Review Article Roots and Tuber Crops as Functional Foods ... · Cannas Canna edulis Cannaceae Buthsarana(SriLanka) Maranta arundinacea L. Marantaceae Arrow root Hulankeeriya(SriLanka)

Review ArticleRoots and Tuber Crops as Functional Foods A Review onPhytochemical Constituents and Their Potential Health Benefits

Anoma Chandrasekara and Thamilini Josheph Kumar

Department of Applied Nutrition Wayamba University of Sri Lanka Makandura 60170 Gonawila Sri Lanka

Correspondence should be addressed to Anoma Chandrasekara anomapriyanyahooca

Received 7 February 2016 Accepted 14 March 2016

Academic Editor Jose M Prieto

Copyright copy 2016 A Chandrasekara and T Josheph KumarThis is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

Starchy roots and tuber crops play a pivotal role in the human diet There are number of roots and tubers which make an extensivebiodiversity evenwithin the same geographical locationThus they add variety to the diet in addition to offering numerous desirablenutritional and health benefits such as antioxidative hypoglycemic hypocholesterolemic antimicrobial and immunomodulatoryactivities A number of bioactive constituents such as phenolic compounds saponins bioactive proteins glycoalkaloids and phyticacids are responsible for the observed effects Many starchy tuber crops except the common potatoes sweet potatoes and cassavaare not yet fully explored for their nutritional and health benefits In Asian countries some edible tubers are also used as traditionalmedicinal A variety of foods can be prepared using tubers and theymay also be used in industrial applications Processingmay affectthe bioactivities of constituent compounds Tubers have an immense potential as functional foods and nutraceutical ingredients tobe explored in disease risk reduction and wellness

1 Introduction

Starchy root and tuber crops are second only in importanceto cereals as global sources of carbohydrates They providea substantial part of the worldrsquos food supply and are alsoan important source of animal feed and processed productsfor human consumption and industrial use Starchy rootsand tubers are plants which store edible starch material insubterranean stems roots rhizomes corms and tubers andare originated from diversified botanical sources Potatoesand yams are tubers whereas taro and cocoyams are derivedfrom corms underground stems and swollen hypocotylsCassava and sweet potatoes are storage roots and cannaand arrowroots are edible rhizomes All these crops canbe propagated by vegetative parts and these include tubers(potatoes and yams) stem cuttings (cassava) vine cuttings(sweet potatoes) and side shoots stolons or cormheads (taroand cocoyam)

The contribution of roots and tubers to the energy supplyin different populations varies with the country The relativeimportance of these crops is evident through their annual

global production which is approximately 836 million tonnes[1] Asia is the main producer followed by Africa Europeand America Asian and African regions produced 43 and33 respectively of the global production of roots and tubers[1] A number of species and varieties are consumed butcassava potatoes and sweet potatoes consist of 90 globalproduction of root and tuber crops [1]

Nutritionally roots and tubers have a great potential toprovide economical sources of dietary energy in the formof carbohydrates (Table 1) The energy from tubers is aboutone-third of that of an equivalent weight of rice or wheatdue to high moisture content of tubers However high yieldsof roots and tubers give more energy per land unit per daycompared to cereal grains [2] In general the protein contentof roots and tubers is low ranging from 1 to 2 on a dryweight basis [2] Potatoes and yams contain high amountsof proteins among other tubers Sulphur-containing aminoacids namely methionine and cystine are the limiting onesin root crop proteins Cassava sweet potatoes potatoes andyam contain some vitamin C and yellow varieties of sweetpotatoes yam and cassava contain 120573-carotene Taro is a good

Hindawi Publishing CorporationInternational Journal of Food ScienceVolume 2016 Article ID 3631647 15 pageshttpdxdoiorg10115520163631647

2 International Journal of Food Science

Table 1 Nutritional composition of selected tuber crops

Nutrients (per 100 g) Potatoes Sweet potatoes raw Cassava raw Yam rawWhite flesh and skin raw Red flesh and skin raw

Proximate compositionEnergy (kcal) 690 70 860 1600 1180Protein (g) 17 19 16 14 15Total lipid (fat) (g) 01 01 01 03 02Carbohydrate by difference (g) 157 159 201 381 279Fibre total dietary (g) 24 17 30 18 41Sugars total (g)g 12 13 42 17 05

MineralsCalcium Ca (mg) 9 10 30 16 17Magnesium Mg (mg) 21 22 25 21 21Potassium K (mg) 407 455 337 271 816Phosphorus P (mg) 62 61 47 27 55Sodium Na (mg)m 16 18 55 14 9

VitaminsTotal ascorbic acid (mg) 1970 860 240 2060 1710Thiamin (mg) 007 008 008 009 011Riboflavin (mg) 003 003 006 005 003Niacin (mg) 107 115 056 085 055Vitamin B-6 (mg) 0203 0170 0209 0088 0293Folate (120583g-DFE) 18 18 11 27 23Vitamin E (mg) 001 001 026 019 035Vitamin K (120583g) 16 29 18 19 23Vitamin A (IU)IU 8 7 14187 13 138

Source USDA [105]

source of potassium Roots and tubers are deficient in mostother vitamins and minerals but contain significant amountsof dietary fibre [2] Similar to other crops nutritional valueof roots and tubers varies with variety location soil type andagricultural practices among others

The burden of noncommunicable diseases (NCDs)increases globally in both developed and developing coun-tries and plays a pivotal role as the major cause of deathOxidative stress which would be harbored by both endoge-nous and exogenous factors contributes immensely to theetiology of NCDs as well as the aging processThe associationbetween plant food intake and reduced NCDs episodes hasbeen themain focus of a number of scientific investigations inthe recent past Furthermore identification of specific plantconstituents which convey health benefits is of much interestFoods of plant origin consist of a wide range of nonnutrientphytochemicals They are synthesized as secondary metabo-lites and serve a wide range of ecological roles in home plants[3] Tubers and root crops are significant sources of a num-ber of compounds namely saponins phenolic compoundsglycoalkaloids phytic acids carotenoids and ascorbic acidSeveral bioactivities namely antioxidant immunomodula-tory antimicrobial antidiabetic antiobesity and hypocholes-terolemic activities among others are reported for tubers androot crops

This review focuses on the bioactivities of phytochemicalsand their distribution in starchy roots and tuber crops

Furthermore the effect of processing on bioactive com-pounds of roots and tubers is also discussed

2 Roots and Tuber Crops

Plants producing starchy roots tubers rhizomes cormsand stems are important to nutrition and health They playan essential role in the diet of populations in developingcountries in addition to their usage for animal feed andfor manufacturing starch alcohol and fermented foods andbeverages

Roots and tuber crops are important cultivated stapleenergy sources second to cereals generally in tropical regionsin the world They include potatoes cassava sweet potatoesyams and aroids belonging to different botanical families butare grouped together as all types produce underground foodAn important agronomic advantage of root and tuber crops asstaple foods is their favourable adaptation to diverse soil andenvironmental conditions and a variety of farming systemswith minimum agricultural inputs In addition variationsin the growth pattern and adopting cultural practices makeroots and tubers specific in production systems Howeverroots and tuber crops are bulky in nature with high moisturecontent of 60ndash90 leading them to be associated withhigh transportation cost short shelf life and limited marketmargin in developing countries even where they are mainly

International Journal of Food Science 3

Table 2 Different types of tuber crops commonly consumed in world

Botanical name Family Common namePotatoes Solanum tuberosum SolanaceaeCountry potatoHausa potato Solenostemon rotundifolius Lamiaceae (mint family) Innala ratala (Sri Lanka)

Cannas Canna edulis Cannaceae Buthsarana (Sri Lanka)

Maranta arundinacea L MarantaceaeArrow rootHulankeeriya (Sri Lanka)Aru aru arawak (India)

Taro Xanthosoma sagittifolium Araceae

Kiriala (Sri Lanka)Keladi (Malaysia)Phueak (Thailand)Khoai mon (Vietnam)Sato-imo (Japan)

Yam Dioscorea alata Dioscoreaceae

Purple yam greater yamGuyana water yamWinged yamRaja ala (Sri Lanka)Ube (Philippines)

Sweet potatoes Ipomoea batatas Convolvulaceae Camote batataShakarkand

Cassava Manihot esculenta Euphorbiaceae Yuxco mogo maniocmandioca kamoteng kahoy

Elephant foot yam Amorphophallus paeoniifolius Araceae White pot giant arum stink lily

cultivated Table 2 presents commonly consumed starchytuber and root crops worldwide

21 Potatoes (Solanum tuberosum) Potato is currently thefourth most important food crop in the world after maizewheat and rice with a production of 368million tonnes [1] Itranks the third after rice and wheat in terms of consumptionPotato is a crop of highland origin and has been domesticatedin the high Andes of South America and has become a majorfood crop in the cool highland areas of South America Asiaand Central and Eastern Africa [4]

In developed countries potatoes play a pivotal role in thediet compared to those of the developing ones The energyintake from potatoes by an individual in developed anddeveloping countries was 130 and 41 kcalday respectively[5] Potatoes provide significant amounts of carbohydratespotassium and ascorbic acid in the diet [6] Furthermorethey contribute to 10 of the total folate intake in some Euro-pean countries such as Netherlands Norway and Finland[7] In addition ascorbic acid present in potatoes protectsfolates from oxidative breakdown [8] About 50 of therecommended dietary allowance (RDA) of vitamin A maybe provided by 250 g of genetically carotenoid enrichedpotatoes [9] Potatoes have several secondary metaboliteswhich demonstrated antioxidant as well as other bioactivities[10]

22 Sweet Potatoes (Ipomoea batatas L) The origin of sweetpotato is Central America but at present it is widely grownin many tropical and subtropical countries in different eco-logical regions It is the seventh largest food crop grownin tropical subtropical and warm temperate regions in the

world [11] Sweet potato can be grown all around the yearunder suitable climatic conditions and complete crop lossunder adverse climatic conditions is rare thus it is consideredas an ldquoinsurance croprdquo The crop is particularly importantin Southeast Asia Oceania and Latin America regions andChina claims about 90 of total world production Sweetpotatoes are considered as a typical food security crop fordisadvantaged populations as the crop can be harvested littleby little over a long period of time National Aeronautics andSpace Administration (NASA) has selected sweet potatoesas a candidate crop to be grown and incorporated into themenus for astronauts on space missions due to their uniquefeatures and nutritional value [12] The consumption of 125 gorange fleshed sweet potatoes rich in carotenoids improvesvitamin A status of children especially in developing coun-tries [13] In addition sweet potatoes are rich in dietaryfibre minerals vitamins and bioactive compounds such asphenolic acids and anthocyanins which also contribute to thecolor of the flesh

