Quantitative determination of active Bowman-Birk isoinhibitors, IBB1 and IBBD2, in commercial soymilks

•Isolation of major serine protease inhibitors, Bowman-Birk and Kunitz, from soybean.•Quantification of active Bowman-Birk isoinhibitors from soymilk.•Significant variation in amounts of Bowman-Birk inhibitors among soymilks.•Physiologically relevant amounts of active Bowman-Birk inhibitors in soymilks. Naturally-occurring serine protease inhibitors of the Bowman-Birk family exert their potential chemopreventive and/or therapeutic properties via protease inhibition. In this study, we have quantified the amounts of active BBI isoinhibitors, IBB1 and IBBD2, in six commercial soymilks. By using cation exchange chromatography, the BBI isoinhibitors were isolated and their specific trypsin inhibitory activity was used to estimate their amounts in soymilk samples. IBB1 and IBBD2 concentrations ranged from 0.44 to 5.20 and 0.27 to 4.60mg/100ml of soymilk, respectively; total BBI, considered as the sum of both isoinhibitors, ranged from 0.60 to 9.07mg/100ml of soymilk. These data show that physiologically relevant amounts of active BBI are present in commercial soymilk and may exert potential health-promoting effects.