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SweetPotato

SweetPotato Chemistry,Processing,and Nutrition

Editedby TAI-HUAMU

InstituteofFoodScienceandTechnology,Chinese AcademyofAgriculturalSciences;KeyLaboratoryof Agro-ProductsProcessing,MinistryofAgricultureand RuralAffairs,Beijing,P.R.China

JASPREETSINGH

SchoolofFoodandAdvancedTechnologyand RiddetInstitute,MasseyUniversity,PalmerstonNorth, NewZealand

AcademicPressisanimprintofElsevier

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ListofContributors

LawrenceAkinolaArogundade

InstituteofFoodScienceandTechnology,ChineseAcademyofAgriculturalSciences; KeyLaboratoryofAgro-ProductsProcessing,MinistryofAgricultureandRuralAffairs, Beijing,People’sRepublicofChina;ChemistryDepartment,CollegeofPhysicalSciences, FederalUniversityofAgriculture,Abeokuta,Nigeria

KojiIshiguro

DivisionofFieldCropResearchandDevelopment,HokkaidoAgriculturalResearch Center,NARO,Hokkaido,Japan

LovedeepKaur

SchoolofFoodandAdvancedTechnologyandRiddetInstitute,MasseyUniversity, PalmerstonNorth,NewZealand

SunanthaKetnawa

GraduateSchoolofHorticulture,ChibaUniversity,Matsudo,Japan

NasirMehmoodKhan

InstituteofFoodScienceandTechnology,ChineseAcademyofAgriculturalSciences; KeyLaboratoryofAgro-ProductsProcessing,MinistryofAgricultureandRuralAffairs, Beijing,People’sRepublicofChina;DepartmentofBiotechnology,ShaheedBenazir BhuttoUniversity,Sheringal,Pakistan

RieKurata

DivisionofUplandFarmingResearch,KyusyuOkinawaAgriculturalResearchCenter, NARO,Miyakonojo,Japan

Peng-GaoLi

InstituteofFoodScienceandTechnology,ChineseAcademyofAgriculturalSciences; KeyLaboratoryofAgro-ProductsProcessing,MinistryofAgricultureandRuralAffairs, Beijing,People’sRepublicofChina;SchoolofPublicHealth,CapitalMedicalUniversity, Beijing,People’sRepublicofChina;BeijingKeyLaboratoryofEnvironmental Toxicology,CapitalMedicalUniversity,Beijing,People’sRepublicofChina

Dai-FuMa

XuzhouSweetPotatoResearchCenter,ChineseAcademyofAgriculturalSciences, NationalSweetPotatoImprovementCenter,Xuzhou,People’sRepublicofChina

Meng-MeiMa

InstituteofFoodScienceandTechnology,ChineseAcademyofAgriculturalSciences; KeyLaboratoryofAgro-ProductsProcessing,MinistryofAgricultureandRuralAffairs, Beijing,People’sRepublicofChina

Tai-HuaMu

InstituteofFoodScienceandTechnology,ChineseAcademyofAgriculturalSciences; KeyLaboratoryofAgro-ProductsProcessing,MinistryofAgricultureandRuralAffairs, Beijing,People’sRepublicofChina

YoshiyukiNakamura

DivisionofFieldCropResearch,InstituteofCropScience,NationalAgricultureand FoodResearchOrganization(NARO),Tsukuba,Japan

YukiharuOgawa

GraduateSchoolofHorticulture,ChibaUniversity,Matsudo,Japan

FredrickO.Ogutu

InstituteofFoodScienceandTechnology,ChineseAcademyofAgriculturalSciences; KeyLaboratoryofAgro-ProductsProcessing,MinistryofAgricultureandRuralAffairs, Beijing,People’sRepublicofChina;FoodTechnologyDivision,KenyaIndustrial ResearchandDevelopmentInstitute,Nairobi,Kenya

TomoyukiOki

GraduateSchoolofHealthandNutritionSciences,NakamuraGakuenUniversity, Fukuoka,Japan

ShigenoriOkuno

DepartmentofPlanning,KyusyuOkinawaAgriculturalResearchCenter,NARO, Kumamoto,Japan

IselaCarballoPérez

InstituteofFoodScienceandTechnology,ChineseAcademyofAgriculturalSciences; KeyLaboratoryofAgro-ProductsProcessing,MinistryofAgricultureandRuralAffairs, Beijing,P.R.China;InstituteofFoodResearch,Havana,Cuba

JaspreetSingh

SchoolofFoodandAdvancedTechnologyandRiddetInstitute,MasseyUniversity, PalmerstonNorth,NewZealand

TerumiSugawara

CropDevelopmentandAgribusinessResearchDivision,KyusyuOkinawaAgricultural ResearchCenter,NARO,Kumamoto,Japan

Hong-NanSun

InstituteofFoodScienceandTechnology,ChineseAcademyofAgriculturalSciences; KeyLaboratoryofAgro-ProductsProcessing,MinistryofAgricultureandRuralAffairs, Beijing,People’sRepublicofChina

KazunoriTakamine

DivisionofShochuFermentationTechnology,EducationandResearchCenterfor FermentationStudies,FacultyofAgriculture,KagoshimaUniversity,Kagoshima,Japan

MiaoZhang

InstituteofFoodScienceandTechnology,ChineseAcademyofAgriculturalSciences; KeyLaboratoryofAgro-ProductsProcessing,MinistryofAgricultureandRuralAffairs, Beijing,People’sRepublicofChina

Preface

Sweetpotato,commonlyknowninChinaasHongshu,Baishu,Digua, Fanshu,Hongyu,andHongshao,isanannualorperennialherbofthe Convolvulaceae family.Sweetpotatocultivationischaracterizedbylowinput,high-yield,droughttolerance,andresistancetoinfertility,andsweet potatoisanimportantfoodcropafterrice,wheat,corn,andpotato.The productionofsweetpotatoesishighestinAsia,followedbyAfrica,then theAmericasandOceania.