23 Cassava (Manihot esculenta) Cassava is the most widelycultivated root crop in the tropics and because of longgrowth season (8ndash24 months) its production is limited tothe tropical and subtropical regions in the world Cassava is aperennial shrub belonging to the family Euphorbiaceae Thegenus Manihot comprises 98 species and M esculenta is themost widely cultivated member [14] Cassava originated inSouth America and subsequently was distributed to tropicaland subtropical regions of Africa and Asia [15] Cassavaplays an important role as staple for more than 500 millionpeople in the world due to its high carbohydrate content[15] A number of bioactive compounds namely cyanogenic


glucosides such as linamarin and lotaustralin noncyanogenicglucosides hydroxycoumarins such as scopoletin terpe-noids and flavonoids are reported in cassava roots [15ndash17]

24 Yams (Dioscorea sp) Yam is a member of the mono-cotyledonous family Dioscoreaceae and is a staple food inWest Africa Southeast Asia and the Caribbean regions [18]Yam is consumed as raw yam cooked soup and powderor flour in food preparations Yam tubers have variousbioactive components namely mucin dioscin dioscorinallantoin choline polyphenols diosgenin and vitamins suchas carotenoids and tocopherols [19 20] Mucilage of yamtuber contains soluble glycoprotein and dietary fibre Sev-eral studies have shown hypoglycemic antimicrobial andantioxidant activities of yam extracts [21 22] Yams maystimulate the proliferation of gastric epithelial cells andenhance digestive enzyme activities in the small intestine[23]

25 Aroids Aroids are tuber or underground stem bearingplants belonging to the family Araceae There are severaledible tubersstems such as taro (Colocasia) giant taro(Alocasia) tannia or yautia (Xanthosoma) elephant footyam (Amorphophallus) and swamp taro (Cyrtosperma) Theorigin of tannia is South America and the Caribbean regions[4] Colocasia originating in India and Southeast Asia is astaple food inmany islands of the South Pacific such as TongaandWestern Samoa and in PapuaNewGuinea Furthermoretaro is the most widely cultivated crop in Asia Africa andPacific as well as Caribbean Islands

26 Minor Tuber Crops

261 Canna Canna is rhizomatous type tuber which iswidely distributed throughout the tropics and subtropicsThegenus Canna belongs to the family Cannaceae The edibletypes of Canna edulis originated in the Andean region orPeruvian coast and extended from Venezuela to northernChile in South America It is commercially cultivated inAustralia for the production of starch

262 Arrowroot Maranta arundinacea L (West Indianarrowroot) is cultivated for its edible rhizomes It belongsto Marantaceae and is believed to have originated in theNorthwestern part of South America Arrowroot has beenwidely distributed throughout the tropical countries likeIndia Sri Lanka Indonesia the Philippines and Australiaand West Indies

27 Bioactive Compounds in Tuber Crops Bioactive com-pounds in plants are secondary metabolites having phar-macological or toxicological effects in humans and ani-mals Secondary metabolites are produced within the plantsbesides the primary biosynthesis associated with growth anddevelopment These compounds perform several essentialfunctions in plants including protection from undesirableeffects attraction of pollinators or signaling of essentialfunctions

271 Phenolic Compounds Phenolic compounds have anaromatic ring with one or more hydroxyl groups and actas antioxidants They are derived from biosynthetic precur-sors such as pyruvate acetate a few amino acids acetyl-CoA and malonyl-CoA following the pentose phosphateshikimate and phenylpropanoid metabolism pathways Inplants phenylalanine and to a lesser extent tyrosine are thetwo major amino acids involved in the synthesis of pheno-lic compounds [3] Major groups of phenolic compoundsabundantly found in plants are simple phenolics phenolicacids flavonoids coumarins stilbenes tannins lignans andlignins The quantity of phenolic compounds present in agiven species of plantmaterial varies with a number of factorssuch as cultivar environmental conditions cultural practicespostharvest practices processing conditions and storage[3] Two classes of phenolic acids hydroxybenzoic acidsand hydroxycinnamic acids are found in plant materialsCompounds with a phenyl ring (C

6) and a C

3side chain

are known as phenylpropanoids and serve as precursors forthe synthesis of other phenolic compounds Flavonoids aresynthesized by condensation of a phenylpropanoid com-pound with three molecules of malonyl coenzyme A Thephenolics present in tubers render several health benefitsnamely antibacterial anti-inflammatory and antimutagenicactivities among others

272 Saponins and Sapogenins Saponins are high molecularweight glycosides consisting of a sugar moiety linked to atriterpene or steroid aglycone The aglycone portion of thesaponinmolecule is called sapogenin Depending on the typeof sapogenin present saponins are divided into three groupsnamely triterpene glycosides steroid glycosides and steroidalkaloid glycosides Saponins having a steroid structure areprecursors for the chemical synthesis of birth control pills(with progesterone and estrogen) similar hormones andcorticosteroids [24] According to recent findings steroidalsaponins could be a novel class of prebiotics to lactic acidbacteria and are effective candidates for treating fungal andyeast infections in humans and animals [25]

273 Bioactive Proteins The protein contents of roots andtuber crops are variable The global contribution of proteinsfrom roots and tubers in the diet is less than 3 However inAfrican countries this contribution may vary from 5 to 15[4]

Dioscorin is the main storage protein found in tropicalDioscorea yams It accounts for 90 of water extractablesoluble proteins in a majority ofDioscorea species Dioscorinwas reported to have carbonic anhydrase and trypsininhibitor activities [26] Furthermore dehydroascorbatereductase and monodehydroascorbate reductase activities ofdioscorin in the presence of glutathione have been reported[27] Dioscorin from fresh yam (Dioscorea batatas) exhib-ited DPPH radical scavenging activity [28] and showedbeneficial effects in lowering blood pressure [19 29] Inaddition dioscorin demonstrated angiotensin convertingenzyme (ACE) inhibitory and antihypertensive activitieson spontaneously hypertensive rats [29 30] The dioscorinfrom yam exhibited carbonic anhydrase trypsin inhibitor


dehydroascorbate reductase (DHA) and monodehydroa-scorbate reductase (MDA) activities and immunomodulatoryactivities [18 26 27]

Sporamin is a soluble protein and is the main storageprotein in sweet potato roots and accounts for about 60ndash80of its total proteins [31] The sporamin of sweet potatoes isinitially known as ipomoein It is a nonglycoprotein withoutglycan and is stored in the vacuole in the monomeric formSporamin is initially produced as preprosporamin whichis synthesized by the membrane-bound polysome in theendoplasmic reticulum (ER) [32] Sporamin is a trypsininhibitor with a Kunitz-type trypsin inhibitory activity whichhas potential application in the transgenic insect resistantplants [33] Furthermore sporamin showed various antiox-idant activities related to stress tolerance such as DHA andMDA reductase activities [34]

274 Glycoalkaloids Glycoalkaloids are an important classof phytochemicals found in many species of the gen-era Solanum and Veratrum [35] Alkaloids are nitrogen-containing secondary metabolites found mainly in severalhigher plants and microorganisms and animals [36] Theskeleton of most alkaloids is derived from amino acids andmoieties from other pathways such as those originatingfrom terpenoids The primary function of alkaloids in plantsis acting as phytotoxins antibactericides insecticides andfungicides and as feeding deterrents to insects herbivorousmammals and mollusks [37] There are two main glycoal-kaloids in commercial potatoes These include 120572-chaconineand 120572-solanine which are glycosylated derivatives of theaglycone solonidine Wild potatoes (Solanum chacoense) andegg plants contain the glycoalkaloid solasonine The majorglycoalkaloid reported in tomatoes is 120572-tomatine which isa glycosylated derivative of aglycone tomatidine Steroidalalkaloids and their glycosides present in several species ofSolanum are known to possess a variety of biological activitiessuch as antitumour antifungal teratogenic antiviral andantiestrogenic activities Certain glycoalkaloids are used asanticancer agents [38 39] The steroidal alkaloid glycosidesshowed cytotoxic activity against various tumour cell lines[40]

275 Carotenoids Carotenoids are among the most wide-spread natural pigments with yellow orange and red col-ors in plants The carotenes are hydrocarbons soluble innonpolar solvents such as hexane and petroleum ether Theoxygenated derivatives of carotenes xanthophylls dissolvebetter in polar solvents such as alcohols [41] The majorityof carotenoids are unsaturated tetraterpenes with the samebasic C 40 isoprenoid skeleton resulting from the join-ing of eight isoprene units in a head-to-tail manner withthe exception of the tail-to-tail connection at the centreCarotenoids play important biological roles in living organ-isms In photosynthetic systems of higher plants algae andphototrophic bacteria carotenoids participate in a variety ofphotochemical reactions [42] Carotenoids either isolatedfrom natural sources or chemically synthesized have beenwidely utilized due to their distinctive coloring properties

as natural nontoxic colorants in manufactured foods drinksand cosmetics Carotenoids possess numerous bioactivitiesand play important roles in human health and nutritionincluding provitamin A activity antioxidant activity reg-ulation of gene expression and induction of cell-to-cellcommunication [43] which are involved in amyriad of healthbeneficial effects It has been demonstrated that zeaxanthinand lutein are stable throughout artificial digestion whereas120573-carotene and all-trans lycopene are degraded in the jejunaland ileal compartments Among the isomers the stability of5-cis lycopene is superior to that of all-trans lycopene and 9-cis lycopene [44] Yellow varieties of sweet potatoes and yamsare good sources of carotenoids

276 Ascorbic Acid Ascorbic acid also known as vitamin Cis a water-soluble vitamin It naturally occurs in plant tissuesprimarily in fruits and vegetables Ascorbic acid occursin considerable quantities in several root crops Howeverthe level could be reduced during cooking of roots unlessskins and cooking water are utilized Root crops if carefullyprepared can make a significant contribution to the vitaminC content of the diet As reported by the 1983 NutritionalFood Survey Committee potatoes serve as a principal sourceof vitamin C in British diets providing 194 of the totalrequirement [2] In general yams contain 6ndash10mg of vitaminC100 g and may vary up to 21mg100 g In addition thevitamin C content of potatoes is very similar to those ofsweet potatoes and cassava The concentration of ascorbicacid varies with the species location crop year matu-rity at harvest soil and nitrogen and phosphate fertilizers[2]

3 Bioactivities of Phytochemicals inRoots and Tubers

31 Antioxidant Activity Accumulating research evidencesdemonstrate that oxidative stress plays a major role inthe development of several chronic diseases such as dif-ferent types of cancer cardiovascular diseases arthritisdiabetes autoimmune and neurodegenerative disorders andaging Though internal antioxidant defense systems eitherenzymes (superoxide dismutase catalase and glutathioneperoxidase) or other compounds (lipoic acid uric acidascorbic acid 120572-tocopherol and glutathione) are availablein the body external sources of antioxidants are needed asinternal defense system may get overwhelmed by excessiveexposure to oxidative stress A number of studies havereported the antioxidant activities of several roots and tubercrops

