sterility 63601 tetra pak document
TRANSCRIPT
-
7/28/2019 Sterility 63601 Tetra Pak Document
1/16
An introductionto commercial sterility
-
7/28/2019 Sterility 63601 Tetra Pak Document
2/16
3 Introduction
4 Histor y
4 Single-cellriendsandenemies
5 Thelogarithmicorder
7 Approachingabsolutesterility
8 Aweaklinkbreaksthechain
9 Meetingmarketrequirements
10 Howmanysamples?
11 Increasingsterilizationeciency
12 Amixtureoremedies
13 UHTtreatment
14 Microltration
15 Summar y
Index
-
7/28/2019 Sterility 63601 Tetra Pak Document
3/16
Thepurposeothisbookletistoprovideabasicunder-
standing othe microbiologicalaspects oaseptictechnologywiththeocusontheprocessingpart.We
donotaimtocovereverythingindetail,butinsteadtry
togiveyouagoodoverviewotheimportanceocom-
mercialsterilityandhowtoachieveit.Iyouneedmore
detailedinormation,donothesitatetocontactusat
TetraPak.Wearehappytoassistyouwithourcompe-
tenceandexperience.
Introduction
Allqualityisbasedoncompetence.
-
7/28/2019 Sterility 63601 Tetra Pak Document
4/16
History
The destruction o microorganisms
EvenbeoreLouisPasteurprovedoveracenturyagothatmicroorganismscausedermentationanddis-
ease,NicolasAppert,aParisianconectioner,irst
succeededinpreservingcertainoodsinglassbottles
thathadbeenkeptinboilingwaterorvaryinglengths
otime.Thishappenedintherstdecadeothe1800s
Single-cell riends and enemies
SporesposethemajorchallengetoUHT(ultrahigh
temperature)processinganddeterminethesteriliza-
tionparameters.
Microorganismscarryoutinnumerableunctions
thatareessentialtolieonearth.However,asregards
oodproducts,theyarepublicenemynumberone.
Manybacteria,someowhicharepathogenictoman,
areresponsibleortherapidspoilageoood.Applying
asuitabletemperature(e.g.72Cor15s)degrades
proteins,essentialcomponentsolivingcells,andsoit
isquiteeasytokillvegetativebacteria.
Themajorproblemisbacterialspores.Theseare
diculttokillbecausetheyhavethickprotectivewalls
whichincreasetheirresistancetoheat,drying,reez-
ing,chemicalagentsandradiation.Thisiswhyspores
posethebiggestchallengetoUHTprocessingandde-
terminetheparametersusedorsterilization.
andby1839,tin-coatedsteelcontainerswerewidelyinuse.Thusbeganthebirthohighheattreatmentand
canningasameansopreservingood.
Today,acombinationocontinuousheat-treatment
andasepticpackagingproduceshighqualityliquid
oodinacost-eectiveway.
-
7/28/2019 Sterility 63601 Tetra Pak Document
5/16
The logarithmic order
A never-ending story
Asepticprocessinginvolvesoneormoreseparatester-ilization stepsaimed at killingall microorganisms.
Whenapplyinga sterilizationprocedure,e.g.using
heat,notallbacterialsporesarekilledatthesametime.
Acertainnumberwillbekilledwithinagivenunito
timeasshowninthetablehere.Theprinciplebehind
thekillingprocessisindependentothesterilization
temperature.
Whenthenumberosurvivingsporesisplotted
againsttheirlogarithmicreduction,weobtainastraight
lineasshowninFigure1.Thisstraightlineiscommonly
knownasthelogarithmicorderodeath,andtheslope
othelineindicatestherateodestruction.
Fig. 1. A typical graph o the logarithmic order o death or bacterial spores
during sterilization. The steeper the slope, the higher the rate o killing ef-ciency. The initial microbial load is here assumed to be 100 000 bacterialspores o equal resistance. D is the decimal reduction time.