Sweetpotatorootsandleavesarerichinavarietyofnutrientsrequired bythehumanbody,suchasstarch,protein,dietaryfiber,lipids,polyphenols,carotenoids,vitamins,andmineralelementssuchaspotassiumand calcium,dependingondifferentvarieties.Basedonitsexcellentnutritional value,researchontheextractionandstructural,physicochemical,andfunctionalpropertiesoffunctionalcomponentsinsweetpotatoandits by-productsfromindustrialprocessinghavegainedwidespreadattention. Sweetpotatohasalsobeenprocessedintoflour,flakes,granules,paste, purees,chips,cannedproducts,beverages,andvarioussnackfoods.In addition,sweetpotatoisusedasanimportantsupplementfordifferent stapleproductsinthefoodindustry,suchassweetpotatosteamedbreads, bakedbreads,noodles,andpancakes,etc.Toimprovehumandietarynutrition,itisimportanttosupportresearch,development,andapplicationof thenutritionalandfunctionalcomponentsextractedfromsweetpotatoand itsby-products,aswellastheexistingandnewsnackandstaplefoods.This willbeofgreatsignificanceinincreasingtheconsumptionproportionof sweetpotatoinpeople’sdailydiet.Itisalsoaninevitabletrendforthe sustainabledevelopmentofagriculturalproductionandtheimprovement ofhumandietaryhabits.

Thebook SweetPotato:Chemistry,Processing,andNutrition wascompiled basedontheresearchachievementsofallthecontributors.Thisbook includes14chapters.Chapter1,Sweetpotato:chemistry,processing,and nutrition anintroduction,introducesoverallinformationonsweet potato.Chapter2,Sweetpotato:originandproduction,focusesontheoriginandproductionofsweetpotatoesintheworld.Chapter3,Sweet potatostarch,focusesonthestructureandphysicochemicalpropertiesof sweetpotatostarch,aswellastheeffectsofphysicalandchemicalmodifications.Chapter4,Sweetpotatoproteinanditshydrolysates,introducesthe

recoveryandcomposition,gelationandemulsifyingpropertiesofsweet potatoprotein,aswellasthepreparationandantioxidantactivityofits hydrolysates.Chapter5,Sweetpotatodietaryfiber,introducestheefficient manufacture,andphysicochemicalandfunctionalpropertiesofsweet potatodietaryfiber,aswellastheextractionmethods,composition,and physicochemicalandfunctionalpropertiesofsweetpotatopectinaffected byultrasonicmodification.Chapter6,Sweetpotatolipids,introducesthe lipidandfattyacidcompositionsofdifferentvarietiesofsweetpotato,and theantiproliferativeeffectandcellmigrationinhibitionofsweetpotato lipids.Chapter7,Sweetpotatopolyphenols,introducesthemaincategories,theindividualphenoliccomposition,physiologicalfunctions,processingstability,andutilizationofpolyphenolsfromsweetpotatorootsand tops.Chapter8,Sweetpotatocarotenoids,describesthecomposition, content,analyticalmethod,physiologicalfunctions,andretentionduring processingofcarotenoidsfromsweetpotatorootsandtops.Chapter9, Sweetpotatomicrostructure,starchdigestion,andglycemicindex,introducesthemicrostructureandglycemicfeaturesofsweetpotato. Chapter10,Sweetpotatostaplefoods,presentsthedefinition,types,main rawingredients,anddevelopmentofsweetpotatostaplefoods; Chapter11,Sweetpotatosnackfoods,introducesaseriesofcommon sweetpotatosnacks,includingsweetpotatochips,roastsweetpotatoes, sweetpotatobiscuits,driedsweetpotatoslices,sweetpotatocakes,doughnuts,extrudedsweetpotatosnacks,andthepackagingthereof.Chapter12, Sweetpotatofermentationfood(sweetpotato shochu),introducesthesweet potato shochu manufacturingmethodsandthefactorsaffecting shochu aroma,andbrieflydiscussesitspotentialhealthbenefits.Chapter13, Qualityevaluationofsweetpotatoproducts,describesJapanesesweet potatovarietiesforfoodandtheirchemicalpropertiesonthesweetnessand textureofsteamedstorageroots.Chapter14,Globalmarkettrends, challenges,andthefutureofthesweetpotatoprocessingindustry,introducestheglobalmarkettrends,challenges,andfutureofthesweetpotato processingindustry.Thepurposeofthisbookistoprovideareferenceand guidanceforthechemistry,processing,andnutritionofthesweetpotato, andtoprovidebasicinformationforscientificinnovationsinthesweet potatoindustry.

Wethankallthecontributors,Ms.SusanIkeda,andElsevierwho madethisbookpossible.

Tai-HuaMu1 andJaspreetSingh2

1InstituteofFoodScienceandTechnology,ChineseAcademyofAgriculturalSciences; KeyLaboratoryofAgro-ProductsProcessing,MinistryofAgricultureandRural Affairs,Beijing,P.R.China 2MasseyInstituteofFoodScienceandTechnology,MasseyUniversity,PalmerstonNorth, NewZealand

CHAPTER1

Sweetpotato:chemistry, processing,andnutrition—an introduction

Tai-HuaMu1 andJaspreetSingh2

1InstituteofFoodScienceandTechnology,ChineseAcademyofAgriculturalSciences;KeyLaboratoryof Agro-ProductsProcessing,MinistryofAgricultureandRuralAffairs,Beijing,People’sRepublicofChina 2SchoolofFoodandAdvancedTechnologyandRiddetInstitute,MasseyUniversity,PalmerstonNorth, NewZealand