Methanolic extract of potatoes demonstrated high phe-nolic content and strong antioxidant activity as determinedby 22-diphenyl-1-picrylhydrazyl (DPPH) radical scavengingactivity [45] Authors further showed that the total phenoliccontent (TPC) ranged from 166 to 32mg gallic acid equiv-alents (GAE)100 g dry sample and EC 50 of DPPH radicalscavenging activity was 94mgmL (dry matter)

Several authors reported that the peels of sweet potatopossessed a potent wound healing effect which appears to


Table 3 Percentage of 22-diphenyl 1-1-picrylhydrazyl (DPPH) radical scavenging activity flavonoids and phenolic content of selected tubercrops

DPPH inhibition Flavonoids Total phenolicsSt Vincent yam (Dioscorea alata) 189 plusmn 056 39065 plusmn 4063 1603 plusmn 079

Water yam (Dioscorea alata) 9583 plusmn 021 41052 plusmn 2022 1310 plusmn 103

Coco yam (Xanthosoma sp) 1259 plusmn 066 14531 plusmn 561 939 plusmn 068

Sweet potatoes (Ipomoea batatas) 2801 plusmn 134 16534 plusmn 581 437 plusmn 027

Potatoes (Solanum tuberosum) 2047 plusmn 138 8521 plusmn 432 1826 plusmn 135

Yellow yam (Dioscorea cayenensis) 1355 plusmn 052 15067 plusmn 3034 343 plusmn 019

Source Dilworth et al [49]

be related to the free radical scavenging activity of the phy-toconstituents and their ability in lipid oxidation inhibition[46 47] The healing effect of sweet potato fibre for burnsor decubital wounds in a rat model was demonstrated andthe reduction in size and changes in the quality of thewounds were observed [48] They further found that the ratstreated with sweet potato fibre covering had reduced woundarea compared to those of the control Petroleum etherextract of sweet potato had shown significant closure of scararea for complete epithelialization compared to the control[46]

The methanolic extracts of the peels and peel bandage ofsweet potato roots were screened for wound healing effect byexcision and incisionwoundmodels onWistar rats [47]Theyfurther showed that hydroxyproline content was found to besignificantly increased in the test group compared to that ofwounded control group Increased hydroxyproline contentleads to enhancement of collagen synthesis which improveswound healing In addition the content of malondialdehydedecreased in test groups compared to that of wounded controlgroup indicating lipid oxidation inhibitory effect of sweetpotato peels [47] Water yam (Dioscorea alata) was reportedto possess the highest DPPH radical scavenging activity of96 among different selected tuber crops such as sweetpotato potato coco yam and other Dioscorea yams (Table 3[49])

Cornago et al [50] showed the TPC and antioxidantactivities of two major Philippine yams of Ube (purple yam)and Tugui (lesser yam) Purple yam (Dioscorea alata) andlesser yam (Dioscorea esculenta) had a TPC which rangedfrom 699 to 4218mg GAE100 g dry weight The purpleyam variety Daking had the highest TPC and antioxidantactivities as measured by DPPH radical scavenging activityreducing power and ferrous ion chelating capacity whereasvarieties Sampero and Kimabajo showed the lowest TPC andantioxidant activities

Hsu et al [51] studied the antioxidant activity of water andethanolic extracts of yam peel on tert-butyl hydroperoxide(t-BHP) induced oxidative stress in mouse liver cells (Hepa1ndash6 and FL83B) Ethanolic extracts of yam peel exhibiteda better protective effect on t-BHP treated cells comparedto that of water extracts Furthermore it was observed thatethanolic extract increased catalase activity whereas waterextract decreased it According to Chen and Lin [52] heatingaffected the TPC antioxidant capacity and the stability

of dioscorin of various yam tubers Raw yams containedhigherTPC than their cooked counterparts Furthermore theDPPH radical scavenging activities declined with increasingtemperature TPC and dioscorin content of yam cultivars(Dioscorea alata L var Tainung number 2) and keelungyam (D japonicaThunb var pseudojaponica (Hay) Yamam)correlated with DPPH radical scavenging activity and ferrousion chelating effect [52] Phytochemicals of yams seem toenhance the activities of endogenous antioxidant enzymesThe administration of yams decreased the levels of 120574-glutamyl transpeptidase (GGT) low density lipoprotein andtriacylglycerol in serum of rats in which hepatic fibrosis wasinduced by carbon tetrachloride [53] Treatment of rats withyams increased the antioxidant activities of hepatic enzymesnamely glutathione peroxidase and superoxide dismutase[53]

Extracts of flavonoids and flavones from potatoes showedhigh scavenging activities toward oxygen radicals Potatoesscavenged 94 of hydroxyl radicals [54]Themajor phenoliccompound reported in potato was chlorogenic acid whichconstituted more than 90 of its phenolics The range ofhydrophilic oxygen radical absorbance capacity (ORAC) of200 to 1400 120583mol trolox equivalents100 g fresh weight andthe lipophilic ORAC range of 5 to 30 nmol alpha-tocopherolequivalents100 g fresh weight were reported for potatoes[55]

Using a rat model it was shown that ethanolic extractsof purple fleshed potato flakes had effective free radicalscavenging activity and inhibition of linoleic acid oxidation[56] Further potato extracts enhanced hepatic manganesesuperoxide dismutase (SOD) CuZn-SOD and glutathioneperoxidase (GSH-Px) activities as well as mRNA expressionsuggesting a reduced hepatic lipid peroxidation and animproved antioxidant potential

Recently Ji et al [57] reported the contents of phenoliccompounds and glycoalkaloids of 20 potato clones and theirantioxidant cholesterol uptake and neuroprotective activitiesin vitro Peels of purple and red pigmented potato clonesshowed higher phenolic content compared to those of yellowand unpigmented clones [57] Chlorogenic acid (50ndash70)and anthocyanins namely pelargonidin andpetunidin glyco-sides were identified as major phenolic compounds presentin potatoes In addition major glycoalkaloids present inpotatoes 120572-chaconine and 120572-solanine and their contents werereduced by granulation process Peels of potato clones showed


the highest DPPH radical scavenging activity followed byflesh and granules [57]

A few studies have reported the antioxidant activities ofcassava roots A recent study [58] showed that the antioxidantactivities of organically grown cassava tubers were higherthan those of mineral-base fertilized roots They found thatTPC and flavonoid content (FC) were significantly higherfor organic cassava compared to those of cassava grown withinorganic fertilizers

32 Antiulcerative Activities The antiulcerative activity ofsweet potato roots was studied in a ratmodel [59]The extractof sweet potatoes did not show any toxic or deleterious effectsby oral route up to 2000mgkg Furthermore superoxide dis-mutase (SOD) catalase (CAT) glutathione peroxidase (GPx)and glutathione reductase (GR) activities were significantlyelevated by administration of tuber extracts in treated ratsindicating the ability of restoring enzyme activities comparedto the control Kim et al [60] showed that butanol fractionof sweet potato could be a better source for treating gastriculcers induced by excessive alcohol intake

33 Anticancer Activities Cancer is a leading cause of deathworldwide and it is mostly related to unhealthy food habitsand lifestyle It is important to find ways to reduce andprevent the risk of cancer through dietary components whichare present in plant foods Cancer is a multistage diseasecondition and tapping at any initial stage could help attenuatethe disease condition Root and tuber phytochemicals havedemonstrated anticancer effects in several types of carcinomacell lines and animal models

Huang et al [61] showed that aqueous extract of sweetpotatoes had higher antiproliferative activity than that ofethanol extracts Cell proliferation was analyzed at 48 h afterhuman lymphoma NB4 cells which had been cultured withseveral concentrations of extracts 0 25 50 100 200 400 800or 1000 120583g of dry mattermL in the media using the micro-culture tetrazolium treatment (MTT) assay The phytochem-icals present in sweet potato roots may exert a significanteffect on antioxidant and anticancer activities Furthermoreantioxidant activity is directly related to the phenolics andflavonoid contents of the sweet potato extracts An additiverole of phytochemicals was also found which may contributesignificantly to the potent antioxidant activity and antipro-liferative activity in vitro [61] Furthermore two antho-cyanin pigments namely 3-(661015840-caffeylferulylsophoroside)-5-glucoside of cyanidin (YGM-3) and peonidin (YGM-6)purified from purple sweet potatoes effectively inhibitedthe reverse mutation induced by mutagenic pyrolysates oftryptophan (Trp-P-1 Trp-P-2) and imidazoquinoline (IQ)in the presence of rat liver microsomal activation systems[62]

A greater inhibition of carcinogenesis was shown by redpigmented cultivar of potatoes compared to a white RussetBurbank cultivar in breast cancer induced rats [63] Thered cultivar of potatoes was reported to have high levels ofanthocyanins and chlorogenic acid derivatives

According to Madiwale et al [64] purple fleshed potatoshowed higher potential in suppressing proliferation and

elevated apoptosis of HT-29 human colon cancer cell linescompared with white fleshed potato It was interesting tonote that storage of potatoes affected their antioxidant andanticancer activities and TPC The extracts from both freshand stored potatoes inhibited cancer cell proliferation andelevated apoptosis but anticancer effects were higher in freshpotatoes than in stored tubers The study further demon-strated that storage duration had a strong positive correlationwith antioxidant activity and percentage of viable cancer cellsand a negative correlation existed with apoptosis inductionThese findings further elaborated that antioxidant activityand phenolic content of potatoes increased with storage butantiproliferative and proapoptotic activities were decreased[64]

In addition to phenolic compounds saponins present inroots and tubers play a pivotal role as anticancerantitumouragentsThere are several groups of saponins namely cycloar-tanes ammaranes oleananes lupanes and steroids demon-strating strong antitumour effect on different types of cancersFor instance cycloartane saponins possess antitumour prop-erties in human colon cancer cells and tumour xenografts[65] They downregulated expression of the hepatocellu-lar carcinoma (HCC) tumour marker 120572-fetoprotein andsuppressed HepG2 cell growth by inducing apoptosis andmodulating an extracellular signal-regulated protein kinase-(ERK-) independent NF-120581B signaling pathway [65] Further-more oleananes saponins exerted their antitumour effectthrough various pathways such as anticancer antimetastasisimmunostimulation and chemoprevention pathways [65]

Several studies have shown that glycoalkaloids such as120572-chaconine and 120572-solanine present in tubers are potentialanticarcinogenic agents [66] Glycoalkaloids showed antipro-liferative activities against human colon (HT-29) and liver(HepG2) cancer cells as assessed by the MTT assay [66]

Wang et al [67] reported that the aqueous extract ofyam (Dioscorea alata) inhibited the H

2O2-CuSO

4induced

damage of calf thymus DNA and protected human lym-phoblastoid cells fromCuSO

4induced DNA damage Extract

of water yam contains a homogenous compound with asingle copper-binding site and also is a good natural safe(redox inactive) copper chelator In addition to phenoliccompounds saponins and mucilage polysaccharides presentin yams are responsible for this activity Furthermore water-soluble mucilage polysaccharides are the most importantcopper chelators in extract of water yam Thus Dioscoreaalata aqueous extracts could serve as potential agents inthe management of copper-mediated oxidative disorders anddiabetes [67]

