Angiotensin I-Converting Enzyme Inhibitory Activity of Soy Protein Digests in a Dynamic Model System Simulating the Upper Gastrointestinal Tract

Abstract

The objective of this study was to investigate whether peptides with inhibitory activity against angiotensin I-converting enzyme (ACE) would be produced by digestion of isolated soy protein (ISP) in a dynamic model system simulating gastrointestinal conditions. Using the model system, 5% ISP solution was pumped into the stomach reactor containing pepsin and HCl. The peptic digest was continuously pumped into the duodenum reactor containing pancreatin and Oxgall bile. The effects of blanching (100 °C, 10 min) followed by pasteurization (75 °C, 15 s) or sterilization (121 °C, 20 min) of ISP before digestion on the inhibitory activity were also investigated. During the first 30 min of digestion, significantly higher (P < 0.05) ACE-inhibitory activity was generated from unheated ISP after sequential digestion in both reactors compared with after peptic digestion only in the stomach reactor. However, at 90 min, subsequent digestion by pancreatin of unheated and blanched-sterilized ISP decreased ACE-inhibitory activity compared with peptic digestion alone. The IC 50 values at the end of 90 min digestion in both reactors were 0.38 ± 0.01, 0.37 ± 0.02, and 0.44 ± 0.02 mg/mL for unheated, blanched-pasteurized, and blanched-sterilized ISP, respectively. The results suggest the potential production of peptides with ACE-inhibitory activity upon physiological digestion of soy protein, including products that have been subjected to heat processing. Although clinical trials would be required to provide final evidence of efficacy of the soy peptides, the present findings support the application of soy protein as an ingredient for functional foods.