Angiotensin I-converting Enzyme Inhibitory Peptides Derived From The Enzymatic Digest Of Soybean Protein

Soybean contains about 40%protein with well-balanced amino acid and enough essential amino acid.In China the soybean resources are abundant and the price is low.Therefore,the study and utilization of soybean protein isolates have been drawn scientist's much attention. Soybean peptides(SP) are compounds with small molecular weight obtained from hydrolysis of soybean protein isolates.Studies showed that SP were superior to soybean protein isolates in both nutritional value and physiological functions.Compare to soybean protein,soybean peptides do not show fishy smell,would not be denatured,deposited in acid solution,flocculated by heat,and is more soluble,etc.Moreover,the soybean peptides show many biological function such as lowering blood pressure,which suggest the potential use of soybean peptides to prevent angiocardiopathy and related disease.Therefore,the preparation of soybean protein isolates and procedure of ACEI production from soybean protein were studied systematically in this work.In the present study,we did not use soybean protein isolates from market because they contan additivesand many other unknown factors that would bring uncontrollable factors in soybean powder hydrolysis.Soybean protein isolates were prepared through dissolving the soybean proteins with alkali and depositing with acid.Optimumized extraction conditions were obtained after single-factor experiments based orthogonal experiment.That is 1:40 for the ratio of solid to liquid,40~C for reacting temperature,and the reaction would be conducted under pH9.0.Then the physico-chemical parameters,amino acids and thermal denaturation temprture of the product were determined.Four type of enzymes,Alcalase,Neutrase,Protames,Flavourzyme,were used to hydrolyze prepared soybean protein isolates and degree of hydrolysis(DH) were analyzed using pH-start method,respectively.ACE inhibitory activity of the product were studied by HPLC.The results showed that hydrolysis ability of these enzyme is Alcalase＞Protames＞Neutrase＞Flavourzyme; The ACE inhibitory activity of product form Alcalase is the best.Optimum process for producting ACE inhibitory peptides using Alcalase was temperature 60℃,pH8.0,[S]=4%, [E]/[S]=4%,DH%=14.4%.The hydrolysate were debittered using Flavourzym.This precedure, however,also induce decrease of ACE inhibitory of the hydrolysate and is not suitable.The amino acids show just a little change after hydrolysis,suggeest that Alcalase hydrolysis is milder, saftier and has no side-effect than other chemical method.