chapter-10-food-preservation

Chapter10FoodPreservationDefinitionandcategoriesInthefoodindustry,werefertotheprocessingstepsrequiredtoeliminatethepotentialforfoodborneillnessaspreservationprocesses.Pasteurizationinoneofthetraditionalpreservationprocesses;andcommercialsterilizationisamoreintensethermalprocesstoreducethepopulationofallmicroorganismsinproducts;Recently,technologiessuchashighpressureandpulsedelectricfieldhavebeeninvestigatedforpreservationoffoods.PreviewofHeatProcessforpreservationInactivationofmicroorganismsbyheatisafundamentaloperationinfoodpreservation.heatisusedtoinactivatemicroorganismsandinducechemicalchangesthataffectquality.SterilizationTheterm“sterilization”usedinthischapterreferstotheachievementofcommercialsterility,definedasaconditionwheremicroorganismsthatcauseillness,andthosecapableofgrowinginthefoodundernormalnonrefrigeratedstorageanddistribution,areeliminated.SystemRequirementThemajorproductioncostsareoverheadandlabor,plantswithhighproductioncapacityareinclinedtousesystemsthathavehighcapitalizationandlowlaborrequirements.Productswithsuperiorqualitywillresultfromsystemscapableofhigh-temperature,short-timetreatments.MicrobialsurvivorcurvesFirst-ordermodelkisrateconstant,Nismicrobialpopulation,tistimeTheslopeofthestraightlineisk,andisinverselyrelatedtothedecimalreductiontimeDDvalueisthetimerequiredforaonelog-cyclereductioninthepopulationofmicrobial.kNdtdNDtNNloglog0DtNN/010/kteNN0/Dk303.2(10-1)Fig.10-1ShapeofMicrobialInactivationCurvesMicrobialinactivationproceedsinalogarithmicfunctionwithtimeaccordingtoEquation.However,althoughthemostcommoninactivationcurveisthelinearsemi-logarithmicplotshowninFig.10-1A,severalothershapesareencounteredinpractice.Figure10-1Bshowsaninitialriseinnumbersfollowedbyfirst-orderinactivation.Thishasbeenobservedwithveryheatresistantsporesandmaybeattributedtoheatactivationofsomesporesthatotherwisewouldnotgerminateandformcolonies,beforetheheattreatmentreachedtheseverityneededtocausedeathtotheorganism.Figure10-1Cshowsaninactivationcurvethatexhibitsaninitiallagorinductionperiod.Verylittlechangeinnumbersoccursduringthelagphase.Figure10-1Drepresentstheinactivationcurveforamixedculture.Theinactivationofeachspeciesisassumedtobeindependentofeachother.Figure10-1Eshowsaninactivationcurvethatexhibitstailing.TailingisoftenassociatedwithveryhighN0valuesandwithorganismswhichhaveatendencytoclump.Asinthecaseofalagintheinactivationcurve,theeffectoftailingisnotconsideredinthethermalprocesscalculationunlessthecurveisreproducibleandtheeffectofinitialnumberandtemperaturecanbequantified.Example10.1Thefollowingdatawereobtainedfromathermalresistanceexperimentconductedonasporesuspensionat112℃:DeterminetheDvilueofthemicroorganism.Time(min)Numberofsurvivors010641.1×10581.2×104121.2×103ApproachThemicrobialpopulationwillbeplottedonasemilogplottoobtaintheslope.Solution①Onasemiloggraphpaper,plotthenumberofsurvivorsasafunctionoftime.Fromthestraightlineobtained,determinethetimeforone-logcyclereductioninthepopulationofspores,whichgivestheDvalueas4.1mins.②Alternatively,thisproblemcanbesolvedusingaspreadsheetbyfirsttakingthenaturallogarithmofthenumberofsurvivorsandenteringthedatainalinearregressionmodel.TheDvalueof4.1minutesisobtained.InfluenceofExternalAgentsThesurvivorcurvesformicrobialpopulationsareinfluencedbyexternalagents.Asthemagnitudeofpreservationagents,suchastemperature,pressure,pulsedelectricfields,increase,therateofthemicrobialpopulationreductionincreases.Arrheniusequation:Theseconstantsaredeterminedfromexperimentaldatabyplottinglhkversus1/TA,andtheslopeofthelinearcurveisequaltoEa/Rg.AgaTREBklnln(10-2)ZValueTraditionalthermalprocessinghasusedtothermalresistanceconstantztodescribetheinfluenceofTondecimalreductiontime,D.zisdefinedastheincreaseintemperaturenecessarytocausea90%reductioninthedecimalreductiontimeD.21loglog12TTDDTTz)(303.221AAgaTTzREAgRRTRPPVkk)(lnlnVisActivationVolumeconstant,PRisareferencepressure(10-3)Example10.2TheDforasporesuspensionweremeasuredatseveraltemperatures,asfollows::Determinethezvalueforthespores.T(℃)D(min)10427.510714.51107.51131164.02.2ApproachTheDvaluewillbeplottedversustemperatureonsemilogcoordinatesandthezvalueisestimatedfromtheslopeoftheestablishedstraightline.Solution①Usingsemiloggraphpaper,theDvaluesareplottedversustemperature.②Astraightlinethroughtheplottedpointsisestablished.③Basedonthestraight–linecurve,atemperatureincreaseof11℃isrequiredforaonelog-cyclereductionintheDvalue.④Basedontheaboveanalysis,z=11℃.⑤Alternately,zcanbeestimatedusingalinearregressionprogramtoanalyzetherelationshipbetweenlogarithmofDvaluesversustemperature.Thezvalueis11.1℃ThermalDeathTimeFThethermaldeathtimeFisthetotaltimerequiredtoaccomplishastatedreductioninapopulationofvegetativecellsorspores.ThistimecanbeexpressedasamultipleofDvalue.99.99%reduction:F=4DAtypicalFinthermalprocessingofshelf-stablefoodsisF=12D.zTFisthethermaldeathtimeforatemperatureTandathermalresistanceconstantzFfornon-thermalprocesseswouldhavethesamerelationshiptotheSurvivorcurve,orrat