Purification of soybean Kunitz trypsin inhibitor and the mechanism of its passivation by lysine and disulfide bond modifications

Soybean trypsin inhibitor(STI)was selectively recovered from soybean whey, a by-product of soybean protein production, by ammonium sulfate salting and the STI was purified up to 5.46-fold (Compared to STI in soybean whey). After purification with a Superdex 75 increase gel filtration preloader column, a 91.5% electrophoretically pure soybean Kunitz trypsin inhibitor(SKTI)was obtained by optical density analysis with a purification ploidy of 33.32-fold and a specific activity of 1072.9 U/mg, and a single band protein with a molecular weight of 20 kDa on SDS-PAGE. SKTI's 85.65% inhibitory activity was maintained after heating at 80 degrees C for 30 min, and there was no significant change in inhibitory activity in the range of pH 3-10. The secondary structure of SKTI did not change with temperature and pH showing good stability. By chemical bond modification of SKTI, the activity of SKTI was found to have an important connection with lysine and disulfide bond. This study set up a process for the rapid preparation of STI by salinization and the related properties of SKTI was explored to provide more potential for the treatment of soy protein production waste and the application of STI in the food field in the future.