34 Immunomodulatory Activities Purified dioscorin fromyam tubers showed immunomodulatory activities in vitro[18] The effects of dioscorin on native BALBc mice spleencell proliferation were assayed by MTT assay It was foundthat dioscorin stimulated RAW 2647 cells to produce nitricoxide (NO) in the absence of lipopolysaccharide (LPS) con-tamination Yam dioscorin exhibited immunomodulatoryactivities by the innate immunity which is a nonspecificimmune system which comprises the cells and mechanismsthat defend the host from infection by other organisms in


a nonspecific manner Dioscorin was reported to stimulatecytokine production and to enhance phagocytosis Further-more the released cytokines may act synergistically withphytohemagglutinin (PHA) which is a lectin found in plantsthat stimulate the proliferation of splenocytes [18]

Several studies have demonstrated the immune activity ofyam mucopolysaccharides (YMP) In vitro cytotoxic activityof mouse splenocyte against leukemia cell was increasedin the presence of YMP of Dioscorea batatas at 10 120583gmL[68] Furthermore the production of IFN-120574 was significantlyincreased in the YMP treated splenocytes suggesting theircapability of inducing cell-mediated immune responses Inaddition YMP at a concentration of 50120583gmL increaseduptaking capacity and lysosomal phosphatase activity ofperitoneal macrophages [68]

Dioscorea phytocompounds enhancedmurine splenocyteproliferation ex vivo and improved regeneration of bonemarrow cells in vivo [69] Mice which were fed with aDioscorea extract recovered damaged bone marrow pro-genitor cell populations that had been depleted by largedoses of 5-fluorouracil (5-FU) Furthermore they reportedthat the phytocompound(s) responsible for these bioactiv-ities had a high molecular weight (ge100 kDa) and weremost likely polysaccharides They postulated those high-molecular-weight polysaccharides in DsCE-II act on specifictarget cell types in the GI tract (dendritic cells intesti-nal epithelial cells and T-cells) to mediate a cascade ofimmunoregulatory activities leading to the recovery of dam-aged cell populations following 5-FU or other chemicalinsults in the bone marrow spleen or other immune cellsystems [69]

Dioscorea tuber mucilage from Taiwanese yams (Dios-corea Japonica Thunb var) showed significant effects on theinnate immunity and adaptive immunity on BALBc micethrough oral administration [70] In addition it was foundthat the specific antibodies rapidly responded against foreignproteins (or antigens) in the presence of yam mucilageMucilage from these yam varieties exhibited a stimulatoryeffect on phagocytic activity by granulocyte and monocyte(ex vivo) on peritoneal macrophages and on the RAW 2647cells (in vivo) of mice [70]

Yams (Dioscorea esculenta) showed anti-inflammatoryactivity on carrageenan induced oedema in the right hindpaw of Wistar rats [71] However this activity was short livedas it was quickly removed from the system after reaching thepeak within 2 hours Phytochemical screening ofD esculentaconfirmed the presence of saponins 120573-sitosterol stigmas-terol cardiac glycosides fats starch and diosgenin whichcould be responsible for the observed activity [71] Diosgenincontained in Chinese yam was an immunoactive steroidalsaponin which also showed prebiotic effect Diosgenin hadalso beneficial effects on the growth of enteric lactic acidbacteria [25]

The impact of the consumption of pigmented potatoes onoxidative stress and inflammatory damages has been demon-strated in humans [72] Participants were given white yellow(high concentrations in phenolic acids and carotenoids) orpurple fleshed (high content of anthocyanin and phenolicacids) potato once per day in a randomized 6-week trial

which reported good compliance The results showed thatthe consumption of pigmented potatoes was responsible forelevated antioxidant status and reduced inflammation andDNA damage which was observed through the reductionof inflammatory cytokine and C-reactive protein concentra-tions [72] Methanolic extracts of A campanulatus (Suran)tuber also showed immunomodulatory activity [73] Authorsindicated that the presence of steroids and flavonoids inA campanulatus (Suran) tuber may be responsible for theobserved immunomodulatory activity [73]

35 Antimicrobial Activity Yam varieties with their phenoliccompounds are potential agents with antimicrobial efficacySonibare and Abegunde [74] reported that the methano-lic extracts of Dioscorea yams (Dioscorea dumetorum andDioscorea hirtiflora) showed antioxidant and antimicrobialactivities Antimicrobial activity was determined by the agardiffusion method (for bacteria) and pour plate method (forfungi) Nonedible D dumetorum showed the highest in vitroantibacterial activity against Proteus mirabilis The methano-lic extracts from D hirtiflora demonstrated antimicrobialactivity against all tested organisms namely Staphylococcusaureus E coli Bacillus subtilis Proteus mirabilis Salmonellatyphi Candida albicans Aspergillus niger and Penicilliumchrysogenum

36 Hypoglycemic Activities Diabetes mellitus is a chronicdisorder marked by elevated levels of glucose in the bloodand life-threatening complications that can untimely lead todeath Extracts of sweet potato peels have shown reducedplasma glucose levels of diabetic patients [75] The extractof white skinned sweet potatoes (WSSP) reduced hyperinsu-linemia in Zucker fatty rats by 23 26 60 and 50 after 3 46 and 8 weeks respectively starting the oral administrationof WSSP similar to troglitazone (insulin sensitizer) [76] Inaddition blood triacylglycerol (TG) free fatty acid (FFA)and lactate levels were also lowered by the oral administrationof WSSP In histological examinations of the pancreas ofZucker fatty rats remarkable regranulation of pancreatic isletB-cells was observed in the WSSP and troglitazone groupsafter 8 weeks of treatment Based on these findings it was con-cluded thatWSSPwas likely to improve the abnormal glucoseand lipid metabolism in insulin-resistant diabetes mellitusIn support of these observations ingestion of 4 g of caiapothe extract of WSSP per day for 6 weeks reduced fastingblood glucose and total as well as low density lipoprotein(LDL) cholesterol in male Caucasian type 2 diabetic patientswho were previously treated by diet alone [75] Howeversignificant changes were not observed between low dose ofcaiapo and placebo The improvement of insulin sensitivityas determined by the frequently sampled intravenous glucosetolerance test (FSIGT) indicated that caiapo extracts showedbeneficial effects via reducing insulin resistance Later Ludviket al [77] confirmed the beneficial effects of caiapo on glucoseand serum cholesterol levels in type 2 diabetic patients treatedby diet alone for 3 months after administration for thestudy Improved fasting blood glucose levels and glucoselevels during an OGTT and in the postprandial state as


well as improvement in long-term glucose control were alsoobserved as expressed by the significant decrease in HbA1c[77]

Ethanolic extract of tubers of Dioscorea alata showedan antidiabetic activity in alloxan-induced diabetic rats [78]Diabetic rats with administered yam extract exhibited sig-nificantly lower creatinine levels which could be a result ofimproved renal function by reduced plasma glucose leveland subsequent glycosylation of renal basement membranesSeveral bioactive compounds including phenolics wereidentified in the ethanolic extract of D alata These includehydro-Q9 chromene 120574-tocopherol 120572-tocopherol feruloylglycerol dioscorin cyanidin-3-glucoside catechin procyani-din cyanidin peonidin 3-gentiobioside and alatanins A Band C [78]

37 Hypocholesterolemic Activity Cardiovascular diseases areamong the leading causes of death worldwide It is wellknown that diet plays an important role in the regulationof cholesterol homeostasis External agents possessing antic-holesterolemic activities continuously show beneficial effectson risk reduction and management of the disease condi-tions

Diosgenin a steroidal saponin of yam (Dioscorea)demonstrated antioxidative and hypolipidemic effects in vivo[79] Rats fed with a high-cholesterol diet were supplementedwith either 01 or 05 diosgenin for 6 weeksThe lipid profileof the plasma and liver lipid peroxidation and antioxidantenzyme activities in the plasma erythrocyte and gene expres-sion of antioxidative enzymes in the liver and the oxidativeDNA damage in lymphocytes were measured Diosgeninshowed pancreatic lipase inhibitory activity protective effectof liver under high-cholesterol diet reduced total cholesterollevel and protection against the oxidative damaging effects ofpolyunsaturated fatty acids [79] Steroidal saponins of yamsare used for industrial drug processing Saponins such asdioscin and gracilin and prosapogenins of dioscin have longbeen identified from yam The content of dioscin was about27 (ww) Diosgenin content was about 0004 and 012ndash048 in cultivated yam and wild yam respectively Theantihypercholesterolemic effect of yam saponin is related toits inhibitory activity against cholesterol absorption [80]

The effect of yam diosgenin on hypercholesterolemia hadbeen also reported by Cayen and Dvornik [81] Hyperc-holesterolemic rats fed with yam (Dioscorea) showed thatdiosgenin had decreased cholesterol absorption increasedhepatic cholesterol synthesis and increased biliary choles-terol secretion without affecting serum cholesterol level Inagreement with this finding several studies showed thatdiosgenin in some Dioscorea could enhance fecal bileacid secretion and decrease intestinal cholesterol absorption[82 83] The relative contribution of biliary secretion andintestinal absorption of cholesterol in diosgenin-stimulatedfecal cholesterol excretionwere studied usingwild-type (WT)and Niemann-Pick C1-Like 1 (NPC1L1) knockout (LIKO)mice NPC1L1 was recently identified as an essential proteinfor intestinal cholesterol absorption [84] Diosgenin signifi-cantly increased biliary cholesterol and hepatic expression of

cholesterol synthetic genes in both WT and LIKO mice Inaddition diosgenin stimulation of fecal cholesterol excretionwas primarily attributable to its impact on hepatic cholesterolmetabolism rather thanNPC1L1-dependent intestinal choles-terol absorption [85]

Native protein of dioscorin purified from D alata (cvTainong number 1) (TN1-dioscorin) and its peptic hydroly-sates presentedACE inhibitory activities in a dose-dependentmanner [29] According to kinetic analysis dioscorin showedmixed noncompetitive inhibition against ACE Dioscorinfrom Dioscoreamight be beneficial in controlling high bloodpressure [85]

