Cereal Chem 46:518 - 526.  |  VIEW ARTICLE
An Evaluation of Natural vs. Synthetic Substrates for Measuring the Antitryptic Activity of Soybean Samples.

M. L. Kakade, N. Simons, and I. E. Liener. Copyright 1969 by the American Association of Cereal Chemists, Inc. 

The casein digestion method of Kunitz for the measurement of trypsin inhibitor activity of soybean extracts has been modified to obtain more accurate and reproducible results. The modification involved the use of 2% casein (instead of 1%) and the mathematical transformation of absorbance readings (A) at 280 millimicrons to A3/2. The use of the synthetic substrate, benzoyl-DL-arginine-p-nitroanilide (BAPA), proved to be a convienient and reliable method of assaying trypsin inhibitor activity provided one takes into account the competitive nature of the inhibition. The latter effect could be largely compensated for by extrapolating the trypsin inhibitor activity, expressed as trypsin units inhibited per ml. extract, to zero concentration of the inhibitor. Although a series of soybean samples could be ranked in the same relative order of inhibitor activity by using either casein or BAPA, the quantity of trypsin inhibited was consistently higher when BAPA was employed as the substrate.