International Journal of Food and Nutritional Science

Int J Food Nutr Sci | Volume 3: Issue 1

Copyrights: © 2016 Arora, A. This is an Open access article distributed under the terms of Creative Commons At-tribution 4.0 International License.

Research Article

Jhumur Banerjee1, Antonio F. Patti2, Douglas MacFarlane2, R. Vijayaraghavan2, Ramkrishna Singh1, Amit Arora1,3*

Abstract Inthisstudy,effectofdryingmethodandtimetemperatureregimeofextractiononqualityofmangokernellipidwasevaluated.Hotairdryingrequireddryingofseedsforlongintervalsandexposuretohighertemperature,whereasmicrowavedryingwasfoundtobequickduetoheatinginducedatthemolecularlevel.Thedryingtimeunderoptimizedconditionsformicrowavewasreducedby34foldswhencomparedwithhotairdrying.Parametersincludingdryingtemperature,extractiontime,lipidyieldandfat-tyacidprofilewereevaluated.Thestudyshowsthatmodificationofextractionmethodfor lower temperatureand lesser timedoesnotalter thequalityandquantityof lipidsfrommangokernel(10.8%).Structuralchangesinducedduetodryingwerestudiedusingscanningelectronmicroscopy.Statisticalanalysisshowedthatdryingconditionsandex-tractionconditionsaffectedthelipidyield.Thefurthercomparisonbetweentwomethodswasdoneintermsoffattyacidprofilesandoxidativestability.Thestabilityoflipidwasestimatedbymeasuringtheratiooflinoleicacidtopalmiticacidforallextractioncon-ditions.TheratioofC18:2/C16wassimilarformicrowaveirradiationwhencomparedtohotairdriedsamples(1.0-1.2).Itwasconcludedthatmildmicrowavepowerlevel(180W)helpsinquickdryingofkernels.Thestructurewasfoundtobeintactwithmini-maldamagetostarchgranules.Lowermicrowavepowerlevelhelpedinretentionofthelipidyieldandqualitywhilehighermicrowavepower levels significantlyaffected theunsaturated fatty acids.

*Corresponding author: AmitArora, Indian Institute ofTechnology, Powai,Maharashtra, India,Tel: +91(22)-2576-7293;E-mail:aarora@iitb.ac.in

Received Date: February 13, 2016Accepted Date: May 11, 2016Published Date: May 16, 2016

Keywords:Mangokernel;Microwave;Fattyacids;Scanningelectronmicroscopy

Introduction

Worldwideproductionofmangopulphasreachedmorethan1.5milliontonneswithanannualproductionoffruitcrossing43milliontonnes.Asiaaccountsfornearly84%oftotalpulpproductioninwhichIndiaisthelargestproducer[1].Nearly18.4milliontonnesofMangofruitsproductionwasrecordedin2014[2].Industriesprocessthemangofruitsforpulpproductionandgenerateahugequantityofwastewhichvariesfrom25-40%.Compostingandbiogasformationismainlyfollowedinlargeindustries,whileinsmallscaleindustries;thewasteisdisposedatafarsite.Thecurrentdisposalmechanismlacksvalueadditionofwasteandmanyimportantnutrientssuchasbioactivecompoundsarelost.Thewastealsobeingrichinmoistureleadstoenvironmentalpollution.Limitedlandfillingareaespeciallyindevelopingcountriesposedisposalchallenges. AsshowninFigure1,themangoprocessingwastemainlyconsistsofpeelsandseeds.Mangopeelsproximatecomposition

Effect of Drying Methods and Extraction Time-Temperature Regime on Mango Kernel Lipids

1IITB-MonashResearchAcademy,IITBombay,Mumbai,Maharashtra,India,4000762SchoolofChemistry,FacultyofScience,MonashUniversity,Claytoncampus,VIC,Australia3IndianInstituteofTechnology,Powai,Maharashtra,India

DOI: 10.15436/2377-0619.16.048

Citation: Arora, A., et al. Effectof Drying Methods and ExtractionTime-Temperature Regime on MangoKernelLipids. (2016) IntJFoodNutrSci3(1):229-338.

