Effect of solvents extraction on phenolic content and antioxidant activity of the byproduct of eggplant

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Industrial

Crops

and

Products

j o u r n al ho me p ag e :w w w . e l s e v i e r . c o m / l o c a t e / i n d c r o p

Effect

of

solvents

extraction

on

phenolic

content

and

antioxidant

activity

of

the

byproduct

of

eggplant

Lila

Boulekbache-Makhlouf

∗

,

Lamia

Medouni,

Sonia

Medouni-Adrar,

Lynda

Arkoub,

Khodir

Madani

FacultédesSciencesdelaNatureetdelaVie,Laboratoire3BS,UniversitéA.MiradeBejaia,Bejaia06000,Algeria

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received20February2013

Receivedinrevisedform30May2013 Accepted11June2013 Keywords: Solvents Extraction Antioxidants Antioxidantactivity EggplantPeel Solanummelongena

a

b

s

t

r

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c

t

Eggplantisoneofmostcommonvegetablesconsumedallaroundtheworld.Thisstudyhasassayed antioxidantsfromthebyproduct(peel)ofeggplant(Solanummelongena),usingthreeextractionsolvents: 70%methanol,70%ethanoland70%acetone.Foreachsolvent,contentoftotalphenolics,flavonoids, tan-nins,andtotalanthocyaninswerequantified.Antioxidantactivityofdifferentextractswerescreened usingtheferricreducingpower,1,1-diphenyl-2-picrylhydrazyl(DPPH•)radicalscavenging,hydrogen peroxide(H2O2)scavengingandmetalchelatingactivities.Theresultsshowedthat70%methanolis

thebestsolventfortheextractionofanthocyanins(82.83±1.07mgDGE/100gDP),whereas,70% ace-toneisthebestsolventfortheextractionoftotalphenolics,flavonoidsandtannins(29.3±1.23mg GAE/100gDE;18.5±0.07mgQE/100gDEand5.37±0.22mgTAE/100gDE,respectively).Anthocyanic extractshaveexhibitedthehigherreducingpower(39±2.5mgQE/100gDE)andscavengingactivity (IC50=2.88±0.02mg/mL),whereasthephenolicextractshaveshownthehighestmetalchelatingactivity

(18.53±0.4%).

© 2013 Elsevier B.V. All rights reserved.

1. Introduction

Antioxidantcomponentsaremicroconstituentspresentinthe dietthatcandelayorinhibitlipidoxidation,byinhibitingthe ini-tiationorpropagationofoxidizingchainreactions, andarealso involvedin scavengingfree radicals(Othmanet al.,2007). Epi-demiologicalstudies have shown that high fruit and vegetable consumptionhashealthbenefitsinthepreventionofchronic dis-eases(Cheeletal.,2007).Thesefoodsarereportedtocontainawide varietyofantioxidantcomponents,includingphenoliccompound (Arancibia-Avilaetal.,2008).Phenolicsareantioxidantswithredox properties,which allowthemtoactas reducingagents, hydro-gendonators,andsingletoxygenquenchers.Theyhavealsometal chelationproperties(Proestosetal.,2006).Theoxygen consump-tioninherentincellgrowthleadstogenerationofaseriesofreactive oxygenspecies(ROS),theseROSaremoleculessuchas superox-ideanionradicals(O•2)andhydroxylradicals(OH•).However,non

freeradicalspeciessuchashydrogenperoxide(H2O2)andsinglet

oxygen(1_O

2)areformedinvivoalso.Bothoxygenspeciesplaya

∗ Correspondingauthor.Tel.:+2130552932738;fax:+21334214762. E-mailaddresses:lilaboulekbachemakhlouf@yahoo.fr

(L.Boulekbache-Makhlouf),madouni.lamia@yahoo.fr(L.Medouni),

madouni1@hotmail.com(S.Medouni-Adrar),lyndaarkoub@yahoo.fr(L.Arkoub),

madani28dz2002@yahoo.fr(K.Madani).

positiveroleinenergyproduction,phagocytosis,regulationofcell growthintercellularsignaling,andsynthesisofbiologically impor-tantcompounds(Gülc¸inet al.,2005).Howeverduringoxidative stress,largeamountsoftheseROScanbeproductsandmaybe dangerousbecauseoftheirabilitytoattacknumerousmolecules, includingproteins,lipids(Halliwelletal.,1992)andDNA(Gülc¸in etal.,2005).

