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90 ThermalocessingProfoodsF
xpectedune process viationsde in thermal processing of w-acidlo
cannedfoods.Itypesci(cid:222)calladdressedthelemprobposedybcurrent
systemsthatyutomaticallaxtendeprocesstimetatheredevrecoretort
temperature for the xtente needed to reach the gettar lethality ( F )
o
speci(cid:222)edfortheproduct.
4.6.1. On-lineolocntrategiesstrleapplicabtow-acidlooodsfthat
canbeathmematicallymodeled
The orkw presented in this paper addressed these lemsprob yb de-
scribingelvnocontrolgiestratesthatalsotreattheretorttemperature
as the ontrolc le,ariabv rather than process time lone,a in accom-
plishing on-line ocrrection of a process viation.de In the case of
cookroomschedulingistuations,on-lineocrrectionofaviationdeis
accomplishedybhocosingnaoptimumhigheroncstantretort-temper
ature for the remainder of the process that willrevdelithe speci(cid:222)ed
gettarlethalitywithintheoriginalprocesstimeremaining.Whenthe
viationde occurs late in the process requiring orcrection ta the up-
per limit of retort temperature, this ouldw be a minimum xtendede
process time. In a further and neve broader application, the paper
described on-line orcrection of processviationsdeoccurring during
a grammedprepro leariabv or dynamic retort temperature process,
such as a ramp-up and wnramp-do pro(cid:222)les, that might be chosen
to maximize nutrient retention in a conduction-heated food. In this
situation, an optimum combination of retort temperature and pro-
cesstimeishocsenfortheremainderoftheprocessthatwillrevdeli
the aximmum lepossib nutrient retention iwthin the pesci(cid:222)ed gettar
.lethalityExamples erewenvgi for the case of solid product -under
going a oncduction-heating process in ferentdif hasped onctainers
ylindrical(c can and retort pouch), sa ellw sa liquid product -under
going a forcedection-heatingvconprocess inylindricalccans under
mechanicalagitation.
4.6.2. On-lineolocntrategiesstrleapplicabtoyan-wacidlooodsf
The gytrsate is intended for easy implementation in yna cannery
around the orldw with no need for on-site access to computers,
-basedcomputer control ysstems, nda/or computer aresoftw of yna
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eFigur4.16. Automatedhuttlesbatchetorrtystem.s(CourtesyofAX,ALLP
vington,CoLA.)
eFigur4.17. FMChuttlessystemforautomatedbatchetorrtoading/unloading.l
(CourtesyofJBTech,oodTFyorfmerlFMCech,oodTFMadera,CA.)
89
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92 ThermalocessingProfoodsF
TTR (cid:4) wNeretorttemperature
TTR estwLotemperatureduringtheviationde i
i
t eimT
t Correctedprocesstime
D
t lishedPreestabprocesstimetaretorttemperatureTTR
TRT
U Globalheattransfer(cid:222)cientoefc
(cid:1) t Durationofviationde i
i
keerGsrettel
(cid:6)
(cid:2) Thermalvityfusidifoffood( (cid:2) = k (cid:3) C )
p
(cid:3) Densityoffood
(cid:5) ferentialDiforlanaboperator
(cid:6) (cid:6) (cid:6)
( (cid:5) = (cid:4) (cid:4) x + (cid:4) (cid:4) y + (cid:4) (cid:4) z )
(cid:6) (cid:6) (cid:6)
(cid:5) 2 Laplaceoperator( (cid:5) 2 = (cid:4) 2 (cid:4) x 2 + (cid:4) 2 (cid:4) y 2 + (cid:4) 2 (cid:4) z 2 )
wledgmentAckno
Ricardo Simpson is grateful for the (cid:222)nancial upsport videdpro yb
CONICYTthroughtheFONDECYTproject1050810.
secnerefeR
,osnolA,.A,agnaB,.JdnaraM-zere,nitP.R.3991Awneygetartsrofehtlortnoc
ofpressureduringhetcoolingtagesoftheterilizationsprocessniteamsretors.t
arPt I. A preliminary.tudysoodFand ioproductsB Processing, ansrThemEIc ,
71(c):197—205.
