Preparation Of Angiotensin Ⅰ Converting Enzyme Inhibitory Peptides From Whey Protein By Protease Hydrolysis

Angiotensin-1 -converting enzyme(ACE) plays an important physiological role in regulating blood pressure. ACE converts an inactive form of decapeptide, angiotensin I , to a potent asoconstrictor, octapeptide angiotensin II, and inactivates bradykinin, which has a depressor action. Currently, many ACE inhibitors have been used as antihypertensive agents. In the present study, the ACE inhibitory peptides were prepared from whey protein with protease hydrolysis.A reliable assay method of ACE inhibitory peptides with high accurance and repeatability was modified and established, and it can be used to determine the ACE inhibitory activities of all kinds of samples.Taking ACE inhibitory activity as index, after screening of several commercial proteases, alcalase was used to hydrolyze whey for production of ACE inhibitory peptide.Taking ACE inhibitory activity and the degree of hydrolysis as indexes, orthogonal rotational regression design was used to optimize the hydrolysis conditions of whey protein with alcalase. The optimal hydrolysis conditions of whey were: temperature 50℃, substrate concentration 5%, enzyme to substrate ratio 5.5%, hydrolysis time 6 hours. In these conditions, whey hydrolysates IC₅₀ was 0.97mg/mL,Ultrafiltration was applied to isolated ACE inhibitory peptides.The optimal ultrafiltration condition for 6KDa membrance was at 20°C with pressure 0.1 MPa. After ultrafiltration the ACE inhibitory activities of the permeates and potentates separately increased 34% and 19.58%.Salt was removed by ion exchange resin at a flow rate of 50r/min with desalinization rate of approximate 80% and nitrogen recovery rate of 90%. No differences were observed on the ACE inhibitory activity of samples.An optimum processing technology of ACE inhibitory peptides was established as : whey→hydrating→protease hydrolysis→hydrolysate →desalinization by ion exchange resin→freeze drying→ACE inhibitory peptides. In this processing technology, high ACE inhibitory activities and low protein loss were obtained with direct desalinization of whey hydrolysates.