Soybean is used in processed foods worldwide. Because soybean can cause adverse reactions in some atopic
patients, appropriate labeling regarding its content in processed foods is needed to better protect consumers. In the
previous study, we developed a reliable sandwich Enzyme Linked Immunosorbent Assay (ELISA) method with high
sensitivity and specificity for detecting soybean proteins by using antibody to Gly m Bd 30K, which was originally
characterized as a vacuolar protein with a molecular mass of 34 kDa in soybean. The ELISA displayed satisfactory
repeatability and reproducibility in an interlaboratory evaluation. However, it could not detect soybean protein in
fermented soybean products. We therefore developed an extraction method combined with a heating process to inhibit
soybean protein degradation by microbial proteolytic enzymes in fermented soybean products. This extraction method
enables the sensitive detection of soybean protein in fermented soybean products such as natto and miso. It was able to
detect with high-sensitivity soybean protein present at 10 μg/g levels in model processed foods. This method is suitable
for quantifying soybean protein in processed foods without the degrading effects of microbial proteolytic enzymes. The
present extraction method can be used sensitively to monitor labeling systems in a reliable manner and should be useful
for the mandatory inspections required under Japanese regulations