Food Preservation

Introduction
Definition
Methods of preparation

1. FOOD PRESERVATION
BY
MRS.P.HEPZIBAH ARULMANI
TUTOR
SRMTCON

2. DEFINITION
Itcanbedefinedasthesciencethatdealswith
theprocessofthepreventionofdecayorspoilageof
food,thusallowingittobestoredinafitcondition
forfutureuse.
Preservationoffoodincreasestheselflifeoffoods
andthusultimatelyensuresitssupplyduringtimesof
scarcityandnaturaldrought.

3. FOOD SPOILAGE
Foodspoilageisastateinwhichfoodisdeprivedof
itsgoodoreffectivequalities.Deterioationorspoilage
startsfromthetimefoodisharvested,slaughteredor
manufacturedandresultsinundesirablechangesin
thephysicalandchemicalcharacteristicsoffood.

4. CAUSES OF FOOD SPOILAGE
•Growthandactivityofmicroorganismssuchas
bacteria,yeastandmoulds.
•Activitiesoffoodenzymesandotherchemicalreactions
withinthefood.
•Non-enzymaticreactionsinfoodsuchasoxidationand
mechanicaldamage.
•Inappropriatetemperaturesforagivenfood.
•Gainorlossofmoisture
•Reactionwithoxygenandlight.
•Insectsandrodents.

5. NEED FOR PRESERVATION
•Toincreasetheshelf1ifeoffoods.
•Topreparenewproductslikejams,papads,pickles,etc.
Suchproductsareenjoyedbyeveryoneandalltheyear
round.
•Processingreducesthebulkoffruitsandvegetables.
Thestorageandtransportationbecomeseasier
•Helpsinutilizingthefoodstuffswhenavailablein
excess.

6. PRINCIPLE OF FOOD PRESERVATION
•Preservationordelayofmicrobialdecomposition:
Thatisarchivedby:
•Keepingoutmicroorganisms(asepsis)
•Removalofmicroorganisms,i.e.,byfiltration
•Hinderingthegrowthofactivityof
microorganisms,i.e.,bylowtemperature,drying,
anaerobicconditions,&
•Killingthemicroorganisms,i.e.,byheatorradiations.

7. Cont;
•Preservationordelaybyself–decompositionof
food.Thisisbroughtaboutby:
•Destructionorinactivationoffoodenzymesi.e,by
blanching&
•Preservationordelayofchemicalreactionsi.e,
preservationofoxidationbymeansofanantioxidant.
•Preservationofdamagecausedbyinsects,animals&
mechanicalcauses.

8. METHODS OF FOOD PRESERVATION
Saltingofmeat,fishandvegetableswastheoldestmethodof
preservation.Picklinginsaltandvinegar,sundryingand
preservingoffruitsandvegetablesinsugarandhoneyare
amongtheothermethods.
Foodscanalsobepreservedbyfreezing.Byremovingthe
causeoffoodspoilage,foodscanbepreserved.Whengrowth
ofmicroorganismisonlyretarded,preservationistemporary.
Whenspoilageorganismsarecompletelydestroyed,amore
permanentpreservationisachieved.

9. Cont;
Thediscoveryofcanningasastandardtechniqueof
preservingfoodsinsealedcontainerssubjecttohigh
temperaturewasestablishedin1810byNicholas
Appert.]
Around1860,LouisPasteurdiscoveredthatmicrobes
werethemaincauseofspoilageandintroducedaheat
treatmentknownaspasteurisationtotheworld.

10. BY PREVENTING FOOD CONTAMINATION
(ASEPSIS)
•Processofpreventingcontaminationoffoodbyspoilage
micro-organismsiscalledasepsis.
•Innertissueofhealthyanimalandplantsdonotcontain
micro-organismsandifpresenttheyusuallydonotspoil
food.
•Therefore,microbialdecompositionoffoodcanbe
preventedbypreventingcontaminationoffoodby
spoilageorganisms.
•Severalfoodslikeeggcontainsnaturalcoveringaround
foodthatprevententryofspoilageorganismintothe
food.

11. Cont;
•Nowadays,varietyofsuchartificialbarrieraremade
aroundthefoodtopreventcontamination.
•For.eg.fruitsandvegetablesarestoredforyearsby
coatingthewaxaroundthem.
•Someotherartificialbarriersthatpreventthe
contaminationincludeswrappers,cartoonsandcans.
•Safehandlingoffoodandgoodpersonalhygieneof
foodhandlerareimportantmethodtopreventor
minimizecontaminationoffoodbyspoilageorganisms.
•Most spoilage micro-organisms enter into the food by
contamination from external sources like water, air etc.

