COMMERCIAL SOYBEAN LECITHINS - A SOURCE OF HIDDEN ALLERGENS

Soybeans are known to be allergenic for adults as well as for infants. Processed products derived from soybeans are used in a wide spectrum of foods, drugs and other industrial products. In particular, soybean lecithins are used as stabilizers and emulsifiers and may not be suspe cted as possible source of allergens. To test this hypothesis, six com mercial soy lecithins were investigated for residual allergenicity and compared with extracts from raw and heat-treated soybeans. They were characterized, the protein content was determined by enzyme-linked imm unosorbent assay (ELISA) and allergens were analyzed with specific IgE from patients' sera using the enzyme allergosorbent test (EAST), EAST inhibition and protein blotting followed by immunodetection. For furt her characterization a polyclonal antiserum directed against soybean e xtract and a monoclonal antibody (mAb 025) directed against the acidic subunit of the soybean storage protein glycinin were used. The EAST s tudies revealed that three of six sera from patients with allergy to s oybeans contained IgE to four soy lecithins (Topcithin 50, Topcithin 3 00, Emulfluid FD 12, Epikuron 100 I'), the same lecithins which were f ound to contain residual proteins. Two lecithins with a protein conten t of less than 20 ppb did not bind IgE. EAST inhibition showed that th e allergens from soy lecithin were immunologically more closely relate d to allergens from heat-treated soybeans than to those from raw soybe ans. Protein blotting and immunodetection of the protein extract from the lecithins resulted in various allergen bands between 14 kDa and 94 kDa. A heat-stable allergen of 39 kDa was recognized by the monoclona l antibody and thus identified as a subunit of glycinin. The results o btained were confirmed by a mediator release assay based on a rat baso phil leukemia cell line. Lecithins that contained residual proteins ca used a specific mediator release, suggesting that these products may i nduce allergic symptoms. Our results show that soybean lecithins are c apable of introducing hidden allergens to processed foods and that the IgE binding potential corresponds to the total protein determined by ELISA. Furthermore, it appears to be possible that by monitoring the p rotein content soy lecithins can be applied which may be safe for the allergic consumer.