Screening And Fermentation Characteristics On ACE Inhibitory Activity Of Lactic Acid Bacteria In Traditional Fermented Milk Of Tibet In China

In this paper, 44 samples of traditional fermented milk and lactic acid bacteria isolated from these samples were evaluated for ACE-inhibitory activity. Through preliminary screening, further screening experiments and optimization of fermentative conditions, three strains of Lactobacillus helveticus were screened out and fermented characteristics of these strains were investigated. The main results were as follows:Firstly, 9 samples with ACE-inhibitory activity above 70% were selected from 44 samples. ACE-inhibitory activity of these samples was negatively correlated with pH value, free amino nitrogen, protein content and titration acidity.Secondly, 29 strains of L.helveticus isolated from 44 samples were involved in screening by fermenting 11% skim milk for higher production of ACE-inhibitory peptides. 3 strains of L.helveticus IMAU60208, L.helveticus IMAU60201 and L.helveticus IMAU60210 were screened out for producing higher levels of ACE-inhibitory peptides. ACE-inhibitory activity of fermented milk by L.helveticus was positively correlated with titration acidity and contents of VPP and IPP (p<0.05).Thirdly, 29 non-L.helveticus-strains isolated from 9 samples with ACE-inhibitory activity above 70% were invoved in screening by fermenting 11% skim milk for higher production of ACE-inhibitory peptides. ACE-inhibitory activity of fermented milk by non-strains of L. helveticus was positively correlated with OD value and contents of VPP and IPP (p<0.05) and negatively correlated with pH value, free amino nitrogen and titration acidity.Finally, based on ACE-inhibitory activity , the optimal fermentation condition of these strains was determined to ferment 11% skim milk at 37℃with an inoculum of 5×106 cfu/g. During 48h fermentation, higher ACE-inhibitory activities of L.helveticus IMAU60208, L.helveticus IMAU60201 and L.helveticus IMAU60210 were observed at 12h, 24h and 24h, respectively. The highest concentration of VPP and IPP with three strains were 4.053 and 1.584μmol/L(30h) , 5.025 and 1.888μmol/L (30h), 4.171μmol/L (48h) and 1.407μmol/L (10h), respectively. It suggested that in the present study it can provide important consultation for further research of promoting ACE-inhibitory activity in fermented milk and antihypertensivefunction of Lactic acid bacteria. In addition, three strains of high ACE-inhibitory activity and production of VPP and IPP content were screened out for development of antihypertensive functional dairy products.