Lunasin and Bowman-Birk protease inhibitor (BBI) in US commercial soy foods

The inverse association between the intake of soybean foods and cancer incidence and mortality rates supported by published literature has led to studies on identifying bioactive components. The cancer preventive properties of the soybean peptides lunasin and Bowman-Birk protease inhibitor (BBI) have been demonstrated by in vitro and in vivo assays. Since there is no comprehensive information on the concentrations of these two peptides, US commercially available soy foods, including soy milk, soy-based infant formula, tofu, bean curd, soybean cake, tempeh, natto, miso and su-jae samples, were analyzed for lunasin and BBI. Both peptides were present in most of the products, in varying concentrations, depending mainly on the soybean variety and the manufacturing process. Lunasin and BBI were absent in the fermentation products natto and miso, suggesting that fermentation destroys both peptides. To study the bioavailability of lunasin and BBI, three soy milk samples with different concentrations of these peptides were subjected to an enzymatic hydrolysis process simulating physiological digestion. The results confirm the important role BBI plays in the protection of lunasin from digestion by pepsin and pancreatin.