12. BY REMOVING MICROORGANISMS FROM
CONTAMINATED FOOD
•Itissecondlevelofpreservationofmicrobial
decompositionoffood.
•Ifcontaminationoffoodbyspoilageorganismisnot
prevented,spoilageoffoodstillcanbepreventedby
removingcontaminatedmicro-organismsfromthe
food.
•Sometechniquesthatpreservefoodbyremoving
micro-organismsinclude:

13. FILTRATION:
•Itisonlyonesuccessfulmethodforremovingmicro-
organismsfromcontaminatedfood.
•Unfortunately,thismethodisapplicableonlyforclear
liquidlikeclearfruitjuice,beveragesetc.
•Toremovemicro-organisms,liquidfoodisfiltered
throughsterilebacterialfilter.

14. CENTRIFUGATION /SEDIMENTATION:
•Centrifugationremovessomebutnotallmicro-
organismsfromcontaminatedliquidfood.
•Whenliquidfoodiscentrifugedsuspendedparticle,
debrisandsomemicro-organismssettletothebottom
whichislaterseparatedandremovefromthefood.
•Thistechniqueiscommonlyusedformilkindairy
industries.

15. WASHING:
•Thismethodiscommonlyusedforvegetableandfruits.
Dustsandmicro-organismspresentonthesurfaceofwhole
vegetableandfruitsareremovedbywashingwithsterile
water.
•Onelimitationofwashingisthatitincreaseswateractivity
ofsomefoodandhencefacilitatesgrowthofremaining
spoilageorganisms.
•Furthermore,ifwashingwaterisnotsterile,itadds
spoilageorganismsinfood.

16. Cont;
TRIMMING:
•Trimmingistheprocessofremovingspoiledpartsof
foodlikevegetablesandfruitsbycutting.
•Trimmingpreventsspreadofmicro-organismsfrom
spoiledpartintoinnerhealthytissue.

17. BY INHIBITING OR KILLING
MICROORGANISMS
Differentmethodsthatpreservefoodeitherbykilling
micro-organismsorbyslowingdowntheirgrowth
andactivityincludes:
–PreservationofHightemperature(Heat)
–Preservationbylowtemperature
–PreservationbyDrying
–PreservationbyRadiation(irradiation)
–Chemicalagentsusedinpreservationoffood

18. Preservation of food byHigh temperature(Heat):
•Heat is the most commonly used method of food
preservation.
•Heat kills spoilage of micro-organisms by denaturation
of cytoplasmic protein and enzyme.
•Two types of heat i.e. dry heat and moist heat are used in
preservation of food.
•Moist heat is more effective in killing micro-organisms
than dry heat.
•Heat causes denaturation of protein and enzyme by
breaking down their bonds.
•Breaking of bond occurs by two mechanisms i.e.
hydrolysis and oxidation.

19. Cont;
•Hydrolysis require water but oxidation does not.
•Hydrolysis require less energy (heat) for breaking of
bond than oxidation.
•Therefore, if moisture is present in food, bonds of
protein and enzymes are broken down by hydrolysis
even at lower temperature.
•This is the reason why moist heat can kill micro-
organisms completely at condition of 121.5
o
C for 15
min but dry heat requires 160
o
C for 1-2hrs to kill the
same organisms.
•Various factors affect killing of micro-organisms in
food by heat.

20. Cont;
Somesuchfactorsinclude:
Time-temperaturerelationship
Densityofmicro-organismsinfood,ifdensityishigh,
highertemperatureisneeded.
Typesofmicro-organismspresentinfood,e.g.Sporeare
difficulttokillthanvegetativecells
Growthstageofmicro-organisms,e.g.micro-organisms
presentinlogphaseareeasilykilledbutmicro-
organismspresentinlatelogphaseandstationaryphase
aresomewhatheatresistant.

21. Cont;
Micro-organismsindryfoodaredifficulttokillthan
inmoistfood.
Iffoodisacidicoralkaline,micro-organismspresent
inlogphaseareeasilykilledbyheat.Ontheother
hand,iffoodisneutral,hightemperatureisneededto
killthesameorganisms.
Penetrationofheatintoinnerlayeroffoodalso
affectskillingofmicro-organisms.