Arora, A., et al. 229

showsthepresenceofasignificantamountofpectin,phenolicsandcarotenoidslikebioactive[3,4]. They play an important role as health-promotingadditivesinfoodindustry.Thespentpeelfrompectinextractionmayalsobeusedforutilisationofcellulosewhichisaround35%.Mangokernelsarefoundtoberichinstarch(50-60%),lipids(8-14%)andprotein(6-10%).Afewreportsonchar-acterizationofproteinshowedthatitcanbeagoodsourceforessentialaminoacids[5].Researchershavealsoshowngreatinterestinmangokernellipidsduetopeculiarfattyacidprofile(Saturatedfattyacid48-55%;unsaturatedfattyacid45-52%).Mangokernellipids have been used as a valuable substitute for cocoa butter in food items[6].Thecocoabutterconsistsofsaturated(60-65%)andunsaturatedfattyacids(35-40%).Thefattyacidsfrommangokernelswerealsousedasalipidbaseincosmeticse.g.lipsticksandemollients,inpreparationofbiosurfactantsetc.Thetendencyofkernellipidstostaypartlysolidatroomtemperaturemakesitusefultobeusedinfoodandcosmeticproductsespeciallyfordevelopingcountries.Thelipidcanalsobeblendedwithotheroilswhichrequiresuchapplicationsandtheratiocanbetunedaspertheproductdesirability.

Figure 1:Massbalanceformangoprocessing.

Extractionof lipidsfrommangokernel iscarriedoutbyusingvariousphysical,chemicaland/orcombinationof theseprocesses.Coldpressormechanicalexpellerisacommonlyusedindustrialmethodwherelossoflipidsissignificant[7,8]. Another methodforoilextractionisSoxhletextractionorhotsolventpercolationmethod.Theyieldobtainedinthismethodishighbutitsuffersdisadvantageoflargeamountofsolventusage.Hexaneismainlyusedassolventwhichistoxicinnatureandreportedtobeenvironmentallyhazardous.Thelargesolventusagealsoincurshighprocesscost.Alsowithnonpolarsolvents,dryingofmaterialbecomesanecessarystepbeforelipidsextraction.Theyieldofmangokernellipidsusinghotairdryingfollowedbyconventionalextractionvariesfrom7-9%forIndianvarieties[7-9].Otherrecentlydevelopedmethodsincludesupercriticalfluidextractionusingcarbondioxideinwhichyieldwasfoundtovaryfrom6.5to13.5%[10]. Dryingisoneofthemostimportantunitoperationinvolvedbeforeoilextractionastheyieldoftheextractedoilisdepen-dent on the moisture content of the material[11].Dryingisthemostenergyintensiveoperation.Commonlyusedmethodsfordryingaresundrying,solardrying,hotairdrying,vacuumdrying,freezedryingorcombinationofthesemethods(Sonwai,Kaphueakngam&Flood2014).Hotairdryingandfreezedryingareenergyintensiveprocesses[12].The product attributes in case of freeze dried sam-plesaresuperiorascomparedtoanyotherdryingmethod.Sundryingrequireslongintervalsofsunlightexposure.Thelimitationsassociatedwithsundryingareinconsistentavailabilityofsunlight,longhours,weatherconditionsanddamagetosamplesduetoenvironmentalfluctuations.Freezedryingisanenergyintensivenon-disruptivetechniquebutisnotwidelyapplicableduetohighercost.Hotairdryingiscommonlyfollowedinfoodprocessingindustriesowingtoitssimplicity,developmentoveryearsandprecisecontrolofparametersascomparedtoabovetwotechniques.Thetemperaturecanbevariedoveralargerangeandthus,qualitativeparameterscanbewellstudiedundercontrolledconditions. Microwavedryingisanoveltechniquewhichacceleratestheremovalofmoistureduetovibrationofwatermoleculesandvolumetricheating.Thetechniquewasreviewedforitsenergyefficiencyandquickerdryingascomparedtoothermethods[13-15].Microwaveshavebeenusedfordryingoffruitsandvegetableslikecarrot,spinachleavesandmushroom.Thequalityattributeswerefoundtobeacceptabletothatofcommercialproducts[16,17].Previousstudiesconcerningextractionofmangokerneloilhavefocussedonapplicationofhotairdryingonyieldofoil,phenolicandantioxidantcapacity[18].However,effectofdryingmethodsonstructuralmorphologyinrelationtooilextractionhasnotbeenreported.Also,itwouldbeimportanttounderstandhowvariousex-tractiontime-temperaturescombinationsforagivendryingconditionbringchangesintheoilextractabilityandoilquality.Aquickandeffectivedryingmethodpriortomangokernellipidextractionisthus,neededtodesignasustainableextractionprocess.Theextractionmethodmodificationmayaddfreshinsightintomangokernellipidextractionwhichmayfurtherbeusedasanessentialoil for various applications. Thepresentstudyaimsto(i)evaluateandcomparetheeffectofhotairdryingandmicrowavedryingonstructuralmor-phologyofmangokernelpowderand(ii)assesstheeffectofdifferentextractiontemperature-timecombinationsonlipidyields