Ball, .C.O 1928. Mathematical solution of emslprob on hertalm processing of
dennac.doofytisrevinUforofilaC.aindehsilbuPnicilPbuhtlaeH,1N2,.542—51
w,.,Bigelo.DWoharB,t.S.,GRichardson,A.C.andall,B.C.O1920.Heatpenetra-
tionniprocessingcannedoods.full.BNo.16-Les.R.Labatl.NCannersAssn.,
ashington,WDC.
Blattner,M..F2004.ancesAdvinautomatedetorrtcontrol,andsy(cid:213)odatwnepack-
aging.PresentationatFTISymposium,2004IFTMeeting,Lasas,geVNV.
Datta,.K.,Aeira,xeTA.A.,andManson,.E.J1986.-basedComputerretortcontrol
giclo orf on-line correction of process viations.de ournalJ ofoodFScience ,
51(2):480—483,507.
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On-LineoloCntrgiesateStr 91
kind. This gystrate setak into account the duration of the viationde
in addition to the magnitude of the temperature drop. It calculates
a pr(cid:210)oportional(cid:211) xtendede process time ta thereedvrecoretort tem-
peraturethatwillrevdelithe(cid:222)nalspeci(cid:222)edgettarlethalitywithrevy
littleervprocessingoincomparisontocurrentindustrypractice.Re-
sults from na evxhaustie search routine using the xomcple method
support the giclo nad rationale behind the gytsrate ybiwngsho that
theproposedgystratewillysawalresultinaorcrectedprocessthatde-
rsevlinolessthanthe(cid:222)nalgettarlethalityspeci(cid:222)edfortheyoriginall
scheduledprocess.
ListofSymbols
A aerA
a and b Constantoflinearequationdescribingretort
temperaturepro(cid:222)leT(TR (t) = a + bt )
b (cid:4) wNelospeofthelinearequationdescribingretort
temperaturepro(cid:222)leT(TR (cid:4)(t) = a (cid:4) + b (cid:4)t )
a (cid:4) wNeoncstantofthelinearequationdescribingretort
temperaturepro(cid:222)leT(TR (cid:4) (t) = a (cid:4) + b (cid:4)t )
C Heatcapacityoffood
p
CUT Come-uptime
E gyEnerperassmunit
F Sterilizingaluevat121.1 (cid:2) C
o
F F alue-vcalculatediwththeproportionalorcrection.
proportional
F F alue-vspeci(cid:222)edfornormalscheduledprocess
LOT
f Ratefactor(relatedtolopesofgsemi-loheat
penetrationucr)ev
f and f Heatingndacoolingratefactors(relatedtolospeof
h c
gsemi-loheatpenetrationurc)ev
j Dimensionlesslagfactor( j = TRT (cid:138) T A )
TRT (cid:138) IT
j and j Heatingndacoolinglagfactors
h c
k Thermalvityocnductioffood
l Heightofcannedocntent
M Productassm
n Numberofviationsdeoccurringduringtheprocess.
TTR eRtorttemperature
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94 ThermalocessingProfoodsF
eira,eixT.A.AandManson..E.J1982.Computercontrolofbatchretortoperations
htiwenil-nocronoitcerofssepcor.snoivtaide oodFgyhnoloecT ,36(4):85—90.
eira,eixT.A.Aander,uckT.S.G1997.On-lineetorrtscontrolnihertalmsterilization
ofcannedoofds. oodFolContr ,8(1):13—20.
eira,eixT.A.,ABalaban,.,M.OGer.M.,er,mSadahira,S.PM.S.,eira-Neto,eix.,TR.O
anditali,VA.A.1999.Heattransfermodelperforanceminsimulatingprocess
viations.de ournalJofoodFScience ,64(3):488—493.
onVetinger,O K. 1997. L ogica« para el control en l «aenı led osepcor de -lireets
izaci on«comercial.esisTEscueladeAlimentos.onti(cid:222)ciaPersidadvniUCat acilo«
dealparaV «ıso,alparaV «,osı.elihC
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On-LineoloCntrgiesateStr 93
yliger,He.TL.2004).(ancesdvAinretortcontrolorfbatchandcontinuoussystems.
