Effect of Organic and Conventional Management on Bio-Functional Quality of Thirteen Plum Cultivars

13 Pages·2015·0.26 MB·English

RESEARCHARTICLE
Effect of Organic and Conventional
Management on Bio-Functional Quality of
Prunus salicina
Thirteen Plum Cultivars (
Lindl.)
FranciscoJuliánCuevas1,InmaculadaPradas1,MaríaJoséRuiz‐Moreno1,Francisco
TeodoroArroyo2,LuisFelipePerez-Romero2,JoséCarlosMontenegro1,José
ManuelMoreno‐Rojas1*
1 PostharvestTechnologyandAgrifoodIndustryArea,AndalusianInstituteofAgriculturalandFishering
ResearchandTraining(IFAPA),AlamedadelObispo,Córdoba,Spain,2 OrganicProductionandNatural
Resources,AndalusianInstituteofAgriculturalandFisheringResearchandTraining(IFAPA),LasTorres-
Tomejil,Seville,Spain
* [email protected]
OPENACCESS
Abstract
Citation:CuevasFJ,PradasI,Ruiz‐MorenoMJ,
ArroyoFT,Perez-RomeroLF,MontenegroJC,etal.
(2015)EffectofOrganicandConventional Inthisstudy,thirteenJapaneseplumcultivars(PrunussalicinaLindl.)grownunderconven-
ManagementonBio-FunctionalQualityofThirteen tionalandorganicconditionswerecomparedtoevaluatetheinfluenceoftheculturesystem
PlumCultivars(PrunussalicinaLindl.).PLoSONE
onbioactivecompounds.Theirorganicacidscontent(malic,citric,tartaric,succinic,shiki-
10(8):e0136596.doi:10.1371/journal.pone.0136596
mic,ascorbicandfumaricacid),totalpolyphenols,totalanthocyanins,totalcarotenoidsand
Editor:AndreaMotta,NationalResearchCouncilof
antioxidantcapacity(FRAP,ABTS)wereevaluated.Thestudywasperformedduringtwo
Italy,ITALY
consecutiveseasons(2012and2013)intwoexperimentalorchardslocatedattheIFAPA
Received:May6,2015
centreLasTorres-Tomejil(Seville,SWSpain).Theculturesystemaffectedallthestudied
Accepted:August6,2015 parametersexceptfortotalcarotenoidcontent.Theorganicplumshadsignificantlyhigher
Published:August27,2015 polyphenolandanthocyaninconcentrationsandagreaterantioxidantcapacity.Addition-
ally,significantdifferencesbetweencultivarswerealsofound.‘Showtime’and‘Friar’were
Copyright:©2015Cuevasetal.Thisisanopen
accessarticledistributedunderthetermsofthe thecultivarswiththehighestpolyphenolconcentrationandantioxidantcapacity.‘Black
CreativeCommonsAttributionLicense,whichpermits Amber’hadthehighestanthocyanincontentand‘LarryAnn’and‘Songold’thehighest
unrestricteduse,distribution,andreproductioninany carotenoidcontent.‘Sapphire’and‘Blackamber’werethecultivarswiththehighestconcen-
medium,providedtheoriginalauthorandsourceare
trationofascorbicacid.Ourresultsshowedastrongyeareffect.Inconclusion,organicman-
credited.
agementhadanimpactontheproductionofphytochemicalcompoundsinplums.
DataAvailabilityStatement:Allrelevantdataare
withinthepaperanditsSupportingInformationfiles.
Funding:Thisworkhasbeenfundedbyinternal
fundsfromAndalusianInstituteofAgriculturaland
FisheringResearchandTraining(IFAPA)through
Introduction
Project'Caracterizaciónorganolépticayfuncionalde
productosecológicos.Utilizacióndetécnicas ThegenusPrunusincludesanimportantnumberoffruitcrops:peach(P.persica),apricot(P.
isotópicasparaladiferenciaciónentreproducto armeniaca),cherry(P.avium),almond(P.dulcis)andplum(P.salicina).Plumsaremainly
ecológicoyconvencional'(PP.AVA.AVA201301.7),
consumedfreshandarebecomingincreasinglypopularasaresultoftheirattractiveappear-
EuropeanCommissionwithEuropeanSocialFund
anceandextraordinaryflavour.Spainproducesabout8%ofthetotalEuropeanplumproduc-
(ESF)andEuropeanRuralDevelopmentFund
(ERDF).FranciscoJuliánCuevasisgrantedbythe tion(3rdposition)andisthemainexporter(seasonalmarket)intheworld[1].
