Fish silage.ppt

Fish processing technology

1. Fish silage
Theproductoftheprocessofpreservingandstoringwetbiological
materialinasilo(apitorairtightcontainer)iscalledsilage.
Silageproductionisconsideredoneofthebestwaysofpreserving
agroandanimalwastes.
Theword“silo”hastraditionallybeenusedinconjunctionwith
greenforage,preservedeitherbyaddedacidorbytheanaerobic
productionoflacticacidbacteria.
Theterm“fishsilage”hasbeenadoptedforanalogousproductsof
wholefishorpartsoffish.
Fishsilagecanbedefinedasaliquidproductmadefromwholefish
orpartsoffishtowhichnoothermaterialhasbeenaddedother
thananacidandinwhichliquefactionofthefishmassisbrought
aboutbyenzymesalreadypresentinthefish.

2. Fishsilageisproducedbyaddinginorganicororganicacidstothe
comminutedfishorbytheacidsproducedbytheanaerobic
microorganismsintroducedintothesystem.
Fishsilageproducedunderidealconditionscanbekeptformore
than1yearundertropicalconditions.
ThefirstcommercialproductionoffishsilagewasstartedinDenmark
in1948.
TypesofFishSilage:
Theprincipleofsilageproductionisthepreservationofmaterialsfrom
microbialdegradationbyadditionofchemicalsorotheragentsof
chemicalormicrobialoriginormicroorganisms.Silagesareclassified
accordingtothenatureoftheagentsemployedfortheproduction.

3. AcidSilage:
Amongmineralacids,sulphuricacid(50-75%)oramixtureofsulphuric
andhydrochloricacidsisusedtoproducesilage.Theproduceretains
thefreshacidicsmellevenaftermonthsofstorageattropical
temperatures.Thissilagehastobeneutralisedpriortofeedinganimals.
Themostcommonlyusedorganicacidsarepropionic,aceticandformic
acids.A3%byweightofformicacid(85-90%)isaddedtothewell-
groundfishmince.Silagepreservedwithformicacidhasashelf-lifeup
to1yearatambienttemperaturesofthetropicalcountries.
Asorganicacidsaremoreexpensivethanmineralacids,useofa
mixtureofinorganicandorganicacidsforsilageproductionisalso
recommended.
Cheapmineralacidslikesulphuricacidorhydrochloricacidareused
tolowerthepHandorganicacidslikepropionicorformicareaddedto
itforantimicrobialactivity.

4. BiologicalSilage:
Biologicalsilageproductionemploystheprincipleoffermentationby
microorganismsthatproducelacticacid.
Streptococcusfaecalis,Lactobacillusplantarum,L.brevis,L.cerevicae,
andL.mesenteroidsaresomeofthebacteriacommonlyusedinsilage
production.
Amongthem,L.plantarumisthebestsuitedforfishsilageproduction.
ItcantolerateaverylowpHandhighsaltcontentupto8%.
Theyfermentthesugarspresentinthemediumtoorganicacid,
predominantlylacticacid,thusloweringthepH.
AtlowpH,growthofputrefyingorganismsisinhibitedbycompetitive
inhibitionandalsobytheactionofcertainantibioticsproducedinthe
system.

5. Asfishcontainonlyasmallquantityofstarchorcarbohydrate,theyare
addedinsilageproductiontofacilitatemicrobialfermentation.
Differentworkershaveusedcerealmeal,molasses,topiocameal,ragi
andothermaterials,insilage.
Theprocessofconversionofcarbohydratetolacticacidby
fermentationisanaerobic.
Itcanbedividedintothreestages.Thefirststageisthehydrolysisof
starchtomaltosebyamylase.
Inthesecondstage,maltoseisconvertedtoglucosebymaltase.Both
thesestagesrequirestarchhydrolyzingenzymesandhencerequire
additionofsubstanceslikemolassesorfermentedcerealslikeragito
facilitatemicrobialfermentation.
Thelaststageisconversionofglucosetolacticacidbythebacteria.

