Evaluating ACE Inhibitory Activity Of Soybean Protein Isolate Hydrolysateby Simulated In Vitro Gastrointestinal Digestion Model

In order to explore whether the angiotensin-converting enzyme(ACE) inhibitorypeptides can keep their original ACE inhibitory activity or notafter digestiionbygastrointestinal tract enzymes, we used simulated in vitro gastrointestinal digestion model toevaluate the changes of ACE inhibitory activities of soybean peptides prepared by enzymatichydrolysis and fermentation.Firstly, the soybean protein hydrolysates with different degree of hydrolysis wereprepared using soy protein isolate(SPI) as raw material and Alcalase protease as catalyzer,their ACE inhibitory activities were further evaluated before and after simulated in vitrogastrointestinal digestion. The results show that the molecular weight of SPIH were graduallysmaller, theTCA-soluble protein content of SPIH increased, and ACE inhibitory activitiesenhanced significantly during the hydrolysis for1h,2h and3h by Alcalase protease; Aftersimulated in vitro gastrointestinal digestion, all the ACE inhibitory activities of SPIHdecreased, while the activities of SPI increased, so both of them has no significant difference,indicating that it may be not necessary to prepareACE inhibitory peptides functional foodbyAlcalase enzymatic hydrolysis method.Secondly, the soybean protein hydrolysates were prepared using high-temperaturesoybean meal (HSM) as raw material and Alcalase protease as catalyzer, their bitterness valueand ACE inhibitory activities were further evaluated after embedding withα-Cyclodextrins(α-CD) andβ-Cyclodextrins(β-CD) and followed simulated in vitro gastrointestinal digestion.The results showed that the HSMH with the ACE inhibitory activity of78.85%can be madeunder the conditions as followed:Alcalase protease1500U/g, temperature50℃, pH value8.5and the substrate concentration4%.Compared to SPIH, HSMH contained18.86%carbonhydrate, the bitterness value was significantly lower, while the ACE inhibitoryactivities still had no changes after simulated in vitro gastrointestinal digestion, indicatingthat there may be a certain substance in HSMH which was able to protect them from furtherdigestion and mask the bitterness more effective than α-CD and β-CD.Finally, soybean yogurts (SY) were prepared by fermenting soybean milk (SM) withstarter culture1(Lactobacillus Casei-01，Lactobacillus Helveticus-B02) and starter culture2 （Lactobacillus subsp. cermoris, Lactococcus lactics subsp. lactis, Leuconostocmesenteorides subsp. cremotis, Lactococcus lactis subsp. lactis biovar siacetylactis，Streptococcus thermophilus）respectively, then their properties and ACE inhibitory activitiesafter simulated in vitro gastrointestinal digestionwere analysed. The results showed that thetwo starter culturesall hadthe ability toproduce acid, the number of viable total Lactobacillusbacterium countreached1×106cfu/mL,7S globulin of SY was hydrolysed significantly.After simulated in vitro gastrointestinal digestion, the ACE inhibitory activitiesof SY werenearly equal to that of SM, implying the fermentation of SM had no significant impact on theACE inhibition activities, more over, the food ingredients in SY had no protective effect too.