PLOSONE|DOI:10.1371/journal.pone.0136596 August27,2015 1/13
OrganicandConventionalManagementinBiofunctionalPlumQuality
researchcontractfundingbyAndalusianInstituteof Europeansdemandhighqualityfreshproducts,especiallythosewithhighorganoleptic
AgriculturalandFisheringResearchandTraining qualityandnutritionalvalue[2].Forthisreason,thosecharacteristicshavebeenimportant
(IFAPA)andEuropeanSocialFund(ESF).Maria
targetsforbreedingduringthelastdecade[3].Arecentsurveyshowedthatthedemandfor
JoséRuizMorenoisgrantedbyapostdoctoral
organicproductsbyEuropeanconsumersincreasedfourfoldduringthelastdecadewhilethe
researchcontractfundingbyAndalusianInstituteof
AgriculturalandFisheringResearchandTraining areadevotedtotheircultivationonlydoubled[4].InAndalusia,ahugeincreaseintheland
(IFAPA)andEuropeanSocialFund(ESF). dedicatedtoorganicfarmingtookplace(sevenfoldintheperiod,2001–2013).Atpresent,
Andalusiaproducesmorethan50%ofthetotalSpanishproductionoforganicfruitandvegeta-
CompetingInterests:Theauthorshavedeclared
thatnocompetinginterestexist. bles[5].
EuropeanUnionguidelinesregardingorganicproduction[6]forbidstheuseofsynthetic
products(fertilisersandplantprotectionmethods).Theprinciplesfororganicagricultureare
similarinthedifferentEuropeancountriesandtheinputspermittedareregulatedbylaw.
Ontheonehand,severalreviewsandarticlesgenerallystatethatorganicfruitsandvegeta-
bleshaveahigheramountofmicronutrientsandhealth-relatedsecondarymetabolites,such
asphenoliccompounds[7],carotenoids[8],vitamins[9,10]andglucosinolates[11].Onthe
otherhand,otherstudieshavenotfoundthesameeffectonthefinalfruitquality[12,13],
emphasisingtheimportanceoftheenvironmentalparameters(i.e.temperature,irradiation
incidence,ripeness,irrigation,etc.)andnutrientdilution(differentfruitmoisture).
Theuseofpesticideswasreportedtoaffectthesecondarymetabolismofplants,increasing
ordecreasingtheconcentrationsofphenoliccompounds,dependingonthemechanismof
actionofthepesticide[14].Severalherbicidesreducecarbonfixationbyplants,decreasingthe
proportionofcarbonavailableforthesynthesisofprimaryandsecondarymetabolites.Other
herbicidesblocktheshikimatepathway,reducingthesynthesisofaromaticaminoacidsatthe
onsetofthesynthesisofphenoliccompounds[15].
Thequantityandqualityofthebioactivecompoundsinfruitisstronglyrelatedtoitsgeno-
type[16–19].Plumshaveawidegeneticbasisthatisreflectedindifferentcontentsofantioxi-
dantcompounds[20–22].Thenutritionalqualityofplumsalsodependsonseveralpre-harvest
andpost-harvestfactorssuchasirrigation[23],salinity[24],therootstockused[25],mulching
[26]andpostharvesttreatments[27]suchasmethyljasmonateandmethylsalicylate[28].
Plumfruitscontainimportantsecondarymetabolitessuchasflavonoidsandphenolicacids
withahighantioxidantcapacity[29].Phenoliccompoundsareprimarilyresponsiblefor
plums’antioxidantcapacity[30,31].Themaingroupofphenoliccompoundsinplumsare
hydroxicinnamicacidderivates(chlorogenicacid,neochlorogenicacidandquercetin)[32].
Anthocyaninsareabundantinpeel[33];theyareresponsibleforitscolour[34]andare
affectedbyfactorssuchastreepositionandshading[35].Carotenoidsarenaturalfat-soluble
pigmentswithanantioxidantcapacity[36],themainoneinplumsbeingβ-carotene,whichis
mainlyfoundinpeel[37].
MaterialandMethods
Plantmaterial,experimentaldesignandtreatments
Thestudywascarriedoutin2012and2013intwoexperimentalorchardslocatedatIFAPA
‘LasTorres-Tomejil’(Seville,Spain)(37°30’48”N;5°57’46”W).IFAPAistheownerofthe
fieldsusedfortheexperimentandtheyareintendedforresearchpurposes.Thirteendifferent
plumcultivarswerechosen(Table1).Theexperimentaldesignwasatotalrandomizeddesign
withthreereplicates.Thefertilisationappliedintheorganicorchardswasanimalmanureand
covercrop,whilethefertilizerusedintheconventionalorchardsisdetailedinDazaetal.[38].
