Objective: To investigate if angiotensin converting enzyme inhilitory(ACEI) peptides would be produced from SPI digested by a batch digestion system using enzymes similar to digestive enzymes in humans.Method: Simulate the conditions of human gastrointestinal digestion in a model digestion system in vitro and produce soy peptides from SPI digested using pepsin and pancreatin.In addition to monitoring ACEI activity in the total soy protein digest,the possibility of generating soy peptide fractions with more potent activity than the unfractionated digest was investigated by measuring activity of fractions obtained after ultrafitration,anion exchange,and RP-HPLC.Results: The generation of ACEI activity in SPI was determined after sequential digestion with pepsin and pancreatin.The inhibitory activity was highest within the first 20 min at pepsin digestion and decreased upon subsequent digestion with pancreatin.An IC50 value of 0.28?0.06 mg/ml was determined after 180 min of digestion,while no ACEI activity was measured for the undigested SPI at 0.73 mg/ml.Chromatographic fractionation of the SPI digest resulted in IC50 values of active fractions ranging from 0.13?0.03 to 0.93?0.08 mg/ml.Conclusion: Many different peptides with ACEI activities were produced after pepsin-pancreatin digestion of SPI in vitro and lead to the speculation that physiological gastrointestinal digestion could also yield ACE inhibitory peptides from SPI.