Contribution of Trypsin Inhibitors to the Deleterious Effects of Unheated Soybeans Fed to Rats

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Abstract
The trypsin inhibitors present in a crude extract of unheated soybean flour were selectively removed by passage through a column of Sepharose-bound trypsin. This inhibitor-free extract was fed to rats at a level of 10% protein and evaluated with respect to protein efficiency ratio (PER), weight of the pancreas, and protein digestibility. A comparison was made with the original extract from which the inhibitor had not been removed, both in its native and heated states. From the results obtained it could be concluded that approximately 40% of the growth-depressing as well as 40% of the pancreatic hypertrophic effect of the original unheated extract could be accounted for by the trypsin inhibitors. No differences in the digestibility of the protein in vivo were observed as a consequence of the removal of the inhibitor or by heat treatment. In vitro digestion studies, however, showed that the trypsin inhibitors accounted for only about 40% of the increased resistance of the protein of the original extract to attack by trypsin. It is believed that the reduced PER and pancreatic hypertrophy that persist in the absence of the trypsin inhibitor is primarily due to the refractory nature of native protein to attack by trypsin unless denatured by heat treatment.