PresentationatFTISymposium,2004IFTMeeting,Lasas,geVNV.
orth,wHolds.S.D1997. ThermalocessingProfedgkaacoodsPF .eikcalBcimedacA
&Professional,London.
Larkin. 2002.ersonalPommunication.C Branch Chief, National enterC orfoodF
Safety,andgyechnolooodFTandrDugdministrationAA/NCFST),FD(Chicago,
IL.
Manson,.E.,JZahradnik,.,.WJandStumbo,C.R.1970.aluationEvofethalityland
nutrientetentionsrofconduction-heatingoodfinrectangularcontainers. oodF
gyhnoloecT ,24(11):1297—1301.
Manson, .E.,J Zahradnik,.,.WJand Stumbo, C.R. 1974. aluationEv of hertalm
processes orf conduction heating oodsf in -shapedpear containers. ournalJ of
oodFScience ,39:276—281.
Noronha,.,JHendrickx,M.,anVy,LoeA.,and.obbak,T1995.PwNeesmi-empirical
approach to handle leariabtime-v boundary conditions during terilizations of
evnon-conductiheatingoofds. ournalJofoodFEngineering ,24:249—268.
Pham,..TQ1987. Calculation of hertalm process ethalityl for conduction-heated
cannedoofds. ournalJofoodFScience ,52(4):967—974.
Saguy, I. and arel,K M. 1979. Optimal retort temperature pro(cid:222)le orf optimizing
thiamine retention ni conduction-type heating canned oods.f ournalJ ofoodF
Science ,44,1485—1490.
Simpson, R., ris,A I., andores,rT.A.J 1989. Sterilization of conduction-heated
foods inal-shapedvocontainers. ournalJ ofoodFScience , 54(5): 1327—1331,
1363.
Simpson,R.2004.Controlgicolforon-linecorrectionofbatchsterilizationpro-
cessesleapplicabtoyankindofcannedood.fSymposiumofTheralmprocess-
ingnihet21stcentury:Engineeringodellingmandautomation,atIFTMeeting,
2004,Lasas,ge.VVN
Simpson, R., Mitchell, M. and,AlmonacidS. 2004. Mathematical modelel-vde
opment,xperimentalealidationvand process optimization: leretorabtpouches
edpackwithseafoodinconefrustumhape.s ournalJofoodFEngineering ,63(2):
153—162.
Stumbo, C.R. 1973. gyThermobacteriolo nioodFocessingPr , 2nd ed. cadAemic
Press,wNeork.Y
eira,eixT.,ADixon,.,JZahradnik,.,Jand,ZinsmeiterG.1969.Computeroptimiza-
tionofnutrientetentionrnihetthermalprocessingofconduction-heatedfoods.
oodFgyhnoloecT ,23(6):845—850.
eira,eixT.A.,A,ZinsmeisterG.E.,andZahradnik,..WJ1975.Computersimulation
ofleariabvretortcontrolandcontainergeometryasaelpossibeansmofv-mproi
inghiaminetetentionrniy-processedhertallmoods.f ournalJofoodFScience ,
40(3):656—659.
eira,eixT.A.A1992.Thermalprocesscalculations.nI HandbookofoodF-Engineer
gni ,.R.DeldHmanand..BDLund(eds.).Marcel,erDekkncI.,wNeork,Ypp.
563—619.
