Use of the pH Stat to Evaluate Trypsin Inhibitor and Tryptic Proteolysis of Soy Flours

Heated soy flours have been analyzed by the pH stat successfully for tryptic proteolysis and for residual trypsin inhibitor in previous studies. Unheated soy flours give a sudden release of hydrogen ion followed by a constantly decreasing proteolysis rate and consequently are difficult to analyze. We have found that by adjusting the pH of the trypsin preparation to 9 (the pH of the analysis) the pH stat method measured proteolysis and trypsin inhibitor in unheated soy flours. The unheated soy protein was hydrolyzed at 40% of the rate of heated soy protein and contained 68 mg/g of Kunitz trypsin inhibitor equivalents.