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uce f. :du

Maturationand

MaturityIndices

0- ux

MichaelS.Reid

g- d: 3

MATURATIONANDMATURITYINDICES55

or initionlacks or theyoungfruit,orthefullydevelopedfruit. maturity

56CHAPTER6

Figure6.1

(Watadaetal.1984) <::0 'j;; 'E

Development.s:

OJCI I

Thisencouragesgrowersandshippersto

expediteordelayharvestingtheircropto takeadvantageofpremiumprices,Themini- mummaturitystatementsinthegradestan- dardsexisttopreventthesaleofimmature orovermatureproductandtheconsequent lossofconsumerconfidence.Objective maturityindicesenablegrowerstoknow whethertheircommoditycanbeharvested whenthemarketisbuoyant.

Efficientuseoflaborresources.vVith

manycropstheneedforlaborandequip- mentforharvestingandhandlingisseasonal.

Inordertoplanoperationsefficiently,grow-

ersneedtopredictthelikelys~artingandfin- ishingdatesfortheharvestofeachcommod- ity.Objectivematurityindicesmevitalfor accuratepredictionofharvestdates.

Growth

Maturation

Physiological

---maturity--- n~ipening---

Senescence

Horticulturalmaturity

Sproutsn__-Stemsandleavesnn-

asparagus,celery,lettuce,cabbage

Inflorescences

artichoke,broccoli,cauliflower

Partiallydevelopedfruit

cucumber,-greenbean,okra,sweetcorn

Fullydevelopedfruit

apple,-pear,citrus,tomato

RootsandtubersSeeds

carrot,onion,potatodribean ?~~_dlings

CutandpottedPotted

foliagefloweringCut nurserystockplantsflowers

OrnamentalcropsSeeds

CHARACTERISTICSOFAt1ATURITY

INDEX

Maturitymeasuresmadebyproducers,han-

dlers,andqualitycontrolpersonnelmustbe simple,readilyperformedinthefieldor orchard,andrequirerelativelyjinexpensive equipment.Theindexshouldpreferablybe objective(ameasurement)ratl;J.erthansub- jective(anevaluation),TheinClexmustcon- lifeofthecommodityforallgrowers,dis- tricts,andyears.Ifpossible,theindex shouldbenondestructive.

Thesearchforanobjectivedetermination

ofmaturityhasoccupiedtheattentionof manyhorticulturistsworking':'lithawide rangeofcommoditiesformanyyears.The numberofsatisfactoryindicesthathavebeen suggestedisneverthelessrathersmall,and formostcommoditiesthesearchforasatis- factorymaturityindexcontinues,

Tworatherdifferentproblemswillbe

addressedhere,Thefirstprobh~mishowto measurematurityatharvestoratasubse- quentinspectionpoint.Thesecondand morecomplexproblemishowtopredictthe timeatwhichacommoditywillmature.For bothproblems,similartechniq:uesmaybe appropriate,butthewaysinwhichtheyare applieddiffer.

DEVelOPINGAMATURITY,INDEX

Manyfeaturesoffruitsandvegetableshave

beenusedinattemptingtoprovideadequate estimatesofmaturity.Examplesofthosethat

Thematurityindexforacommodityisa

measurementormeasurementsthatcanbe usedtodeterminewhetheraparticular exampleofthecommodityismature.These indicesareimportanttothetradeinfresh fruitsandvegetablesforseveralreasons.

Traderegulations.Regulationspublished

bygrowergroups,marketingorders,orlegal- lyappointedauthorities(suchasthestate departmentsofagricultureandtheUSDA) frequentlyincludeastatementofthemini- mum(andsometimesmaximum)maturity acceptableforagivencommodity.Objective fewcommodities,andmostregulationsrely onsubjectivejudgmentsrelatedtothebroad definitionsquotedabove.

Marketingstrategy.Inmostmarketsthe

lawsofsupplyanddemandcreateprice incentivesfortheearliest(orsometimesthe latest)shipmentsofparticularcommodities. use,areshownintable6.1.Thewiderangeof methodsthathavebeendevisedtomeasure thesefeaturesaresummarizedintable6,2.

Thestrategyfordevelopingamaturity

indexis .Todeterminechangesinthecommodity throughoutitsdevelopment. .Tolookforafeature(size,color,solidity, etc.)whosechangescorrelatewellwiththe stagesofthecommodity'sdevelopment. .Tousestoragetrialsandorganoleptic assays(tastepanels)todeterminethe value(orlevel)ofthematurityindexthat definesminimumacceptablematurity.