Sweetpotato(Ipomoeabatatas[L.]Lam)isadicotyledonousplant belongingtothefamily Convolvulaceae.Theplantbearswhiteandpurple sympetalousflowersandhaslargenutritiousstorageroots.Sweetpotato rootsdevelopmainlyasstorageroots,bearingalternateheart-shapedor palmatelylobedleaves,whicharelongandtapered.Thesweetpotato rootshaveasmoothskinthatisyellow,orange,red,brown,purple, and/orbeige,andhasfleshthatisbeigetowhite,red,pink,violet,yellow,orange,orpurpledependinguponthecultivar.Theroots,leaves, andstemsofsweetpotatoesarealledibleandnutritious,andtheseplaya vitalroleinensuringthefoodsecurityofmanydevelopingcountries.The world’sannualproductionofsweetpotatoeswas105millionmetrictons in2016,withapproximately95%ofsweetpotatoesbeinggrownin developingcountries,andwithChinarankedasthebiggestproducer (FAOSTAT,2016).Theworld’sproductionofsweetpotatoesiscurrently stable,asistherankingoftheregionsandcontinents.Sweetpotato productioninAsiaisconsiderablyaheadoftheothercontinents,followed byAfrica,SouthAmerica,Caribbean,NorthandCentralAmerica, Europe,andlastlyOceania(FAOSTAT,2016).Asaversatilecrop,sweet potatoescanbeusedforawiderangeofpurposes.Sweetpotatorootsand leavesarerichinstarch,protein,dietaryfiber,lipids,polyphenols, carotenoids,vitamins,andmineralelementssuchaspotassiumandcalcium dependingonthedifferentvarieties.Sweetpotatoescanalsobeutilizedas arawmaterialtoextractdifferentfunctionalcomponentswithhigher nutritionalvalue.

Starchisthemajorcomponentofsweetpotatodrymatterandconsists ofamyloseandamylopectinwithvaluesrangingfrom13.33%to26.83% and73.17%to86.67%,respectively(Abegundeetal.,2013).Sweetpotato starchgranulesvaryfrompolygonaltoroundtocupuliform/bellshapes withgranulesizesrangingfrom2to42 μm(Chenetal.,2003).The digestibility,syneresispercentage,swellingpower,andsolubilityofsweet potatostarchesareintherangesof10.35% 15.15%,32.45% 44.68%, 13.46 26.13g/g,and8.56% 19.97%,respectively(Abegundeetal., 2013).Sweetpotatostarchescanbemodifiedbyphysicalandchemical methodstoimprovetheirphysicochemicalcharacteristicsandresistance towardsdigestiveenzymesduringstarchdigestion(Yuetal.,2015,2016), whichcanaidinthembeingabletoserveasfunctionaladditivesinfood.

Sweetpotatocontainsapproximately1.73% 9.14%ofproteinona dryweightbasis.Sweetpotatoprotein(SPP)ismainlycomposedofsporamins,whicharerichinessentialaminoacids,andSPPiscomparable withothersuperiorqualityvegetableproteins(Muetal.,2009). UnfortunatelySPPisgenerallydiscardedasindustrialwasteduringsweet potatostarchprocessing.SPPpossessesgoodgelationandemulsifying propertiesandcaneasilyberecoveredbyisoelectricprecipitationor ultrafiltration/diafiltrationprocessedmethods(ArogundadeandMu,2012; Arogundadeetal.,2012;Khanetal.,2014).SPPhydrolysates(SPPH) shownoteworthyantioxidantactivity,andSPPHcouldbeobtainedby enzymatichydrolysisunderhighhydrostaticpressure(Zhangand Mu,2017).

Sweetpotatodietaryfibercouldbeextractedfromsweetpotatopulp, whichisthedehydratedresidueproducedduringsweetpotatostarch manufacturing.Sweetpotatopulpconsistsof49.7%dietaryfiber,whichis richinpectin(39.5%),cellulose,hemicellulose,andlignin(Takamine etal.,2000).Sweetpotatodietaryfiberexhibitsgoodphysicochemical andfunctionalproperties.Inparticular,sweetpotatopectinobtainedby sonication-inducedmodificationshowedlowermolecularweight,higher galacturonicacidcontent,andstrongerantioxidantcapacitywhen comparedtounmodifiedsamplesandcouldinduceapoptosis-likecell deathincoloncancer(OgutuandMu,2017;Ogutuetal.,2018).

Lipidsarepresentinalmostallfoodsandplayanimportantrolein humannutritionandthesensoryaspectsoffood.Thetotallipids(TLs) contentofdifferentcultivarsofsweetpotatonormallyrangesfrom0.72% to1.44%,consistingof36.74% 61.04%ofneutrallipids(NLs),30.29% 49.25%ofglycolipids(GLs),and7.05% 17.07%ofphospholipids(PLs).

Thefattyacids(FAs)insweetpotatoTLs,NLs,GLs,andPLsincludedifferentpercentagesofpalmiticacid(C16:0),stearicacid(C18:0),oleicacid (C18:1),linoleicacid(C18:2),linolenicacid(C18:3),andarachidicacid (C20:0).Sweetpotatolipidshavebeenreportedtohavecertainanticancer effects,especiallyGLswiththecontributionofmonogalactosyldiacylglycerolanddigalactosyldiglyceride(Zhao,2014).

Polyphenolsarecomposedofavarietyofcomponents,andtheir ingestionforhealthreasonsiscurrentlywidelyrecommendedinmost developedcountries.Sweetpotatopolyphenoliccompoundsareseparated intotwomaincategories:flavonoidsandphenolicacids.Flavonoidsare mainlyfoundinsweetpotatotuberousroots,andincludeanthocyanins, rutin,andquercetin,butarealsofoundinsweetpotatotops,forexample, quercetinglycosides.Sweetpotatophenolicacidsconsistofamixtureof caffeicacidandcaffeoylquinicacidderivatives,whicharecommonlypresentinallpartsofsweetpotatoleaves,petioles,stems,andtuberousroots.

