Changes in activities and contents of two protease inhibitors (Kunitz trypsin inhibitor and Bowman-Birk inhibitor) in soybeans during heating processes

Authors: Liu, Keshun; Woolman, Michael

Submitted to: World Congress of Food Science and Technology
Publication Type: Abstract Only
Publication Acceptance Date: 9/10/2024
Publication Date: 9/10/2024
Citation: Liu, K., Woolman, M.J. 2024. Changes in activities and contents of two protease inhibitors (Kunitz trypsin inhibitor and Bowman-Birk inhibitor) in soybeans during heating processes. World Congress of Food Science and Technology. Session 3.20, Nutrition & Health, Alternative Proteins 4. https://iufost2024-italy.com/scientific-program-and-speakers/.

Interpretive Summary:

Technical Abstract: Soybeans (Glycine max) contain about 40% protein and 20% oil and have been the most valuable legume and oilseed for food and feed. Yet, the natural presence of two proteinase inhibitors in soybeans, namely Kunitz trypsin inhibitor (KTI) and Bowman-Birk inhibitor (BBI), exert antinutritional effects. Therefore, for food or feed, raw soybeans must undergo a heating process to inactivate the inhibitors. There are two parameters of interest when we describe protease inhibitors in soybeans and other proteinaceous materials. One is inhibitor activity, and the other is inhibitor concentration. It is the content of a reactive inhibitor that determines its inhibitory activity toward a protease. Historically, trypsin inhibitor activity in soybeans and soy products has been the primary interest for measurement. However, such measurement does not differentiate KTI from BBI in any way because both inhibit trypsin. Recently, at our USDA laboratory, a new methodology was developed and reported elsewhere, for measuring both protease inhibitor activity and contents of the two inhibitors. In this presentation, we report a new study where soybeans were heated by boiling, steaming and oven toasting. Changes in protease inhibitory activities and contents of two inhibitors were monitored with heating time. It was found that the pattern of changes in these parameters with heating time varied with heating method. Yet, regardless of this difference, by any of the three heating methods, trypsin inhibitor activity decreased faster than chymotrypsin inhibitor activity, and KTI was inactivated faster than BBI. The last two observations mutually explained each other. It was concluded that unlike raw soybeans, BBI can be a major protease inhibitor in heated soybeans.