UNIT SPORES KILLED TOTAL LOGARITHMICOF TIME SURVIVORS PER UNIT TIME ACCUMULATED REDUCTION
0 100000 0 0 01 10000 90000 90000 12 1000 9000 99000 23 100 900 99900 34 10 90 99990 45 1 9 99999 5
6 0.1 0.9 99999.9 6
7 0.01 0.09 99999.99 78 0.001 0.009 99999.999 8
1000000
100000
1000
100
10
1
0.1
1.01
0.001
0.0001
NUMBER OF SPORES
TIME
1 2 3 4 5
D
-
7/28/2019 Sterility 63601 Tetra Pak Document
6/16
-
7/28/2019 Sterility 63601 Tetra Pak Document
7/16
Approaching absolute sterility
Asalogarithmicunctionnevercanreachzerobutonly
approachit,absolutesterilitynevercanbereachedorguaranteed.Theeciencyoasterilizationprocessis
expressedbythenumberodecimalreductionsinthe
countoresistantspores.TheD-value(decimalreduc-
tiontime)isnormallyusedtoindicatethekillingrate,
i.e.thetimerequiredatacertaintemperaturetokill
90%othespores,whichisthesameasreducingtheir
numberbyonelogarithmunit.Measuredunderthe
sameconditions,theD-valuewillbeaectedbythe
speciesobacteria.
The result o a heat sterilization process
depends on:theinitialnumberomicroorganisms;
thedecimalreductiontime(heat-resistance)
omicroorganisms;
thetimeandtemperatureoheatexposure.
AnotherimportantparameteristheZ-value,
whichisthechangeintemperatureneeded
toaltertheD-valuebyaactoroone
logarithmunit.
Absolutesterilitycanneverbereachedorguaranteed.
Fig. 2. The Z-value is the increase in temperature needed to achievethe same lethal action or the same eect in one-tenth o the time.
1000
100
10
1
0.1
D-VALUE
TEMP C
120 130 140 150 160
Z
-
7/28/2019 Sterility 63601 Tetra Pak Document
8/16
A weak link breaks the chain
Asepticprocessingandpackagingisrathercomplex
becausea minimum othree dierentsterilizationstepsare required toachieveaseptic llingo the
liquidoodproduct.Sterilizationiscarriedout:
ontheequipmentpriortoproduction;
ontheliquidoodproduct;
onthepackagingmaterialsurace.
Theperormanceleveloanasepticplantmustbere-
gardedastheperormancelevelotheentireprocess
ratherthanthatoasinglecomponentotheproduc-
tionline.Eachlinkintheprocessingandpackaging
chainmustbeequallystrong.
Eachlinkintheprocessingandpackaging
chainmustbeequallystrong.
Rawmaterial
Pre-processing
UHTtreatment
Asepticpackaging
Sterilization
Packagingmaterial
-
7/28/2019 Sterility 63601 Tetra Pak Document
9/16
Meeting market requirements
Theprocessingresultisnotdeterminedbytheprocess-
ingactorsalonebutalsobythequalityorawmate-rial,pre-processingprocedures,environmentaland
operativeparametersaswellasmaintenance.Absolute
sterilitydenedasthetotalabsenceomicroorgan-
ismsisnotpossibleorthereasonmentionedearlier
andthuscannotbeguaranteed.
Commercial sterility
AccordingtotheWHO/FAO,commercialsterility
olow-acidoodisdenedasollows:
Commercial sterility means the absence o
microorganisms capable o growing in the
ood at normal non-rerigerated conditions
at which the ood is likely to be held during
manuacture, distribution and storage.
(Re: Codex Alimentarius Commission (WHO/
FAO) CAC/RCP 0-)
TheEUdenestheheattreatmentnecessaryto
achievingcommercialsterility.
UHT treatment is achieved by a treatment:
(i) involving a continuous ow o heat at a
high temperature or a short time (not less
than C in combination with a suitable
holding time) such that there are no viable
microorganisms or spores capable o grow-
ing in the treated product when kept in an
aseptic container at ambient temperature,
and (ii) sufcient to ensure that the products
remain microbiologically stable ater in-
cubating or days at 0C in closed con-
tainers or or seven days at C in closed
containers or ater any method demonstrat-
ing that the appropriate heat treatment has
been applied. (Re: Commission Regulation
(EC) No /00 (amending Regulation
(EC) No /00)).
