Identification of IgE-binding proteins in soy lecithin.
BACKGROUND
Soy lecithin is widely used as an emulsifier in processed foods, pharmaceuticals and cosmetics. Soy lecithin is composed principally of phospholipids; however, it has also been shown to contain IgE-binding proteins, albeit at a low level. A few clinical cases involving allergic reactions to soy lecithin have been reported. The purpose of this investigation is to better characterize the IgE-binding proteins typically found in lecithin.


METHODS
Soy lecithin proteins were isolated following solvent extraction of lipid components and then separated on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The separated lecithin proteins were immunoblotted with sera from soy-sensitive individuals to determine the pattern of IgE-binding proteins. The identity of IgE-reactive bands was determined from their N-terminal sequence.


RESULTS
The level of protein in six lecithin samples obtained from commercial suppliers ranged from 100 to 1,400 ppm. Lecithin samples showed similar protein patterns when examined by SDS-PAGE. Immunoblotting with sera from soy-sensitive individuals showed IgE binding to bands corresponding to 7, 12, 20, 39 and 57 kD. N-terminal analysis of these IgE-binding bands resulted in sequences for 3 components. The 12-kD band was identified as a methionine-rich protein (MRP) and a member of the 2S albumin class of soy proteins. The 20-kD band was found to be soybean Kunitz trypsin inhibitor. The 39-kD band was matched to a soy protein with unknown function.


CONCLUSIONS
Soy lecithin contains a number of IgE-binding proteins; thus, it might represent a source of hidden allergens. These allergens are a more significant concern for soy-allergic individuals consuming lecithin products as a health supplement. In addition, the MRP and the 39-kD protein identified in this study represent newly identified IgE-binding proteins.
Gu
X
X
Department of Food Science and Technology, University of Nebraska, Lincoln, NE 68583-0919, USA.
Beardslee
T
T
Zeece
M
M
Sarath
G
G
Markwell
J
J
D000293:Adolescent; D000485:Allergens / Q000276:immunology*; D000936:Antigen-Antibody Complex / Q000276:immunology; D002648:Child; D005260:Female; D006801:Humans; D006967:Hypersensitivity / Q000276:immunology*; D015151:Immunoblotting; D007073:Immunoglobulin E / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D010713:Phosphatidylcholines / Q000276:immunology*; D030262:Soybean Proteins / Q000276:immunology; D013025:Glycine max / Q000276:immunology*
D000485:Allergens; D000936:Antigen-Antibody Complex; D010713:Phosphatidylcholines; D030262:Soybean Proteins; D007073:Immunoglobulin E