Nutritional Value of Cassava for Use as a Staple Food and Recent ...

Nutritional Valueof Cassava for

Use as a StapleFood and Recent

Advances forImprovement

Julie A. Montagnac, Christopher R. Davis,and Sherry A. Tanumihardjo

ABSTRACT: Cassava is a drought-tolerant, staple food crop grown in tropical and subtropical areas where manypeople are afflicted with undernutrition, making it a potentially valuable food source for developing countries. Cas-sava roots are a good source of energy while the leaves provide protein, vitamins, and minerals. However, cassavaroots and leaves are deficient in sulfur-containing amino acids (methionine and cysteine) and some nutrients arenot optimally distributed within the plant. Cassava also contains antinutrients that can have either positive or ad-verse effects on health depending upon the amount ingested. Although some of these compounds act as antioxidantsand anticarcinogens, they can interfere with nutrient absorption and utilization and may have toxic side effects. Ef-forts to add nutritional value to cassava (biofortification) by increasing the contents of protein, minerals, starch,and �-carotene are underway. The transfer of a 284 bp synthetic gene coding for a storage protein rich in essentialamino acids and the crossbreeding of wild-type cassava varieties with Manihot dichotoma or Manihot oliganthahave shown promising results regarding cassava protein content. Enhancing ADP glucose pyrophosphorylase ac-tivity in cassava roots or adding amylase to cassava gruels increases cassava energy density. Moreover, carotenoid-rich yellow and orange cassava may be a foodstuff for delivering provitamin A to vitamin A–depleted populations.Researchers are currently investigating the effects of cassava processing techniques on carotenoid stability and iso-merization, as well as the vitamin A value of different varieties of cassava. Biofortified cassava could alleviate someaspects of food insecurity in developing countries if widely adopted.

IntroductionCassava is to African peasant farmers as rice is to Asian farm-

ers, or wheat and potatoes are to European farmers (Dixon A;Intl. Inst. of Tropical Agriculture in Nigeria; personal commu-nication). Because cassava (also called manioc or yucca, withvarious spellings) is drought-tolerant and its mature roots canmaintain their nutritional value for a long time without water,cassava may represent the future of food security in some devel-oping countries.

Cassava originated in the New World. Today it is a staple foodand animal feed in tropical and subtropical Africa, Asia, and LatinAmerica, with an estimated total cultivated area greater than 13million hectares, of which more than 70% is in Africa and Asia

MS 20081074 Submitted 12/29/2008, Accepted 3/2/2009. Author Montagnacis with SupAgro Montpellier, Ecole Nationale Superieure Agronomique ofMontpellier, 02 Place Pierre Viala, 34060 Montpellier Cedex 1, France. Au-thors Davis and Tanumihardjo are with Univ. of Wisconsin-Madison, Dept. ofNutritional Sciences, 1415 Linden Drive, Madison, WI 53706, U.S.A. Directinquiries to author Tanumihardjo (E-mail: [email protected]).

(EL-Sharkawy 2003). Approximately 500 million people dependon it as a major carbohydrate (energy) source, in part because ityields more energy per hectare than other major crops (Table 1).Cassava is grown predominantly by small-scale farmers with lim-ited resources in marginally fertile soils; it is resistant to adverseenvironments and tolerates a range of rainfall (El-Sharkawy 2003).Tapioca, a commercially important starch product common in theUnited States, is produced from cassava roots. Figure 1 illustratesthe widespread use and daily consumption of cassava and itsproducts.

Cassava is grown in areas where mineral and vitamin deficien-cies are widespread, especially in Africa. A marginal nutrientstatus increases the risk of morbidity and mortality. Therefore,improving the nutritional value of cassava could alleviate someaspects of hidden hunger, that is, subclinical nutrient deficien-cies without overt clinical signs of malnutrition. The relationshipbetween hidden hunger and food insecurity has been reviewedelsewhere (Tanumihardjo and others 2007). The most commonmicronutrient deficiencies worldwide are those of vitamin A,iron, and iodine. The process of adding nutritional value to acrop is called biofortification (Tanumihardjo and others 2008).

C© 2009 Institute of Food Technologists R© Vol. 8, 2009—COMPREHENSIVE REVIEWS IN FOOD SCIENCE AND FOOD SAFETY 181

CRFSFS: Comprehensive Reviews in Food Science and Food Safety

Table 1 --- Maximum recorded yield and food energy ofimportant tropical staple crops.a

Annual yield Daily energy productionCrop (tons/hectare) (kJ/hectare)

Fresh cassava root 71 1045Maize grainb 20 836Fresh sweet potato root 65 752Rice grain 26 652Sorghum grain 13 477Wheat grain 12 460Banana fruit 39 334aAdapted from EL-Sharkawy (2003).bAll grains reported as dry.