Eggplant,Solanummelongena,isacommonandpopular veg-etablecropgrowninthesubtropicsandtropics(Sarkeretal.,2006). Eggplantis nativetosoutheasternAsiaand great proportionof worldproductionisproducedinAsiaandMediterraneanbasin.The mostcultivatedvarietyinAlgeriaistheelongatedovoidinadark purpleskin.Itsfruitisprimarilyusedasacookingvegetablefor thevariousdishesallovertheworld(Demiretal.,2002;Hanson etal.,2006).Itcontainsascorbicacidandphenolics,bothofwhich arepowerfulantioxidants(Vinsonetal.,1998).Studieshaveshown thateggplantextractssuppressthedevelopmentofbloodvessels requiredfortumorgrowthandmetastasis(Matsubaraetal.,2005), andinhibitinflammationthatcanleadtoatherosclerosis(Hanetal., 2003).

Different solventsystems have beenused forthe extraction of polyphenols from plant material. The yield and antioxidant activity of natural extracts is dependent on the solvent used forextraction.Severalprocedureshavebeenproposed(Pokorny and Korczak,2001): extractionusingfats and oils, organic sol-vents,aqueousalkalinesolutionsandsupercriticalcarbondioxide.

0926-6690/$–seefrontmatter © 2013 Elsevier B.V. All rights reserved.

Aqueousmixturesofethanol,methanolandacetone,arecommonly used(Hayounietal.,2007).WangandHelliwell(2001)reported thataqueousethanol wassuperiortomethanolandacetonefor extractingflavonoidsfromtea.However,inanotherwork,water wasfoundtobebettersolvent,forextractingteacatechins,than were80%methanolor70%ethanol(Hayounietal.,2007).Forthis reason,theextractionmethodofphenolicsdiffersfromplant sub-stratetoanother and anidealextractionmethodfor particular phenolicclasseshastobeindividuallydesignedandoptimized.

Thechoiceofourinvestigationisbasedontwocriteria:first,to enhancethepeel(byproduct)ofeggplant,whichisagoodsource ofbioactivesubstances(anthocyanins)aslongastheAlgerian peo-pledonotconsumeit.Thereforethefirstobjectiveofthisstudy istoevaluateseveraltypesofphytochemicalsthatarepresentin thedriedpowderofpeeleggplant.Thesecondcriterionistoselect thesolventthatledtotheextractswiththehighestantioxidant capacity.

In this study extracts were obtained from dried powder of peelseggplantusingdifferentorganicsolvents:70%methanol,70% ethanoland70%acetone.Efficiencyofextractionwasdetermined bymeasuringthetotalphenols,flavonoids,tannins,total antho-cyaninandantioxidantactivity(ferricreducingpower,scavenging effectof1,1-diphenyl-2-picrylhydrazyl(DPPH•)radical, scaveng-ingcapacityofhydrogenperoxideandmetalchelatingactivity).

2. Materialsandmethods

2.1. Chemicalsandsamplepreparation

AllchemicalswerepurchasedfromSigma(representedby Alge-rianChemicalSociety,Setif,Algeria).Fresheggplant(S.melongena) waspurchased from local market,Bejaia city,Algeria. A previ-ouslydevelopedmethoddescribedandsuggestedpeelseparation frompulptissuebyimmersioninethyleneglycolat35◦C.Butthis practicedidnotpreserveanthocyaninfrompolyphenol oxidase oxidativeactivity(Spagnaetal.,2003),forthisreasonpeelswere removedusingasharpknife(Todaroetal.,2009),driedinthe dry-ingovenat40◦Cduring4days,andgroundtogranulometrylower than250␮m.