6. Smallamountsofaceticacid,propionicacidandethylalcoholarealso
producedinthisprocess.
Lacticacidbacteriadestroyspoilageorganismsbycompetitive
inhibitionandalsobyproducingantibioticsandotherantimicrobial
chemicals.
Thelacticacid-producingbacteriaaredividedintotwogroups,
homofermentativeandheterofermentative.Thehomofermentative
bacteriaconverteveryglucosemoleculeintotwomoleculesoflactic
acid,whereasheterofermentativeonesproducelacticacid,aceticacid,
ethylalcohol,mannitol,dextransandcarbondioxide.
TheprimarycatabolismofhexosesbylacticacidbacteriaIinbothtypes
offermentationisreportedtobedifferent.Hence,insilageproduction,
itisdesirabletouseastarterculture,containingpredominantly
homofermentativelactobacillus.Usually,fishcontainsonlyaverysmall
quantityoflacticacid-producingbacteria.Thisisonereasonwhya
starterculturecontaininglactobacillusisinvariablyusedinmicrobial
fermentationoffish.

7. RawMaterials:
Fishofallspeciesandfishwastescanbeconvertedintosilage.
Silageisproducedbyofusingby-catchesfromshrimptrawlers,fresh
fishandfishoffal.
Fattyfishmayposetechnologicalproblemsasthesilageproducedis
susceptibletorapidlipidoxidation.
Whensilageisproducedfromfattyfish,oftentheformationofan
emulsionphaseisseen.Thisemulsionoccludessizeablequantifiesof
proteinsthatarethuslostastheyarenoteasilyrecoverableevenon
centrifugation.Fattysilagegivesafishytainttomilkofcattle,eggsof
poultry,andmeatofpigsandchicken.
Fattyfishesarenotgenerallypreferredinsilageproduction.

8. Whenfattyfishesareused,lipidsareseenfloatingonthetopofthe
silage,renderingthesilageanaerobic.
Intheindustrialproductionofsilage,de-oilingequipmentsareused
toremoveexcessfat.
Lipidoxidationresultsintheformationofseveralvolatilecarbonyl
compounds.Someoftheminteractwithproteinsandmakethesilage
nutritionallypoor.
Aleanfishwithlipidcontentlessthan2%(w/w)isadesiredraw
materialforsilageproduction.
Silagepreparedfromspoiledfishwhenfedtochickscausedmortality
andpoorgrowth.
Butsilageproducedfroma1:1mixofspoiledfishandgoodfishgave
goodgrowthandnomortality.

9. ProductionofAcidSilage:
Thecostisthedecisivefactorinselectinganacidforsilage
production.
Allequipments,tanksandvesselsmustbeacidresistant.
Forsmall-scaleproduction,notmanyequipmentsareneeded.
Thepulpedmaterialcanbemixedmanuallywithanadequatequantity
ofacidandstoredinacontainer.
Forlarge-scaleproduction,thefollowingequipmentsareneeded:
1)Meat mincer for mincing the whole fish into suitable sizes.
2) Mixer or homogeniser for homogenising the fish mince and acid
together.
3) A mechanical stirrer for agitating the slurry in the tank.

10. 4)Mechanicalpumpformeasuringandaddingacidtotheslurry.
5)Tanksforsilageproductionandsubsequentstorage:Silagecanbe
storedindrumsmadeofsteelorpolyethylene.
6)De-oilingequipment:Aftertheliquefactionofthesilage,thefishoil
floatsonthetop.Theexcessoilmustberemoved,sincehighoil
contentinsilageislikelytocreatenutritionalproblems
Thewholefishiscomminutedinamechanicalmincer.
Addtherequiredquantityofacidoracidmixture(normally2—3%
w/w)andmixtheslurrywell.
Afterthisprocessthewholematerialbecomesagoodpaste.
Storethepasteinadrumorlargetankfor15—20dayswithdaily
stirring.
Ithasashelf-lifeofover1yearundernormalconditionsofstorage.
Thewholeprocesscanbeautomated.

11. Commonly used acid or acid mixtures are:
1)Formic acid (90%) 3% (w/w) of fish mince
2)2) Mixture of 2.5% (w/w) of sulphuric, formic and propionic acids
(1:1:0.5),
3) A mixture of 3% (w/w) of 90% formic acid and 95% propionic acid, (1:1
w/w).
4) Three per cent w/w of 90% formic acid, 95% propionic acid and
concentrated sulphuric acid (1:0.5:2 v/v).
5) 15% (v/w) of sulphuric acid (25 or 30% strength).
6) A mixture of formic acid (1%) and hydrochloric acid having pH 2 to 3
Between formic acid and sulphuric acid formic acid is the choice,
because it gives a higher pH compared to one obtained with sulphuric
acid

12. Forthesuccessfulproductionofaddsilage,thefollowingprecautionsare
recommended
1)Thematerialshouldbereducedinsize,preferablytopiecesnolonger
than3—4mmindiameter.
2)Acidshouldbethoroughlydispersedthroughoutthemincedfishto
avoidpocketsofuntreatedmaterialwherebacterialspoilagecan
continue.
3)Periodicagitationisnecessarytobringaboutrapidliquefaction.
4)Temperaturesofatleast20°Caredesirable,sincebelowthis
temperatureliquefactionisratherslow.Theenzymesresponsiblefor
liquefactioncanbeinactivatedastemperaturerisesbutsamples
heatedto40°Chavebeenfoundtoliquefyrapidly.