Micronutrients present in staple crops that are being targeted forbiofortification include vitamin A, iron, and zinc. Cassava hasbeen targeted for biofortification because of its unique geograph-ical distribution and its importance as a staple food. This reviewdescribes the nutritional value and improvements that researchershave achieved in the cassava plant.

Nutritional Value of Cassava RootsThe composition of cassava depends on the specific tissue (root

or leaf) and on several factors, such as geographic location, va-riety, age of the plant, and environmental conditions. The rootsand leaves, which constitute 50% and 6% of the mature cassavaplant, respectively, are the nutritionally valuable parts of cassava(Tewe and Lutaladio 2004). The nutritional value of cassava rootsis important because they are the main part of the plant consumedin developing countries. In Table 2, the proximate, mineral, andvitamin compositions of cassava roots and leaves are reported. InTable 3, the nutrient composition of raw cassava is compared toother staple crops, such as wheat and corn, and some vegetableand animal foods.

MacronutrientsCassava root is an energy-dense food. In this regard, cassava

shows very efficient carbohydrate production per hectare. It pro-duces about 250000 calories/hectare/d, which ranks it beforemaize, rice, sorghum, and wheat (Okigbo 1980). The root isa physiological energy reserve with high carbohydrate content,which ranges from 32% to 35% on a fresh weight (FW) basis,and from 80% to 90% on a dry matter (DM) basis. Eighty percentof the carbohydrates produced is starch (Gil and Buitrago 2002);83% is in the form of amylopectin and 17% is amylose (Raweland Kroll 2003). Roots contain small quantities of sucrose, glu-cose, fructose, and maltose (Tewe and Lutaladio 2004). Cassavahas bitter and sweet varieties. In sweet cassava varieties, up to17% of the root is sucrose with small amounts of dextrose andfructose (Okigbo 1980; Charles and others 2005). Raw cassavaroot has more carbohydrate than potatoes and less carbohydratethan wheat, rice, yellow corn, and sorghum on a 100-g basis(Table 3). The fiber content in cassava roots depends on the vari-ety and the age of the root. Usually its content does not exceed1.5% in fresh root and 4% in root flour (Gil and Buitrago 2002).

The lipid content in cassava roots ranges from 0.1% to 0.3% ona FW basis. This content is relatively low compared to maize andsorghum, but higher than potato and comparable to rice (Table 3).The lipids are either nonpolar (45%) or contain different types ofglycolipids (52%) (Hudson and Ogunsua 1974). The glycolipidsare mainly galactose-diglyceride (Gil and Buitrago 2002). Thepredominant fatty acids are palmitate and oleate (Hudson andOgunsua 1974). The protein content is low at 1% to 3% on a DM

basis (Buitrago 1990) and between 0.4 and 1.5 g/100 g FW (Brad-bury and Holloway 1988). In contrast, maize and sorghum haveabout 10 g protein/100 g FW. The content of some essential aminoacids, such as methionine, cysteine, and tryptophan, is very low(Table 4). However, the roots contain an abundance of arginine,glutamic acid, and aspartic acid (Gil and Buitrago 2002). About50% of the crude protein in the roots consists of whole proteinand the other 50% is free amino acids (predominantly glutamicand aspartic acids) and nonprotein components such as nitrite,nitrate, and cyanogenic compounds. The presence of cyanogeniccompounds, which predominate in bitter varieties, and processesto reduce them were recently reviewed by Montagnac and others(2009).

Minerals and vitaminsCassava roots have calcium, iron, potassium, magnesium, cop-

per, zinc, and manganese contents comparable to those of manylegumes, with the exception of soybeans (Table 5). The calciumcontent is relatively high compared to that of other staple cropsand ranges between 15 and 35 mg/100 g edible portion. Thevitamin C (ascorbic acid) content is also high and between 15 to45 mg/100 g edible portions (Okigbo 1980; Charles and others2004). Cassava roots contain low amounts of the B vitamins, thatis, thiamin, riboflavin, and niacin (Table 6), and part of these nu-trients is lost during processing. Usually the mineral and vitamincontents are lower in cassava roots than in sorghum and maize(Gil and Buitrago 2002).

The protein, fat, fiber, and minerals are found in larger quan-tities in the root peel than in the peeled root. However, the car-bohydrates, determined by the nitrogen-free extract, are moreconcentrated in the peeled root (central cylinder or pulp) (Gil andBuitrago 2002). Thus, cassava roots are rich in calories but lowin protein, fat, and some minerals and vitamins. Their nutritionalvalue is, consequently, lower than those of cereals, legumes, andsome other root and tuber crops.

