Preparation Of Angiotensin-Converting Enzyme Inhibiting Peptides From Oat Protein With Utrasonic Assisted Zymohydrolysis

In recent years, the rapid growth of the number of hypertensive patients seriously affectes human health. Preparation of Angiotensin-converting enzyme (ACE) inhibiting peptide from food resource becomes a research hotspot recently owing to its natural and non-toxic side effects. In order to improve enzymolysis technology for preparation of ACE inhibiting peptides from oat-seed protein, the following researchs were carried out in this paper:Oat protein was extracted by tranditional method of the solubization with alkali and precipitation with acid, the purity of oat protein is 58.33%, and the extraction rate of oat protein is 60.73%.Six protein enzymes were selected for optimal one, and inhibition rate of ACE was determined. Alcalase protein enzymes showed the better inhibitory effect. The effects of hydrolyzation time, substrate concentration, enzyme amount, temperature and pH on inhibitory activity were studied by,orthogonal exp erimental design. The optimal hydrolysis conditions were obtained as follows:reaction temperature 50℃, reaction time 90min, enzyme amount 2%, substrate concentration 5%, pH value 9. Under the optimal conditions, half inhibiting concentration IC50 value for ACE of hydrolysates was 0.533 mg/mL.In order to study the influences of ultrasonic on the hydrolysis, two reaction models, which were the ultrasonic pretreatment of oat-seed protein solution followed by enzymolysis and the enzymolysis under ultrasonic irradiation, were investigated in preparation of ACE inhibiting peptide from oat-seed protein. Compared with traditional enzymatic hydrolysis without ultrasonic treatment, effects of ultrasonic power, ultrasonic time and the ratio of on-time and off-time were investigated when the inhibitory activity of ACE and degree of hydrolysis(DH) were taken as evaluation indexes, The results showed that both models have increased inhibitory activity of hydrolysate to ACE, but no influence on DH, and former is more significant. The optimum conditions of ultrasonic pretreatment were ultrasonic power 500W, ultrasonic pretreatment time 20 min and the ratio of ultrasonic on-time and off-time 2s/2s. Under the optimum conditions, half inhibiting concentration IC50 value of ACE decreased from 0.533 mg/mL to 0.299 mg/mL, and the time of enzymolysis reduced from 90 min to 60 min.ACE inhibiting peptides enriched by membrane ultra-filtration with MWCO of 10, 8,5 and 3 kDa, and ACE inhibiting rate was determined, it was found that high activity of ACE inhibitory peptides were mainly focused small molecular weight peptides, and the peptide with molecular weight less than 3kDa had the highest activity.Study on enzymolysis kinetic of oat protein with and without ultrasonic pretreatment, the Vmax and Km was determined. The Vmax has little change, but Km increased significantly. It was indicated that the influences of ultrasonic pretreatment on enzymatic reaction kinetics were achieved by the way of changing the affinity of enzyme to substrate.The enzymolysis kinetic equation model after ultrasonic pretreatment was established as following:The model has good fitting with test data, the average relative error was 7.05%.