Sweetpotatocarotenoidsaremainlydistributedinorange-and yellow-fleshedsweetpotatoroots,aswellassweetpotatoleaves. Approximately90%ofthecarotenoidsinorange-fleshedsweetpotatoes are β-carotene(Kimuraetal.,2007).Luteinisamemberofthexanthophyllfamilyofcarotenoids,andithasbeenfoundintheconstituentparts ofsweetpotatotops.Sweetpotatocultivarswithahighcontentofcarotenoidsanddeeporangeoryellowfleshhavebeendeveloped.Sweet potatocarotenoidsshowgoodantioxidantactivitiesandcouldbeusedas asolutiontovitaminAdeficiency.

Nowadayssweetpotatoeshavebeenusedasanimportantsupplement fordifferentstapleproductsinthefoodindustry,suchassweetpotato steamedbreads,bakedbreads,noodles,andpancakes.Sweetpotatoeshave alsobeenusedtoproducesnackfoods,suchassweetpotatochips,roast sweetpotatoes,biscuits,driedslices,cakes,doughnuts,andextruded snacks.Inaddition,sweetpotatoesareusedtoproducefermentedfoods, forexample,sweetpotato shochu,whichisadistilledalcoholicbeverage. Furthermore,toensuretheconsumersgethighqualityproducts,thequalityevaluationofsweetpotatoproductsisimportant.Insummary,the sweetpotatoprocessingindustryhasgoodopportunitiesbutatthesame timesomedifficultchallenges.Thescientistsandresearchersworkingin theareaoffoodprocessingmayneedtoseekfurthercooperationwith sweetpotatobreedersandgrowerstomaximizetheutilizationofsweet potatoesfordifferentfoodprocessingapplications.

References

Abegunde,O.K.,Mu,T.-H.,Chen,J.-W.,Deng,F.-M.,2013.Physicochemical characterizationofsweetpotatostarchespopularlyusedinChinesestarchindustry. FoodHydrocol.33(2),169 177.

Arogundade,L.A.,Mu,T.-H.,2012.Influenceofoxidativebrowninginhibitorsand isolationtechniquesonsweetpotatoproteinrecoveryandcomposition.Food Chem.134(3),1374 1384.

Arogundade,L.A.,Mu,T.-H.,Añón,M.C.,2012.Heat-inducedgelationpropertiesof isoelectricandultrafilteredsweetpotatoproteinisolateandtheirgelmicrostructure. FoodRes.Int.49(1),216 225.

Chen,Z.,Schols,H.,Voragen,A.,2003.Physicochemicalpropertiesofstarchesobtained fromthreevarietiesofChinesesweetpotatoes.J.FoodSci.68(2),431 437.

FAOSTAT,2016.Productionofcrops.Availablefrom: , http://faostat3.fao.org/browse/ Q/QC/Ex .

Khan,N.M.,Mu,T.-H.,Zhang,M.,Arogundade,L.A.,2014.TheeffectsofpHand highhydrostaticpressureonthephysicochemicalpropertiesofasweetpotatoprotein emulsion.FoodHydrocol.35,209 216.

Kimura,M.,Kobori,C.N.,Rodriguez-Amaya,D.B.,Nestel,P.,2007.Screeningand HPLCmethodsforcarotenoidsinsweetpotato,cassavaandmaizeforplantbreeding trials.FoodChem.100(4),1734 1746.

Mu,T.H.,Tan,S.S.,Xue,Y.L.,2009.Theaminoacidcomposition,solubilityand emulsifyingpropertiesofsweetpotatoprotein.FoodChem.112(4),1002 1005.

Ogutu,F.O.,Mu,T.-H.,2017.Ultrasonicdegradationofsweetpotatopectinandits antioxidantactivity.Ultrason.Sonochem.38,726 734.

Ogutu,F.O.,Mu,T.-H.,Sun,H.,Zhang,M.,2018.Ultrasonicmodifiedsweetpotato pectininducesapoptosislikecelldeathincoloncancer(HT-29)cellline.Nutr. Cancer70(1),136 145.

Takamine,K.,Abe,J.-i,Iwaya,A.,Maseda,S.,Hizukuri,S.,2000.Anewmanufacturing processfordietaryfiberfromsweetpotatoresidueanditsphysicalcharacteristics. J.Appl.Glycosci.47(1),67 72.

Yu,S.X.,Mu,T.H.,Zhang,M.,Ma,M.M.,Zhao,Z.K.,2015.Effectsofretrogradation andfurtheracetylationonthedigestibilityandphysicochemicalpropertiesofpurple sweetpotatoflourandstarch.Starch-Stärke67(9 10),892 902.

Yu,S.X.,Mu,T.H.,Zhang,M.,Zhao,Z.K.,2016.Effectsofinorganicsaltsonthe structuralandphysicochemicalpropertiesofhigh-hydrostatic-pressure-gelatinized sweetpotatostarch.Starch-Stärke68(9 10),980 988.

Zhang,M.,Mu,T.-H.,2017.Identificationandcharacterizationofantioxidantpeptides fromsweetpotatoproteinhydrolysatesbyAlcalaseunderhighhydrostaticpressure. Innovat.FoodSci.Emerg.Technol.43,92 101.

Zhao,S.-T.,2014.StudyontheLipidCompositionandAnti-cancerActivityofSweet Potato.XinjiangAgriculturalUniversity.