22. DIFFERENCE BETWEEN DRYHEAT AND
MOIST HEAT
DRY HEAT
•It is less effective in killing
micro-organisms.
•It damages protein and enzyme
by oxidation.
•It is especially valuable to
sterilize the food whose quality
is damaged by moisture (e.g.
flour) and for lipids foods.
•Dry heat is applied to the food
by spraying moisture free
heated air over the food and by
hot air oven.
•Conditions for sterilization is
160
o
C for 1-2 hrs.
MOIST HEAT
•It is more effective in killing
micro-organisms
•It damages protein and enzyme
by hydrolysis or coagulation.
•Moisture cannot penetrate into
hydrophilic lipid food and
moisture damage the quality of
powder foods like flour.
•Moist heat can be applied by
boiling the food in water or by
spraying heated steam over the
food.
•Conditions for sterilization is
121.5
oC
for 15 minutes.

23. Cont;
Sometechniqueoffoodpenetrationbyheatincludes:
PASTEURIZATION:
•Pasteurizationisaselectiveorgentleheatingtechnique
originallydevelopedbyLewisPasteurformilkand
milkproducts.
•Nowadays,pasteurizationisalsousedforpreservation
ofotherbeverageslikebeer,fruitjuiceetc.
•Pasteurizationisaselectiveheatingtechniqueandit
killssomebutnotallmicro-organismspresentinmilk.
•Ifmilkiscontaminatedbysomediseasecausing
micro-organisms,milkcannotbeheatedatboiling
temperaturetokillthesemicro-organisms.

24. Cont;
•Itisbecauseheatingathightemperaturebringsseveral
undesirablechangesinmilk.E.g.itkillsbeneficiallactic
acidbacteriapresentinmilk.
•Similarly,caseinproteinprecipitate,lactosecaramelizes,
flavorofmilkchanges.
•Suchmilkbecomesunsuitableforproductionofmilk
productslikeicecream,cheese.
•Similarly,beverageslikebeerandfruitjuicecannotbe
heatedathighertemperaturebecauseitbringsseveral
undesirablechangesinflavor,tasteetc.

25. Cont;
•Inpasteurization,milkandbeveragesareheatedatlower
temperaturethatkillsspoilageorpathogenicorganisms
withoutbringingundesirablechangesintheproduct.
•Therearethreetechniquesofpasteurizationofmilkwhich
differintheirtime-temperaturerelationship.
•Time-temperaturerelationofpasteurizationareselectedon
thebasisofthreebacteriawhicharetransmittedthrough
milk(Mycobacteriumbovis,CoxiellaburetiiandBrucella
abortus).

26. Cont;
•Lowtemperatureholding(LTH)orVatpasteurization:
–Inthismethod,milkisheatedat62.8
o
Cfor30
minutes.
•Hightemperatureshorttime(HTST)method:
–Inthismethod,milkisheatedat71.7
o
Cfor15
seconds.
•Ultra-pasteurization:
–Inthismethod,milkisheatedatabout137.8
o
Cfor2
seconds.

27. CANNING:
•Canningistheprocessofpreservationoffoodbykeeping
theminsealedcontainerandthenheatingthecontainer.
•CanningtechniqueswasoriginallydevelopedbyNicoles
Appert.
•Therearetwotypesofcannedfoodi.e.heatedand
unheatedcannedfood.
•Duringcanningatfirstrawfoodiswashedandthen
processed.
•Thenprocessedfoodisplacedintoasuitablecanandthe
canisthenheated.
•Sealedcanscanbeheatedeitherbyimmersingitinto
boilingwaterorbysprayofsuper-heatedsteamorheated
dryair. -Cont;

28. Therearetwosystemofcanning,
–i.e.hotpacksystemandcoldpacksystem.
•Inhotpacksystem,rawfoodispreheatedbefore
packingintothecanandincoldpacksystem,foodis
notpreheated.
•Canningiscommonlyusedforpreservationofmany
foodslikevegetable,meat,fishetc.
•Cannedfoodismicrobiologicallymorestableand
remainunspoiledforlongtime.