13. Duringautolysis,proteinsarebrokendowntopeptidesandamino
acids.
WhenthepHisaround3.0bothexo-andendopeptidasespresentin
thedigestivetractoffishaswellasintissuesareactive,bringing
abouteffectiveautolysisneededforgoodsilage.
Thepreservativeprincipleinsilageisduetothereservoirofun-ionised
moleculesofacidsthatcancrossthebacterialcellmembraneand
onceinsidedissociateinthecytoplasm,bringingdownthepHand
therebythedeathofthecell.
Forthisreason,organicacidslikeformicandpropionicacids,which
existmostlyintheun-ionisedstateevenatfairlylowconcentrations,
arebetterthaninorganicacids,whichremainun-ionisedathigh
concentrations.
Whilebacterialgrowthisreadilyinhibitedbyeitherkindofacid,fungal
growthisinhibitedbyonlyorganicacidsattheconcentrations
encounteredinfishsilage.

14. BiologicalSilage:
Duringtheproductionofbiologicalsilage,thewholefishorfishwasteis
comminutedtogetauniformmix.
Addmolasses(10%w/w)and30%water(w/w)tothismixandstirwell.The
resultantthickslurryiscookedfor20minutes.
Cookingkillsallundesirablemicroorganismspresentinthefishpaste.Transfer
theslurrytolargebitumen-coatedvesselsorcementtanks.
Innoculatewithastartercultureofthelacticacidbacteria(e.g.,Lactobacill!us
plantarum)18—20hoursoldandstirwell.
Keepitfor15—20days,stirringdaily,afterwhichthesilageisready.Ithasa
shelf-lifeofupto1yearundernormalconditionsofstorage.
TheprecookedsilageshowsrapidfermentationandreachesapHof4.4within
72hours,whileuncookedsilageattainsapHofonly5.
Also,uncookedsilageshowsmoredegradationofproteinsbyautolysisas
indicatedbythealphaaminonitrogenvalues.

15. Fishisapoorsourceofcarbohydratesneededforlacticacidbacteriato
fermentandproducelacticacidinthesilage.
Usually,molassesorothercarbohydratematerialsareaddedforthispurpose,
Fish:molassesratioof100:5isusuallyfollowed.
Theuseofmolassesortapiocaisideallysuitedtotropicalcountriesasthey
areabundantlyavailable.
AsatisfactorypHaround4canbeobtainedonlywhenmolassesconcentration
isintherangeof10%andabove.
Lacticacidbacteriafermentsugarsandproducelacticacid,whichlowersthe
pHaslowas4.5.AtthislowpH,growthofmanyputrefyingorganisms;moulds
andpathogenslikeSalmonellaandClostridiumbotulinumarepreventedor
inhibited.
Ifsufficientcarbohydrateisnotpresentinthemedium,requiredlevelsofacid
willnotbeproduced.Thisisthereasonwhysilagewith5%addedmolasses
gotputrefiedwithin7days.Nutritionally,biologicalsilagesaresuperiortoacid
silages.

16. Biochemical Changes Associated with Silage Production and Storage
Autolysis:
Inadeadfish,autolysisisanaturalprocessaidingputrefaction.
Enzymespresentinthedigestivetractaswellasintissuesare
responsibleforautolysis.
Afterpost-mortemchanges,themusclepHfallstoaslowas4because
oftheanaerobicbreakdownofmuscleglycogenproducinglacticacid.
AtthispH,mostproteasesareactiveandcausethebreakdownof
muscleproteins.
Infact,proteasesaremainlyresponsibleforautolysis.
Apartfromthesechanges,lipidhydrolysisisalsotakingplace
concomitantlybyactionoflipasesreleasingfreefattyacids.