Speciying quality levels
Thepracticalconsequencesoabsolutesterilitybeingunobtainable means establishing microbiological
specicationsortheend-product.Thisisnecessaryin
ordertodevelopaviablequalitycontrolprogramme.
Suchspecicationsoracceptancequalitylevels(AQL)
ormanintegralpartoacompanysqualitypolicy.
A microbiolog ical A QLor long- li ep r oducts
shouldbeexpressedasamaximalacceptabledeect
rate.Acleardistinctionhastobemadebetweenthe
maximalacceptabledeectiveratesandthegoalo
production.Regardlessoestablishedmaximalaccept-
abledeectrates,thegoaloproductionmustalways
beperection.
Sampling procedure
Amaximalacceptabledeectrateoaround1per1000
to10000samplesisgenerallyapproved.Inorderto
detectsuchdeectrates,samplingstatisticsmustbe
introduced.Thisincludesdeningtheleveloproba-
bility(condencelevel)tobeusedwhencheckingor
deectrates.Usually,a9095%condencelevelo
achievingacorrectresultisused.
-
7/28/2019 Sterility 63601 Tetra Pak Document
10/16
0
How many samples?
More samples will improve the detection level
Todeterminehowmanysamplesweneedtotaketodetectadeectiveproduct,letslookatatypicalex-
ample.Howmanysamplesarerequiredtodetect
adeectrateo1per1000with90%probability?
Thisproblemissolvedwiththehelpotherandom
samplingcurveor90%probabilityshowninFigure3.
Iweollowthe1%gureuptowherethecurveinter-
sectsthey-axiswegettheresult240.For0.1%(1per
1000)theanswertothequestionis2400.Thestatistical
resultsareaectedonlybythesamplingsizeandnot
bythetotalnumberounitsproduced.
Letstakeanotherexampleusingthesame90%
probabilitycurve.Iwetake50samplesromabatch
andnoneothemaredeective,whatisthedeect
rate?
Inthiscasewetakeahorizontallinerom50sam-
plesonthey-axis,andwhereitintersectsthe90%
curveisthedeectrateatthisleveloprobability:less
than5%,orabout5samplesper100units.Moresam-
pleswillimprovethedetectionlevel.
Todetectadeectrateo1per1000with95%
probability,wewouldneedtotake3000samples.
Analytical methods
Therearemanymethodsavailableordetectingbac-
teriaandestimatingtheirnumber.Themostcommon
onesaregiveninthetablebelow.
Analytical method Accuracy Cost
Bacteriologicalplating BacterialATP
Sensory
pH
Fig. 3. The relation between deective product samples
in percent and the total number o samples to be analysedor bacteria needed to fnd one or more deects in samplesat 90 and 95% levels o probability.
Highlysensitivemethodsdetectthemostbacteriabut
arealsothemostexpensive.Inbacteriologicalplating,asampleoliquidoodisspreadoutonnutrientagar
platesandanycoloniesthatariseromindividualbac-
teriaaterincubationarecountedtoestimatethecon-
centrationobacteriaintheproduct.Severalmethods
areavailablethatdisruptthebacterialwallsothata
compoundcalledadenosinetriphosphate(ATP)present
invegetativecellscanleakoutandbemeasuredto
estimatethenumberoviablebacteria.SensoryandpH
methodsarethecheapestbuthavepooraccuracy.
Whichmethodischosendependsonabalance
betweenthemaximalacceptabledeectrate,analytical
costandthecompetenceocompanypersonnel.
AccordingtotheEuropeanCouncilDirective,random
samplesoUHTmilkmustbecheckedusingthebacte-
riologicalplatecounttechnique,althoughthenumber
osamplesisnotstated.
Thestatisticalresultsareaectedonlybythesamplingsizeandnotby
thetotalnumberounitsproduced.
300
200
100
0
NUMBER OF SAMPLES
DEFECT RATE %
1 1.5 2 3 4 5 6 7 8 910
-
7/28/2019 Sterility 63601 Tetra Pak Document
11/16
Increasing sterilization efciency
Theeciencyoasterilizationprocesscanbeexpressed
asthenumberodecimalreductionsinmicrobialpopulationachievedbytheprocess.
