Breeding Of High-yielding Strains Of ACE Inhibitory Products Through The N~+ Implanting Into Lactobacillus Bulgarius

In organism many systems affect the blood pressure in which renin-angiotensin system and bradykinin-Kallikrein system are two important modulators for blood pressure control system. Angiotensin converting enzyme (ACE) plays an important regulatory role in these two systems, and ACE inhibitors can transform the angiotensinⅠ(AngⅠ) into angiotensinⅡ(AngⅡ). Currently, most drugs used to treat high blood pressure are synthetic ACE inhibitory peptides. The antihypertensive effect was significant, while the side-effects were also large. Although the antihypertensive effect of ACE inhibitory peptides attained from lactic acid bacteria are weaker than synthetic ACE inhibitory peptides, but it was much safer and has no side-effects for the people with normal blood pressure. Therefore, ACE inhibitory peptides from lactic acid bacteria have become the focus of research and development. It can achieve safety effect to lower the blood pressure.Experiment 1: This study compared the basic growth characteristics and ACE inhibition rates among nine strain lactobacillus Bulgaria in our laboratory. It was shown that the density, titratable acidity and biomass are very different of different strain curds. The ACE inhibitory activity among different strains was also different. It was also found that the four strains which can produce more ACE inhibitor show the common characteristic. That is they had a higher titratable acidity and good growth in the fermented milk.Experiment 2: We selected and bred lactobacillus Bulgaria through N+ implantation technique based on the ACE inhibition rate. We set five dose gradient (0.5, 1.0, 1.5, 2.0, 2.5×1015 ions/cm2) when the N+ implantation energy is 20 KeV. It is shown that the surviral rate of strains shows a "saddle shape" curve along with the increase of injection. Through the experiment, we established the best ion mutation parameters: energy of 20 KeV, a dose of 1.5×1015 ions/cm2. Under this condition, we obtained four strains: M601, M602, M603 and M606. At last, we obtained the high-yield strains M602-4-1 through the stability experiments.Experiment 3: We used the L9 (34) orthogonal experimental design to study high-yield strain M602-4-1. We studied the impact of different concentrations of skim milk, inoculums size, fermentation time and fermentation temperature upon the yield of the ACE inhibitory peptides, and we established the optimum culture conditions. We got an optimum culture medium MRS-N3 based on the growth characteristics of high-yield strains which grew in 5 different ratios of nitrogen culture-medium. Strains in this mediun grew better than in MRS medium.Experiment 4: The comparison of growth performance between mutagenesis high-yield strains M602-4-1 and starting strains M602 in biomass, titratable acidity, viscosity, and morphology. It was shown that high-yield strains have increased in biomass, titratable acidity and viscosity, and the morphous greatly changed after mutated.