Chen et al [23] reported the effects of Taiwanrsquos yam(Dioscorea alata cv Tainung number 2) onmucosal hydrolaseactivities and lipid metabolism in male Balbc mice Highlevel of Tainung number 2 yam in the diet (50ww) reducedplasma and hepatic cholesterol levels and increased fecalsteroid excretions in mice model This could be due to theloss of bile acid in the enterohepatic cycle to fecal excretion[23] They further suggested that the increased viscosity ofthe digest and the thickness of the unstirred layer in thesmall intestine caused byTainungnumber 2 yamfibre (orandmucilage) decreased the absorption of fat cholesterol andbile acid Short term (3-week) consumption of 25 Tainungnumber 2 yam in the diet could reduce the atherogenic indexbut not total cholesterol level in nonhypercholesterolemicmice Furthermore additional dietary yam (50 yam diet)could consistently exert hypocholesterolemic effects in thesemice [23] However Diosgenin was not elucidated in Tainungnumber 2 used in this study [23] Thus authors suggestedthat diosgenin might not be involved in the cholesterollowering effect of Tainung number 2 yam Dietary fibreand viscous mucilage could be active components for thebeneficial cholesterol lowering effects of yam Furthermoreshort term consumption (3-week) of 25 uncooked keelungyam effectively reduced total blood cholesterol levels and theatherogenic index in mice Authors indicated that the activecomponents for the lipid lowering effects may be attributedto dietary fibre mucilage plant sterols or synergism of theseactive components [23]

38 Hormonal Activities Yam (Dioscorea) has the abilityto reduce the risk of cancer and cardiovascular diseases inpostmenopausal women [86] It was shown that the levels ofserum estrogen and sex hormone binding globulin (SHBG)increased significantly after subjects had been on a yam dietfor 30 days Furthermore three serum hormone parametersmeasured namely estrogen estradiol and SHBG did notchange in those who were fed with sweet potatoes as thecontrol The risk of breast cancer which increased by estro-gens might be balanced by the elevated SHB and the ratioof estrogen plus estradiol to SHBG Authors further showedthat high SHBG levels had a protective effect against theoccurrence of type 2 diabetes mellitus and coronary heartdiseases in women [86]

Chronic administration of Dioscorea may enhance bonestrength and provide insight into the role of Dioscorea inbone remodeling and osteoporosis during the menopause[87] Administration of Dioscorea to ovariectomised rats


decreased the porosity effect on bones and increased theultimate force of bones The changes in biochemical andphysiological functions seen in these animals were similar tothose in menopausal women [87]

39 Antiobesity Differentiation and proliferation inhibitoryactivity of sporamin of sweet potato roots in 3T3-L1 pread-ipocytes were reported [84] Sporamin did not exhibitany cytotoxic activity toward the model cell line 3T3-L1preadipocytes which have frequently been used to studydifferentiation of adipocytes in vitro Concentration rangeof 0025 to 1mgmL sporamin showed antidifferentiationand antiproliferation effects on 3T3-L1 cells similarly to002mgmL berberine Berberine is a traditional Chinesemedicine used as an antimicrobial and antitumour agent [84]Hwang et al [88] demonstrated that purple sweet potatois a potential agent which can be used for the preventionof obesity Anthocyanin fractions of purple sweet potatoinhibited hepatic lipid accumulation through the induc-tion of adenosine monophosphate activated protein kinase(AMPK) signaling pathways AMPK plays an important rolein the regulation of lipid synthesis in metabolic tissues [88]Anthocyanin dose of 200mgkg of body weight per dayreducedweight gain and hepatic triacylglycerol accumulationand improved serum lipid parameters in mice fed for 4weeks with purple sweet potatoes Furthermore anthocyaninadministration increased the phosphorylation of AMPK andacetyl coenzyme A carboxylase (ACC) in the liver andHepG2 hepatocytes These authors further suggested thatanthocyanin fractionmay improve high fat diet induced fattyliver disease and regulate hepatic lipid metabolism [88]

4 Effect of Processing on Bioactivities ofRoots and Tubers

Tuber crops are processed in a number of ways before theyare consumed and these include hydrothermal treatmentssuch as boiling frying baking and roasting dehydration andfermentation Depending on the region and country differenttypes of foods are prepared at domestic and industrial levels

Major proportions of cassava produced in Africa andLatin America are processed into fermented foods and foodadditives such as organic acids and monosodium glutamateLactic acid bacteria and yeasts are two major groups ofmicroorganisms used for cassava fermentation Those fer-mented foods from cassava include gari fufu lafun chick-wanghe agbelima attieke and kivunde in Africa tape in Asiaand ldquocheeserdquo bread and ldquocoated peanutrdquo in Latin America[89] Sweet potatoes also may be fermented into soy saucevinegar lactojuices lactopickles and sochu (an alcoholicdrink produced in Japan) and yams may be fermented intofermented flour Furthermore yams are used in a number offoods Greater yams (Dioscorea alata L) commonly knownas ube in the Philippines are utilized in sweetened fooddelicacies due to their attractive violet color and unique tasteUbe is used in a number of native delicacies such as halaya(yam pudding with milk) sagobe (with parboiled chocomilkand glutinous rice balls) puto (rice cake) halo-halo hopia

and different types of rice cake using glutinous rice such assuman sapin-sapin bitso and bibingka It can also be usedas an ingredient for flavour andor filling in ice cream tartsbread and cakes Different food processing conditions alterthe content of phytochemicals as well as their bioactivities

Processing conditions such as peeling drying and sul-phite treatment could change physiochemical properties andnutritional quality of sweet potato flour [90] Sweet potatoflour is generally used to enhance characteristics of foodproducts through color flavour and natural sweetness and issupplemented nutrients It also serves as substitute for cerealflours which particularly contain gluten which is not suitedfor individuals diagnosed with celiac disease [91] Peeled andunpeeled sweet potato flour with or without sulphite treat-ment showed higher browning indices at 55∘C and decreasedwith increasing drying temperatures [90] Furthermore 120573-carotene content of all flours decreased with increasingtemperature Total phenolic content decreased at a higherdrying temperature for peeled and unpeeled sweet potatoflour without sulphite treatment Unpeeled sweet potato flourhad higher phenolic content which was contributed by thetuber skin [92] Sweet potato flour with sulphite treatmentshowed higher phenolics and ascorbic acid contents andthis could be due to the inactivation of polyphenol oxidaseby sulphites Sulphite reacts with quinines and inhibits thepolyphenol oxidase activity and depletes oxygen content [93]

Shih et al [94] demonstrated the physiochemical andphysiological properties and bioactivities of sweet potato dryproducts made from two varieties yellow (variety Tainong57) and orange (variety Tainong 66) using different pro-cessing methods such as freeze-drying hot air-drying andextrusion Antioxidant contents were different between 70methanolic extracts of yellow and orange sweet potatoes Inaddition differences of antioxidant activity were observedamong freeze-dried hot air-dried and extruded samples[94] The freeze-dried samples of orange potatoes showedhigh phenolics 120573-carotene and anthocyanin contents andfree radical scavenging activities compared to those of yellowsweet potatoes The extrusion process significantly increasedthe DPPH radical scavenging activity and TPC whereasanthocyanin and 120573-carotene contents were decreased Theincrease in the level of phenolic acids after extrusion couldbe due to the release of the bound phenolic acids and theirderivatives from the cell walls of the plant matter [94] TheDPPH radical scavenging activity was higher for hot air-dried samples compared to those of freeze-dried yellow sweetpotatoes but this trendwas opposite for orange sweet potatoes[94] They also reported that the methanolic extracts ofsweet potatoes had immunomodulatory activities Methano-lic extracts of sweet potatoes increased the proliferation ofthe lectin concanavalin A (Con A) stimulated splenocytesof BALBc mice in a concentration dependent mannerFreeze-dried sweet potatoes had the highest mitogenic indexcompared to that of hot air-drying and extrusion processingsamples of both yellow and orange sweet potatoes Phenoliccompounds anthocyanins and 120573-carotene could be respon-sible compounds for the observed bioactivities [94 95]

The retention of 120573-carotene decreased with the dura-tion of boiling steaming and microwave cooking [96] It


Table 4 Content of phenolic compounds during various processing methods of purple yam (Dioscorea alata)

Fresh yam Blanched Frozen Vacuum fryingTotal phenolic content (mg gallic acid equivalent100 g) 478 plusmn 1162 306 plusmn 77 293 plusmn 893 204 plusmn 549

Total anthocyanin content (mg100 g) 310 plusmn 235 126 plusmn 165 126 plusmn 154 792 plusmn 103

Sinapic acid (mg100 g) 135 plusmn 527 931 plusmn 753 9173 plusmn 571 555 plusmn 332

Ferulic acid (mg100 g) 313 plusmn 108 1594 plusmn 115 1577 plusmn 105 948 plusmn 111

Source Fang et al [103]

was found that 50-minute boiling reduced one-third of 120573-carotene content Furthermore steaming reduced highercontent of 120573-carotene compared to that of boiling It wasnoted that microwave cooking had the highest loss Authorssuggested that long cooking time leads to high reductions in120573-carotene content of sweet potatoes [96]

Different cookingmethods affect the phenolic contents ofpotatoes [97] A significant loss in phenolic contents of peeledand unpeeled potatoes was observed during boiling andbaking Furthermore boiling caused loss of protocatechuicand caffeoylquinic acids of peeled potatoes by 86 and 26respectively In addition microwave cooking resulted inloss of 50 to 83 of protocatechuic acid and 27 to 64of caffeoylquinic acids in peeled potatoes Interestingly thelosses were reported to be lower in unpeeled potatoes thanthose in peeled potatoes [97]The reported losses in phenoliccontents could be due to a combination of degradation causedby leaching into water heat and polyphenol oxidation [1098] Potatoes cooked with peel had a high amount of totalphenolics in the cortex and internal tissues [99]This has beenattributed to the migration of phenolics from the peel intoboth cortex and internal tissues of the tuber [10] Navarreet al [100] also showed the effects of cooking (microwavecooking boiling and steaming) on the phenolic contents ofpotatoes and the results showed that none of these methodsdecreased the content of chlorogenic cryptochlorogenicand neochlorogenic acids Furthermore it was found thatflavonols (rutin) remained during cooking however therewas an increase in phenolic contents of stir-fried potatoesDifferent processing methods decreased the anthocyanincontent due to the effect of high temperature enzyme activitychange in pH and presence of metallic ions and proteins[101 102] Another study showed that anthocyanin content inraw potatoes was higher than that of potato chips and Frenchfries which were processed by deep frying [103]

Fang et al [103] identified themajor phenolic compoundsin Chinese purple yam and their changes during vacuumfrying (Table 4) They demonstrated that 40 and 63 ofanthocyanin remained after blanching and vacuum fry-ing respectively [103] Furthermore hydroxycinnamic acidsnamely sinapic acids and ferulic acids showed higher stabil-ity than that of anthocyanins and freezing did not influencethe phenolic contents due to short freezing time of 20 hours[103]

Different dehydration methods used to produce yamflours could affect their antioxidant activities [104] Freeze-dried yam flours had the strongest DPPH radical scavengingactivities compared to tjose of hot air-dried or drum-driedyam flours Chen and Lin [52] also reported the negative

impact of temperature on the content of phenolic compoundsand dioscorin and antioxidant activities of yam cultivarsChen et al [104] further showed the effect of pH on phenoliccontents antioxidant activity and stability of dioscorin invarious yam tubers The TPC observed of yam varieties werethe highest at pH 5 and gradual decrease was observed withincreased pH The DPPH radical scavenging activity showeda similar pattern to those of phenolic contents of yams at pH5 but ferrous ion chelating capacity was found to be high forall yams at pH 8 [104]