29. Cont;
•Itisbecauseanymicro-organismpresentinrawfoodare
killedduringheatingthecanandsealedcontainerprevents
entryofspoilageorganismintothefood.
•Defectivecanningisnotsafeforpreservationoffood.
For.eg.ifcannedfoodisnotproperlyheated,some
thermophilicorganismandendosporeofbacteriapresentin
rawfoodarenotkilled.
•Suchsporesthengerminateandcausespoilageofthefood
evenifthecanisintact.

30. Cont;
•Furthermore,canmustbecompletelyfilledwithfood.
•Ifanyspaceorairispresentinsidethecan,thisaerobic
conditionfacilitatesgerminationofsurvivingspores.
•Similarly,canusedforpackagingthefoodmustbe
completelysealed.
•Ifanybreaksorleaksarepresentincanmanyspoilage
organismsenterintothefoodandspoilthefood.
•Furthermore,airentersintothecanthroughleaksthat
facilitatesgerminationofsurvivingspores.

31. Cont;
BLANCHINGORSCALDING:
•Blanchingistheprocessofwashingvegetablesorfruits
inwarmwaterbeforestorage.
•Advantagesofblanchingincludes:
–Itinactivatesenzymeoffoodthatcauseself-
decomposition.
–Itreducesnumberofmicro-organismspresentonthe
surfaceoffood.
–Itbringswiltingofleafyvegetablesandhelpsin
packaging.
–Itenhancesfixingofintensegreencoloroffruits
andvegetables.

32. Cont;
ROASTING:
•Itisusedformeatandmeatproducts.
•Duringroastinginternaltemperatureofmeatreaches
(80-85)
o
C.
BAKING:
•Itisusedforbread,cakeandotherbakeryproducts.
•Duringbakingtemperaturemaximumof97
o
Cis
reached.
FRYING:
•It is used for vegetable, meat, fish etc.
•During frying outer surface of food becomes very hot
but internal temperature of food never exceed 100
o
C.

33. Cont;
COOKING:
•Duringcookingtemperaturearound100
o
Cisreached.
SIMMERING:
•Itistheprocessofgentleboilingoffoodwiththe
temperatureofabout100
o
C.
Preservation of food by low temperature:
•Low temperature is commonly used physical method of
preservation of food.
•Low temperature preserves food by:
–Slowing down growth and activity of spoilage organism
in food.
–By slowing down the rate of chemical reaction or other
enzymatic activity that cause self-decomposition of food.
–Sometimes low temperature kills spoilage organism in
food. E.g. in case of deep freezing.

34. Cont;
Differentmethodsoffoodpreservationbylowtemperature
Commonorcellarstorage:
•Commonstorageisthetechniqueofpreservationofcertain
foodslikepotato,onionetc.inhomebyspreadingthemin
coldroom.
•Incommonstorage,storagetemperatureisslightlylower
thanthatofoutsideair.
•Butthistechniquefoodisnotstoredforlongtimebutitis
stillusedwherecoldstorageandfacilitiesarenotavailable.

35. Chillingorcoldstorage:
•Inchillingorcoldstorage,storagetemperatureis
usuallybetween(0-10)
o
C.
•Atthistemperature,growthandactivityofmostbacteria
exceptpsychrophilesissignificantlysloweddown.
•Therefore,bychillingstorage,foodcanbestoredfor
longtimethancommonstorage.
•However,ifpsychrophilicorganismsarepresentinfood,
theygrowinfoodandcausespoilage.

36. Cont:
•Selectionofappropriatetemperatureisveryimportant
becausequalityofsomefoodisdamagedatlower
temperaturestoragetemperatureofsomefoodare(10-
12.8)
o
Cforsweetpotato,(13.3-16.7)
o
Cforbanana
etc.
•Thismethodismostcommonlyusedforshortterm
storageofhighlyperishablefoodslikemeat,milk,fish
etc.
•Fishisstoredbyplacingitincoldice.

37. Freezingorfrozenstorage:
•Infreezingstorage,storagetemperatureisbetween(-15
to-29)
o
C.
•Atthistemperature,growthofevenpsychrophilic
bacteriaiscompletelyinhibited.
•Therefore,foodkeptinfrozenstorageremainfreshin
longtimewithoutundergoingmicrobialdecomposition.
•Furthermore,self-decompositionoffoodoccursvery
rarelyornotatallatthistemperature.
•Sometimes,freezingalsokillsspoilageorganisms
presentinfood.
•Therefore,frozenstorageisveryeffectivemethodof
foodpreservationamongthesethreetechniques.