2.2. Quantificationofantioxidants

2.2.1. Carotenoids

Carotenoidsarepigmentsinsolubleinwaterandsolublein apo-larsolventslikehexane.Thecarotenoidscontentwasevaluatedby Soto-Zamoraetal.(2005)method.10mLofsolventmixture (hex-ane,acetoneandethanol,1:5/2:5/2,v/v/v)wereaddedto0.5gof driedpowder.After3minofstirring,1mLofpotassium hydrox-ide(KOH,1M)wasaddedandthemixturewasincubatedduring 40min,thentheabsorbanceof upperphasewasdeterminedat 450nm.␤-Carotenewasusedasthestandardandtheresultswere expressedasmg␤-caroteneequivalentper100gofdrypowder (mg␤CE/100gDP).

2.2.2. Anthocyanins

10mLofsolvents(70%methanol,70%ethanoland70%acetone) containing0.2%offormicacidwereaddedto1gofdriedpowder. Afterstirringfor40min,thehomogenizedsampleswerethen cen-trifugedat5000rpmfor20minat4◦C.5mLofdifferentsolvents wereaddedtothepellet,thesameoperationwasrepeated,then thesupernatantswerecollected(Wangetal.,2008).

Total anthocyanins were determined by a pH differential method(Prioretal.,1998).Absorbancewasmeasuredat510nm

andat700nminbuffersatpH1.0and4.5.Theconcentrationof anthocyaninswasobtainedusingthefollowingequation:

C (mg/l)₌ A·MW·DF·1000 ˙L

where A=[(A510−A700)pH1.0−(A510−A700)pH4.5],MW

(molec-ular weight) of delphinidin-3-glucoside (465g/mol), ˙ is the molar extinction coefficient of delphinidin-3-glucoside (29,000L/mol/cm),DFisthedilutionfactorandListhelengthof vessel(1cm).

Resultswereexpressedasdelphinidin-3-glucosideequivalent per100gofdrypowder(mgDGE/100gDP).

2.3. Phenoliccompounds

2.3.1. Preparationoftheextracts

Driedpowder(0.5g)wasextractedwith50mLof70%methanol, 70%ethanoland70%acetone.Theextractionwascarriedoutat roomtemperature,usingmagneticblender.After40min,the solu-tionwascentrifugedfor25minat4000×g(10◦C),thesupernatant wasfiltered(Whatmanpaperno.4)andstoredunderrefrigerated conditionsuntilused.

2.3.2. Quantification

Theamountoftotalphenolicsintheextractwasdetermined usingtheFolin–Ciocalteureagentand gallicacidasstandardas describedbySingletonandRossi(1965).

Thetotalflavonoidscontentwasdeterminedbythe method-ologyofQuettier-Deleuetal.(2000)andquercetinwasusedas standard.

Tannins wereestimatedspectrophotometricallyaccording to theprotocoldevelopedbyHagermanandButler(1978)andtannic acidwasusedasstandard.Allanalyseswereperformedintriplicate andthemeanvaluewascalculated.

2.4. Antioxidantactivity

Severalmethodshavebeendevelopedtoassayfreeradical scav-engingcapacityandtotalantioxidantactivityofplantextracts.The mostcommonandreliablemethodinvolvesthedeterminationof thedisappearanceoffreeradicalsusingaspectrophotometer.In ourstudy,weusedfourmethods:reducingpower,metalchelating activity,scavengingoftheradicalDPPHandH2O2activities.

2.4.1. Freeradical-scavengingactivity

TheabilityoftheextractstoscavengeDPPHfreeradicalswas determinedbythemethodof Sujaetal.(2005).100␮Lof vari-ousconcentrationsofthesamplesweremixedwith3mLofDPPH inmethanol(0.1mM).After30minofincubationinthedarkand ambienttemperature,absorbancewasmeasuredat515nm.The percentagescavengingwascalculatedaccordingtothefollowing equation:

%Scavenging=



Abscontr−Aextr

Acontr



×100.

whereAbscontristheabsorbanceofthecontrol(withoutextract)

after30minand Aextr istheabsorbanceofextractafter30min.

