Development of β-conglycinin quantitative method in soybean foods using capillary electrophoresis-based immunoassay

β-Conglycinin (β-CG), a major soy protein, has been associated with the reduction of body fat and triglycerides in the blood. Quantitation of the α, α′, and β subunits in β-CG is desirable to establish the functional properties of β-CG in soybean. Therefore, in this study, we used the Jess System, a capillary electrophoresis-based immunoassay system, for quantifying β-CG in soybean foods. The validity of this method was confirmed using soybeans and processed soy milk. The within-laboratory reproducibility of the total β-CG amount was < 15 %, and its trueness was > 80 %. The β-CG content in the commercially available soybeans, Kori-tofu, soy milk, soy yogurt, Okara powder, and soy meat was determined to be 40.3–148.5, 65.2–97.2, 6.1–7.8, 3.5, 18.0, and 57.5 mg/g, respectively. For the first time in the literature, this method enables the quantitation of individual subunits of β-CG, despite the large variation in the amount of each subunit.