proteins in genetically engineered crops that aligned with this belief. Despite empirical results showing that allergens are no more digestively stable than non-allergens, and that gut exposure favors tolerization over sensitization, regulations have not come into alignment with the current science prompting developers to continue to engineer proteins for increased digestibility. In some rare cases, this could potentially increase sensitization risk.

Gastrointestinal fate of food allergens and its relationship with allergenicity

Food allergens are closely related to their gastrointestinal digestion fate, but the changes in food allergens during digestion and related mechanisms are quite complicated. This review presents in detail digestion models for predicting allergenicity, the fates of food allergens in oral, gastric and duodenal digestion, and the applications of digestomics in mapping IgE-binding epitopes of digestion-resistant peptides. Moreover, this review highlights the structure-activity relationships of food allergens during gastrointestinal digestion. Digestion-labile allergens may share common structural characteristics, such as high flexibility, rendering them easier to be hydrolyzed into small fragments with decreased or eliminated allergenicity. In contrast, the presence of disulfide bonds, tightly wound α-helical structures, or hydrophobic domains in food allergens helps them resist gastrointestinal digestion, stabilizing IgE-binding epitopes, thus maintaining their sensitization. In rare cases, digestion leads to increased allergenicity due to exposure of new epitopes. Finally, the action of the food matrix and processing on the digestion and allergenicity of food allergens as well as the underlying mechanisms was overviewed. The food matrix can directly act on the allergen by forming complexes or new epitopes to affect its gastrointestinal digestibility and thereby alter its allergenicity or indirectly affect the allergenicity by competing for enzymatic cleavage or influencing gastrointestinal pH and microbial flora. Several processing techniques attenuate the allergenicity of food proteins by altering their conformation to improve susceptibility to degradation by digestive enzymes. Given the complexity of food components, the food itself rather than a single allergen should be used to obtain more accurate data for allergenicity assessment. PRACTICAL APPLICATION: The review article will help to understand the relationship between food protein digestion and allergenicity, and may provide fundamental information for evaluating and reducing the allergenicity of food proteins.