IndexExamples

---.~--_._---------- """'---~-_.- tomatoes

Nettingofsomemelons

Glossofsomefruits(develop-

mentofwax)

SizeAllfruitsandmanyvegetables

Shape

Angularityofbananafingers

Fullcheeksofmangoes

Compactnessofbroccoliand

cauliflower lettuce,cabbage,Brusselssprouts

Solidity

Texturalproperties:

------n

FirmnessApples,pears,stonefruits

TendernessPeas

ExternalcolorAllfruitsandmostvegetables

intomatofruits

Fleshcolorofsomefruits

Compositionalfactors:

.--.__n--

Starchcontent

SugarcontentApples,pears

Apples,pears,stonefruits,grapes

melons,kiwifruit--

Citrus

fruits

Juicecontent--.-

Oilcontent

Avocados

57
.Whentherelationshipbetweenchangesin thematurityindexquantityandthequality andstoragelifeofthecommodityhasbeen determined,anindexvaluecanbeassigned fortheminimalacceptablematurity. .Totesttheindexoverseveralyearsandin severalgrowinglocationstoensurethatit consistentlyreflectsthequalityofthehar- vestedproduct.

FEATURESUSEDASMATURITYINDICES

Chronologicalfeatures

Forcertaincrops(fast-rotationvegetables,

suchasradish,andperennialtreecrops growinginshortsummerenvironments), maturitycanbedefinedchronologically,for example,asdaysfromplantingorasdays domperfect,buttheydopermitadegreeof planning,andtheyarewidelyused.Forsome crops,thechronologicalmethodisrefinedby calculatingheatunitsaccumulatedduring thegrowingperiod,whichmodulatesthe chronologicalindexaccordingtotheweather patternduringthegrowingseason.

Physicalfeatures

Awiderangeofphysicalfeaturesareusedto

assessthematurityofvariouscommodities.

Size,shape,andsurfacecharacteristics.

Changesinthesize,shape,orsurfacecharac-

teristicsoffruitsandvegetablesarecommon- lyusedasmaturityindices.Forexample,veg- etablesinparticularareharvestedwhenthey havereachedamarketablesizeandbefore theybecometoolarge.Maturityinbananasis determinedbymeasuringthediameterofthe fingers;changesinthesurfaceglossorfeel (waxiness)areusedasapracticaltoolinhar- vestingofsomemelonssuchashoneydew (seechapter33,table33.4).

Abscission.Inmanyfruits,duringthe

laterstagesofmaturationandthestartof ripening,aspecialbandofcells,theabscis- sionzone,developsonthestalk(pedicel) thatattachesthefruittotheplant.The abscissionzonepermitsthefruittoseparate fromtheplant.Measuringthedevelopment ofthiszone(degreeofseparation)ispossibly theoldestofallmaturityindices.Abscission force(theforcerequiredtopullthefruit fromthetree)isnotgenerallyusedasafor- malmaturityindex,butthedevelopmentof theabscissionzone,or"slip,"inthenetted

58CHAPTER6

Accuratedevicesemployin~state-of-the-art

electronicsandopticsnowipermitobjective colormeasurements.Asth~priceofsuch deviceshasfallen,theyha~ereplacedcom- parisontechniquesinmantcases.Forexam- ple,digitalcolorexaminatitnisnowusedin thesortingofmechanically!harvestedpro- cessingtomatoes.

Texture.Maturationofftuitsisoften

Thesetexturalpropertiescarbeusedto

determinematurity.Theya~emeasuredwith I

Table6.2.MethodsofmaturitydeterminationI

[-.r--,'r---+-IN~~~--~ i l i~d;;~r;;;;.W:~:~:~""m;",,;o"...! ..S"bi"';.'I_ObJ';';"'-t"~~"~I !~estr:~~= fullbloomiiIII