IC50wascalculatedastheconcentrationofextractscausinga50%

inhibitionofDPPHradical.

2.4.2. Reducingpower

Thereducing poweroftheextractswasevaluated according to the protocol of Hseu et al. (2008). 1mL of different con-centrations of the samples was mixed with phosphate buffer (1mL, 0.2M, pH=6.6) and potassium ferricyanide [K3Fe(CN)6]

Trichloroaceticacid(TCA)(1mL,10g/100mL)wasaddedtothe solutionwhichwasthencentrifugedfor10minat3000×g.The supernatantwasgatheredandmixedwithdistilledwater(1.5mL) andFeCl3(150␮L,0.1g/100mL),andtheabsorbancewasmeasured

at700nm,increasedabsorbanceofthereactionmixtureindicated increasedreducingpower.Resultsareexpressedasmgquercetin equivalentper100gofdriedextract(mgQE/100gDE).

2.4.3. H2O2assay

H2O2 scavengingability of thedifferent extractswas

deter-mined according to Yousfi et al. (2006) method with slight modifications.1.5mLofdifferentextractsweremixedwith0.02mL of30%ofH2O2solution.Absorbancewasreadat530nmatdifferent

times(5–60min).Decreasedabsorbanceofthereactionmixture indicatedincreasedinscavengingability.Thepercentageof inhi-bitionofH2O2radicaliscalculatedusingthefollowingequation:

%InhibitionofH2O2=



_Abs

contr−Absext

Abscontr



×100

whereAbscontristheabsorbanceofthecontrol(withoutH2O2)and

Absextistheabsorbanceinthepresenceoftheextracts,thenthe

timerequiredtoinhibit50%(IT50)ofH2O2radicalwasdetermined.

2.4.4. Metalchelatingactivity

The chelating of ferrous ions by phenolic and anthocyanin extractswasestimatedbythemethodofLimetal.(2007). Accord-ingly,1mLof0.125mMFeSO4 wasaddedto1mLof0.3125mM

ferrozineand1mLofdifferentextracts.Themixturewasshaken vigorouslyandleftstandingatroomtemperaturefor10min.The Absorbanceofthesolutionswasthenmeasured spectrophotomet-ricallyat562nm.Thepercentageofinhibitionofferrozine–Fe2+

complexformationwascalculatedusingtheformulagivenbellow:

%Inhibition=



Acontr−Aext

Acontr



×100

where Acontr is the absorbance of the control, and Aext is the

absorbanceinthepresenceoftheextracts.Thecontroldoesnot containFeSO4andferrozine,complexformationsmolecules.

2.5. Statisticalanalysis

Allexperimentswereconductedintriplicatesandresultsare expressedasmean±standarddeviation(SD).Analysisofvariance wasperformedbyANOVAprocedurewithonefactorforthe deter-minationofphenolicandanthocyanincontents,thescavengingof DPPHandthemetalchelatingactivities.Statisticalanalysisofthe reducingpowerandscavengingofH2O2wereperformedby

anal-ysisofvariancewithtwofactorsinthesoftwareSTATISTICA5.5 Fr.