Theplantprotectionintheconventionalorchardsfollowedintegratedmanagementguidelines.
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Table1. Harvestingdateandcoloursofpeelandfleshofplumcultivars
Genotype Colour1 Harvestingdate
Peel Flesh 2012 2013
G.Japan Yellow Yellow 28/06 25/06
Showtime Red-Purple Yellow 19/06 21/06
Sapphire Purple Yellow 09/07 25/06
SantaRosa Red Yellow 02/07 26/06
Souvenir Red-pink Yellow 09/07 11/07
BlackAmber Dark-purple Amber 09/07 01/07
Fortune Red Amber 26/07 17/07
Friar Dark-purple Amber 30/07 31/08
Primetime Dark-purple Red 24/07 15/07
F.LarryAnn DarkRed Yellow 13/08 05/08
Laetitia Red Orange-Yellow 20/08 05/08
Songold Green-Yellow Yellow 27/08 06/08
Plumlate Dark-purple Amber 17/09 02/09
1Dazaetal.2012
doi:10.1371/journal.pone.0136596.t001
Samplepreparation
Eightfruitspertreeandsixtreespercultivarandtreatmentwereharvestedatcommercial
maturity(Table1)andtransportedtothelaboratoryforanalysis.Then,thefleshandpitwere
separatedandeachsamplefrozeninliquidnitrogenandmilled.Next,theplumpowderwas
lyophilisedandgroundagain.
Extractionmethodforbioactivecompounds
Twodifferentapproacheswerefollowedforquantifyingthebioactivecompounds:hydrophilic
andlipophilicextractions.
Forthehydrophilicextraction,0.1goffreeze-driedplumfruitsweremixedwith2mloface-
tone:water(50:50v/v).Themixtureswerevortexedfor1minthensonicatedfor15minand
finallycentrifugedat5000rpmfor15minat4°C.Thesupernatantsweretransferredtovials,
storedat−80°C,andlaterusedtoanalysetotalphenolics,totalanthocyanins,andantioxidant
capacity(FRAPandABTS).
Forthelipophilicextraction,0.1goffreeze-driedplumfruitsweremixedwith2mloface-
tone:hexane(4.6v/v).Themixtureswerevortexedfor2minandthencentrifugedat5000rpm
for15minat4°C.Thesupernatantsweretransferredtovials,storedat−80°C,andlaterusedto
analysecarotenoidsandantioxidantcapacity(ABTS).
Totalanthocyanins
Thetotalanthocyanincontent(TAC)wasdeterminedfollowingthepHdifferentialmethod
previouslydescribedbyGiustiandWrolstad[39].TheextractwasdilutedinapH1.0solution
(25mMKCl)andinapH4.5solution(0.4MCH CO Na).Theabsorbanceofeachwellwas
3 2
measuredat535nmand700nmafter15minat25°Cwithamicroplatespectrophotometer
(ThermoScientificMultiskanGO).Absorbancereadingswereconvertedintototalmilligrams
ofcyanidin3-glucosideper100gofdry-weightusingthemolarextinctioncoefficientof23900.
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Theabsorbancewascalculatedusingthefollowingequation:
A¼ ðA (cid:2)A Þ (cid:2) ðA (cid:2)A Þ
535 700 pH1:0 535 700 pH4:5
TotalPhenoliccompounds
Totalpolyphenolscontent(TPC)wasdeterminedwiththeFolin-Ciocalteaureagentusingthe
methodofSlinkardandSingleton[40].First,10μlofthehydrophilicextractwasmixedwith
175μlofdistilledwaterandsubsequentlywith12μlofFolin-Ciolcalteaureagent.After3min,
30μlofa20%aqueoussodiumcarbonatesolutionwereadded.Thesampleswerelefttostand
for1hourandwerethenreadat765nmwithaspectrophotometer(previouslydescribed)and
comparedwithaknownconcentrationrangeofsimilarly-preparedgallicacidstandards.The
resultswereexpressedasmilligramsofgallicacidequivalentsper100goffresh-weight(mg
GAE/100gFW).
Carotenoids
Totalcarotenoidcontent(TCC)wasdeterminedfollowingthemethoddescribedbyNagata
andYamashita[41].Absorbanceofthelipophilicextractwasmeasuredat453,505,645and
663nm.Theconcentrationofcarotenoidswascalculatedwiththefollowingequation:
(cid:2)(cid:2)carotenoid ¼ 0:216A (cid:2) 1:22A (cid:2) 0:304A þ 0:452A
663 645 505 453
Antioxidantcapacity
TheantioxidantcapacityofthehydrophilicextractwasmeasuredbytheABTS(ABTSh)and
FRAPassays.Inthecaseofthelipophilicextract,theantioxidantcapacitywasmeasuredonly
bytheABTSassay(ABTS-l).