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Materials and Methods

Raw material Themangoes(Totapurivariety)wereobtainedfromlocalmarket.Pulpwasremovedmanuallyandseedcoatswerewashedwithdistilledwatertoremoveresidualsugarsanddried.Seedcoatswereseparatedfromkernelusingacutterdesignedspecificallyforthispurpose.Thekernelsweregroundanddriedat105±2°Cforproximateanalysis[19].Driedpowderwassieved(≤500µ),packedinairtightcontainersandstoredat4°C.AllreagentswereofanalyticalgradeandprocuredfromMerck,India. Proximate analysis of kernels Themoisture,ash,lipid,proteinandcarbohydrateweredeterminedasperstandardAOACmethods[19].Sugarsweredeter-minedusingphenolic-sulphuricacidmethod.StarchwasquantifiedusingstarchassaykitfromMegazyme[20].

Hot air drying of kernel powder Theinitialmoisturecontentofthegroundkernelwasmeasured.Fordrying,aknownweightofgroundkernelswerekeptinpetriplatesinathinlayeranddriedatdifferenttemperatures.Eachreadingwasmeasuredintriplicate.Hotairdryingat1.0m/sairvelocitywasdoneforatemperaturerangeof40°C,60°C,80°Cand105°Cfordifferenttimeintervals.Themoisturecontentwasdeterminedusingmoistureanalyser(CitizenMB200,India). Formicrowavedrying,mangokernelpowderwaskeptinpetriplatesarrangedatequaldistancesinthemicrowavetray(ModelLGMG607APR,output900W).Kernelswereexposedtofourpowerlevels,i.e.20%(180W),40%(360W),60%(540W)and80%(720W)tillconstantweightwasachieved.MicrowavewassetuptostayONforaminuteandturnOFFfor30secandcyclecontinuedinthisfashionuntilexperimentswerecompleted.ThirtysecondsOFFtimewasmaintainedaftereveryminutetoavoidsampleburningduetooverheating.

Structural and morphological study Scanningelectronmicroscopywasconductedoncontrolandtreatedsamples(FEIQuanta200,Oregon,USA).Topreparethesample,driedpowderswereadheredtoadoublesidedadhesivetape.Platinumcoatingat20kVwasdonefor300spriortovi-sualisationofimages.Themicrographswerestudiedforpresenceofgranulesandstructuraldisruptionduringdrying.

Lipid extraction LipidextractionwascarriedoutusingSoxhletextractionmethod(Dhara,Bhattacharya&Ghosh2010).Tengramsofdriedkernelpowderwasplacedinathimbleandhexanewasusedasanextractionsolvent.Topreventthelipidfromdegradation,40°Cand60°Cwasusedasextractiontemperatureforatimeintervalof2hrsand4hrs.Nosignificantdifferenceinyieldwasfoundforlongerextractionperiods(8-24hrs)duringinitialexperiments,thus,temperatureandtimedurationwaskeptlowtoavoiddegrada-tionoffattyacids.Aftersolventremoval,thelipidwaskeptat40°Cfor24hourstoremovetracesofhexane.Theobtainedlipidwasthenstoredat4°Cinambercolouredcontaineruntilfurtherusage.Theyieldwascalculatedondrybasis.

