Study On The Lactic Acid Bacteria Fermented Milk With Angiotensin Converting Enzyme Inhibitory Effect

Angiotensin-converting enzyme (ACE,EC 3.4.15.1) plays a dual role in the regulation of hypertension in the system of Renin-Angiotensin System(RAS) and Kinin-Kallikrein System(KKS). It can catalyze the production of the vasoconstrictor angiotensin II and inactivate the vasodilator bradykinin. By inhibiting these processes, ACE inhibitors have antihypertensive effects. Peptides derived from milk proteins can have ACE-inhibiting properties and may thus be used as antihypertensive components.By their proteolytic activity in growing in milk, lactic acid bacteria can release the ACE inhibitory peptides to reach the antihypertensive goal.Initially, the angiotensin-I-converting enzyme(ACE) inhibitory activity of fermented milk by 61 strains of lactic acid bacteria was investigated.The results showed that the ACE inhibitory activities were obviously different among the 61 LABs ,and bactobacillus'ACE inhibitory activities were much higher than the bifidobacterium's and coccus'. The acid-productivity of LAB had no correlation with ACE inhibitory activity(Spearman's rank correlation rs=0.422,p<0.05), while the proteolytic activity had a positive relation with ACE inhibitory activity(Spearman's rank correlation rs=0.827,p<0.05). It had also been found that both L.helveticus 6024 and L.helveticus T16 strains with the highest ACE inhibitory rate had the strong acid-productivity and proteolytic activity .The growth and ferment properties were studied for making L.helveticus 6024 into use.The best culture and conditions for multiplicating L.helveticus 6024 had been found as follows: adding milk protone as nitrogen source for MRS, adding 0.5% of L-Cysteine Hydrochloride Monohydrate, optimal temperature 39℃, optimal initial pH 6.5～7.0.It was found that it began logarithmic stage and maximum growth at 3h and 14h,respectively,which was 9.5×108cfu/mL.It was also found that the ferment speed and post acidification had no obvious effects on the ACE inhibitory antivity,while the content of RSM powder had an obvious effects on the ACE inhibitory activity : the content of RSM powder between 4% and 8% had a comparative high ACE inbitory activity which could reach 74.6% when fermenting 12h at 37℃.The quality shares of the fermented milk color,flavor and texture were calculated as 0.254,0.402 and 0.344,respectively , by analyzing the data from the 8 kinds of fermented milk in market .Then associatied with the L.helveticus 6024 and starter fermented milk objective qualities STS,WHC and AV , a preliminary quality evaluating system was established. By the system and orthogonal experiment, the otimum conditions of fermenting were as follows: inoculated 4%, inoculation proportion of the starter and L.helveticus 6024 was 1:2 , added 9% sucrose and 4‰denaturalized starch . The ACEI% of this functional sour milk could reach 48.2%.