This is mainly determined by two actors:
1. Thetemperatureandthelengthotime
i ti sa ppl ie d.
2. Theheat-resistanceobacterialspores
p resent ,D- value.
Someotheractors,e.g.thecomposition,viscosity,uni-
ormityandpHotheliquidoodproduct,willalso
aectthesterilizationeciency.FortypicalUHTpro-
cessingequipmentitcanbeassumedthatanaverage
o910decimalreductionscanbeachievedwithbac-
terialsporesgrowingatambienttemperatures.
Initial spore Spore load/l UHT decimal Spores/l Defect
load /ml reduction in product rate10000=10 4 107 9D 0.01 1:100
100=102 105 9D 0.0001 1:10000
More spores, more problems
Inadditiontotheactorsmentionedabove,thee-
ciencyotheUHTprocessisinfuencedbythespore
contentotheliquidood,i.e.thetotalsporeload,ed
intothenalheat-treatmentsectionotheUHTplant.
Whatistheeectodierentinitialsporeloadson
end-productquality,assumingidenticalprocessing
conditions?Itheproductislledinto1-litrepackages,
thedeectratecanbedeterminedromtheinorma-
tiongiveninthetable.
Figure4illustratestheeectoincreasedsterilization
temperatureoninitialsporeload,andtheeectodi-
erentsporeloadsonthesametemperature.
Fig. 4. Increasing the temperature or a particular initial
spore load achieves a quicker killing rate. Increasing theinitial spore load or a particular temperature leads to a
longer time required to achieve the same spore reduc-tion as or a lower spore load.
105
104
103
102
101
100
10-1
10-2
10-3
10-4
10-5
NUMBER OF SPORES
TIME
High temperature
Low temperature
Sterilizationeciencycanbeexpressedasthenumberodecimalreductionsin
microbialpopulation.
-
7/28/2019 Sterility 63601 Tetra Pak Document
12/16
A mixture o remedies
Theimportanceoinitialsporeloadonsterilization
eciency,andhenceend-productquality,isobvious.Butwhatcanbedonetoimprovethesituation?The
mostimportantmethodsoachievingthisaregiven
belowandsummarizedinthetable.
Improved hygiene
Ahighconcentrationosporesmayalreadybepresent
inmilkatthearm,orbeintroducedintorawmaterials
asaresultopoorpreprocessingroutines.Theanswer
hereistoimprovethelevelohygienebothatthearm
andtheprocessingplant.However,itisdiculttocon-
trolwhathappensonaarmanditisnotalwayspos-
sibletochangemilksuppliers.
Spore reduction
Agoodwayoimprovingtheend-productistoreduce
thesporecontentorawmaterialsbeoretheliquid
oodisheat-treated.Processessuchasbactougation
andmicroltrationarespeciallydesignedtogreatly
reducethesporecontentomilk.
Eective heat treatmentAnincrease intemperatureand/orprolongingthe
productholdingtimeduringheattreatmentwillresult
inamoreeectivesterilizationprocess.Asaconse-
quence,thenumberodecimalreductionswillincrease
andthedeectlevelwilldecrease.
Spore reduction remedies
Process Remedial action to reduce spore count Ef fectiveness
Milking Improvearmhygiene Helpulbuthardtocontrol
Changesuppliers
Preprocessing Improveplanthygiene Helpul
Sporereduction Bactougation,microltration
orothermeasure Eective
UHTtreatment Increasetemperature
Prolongholdingtime Veryeective
SporereductionandimprovedUHTtreatmentarethemosteectivemeans
oincreasingsterilizingeciency.
-
7/28/2019 Sterility 63601 Tetra Pak Document
13/16
UHT treatment
Two principles
TherearetwodierentUHTmethodsusedintheliquidoodindustry directand indirect heating.
Whichonetousedependsonanumberoactor ssuch
asdesiredendproductqualitylevelandproduction
economy.