3. Resultsanddiscussion 3.1. Antioxidantconcentrations

3.1.1. Anthocyaninscontent

Anthocyaninsare the largest class with antioxidant activity in thepeel eggplant(Yi et al.,2009).Therefore, it is necessary toextractthemefficiently.Forthispurpose,threesolventswere chosen(70% acidified methanol,70% acidified ethanol and 70% acidifiedacetone).Table1showsthecontentsofthethree antho-cyaninextracts,whicharesignificantlydifferent(p<0.05),theyare about51.56_±4.87and82.83_±1.07mgDGE/100gDPforacetone andmethanolicextracts,respectively.Valueobtainedforethanolic extractisabout62.92±0.15mgDGE/100gDP.Todaroetal.(2009)

reported a value of 76.44±3.82mg of delphinidin-3-rutinoside equivalent/100goffreshpeel,usingacidifiedethanolassolvent. However,astudyonthewholefruitofeggplant,hasshowna con-tentof 0.53±0.012mg cyanidin-3-glucosideequivalent/100gof freshfruit(Nishaetal.,2009).Thisdataconfirmsthatanthocyanins areconcentratedinthepeelofthefruit.

3.1.2. Carotenoidscontent

Thehighhydrophobicityofcarotenoidsdeterminestheir distri-butioninthecellularenvironment,thesecompoundsareassociated withlipidbilayermembranes.Thecarotenoidscontentofthe sam-plewasabout0.74±0.013mgE␤C/100gDP.Noresultshavebeen publishedonthecarotenoidscompositionof thepeeleggplant. However,Couplan(1998)reportedavalue(0.65mg/100goffresh weightofeggplantfruit)closetothatobtainedinthepresentstudy. Theseresultsshowthatcarotenoidsareconcentratedinthepeelof thefruit.

3.1.3. Phenoliccontents

3.1.3.1. Total phenolic contents. Total phenolic contents varied in the different extracts (Table 1). It is about 29.39±1.23mg GAE/100gDE,26.61_±0.67mgGAE/100gDEand13.53_±0.21mg GAE/100gDE,for70%aqueousacetone,70%aqueousmethanol and70%aqueousethanol,respectively.Todaroetal.(2009)found thatthephenoliccontentofacidifiedethanolicextractoffresh egg-plantpeelsis188.73±73␮gGAE/mLofextract.Intheotherhand, Nishaandhiscollaborators(2009)havereported49.02±1.3mg GAE/100gDEinthemethanolicextractandEun-Juetal.(2011) havefound55.19±1.3mgGAE/100gDEin70%ethanolicextract offresheggplantpeel.Thesevaluesaresignificantlyhigherthan thoseobtainedinourstudy.Thesedifferencesinphenoliccontents mightbeduetotheconditionofthepeelfruit(freshordried).

3.1.3.2. Flavonoids contents. Flavonoids contents of different extractsaregivenin Table1.Therewasa significantdifference betweenflavonoidscontentofacetonicextractandthetwoother extracts(p<0.05);butthereisnodifferencebetween methano-lic and ethanolic extracts(p<0.05).The highest level hasbeen detectedin acetonic extract (18.52±0.07mg QE/100gDE), fol-lowed by methanolic and ethanolic extracts (16.26±0.26 and 16.13±0.12mg QE/100g DE,respectively). Eun-Ju et al. (2011) haveestimatedthetotalflavonolscontainin70%ethanolextract of fresh peel eggplant, they found about 6.19±0.28mg cate-chinequivalent/100gDE.Noresultshavebeenpublishedonthe flavonoidscontentofthepeeleggplant.

3.1.3.3. Tannins content. Resultsshownin Table1revealsa sig-nificantdifferencebetweentannincontentsofthethreesolvents extracts(p<0.05).Indeed,contentof70%acetoneextractpresent thehighestlevelamongthethreeextracts,itisabout5.37±0.22mg TAE/100gDE,followedbythemethanolextractwithavalueof 4.26±0.28mgTAE/100gDE;theethanolextracthasthelowest content(3±0.11mgTAE/100gDE).Noresultshavebeenpublished onthetanninscompositionofthepeeleggplant.However,Alkurd etal.(2008)obtained413.7mgTAE/100gDEintheeggplantwhole fruit,thiscontentis100timeshigherthanthatobtainedin our study.