I.,..II

I-~~~~~;;~~~-

~~~~;~~~r~~~~~;-~:~~~-t l---~---I i----~---!---~~--1

1---~-

l l b..I I!!. ~clsslonayer~~!!I:i1

I---+-rjt-I~

1p:~~y~-~~---~-l~-t--~~

!Texturalproperties:I;I!IiI

IToughness

I

Texturometer,fibrometer(also::IxIxII

jchemicalmethodsfordeter-.I!IiI iIminationofpolysaccharides)_L---~Il--~I

IColor,externalLightreflectance'IxIIIxI

l ----~---~---\--l---~--I I I I h ..III I

IIgtemissioni!I

I--~-!Visualexamination

ix+-+~I

I-".:~':~;'?"'""'~~;;;;;'d"i"~---I

~,1

1.~-dI

f--Ii f

U~l:~]~~~:~:~~~~l...~J~_:.f-=~+r=~--J

I muskmelons(seechapter33,fig.33.9)is usedtodeterminetheirmaturity.

Color.Thecolorchangethataccompanies

maturationinmanyfruitsiswidelyusedasa maturityindex.Objectivemeasurementof colorrequiresexpensiveequipment(fig6.2), andalthoughthehumaneyeisunableto giveagoodevaluationofasinglecolor,itis extremelysensitivetodifferencesbetween colors.Colorcomparisontechniquesare thereforecommonlyusedtoassessfruit maturity(fig6.3).Colorswatchesmaybe usedtodetermineexternalorinternalcolor. I instrumentsthatmeasuretheforcerequired topushaprobeofknowndiameterthrough thefleshofthefruitorvegetable(fig6.4).

Thesolidityoflettuce,cabbage,andBrussels

sproutsisanimportantqualityandmaturity characteristic.Inthecaseoflettuce,gamma- rayequipmenthasbeendevisedtomeasure headfirmness,butthetechniquehasnot beenadoptedcommercially.

Chemicalchanges.Thematurationof

fruitsandvegetablesisoftenaccompanied byprofoundchangesintheirchemicalcom- position.Manyofthesechangeshavebeen usedinstudiesofmaturation,butrelatively fewhaveprovidedsatisfactorymaturity indicesbecausetheyusuallyrequiredestruc- tivesamplingandcomplexchemicalanaly- sis.Chemicalchangesthatareusedfor

Figure6.2

Figure6.3

Colormatchingusedformaturitygrading.

III "'00""°''"0""omi'N",WFigure6.459

UsingtheUCfirmnesstestertomeasureth

nessofapples.

Figure6.6

60CHAPTER6

maturityestimationincludethechangein totalsolublesolids,measuredusingarefrac- tometer(fig.6.5);changesinthedistribu- tionofstarchinthefleshofthecommodity, measuredusingastarch-iodinereaction(fig.

6.6);acidity,determinedbytitration;and

thesugartoacidratio,whichisusedasthe legalmaturityindexforcitrus.

Theunsatisfactorynatureofchemical

testsformaturityisexemplifiedbytheold oilcontentmeasurementforavocados, whichhasbeenreplacedbythedetermina- tionofpercentdryweightbecauseofthe time-consumingandcomplexnatureofoil determination.

Frenchscientistshavedevelopedaninter-

estingapproachtoobjectivematurity(and quality)determinationofharvestedmelons; theyremoveaslendercylinderoffleshfrom eachmelonandrapidlydetermineitssugar contentbymeasuringtherefractiveindexof thejuice.Theouterportionofthecylinderis replaced,andthemelonisacceptedorreject- edbasedonthesugarreading.

Newopportunitiesinchemicalanalysis

areexemplifiedbythedevelopmentofnear- infraredtechnologiesforexaminingthecom- positionoffruitsandvegetables,andrapid sensortechnologyfordeterminingvolatile profilesinharvestedproducts.Theformeris abletomeasuresugarsinfruitsnondestruc- tively,andthelatterissufficientlyrapidto enabledeterminationofmelonmaturityin thefield.Researchershavefound,forexam- ple,thatthesugarcontentofpeachescanbe accuratelydeterminedusingnear-infrared absorptionprofiles.Asmelonsmature,their productionofaromavolatilesincreasesdra- matically.Aninstrumenthasbeendeveloped thatenablesthisincreasedproductiontobe anindicatorofharvestreadiness.

Physiologicalchanges.Thematurationof

commoditiesisassociatedwithchangesin theirphysiology,asmeasuredbychanging patternsofrespirationandethyleneproduc- tion.Theproblemwithusingthesecharac- tyinabsoluteratesofethyleneproduction andrespirationamongsimilarindividualsof thesamecommodity.Thetechniquesarealso complexandexpensivetoimplementona commercialscale.Nevertheless,therateof ethyleneproductionofasampleofapplesisquotesdbs_dbs47.pdfusesText_47

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