Changes in activity, antigenicity, and molecular size of rice bran trypsin inhibitor by in vitro digestion.

Rice bran trypsin inhibitor (RBTI) was digested by pepsin alone or by pepsin and pancreatin with or without bovine serum albumin (BSA) to clarify the changes in trypsin inhibitory activity, apparent antigenicity, and molecular size of RBTI. In vitro pepsin digestion of RBTI in the absence of BSA caused the gradual loss of the trypsin inhibitory activity and antigenicity. This was mostly due to a progressive degradation of the native 14.5-kDa RBTI molecule to small molecular mass products. The presence of BSA in the digestion mixture prevented the RBTI degradation and was accompanied with a considerable protection of the activity and antigenicity. Similar results were also given by in vitro pepsin-pancreatin digestion. These findings suggest that RBTI may be present in its active form in the gastrointestinal tract when fed to animals, especially with a dietary protein.