February 18/Obesity, Fitness & Wellness Week -- "Food-dependent exercise-induced anaphylaxis (FDEIA) due to soybeans is a rare disorder. The allergen responsible for FDEIA due to soybeans has not yet been determined," scientists writing in the journal Clinical and Experimental Allergy report.

"We characterized the clinical features of a patient with FDEIA due to tofu, who was well tolerant to drinking soy milk. We then sought to identify the responsible soybean allergen(s) in that patient. We further studied whether different stabilities of the allergen(s) to pepsin digestion between two soybean products are related to their clinical allergenicity. Skin prick tests and provocation tests using soybean products were performed to detect the responsible food and other factors that induced the allergic symptoms. Specific IgE to various soybean allergens were examined by ImmunoCAP((R)), ELISA and protein microarray assays. Immunoblotting for soybeans and soybean products using the patient's serum was also performed. Soybean products were serially digested by pepsin to disclose the stability of the allergens. Provocation with ingestion of tofu and exercise induced the allergic symptoms, while ingestion of soymilk and exercise did not. Immunoblot analysis, ELISA and protein microarray assay revealed that beta-conglycinin mainly reacts with IgE antibodies in the patient's serum. By immunoblot analysis, beta-conglycinin in soymilk completely disappeared after pepsin digestion within 20 minutes, whereas beta-conglycinin in tofu was almost intact after more than 120 minutes of pepsin digestion. We identified beta-conglycinin as the causative allergen in a patient with FDEIA induced by tofu," wrote A. Adachi and colleagues.

The researchers concluded, "The difference in resistance to pepsin digestion between tofu and soymilk suggests that the presence of undigested allergens in the digestive tract is a prerequisite for the development of FDEIA."

Adachi and colleagues published their study in Clinical and Experimental Allergy ("Soybean beta-conglycinin as the main allergen in a patient with food-dependent exercise-induced anaphylaxis by tofu: food processing alters pepsin resistance." Clinical and Experimental Allergy, 2009;39(1):167-173).

Additional information can be obtained by contacting A. Adachi, Hyogo Prefectural Kakogawa Hospital, Dept. of Dermatology, 770-1 Awazu, Kakogawa 6758555, Japan.

From the February 16, 2009, Prepared Foods E-dition