ABTS(cid:129)+radicalscavengingactivity
Theantioxidantcapacityofthesampleswasalsomeasuredbythedegreeofsuppressionofthe
ABTS(cid:129)+radicalcationproducedbythereactionofABTS(cid:129)+(2,2-azino-di-[3-ethylbenzthiazo-
linesulphonate]).Thedatawerecomparedwiththeantioxidantactivityofstandardamounts
ofTrolox.
Thestocksolutionwaspreparedwith8mlofwater,1mlofacetatebuffer(0.1M,pH5),1
mlofABTS(5.5mg/ml)andasmallamountofMnO (toactivatetheABTSradicalcation).
2
Thesolutionwasfilteredthroughafilterof0.45μmtoremovetheexcessMnO .Theradical
2
reagentwaspreparedbydilutingthestocksolutionwithpurewatertoanabsorbanceequalto
1measuredat414nm.Twoμlofpreviously-dilutedhydrophilicextractand200μlofradical
reagentwereaddedtotheplate.Aftershakinginthemicroplatereader,theabsorbanceof
eachwellwasmeasuredat414nmafter50minat25°Cwiththespectrophotometerdescribed
above.
Tomeasuretheantioxidantcapacityinthelipophilicextract,theABTSradicalcationwas
activatedwithpotassiumpersulfateandthemixturewaslefttostandinthedarkatroomtem-
peraturefor12-16hoursbeforeuse.Thesolutionwasdilutedwithethanoltoanabsorbanceof
1at414nm.Next,40μloflipophilicextractwasaddedto180μlofABTSsolution.Absorbance
wasmeasuredat414nmafter50minat25°C.
Ferricreducingantioxidantcapacity(FRAP). TheFRAPassaywasperformedaccording
tothemethodofBenzieandStrain[42]withsomemodifications.Inshort,theFRAPreagent
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waspreparedbymixing0.3Macetatebuffer(pH3.6),asolutionof10mMTPTZin40mM
HCl,and20mMFeCl 6H Oat10:1:1(v/v/v).Then,2μlofthepreviouslydilutedsamplewere
3 2
addedtothewellcontaining200μlofFRAPreagent.Aftershakinginthemicroplatereader,
theabsorbanceofeachwellwasmeasuredat593nmafter40minat37°Cwiththespectropho-
tometerdescribedabove.
Theantioxidantcapacity(ABTS(cid:129)+andFRAPassays)wasexpressedasμmoloftroloxequiv-
alentper100gramoffreshweight(μmolTE/100gFW).
Organicacids(Ascorbic,Citric,Fumaric,Malic,Shikimic,Succinicand
Tartaricacid)
Freeze-driedplum(100mg)wasextractedwith3%meta-phosphoricacidinwater(v/v)(3ml).
Thesampleswererefrigeratedfor10minandvortexedfor30secondsevery5min.Thesam-
pleswerecentrifugedat5000rpmfor15minat4°Candfilteredthrougha0.45μmpore-size
filter.TheextractswereimmediatelymeasuredbyUHPLC-DAD.
TheorganicacidsweremeasuredusingaDionexUltimate3000UHPLCsystem(Thermo
Scientific)equippedwithaphotodiodearraywithamultiplewavelengthdetector.A4.0x250
mm,5μmAcclaimorganicacidcolumnequippedwithanAcclaimorganicacidguardcolumn
(4.6x10mm,5μm)wasused.Themobilephaseconsistedof0.2%metaphosphoricacidin
wateradjustedtopH2.5usingmetaphosphoricacid.Theflowratewas0.6mlmin-1(isocratic)
andthesampleinjectionvolumewas20μl.Thecolumntemperaturewassetat35°C.Peaks
wererecordedat210nmformalic,tartaric,citric,fumaric,shikimicandsuccinicacidsandat
260nmforascorbicacid.Alltheabovementionedorganicacidswereidentifiedandquantified
usinganexternalcalibrationcurvepreparedwithauthenticstandardsandtheconcentrations
expressedasmg/100goffreshweight(FW).
Thetotalorganicacidscontent(TOAC)wasdetermined,calculatedasthesumoftheindi-
vidualcompounds.
Statisticalanalysis
ThestatisticalanalysiswasperformedusingStatistixsoftware(v.9.0).Valuesaregivenas
means.Thedataweresubjectedtoananalysisofvariance(ANOVA),followedbyacompari-
sonofmeansaccordingtotheleastsignificantdifference(LSD)test.DifferencesatP<0.05
wereconsideredtobestatisticallysignificant.
