Abstract: In this research, difference soybean peptides were prepared by hydrolyzing soybean protein isolate with alcalase, pepsin, trypsinase,p apaina ndn eutrase respectively,a ndt hed ifference oft heira ngiotensinc onverting enzyme (ACE)i nhibiting activities was studied. Comparison experiments on peptides increments, relationship between degree of hydrolysis (DH) and ACE inhibitoryr ate, relation betweenu ltrafiltrateo fp eptidesa ndA CEi nhibitoryr atea nde lectrophoretics eparation werec onducted. The result showed that the peptides increments by alcalase hydrolysis were the largest, and the sequent order in turn was pepsin >papain>neutrase, but trypsinase was abnormal. The degree of hydrolysis (DH) increased with prolongation of time. The biggest Dh of alcalase was 21%, and the sequent order in turn was pepsin>papain>neutrase, but trypsinase was only 9%. ACE inhibitory rate of alcalase, pepsin, papain, neutrase and trypsinase hydrolysates at the biggest DH, were 44.9%, 43.5%, 23.1%, 23.5% and 15.7% respectively. Peptides with above 1000 daltons molecular weight have the strongest inhibitory effects on ACE. Small molecular peptides by alcalase and pepsin amounted for 71.3% and 69.4% of all the peptides respectively, and the ACE inhibitory rate of the small molecular peptides by alcalase, pepsin, papain, neutrase and trypsinase were 64.57%, 78.49%, 47.3%, 45.7% and 29.6% respectively. So it can be concluded that papain was optimum for ACE inhibiting peptide preparation among 5kinds of protease, and the sequent order in ture: alcalase>papain>neutrase>trypsinase.

Key words: soybean protein isolate, protease, angiotensin converting enzyme(ACE) inhibitor, ultrafiltration