| Fermented yoghurt was rich of nutrition. Probiotics starter cultureis a class of biological products with high concentration of probioticswhich can be used as probiotics stains to make yoghurt. Spray dryingprocess is a kind of high efficient method to make bacterial powder. Theprocess used to make probiotics starter cultures by spray drying hadbeen studied. Take Lactobacillus bulgaricus and Lactobacillusacidophilus as major probiotics stains. First, by the centrifugalseparation process obtained the probiotics from the fermentation whichthe probiotics cultured in MRS culture medium. Second, putting thebacterias into the condensed milk and using the heterogeneous machinesto make them uniformly dispersed， by which the high concentration ofbacterial suspension had gotten. Finally, the bacterial powder was madeby the spray drying process from the bacterial suspension. The mainresearch results are as follows:Involve of the comparative analysis of different medium, the resultwas that: the optimal concentration of whey powder culture medium is7%, cultured in which can achieve the highest cell concentration2.6×10~8cfu/mL and7.7×10~8cfu/mL of LB. The highest cellconcentration get in milk culture medium is8.6×10~8cfu/mL and9.0×10~8cfu/mL of LB. The growth of probiotics can be promoted by thewhey powder. The cell concentration could achieve to1.6×10~9cfu/mLand2.7×10~9cfu/mL of LB when added3%whey powder into the milkculture medium. In comparison, the cell concentration reached to1.1×10~9cfu/mL and5.3×10~9cfu/mL of LB in MRS culture medium.Probiotics cultured in all of the four culture mediums can achieve veryhigh cell concentration, The MRS culture medium was selected becauseit was easier to separate the cells by centrifuge. The thermotolerance of the probiotics improved by the heat shocktreatment. Depend on the change of viable bacterial count in differentheat treatments, we can see, LA and LB had highest resistance whenthey were cultured11hours. The optimal heat shock treatmentcondition is45℃,30min of LA and50℃,20min of LB from theexperiment separately. The probiotics after heat shock treatment almostone order of magnitude higher though the5min water bath heattreatment in80℃than original directed to the heat treatment.The best centrifugal condition of LA and LB is6000r/min,10min,4℃. The highest bacteria survival rates achieved to91.9%and89.5%,separately.Cells suspended experiment: the change of characters in milkthrough concentration and skim was analyzed by property analyzer. Itwas found that the property of milk which concentrated to1/2wasappropriate to act as protective agent of cells， not only hardness,consistency, cohesiveness and viscosity index were smaller that havepositive effect to the dispersing of bacteria cells in the concentratedmilk. The protective experiment of different condensed milk to thebacteria cells was found that1/2concentrated milk could complete toprotect the probiotics cells than any other milk by other process, whichnot only protect the probiotics cells well but also the better dispersingwas good. Put the bacterial liquid（the rate of fermented liquid and skimmilk is10：1） which had been shocked for2minutes before homey in1/2concentrated milk. It could spread the cells utterly in theconcentrated milk. The results show that homogenization twice couldget the best condition, more than twice the cell concentration woulddecline. Hatch not only promoted the cells adaptability in concentratedmilk but also increased the cells concentration, somehow.The spray drying experiment for the bacterial liquid: the out windtemperature was set at80℃, different temperatures were selected forthe into-wind. The highest survival rate of probiotics is2.6%. Thehighest cell concentration was2.0×10~9cfu/g with particles uniformlyand well dispersion. Compared to the fermented liquid spawn, the probiotics powder has better performance in fermentation. |
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