ResultsandDiscussion
Effectofcultivationsystem
Theorganicplumshadahigherantioxidantcapacity(ABTS-h,ABTS-landFRAPassays),
TPCandTACthantheconventionalones(Table2).Thevaluesdifferedbybetween5–10%.
TCCwasnotaffectedbythemethodofcultivation.
Severalpublicationshaveshownthatlowernitrogenapplicationresultsinahigheraccumu-
lationofphenoliccompounds,whereashigherlevelsofnitrogenfertilizationpromotethefor-
mationofcarotenoidsandchlorophylls[43].Thefirstisinagreementwithourdata(TAC,
TPC),whilethelatterwouldsuggestahigherTCCvalueinconventionalplums.However,
otherauthors[44]observedthattheTCCishighlytemperaturedependentandthiscouldbe
thereasonfortheresultsobtained.
Organicgrowingsystemsarerelatedtoacertainlevelofstress(restrictedandlimiteduse
ofpesticidesandfertilizers),whichcouldleadtotheaccumulationofsecondarymetabolites
responsibleforplantdefence[7,45].Themostimportantsecondarymetabolitesinplumsare
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Table2. Effectsofcultivationsystem,genotypeandyearofharvestontheanthocyanins,polyphenols,antioxidantcapacity,andcarotenoidsof
plums.
Hydrophilicextraction Lipophilicextraction
TAC(mgGAE/ TPC(mgGAE/ ABTS-h(umols FRAP(umolsTEAC/ ABTS-l(umols TCC(mg/100
100gFW) 100gFW) TEAC/100gFW) 100gFW) TEAC/100gFW) gFW)
Cultivationsystem
(CS)
Conventional 6.21b 139.3b 1158b 1353b 5.41b 0.18
Organic 7.30a 150.8a 1253a 1495a 5.93a 0.19
Significance * *** *** *** ** ns
Genotype(G)
G.Japan - 71.7h 552f 615h 5.15de 0.14de
Showtime 4.25cd 255.7a 2651a 2375a 5.65cd 0.28b
Sapphire 2.10def 128.1ef 1057cd 1125efg 3.85f 0.14de
SantaRosa 2.72def 93.2g 665f 775h 3.90f 0.13de
Souvenir 0.55f 118.2f 943de 1018g 6.00cd 0.26b
BlackAmber 29.82a 150.2d 1168c 2023b 5.60cd 0.21c
Fortune 2.21def 139.5de 1164c 1334d 7.21b 0.21c
Friar 18.17b 199.4b 1485b 2076b 5.97cd 0.16d
Primetime 6.40c 177.8c 1489b 1913b 4.62ef 0.07f
F.LarryAnn 3.12de 129.4ef 1144c 1295de 6.31bc 0.35a
Laetitia 0.70ef 119.2f 884e 1089fg 5.36de 0.11e
Songold - 169.3c 1370b 1627c 8.38a 0.33a
Plumlate 4.25cd 134.2def 1099c 1247def 5.76cd 0.07f
Significance *** *** *** *** *** ***
Year(Y)
2012 4.75b 133.1b 1163b 1265b 5.44b 0.22a
2013 8.76a 157.0a 1248a 1583a 5.91a 0.16b
Significance *** *** *** *** * ***
G*CS ns ns Ns ns Ns ns
G*Y *** *** *** *** *** ***
CS*Y ns ns * * Ns ns
G*Y*CS ns ns Ns ns * ns
TAC=Totalanthocyaninscontent,TPC=totalpolyphenoliccontent,ABTS-h=ABTSantioxidantcapacityassayonhydrophilicextraction,FRAP=FRAP
antioxidantcapacityassayonhydrophilicextraction,ABTS-l=ABTSantioxidantassayinlipophilicextractionandTCC=totalcarotenoidcontent.Means
withdifferentlettersinthesamecolumnpresentsignificantdifferences.Significancelevel:ns=nonsignificant,
*=P<0.05,
**=P<0.01,
***=P<0.001
doi:10.1371/journal.pone.0136596.t002
polyphenols[32],whosecontentcommonlyincreasesinstressfulconditions,aswasobserved
inthesamplesanalyzed.Shikimicacidistheprecursorofphenylalanine[46],andtherefore
precursorofthephenylpropanoidbiosynthesis[47].Inourcase,ahigheramountofshikimic
acidandTPCwerefoundintheorganicorchards.Theseresultswereinagreementwiththelit-
eraturepublishedinPrunusgenus[8]andotherfruits[48,49,50,51].
