Immunoassays for Bowman–Birk and Kunitz Soybean Trypsin Inhibitors in Infant Formula

Because the consumption of soybean inhibitors of digestive enzymes in processed foods may have both beneficial and adverse health-related effects, reliable and rapid analytical methods for these inhibitors are needed. Monoclonal antibody–based sandwich enzyme-linked immunosorbent assays (ELISAs) were developed for the 2 major soybean protease inhibitors, the Kunitz trypsin inhibitor (KTI) and Bowman-Birk inhibitor (BBI) of trypsin and chymotrypsin. The ELISAs had limits of quantification of approximately 1 and 3 ng/mL for BBI and KTI, respectively, and were used to measure active inhibitors in soy infant formulas. Results were compared with enzymatic analyses and demonstrated that most of the trypsinand chymotrypsin-inhibitory activities of infant formula were due to constituents other than KTI and BBI. The sandwich ELISA for BBI was also effective in detecting soybean germplasm with atypically low levels of BBI.