Fatty acid profile and qualitative tests Thefattyacidprofilewasdeterminedtocompareanychangesinfattyacidcompositionduetodifferentdryingmethods.Thefattyacidcompositionwasdeterminedusinggaschromatographyequippedwithaflameionizationdetector(PerkinElmer,AutosystemXL).Forflameionizationdetector,columnusedwasPE-FFAP,carriergasnitrogen,Injectiontemperatureanddetectortemperaturewaskeptat250°C.Thequalitativeparameterssuchasperoxidevalue(PV),iodinevalue(IV),saponificationvalue(SV)andacidvalue(AV)weredeterminedasperthestandardprotocolsofFSSAI(FSSAI2012).

Statistical analysis ThedifferencebetweenvarioussetofresultswastestedusingonewayANOVAwithDunnett’spost-test(Minitab;version16).Theresultswereexpressedasmean±standarderror.Thesignificanceofdatawasrepresentedintermsofpvalue(p<0.05wasconsideredassignificant).Alltestswereperformedintriplicates.

Results and Discussion

Proximate analysis TheproximateanalysisTable1showedthatmangokernelisrichlyconstitutedofcarbohydrates(58±2%starches)withaninitialmoisturecontentof54.5±3.0%.Theproteincontentwasfoundtobe7.5%.Theaveragelipidcontentwasfoundtobe12.4%.

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Table 1:ProximateanalysisofTotapurimangokernelsCONSTITUENTS QUANTITYEnergy 411.3K.calMoisture 7.8±1%Fat 11.5±1.4%Protein 7±0.3%TotalSugars 15.6±2.0%Starch 54±0.6%Ash 2.1±0.2%

Drying curves Themoisturecontent(w.b)asafunctionoftimeforconventionaldryingandmicrowavedryingareshowninFigure2andFigure3.Conventionalmethodofdryingtooksignificantlylongertimethanmicrowave.Microwavesreducedthedryingtimeto14minuteswhenusedatpowerlevelof180Wwhileat540W,anexposureof11minutesreducedthemoisturecontentto7.5%.Char-ringofsampleswasobservedbeyond540W.Forhotairdrying,itwasnotedthatdryingiscontinuouswithtimeandlagtimewasnotobservedwhencomparedwithmicrowavedryingcurves.Thismaybeduetovibrationofwatermoleculesincaseofmicrowaveexposureandsurfacemoistureremovalafterdiffusionofmoisturefromcoreofthestructuretoouterlayersduetohydrogenbondbreaking.However,lagtimeinmicrowavedryingprocesswassmallandmaynothaveapracticalsignificance.

Figure 2:Conventionalhotairdryingofmangokernels(Ddenotesdryingtemperaturein°C)

Figure 3:Microwavedryingofkernelsfordrying(20%power:180W,40%power:360W,60%power:540W)

Scanning electron microscopy OverallstructureofmangokernelpowderasshowninFigure4.Indicatedpresenceofovalandcircularstarchgranules.Thegranuleswerefoundtobepresentinsidelayeredcomplexeswhichmaybeconsistingofprotein,lipidsandstructuralcarbo-hydrates.Similarfindingswerereportedearlierforwheatstarch[21]. Increase indryingtemperaturewasfoundtoaffect theovalgranuleswhichmaybedue todisruptionofstarchgranulesabove theirgelatinization temperature,whichwas found tostartat

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73.4°Casreportedpreviously(Kittiphoom2012).Inboththedryingmethodsthelayersstartedtodisappearfromthesurfaceofstarchgranulesasdryingtemperatureandmicrowavepowerlevelwasincreased.Structuraldisruptionwasclearlyvisibleunderhotairdryingconditionat105°C.Mildmicrowavedryingconditionswerefoundtoaffectthegranulestoalesserextentascomparedtohighestmicrowavepowerlevelinwhicharubberymassmaybeseenalongwithnointactgranules.Thestructuralchangemaybeduetoswellingofstarchgranulesinthepresenceofsignificantmoisture.Similarresultswereobtainedinstudiesperformedoncookedpastainpreviousreportswhereitwasconcludedthatpostcookingtheproteinandstarchlayersarenotdistinguishableandamyloseleachesoutfromthestarchgranulesforminglayers[21].Thus,theimageswerefoundtobeagoodevidenceofstructuralchangesduetodrying.

