Degradation of wheat allergen in Japanese soy sauce

Soy sauce is a traditional fermented seasoning of East Asian countries and is available throughout the world. Wheat and soybeans are the 2 main raw materials of soy sauce, and soy sauce also contains a high concentration of salt. Since wheat allergy is considered a serious problem globally, it is significant to examine the allergenicity of soy sauce. In this study, by immunoblotting, inhibition ELISA and direct ELISA using sera from 5 children with wheat allergy, it was clearly demonstrated that wheat allergens were degraded into amino acids and peptides losing the IgE-binding ability in both salt-soluble and salt-insoluble fractions of soy sauce during fermentation. Furthermore, no wheat allergen was detected in 10 items of commercial soy sauce in Japan, by inhibition ELISA or direct ELISA using the sera of patients. In the brewing process of soy sauce, first salt-insoluble wheat allergen was solubilized to salt water during the koji stage (mold cultivation and enzyme production), and second both the resultant salt-solubilized and initially salt-soluble wheat allergens were completely degraded during the moromi stage (fermentation) by microbial proteolytic enzymes. Therefore, it was concluded that no wheat allergen is contained in soy sauce.