High Cell-Density Culture Of Lactobacillus Acidophilus And Dairy Starter Cultures

Lactobacillus acidophilus is one of the beneficial bacteria existed in human intestine, and has an important role in the promotion of human health and disease prevention. In this paper, we choose Lactobacillus acidophilus La-1as the research object, to seek a suitable proliferation medium for industrial production. Proliferation of cultured ways and process technology to improve the number of bacteria per unit volume were studied, ways of cell concentration and separation, vacuum freeze-drying, etc were researched. Explore the process of freezc-dried lactic acid bacteria to survive in the suitable conditions to improve cell survival rate of freeze-dried dairy starter cultures. For the popularization and application of freeze-dried dairy starter cultures provide a scientific basis.In order to ensure that the Lactobacillus acidophilus has a higher number of viable cells, we must choose the right improving the environmental conditions, seeking a suitable proliferation medium and adding growth-promoting substances and other aspects of optimization. Search the medium of corn flour, yeast extract liquid medium, whey powder medium, wort medium as based medium, use the MRS liquid medium as the control medium. By experimental research choose the suitable whey medium as basal medium. Use the Minitab software optimized the whey medium, the optimized result is whey powder12.99%, glucose2.75%, NH4H2PO40.52%. Through a series of studies determined the Lactobacillus acidophilus La-1optimal culture conditions, ultimately determined the optimum temperature for the37℃, the optimal inoculum4%, and the optimum pH of6.5.Using the hollow fiber membrane module with aperture0.1μm, effective filtration area of1.5m2established the hollow-fiber membrane bioreactor. Using the membrane separation discharge the lactic acid bacteria metabolites, so that the lactic acid bacteria to be concentrated. Then feeding fresh medium prepared in the tank for feeding operation, control pH6.0, to achieve high-density growth of lactic acid bacteria to improve the yield of lactic acid bacteria per unit volume. Take advantage of this device, the final number of viable Lactobacillus acidophilus come to3.1x1010cfu/mL.The collection of bacterial processes, drying processes and bacterial protective agent has been optimized. Collected the bacteria from lactic acid bacteria culture by centrifugation, under the conditions of6000rpm for15min, the final survival rate is30.23%. Select vacuum freeze-drying to prepare freeze-dried dairy starter cultures, from a large number of protective agents select the skim milk, trehalose, sodium glutamate as the composition of the protective agent, through the use of SAS software to conduct three kinds of components optimization formula to determine the best protective agent for the skim milk powder10.19%,3.14%trehalose,3.00%sodium glutamate. The final finished product starter cultures obtained the number of viable lactic acid bacteria reached3.57x1010cfu/g. Storage the freeze-dried dairy starter cultures after three months is still the number of viable1x1010cfu/g or more. That means the product starter cultures meet the commercial requirements, and achieve the desired goal.