Sweetpotato:origin andproduction

Tai-HuaMu1 andPeng-GaoLi1,2,3

1InstituteofFoodScienceandTechnology,ChineseAcademyofAgriculturalSciences;KeyLaboratoryof Agro-ProductsProcessing,MinistryofAgricultureandRuralAffairs,Beijing,People’sRepublicofChina

2SchoolofPublicHealth,CapitalMedicalUniversity,Beijing,People’sRepublicofChina

3BeijingKeyLaboratoryofEnvironmentalToxicology,CapitalMedicalUniversity,Beijing,People’ s RepublicofChina

Origin

Botanicalcharacteristicsofsweetpotatoes

Thesweetpotato(Ipomoeabatatas[L.]Lam)isadicotyledonousplantthat belongstothefamilyConvolvulaceae.Itisanherbaceousperennialvine thathaswhiteandpurplesympetalousflowers,largenutritiousstorage roots,andalternateheart-shapedorpalmatelylobedleaves.Thelarge, starchy,sweet-tastingtuberousrootsarebyfarthemostimportantpartof theplant.Itisastorageroot,notatuberorthickenedstemlikethe potato(Solanumtuberosum).Itisalsodifferentfromyams.Theyarenot relatedtoeachotherdespiteaphysicalandcompositionalsimilarity.

Therootsofsweetpotatoesarelongandtapered,withasmoothskin whosecolorrangesbetweenyellow,orange,red,brown,purple,and beige.Itsfleshrangesfrombeigetowhite,red,pink,violet,yellow, orange,andpurple(Fig.2.1).Thestoragerootcontainsalargeamountof starchthatcanbeturnedintoenergyinthehumanbodysotherootcan beconsumedasastaplefoodinsteadofotherstaplefoodcropssuchas rice,wheat,andcorn.Theroots,leaves,andstemsofsweetpotatoesare alledibleandnutritious,andthusthecultivationofthesweetpotatocan playavitalroleinensuringthefoodsecurityofmanydevelopingcountries.Meanwhilethenutritionalneedsofthepeopleinthesecountries canalsobemetbyproperconsumptionofthewholeplant.Each100gof thefreshrootprovidesanenergeticvalueof85kcal,whichisgreaterthan thatforpotatoesbutlessthanforcereals.Therootalsoprovidesasmall amountofproteinandrelativelyhigheramountsofvitaminsandminerals thancereals.Somevarietiesofsweetpotatoescontainaveryhighamount

of β-carotenethatcanbeconvertedintovitaminAinthehumanbody, thusthecultivationandconsumptionofthesevarietieshavebeenrecommendedasanapplicableapproachtopreventtheepidemicofvitaminA deficiencythatiswidespreadinmanydevelopingcountries.Theyoung leaves,shoots,andvineoftheplantareagoodsourceofdietaryfiber,as wellasofmanyvitamins,minerals,andantioxidantmolecules,which makesthesweetpotatoanexcellentvegetable.Nowadays,tofullyutilize thevalueoftheplant,theyoungleaveshavebeenmadeintoteasand powderdrinksforhumanconsumption.

Theoriginandthedisseminationofsweetpotatoes aroundtheworld

Astotheoriginofsweetpotatoes,itisnowwidelyacceptedthatthe plantoriginatedfromthetropicalregionsintheSouthandCentral America.AlthoughitisnowmainlyproducedinChina,theplantisnot nativetoChina.InfacttheplantwasintroducedtoChinaonlyabout 631yearsago.Accordingtomostofthesources,theoriginanddomesticationofsweetpotatoesarethoughttobeineitherCentralAmericaor SouthAmerica(Austin,1988).InCentralAmerica,sweetpotatoes weredomesticatedatleast5000yearsago(Bovell-Benjamin,2014; Nishiyama,2006).

Theplantwasthenbroughttoothertropicalandsubtropicalregions aroundtheworldandbecamepopularintheislandsofthePacificOcean (Bovell-Benjamin,2014;Nishiyama,2006).ArcheologistshavefoundprehistoricremnantsofsweetpotatoesinPolynesiafromaboutCE 1000 1100accordingtoradiocarbondating.Theyhavehypothesized thatancientPolynesiansmayhaveinteractedwithpeopleonthewest coastofSouthAmericaandbroughtsweetpotatoestotheislandsof thePacificOceanlongbeforetheEuropeanssetfootonthecontinent.

Figure2.1 Sweetpotatowithdifferentfleshcolor.

ByanalyzingtheDNAof1245sweetpotatovarietiesfromAsiaandthe Americas,researchershaveproventhattherootvegetablehadmadeitall thewayfromtheAndestoPolynesianearly400yearsbeforeChristopher ColumbuslandedintheNewWorldin1492(Roullieretal.,2013).

PolynesianandEuropeanvoyagersthenspreadsweetpotatoesrapidly tootherpartsoftheworld.ItwasfirstdiffusedthroughoutPolynesia,in alreadypopulatedislandssuchasHawaii,EasterIsland,andsomeother islandsofeasternPolynesia,andthenintoNewZealandaroundCE 1150 1250.Duringthe16thcentury,SpanishandPortuguesetraders andtravelersintroduceditintothePhilippinesandIndonesia.Fromthese points,localtraders,Europeantravelers,orboth,mayhavedistributed sweetpotatoesintotherestoftheAsia.Itwasintroducedfromthe PhilippinesasafoodcroptoFujianProvinceofChinainabout1387,to Japaninabout1735(Takegoshi,2003)andtoKoreainabout1764(Kim, 2012).Becauseitsplantingmaterialcanbemultipliedgreatlyfromavery fewrootsandduetoitshighadaptability,sweetpotatoesspreadquickly throughoutAsia,LatinAmerica,andAfricaduringthe17thand18thcenturies.Nowthesweetpotatoiswidelycultivatedthroughouttropicaland warmtemperateregions,whereverthereissufficientwatertosupportits growth(O’Hairetal.,1990).

NotablytheintroductionandcultivationofsweetpotatoesinChina inthelateMingdynastygreatlyalleviatedthefoodshortageatthattime andpromptedthecentralgovernmentofthefollowingQingdynastyto enlargethesweetpotatocultivationareainChinaandspreadittoother farthernorthregionsinAsia.Nowadays,sweetpotatoesareplantedin almosteveryprovinceofChina,eveninthecoldestHeilongjiang ProvinceinthefarnorthofChina.

