TRYPSIN INHIBITORS OF RAW AND HEAT-TREATED SOYBEAN MEALS (ANHYDROTRYPSIN, AFFINITY CHROMATOGRAPHY)

Soybean proteins have experienced widespread use in human foods. The nutritional value of soybean protein products is improved by heat treatment and the trypsin inhibitors initially present are largely destroyed at the same time. In evaluating the effects of long term consumption of soy protein products, it is desirable to know how the population of trypsin inhibitors changes during the heating process. Affinity chromatography was used to isolate protein trypsin inhibitors from heat-treated soy flours where the residual inhibitors represent only about 10% of the original activity. These isolated inhibitors, together with soybean polysaccharides isolated by extraction procedures were analyzed for activity. About 1% of the total trypsin inhibitor activity of raw soy flour and as much as 10% of the toasted soy flour activity is attributable to the polysaccharides. Three protein trypsin inhibitors of raw flour account for half of the inhibitor activity and 8 trypsin inhibitors are responsible for 94% of the activity. Ten additional inhibitors account for the remainder. In toasted soy flour 38% of the total inhibitor activity is due to a single protein inhibitor. Three of the protein inhibitors account for 69% of the activity in toasted flour. The remaining 9 protein trypsin inhibitors found in toasted flour are responsible for nearly a third of the activity. During the toasting process, active Kunitz soybean trypsin inhibitor decreases from 1.8% of raw soy flour protein to only 0.57% of the toasted and 0.33% of overtoasted soy flour proteins. The Bowman-Birk inhibitor family comprises 0.38%, 0.04%, and 0.01% of raw, toasted, and overtoasted soy flour proteins, respectively. At the same time trypsin inhibitor artifacts, which appear as a result of the toasting process, increase to 0.21% and 0.40%, respectively, of toasted and overtoasted soy flour proteins. These artifacts do not appear as components of raw soy flour