Study On High Cell Density Culture Of Lactococcus Lactis Subsp.lactis BL19

High density culture is a very important step in the preparation of starter cultures,which has important theoretical and practical significance for the industrial production of fermented products.In this thesis,a strain of Lactococcus(L.)lactis subsp.lactis BL19(IMAU11919)was used as the research object.The single factor screening test,compound test and response surface design were used to study its bacteriogenic medium formulation,static culture conditions and high cell density fermentation.The conclusions were as follows:(1)Based on M17 medium,after screening of carbon source,nitrogen source,total amount and proportion of carbon and nitrogen,buffer salts,trace elements and growth factors,the optimum culture medium was obtained,and the optimum culture medium were as follows:5.10 g/L of trehalose,15.31 g/L of sucrose,14.79 g/L of yeast peptone,44.38 g/L of yeast extract,19.63 g/L of potassium dihydrogen phosphate,4.04 g/L of sodium hydroxide,0.20 g/L of MgSO4·7H2O and 0.50 g/L of VB2.(2)The optimum static culture conditions of L.lactis subsp.lactis BL19 were as follows:The maximum cell density was obtained when the initial pH was 7.7,the inoculation amount of 1%and the incubation temperature was 30? for 5-6 h.The viable cell number was(8.03±0.59)× 109 CFU/mL,which was 2.67 times higher than that before optimization((3.00±0.51)×109 CFU/mL).(3)The best culture medium was selected and the best high density culture technology was obtained by the experiment in 5L fermentor.At constant pH 5.5,the neutralizer was 25%of NH3·H2O.In the fermentor,the cell growth rate was fast and the cell density was significantly increased.The number of viable cells was(1.82±1.01)×1010 CFU/mL,which was 6.07 times higher than that before high density culture(3.00±0.51)×109 CFU/mL,and the cost was reduced by 68%per liter of culture medium.In this study,through study on high-density culture of L.lactis subsp.lactis BL19,its preparation technology with low cost and high viable count was obtained.These data can provide the theoretical basis for industrialized production and application of L.lactis subsp.lactis BL19 microecological preparation.