Direct heating
Whenusingdirectheating,theproductisbroughtinto
directcontactwithhotsteamunderstrictlycontrolled
conditions.Thesterilizationtemperature(140Cor4
sec)israpidlyreachedandaterholding,thetempera-
tureisloweredbyfashcoolinginavacuumvessel.The
rapidheatingandcoolinggivesminimalheat-loadon
theproductwithahigh-qualityproductastheresult.
Indirect heating
Inthismethodapartitionisplacedbetweentheprod-
uctandtheheatingorcoolingmedium.Theprinciple
isthatahotmediumisfowingononesideothepar-
titionandtheproductontheother.Thepartitionis
heatedupandtranserstheheatovertotheproduct
lowwithoutanydirectcontactbetweenthehotmediumandtheproduct.Thesameprincipleapplies
tocooling.
Thisprocedureisdoneinwhatisreerredtoasaheat
exchanger.Whichonetochoosedependsonseveralactors,e.g.productfowrate,physicalpropertieso
theliquid,requiredrunningtime,cleaningrequire-
mentsetc.
Theollowingthreetypesoheatexchangersarethe
mostwidelyused:
Plateheatexchangers(PHE)aremainlyused
orsmoothlowviscousliquidproducts.
Tubularheatexchangers(THE)canalsohandle
productswithparticlesuptoacertainsizeand
oerlongerrunningtimes.Themaximumsize
oparticlesdependsonthediameterothetube.
Scraped-suraceheatexchangers(SSHE)are
speciallydesignedorheatingandcoolingo
viscous,stickyandlumpyproducts,withor
w it houtpart icles.
TheeciencyandfexibilityoUHTprocessingarecon-
tinuouslybeingimproved.OnetypeoUHTmodule
incorporatesboth directand indirect heating with
tubularheatexchangerstoprovidedierentcombina-tionsoheattreatmentinonesystem.
-
7/28/2019 Sterility 63601 Tetra Pak Document
14/16
Microfltration
Microltrationminimizesthebacterialandsporecontentomilkinacost-eectiveway.
AcombinationomembraneltrationandUHTtreat-
mentisproventobethemosteectivemethodoincreasingsterilizingeciency.
Byusingamicroltrationmembrane,99.5-99.95%
obacteriaandsporesareeectivelyremovedinacost-
ecientway.Thisisachievedbylettingtheliquidsub-
stancepassoveramembraneathighspeedunder
pressureinaclosedsystem.
Themembranehasveryspecicpropertiesthat
onlyallowthebacteriaandsporesoamaximumsize
topassthroughthemembrane.Sincethesizeand
weightotheunwantedbacteriaandsporesareknown,
thelterusedisconstructedwithappropriatepore
sizestoremovethesepartsromtheliquidandletthe
smallerprotein,lactose,mineralandwatermoleculespassontonalUHTtreatment.
Themainbenetsothisprocedurearethatthe
productwillbemorepuriedbeoreUHTtreatment
andthenalproductwillnotcontainanydeadspores.
Thisgivesanend-productwithhigherquality,better
tasteandlongershel-lie.
-
7/28/2019 Sterility 63601 Tetra Pak Document
15/16
Summary
SporesposethebiggestchallengetoUHTprocessing
anddeterminethesterilizationparameters. Absolutesterilitycanneverbereachedorguaranteed.
Eachlinkintheprocessingandpackagingchainmust
beequallystrong.
Acceptancequalitylevels(AQL)ormanintegralpart
oacompanysqualitypolicy.
Statisticalresultsareaectedonlybythesamplingsize
andnotbythetotalnumberounitsproduced.
Moresampleswillimprovethedetectionlevel.
Sterilizationeciencycanbeexpressedasthenumber
odecimalreductionsinmicrobialpopulation.
SporereductionandimprovedUHTtreatmentarethe
mosteectivemeansoincreasingsterilizingeciency.
-
7/28/2019 Sterility 63601 Tetra Pak Document
16/16
Tt Pk, n ProTecTs whaTs good tmk blnin t t Tt Pk gup.
2
008TetraPakProeingsytem.
code63601en4