17. Proteolysisisacomplexphenomenonmediatedbyseveralproteases
presentinthefish.
EachproteasehasadifferentpHoptimumandtemperatureoptimum.
Mostdigestiveproteasespresentinthefishhaveoptimumactivityat45—
50°C.
Butautolysistakesplaceatlowertemperatures.Thecriticaltemperature
forthecommencementofautolysisisaround20°Cforcold-waterfishand
around30°Cfortropicalfish.
Enzymaticbreakdownofproteinsmaketheproductbitterbecauseofthe
productionofbitterpeptides.
Itwasalsoreportedthatliberatedfattyacidsfromlipidhydrolysiscause
solubilisationofproteins.
Consequently,fattyfishcangivefeweryieldsofliquefiedproteins.
Theyieldofsolubilisedproteinsmayvarydependingontherawmaterial,
thefleshgivingthelowestandviscerathehighest.
Proteølysisgivesalargeresiduecontainingunhydrolysedproteins.

18. Althoughthefishvisceracontainsanumberofproteinases,itis
usuallytheacidproteinaseslikepepsinandcathepsinsBandD,
thatactivelycontributetotheautolyticprocessbecauseoftheacid
pHofthesilage.
ThepHofthesilagealsodeterminestheextentofthebreakdown
andnatureoftheproteolyticproductsformed.
AlowpH(3.0orlower)limitsthehydrolysistomostlyendo-
proteinasesresultinginalesserdegreeofhydrolysis(65—70%),and
agreateramountoflongerpeptidefragments.
AhigherpH(3—4),extendstheproteolyticrangetoexopeptidases
aswell,increasingthedegreeofhydrolysis(upto80%)and
producingmostlyaminoacidsandsmallpeptidefragments.
Uponliquefactionofthesilage,whichcantakefrom3to7days,
dependingonthetemperatureandnatureofrawmaterial,thesilage
separatesinto3or4layers.Anoilylayerfloatsatthetop,
sometimeswithanunderlyingemulsifiedlayer.Amiddleaqueous
layerformsmostofthesilageandsedimentorsludgecontaining
undigestedprotein,scalesandbonesisfoundatthebottom.

19. NatureofAcids:
Itisseenthatdifferentacids,organicandmineral,havedifferent
ratesofliquefactiongivingvaryingamountsofsilage.
InpH2(inensilationwithsulphuricacid)onlyacidendo-peptidases
andaweakexo-peptidasesactivityarepresent,slowingthe
formationofaminonitrogenduringantolysis.Correspondingly,the
amountofshortpeptidesandaminoacidsarehigherinsilagewith
formicacidthanintheonewithsulphuricacid
AtpH3.0therateofautolysisandyieldofsilageweremarkedlylow.
Herringsilagewasbetterautolysedwhenformicacidwasused
aloneratherthaneithersulphuricacidorphosphoricacid,because
theformergavepH4.5andthelatter3.1.
LipidOxidation:
Unsaturatedlongchainfattyacidsreleasedfromfishbylipid
hydrolysisbylipasesabsorboxygenandundergorapidauto-
oxidation,releasingalargenumberofvolatilecarbonylsand
makingthesilagerancid.
Therateoflipidoxidationisdirectlyrelatedtoexposuretosunlight,
presenceofpro-oxidantsandconcentrationofheavymetals,
temperature,andotherfactors.

20. Oxidizedlipidsareresponsibleforthepoornutritionalqualityofthe
silage.
Hence,silageproducedfromfattyfishhasshortershelf-lifethanone
producedfromleanfish.
AdditionofantioxidantslikeBHA,BHTandethoxyquincan
substantiallyretardthedevelopmentofranciditybutareseldomadded
insilage.
Oxidizedlipidsalsointeractwithproteinsrenderingthem
unacceptabletoproteases.
PresenceofMicroorganisms:
Preprocesshandlingoffishplaysinimportantroleinthemicrobial
qualityofsilageproduced.
Therawmaterialmayharbourpathogens.However,cookingor
pasteurisationcandestroymostbacteria.
Manyorganismsusuallyseeninfisharesensitivetoacidityand
pathogenslikeVibriocholeraeandSalmonellaaretotallydestroyedat
pH4—5.
Butsporesofmanyorganismsarelikelytooccur.Hence,itis
recommendedthatsilageshouldbeproperlycookedpriortofeeding
animals.

