| It is significant to study the downstream bioengineering technology of lactic acid bacteria (LAB), which is full of theoretic significance and wide prosperity. Biotechnological characteristics, high-density cultivation, concentrated cultures production and their theories, new products development, etc. were studied here systemically with 28 strains thermophilic LAB and 8 strains mesophilic lactococcus. The results were following:There were different lactose transport lactose metabolism systems and relative enzymes which affected their growth in milk between thermophilic LAB and lactococcus. Maximal acid production amount and acid production rate were different distinctly between the two kinds of lactic acid bacteria. Proteolysis capacities of LAB contributed to their proliferation in milk. LA32 was screened with good therapeutic properties.The plasmid of 23kb was found in the Lac. delbrueckii ssp. bulgaricus (LDB). L. acidophilus (LA) and L. lactis ssp. lactis (LLL). The plasmid of 28kb was also found in the L. lactis ssp. lactis. It is important to study the natural plasmids of LAB for constructing food grade vectors and molecular breeding of LAB strains with good characteristics.Based on single factor experiments and biological characteristics of LAB, a new culture medium suitable for high-density cultivation of LDB was designed. The pH value internal-controlled whey-based culture medium was more nutritious and better buffering capacities than MRS and milk medium for LDB growth. Specific growth rate of LDB in the optimum medium was 0.9218 h-1, its shortest generation time was 38.79 min.Using Logistic equation as cell growth kinetics model, the kinetics equation for LDB in fed-batch cultivation was Cx(t)=0.2503 e0.3847t/ {1- (0.2503/3.628) (1-e03847')} ;theone for LLL in fed-batch cultivation was Cx(t)=0.2472 -e020921/ {l-(0.2472/2.128)(1- e0.2092t) }.It provided a theoretic model for magnification of experiments industrial production , optimization of the process.At 42 ℃, the specific growth rates of Str. salivaricus ssp. thermophilus (ST), LA and LDB were 0.5649 h-1, 0.5260 h-1 and 0.5931 h-1 respectively; at 30 ℃, the specific growth rates of LLL, LLD and L. lactis ssp. cremoris (LLC) were 0.4770 h-1 , 0.2534 h-1 and 0.2765 h-1 respectively. With more inoculation amount, biomass increased and specific growth rate decreased. While soluble oxygen content in the medium increased, biomass of LAB decreased. It was not suitable to use stir process in the incubation of LAB.Initial pH value, incubation temperature and incubation time were selected as the threekey factors to optimize the incubation conditions. The actual value mathematics model was: y=-77.2404+9.0272 X1 +1.0836 x2+2.0864 x3 -0.0093 x22-0.0211 x2 x3-0.0164 x32 The optimum parameters were: the initial pH of medium 6.7-6.9, incubation temperature 37~39℃, incubation time 18~21h. Under these conditions, the biomass of LDB was no less than 5.0.The influences of the latest cultivation technology on high-density cultivation of LAB were studied. Compared with common cultivation mode, constant pH value cultivation technology overcame acid injury due to pH value drop and lactic acid accumulation to a certain degree. The number of LA was up to 3.89X 109cfu/mL at pH5.5 during constant pH value cultivation. Theoretic analysis showed that dilute rate was approximately equal to specific growth rate, i.e. u D, under the quasi-constant state during the whole nutritious materials supplement fed cultivation. The determined initial material supplement rate was 5.874X 10-4 m3/h at the end of logarithmic growth period in the incubation of LDB. The density of LDB was 1.0 X 1010cfu/mL under the conditions.Micro-filtration membrane technology was first used for concentration of LAB. The results showed that the concentrated ratio of micro-filtration, ultra-filtration, centrifugal concentration were 19.1, 16.9 15.9. and the concentration of LAB were 1.15 X 1010cfu/mL, 9.79 X 109cfu/mL 5.38 X 109cfu/mL respectively. Scan electrician micros...
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