Preparation, Isolation And Modification Of Casein ACE Inhibitory Peptides

The resources of milk protein are abundant in China. They not only have a highnutritional value, but also an important source of various bioactive peptides. In particular,casein angiotensin-converting enzyme (ACE) inhibitory peptides have aroused scientists’attention increasingly due to its economy and safty. In this paper, casein was hydrolyzed bytwo steps and the peptides with high ACE inhibitory activity were obtained throughseparation and amino acid sequence determination. The casein hydrolysate after desalinationwas then modified by Maillard reaction for the further improvement of ACE inhibitoryactivity.The conditions of two-step hydrolysis were obtained through response surfaceexperiment. The optimal conditions of fist step hydrolysis were: Neutrase1.5MG,[S]=50mg/mL, t=60min, T=49°C,[E]/[S]=2.9%(w/w), pH=7.1. The optimal conditions of secondstep hydrolysis were: Alcalase2.4L, t=120min, T=64°C,[E]/[S]=2.5%(w/w), pH=9.2.According to this conditions, the DH of hydrolysate was20.71%, the IC50of ACE inhibitoryactivity was0.32mg/mL and the peptides ratio of molecular weight distributed between180Da～1000Da was80.08%. These results indicated that two-step hydrolysis of casein couldproduce the peptides with high ACE inhibitory activity and low molecular weight effectively.Then casein hydrolysate was purified by macroporous adsorption resin, gel filtrationchromatography, RP-HPLC and LC-ESI-MS/MS, four ACE inhibitory peptides LY, WKQ,WQV and LQSW were obtained, the IC50were23.8,48.5,40.8and28.0μg/mL, respectively.The wet-heating and dry-heating Maillard reactions were used respectively to modifydesalting casein hydrolysate. The optimal conditions of wet-heating Maillard reaction were:xylose/peptides=2:1, T=110°C, t=2h, pH=9.0, peptides concentration=50mg/mL, the ACEinhibitory activity was75.12±1.46%(0.2mg/mL). The optimal conditions of dry-heatingMaillard reaction were: xylose/peptides=1:1, T=50°C, t=12h, pH=8.0, relativehumidity=69%, the ACE inhibitory activity of was61.20±1.86%(0.2mg/mL). The resultsindicated that Maillard reaction under appropriate conditions could improve ACE inhibitoryactivity of casein hydrolysate, and wet-heating method was particularly significant.Lastly, the structure and property of MRPs were analysised. Comparing to dry-heatingMRPs, wet-heating MRPs has a deeper color and reaction degree. These two MRPs all have agood gastrointestinal digestion, heating and acid/alkali resistance.Therefore, this study obtained four ACE inhibitory peptides and improved the ACEinhibitory activity of casein hydrolysate through Maillard reaction. The new thought wasprovided for development of casein antihypertensive peptides products.