Thelevelsofantioxidantsinpeeleggplantaresignificantly dif-ferent(p<0.05).Theyareclassedasfollows:Anthocyanins>total polyphenols>flavonoids>tannins>carotenoids.Theresultsof dif-ferentextractsshowsthatpeelofeggplantcontainthehighestlevel ofanthocyaninsincomparisonwiththetotalpolyphenols,tannins, flavonoidsandcarotenoids;thesedataindicatethatthemajorityof polyphenolsfromthepeelofeggplantareanthocyanins.Because anthocyaninsbelongtothegroupofpolyphenolsandflavonoids subgroup,thehighestcontentofanthocyanins,comparedtothat

Table1

Concentrationofantioxidantsinpeeleggplant.

Solvents Totalphenolic(mgGAE/100gDE) Flavonoids(mgQE/100gDE) Tannins(mgTAE/100gDE) Anthocyanins(mg␤CE/100gDM) Methanol 26.61±0.67b _16.26±0.26b _4.26±0.28b _82.83±1.07a

Ethanol 13.53±0.21c _16.13±0.12b _3±0.11c _62.92±0.15b

Acetone 29.39±1.23a _18.52±0.07a _5.37±0.22a _51.56±4.87c

Valuesareaverages±standarddeviationoftriplicateanalysis;differentlettersinsamecolumnindicatesignificantdifference(p<0.05).Resultsarerankedinascending order;a>b>c.

oftotalpolyphenolsandflavonoids,canbeexplainedbythe condi-tionsofextractionofanthocyanins(BrouillardandDubois,1977).

3.2. Antioxidantactivityoftheextracts

3.2.1. Freeradicalscavengingactivity

Solventsusedforpolyphenolextractionhadsignificanteffects on DPPH scavenging capacity determination for peel eggplant (Table 2). This activity varied significantly (p<0.05) between 58.81±1.1%and 63±0.48%.Methanol extract exhibitthe high-estactivity,comparativelytotheacetonicandethanolicextracts. Activityofanthocyaninextractsissignificantlydifferent(p<0.05) and the methanolic extract exhibited the highest capacity (68.08±0.57%).Statisticalanalysisrevealedasignificantdifference (p<0.05)betweentheradicalscavengingactivityofpolyphenolic andanthocyaninextracts.Indeed,anthocyaninextractsshowedthe bestactivity.

Theconcentration of anantioxidant neededto decreasethe initialDPPHconcentrationby50%(IC50)iswidelyusedto

evalu-atetheantioxidantactivity(Atouietal.,2005).Resultspresented in Table 2 shows that for polyphenolic extracts, the acetonic extractdoesnotrequireahighconcentration(3.97±0.95mg/mL) toinhibit50%ofDPPHcomparativelytothetwootherpolyphenolic extracts (p<0.05). As for anthocyanin extracts, the methano-lic extract requires only 2.88±0.02mg/mL to inhibit 50% of DPPH radical. Indeed, considering the polyphenolic extracts, methanolicandacetonicextractsexhibitsimilaractivity(4±0.20 and3.97±0.95mg/mL,respectively)whichisstatisticallyhigher (p<0.05)thanthatofethanolicextract(4.05±0.08mg/mL).Inthe caseofanthocyaninextracts,amongsolventstestedthehighest antioxidantactivitywasobservedformethanolfollowedby ace-tone and ethanol extracts (p<0.05). It is also noteworthy that theanthocyanin extractsshowedthehighest antiradicalpower (p<0.05)comparedtophenolicextractsforallthesolventsused. Eun-Juetal.(2011)reportedthat70%ethanolextractoffreshpeel ofS.melongenadecrease50%ofDPPHradicalataconcentrationof 0.98±0.33mg/mL,thisvalueislowerthanthatfoundinourstudy (4.05±0.0.8mg/mL) withthe same solvent.In the otherhand, Nishaetal.(2009)reportedanIC50value(0.228mg/mL)lowerthan

thatobtainedinourstudyformethanolicextract(4±0.2mg/mL). Thesedifferencescanbeexplainedbythedifferentstatesofthe fruit(freshordried).