Organicacidshaveanimportantroleincellmetabolismandalsocontributetothefinal
qualityoffreshfruit.Sevenorganicacidswereidentifiedandquantified:malic,citric,tartaric,
fumaric,succinic,ascorbicandshikimicacids.Wefoundmanypublicationsaboutascorbic
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acidandplums[37,52,53,54]andprunes[55]whiledeeperstudiesregardingoverallstudyof
organicacidsinPrunussalicinaL.[56]werescarce.
Inourcase,theplumscultivatedinanorganicsystemobtainedhighervaluesforTOAC
(1475mg/100gFWvs1409mg/100gFWforconventionalones),therefore,theproductionsys-
temwasshowntohaveasignificanteffect(Table3).Additionally,theplumsgrownunder
organicconditionsshowedsignificantlyhigherconcentrationsofmalic,succinic,tartaricand
shikimicacids.Otherorganicacids,suchascitric,ascorbicandfumaricacid,werenotaffected
bythecultivationsystem.Regardingthisresults,Lombardietal[15]didnotfinddifferences
incitricandmalicacidcontentonPrunusdomesticaL.betweenorganicandconventional
orchards.Theseresultsarepartlyinagreementwiththedataweobtained.Thisfactcouldbe
relatedwiththedifferencebetweenthetwospeciesunderstudy(PrunussalicinaL.andPrunus
domesticaL.).
Stressfulconditionssuchaswatersupply[57],soilconditions[58],etc.,couldleadtoa
higheramountoforganicacidsinplums,dependingontreeresponses.Severalauthors[59]
suggeststhathigheramountsofnitrogenfertilizationleadtoareductioninascorbicacidcon-
centrationinmanyfruits[60,61]andvegetables[62,63],whichisincontrastwiththeresults
obtainedinourresearchwherenodifferenceswerefoundbetweentheorganicandconven-
tionalcultivationmethods,inwhichfertilizationwasverydifferent.Thiscontroversialmatter
issupportedbyotherpublicationsinwhichsimilarresultstoourswerefound[62,64,65,66]
Effectofgenotype
Significantdifferencesinthephytochemicalcontentwerefoundamongdifferentplumgeno-
typesandthebiosynthesisofphytochemicalcompoundsinplantsisknowntobestrongly
influencedbygenotype[67].'Showtime'showedthehighestvaluesforTPC,ABTS-h,FRAP
amongallthecultivarsaswellasahighTCC.'Songold'recordedthehighestvaluesforcaroten-
oidsandABTS-l.'GoldenJapan'and'SantaRosa'presentedthelowestvaluesforABTS-hand
FRAP.'GoldenJapan'alsohadthelowestTPC.'Blackamber'wasthecultivarwiththehighest
anthocyanincontent,followedby'Friar',bothofthesehavingdarkpurpleskin.Thequantifica-
tionofTACwasfeasibleforallthecultivarsstudiedexceptfor'Songold'and'GoldenJapan',
cultivarswithyellowskinandflesh.
'GoldenJapan'waspreviouslycharacterizedasacultivarwithalowantioxidantcapacity
[68],inagreementwithourresults;while'Showtime'presentedthehighest(2650.6μmolET/
100gFW)antioxidantcapacity.Theseresultsshowedanimportantgenotypeeffectinthesam-
pleofplumsunderstudy.
ThereweresignificantdifferencesamongcultivarsinTOAC(Table3).Thehighestvalues
weremeasuredforthe‘Showtime’cultivar(2304mg/100gFW)followedby'SantaRosa'(1877
mg/100gFW),andthelowestoneswerefoundfor'Plumlate'(943mg/100gFW).
MalicacidwasthemajorcontributortotheTOACwitharangebetween86–96%depending
onthecultivar.ThesefindingswereinagreementwithSinghetal.[56].Tartaricacidwasthe
secondmostabundantorganicacidfollowedbycitric,succinic,shikimic,ascorbicandfumaric
acids.
‘Showtime’wasthecultivarwiththehighestcontentofmalicandcitricacids,bothrelated
tosourtaste.Thehighestconcentrationsforascorbicacidwerefoundforthe'Sapphire'and
'Blackamber'cultivars.
TheTOACdatafoundinourstudywereconsistentwiththeliterature[56]anddifferences
intheTOACbetweencultivarswerealsopreviouslydescribed[69].Ascorbicacidcontentin
plumsislow[37,70]soitscontributiontotheirantioxidantcapacityispracticallynegligible.
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Table3. Effectsofcultivationsystem,genotypeandyearofharvestonthemalic,citric,ascorbic,succinic,tartaric,fumaric,shikimicandtotal
organicacidscontentinplums.