38. Cont;
•Killingmechanismoffreezingisduetoformationof
ice-crystalanddehydrationofmicrobialcell.
•Whenfoodisfrozen,surroundingwaterfreezesto
formice-crystals.
•Thencytoplasmicwaterfrommicrobialcell
continuouslydiffusesoutandisaddedinsurrounding
ice-crystal.
•Theremainingcytoplasminmicrobialcellgradually
becomesmoreandmoreconcentrated.
•Highsaltconcentrationinremainingcytoplasmkillthe
microbialcellbycausingmechanicaldamagetothe
cell.

39. Cont;
•Therearetwomethodsoffreezingthefoodi.e.quick
freezingandslowfreezing.
•Slowfreezingismoreeffectiveinkillingmicrobial
cellbutquickfreezingisconsideredmoreappropriate
forpreservationoffood.
•Whenfoodisfrozenveryslowly,thereissufficient
timeforcytoplasmicwatertodiffuseout.
•Inthiscasemicrobialcellisdehydratedtogreater
extent.Similarly,largerice-crystalareformeddueto
continuousadditionofdiffusedwaterintoice.
•Largericecrystalgivesmoremechanicaldamageto
microbialcell.

40. •However, if larger ice-crystal are formed in food, it gives
more mechanical damage (causes cracking of food) to the
food.
•Therefore, quick freezing is commonly used for food
preservation.
•Although, frozen storage completely prevents microbial
decomposition, it brings several undesirable changes in some
food.
•Some such examples include:
–Protein of food e.g. meat may become dehydrated so that
the food becomes very tough and rigid.
–Myoglobin present in meat may be oxidized into brown
colored meat-myoglobin.
–Fat present in food may be hydrolyzed or oxidized.
–Ice-crystals formed on surface of food evaporate and give
mechanical damage on the surface of food. This damage is
called freeze-burn.

41. Methodsoffreezing:
Quickfreezing:
–Inquickfreezing,temperatureofthefoodlowered
veryquickly.
–Foodisfrozenquicklybyimmersingfoodinto
solutionofrefrigerant.For.eg.fishfrozenby
immersingitintofrozensolutionofNaCl.
–Byblowingfrigidair(at-17.8to-34.4
o
C)overthe
foodtobefrozen.

42. Cont;
Slowfreezing:
–Inthisprocess,temperatureofthefoodislowered
veryslowly.
–Foodisfrozenslowlybyplacingitinsidethe
mechanicalrefrigerator.
–Thistechniqueiscommonlyusedtofreezefoodin
home.
–However,slowfreezingformslargerice-crystalin
foodandgivemoremechanicaldamage.
–Therefore,quickfreezingispreferredoverslow
freezing.

43. SLOW FREEZING
•It is more effective in killing
micro-organisms in food.
•Larger ice-crystals are
formed.
•Microbial cell is dehydrated
to greater extent.
•It gives more mechanical
damage due to formation of
larger ice-crystal.
•Micro-organisms may adopt
slowly to lower temperature.
•Cold shock does not occur.
QUICK FREEZING
•It is less effective in killing
micro-organisms in food.
•Smaller ice-crystals are
formed.
•Microbial cell is dehydrated
to lesser extent.
•It gives less mechanical
damage due to formation of
larger ice-crystal.
•There is no time for
adaptation.
•Microorganisms may be
killed by cold shock.

44. PreservationoffoodbyDrying:
•Manyspoilagemicro-organismsarehighlysusceptible
todrying.
•Somespoilageorganismsarekilledrapidlybydrying
andgrowthofmostotherorganismisloweredor,
inhibitedbydrying.
•Therefore,microbialdecompositionoffoodcanbe
preventedoratleastminimizedbydryingthefood.
•Therearedifferentprocessesofdryingfood.
•Dryingisperformedbyeitherevaporationofwater
fromthefoodorbyloweringA
wvalueoffoodby
additionofsaltandsugar.
-Cont;

45. •Duringdryingoffoodbyevaporation,severalparameters
liketimeofdrying,humidityofair,temperatureoftheair
etc.shouldbecontrolled.
•Impropercontrolofthisparameterbringsseveral
undesirablechangesonfood.
•For.eg.iffoodisdriedquicklybyplacingitinveryhot
environment,moistureisevaporatedonlyfromthesurface
butnotfrominnerlayeroffood.
•Inthiscase,veryhardlayerisformedonsurfacethat
preventsfurtherdehydrationoffood.
•Thisdefectiscalledcasehardening.

