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OILSTABILITYINDEXTechnicalBulletinMedallionLaboratoriesByBrianNelsonINFO@Medlabs.comPhone800-245-5615OilStabilityIndex(OSI)isanAmericanOilChemistsSociety(AOCS)approvedmethodthatdeterminestherelativeresistanceoffatandoilsamplestooxidation.ItreplacestheoutdatedAOM(ActiveOxygenMethod),whichwasmorelaborintensive,requiredchlorinatedsolvents,andwasgenerallynotperformedinaconsistentmannerfromlaboratorytolaboratory.Allfatsandoilsarepronetooxidation.Therapidityofoxidationdependsonthedegreeofunsaturation,thepresenceofantioxidants,andpriorstorageconditions.IntheOSIanalysis,therateofoxidationisslowuntilanyresistancetooxidationisovercome.Thistimeisknownastheoxidationinductionperiod.Aftertheinductionperiod,therateofoxidationincreasesdramatically.Unlikeperoxidevalueandfreefattyacidanalyseswhichgiveanideaofhowgoodorbadanoilisataparticulartime,theOSIanalysishaspredictivevalue.OSIcanbeusedtocomparevariousoilstopredicttheirrespectiveshelflives.TheOSIanalysiscanalsobeusedtoevaluatetheeffectivenessofantioxidantsordeterminehowmuchlongerafryingoilcanbeusedbeforeitgoesbad.SCOPETheOSImethodisapplicableingeneraltoallfatsandoils.Themostcommonoilsanalyzedarerefinedplantoils(i.e.Soybean,Palm,Peanut,Sunflower,Corn,Coconut,andCanola).TheOSItimescanrangefromlessthantwohourstoover100hours.However,forsamplessusceptibletorapidoxidation,(OSItimes<3h),themethod’sprecisionisdecreasedcomparedtomorestablesamples.TypicalOSITimesforMiscellaneousOils*RefinedOilTypeOSITime@110°C(Hours)AOMTime(CalculatedfromOSITime)Sunflower3-66.8-14.0Soybean4-129.2-28.6Corn9-1521.3-35.9Palm20-3048.0-72.2Misc.Shortening25-7060.1-169.1*Hydrogenationandtheuseofantioxidantscansubstantiallyincreasethesetimes.ASSAYPRINCIPALA5.0gsampleofoilormeltedfatisweighedintoadisposableglasstesttube.Thetesttubeisthenplacedinaheatingblockatatemperatureof110°C.Clean,dryairisbubbledthroughthesample,andtheeffluentstreamofairisbubbledthroughacollectiontubefilledwithultrapurewater.Anelectrodeisplacedinthew
