Study Of The Production Of Direct-to-vat Yoghurt Culture Using Freeze-drying Technology

Countering the yoghurt culture application actuality in our country This experimentsysternticaly studied manufacture mechanisms and tecniques of direct-to-vat yoghurtculture.the sourceful bacteria were: streptococcus thermophilius and lactobacillus balgaricuswhich were chosen and optimized to propagateThe results of S.t and L.b grown on the six cultures showed: The recovery was good onthe culture which contained milk contents (e.g whey and casein hydro1ysates) and naturalstimulated growh substances(e.g tomato juice).Thingking of the manufacturing cost and theneed of low content of total solid(TS) of the culture, We tested the stimulated growth effect ofmilk and whey with different concentrations. ratios and hydrolysis conditions(E:trysint:30or60min pH=8),enzyme-treated whey was apparently superior to whey; Enzyme-treatedmilk is not ideal The middle content of TS milk(4%) and enzyme-treated milk(5%)(the ratio isl:l) gained the best stimulated effect,high content of TS and low content of TS were bothunsatisfactory for S.t's and L.b's growth.The simple factor experiment of stimulated growthgene showed that yeast powder. tomato juice,malt juice and beer were all effective stimulatedgrowth genes.The effects of Val and formic acid were also apparent. using the quadratic designL9(⁴₃)(the results of two group L9(⁴₃) were added) to determine the best stimulated growthgenes formula of the milk and whey based culture:S.t:5%tomato juice 5%malt juice 0.7%yeast powder 0.05% Val 2% lactoseL.b: 5%tomato juice 5%malt juice 0.7%yeast powder 70mg/kg formic acid 2%lactoseGrown on this culture for l2hrs at 37℃, S.t and L.b got to 5.20×l0°cfu/ml and4.75x l0⁸cfu/ml respectively .Calcium carbonate was not suitable as the stimulated salt. Usesat design to determine the cultivting equation and the optimum cultivitingconditions:S.t:Y=0.58-0.038x₁,-0.004x₂-0.002x₁+0.004x₁x₂-0.00llx₁x₃-0.0l9x₂+0.002x₂x₃-0.0l8x²₃ (T:4l .8Ph:6.1t:4.6hrs)L.bY=0.494+0.003x₂0.008x₃-0.023x₃-0.0l8x²₂-0.002x₂x₃-0.0l4x²₃(42.5℃ pH:5.9 t:4.7hrs)cultivated under these conditions, the two bacteria respectively increased to 5.80×l0⁹cfu/mland 3.05 × l0⁹cfu/ml.The concentrating enrichment conditions were studied and chosen, the results illstfuedthat rpm and temperature were two dminam factors.High rpm and relatively low tenmperaturewere helpful for bacteria's concentrating.The addition of protein solvent reduced the proteinparcels of the culture,thus improved the centrifugation concentheing times .The bacteria filterhad little inflence on the bacteria's morphlogy,but the operating process was labour-lost andlII$Jh$&k# #$ImattPMMAaffix*mghWrt @1*tt&xwith low productivityso not suitavble for large-scale production.Milk was used as freeze-drying medium (S.t:l5% L.b:l0%).Based on this medium,simplefactor experiment ofcryoprotectan showed: adnitol. Vc. glycerol. sugar and kelp juice werevery effective protective agents .Sodium glutrnate was with high performance for S.t and Cyswas with high performance for L.b.The effect of adnitol was the best for both S.t and L.b,butits high price limited its utilitythe quadratic rOtary combination design was used to institUte thecryoprotectam model and the optimum formula: ^S.TtY=0.8440-0.0643X,'-0.0646X,.0695X,' (5%sugar 2%glycero1 0.8% sodium glutamate l%Vc 5%kelp juice) -L.btY =0.7253-0.0692xl- 0.030lxl'- 0.0l86x2- 0.0556x3+0.0l59x,x2-0.0337x32(1%glycerol Vc0.3% 0.l%Cys ).In the above formul4the survivaI of S.t and L.b got to 84% and 79%. In the S.t's model eachtWo combined cryoproteCtams acted similarly and every one cryoprotectam have better effectnear its zero level;in L.b's model the protective effect of Cys and Vc combined wasapparent.low concentration was helpful for glycerol to protect bacteria aginast freeze-drying.The e1ectron micrograPhy resultS illstrated that the addition of cryoprotectan madefreeze-drying medium form netWork strUCtUr...