5 Conclusions

Roots and tubers are important diet components for humansand add variety to it In addition to themain role as an energycontributor they provide a number of desirable nutritionaland health benefits such as antioxidative hypoglycemichypocholesterolemic antimicrobial and immunomodula-tory activities A variety of foods can be prepared usingtubers and type and usage vary with the country and regionProcessing affects the bioactivities of constituent compoundsTubers may serve as functional foods and nutraceuticalingredients to attenuate noncommunicable chronic diseasesand to maintain wellness

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

This research was supported by the Research Grant Schemeof Wayamba University of Sri Lanka through a grant(SRHDCRP0413-09) to Anoma Chandrasekara

References

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Plantains and Bananas in Human Nutrition vol 24 of Food andNutrition Series Food and Agriculture Organization RomeItaly 1990

[3] M Naczk and F Shahidi ldquoPhenolics in cereals fruits andvegetables occurrence extraction and analysisrdquo Journal ofPharmaceutical and Biomedical Analysis vol 41 pp 1523ndash15422006

[4] FAO Production Year Book vol 53 Food and AgricultureOrganization Rome Italy 1999

[5] B Burlingame B Mouille and R Charrondiere ldquoNutrientsbioactive non-nutrients and anti-nutrients in potatoesrdquo Journal


of Food Composition and Analysis vol 22 no 6 pp 494ndash5022009

[6] A L Hale L Reddivari M N Nzaramba J B Bamberg andJ C Miller Jr ldquoInterspecific variability for antioxidant activityand phenolic content among Solanum speciesrdquo American Jour-nal of Potato Research vol 85 no 5 pp 332ndash341 2008

[7] D A Navarre A Goyer and R Shakya ldquoNutritional valueof potatoes Vitamin phyto-nutrient and mineral contentrdquo inAdvances in Potatoes Chemistry and Technology J Singh and LKaur Eds Elsevier Amsterdam The Netherlands 2009

[8] HMcNulty andK Pentieva ldquoFolate bioavailabilityrdquoProceedingsof the Nutrition Society vol 63 no 4 pp 529ndash536 2004

[9] G Diretto S Al-Babili R Tavazza V Papacchioli P Beyerand G Giuliano ldquoMetabolic engineering of potato carotenoidcontent through tuber-specific overexpression of a bacterialmini-pathwayrdquo PLoS ONE vol 2 no 4 article e350 2007

[10] R Ezekiel N Singh S Sharma and A Kaur ldquoBeneficial phyto-chemicals in potato-a reviewrdquo Food Research International vol50 no 2 pp 487ndash496 2013

[11] G J Scott ldquoTransforming traditional food crops productdevelopment for roots and tubersrdquo in Product Development forRoot and Tuber Crops vol 1 pp 3ndash20 Asia International PotatoCenter 1992

[12] A C Bovell-Benjamin ldquoSweet potato a review of its pastpresent and future role in human nutritionrdquo Advances in Foodand Nutrition Research vol 52 pp 1ndash59 2007

[13] P J van Jaarsveld D W Marais E Harmse P Nestel and D BRodriguez-Amaya ldquoRetention of 120573-carotene in boiled mashedorange-fleshed sweet potatordquo Journal of Food Composition andAnalysis vol 19 no 4 pp 321ndash329 2006

[14] N M A Nassar D Y C Hashimoto and S D C FernandesldquoWild Manihot species botanical aspects geographic distribu-tion and economic valuerdquoGenetics andMolecular Research vol7 no 1 pp 16ndash28 2008

[15] I S Blagbrough S A L Bayoumi M G Rowan and J RBeeching ldquoCassava an appraisal of its phytochemistry andits biotechnological prospectsmdashreviewrdquo Phytochemistry vol 71no 17-18 pp 1940ndash1951 2010

[16] H Prawat C Mahidol S Ruchirawat et al ldquoCyanogenic andnon-cyanogenic glycosides from Manihot esculentardquo Phyto-chemistry vol 40 no 4 pp 1167ndash1173 1995

[17] K Reilly R Gomez-Vasquez H Buschmann J Tohme and JR Beeching ldquoOxidative stress responses during cassava post-harvest physiological deteriorationrdquo Plant Molecular Biologyvol 56 no 4 pp 625ndash641 2004

[18] Y-W Liu H-F Shang C-K Wang F-L Hsu and W-C HouldquoImmunomodulatory activity of dioscorin the storage proteinof yam (Dioscorea alata cv Tainong No 1) tuberrdquo Food andChemical Toxicology vol 45 no 11 pp 2312ndash2318 2007

[19] M M Iwu C O Okunji G O Ohiaeri P Akah D Corley andM S Tempesta ldquoHypoglycaemic activity of dioscoretine fromtubers of Dioscorea dumetorum in normal and alloxan diabeticrabbitsrdquo Planta Medica vol 56 no 3 pp 264ndash267 1990

[20] M R Bhandari T Kasai and J Kawabata ldquoNutritional eval-uation of wild yam (Dioscorea spp) tubers of Nepalrdquo FoodChemistry vol 82 no 4 pp 619ndash623 2003

[21] J E Kelmanson A K Jager and J van Staden ldquoZulu medicinalplants with antibacterial activityrdquo Journal of Ethnopharmacol-ogy vol 69 no 3 pp 241ndash246 2000

[22] Y-C Chan C-K Hsu M-F Wang and T-Y Su ldquoA dietcontaining yam reduces the cognitive deterioration and brain

lipid peroxidation in mice with senescence acceleratedrdquo Inter-national Journal of Food Science and Technology vol 39 no 1pp 99ndash107 2004

[23] H-L Chen C-HWang C-T Chang and T-CWang ldquoEffectsof Taiwanese yam (Dioscorea japonicaThunb var pseudojapon-ica Yamamoto) on upper gut function and lipid metabolism inBalbc micerdquo Nutrition vol 19 no 7-8 pp 646ndash651 2003

[24] I Podolak A Galanty and D Sobolewska ldquoSaponins as cyto-toxic agents a reviewrdquo Phytochemistry Reviews vol 9 no 3 pp425ndash474 2010

[25] C-H Huang J-Y Cheng M-C Deng C-H Chou and T-RJan ldquoPrebiotic effect of diosgenin an immunoactive steroidalsapogenin of the Chinese yamrdquo Food Chemistry vol 132 no 1pp 428ndash432 2012

[26] W-C Hou H-J Chen and Y-H Lin ldquoDioscorins the majortuber storage proteins of yam (Dioscorea batatas Decne)with dehydroascorbate reductase and monodehydroascorbatereductase activitiesrdquo Plant Science vol 149 no 2 pp 151ndash1561999

[27] W-C Hou H-J Chen and Y-H Lin ldquoDioscorins fromdifferent Dioscorea species all exhibit both carbonic anhydraseand trypsin inhibitor activitiesrdquo Botanical Bulletin of AcademiaSinica vol 41 no 3 pp 191ndash196 2000

[28] W-C Hou M-H Lee H-J Chen et al ldquoAntioxidant activitiesof dioscorin the storage protein of yam (Dioscorea batatasDecne) tuberrdquo Journal of Agricultural and Food Chemistry vol49 no 10 pp 4956ndash4960 2001

[29] F-L Hsu Y-H Lin M-H Lee C-L Lin and W-C HouldquoBoth dioscorin the tuber storage protein of yam (Dioscoreaalata cv Tainong No 1) and its peptic hydrolysates exhibitedangiotensin converting enzyme inhibitory activitiesrdquo Journal ofAgricultural and Food Chemistry vol 50 no 21 pp 6109ndash61132002

[30] J-Y Lin S Lu Y-L Liou and H-L Liou ldquoAntioxidant andhypolipidaemic effects of a novel yam-boxthorn noodle in anin vivo murine modelrdquo Food Chemistry vol 94 no 3 pp 377ndash384 2006

[31] P R Shewry ldquoTuber storage proteinsrdquo Annals of Botany vol 91no 7 pp 755ndash769 2003

[32] R Senthilkumar and K-W Yeh ldquoMultiple biological functionsof sporamin related to stress tolerance in sweet potato (Ipomoeabatatas Lam)rdquo Biotechnology Advances vol 30 no 6 pp 1309ndash1317 2012

[33] K-W Yeh J-C Chen M-I Lin Y-M Chen and C-Y LinldquoFunctional activity of sporamin from sweet potato (Ipomoeabatatas Lam) a tuber storage protein with trypsin inhibitoryactivityrdquo Plant Molecular Biology vol 33 no 3 pp 565ndash5701997

[34] W-C Hou and Y-H Lin ldquoDehydroascorbate reductaseand monodehydroascorbate reductase activities of trypsininhibitors the major sweet potato (Ipomoea batatas [L] Lam)root storage proteinrdquo Plant Science vol 128 no 2 pp 151ndash1581997

[35] M F B Dale D W Griffiths H Bain and D Todd ldquoGlycoal-kaloid increase in Solarium tuberosum on exposure to lightrdquoAnnals of Applied Biology vol 123 no 2 pp 411ndash418 1993

[36] I Ginzberg J G Tokuhisa and R E Veilleux ldquoPotato steroidalglycoalkaloids biosynthesis and genetic manipulationrdquo PotatoResearch vol 52 no 1 pp 1ndash15 2009

[37] M Friedman ldquoPotato glycoalkaloids and metabolites roles inthe plant and in the dietrdquo Journal of Agricultural and FoodChemistry vol 54 no 23 pp 8655ndash8681 2006


[38] K-W Kuo S-H Hsu Y-P Li et al ldquoAnticancer activity eval-uation of the Solanum glycoalkaloid solamargine triggeringapoptosis in human hepatoma cellsrdquo Biochemical Pharmacol-ogy vol 60 no 12 pp 1865ndash1873 2000

[39] L-F Liu C-H Liang L-Y Shiu W-L Lin C-C Lin and K-W Kuo ldquoAction of solamargine on human lung cancer cells-enhancement of the susceptibility of cancer cells to TNFsrdquoFEBSLetters vol 577 no 1-2 pp 67ndash74 2004

[40] T Ikeda H Tsumagari T Honbu and T Nohara ldquoCytotoxicactivity of steroidal glycosides from solanum plantsrdquo Biologicaland Pharmaceutical Bulletin vol 26 no 8 pp 1198ndash1201 2003

[41] W Stahl and H Sies ldquoLycopene a biologically importantcarotenoid for humansrdquo Archives of Biochemistry and Bio-physics vol 336 no 1 pp 1ndash9 1996

[42] N I Krinsky ldquoActions of carotenoids in biological systemsrdquoAnnual Review of Nutrition vol 13 pp 561ndash587 1993