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Chapter 5
COMPUTER SOFTWARE FOR ON-LINE
CORRECTION OF PROCESS
DEVIATIONS IN BATCH RETORTS
ArthurA.TeixeiraandMuratO.Balaban
5.1. Introduction
Thermalprocessingofcannedfoodshasbeenoneofthemostwidely
usedmethodsoffoodpreservationduringthetwentiethcenturyand
has contributed significantly to the nutritional well-being of much
of the world’s population. Thermal processing consists of heating
food containers in pressurized retorts at specified temperatures for
prescribedlengthsoftime.Theseprocesstimesarecalculatedonthe
basis of achieving sufficient bacterial inactivation in each container
tocomplywithpublichealthstandardsandtoensurethattheproba-
bility of spoilage will be less than some minimum. Associated with
each thermal process is always some degradation of heat-sensitive
vitamins and other quality factors that is undesirable. Because of
thesequalityandsafetyfactors,greatcareistakeninthecalculation
of these process times and in the control of time and temperature
duringprocessingtoavoideitherunder-oroverprocessing.Theheat
transferconsiderationsthatgovernthetemperatureprofilesachieved
withinthecontaineroffoodarecriticalfactorsinthedeterminationof
timeandtemperaturerequirementsforsterilization.Thischapterwill
Thermal Processing of Foods: Control and Automation Edited by K.P. Sandeep
© 2011 Blackwell Publishing Ltd. and the Institute of Food Technologists. ISBN: 978-0-813-81007-2
95
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96 ThermalProcessingofFoods
focusonthedevelopmentandapplicationofdeterministicheattrans-
fermodelscapableofaccuratelypredictinginternalproducttemper-
ature in response to retort operating conditions, and coupling these
with deterministic models that mathematically describe the thermal
inactivation kinetics of bacterial spores and food quality factors for
thermalprocesssimulation.
5.2. Thermaldeathtimerelationships
Anunderstandingoftwodistinctbodiesofknowledgeisrequiredto
appreciate the basic principles involved in thermal process calcula-
tion.Thefirstoftheseisanunderstandingofthethermalinactivation
kinetics (heat resistance) of food-spoilage-causing organisms. The
secondbodyofknowledgeisanunderstandingofheattransfercon-
siderations that govern the temperature profiles achieved within the
foodcontainerduringtheprocess,commonlyreferredtointhecan-
ningindustryasheatpenetration.
Figure 5.1 conceptually illustrates the interdependence between
the thermal inactivation kinetics of bacterial spores and the heat
transfer considerations in the food product. Thermal inactivation of
bacteria generally follows first-order kinetics and can be described
by logarithmic reduction in the concentration of bacterial spores
with time for any given lethal temperature, as shown in the upper
family of curves in Figure 5.1. These are known as survivor curves.
The decimal reduction time, D, is expressed as the time required to
achieveonelogcycleofreductioninconcentration,C.Assuggested
bythefamilyofcurvesshown,Distemperaturedependentandvaries
logarithmicallywithtemperature,asshowninthesecondgraph.This
is known as a thermal death time curve and is essentially a straight
line over the range of temperatures employed in food sterilization.
Theslopeofthecurvethatdescribesthisrelationshipisexpressedas
thetemperaturedifference,Z,requiredforthecurvetotransverseone
logcycle.Thetemperatureinthefoodproduct,inturn,isafunctionof
theretorttemperature(T ),initialproducttemperature(T ),location
R I
within the container (x), thermal diffusivity of the product (α), and
time(t)inthecaseofaconduction-heatingfood.
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ComputerSoftwareforOn-LineCorrection 97
C
O
T
1
t
Log C 1 T2 C = COexp ( D / 2 . 3 )
D
T
r
Time (t)
T – T
1 D = Dexp ( r )
Log D Z r Z/2.3
Temperature (T)
T
R
X
1
T X2 f (α) T = f (T ,T, x,α,t)
X R I
3
T
1
Time (t)
Figure5.1. Timeandtemperaturedependenceofthermalinactivationkinetics
ofbacterialsporesinthermalprocessingofcannedfoods.
Thus, the concentration of viable bacterial spores during thermal
processing decreases with time in accordance with the inactivation
kinetics, which are a function of temperature. The temperature, in
turn,isafunctionoftheheattransferconsiderationsinvolvingtime,
spatial location, combined thermal and physical properties (thermal
diffusivity),andinitialandboundaryconditions(initialproducttem-
peratureandretorttemperature,respectively).
5.3. Processlethalityandsterilizingvalue
5.3.1. Timeattemperatureforisothermalprocess
Once the thermal death time (TDT) curve (Figure 5.2) has been es-
tablished for a given microorganism, it can be used to calculate the
time–temperature requirements for any idealized thermal process