Production

Sweetpotatoesarenowwidelycultivatedallovertheworldwhereverthe plantcansurviveandthesweetpotatohasbecomeoneofthemost importantfoodcropsintermsofhumanconsumption.Asahigh-yield tuberouscrop,theplantcanbecultivatedinpoorsoilandwaterconditions,suchasinsub-SaharanAfrica,partsofAsia,andthePacificIslands. Withtheadvancementofagronomictechnology,moreandmorevarieties ofsweetpotatoeshavebeenbredtomeettheneedsofeithertheconsumerorthefoodprocessingindustry.

Worldwideproduction

AccordingtothestatisticsfromtheFoodandAgricultureOrganizationof theUnitedNations(FAO),theworld’stotalproductionofsweetpotatoes in2016was105milliontons.Incomparisontoothercropsthatcanbe consumedasastaplefood,sweetpotatoesarethesixthlargestcrop,rankingjustbehindcorn(1060milliontons),wheat(749milliontons),rice (741milliontons),potato(376milliontons),andcassava(277million tons).Althoughthecultivationofsweetpotatoesiswidespreadaround theworld,productionisnotevenlydistributedaroundtheworld.China isthebiggestproducerofsweetpotatoesintheworld.In2016China aloneproduced71milliontonsofsweetpotatoes,accountingfor68%of theworld’stotalproduction.Meanwhilealargenumberofthevarieties oftheplanthavebeencultivatedinChina.

Maincultivationregionsandcountries

Nowadays,morethan100milliontonsofsweetpotatoesareproduced globallyeachyear,approximately95%ofwhicharegrownindeveloping countries.Asiaistodaythelargestsweetpotato-producingregioninthe world.Morethan78milliontonswereproducedinAsiain2016.Africa isthesecondlargestproducer,producing21milliontonsin2016.The Americas,theoriginalhomeofsweetpotatoes,growslessthan5%ofthe world’ssupply.Europehasonlyaverysmallsweetpotatoproduction, mainlyinPortugal.

Todatetherankingoftheregionsandcontinentsintermsoftheir productionofsweetpotatoesisverystable.Asiaisfaraheadofothercontinents,followedbyAfricaandSouthAmerica.Asshownin Table2.1

Table2.1 Annualproductionofsweetpotatoesindifferentcontinents,2014 16 (milliontons).

Asia79.14(75.67%)78.96(76.01%)78.60(74.72%) Africa20.67(19.77%)20.01(19.26%)21.32(20.27%)

Oceania0.88(0.84%)0.90(0.86%)0.91(0.86%) Europe0.05(0.05%)0.05(0.05%)0.05(0.05%)

Total104.57(100%)103.88(100%)105.19(100%)

Source:DatafromFAOSTATDatabase(http://www.fao.org).

theworld’stotalproductionofsweetpotatoeswas105.19,103.88,and 104.57milliontonsintheyears2014 16,respectively.Asiaaccountsfor 74.72%ofglobalproductionin2016,followedbyAfrica(20.27%),South AmericaandtheCaribbean(2.67%),andNorthandCentralAmerica (1.43%).EuropeandOceaniahaveonlyaverysmallsweetpotatoproduction,contributingonly0.86%and0.05%oftheworld’stotalin2016, respectively.Thusitisobviousthatthecultivationofsweetpotatoesis notwidespreadindevelopedcountriesinspiteofthefactthattheyhave farmoreadvancedagriculturaltechnologiesthanmostofthecountriesin AsiaandAfrica.

In2016thetotaloutputofsweetpotatoesinAsiawas78.60million tons. Table2.2 showsthat67.30%oftheworld’stotalproduction wascontributedbyChina,whichproduced70.79milliontonsin2016. Itmeansthatpractically90.07%oftheannualproductioninAsiawas contributedbyChina.ThesecondlargestproducerisNigeria,which accountsfor3.72%oftheglobaloutputin2016.Theoutputfromthe UnitedRepublicofTanzaniaisneartothatofNigeria,contributing 3.63%oftheworld’stotaloutputin2016.Thesharesfromothercountrieswerealllowerthan3%.

InAsiathereare24countriesthatplantsweetpotatoes.Indonesiais behindChinabutheadofIndiaintheranking,withtheproductionof 2.27milliontons(2.16%oftheworldwideoutput)in2016.Theoutput fromIndia(1.47milliontons)isclosetothatoftheUnitedStates,which istheonlyAmericancountrythatranksamongthetop10sweetpotato producersintheworld.TheUnitedStatesproduced1.43milliontonsin 2016,accountingfor1.36%oftheworldtotaloutput.InEurope,there areonlyfourcountriesthatproducesweetpotatoes.Theleading EuropeancountryinsweetpotatoproductionisPortugal,whichproduced22,901tonsin2016,followedbySpain(13,523tons),Italy(12,456 tons),andGreece(3305tons).