Figure 4 (a):Airdriedsamplesofmangokernelpowder Figure 4 (b):Mangokernelshotairdriedat40°C

Figure 4 (c):Mangokernelshotairdriedat60°C Figure 4 (d): Mangokernelshotairdriedat80°C

Figure 4 (e): Mangokernelshotairdriedat105°CFigure 4 (f):Microwavedriedkernels(at180Wpowerlevel)

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Figure 4 (g):Microwavedriedkernels(at360Wpowerlevel) Figure 4 (h):Microwavedriedkernels(at540Wpowerlevel)

Figure 4 (i):Microwavedriedkernels(at720Wpowerlevel)

Lipid yield Theyieldoflipidsfromconventionaldryingatdifferenttemperatureswasrangingfrom8.6-11.5%,whileformicrowaveitwasfoundtobe9.9-11.7%(Figure5).Thebestextractionconditionsoutofeachset(foragivendryingmethodunderdifferentextractionconditions)werecomparedamongrowsandcolumns(Table2).Foragivenextractioncondition,thedifferenceamongyieldswerecomparedatdifferentdryingcondition(Hotair(40°C,60°C,80°C,105°C),andmicrowave(180Wand360W)Thehighestyieldwasgreaterthan11%whichwasobtainedinmostofthedryingandextractionconditions.Itcanbeconcludedthatdryingathighertemperaturesdidnotaffectthelipidyield.Sincethetimerequiredformicrowavedryingissignificantlylessthanhotairdrying,thesamecanbeusedforthedryingmangokernels.Extractionyield(40°C,2h)fromthemangokernelflour,whichwasdriedat40°C,wassignificantlylowerthanotherextractionconditions(p<0.05).Itshowsthatrelativelylowtemperatureandshortertimeposesmasstransferlimitationproblemsduringoilextraction.Athighertemperatures,onewouldexpecthighdiffusioncoefficientoftheoil.Micellaviscositywouldalsoimproveathighertemperatureswhenexposedforlongertimewhichisapparent(Table2).Ingeneral,solventextractioniscarriedoutattemperaturesascloseaspossibletotheboilingpointofsolventwhichinturnimprovesthemiscibilityofoil-solventsystem.Forexample,solventextractionprocesswithn-hexanesolvent(boilingpointis68°C)istypicallykeptat60-70°C.Itisnoteworthythatbyincreasingthetimeofinteractionofsolvent(from2hto4h)withthemicellahelpedinextractingoilevenatlowtemperature(40°C)(Figure5)

Table 2:ComparisonofdryingandextractionconditionsonlipidyieldExtraction D1 D2 D3 D4 D5 D6 D72hr/40°C 8.6±0.5b,2 10.9±0.2a,1 9.2±0.4c,2 10.6±0.3a,1 10.3±0.7a,1 11.0±0.2a,1 10.9±0.2b,1

4hr/40°C 11.3±1.2a,1 11.5±0.2a,1 11.1±0.2b,1 10.5±0.4a,1 10.9±0.3a,1 10.7±0.3ab,1 9.9±0.2c,1

2hr/60°C 11.5±0.6a,1 10.7±0.5a,12 11.3±0.4a,1 9.8±0.4a,2 10.8±0.07a,12 9.8±0.3b,2 10.6±0.2b,12

4hr/60°C 11.2±0.5a,12 11.7±1.1a,123 11.2±0.3a,12 10.4±1.0a,3 10.5±0.2a,123 10.0±0.3b,3 11.7±0.2a,1