[43] H Tapiero D M Townsend and K D Tew ldquoThe role ofcarotenoids in the prevention of human pathologiesrdquo Biomedi-cine and Pharmacotherapy vol 58 no 2 pp 100ndash110 2004

[44] S Blanquet-Diot MahaSoufi M Rambeau E Rock and MAlric ldquoDigestive stability of xanthophylls exceeds that ofcarotenes as studied in a dynamic in vitro gastrointestinalsystemrdquo Journal of Nutrition vol 139 no 5 pp 876ndash883 2009

[45] F Hesam G R Balali and R T Tehrani ldquoEvaluation of antiox-idant activity of three common potato (Solanum tuberosum)cultivars in Iran rdquo Avicenna Journal of Phytomedicine vol 2 no2 pp 79ndash85 2012

[46] R Chimkode M B Patil and S S Jalalpure ldquoWound healingactivity of tuberous root extracts of Ipomoea batatasrdquo Advancesin Pharmacology and Toxicology vol 10 pp 69ndash72 2009

[47] V Panda and M Sonkamble ldquoAnti-ulcer activity of Ipomoeabatatas tubers (sweet potato)rdquo Functional Foods in Health andDisease vol 2 no 3 pp 48ndash61 2011

[48] T Suzuki H Tada E Sato and Y Sagae ldquoApplication of sweetpotato fiber to skinwound in ratrdquoBiological and PharmaceuticalBulletin vol 19 no 7 pp 977ndash983 1996

[49] L Dilworth K Brown R Wright M Oliver S Hall and HAsemota ldquoAntioxidants minerals and bioactive compounds intropical staplesrdquoAfrican Journal of Food Science and Technologyvol 3 no 4 pp 90ndash98 2012

[50] D F Cornago R G O Rumbaoa and I M Geronimo ldquoPhilip-pine Yam (Dioscorea spp) tubers phenolic content and antiox-idant capacityrdquo Philippine Journal of Science vol 140 no 2 pp145ndash152 2011

[51] C-K Hsu J-Y Yeh and J-H Wei ldquoProtective effects ofthe crude extracts from yam (Dioscorea alata) peel on tert-butylhydroperoxide-induced oxidative stress in mouse livercellsrdquo Food Chemistry vol 126 no 2 pp 429ndash434 2011

[52] Y-T Chen andK-W Lin ldquoEffects of heating temperature on thetotal phenolic compound antioxidative ability and the stabilityof dioscorin of various yam cultivarsrdquo Food Chemistry vol 101no 3 pp 955ndash963 2007

[53] Y-C Chan S-C Chang S-Y Liu H-L Yang Y-C Hseu andJ-W Liao ldquoBeneficial effects of yam on carbon tetrachloride-induced hepatic fibrosis in ratsrdquo Journal of the Science of Foodand Agriculture vol 90 no 1 pp 161ndash167 2010

[54] Y H Chu and C L Chang ldquoFlavonoid content of severalvegetables and their antioxidant activityrdquo Journal of the Scienceof Food and Agriculture vol 80 no 5 pp 561ndash566 2000

[55] C R Brown ldquoBreeding for phytonutrient enhancement ofpotatordquo American Journal of Potato Research vol 85 no 4 pp298ndash307 2008

[56] K-H Han K-I Shimada M Sekikawa and M FukushimaldquoAnthocyanin-rich red potato flakes affect serum lipid per-oxidation and hepatic SOD mRNA level in ratsrdquo BioscienceBiotechnology and Biochemistry vol 71 no 5 pp 1356ndash13592007

[57] X Ji L Rivers Z Zielinski et al ldquoQuantitative analysis ofphenolic components and glycoalkaloids from 20 potato clonesand in vitro evaluation of antioxidant cholesterol uptake andneuroprotective activitiesrdquo Food Chemistry vol 133 no 4 pp1177ndash1187 2012

[58] N F Omar S A Hassan U K Yusoff N A P Abdullah P EMWahab and U R Sinniah ldquoPhenolics flavonoids antioxidantactivity and cyanogenic glycosides of organic and mineral-basefertilized cassava tubersrdquoMolecules vol 17 no 3 pp 2378ndash23872012

[59] V Panda and M Sonkamble ldquoPhytochemical constituentsand pharmacological activities of Ipomoea batatas l (Lam)mdashareviewrdquo International Journal of Research in Phytochemistry ampPharmacology vol 2 no 1 pp 25ndash34 2012

[60] J J Kim C W Kim D S Park et al ldquoEffects of sweet potatofractions on alcoholic hangover and gastric ulcerrdquo LaboratoryAnimal Research vol 24 pp 209ndash216 2008

[61] D-J Huang C-D Lin H-J Chen and Y-H Lin ldquoAntioxi-dant and antiproliferative activities of sweet potato (Ipomoeabatatas [L] Lam ldquoTainong 57rdquo) constituentsrdquo Botanical Bulletinof Academia Sinica vol 45 no 3 pp 179ndash186 2004

[62] M Yoshimoto S OkunoM Yoshinaga O YamakawaM Yam-aguchi and J Yamada ldquoAntimutagenicity of sweet potato(Ipomoea batatas) rootsrdquo Bioscience Biotechnology and Bio-chemistry vol 63 no 3 pp 537ndash541 1999

[63] M D Thompson H J Thompson J N McGinley et alldquoFunctional food characteristics of potato cultivars (Solanumtuberosum L) phytochemical composition and inhibition of 1-methyl-1-nitrosourea induced breast cancer in ratsrdquo Journal ofFood Composition and Analysis vol 22 no 6 pp 571ndash576 2009

[64] G P Madiwale L Reddivari D G Holm and J VanamalaldquoStorage elevates phenolic content and antioxidant activity butsuppresses antiproliferative and pro-apoptotic properties ofcolored-flesh potatoes against human colon cancer cell linesrdquoJournal of Agricultural and Food Chemistry vol 59 no 15 pp8155ndash8166 2011

[65] K K-W Auyeung P-C Law and J K-S Ko ldquoAstragalussaponins induce apoptosis via an ERK-independent NF-120581Bsignaling pathway in the humanhepatocellularHepG2 cell linerdquoInternational Journal of Molecular Medicine vol 23 no 2 pp189ndash196 2009

[66] K-R Lee N Kozukue J-S Han et al ldquoGlycoalkaloids andmetabolites inhibit the growth of human colon (HT29) andliver (HepG2) cancer cellsrdquo Journal of Agricultural and FoodChemistry vol 52 no 10 pp 2832ndash2839 2004

[67] T-S Wang C-K Lii Y-C Huang J-Y Chang and F-Y YangldquoAnticlastogenic effect of aqueous extract from water yam(Dioscorea alata L)rdquo Journal of Medicinal Plant Research vol5 no 26 pp 6192ndash6202 2011

[68] EMChoi S J Koo and J-KHwang ldquoImmune cell stimulatingactivity of mucopolysaccharide isolated from yam (Dioscoreabatatas)rdquo Journal of Ethnopharmacology vol 91 no 1 pp 1ndash62004

[69] P-F Su C-J Li C-C Hsu et al ldquoDioscorea phytocompoundsenhance murine splenocyte proliferation ex vivo and improveregeneration of bone marrow cells in vivordquo Evidence-Based


Complementary and Alternative Medicine vol 2011 Article ID731308 11 pages 2011

[70] H-F Shang H-C Cheng H-J Liang H-Y Liu S-Y Liuand W-C Hou ldquoImmunostimulatory activities of yam tubermucilagesrdquo Botanical Studies vol 48 no 1 pp 63ndash70 2007

[71] J O Olayemi and E O Ajaiyeoba ldquoAnti-inflammatory studiesof yam (Dioscorea esculenta) extract on Wistar ratsrdquo AfricanJournal of Biotechnology vol 6 no 16 pp 1913ndash1915 2007

[72] K L Kaspar J S Park C R Brown B D MAthison D ANavarre and B P Chew ldquoPigmented potato consumption altersoxidative stress and inflammatory damage in menrdquo Journal ofNutrition vol 141 no 1 pp 108ndash111 2011

[73] A S Tripathi V Chitra N W Sheikh D S Mohale and A PDewani ldquoImmunomodulatory activity of the methanol extractof Amorphophallus campanulatus (Araceae) Tuberrdquo TropicalJournal of Pharmaceutical Research vol 9 no 5 pp 451ndash4542010

[74] M A Sonibare and R B Abegunde ldquoIn vitro antimicrobial andantioxidant analysis of Dioscorea dumetorum (Kunth) Pax andDioscorea hirtiflora (Linn) and their bioactivemetabolites fromNigeriardquo Journal of Applied Biosciences vol 51 pp 3583ndash35902012

[75] B H Ludvik K Mahdjoobian WWaldhaeusl et al ldquoThe effectof Ipomoea batatas (Caiapo) on glucose metabolism and serumcholesterol in patientswith type 2 diabetes a randomized studyrdquoDiabetes Care vol 25 no 1 pp 239ndash240 2002

[76] S Kusano and H Abe ldquoAntidiabetic activity of white skinnedsweet potato (Ipomoea batatas L) in obese Zucker fatty ratsrdquoBiological and Pharmaceutical Bulletin vol 23 no 1 pp 23ndash262000

[77] B Ludvik B Neuffer and G Pacini ldquoEfficacy of Ipomoeabatatas (Caiapo) on diabetes control in type 2 diabetic subjectstreated with dietrdquo Diabetes Care vol 27 no 2 pp 436ndash4402004

[78] V Maithili S P Dhanabal S Mahendran and R VadivelanldquoAntidiabetic activity of ethanolic extract of tubers ofDioscoreaalata in alloxan induced diabetic ratsrdquo Indian Journal of Phar-macology vol 43 no 4 pp 455ndash459 2011

[79] I S Son J H Kim H Y Sohn K H Son J-S Kim and C-SKwon ldquoAntioxidative and hypolipidemic effects of diosgenin asteroidal saponin of yam (Dioscorea spp) on high-cholesterolfed ratsrdquo Bioscience Biotechnology and Biochemistry vol 71 no12 pp 3063ndash3071 2007

[80] H Y Ma Z T Zhao L J Wang Y Wang Q L Zhou andB X Wang ldquoComparative study on anti-hypercholesterolemiaactivity of diosgenin and total saponin of Dioscorea panthaicardquoChina Journal of Chinese Materia Medica vol 27 no 7 pp 528ndash531 2002

[81] M N Cayen and D Dvornik ldquoEffect of diosgenin on lipidmetabolism in ratsrdquo Journal of Lipid Research vol 20 no 2 pp162ndash174 1979

[82] AThewles R A Parslow and R Coleman ldquoEffect of diosgeninon biliary cholesterol transport in the ratrdquo Biochemical Journalvol 291 no 3 pp 793ndash798 1993

[83] K Uchida H Takse Y Nomura K Takeda N Takeuchi and YIshikawa ldquoEffects of diosgenin and B-sisterol on bile acidsrdquoTheJournal of Lipid Research vol 25 pp 236ndash245 1984