Reasonsfortheimbalanceinsweetpotatoproductionamong

differentregionsandcountries

Thedifferencesintheamountsofsweetpotatoproducedindifferent regionsandcountriesarecausedbymanyfactors.First,inChina’shistory thecentralgovernmenthasplayedanimportantroleinpropagatingand encouragingthecultivationofsweetpotatoesinthevastlandofthisbig country.Asaresultitsoonbecametheworld’slargestgrower.Second, thedemandfortheproductionofsweetpotatoesiscloselyrelatedtoits

Table2.2 Top20countriesintermsoftheannualproduction(milliontons)ofsweetpotatoes,2014 16. 201420152016

China71.5468.41China71.3668.69China70.7967.3

Nigeria3.753.59Nigeria3.833.69Nigeria3.923.72

TheUnitedRepublic ofTanzania

Ethiopia2.702.58Indonesia2.302.21Indonesia2.272.16

Indonesia2.382.28Uganda2.051.97Uganda2.132.02

Angola1.931.84Angola1.931.86Ethiopia1.941.84

Uganda1.821.74Ethiopia1.511.46Angola1.831.74

Vietnam1.401.34TheUnitedStates1.411.35India1.471.4

TheUnitedStates1.341.28Vietnam1.341.29TheUnitedStates1.431.36

Madagascar1.141.09Kenya1.231.19Vietnam1.271.21

India1.091.04India1.231.18Madagascar1.111.06

Rwanda0.940.9Madagascar1.061.02Rwanda0.920.87

Japan0.890.85Rwanda0.930.9Japan0.860.82

Kenya0.760.73Japan0.810.78Mozambique0.730.69

PapuaNewGuinea0.670.64PapuaNewGuinea0.690.66Burundi0.730.69 Burundi0.660.64Brazil0.600.57PapuaNewGuinea0.700.67

Brazil0.530.5Burundi0.580.56Kenya0.700.66

Philippines0.520.5Philippines0.540.52Brazil0.670.64

Cuba0.510.49Cuba0.510.49Haiti0.650.62

Haiti0.510.49Haiti0.490.48Cuba0.590.57

Worldtotal104.57100103.88100105.19100

Source:DatafromFAOSTATDatabase(http://www.fao.org).

uses.Inmanycountrieswheretheannualproductionissmall,sweetpotatoesaremainlyconsumedasavegetable,butinotherregions,suchasin sometropicalareas,especiallyinAfrica,almostallsweetpotatoesareconsumedasastaplefood.Asaresult,Africasoonbecamethesecondlargest growerandconsumerofsweetpotatoes.Third,thecultivationofsweet potatoesiscloselyrelatedtothefinaluses.Chinesehasdevelopedagreat numberofusesforthisstarchyfoodcrop.Inparticular,theinventionof thestarchvermicelli(“fentiao” inChinese)hasgreatlyincreasedthe demandforthiscrop.Vermicellimadefromsweetpotatoesiswidely welcomedinmanykindsofChinesecuisines,suchashotpots,stewed vegetables,andconveniencefastfood.Theuniqueflavor,taste,andphysicochemicalpropertiesmakesweetpotatoesirreplaceablebyotherstarch materialssuchascorn,potato,andcassavastarch.Asaresult,although sweetpotatoesarenolongerusedasastaplefoodinChina,thereisstilla hugemarket.Nowadays,abouthalfofthetotalproductionofsweet potatoesisusedforstarchextraction,theremainderisusedforfresh consumption,animalfeed,orthemanufacturingofotherproducts. Thesefactorskeepthedemandforthecropatastablehighlevel.

Thereareseveralculturalfactorsthatalsoinfluencethecultivationand productionofsweetpotatoes.Itisnotonlyinpoorcountriesorregions thatsweetpotatoesareconsideredasastaplefood.Thisalsoholdstruefor manyotherregionsaroundtheworldinhardtimeswhenthereisacrop failureofotherstaplefoods,becausesweetpotatoesareproductiveand canbegrowninpoorsoilswithlittlefertilizer.Thussincetheyareareliablecropevenincasesofcropfailuresofotherstaplefoods,sweetpotatoesareoftenassociatedwithhardtimesinthemindsofsomepeople. Whenthesepeoplebecameaffluentenoughtochangetheirdiet,they tendtoabandonsweetpotatoesandturntootherfoods.Asaresultthe cultivationareaoftheplantmaydiminishintheseareas.Thegoodnews isthatsweetpotatoesaresodeliciousthattheysoongainthefavorofthe younggenerationandsweetpotatoesbecomepopularagainafteraperiod oftime.Inthemeantime,withtheadvancementofthefoodprocessing technology,moreandmoreindustrialusesofsweetpotatoeshavebeen found,usheringinaneweraofdevelopmentandplantingofthishighyieldcrop.

Importationandexportationofsweetpotatoes

In2016,therewere117countriesthatimportedatotalamountof 306,056tonsofsweetpotatoesfromothercountries.Asshownin

Table2.3,theleadingcountriesintheimportationofsweetpotatoesare theUnitedKingdom(66,128tons),followedbyCanada(50,619tons), theNetherlands(32,096tons),andJapan(21,710tons),clearlydemonstratingthatsweetpotatoesarelovedbypeopleindevelopedcountries too.Manyofthecountriesintheimportingcountries’ list,includingthe UnitedKingdom,Canada,theNetherlands,France,andGermany,do notplantsweetpotatoesthemselvesatall,soalloftheirneedsaremetby importation.Japanisanexceptionasitproduced942,300tonsofsweet potatoesitself.However,productioncouldnotmeetitsowndemands andasaresultitimported21,710tonsfromothercountries.

In2013theworldwidesweetpotatoesimportsamountedtoUS$ 252.11million.Asshownin Fig.2.2,inthepast10yearsbefore2013, theamountwasincreasingcontinuouslyfromUS$85.13millionin2004. After2012thegrowthrateseemstohaveincreased(fromUS$210.15 milliontoUS$252.11million)andthefiguremayprogressivelyincrease inthefuture.

AccordingtothedatafromtheFAOSTATdatabase,in2013the worldwideexportsofsweetpotatoestotaled256,988tons.Interestingly, asshownin Table2.4,Chinaisnotthelargestexporter.Theleading countryintheexportationofsweetpotatoesistheUnitedStates(128,231 tons),followedbyChina(19,870tons)andEgypt(15,651tons).ThereasonmaybeduetothatChinadoesnotexportmuchofsweetpotato,and someothercountriesdonothavemuchtoexport.Thisalsodemonstrates thatincountriesthathavearelativelylargeannualproduction,suchas ChinaandNigeria,sweetpotatoesaremainlyfordomesticconsumption andthedomesticneedsinthesecountriesareverystable.Thisalsoimplies thattheplantingofsweetpotatoesisveryimportantforthesecountries. Whereasformanyothercountries,suchasthecountriesinEurope,the cultivationofthesweetpotatoisbarelysignificantcomparedwiththatof thepotato,whichisconsideredanintegralpartofthedailydiet.In Europe,sweetpotatoesaremainlyconsumedasavegetableorconfectionery.Sporadicimportationinsmallamountsalonecanmeettheirneeds.In thelastfewyearsimportationhasundergoneagradualincreasethanksto thedemandintheindustrialsector(confectionery).