3.2.2. Reducingpower

Figs.1and 2depictthereducingpowerofthephenolic and anthocyaninextracts,respectively.Thephenolicextractwith70% acetoneexhibitedthehighestreducingpowerthanthoseobtained for thetwo othersolvents. The order of the antioxidant activ-itywas:70%acetone>70%methanol>70%ethanol(p<0.05).This differenceisprobablyduetothedegreeofsolubilityofphenolic compoundinthedifferentsolvents.

Theanthocyaninextractwith70%methanol,exhibitedthe high-estreducingpower,whileethanolandacetoneextractshavethe lowestreducingpower(p<0.05).Theorderoftheantioxidant activ-itywas:70%methanol>70%ethanol>acetone70%(p<0.05).

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 1 2 3 4 5 Ab so rb an ce at 70 0 n m Concentraon (μg/mL) M 70% E 70% A 70% _a b c

Fig.1.Reducingpowerofphenoliccompoundofpeeleggplantextracts.Different lettersinsamecolumnindicatesignificantdifference(p<0.05).Resultsareranked inascendingorder;a>b>c.

The reducing power expressed as quercetin equivalent (mgQE/100gofDE)issignificantlydifferent(p<0.05)forthe phe-nolic extracts. Indeed, 70% acetone extract shows the highest content(27±1.02mgQE/100gDE)butnodifference(p<0.05)was observedbetweenmethanolicandethanolicextracts(21±0.9mg QE/100gDEand21±1.4mgQE/100gDE,respectively).

Concerning anthocyanin extracts, and as can be seen in Fig.2,theirreducingpoweraresignificantlydifferent(p<0.05), the highest amount is presented by the methanolic extract (39±2.5mg QE/100g DE), followed by acetonic and ethanolic extracts(33±1.6mgand30±0.6mgQE/100gDE,respectively).

Statistical analysisrevealed a significantdifference(p<0.05) between the reducing power of polyphenolic and anthocyanin

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 0 1 2 3 4 5 Abso rb ance at 7 00n m Concentraon μg/mL MA 70% EA 70% AA 70% a b b

Fig.2.Reducingpowerofanthocyaninsofpeeleggplantextracts.Different let-tersinsamecolumnindicatesignificantdifference(p<0.05).Resultsareranked inascendingorder;a>b>c.

extracts.Indeed,anthocyaninextractsshowedthebestactivity. Thisdifferenceisprobablyduetothehighcontentofantioxidants (anthocyanins)inanthocyaninextracts,whicharethedominant classinthepeeleggplant(Yietal.,2009).Differencefoundbetween extracts, are probably due to the difference in their phenolic contents(polyphenolic and anthocyaninsextracts),and/ortheir electron-donatingactivity.

3.2.3. Scavengingeffectofhydrogenperoxide

Theabilityoftheextractsofpeeleggplanttoscavengehydrogen peroxideisshowninFigs.3and4,respectively.Thedecreasein

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theintensityofthecolorofdifferentextractsinthepresenceof H2O2,resultinginthedecreaseofabsorbance.Thisdiscoloration

istheresultoftheoxidationofphenoliccompoundpresentinthe extracts,afterthereductionofH2O2.

Anotherparameter used in order to evaluatethe inhibitory effectofH2O2radical,isthetimerequiredtoinhibit50%oftheH2O2

radical(IT50).ThelowesttheIT50orthehigheristheantioxidant

activity.Theobtaineddata(Table2),showsthatthepolyphenolic extractwith70%acetonerequiresonly26.1_±0.53mintoscavenge 50%oftheH2O2radical,soitsactivityisstrongercomparedwith

theothertwopolyphenolicextracts(p<0.05).Similarly,the antho-cyaninextractwith70%methanol,requiresonly22.68±0.54min

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A

B

Fig.4.Absorbanceoftheanthocyanicextracts:(A)methanol,(B)ethanol,and(C) acetoneHP:hydrogenperoxide.

