Studies On The Probiotic Stater Culture

Probiotic starter culture plays important role in developing probiotic yoghurt or fermented dairy products. In this paper,Lactobacillus casei BD-Ⅱ,the cholesterol-reducing probiotic strain,was used to prepared starter culture.The biological and fermentation properties was studied.Enrichment medium and proper protectants were choosen with the means of pre-incubation and heat shock to enhance the surviaval rates and activity.The biological and fermentation properties of L.casei BD-Ⅱwas studied.Results:the fermented RSM was coagulated at 10h,at 12h,pH was 4.5 and titratable acidity was 81.5 oT;proteolytic activity determination as the free-amino acid concerntration is 1.35mg/ml;the optimal growth temnperature is 38℃,and the maximum 46℃,minimum 12℃.Antibitotic sensitivity test found that the strain showed significantly sensitive to Tetracycline,Chloramphenicol and Erythromycin,middlingly sensitive to Benzylpenicillin and Ampicillinum,but no sensitivity to Streptomycin,Norflxacin and Gentamycin. Volatile flavor components analysis of fermented skim milk with gas chromatography-mass spectrometry showed the major compounds are ketone,volatile fatty acid ,which proportion are 35.91%and 52.52%.The first three are acetic acid,2-butanone and 2,3-butanedione with 36.26%,14.18%,10.67%,respectively.The acidity of fermented milk changed indistinctively in 0 to 7d,and became 0.16% higher at 14d,shows something post-acidify.When stored in pH4.0 PBS buffer at 4℃for 10 days,the viable cells changed from 6.35×107 cfu/ml to 5.61×106cfu/ml.Mixed fermentaion of Streptococcus thermophilus,Lactobacillus bulgaricus and Lactobacillus casei BD-Ⅱstudy showed optimal conditions are 1:1:3 with inoculum 3%,incubate temperature 39℃.The cogulated time was 6h,4h less than single fermentation.The orthogonality test used to design the optimal enrichment medium of BD-Ⅱ.The best consist of enzyme hydrolysed 10% RSM,0.5%glucose,1.5%peptone,0.3%yeast extract and 0.1mol/LpH5.6 Na2HPO4-citric acid.The viable counts is 8.8×109cfu/ml,1.35 and 0.75 fold higer thant fermented in MRS and 10%RSM.With help of Origin 6.0,kinds of kinetic parameter are estimated,and the kinetic model of batch fermentation growth of BD-Ⅱis N(t)=3.4088/(1+ e3.3560-0.3254t).Relative error of modle value and value of experiment is in the range of 5%.The best cryoprotectant desighed with orthogonality test: NFM powder 100g·L-1 maltodextrin 100g·L-1,L-glutamine10g·L-1,glycerol 30ml·L-1,trehalose 200g·L-1 .The survival rate of lyphilyzation starter is 82.2%,viable counts 4.4×1010cfu/g with it.For optimizing lyphilyzation process,the suspended culture preincubated at 37℃for 60min,and forzen at -40℃for 3h, survival rate is 84.8%,viable counts 4.9×1010cfu/g,the cogulation time is 13h.Application test showed the lyphilyzation starter produced acid slowly than liquid...