Soybean Trypsin Inhibitor Activity - a review

Soybean (Glycine max) is one of the most important source of protein for food and feed globally. Complete utilization of protein in human and animal digestion can be reduced by certain trypsin inhibitory (TI) substances present in fresh soybeans. Two classes of protease inhibitors (polypeptides) are found in soybeans: Kunitz trypsin inhibitor (KTI) and Bowman-Birk trypsin inhibitor (BBI). KTI is primarily responsible for its trypsin inhibitory activity, while BBI has been reported to have nutraceutical properties. The content of TI in soybean depends on the soybean genotype, environmental factors and/or applied technology, especially nitrogen fertilization. The content of TIA in soybeans can be between 18.6 and 74.8 mg inhibited trypsin/g soybean meal, with an average value of 45.9 mg. Genotypes with values above 12 mg/g flour can be called "high KTI" genotypes, and those with content below 6 mg/g flour can be called "low KTI". Researchers have studied the possibilities of reducing these inhibitors. Of these, the most used are thermal methods (boiling, autoclaving, microwave treatment and heating in the oven), but also germination-sprouting leads to a decrease in TI and also fermentation. In this review we present the most important results in the determination of trypsin inhibitors and ways to reduce their content.