Table2

Antiradical(DPPH,H2O2)andmetalchelatingactivitiesofdifferentextracts.

Extract Antiradicalactivity Metalchelatingactivity ScavengingeffectofH2O2

%inhibition IC50(mg/mL) (%inhibition) IT50(min)

M70% 63%±0.48a _4±0.20b _14.24±1.26b _36.97±2.19b E70% 58.81%±1.1%b _4.05±0.08c _3.71±0.21c _46.21±1.50a A70% 59.29%±2.25%b _3.97±0.95b _18.53±0.47a _26.1±0.53c MA70% 68.08%±0.57%a _2.88±0.02c _5.46±0.99b _22.68±0.54c EA70% 64.47±1.53%c _3.32±0.01a _11.23±1.93a _44.4±1.91b AA70% 66.44±2.02%b _3.09±0.73b _2.8±0.05b _48.86±2.45a

Differentlettersinsamecolumnindicatesignificantdifference(p<0.05).Resultsarerankedinascendingorder:a>b>cforphenolicextracts;a_>b_>c_{foranthocyanin}

extracts.

toscavenge50%H2O2,thistimeisconsideredlowercomparedto

thatoftheacetonic(48.86±2.45min)andethanolicanthocyanin extracts(44.4±1.91min)(p<0.05).Thisdifferenceisprobablydue tothetypeofthesolvents,thenatureoftheextractedcompounds andthehighabilityofanthocyaninstoscavengeH2O2radical.

3.2.4. Metalchelatingactivity

Foodsareoftencontaminatedwithtransitionmetalionswhich may be introduced by processing methods. Bivalent transition metal ions play an important role as catalysts of oxidative processes, leading to the formation of hydroxyl radicals and hydroperoxide decomposition reactions via Fenton chemistry (Halliwelletal.,1992).

Theseprocessescanbedelayedbyironchelationand deactiva-tion.Themetalchelatingcapacityisexpressedbythepercentage of inhibition of ferrozine–Fe2+ _{complex formation by different}

extracts.Inthisassaybothextractsofpeeleggplantareinterfered withtheformationofferrousandferrozinecomplex,suggesting thattheyhavechelatingactivityandareabletocaptureferrous ionbeforeferrozine.AsshowninTable2,thepolyphenolicextract with70% acetoneexhibit thehighest percentageofmetal scav-enging capacity (18.53±0.47%), compared to that of theother twopolyphenolicextracts,whichareabout14.24±1.26%forthe ethanolicextractand3.71±0.21%forthemethanolicone(p<0.05). Concerning,theanthocyanicextract,ethanolicextractshowsthe betteractivity(11.23±1.93%)comparativelytothemethanolicand acetonicextractswhichare5.46±0.99%and2.8±0.05%, respec-tively.

4. Conclusion

Eggplant,S.melongena,isacommonandpopularvegetablecrop largelyconsumedintheworld.Itcontainspolyphenols,flavonoids, minerals, vitamins, etc. These are reported to possess numeral medicinalproprietiesaswell.Thepresentstudyevaluatedinvitro antioxidant activities of three solvents extracts of the byprod-uctofeggplant.Resultsshowsthatacetoneisthebettersolvent forphenolic,flavonoidsandtanninsextraction,while,methanol isbetterforanthocyaninextraction.Inthis studywefoundthat peeleggplantispoorincarotenoids.Concerningtheantioxidant activity,highreducingpowerandinhibitionofH2O2activitiesof

phenolicextractwasobservedforacetone,whilethatof antho-cyanicextractwasobservedforthemethanol.Bothofphenolicand anthocyanicextractsissuedfrommethanolshowedthebest scav-engingactivityofDPPHradical.Otherwise,metalchelatingactivity isbetterforphenolicextractissuedfromacetoneandanthocyanic extractissuedfromethanol.Therefore,peelofS.melongenamaybe consideredasourceofimportantphytochemicalswithimportant antioxidantproperties.

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