(D1:40°C, D2:60°C, D3:80°C, D4:105°C, D5:180W, D6:360W, D7:540W; The final moisture contents of dried kernels were 8%, 4.7%, 4.3%, 2.4%, 8.6%, 5.2%, 5.5% respectively. Comparisons were made using one way ANOVA across columns and rows separately. Means that do not share a common letter are significantly different e.g. letters containing “a” in one column are similar, “b” and “c” denotes dissimilarity with values with “a”; the first alphabet shows comparison across the columns (vertical comparison) i.e drying vs different extraction conditions and second numeric post coma denotes comparison across rows (horizontal comparison) i.efor a given extraction condition comparison of lipids yields were donefordifferentdryingmethods).

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Figure 5: Lipidyieldundervariousdryingandextractionconditions

Fatty acid profile and other qualitative parameters ThefattyacidprofileoflipidsextractedfromconventionallydriedseedsandmicrowavedriedkernelswerecomparedandshowninTable3.Oleicacidandstearicacidweretwomajorfattyacidspresentinthemangokerneloil.Thefattyacidprofileinallcasesmatcheswellwithreference.Thequantityofdifferentfattyacidsunderallhotairdryingconditionswasfoundtobeconsistent,irrespectiveofextractionconditions.However,anunusualobservationwasnoticedincaseofhighestmicrowavepowerlevel.Thecontentofoleicacidfoundtodecreasewhenbothdryingandextractionconditionsweretowardshigherrange.Forexample,oleicacidcontentofsamplesdriedat540Wandextractedat60°Cfor4hwerefoundtodecreasefrom44%to41%forhighestmicrowavepowerlevel.Thesimilarobservationswerefoundforlinoleicacid.Toevaluatetheeffectoftheobservationmentionedabove,oilswereextractedpostsdryingatoptimumhotairandmicrowavedryingconditionsselectedfromtheTable3.Oleicacidandlinoleicacidasreportedinoneofthefindings[23]wereshowntoundergothermalandoxidationreactiontoformaldehydes,ketonesandalco-holswhichfurtherundergooxidationintocarboxylicacidswhenfryingofmethyloleateandmethyllinoleateasmodelcompoundswasdoneat180°C.Theresultsobtainedinourstudysuggeststhatrapidandlocalizedheatingconditionsundermicrowavemayhavecauseddegradationofoleicacidwhilemildmicrowavepowerlevelmaybesuitablefordrying.Also,hotairdryingconditiondidnotinitiatethedeteriorationoflipidsbutprominenteffectsmaybeseenonthestarchgranulesathightemperatures.Thedetailedstudyonundergoingchemicalchangesaftermicrowavemayfurtherrequireanunderstandingofgaschromatography-massspectraanalysisforderivatizationandidentificationoftheintermediatecompounds.

Table 3:Fattyacidprofileforhotairandmicrowavedriedsamples

Fatty acid (%)Extraction temperature = 40°C, time = 2 hours

D1 D2 D3 D4 D5 D6 D7Palmitic (C16) 6.8 7.8 6.7 8.3 7.9 7.1 8.4Stearic (C18:0) 36.6 38.02 36.9 35.8 37.5 38.4 36.8Oleic (C18:1) 46.9 43.7 45.1 44.7 43.1 43.5 44.0Linoleic (C18: 2) 7.3 7.8 7.9 8.5 8.9 8.8 8.5Linolenic (C18:3) 0.3 0.4 0.4 0.4 0.3 0 0Unknown 1.9 2.1 2.6 2.0 1.9 2 2.0C18:2/C16 1.07 1.0 1.1 1.0 1.1 1.2 1.0

Fatty acid Extraction temperature = 40°C, time = 4 hours

D1 D2 D3 D4 D5 D6 D7Palmitic (C16) 7.4 7.6 7.3 8.4 7.8 7.8 8.1Stearic (C18:0) 39.3 38.1 38.3 35.3 38.5 37.4 35.9Oleic (C18:1) 44.1 45.1 44.6 44.7 44.8 43.1 45.9Linoleic (C18: 2) 7.0 6.4 7.5 8.6 7.1 8.9 8.2Linolenic (C18:3) 0 0.4 0 0.4 0.4 0.4 0Unknown 2.0 2.1 2.0 2.3 2.1 1.9 1.7C18:2/C16 0.9 0.8 1.0 1.0 0.9 1.1 1.0