Ascorbic Citric Fumaric Malic Shikimic Succinic Tartaric Totalorganic
acid acid acid acid acid acid acid acids
Cultivationsystem
(CS)
Conventional 1.62 24.12 0.49 1313b 3.65b 5.84b 60.18b 1409b
Organic 1.66 24.00 0.50 1369a 3.90a 7.01a 67.67a 1475a
Significance ns ns ns ** *** * *** ***
Genotype(G)
GoldenJapan 1.48de 22.80cde 0.27f 1662c 2.68e 15.21a 48.68efgh 1754c
Showtime 2.02bc 38.16a 0.68c 2169a 3.30d 4.84def 85.30c 2304a
Sapphire 2.49a 20.67e 1.24a 1224efg 3.27d 2.33f 32.02i 1286fg
SantaRosa 1.47de 23.22cd 0.38de 1804b 3.33d 2.85f 41.45h 1877b
Souvenir 1.26ef 23.74c 0.27f 1469d 3.71c 7.92bc 55.34e 1562d
Blackamber 2.29ab 21.33de 0.28ef 1179fg 4.75a 8.50b 53.51ef 1270g
Fortune 1.79c 22.67cde 0.62c 1280e 3.85bc 4.14def 97.15b 1410e
Friar 2.13b 28.34b 0.83b 1216efg 4.92a 6.70bcd 107.2a 1367ef
Primetime 1.73cd 21.93cde 0.38de 1236ef 4.12b 5.83cde 46.50fgh 1316fg
F.LarryAnn 1.50de 23.79c 0.40d 1181fg 4.97a 4.55def 72.58d 1289fg
Laetitia 0.73g 13.19f 0.31def 1055h 2.84e 3.32ef 45.53gh 1120h
Songold 1.06f 29.02b 0.37def 1151g 3.39d 9.00b 50.42efg 1245g
Plumlate 1.38e 23.90c 0.36def 810i 3.95bc 8.30bcd 95.36b 943i
Significance *** ** *** *** *** *** *** ***
Year(Y)
2012 1.75a 24.89a 0.57a 1233b 3.88a 5.05b 54.61b 1324b
2013 1.53b 23.22b 0.42b 1450a 3.67b 7.80a 73.23a 1560a
Significance *** *** *** *** *** *** *** ***
GxCS ns ns ns * ns ns ns *
GxY *** *** *** *** *** *** *** ***
CSxY ns *** ns ns ns ns ns ns
GxYxCS ns ** ns ** ns ns * **
Unit=mg/100gfreshweight.Meanswithdifferentlettersinthesamecolumnpresentsignificantdifferences.Significancelevel:ns=nonsignificant,
*=P<0.05,
**=P<0.01,
***=P<0.001
doi:10.1371/journal.pone.0136596.t003
Yeareffect
Theplumsharvestedin2013showedasignificantlyhigherTPC,TAC,andantioxidantcapac-
ity(ABTS-h,FRAPandABTS-l),whilethoseharvestedin2012showedsignificanthigherTCC
values(Table2).Regardingorganicacids,theplumsharvestedin2013showedhighervalues
forTOAC,malic,succinicandtartaricacids,whilehighervaluesforcitric,ascorbic,fumaric
andshikimicacidswerefoundforthesamplesharvestedin2012(Table3).
Manyparametersareinvolvedinthefactor‘year’,suchasplantnutrientimbalances,irriga-
tion,cropload,fruitcanopypositionandenvironmentalparameters[71].
Climatedatawerestudiedtoidentifytheinfluenceofenvironmentalconditionsonphyto-
chemicalcompoundsduringthetwoyearsunderstudy.Themaindifferenceobservedbetween
PLOSONE|DOI:10.1371/journal.pone.0136596 August27,2015 8/13
OrganicandConventionalManagementinBiofunctionalPlumQuality
thetwoyearswasthevalueforthetotalradiation(TR).In2012,TRwasbetween3and8%
higher(meanmonthlyvalues)thanin2013.
Themechanismofcarotenoidbiosynthesishasbeenshowntobelight-dependent[72],
whichmayexplainourresults,whichshowgreatercarotenoidbiosynthesisin2012(Table2).
Otherstudiesinvolvingplums(‘Laetitia’and‘Songold’)foundthatfruitgrownunder
reducedlightconditionswereconsistentlylessmaturethanthoseexposedtofullsunlight[73].
Inourstudy,ahighercontentoforganicacidswasfoundin2013,theyearwithalowertotal
radiation.Thus,thelowerradiationfoundin2013couldhaveproducedlessmatureplumsand
thereforeahighercontentoforganicacids.
