Antigenicity of the proteins in soy lecithin and soy oil in soybean allergy

Background Soy lecithin and soy oil are usually produced from the hexane ex tract of soybean. Some of the soybean proteins are included in the extract and are therefore present in small amounts in both soy lecithin and soy oil . The antigenicity of the proteins present in defatted soybean has been stu died with respect to soybean allergy, but the antigenicity of those found i n the extract is yet to be investigated. Objective The antigenicity of soy lecithin and soy oil proteins with regard to soybean allergy were investigated. Methods The proteins present in soy lecithin and soy oil were determined ac cording to already established method and analysed by SDS-PAGE. The IgE- an d IgG4-binding abilities of the soy lecithin proteins were investigated by immunoblotting with sera from 30 soybean-sensitive patients, including seve n with a positive challenge test. Immunoblotting of soy oil proteins was pe rformed with the sera from some of these patients. Results In 100 g of sample, the soy lecithin and soy oil contained 2.8 mg a nd 1.4-4.0 mu g of proteins, respectively. The results of SDS-PAGE demonstr ated the presence of only three proteins, with molecular weights of about 5 8-67 kDa in soy oil, and suggested that soy lecithin also contains these pr oteins. The soy lecithin also contained many proteins besides these. In the soy lecithin, the detection rate of only one protein, with a molecular wei ght of 31 kDa, by the serum IgE of patients was significantly different com pared with controls (detection rate: 40%). The proteins with molecular weig hts of 58-67 kDa rarely bound to serum IgE. Only one of the patients who pr esented a positive challenge test had IgE antibodies to soy lecithin protei ns. IgG4-binding proteins were found only rarely in soy lecithin. Neither t he IgE nor the IgG4 present in the patients' sera reacted to any soy oil pr otein. Conclusion Proteins present in soy lecithin and soy oil have little antigen icity with regard to soybean allergy.