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Fatty acid Extraction temperature = 60°C, time = 2hours

D1 D2 D3 D4 D5 D6 D7Palmitic (C16) 8.1 8.3 7.0 8.6 8.8 7.9 8.0Stearic (C18:0) 36.0 36.8 36.9 36.0 33.8 39.2 37.4Oleic (C18:1) 44.6 44.1 45.6 44.8 44.6 43.1 42.5Linoleic (C18: 2) 8.5 8.1 7.8 8.4 10.8 9.8 8.7Linolenic (C18:3) 0.4 0.4 0.4 0 0 0 0Unknown 2.0 2.0 2.0 1.9 1.8 2.01 3.1C18:2/C16 1.04 0.9 1.1 0.9 1.2 1.2 1.0

Fatty acid Extraction temperature = 60°C, time = 4hours

D1 D2 D3 D4 D5 D6 D7Palmitic (C16) 7.6 8.1 7.8 8.3 8.5 7.8 7.5Stearic (C18:0) 37.8 36.5 36.6 35.5 33.1 39.1 40.6Oleic (C18:1) 44 43.8 44.8 45 44.6 42.8 41.1Linoleic (C18: 2) 7.9 8.3 7.9 8.5 10.7 8.1 8.6Linolenic (C18:3) 0.3 0.5 0.4 0.4 0.4 0 0Unknown 2.0 2.5 2.3 2.0 2.5 2.0 1.9C18:2/C16 1.0 1.0 1.0 1.0 1.2 1.0 1.1

(D denotes drying temperature: D1:40°C, D2:60°C, D3:80°C, D4:105°C, D5:180W, D6:360W, D7:540W)

Thevaluesforqualitativeparameterssuchasperoxidevalue,iodinevalue,saponificationvalueandacidvalueareshowninTable4.Peroxidevalue(PV)indicatestheformationofhydroperoxidesinthesystemwhicharetheprimaryoxidationproductofoilsandunstableinnature.Theeffectonoilwhereseedsweredriedat540Wissignificantlydifferentthantherestofthecondi-tions.Thereasonmaybeformationoffreeradicalsathighermicrowavepowerlevels.Thisalsoconcludesthatmildpowerlevelssuchas180WhaslesschangeinPVvaluewhencomparedwithhotairdrying.Similarobservationswerenotedinacidvaluewherethesampledriedat540Wwasfoundtoshowhighestacidvalueamongall,indicatingthepresenceoffreercarboxylicacidgroupsinlipid.TheobservationmaybecorrelatedwithobservedhigherPVandsimilarfindingshavebeenreportedforvegetableoilsasdiscussedbelow.Thevaluesofiodinevalueandsaponificationvaluewerefoundtobesimilarforalltheconditions.

Table 4:ComparisonbetweendryingmethodsfortheireffectonoilqualityDrying conditions Peroxide value

(mequiv/kg of oil)Iodine value (mg/100gm of oil)

Saponification value (mg KOH/g)

Acid value (mg KOH/g)

D2 0.1±0.02 53.0±1.00 189.3±1.0 4.8±0.25D4 0.3±0.02 57.5±0.50 238.1±2.0 5.2±0.47D5 0.3±0.01 57.0±0.75 231.0±0.9 5.4±0.36D7 1.6±0.20 64.3±1.05 181.3±1.2 6.6±0.25

(D denotes drying temperature: D2:60°C, D4:105°C, D5:180W, D7:540W)