46. Differentmethodsofdryingfoodinclude:
Solardrying:
•Inthismethod,foodisdriedbyplacingitinhot
atmosphereofsun.
•Manyfoodslikegrainsandchoppedpiecesof
vegetablesusedformakingpicklesaredriedbythis
method.
Dryingbymechanicaldrier:
•Inthismethod,foodisdriedwiththehelpofsome
mechanicaldrier.
•Liquidfoodlikemilkaredriedbyspraydryingand
drumdryingmethod.
•Someliquidfoodsaredriedbyplacingthemin
vacuumchamberoflowertemperature.

47. Cont;
Dryingbyadditionofsaltandsugar:
•Itisindirectmethodofdrying.
•Whensaltorsugarisaddedinfood,itbindswaterin
theformofshellofhydrationandmakeitunavailable
formicro-organisms.
•Therefore,theydecreasetheamountofavailablewater
(A
w)offood.
•Exampleoffooddriedbythismethodincludes
preservationoffoodbyaddinghighsaltconcentration
andpreservationofmilkbyaddingsugar.

48. PreservationoffoodbyRadiation(irradiation):
•Twotypesofradiationareusedinfoodpreservation.
Theyinclude:
Non-ionizingradiation:
UVlightisanexampleofnon-ionizingradiation.
Application of UV light in food preservation:
•UV light is used to kill micro-organisms present in
clear liquid foods. For.eg. it is used to kill yeast cells
and other micro-organisms in fruit juice.
•It is used to inhibit growth of yeast and mold on
surface of some foods like pickles, vinegar, cheese etc.
UV light is commonly used to prevent surface spoilage
of various foods including pickles, vinegar etc.
•UV light is used to disinfect water used for production
of beverages.

49. Cont;
•Itisusedtokillmicro-organismspresentinairoffood
processingroom.
•Itisalsousedtokillmicro-organismsonvariousfood
processinginstrumentslikeknife,eatingutensils,etc.
•UVlightisusedinrapidageingofmeatinmeat
industries.Ageingistheprocessofdryingmeatby
hangingpiecesofmeatincontrolledenvironment.
Usuallymeatisagedbyhangingitinroomata
temperatureof2.2-3.3
o
C.Atthistemperature,ageing
occursinseveralmonths.

50. Cont;
•Temperatureismaintainedlowertopreventgrowthof
micro-organismsinmeatduringageing.Ifageingis
doneathighertemperaturemicro-organismsgrowin
meatandspoilitbeforeageingtakesplace.
•Inrapidageingtechniquetemperatureofroomis
maintainedaround18
o
CandUVlightisusedto
inhibitgrowthofmicro-organismsinmeatduring
ageing.Atthistemperatureageingoccursin2-3days.

51. Ionizingradiation:(Coldsterilization)
•X-ray,γ-rayandcathoderayareexamplesofionizing
radiation.
•Theyarepowerfuloxidizingagentsandkillthe
microbialcellbyoxidizingvariouscellularmaterials.
•Somecommonionizingradiationusedinfood
industryinclude:
X-ray:
–ProductionofXrayisexpensive.
–Furthermore,itspenetrationpowerislower.
Therefore,itisnotcommonlyusedinfood
preservation.

52. Cont;
•γ-ray:
–Ithasgoodpenetrationpoweranditcanpenetrate
upto20cmeveninsolidfood.
–γ-rayisemittedinalldirectionfromthesource.
Thereforeitisdifficulttomakeγ-raytohitthe
food.
–So,efficiencyofγ-rayinfoodpreservationisonly
10-25%.

53. Cont;
Cathoderay:
–Cathoderayisdirectionalanditisemittedinonly
onedirection.
–Therefore,efficiencyofcathoderayinfood
preservationishigh(upto40-80%).
–Unfortunately,ithaslowerpenetrationpowerand
canpenetrateonlyupto0.5cminsolid.

