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1、AbstractAbstractThisstudyscreenedropyStreptococcusstrainwithviscosityandfermentationperformancefromkefirfermentedmilkbystickysilk-screeningmethodandfurtherconfirmedbyfermentationperformanceinmilk.Thefulllengthsequenceof16srDNAofstrainST-1wasfound100%homologywithStreptococcusthermo
2、philusLMD-9,andthestrainwasclassifiedasStreptococcusthermophilusST-1basedonmorphology，biochemicalcharacteristicsaswellastheresultof16srDNAanalysis.Thecurdwaswellat4.5h,theviscosityarrivedat907mPa·s(64r/min),theaciditywas82°T,andtheevaluationofsense-organswasrelativelywellwhenthemo
3、noxeniewasfermented.at45℃.CamparedwithLactobacillusbulgaricusLB40toyogurtfermention,objectiveindexandthescoreofthesensesfrom1dto7dweregood,whichapproachedtothelevelofcommercialyogurt.Testthetexture,rheological,andsensoryofdifferentyogurtsamples,theresultdisplayedtheyogurtfemention
4、useropystainshavethebestIntegratedquality.Theeffactsofdifferentinoculumconcentration,fermentationtimeandfermentationtemperatureonEPSproducedbyStreptococcusthermophilusST-1wasstudiedinordertogetenoughEPSforfurtherstudy.ThisexperimentalobtainedtheoptimumconditionsbyRSM:inoculumconce
5、ntration4%,fermentationtime14h,fermentationtemperature42℃.TheEPSproductionis346.51±1.05mg/L.ExopolysaccharidesproducedbystrainST-IinskimmilkwerepurificatiedbyanionexchangechromatographyonDEAESepharoseFastFlowcolumn,twopolysaccharidecomponentsEPS-ⅠandEPS-Ⅱwereobtainedbytheelutionof
6、Tris-HClbufferwith0～1.5mol/LNaCl.ChooseEPS-ⅠwhichhadhighcontantcontinuetopurifybyGelfiltrationchromatographyofSepharoseCL-6BcolumnuntilsinglepeakEPS-Aappear,thendetectedbyHPLCtomakesureitwashomogeneouspolysaccharides.EPS-Awasidentifiedasnon-proteinpolysaccharidedetectedbyultraviol
7、etandinfrared,anditwasmadeofgalactoseandglucose(peakarearatio1:1.21),withtheMolecularWeight800000Da,fromtheresultofHPLC.ThereweresomeconclusionsfromrheologicalbehaviorofEPS-Asolution:shear-thinningphenomenonwasfindathighconcentration,nosuchphenomenonoflowconcentrations;Solution’sv
8、iscositydecreasedwiththetemperatu