TheratioofC18:2(linoleicacid)toC16(palmiticacid)denotesastandardforfatdeterioration,linoleicacidbeingsus-ceptibleandpalmiticacidbeingresistanttooxidation[16].Inthisstudyitwasfoundthattheratioobservedmatcheswellwiththereferencevalue.Itdidnotdiffersignificantlyforconventionallydriedkernelsandmicrowavedriedkernels.Linoleicacidthough,wasfoundtobelessorabsentinmicrowavedriedkernelswhichissimilartothereportedfindings.Unsaturatedbondsarepronetooxidativecleavageathighertemperatureoracceleratedreactionsinthepresenceofmicrowaveheating. Previouslymicrowaveswerestudiedforpretreatmentofoilseeds.Astudyoneffectofmicrowaveirradiation(lowerpowerlevels)onrapeseedsexplainstheincreasedyieldofoilthroughcoldpresspostmicrowavetreatment.Thequalitativeparametersoftheextractedoilwerefoundtobesimilartothecontrolsampleswherenopretreatmentwasdone[24].Anotherstudyoneffectofqualitativeparameterspostroastingofsunflowerseedsshowedsignificantdecreaseinoilcontent,increaseinperoxidevalue,anincreaseinfreefattyacidcontentanddecreaseinunsaturatedfattyacidcontent(linoleicacid)whenseedswereexposedto500Wofpowerandroastingwasdonefor10minutes[25].Exposuresofvegetableoilstomicrowaveheatingwerefoundtodeterioratethequalityoflipidssignificantlyascomparedtohotairheating.AnincreaseintheTransisomericformofunsaturatedfattyacidwasalso reported[26-29].Thus,thefindingsofourstudymatchwellwiththephenomenadiscussedabove.

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Extraction Time-Temperature Regime on Mango Kernel Lipids

Conclusion

Thetwodryingtechniques;hotairdryingandmicrowavedryingwerecompared.Thedryingtimeusingmicrowave(180W)wasfoundtoreducesignificantly(by34folds)ascomparedtohotairdrying(60°C).Themorphologicalstudiessuggestedthathigh-ertemperatureofdryingandhighermicrowavepowerlevelschangesthestructureofthekernel.Theeffectofheatingwasfoundtobeprominentonstarchgranulesandoverlappinglayerswhichmayindicateproteindenaturationduetoheating.Athighertempera-ture(105°Chotairdrying/540Wmicrowavepower)theglobulesweredisrupted.Thestatisticalanalysisoflipidyieldssuggestedthatmicrowavedryingandhotairdryingbothwascomparableintermsoflipidyield.Theextractionconditionsunder40°C/4hor60°C/2hwerefoundtoshowlessvariationandthus60°C/2hwaschosenasoptimumsinceitwasclosetoboilingpointofn-hexaneandtimedurationrequiredwasminimum.Thequalityoflipidwasfoundtobeconsistentunderallhotairdryingtemperatureswhilethedegradationofoleicacidandlinoleicacidwereobservedforsamplesdriedat540Wunderthemicrowave.Thoughtheratioofunsaturatedtosaturatedfatremainssimilarinbothtypesofdrying,thesignificantdecreaseinoleicacidcontentforhighestmicro-wavepowerlevelalongwithincreasedperoxidevalueandacidvalueindicateddeteriorationoflipidquality.Thus,fromtheabovestudyitcanbeconcludedthatmangokernelscanbedriedbestat180Wmicrowavepowerlevel.Overall,onthebasisofstructuralchanges,lipidyieldandlipidqualitytheoptimizedconditionswereconcludedasdryingat180Wmicrowavepower,extractionat60°Cfor2h.Modifyingtheconventionalextractionmethodintermsoftime-temperatureregimeworkswellformangokernelsandloweringtheextractiontimeto2hathighertemperaturesdidnotaffecttheyieldoflipidwhendriedwithanymethod.Furtherstudiescanbedoneoneffectofstorageconditionsonlipidquality.Theresidueleftafterlipidremovalunderoptimizedconditionsmayfurtherbeprocessedtorecoverstarchandphenolics,thus,thecompleteprocessmaybedesignedasabiorefinery.

Acknowledgement Wearegrateful to theMinistryofFoodProcessing Industries (MOFPI)underDepartmentofScienceandTechnology(DST)forprovidingfundingthroughtheexternalcompetitivegrantsprogram(ProjectID:SERB/MOFPI/0036/2013).

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