21. DegreeofAutolysisinSilage:
Duringensilationitistheproteolyticenzymesoffishoritsoffalwhich
carryoutextensivehydrolysisoffishproteins.Asaresultamountof
proteinfractiongraduallydecreaseswhilethatofnon-proteinfraction
increases.
Thedegreeofautolysisandproteinsolubilisationinsilagevariedwith
thenatureofrawmaterials,rangingfrom80%intemperatefishesto
40—45%intropicalfisheslikesilverbellies.
Theundigestedproteinsappeartobepeptideaggregatesheldtogether
bynon-covalentforces.
Theundigestedproteininthesludgeatthebottomofthesilageisseen
tobeashighas50%ofthetotalproteinincaseoftropicalfish.
Theexactreasonforthisincompleteproteolysisisnotfullyunderstood
sofar;butpH,temperature,durationofensilationandnatureofraw
materialsappeartoplayanimportantrole.
Ahighdegreeofhydrolysis,resultsinagreaterliquefactionand
digestionoffishandconsequentlyhigheryieldsoftheaqueousphase
ofsilage.
Butthisisnotdesirableduetoseveralreasons.

22. Thelesssolubleaminoacidscanseparatefromthefishsilageon
standing,leachinglossesaregreateruponincorporationofsuch
silagesintofeedsandtheirassimilationispoorer.
Duetothesereasons,severalattemptshavebeenmadetolimitthe
hydrolysisinfishsilages.
Heatingtoinactivateenzymesisanoftenusedapproach,while
additionofformalinisanother.
However,useofformalinisnottoberecommendedasitimpairsthe
performanceofanimalsfedsuchsilages.
Compositionoffishsilage:
Therangeofcompositionis:moisture–70to81%.crudeprotein–15to
17%,ash–2to4%andoil–0.5to13%.

23. Nutritionalvalueofsilage:
Thesilageconcentrateisahighlydigestedproteinhydrolysatewhichis
convenientasaproteinsupplyforweaningcalvesandpigsaswellass
poultry.
Whenhighamountsoffishsilageproteinarefedtomatureruminantsor
fish,theanimalproductionandgrowtharereduced.
Thisisprobablyduetoadverseeffectsofhighlyhydrolysedproteinin
themetabolismoftheseanimals.However,5–10%ofthefeedprotein
maybesubstitutedbysilageproteinwithoutnegativeeffects.
Actually,thereareindicationsthathealth,fertilityandgeneral
appearanceareimprovedwhensomefishsilageproteinisincluded.
Atlowlevelsofinclusionindiet,silagedoesnotproduceanyilleffects
ongrowthofchickenandpigsandservesasidealsubstituteforfish
meal.

24. Fishmealversusfishsilage
Fishmeal
Fishsilage
Capitalcost High Low
Manpower
requirement
Require engg. and tech.
staff
Require unskilled
workers
Storage Require more space than
silage
Requiremorespace
thanmeal
Smell at production
centre
More Less
Transport Cheap Costly
Marketing Established,wellknown Notwellknown

25. Fishsilagehasaninherentdefect,itsliquidconsistency,whichmakes
itdifficulttotransporttodistantplacesandtostore.
FeedingexperimentsinIndiashowedthatitwasextremelydifficultto
convincethefarmerswhorearpoultry,pigsandcowsaboutthe
efficiencyoffishsilageasaproteinsupplementbecauseofthis
disadvantage.
Toovercomethisproblem,asolidfeedmixwascompoundedoutof
boiledfishsilageandricebranpowderintheratio1:3andsun-dried.
Theresultantdrypowderhasabout9%moistureand21%protein.
Itiseasilytransportedandhasextendedshell-lifeatambient
temperaturesinthetropics.
Thericebrancontainsallvitamins,particularlytheBgroup,andmany
othermicronutrientsrequiredforanimals.Thisisanaddedadvantage
inthatsilageisusuallydeficientinvitamins.

26. FeedingtrialsconductedattheLivestockResearchStationat
Kattupakam(undertheGovernmentofTamilNadu,India)onpigsand
poultryforaperiodupto6monthsshowedthatthefeedmixgave
excellentweightgainandfeedconversion.
Anotherproblemsencounteredintheuseofsilageisitslowsolids(dry
matter)content,whichcanincreasethecostoftransportation.
Twoapproacheshavebeentriedtoovercomethisproblem;
Concentratingtheseparatedaqueousphaseofsilagetoahighersolids
contentispracticedinNorwayandDenmark,whilethesilageismixed
withotherfeedingredientsanddriedtoyieldastableproductinmany
southeastAsiancountriesincludingIndia.
Anotableadvantageofacidpreservedsilagesistheabsenceoffly
infestationwhiledrying,whichcanbeaformidableprobleminwhen
dryingfishintheopenforfishmealproduction.