Interactioneffects
Allthecultivarsstudiedhadhigherbioactivecompoundscontentinorganiccultivationsystem
while‘cultivationsystemandgenotype’interactionwasnotsignificantforTAC,TPC,ABTS-l
andTCC(Table2).Thismeansthatcultivationsystemaffectedabovementionedmeasure-
mentsinthesamewayforallstudiedcultivars.
The'genotypexyear'interactionwassignificantandtherefore,thegenotyperesponsesto
theenvironmentalfactors(yeareffect)weredifferent.‘GoldenJapan’showeddifferentconcen-
trationsofalltheparametersstudiedinbothyears.Therefore,thebioactivecompoundsofthe
‘GoldenJapan’cultivarweremainlyaffectedbyenvironmentalconditions.Hydrophilicbioac-
tivecompoundsfor‘Fortune’,‘Plumlate’,‘Sapphire’and‘SantaRosa’werenotsignificantlydif-
ferentinbothyearsand‘BlackAmber’demonstratedthesamebehaviourforthelipophilic
extractandcarotenoidcontent(S1Table).
The'cultivationsystemxyear'interactionwassignificantfortheFRAPassayandABTS-h.
Inthiscase,theplumsharvestedin2013showednosignificantdifferencesbetweenbothgrow-
ingsystems,buttheorganicplumsin2012showedahigherantioxidantcapacitythanthecon-
ventionalones(S1Table).
Correlations
Highcorrelations(S2Table)betweenTPCandbothantioxidantassayswereobserved(r2(cid:3)
0.89forboth).Similarresultswerepreviouslyreportedinplums[32,37,74].
NocorrelationbetweenTPCandTAC(R2=0,401)wasfound.Previousstudiesobserved
thatTACandTPCwerenotwellcorrelatedinotherfruitswithhighTACandTPCvalues
[75].
Moreover,theascorbicacidcontentdidnotcorrelatewellwithdifferentantioxidantcapac-
ityassays(S2Table),sopolyphenolscompounds(TPC)makethebiggestcontributiontothe
antioxidantcapacityofplums.
TheresultsoftheFRAPandABTS-hassaysshowalinearcorrelation(R2=0.794,P<0.001,
N=156),sobothmethodsmaybeusedindistinctlytoevaluatetheantioxidantactivityinthese
typeoffruits.
Conclusions
OrganicplumsampleswerefoundtohavehighervaluesofTAC,TPCandantioxidantcapacity
thanconventionaloneswhilenodifferencesinTCCwerefound.Themainbioactivecom-
poundscontributingtothetotalantioxidantcapacityofplumsarephenols.Genotypesignifi-
cantlyaffectedthecontentofdifferentbioactivecompounds.‘Showtime’hadthehighestTPC
valuesand‘GoldenJapan’and‘SantaRosa’thelowest.
Inconclusion,theorganicgrowingsystemproducedplumswithahighercontentofbioac-
tivecompounds,inadditiontoalowerimpactontheenvironment.
PLOSONE|DOI:10.1371/journal.pone.0136596 August27,2015 9/13
OrganicandConventionalManagementinBiofunctionalPlumQuality
SupportingInformation
S1Table.ANOVAinteractionsbetweencultivationsystem,genotypeandyearfactors,and
effectsontotalanthocyanins,polyphenols,antioxidantcapacityandcarotenoidsvalues.
Meanswithdifferentlettersinthesamecolumnshowsignificantdifferences.P<0.05.TAC=
Totalanthocyaninscontent.TPC=Totalpolyphenolscontent.ABTS-h=ABTShydrophilic
extract.TCC=Totalcarotenoidscontent.ABTS-l=ABTSlipophilicextract.CS:Cultivation
system.G:genotype.Y:year.
(DOCX)
S2Table.Pearson'scorrelationcoefficientsofhydrophilicextractionassays(TAC,TPC,
ABTS-h,FRAP),lipophilicextractionassays(ABTS-landTCC)andorganicacidsvalues.
ns=nonsignificant,(cid:4)=significantP<0.05,(cid:4)(cid:4)=significantP<0.01,(cid:4)(cid:4)(cid:4)=significantP
<0.001.
(DOCX)
AuthorContributions
Conceivedanddesignedtheexperiments:JMMRFTAMJRM.Performedtheexperiments:FJC
IPJMMRMJRMFTALFPRJCM.Analyzedthedata:FJCIPJMMRMJRMFTA.Contributed
reagents/materials/analysistools:FJCIPJCM.Wrotethepaper:FJCIPFTAJMMR.
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