[84] X Zhi-Dong L Peng-Gao and M Tai-Hua ldquoThe differen-tiation- and proliferation-inhibitory effects of sporamin fromsweet potato in 3T3-L1 preadipocytesrdquo Agricultural Sciences inChina vol 8 no 6 pp 671ndash677 2009

[85] R E Temel J M Brown Y Ma et al ldquoDiosgenin stimulation offecal cholesterol excretion in mice is not NPC1L1 dependentrdquoJournal of Lipid Research vol 50 no 5 pp 915ndash923 2009

[86] W-H Wu L-Y Liu C-J Chung H-J Jou and T-A WangldquoEstrogenic effect of yam ingestion in healthy postmenopausalwomenrdquo Journal of the American College of Nutrition vol 24no 4 pp 235ndash243 2005

[87] J-H Chen J S-SWu H-C Lin et al ldquoDioscorea improves themorphometric and mechanical properties of bone in ovariec-tomised ratsrdquo Journal of the Science of Food and Agriculture vol88 no 15 pp 2700ndash2706 2008

[88] Y P Hwang J H Choi E H Han et al ldquoPurple sweet potatoanthocyanins attenuate hepatic lipid accumulation throughactivating adenosine monophosphatendashactivated protein kinasein human HepG2 cells and obese micerdquoNutrition Research vol31 no 12 pp 896ndash906 2011

[89] R C Ray and P S Sivakumar ldquoTraditional and novel fermentedfoods and beverages from tropical root and tuber crops reviewrdquoInternational Journal of Food Science andTechnology vol 44 no6 pp 1073ndash1087 2009

[90] M Ahmed M S Akter and J-B Eun ldquoPeeling dryingtemperatures and sulphite-treatment affect physicochemicalproperties and nutritional quality of sweet potato flourrdquo FoodChemistry vol 121 no 1 pp 112ndash118 2010

[91] L Caperuto J Amaya-Farfan and C Camargo ldquoPerformanceof quinoa (Chenopodium quinoawild) flour in the manufactureof gluten-free spaghettirdquo Journal of the Science of Food andAgriculture vol 81 pp 95ndash101 2000

[92] N I Mondy and B Y Gosselin ldquoEffect of peeling on totalphenols total glycoalkaloids discoloration and flavor of cookedpotatoesrdquo Journal of Food Science vol 53 no 3 pp 756ndash7591988

[93] G M Sapers P H Cooke A E Heidel S T Martin and RL Miller ldquoStructural changes related to texture of pre-peeledpotatoesrdquo Journal of Food Science vol 62 no 4 pp 797ndash8031997

[94] M-C Shih C-C Kuo and W Chiang ldquoEffects of dryingand extrusion on colour chemical composition antioxidantactivities and mitogenic response of spleen lymphocytes ofsweet potatoesrdquo Food Chemistry vol 117 no 1 pp 114ndash121 2009

[95] M Kampa V-I Alexaki G Notas et al ldquoAntiproliferative andapoptotic effects of selective phenolic acids on T47D humanbreast cancer cells potential mechanisms of actionrdquo BreastCancer Research vol 6 no 2 pp R63ndash74 2004

[96] X Wu C Sun L Yang G Zeng Z Liu and Y Li ldquo120573-Carotenecontent in sweet potato varieties from China and the effectof preparation on 120573-carotene retention in the Yanshu No 5rdquoInnovative Food Science amp Emerging Technologies vol 9 no 4pp 581ndash586 2008

[97] A A Barba A Calabretti M drsquoAmore A L Piccinelli and LRastrelli ldquoPhenolic constituents levels in cv Agria potato undermicrowave processingrdquo LWTmdashFood Science and Technologyvol 41 no 10 pp 1919ndash1926 2008

[98] M Takenaka K Nanayama S Isobe andM Murata ldquoChangesin caffeic acid derivatives in sweet potato (Ipomoea batatas L)during cooking and processingrdquo Bioscience Biotechnology andBiochemistry vol 70 no 1 pp 172ndash177 2006

[99] N I Mondy and B Gosselin ldquoEffect of irradiation on discol-oration phenols and lipids of potatoesrdquo Journal of Food Sciencevol 54 no 4 pp 982ndash984 1989

[100] D A Navarre R Shakya J Holden and S Kumar ldquoThe effectof different cooking methods on phenolics and vitamin C in


developmentally young potato tubersrdquo American Journal ofPotato Research vol 87 no 4 pp 350ndash359 2010

[101] M Rein Copigmentation reactions and color stability of berryanthocyanins [Dissertation] University of Helsinki HelsinkiFinland 2005

[102] A Patras N P Brunton C OrsquoDonnell and B K Tiwari ldquoEffectof thermal processing on anthocyanin stability in foods mech-anisms and kinetics of degradationrdquo Trends in Food Science andTechnology vol 21 no 1 pp 3ndash11 2010

[103] Z Fang D Wu D Yu X Ye D Liu and J Chen ldquoPhenoliccompounds inChinese purple yam and changes during vacuumfryingrdquo Food Chemistry vol 128 no 4 pp 943ndash948 2011

[104] Y-T ChenW-T Kao and K-W Lin ldquoEffects of pH on the totalphenolic compound antioxidative ability and the stability ofdioscorin of various yam cultivarsrdquo Food Chemistry vol 107 no1 pp 250ndash257 2008

[105] USDA NAL 2015 httpsfnicnalusdagovfood-composition

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Anatomy Research International

PeptidesInternational Journal of


Hindawi Publishing Corporation httpwwwhindawicom

International Journal of

Volume 2014

Zoology


Molecular Biology International

GenomicsInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


BioinformaticsAdvances in

Marine BiologyJournal of



Signal TransductionJournal of


BioMed Research International

Evolutionary BiologyInternational Journal of



Biochemistry Research International

ArchaeaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014


Genetics Research International


Advances in

Virolog y

Hindawi Publishing Corporationhttpwwwhindawicom

Nucleic AcidsJournal of

Volume 2014

Stem CellsInternational



Enzyme Research



Microbiology


Table 1 Nutritional composition of selected tuber crops

Nutrients (per 100 g) Potatoes Sweet potatoes raw Cassava raw Yam rawWhite flesh and skin raw Red flesh and skin raw

Proximate compositionEnergy (kcal) 690 70 860 1600 1180Protein (g) 17 19 16 14 15Total lipid (fat) (g) 01 01 01 03 02Carbohydrate by difference (g) 157 159 201 381 279Fibre total dietary (g) 24 17 30 18 41Sugars total (g)g 12 13 42 17 05

MineralsCalcium Ca (mg) 9 10 30 16 17Magnesium Mg (mg) 21 22 25 21 21Potassium K (mg) 407 455 337 271 816Phosphorus P (mg) 62 61 47 27 55Sodium Na (mg)m 16 18 55 14 9

VitaminsTotal ascorbic acid (mg) 1970 860 240 2060 1710Thiamin (mg) 007 008 008 009 011Riboflavin (mg) 003 003 006 005 003Niacin (mg) 107 115 056 085 055Vitamin B-6 (mg) 0203 0170 0209 0088 0293Folate (120583g-DFE) 18 18 11 27 23Vitamin E (mg) 001 001 026 019 035Vitamin K (120583g) 16 29 18 19 23Vitamin A (IU)IU 8 7 14187 13 138

Source USDA [105]

source of potassium Roots and tubers are deficient in mostother vitamins and minerals but contain significant amountsof dietary fibre [2] Similar to other crops nutritional valueof roots and tubers varies with variety location soil type andagricultural practices among others

The burden of noncommunicable diseases (NCDs)increases globally in both developed and developing coun-tries and plays a pivotal role as the major cause of deathOxidative stress which would be harbored by both endoge-nous and exogenous factors contributes immensely to theetiology of NCDs as well as the aging processThe associationbetween plant food intake and reduced NCDs episodes hasbeen themain focus of a number of scientific investigations inthe recent past Furthermore identification of specific plantconstituents which convey health benefits is of much interestFoods of plant origin consist of a wide range of nonnutrientphytochemicals They are synthesized as secondary metabo-lites and serve a wide range of ecological roles in home plants[3] Tubers and root crops are significant sources of a num-ber of compounds namely saponins phenolic compoundsglycoalkaloids phytic acids carotenoids and ascorbic acidSeveral bioactivities namely antioxidant immunomodula-tory antimicrobial antidiabetic antiobesity and hypocholes-terolemic activities among others are reported for tubers androot crops

This review focuses on the bioactivities of phytochemicalsand their distribution in starchy roots and tuber crops

Furthermore the effect of processing on bioactive com-pounds of roots and tubers is also discussed

2 Roots and Tuber Crops

Plants producing starchy roots tubers rhizomes cormsand stems are important to nutrition and health They playan essential role in the diet of populations in developingcountries in addition to their usage for animal feed andfor manufacturing starch alcohol and fermented foods andbeverages

Roots and tuber crops are important cultivated stapleenergy sources second to cereals generally in tropical regionsin the world They include potatoes cassava sweet potatoesyams and aroids belonging to different botanical families butare grouped together as all types produce underground foodAn important agronomic advantage of root and tuber crops asstaple foods is their favourable adaptation to diverse soil andenvironmental conditions and a variety of farming systemswith minimum agricultural inputs In addition variationsin the growth pattern and adopting cultural practices makeroots and tubers specific in production systems Howeverroots and tuber crops are bulky in nature with high moisturecontent of 60ndash90 leading them to be associated withhigh transportation cost short shelf life and limited marketmargin in developing countries even where they are mainly




























6) and a C

3side chain













































2O2-CuSO

4induced
















































5 Conclusions


Competing Interests


Acknowledgments


References

























































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology




























6) and a C

3side chain













































2O2-CuSO

4induced
















































5 Conclusions


Competing Interests


Acknowledgments


References

























































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology










6) and a C

3side chain













































2O2-CuSO

4induced
















































5 Conclusions


Competing Interests


Acknowledgments


References

























































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology









































2O2-CuSO

4induced
















































5 Conclusions


Competing Interests


Acknowledgments


References

























































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology






























2O2-CuSO

4induced
















































5 Conclusions


Competing Interests


Acknowledgments


References

























































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology













2O2-CuSO

4induced
















































5 Conclusions


Competing Interests


Acknowledgments


References

























































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology












































5 Conclusions


Competing Interests


Acknowledgments


References

























































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology


































5 Conclusions


Competing Interests


Acknowledgments


References

























































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology























5 Conclusions


Competing Interests


Acknowledgments


References

























































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology













5 Conclusions


Competing Interests


Acknowledgments


References

























































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology




















































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology

















































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology
















































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology















Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology








Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology

Documents

Review Article Roots and Tuber Crops as Functional Foods ... · Cannas Canna edulis Cannaceae Buthsarana(SriLanka) Maranta arundinacea L. Marantaceae Arrow root Hulankeeriya(SriLanka)