54. Applicationsofionizingradiationinfoodprocessing:
•Someapplicationsofionizingradiationinfoodpreservation
includes:
•Lowlevelofionizingradiationisusedtokill
microorganismsonfreshfruitsandvegetables.Itisusedto
killinsectaswellasmicroorganismsonvegetableandfruits.
•Highlevelofionizingradiationisusedtokill
microorganismsandinsectondryvegetableandfruits.
•Ionizing radiation are commonly used to preserve meat and
meat product. For.eg. irradiation is commonly used to inhibit
microorganisms, nematodes and other parasites present in
meat and meat products.

55. Cont;
Undesirablechangesofionizingradiation:
•Inmeat,itincreasespH,damageglutathione,increase
carbonylcompoundandgeneratebadsmelling
compoundlikeH
2Sandmethylmercaptan.
•Infattyfood,itdamagesnaturalanti-oxidantand
increaseschanceofoxidativerancidity.
•Itcauseslossofseveralvitaminslikepyridoxine,
thiamine,vit.C,vit.D,vit.A,vit.B
12.Therefore,it
reducesnutritionalvalueoffood.

56. Chemicalagentsusedinpreservationoffood:
•Differenttypesofchemicalpreservativeareusedto
preservevarietyoffood.
•Chemicalpreservativesareutilizedinfoodpreservation
invariouswaysasgivenbelow:
–Somefoodpreservativesaredirectlymixedwiththe
foodtobepreserved.
–Somechemicalpreservativeareusedinwrapperor
containeroffoodratherthaninfooditself.
–Somechemicalpreservativeareplacedinairof
storageenvironmentoffood.
–Somechemicalpreservativeareusedfortreatmentof
equipmentusedinfoodprocessing.

57. Cont;
•Notallfoodpreservativecanbeusedtopreserveahtypes
offood.
•Itisbecausesomechemicalpreservativebringssome
undesirablechangesfor.eg.changeintaste,smelletc.in
somefood.For.eg.spicesareusuallynotconsidered
suitableforpreservationofmilkandmilkproductbecause
tasteofspicesinmilkproductisnotconsidereddesirable.
•Somechemicalfoodpreservativesusedinpreservationof
foodinclude:

58. a)Organicacids:Examples
I)PROPIONICACIDANDPROPIONATE:
–PropionicacidisnaturallyfoundinSwisscheeseasa
developedpreservativeuptoalevelof1%.
–NaandCapropionatearecommonlyusedtoinhibit
growthofmoldinbakeryproductlikebread.
–Propionicacidandpropionateareeffectagainstmold,
withverylittleornoeffectagainstbacteriaandyeast.
–Thereforetheyareaddedinfoodwhichusually
undergomoldspoilage

59. ii)Benzoic acid and benzoate
–Sodium benzoate us used to preserve variety of food
like jam, jellies, carbonated beverages, fruits etc.
–It is most effective at power pH and it’s anti-
microbial activity decreases with increase in pH.
–Therefore, it is usually used to preserve acidic and
slightly acidic food. At pH of 2.5-4 it is effective
against most bacteria, some yeast and mold.
–Methyl paraben and propyl paraben which are
derivative of benzoic acid are also commonly used to
preserve variety of food.
–Their advantages over benzoate is that they are more
effective at higher pH.

60. iii)Sorbicacidandsorbates:
–SorbicacidanditsCa,NaandKsaltareusedas
antimicrobialagenttopreservevariousfood.
–Theyareeffectiveagainstyeastandmoldbutless
effectiveagainstbacteria.
–TheirantimicrobialactivityishighatlowerpH.
–Thereforetheyareusedinslightlyacidicfoodlike
pickles,fruitjuice,syrupandotherfoodslikecheese,
bakeryproductetc.toinhibitgrowthofmoldandyeast.

61. iv) Acetic acid and acetates:
–Acetic acid and its derivatives like monochloroacetic
acid, peracetic acid, dehydroacetic acid and sodium
diacetate are used as food preservatives.
–Some examples include;
–Dehydroacetic acid is used to treat wrappers of cheese
to inhibit growth of mold on the surface of cheese.
–Acetic acid in the form of vinegar is added in the form
of vinegar is added in pickles to inhibit growth of
microorganisms. Its activity increases with decrease in
pH.
–Sodium diacetate is used in malt syrup. It is also used
to treat wrapper of butter.

