Application of Impedance Microbiology for Evaluating Potential Acidifying Performances of Starter Lactic Acid Bacteria to Employ in Milk Transformation

Impedancemicrobiologyisamethodthatenablestracingmicrobialgrowthbymeasuringthechangeintheelectricalconductivity.Differentsystems,abletoperformthismeasurement,areavailableincommerceandarecommonlyusedforfoodcontrolanalysisbymeanofmeasuringapointoftheimpedancecurve,defined“timeofdetection.”Withthisworkwewantedtofindanobjectivewaytointerpretthemetabolicsignificanceofimpedancecurvesandproposeitasavalidapproachtoevaluatethepotentialacidifyingperformancesofstarterlacticacidbacteriatobeemployedinmilktransformation.TodothisitwasfirstlyinvestigatedthepossibilitytousetheGompertzequationtodescribethedatacomingfromtheimpedancecurveobtainedbymeanofBacTrac4300®.Lagtime(),maximumspecificM%rate(μmax),andmaximumvalueofM%(Yend)havebeencalculatedand,giventhesimilarityoftheimpedancefittedcurvetothebacterialgrowthcurve,theirmeaninghasbeeninterpreted.PotentialacidifyingperformancesofeightystrainsbelongingtoLactobacillushelveticus,Lactobacillusdelbrueckiisubsp.bulgaricus,Lactococcuslactis,andStreptococcusthermophilusspecieshavebeenevaluatedbyusingthekineticsparameters,obtainedfromExceladd-inDMFitversion2.1.Thenoveltyandimportanceofourfindings,obtainedbymeansofBacTrac4300®,isthattheycanalsobeappliedtodataobtainedfromotherdevices.Moreover,themeaningof,μmax,andYendthatwehaveextrapolatedfromModifiedGompertzequationanddiscussedforlacticacidbacteriainmilk,canbeexploitedalsotootherfoodenvironmentorotherbacteria,assumingthattheycangiveacurveandthatcurveisproperlyfittedwithGompertzequation.