Trendinworldwideproductionofsweetpotatoes

Theannualproductionofsweetpotatoesisdeterminedbytheyieldof thecropandtheareasusedtoplantit.Asshownin Fig.2.3,inthelast

Table2.3 Theamount(tons)oftheimportedsweetpotatoesfromothercountriesforthetop60countriesin2013.

CountryValueRankingCountryValueRankingCountryValueRanking

TheUnited Kingdom 66,1281Lebanon203221MacauSAR,P.R. China 40041

Canada50,6192Uruguay168722Oman38142

TheNetherlands32,0963Sweden148523Rwanda36043

Japan21,7104Kuwait135024Hungary29144

Thailand15,3015HongKongSAR, P.R.China 132025ElSalvador28945

TheUnitedStates15,2206RepublicofKorea125326Bahamas27646

Italy14,2747Switzerland123527Romania25247

France14,2088Poland123228TheCzech Republic 24948

Malaysia98099Chile113429Nepal23749

Germany746910Norway110530Slovakia23350 Singapore742811PlurinationalState ofBolivia 101131SouthAfrica21751

SaudiArabia455912Spain100032BruneiDarussalam21252

Haiti368213Namibia90633MainlandChina18753

Niger283514Taiwan,Province ofChina 60034NewZealand18354

Belgium275515Botswana50535RussianFederation16755

Finland257216Austria47736Lithuania14256

China250717Greece44337Bahrain10657

Ireland240418Iceland42938Somalia10658

Mexico226119Denmark42539Maldives10459

TheUnitedArab Emirates 221720Portugal40340Argentina10060

Source:DatafromFAOSTATDatabase(2013)(http://www.fao.org).

Figure2.2 Theimportvalue(US$1000)ofsweetpotatoesaroundtheworldfrom 2004to2013. Source:DatafromFAOSTATDatabase(http://www.fao.org ).

decade,theworldwideareaofsweetpotatocultivationhasincreasedfrom 8,141,292hain2007to8,623,973hain2016.

Figs.2.4 and 2.5 showthattheincreaseintheworldwidecultivation areaismainlycontributedbyAfrica,whichhasincreasedsteadilyfrom 2.86millionhain2008to4.19millionhain2016,anincreaseof46.5%. TheincreaseinthecultivationareainAfricahassuccessfullycounteracted thedecreaseinAsia,whichhasbeenprogressivelydecreasingsince2008, from4.51millionhain2008to3.91millionhain2016,adecreaseof 13.3%.Theyear2015isahistoricmomentthatmarksaturningpoint. ThatwastheyearthatAfricasurpassedAsiaintermsoftheareausedto plantsweetpotatoesandbecametheworld’sleadingcontinentintermsof theareaundersweetpotatocultivation.

Fig.2.5 alsoshowsthatthecultivationareaintheAmericashas increasedinrecentyears,increasingfrom273,726hain2013to 362,126hain2016,anincreaseof32.3%.ConsideringthattheAmericas aretheoriginofsweetpotatoes,theclimateandsoilconditionsaremost suitablefortheirgrowth,andtherearehugeareasoffertile,arablelands intheAmericas,theprospectsareveryattractiveforagreatlyincreased productionofsweetpotatoesintheAmericas.Incomparisontheareas undercultivationinEuropeandOceaniahavebeenverysteadyoverthis sameperiod,withnobigchanges,implyingthatthepeopleinthese

Table2.4 Theamount(tons)oftheexportedsweetpotatoesfromthetop60countriesin2013.

Egypt15,6513India61123Tonga6243

TheNetherlands15,3484Germany58924Hungary5944

Indonesia97975Australia55225Cameroon5745

Spain92466Canada55226Mali5346

Source:DatafromFAOSTATDatabase(2013)(http://www.fao.org).

Figure2.3 Worldwidecultivationarea(ha)ofsweetpotatoes,2007 2016. Source: DatafromFAOSTATDatabase(http://www.fao.org).

Figure2.4 Cultivationarea(hectare)ofsweetpotatoesinAsiaandAfrica, 2007 2016. Source:DatafromFAOSTATDatabase(http://www.fao.org ).

continentsstillhavenotformedthehabitofeatingfoodthatcontains sweetpotatoes.

Aswehavementionedearlier,Africaisnowthelargestsweetpotato cultivationregionintheworld.However,theyieldofsweetpotatoesin Africaisfarlowerthanthatofothercontinents.Asshownin Fig.2.6 the

Figure2.5 Cultivationarea(hectare)ofsweetpotatoesintheAmericas,Europe,and Oceania,2007 2016. Source:DatafromFAOSTATDatabase(http://www.fao.org).

Figure2.6 Comparisonoftheyieldofsweetpotatoesondifferentcontinents, 2007 2016. Source:DatafromFAOSTATDatabase(http://www.fao.org ).

yieldofthecropinAsiaisrelativelyhigherthanthatofothercontinents. In2016theyieldinAsiawasashighas200,823hg/ha.Theyieldin Europewas198,252hg/ha,whichisalsoveryhigh.Buttheyieldsin othercontinentsweremuchlowerthanAsiaandEurope.Forinstance, theyieldinAfricawasonly50,903hg/ha,whichisonlyaboutonefourth