Detection of soybean proteins in fermented soybean products by using heating extraction

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.

The extraction and ELISA methods that we developed enable sensitive detection of soybean protein in soybean products, including fermented foods. These methods should be useful for reliable and sensitive monitoring of product labeling systems and should help to solve the problem of insensitive in soybean labeling of processed foods.