62. v)Nitritesandnitrates:
–NitriteandnitrateofNaandKareusedincuring
solutionorcuringmixtureofmeat.
–Theyhaveslightlybacteriostaticaction,buttheyare
addedinmeatmainlytofixredcolour.
–Inacidenvironment,nitritedecomposedintonitric
acidwhichreactswithhaemepigmentofmeatto
formnitrosomyoglobinthatgivesattractivered
colourtothemeat.
–Nitriteisarealcolourfixativeandnitrateisusedas
asourceofnitrite.
–Nitritecanreactwithsecondaryandtertiaryamine
toformnitrosaminewhichiscarcinogenic.
–Nitriteandnitratearemainlyusedtofixredcolour
tomeatbutnottopreserveit.

63. b)Smoking(woodsmoke):
–Smokingisamethodofpreservationofmeatby
exposingittowoodsmoke.
–Twomainpurposeofsmokingofmeataretoadd
desirableflavorandtopreservethemeat.
–Someotherdesirablechangesincludeimprovement
incolour,drying,andtenderizationofmeat.
–Woodsmokecontainslargenoofvolatile
compoundshavingbacteriostaticandbactericidal
activitythathelpinpreservationofmeat.
–Somesuchcompoundincludeformaldehyde,phenol,
cresol,aliphaticacid,acetaldehyde,ketonesand
others.
–Woodsmokealsocontainsvarietyofflavoring
compoundthatgivedesirableflavortothemeat.

64. c)SO
2andsulphites:
–SO
2andsulphitesareusedinwineindustrytosanitize
equipment'sandtoreducenumberofnormalfloraof
grapemust.
–Inaqueoussolution,SO
2andsulphitesformsulfurous
acidwhichisanti-microbial.
–Fumeofburningsulfurareusedtotreatfruitsand
vegetables.
–SO
2isalsoaddedinfruitjuice,syrupandvarious
wine.

65. d)Sugarandsalt:
–Sugarandsaltareaddedinvarietyoffood.
–For.eg.milkispreservedforlongtimebyaddinghigh
concentrationofsugar.
–Similarly,foodslikepickles,fishetc.arepreservedby
addinghighconcentrationsofNaCl.
–Preservativeactionofsaltandsugarinclude:
–Theybindwaterandmakeitunavailableforgrowthof
microorganismsi.e.reduceA
wvalueoffood.
–Sugarincreasesosmoticpressureandcausesosmotic
lysisofmicrobialcell.
–Theydrawoutmoisturefromfoodandhelpindryingof
thefood.

66. e)Formaldehyde:
–Itishighlypoisonousandisnotpermittedinfood
exceptasaminorcomponentofwoodsmoke.
–Infoodindustry,itisusedtosterilizeequipment
andtokillmicroorganismsinairoffood
processingroom.
–Itishighlyantimicrobialandcankillfungi,
bacteria,sporeandviruses.

67. f)Alcohol:
–Ethanolisanti-microbial.
–Excellentkeepingqualityofsomefoodisdueto
theiralcoholcontent.
–Ethanolcontentofsoftdrinkslikebeerisnot
sufficienttocompletelykillmicroorganismsbutit
slowsdowngrowthandactivityofspoilage
organism.
–Alcoholiccontentofdistilledalcoholicbeveragesis
sufficienttopreventmicrobialspoilage.
–Somefoodproductslikelemonextract(eg.Jolley)
arealsopreservedbyadditionofethanol.

68. g)Ethyleneandpropyleneoxide:
–Ethyleneandpropyleneoxidearegaseous
sterilizingagents.
–Theyareusedtosterilizepackagedfoodlikedried
food.
–Furthermore,ethyleneoxideisalsousedtokill
microorganismsinairoffoodprocessingroom.

69. h)Spicesandothercondiments:
–Spicesandothercondimentsaddedinfoodfortasteand
flavorareanti-microbialandhelpinfoodpreservation.
–Antimicrobialactivitydifferswithtypeofspices.
For.eg.mustard,flourandmustardoilareeffective
againstlikeSaccharomycesbutarelesseffectiveagainst
bacteria.
–Cinnamonandclovesisaddedinfoodareveryeffective
againstbacteria.
–Similarly,garlicandonionmixedinfoodare
bacteriostaticorbactericidal.
–However,notallspicescanbeaddedinalltypesoffood
productsbecausetheirtasteandflavormaybe
consideredundesirableincertainfood.

70. Cont;
i)Antibiotics:
–Useofantibioticsinfoodpreservationisnot
permittedduetoriskofdevelopmentofantibiotic
resistantmicroorganisms.