Processing effects on nutritional valueProcessing cassava can affect the nutritional value of cassava

roots through modification and losses in nutrients of high value.Traditional processing techniques and several edible forms ofcassava roots are illustrated in Figure 2. Analysis of the nutrientretention for each cassava edible product (Table 7) shows that rawand boiled cassava root keep the majority of high-value nutrientsexcept riboflavin and iron. Gari is a common root product thatinvolves grating, fermenting, and roasting. Gari and products ob-tained after retting of cassava root with peel are less efficient thanboiled root in keeping nutrients of high value but are better thanproducts obtained after retting of shucked cassava roots. How-ever, the latter is richer in riboflavin than sun-dried flour. Fufu, animportant staple in Africa, is a mashed cassava root product thatis allowed to ferment with Lactobacillus bacteria (Sanni and oth-ers 2002). Medua-me-mbong is a root product that requires onlyboiling and prolonged washing. However, medua-me-mbong hasthe poorest nutritional value compared to other cassava productswith the exception of calcium content (Favier 1977).

In contrast to boiled cassava, processed root loses a major partof dry matter, carbohydrates, protein, and thus calories. Althoughraw cassava root contains significant vitamin C, it is very sensitiveto heat and easily leaches into water, and therefore almost all ofthe processing techniques seriously affect its content. Boiled cas-sava, gari, and products resulting from retting of cassava root withpeel, retain thiamin and niacin better than products obtained afterretting of shucked cassava roots, smoked-dried flour, and medua-me-mbong. Riboflavin is well retained in boiled cassava, gari,and smoked-dried cassava flour obtained after retting of cassavaroot with peel. In contrast, the losses of vitamin B2 (riboflavin)

182 COMPREHENSIVE REVIEWS IN FOOD SCIENCE AND FOOD SAFETY—Vol. 8, 2009

Nutritional value of cassava . . .

Figure 1 --- Cassava utilization (A) and consumption per day (B) throughout the world (produced by the Intl. Inst. forTropical Agriculture Geospatial lab [Ibadan, Nigeria]) based on FAOSTAT 2003 data at http://faostat.fao.org/site/609/default.aspx.

Vol. 8, 2009—COMPREHENSIVE REVIEWS IN FOOD SCIENCE AND FOOD SAFETY 183


Table 2 --- Proximate, vitamin, and mineral composition ofcassava roots and leaves.

Raw Cassava Cassavacassavaa rootsb,c,d leavesb,c

Proximate composition (100 g)Food energy (kcal) 160 110 to 149 91Food energy (KJ) 667 526 to 611 209 to 251Moisture (g) 59.68 45.9 to 85.3 64.8 to 88.6Dry weight (g) 40.32 29.8 to 39.3 19 to 28.3Protein (g) 1.36 0.3 to 3.5 1.0 to 10.0Lipid (g) 0.28 0.03 to 0.5 0.2 to 2.9Carbohydrate, total (g) 38.06 25.3 to 35.7 7 to 18.3Dietary fiber (g) 1.8 0.1 to 3.7 0.5 to 10.0Ashe (g) 0.62 0.4 to 1.7 0.7 to 4.5VitaminsThiamin (mg) 0.087 0.03 to 0.28 0.06 to 0.31Riboflavin (mg) 0.048 0.03 to 0.06 0.21 to 0.74Niacin (mg) 0.854 0.6 to 1.09 1.3 to 2.8Ascorbic acid (mg) 20.6 14.9 to 50 60 to 370Vitamin A (μg) --- 5.0 to 35.0 8300 to 11800f

MineralsCalcium (mg) 16 19 to 176 34 to 708Phosphorus, total (mg) 27 6 to 152 27 to 211Ca/P 0.6 1.6 to 5.48 2.5Iron (mg) 0.27 0.3 to 14.0 0.4 to 8.3Potassiumg (%) --- 0.25 (0.72) 0.35 (1.23)Magnesium (%) --- 0.03 (0.08) 0.12 (0.42)Copper (ppm) --- 2.00 (6.00) 3.00 (12.0)Zinc (ppm) --- 14.00 (41.00) 71.0 (249.0)Sodium (ppm) 76.00 (213.00) 51.0 (177.0)Manganese (ppm) --- 3.00 (10.00) 72.0 (252.0)aValues were obtained from the USDA Natl. Nutrient database for standard references(http://www.nal.usda.gov/fnic/foodcomp/search/). Nutrient values and weights are for theedible portion.bBradbury and Holloway (1988).cWoot-Tsuen and others (1968).dFavier (1977).eAsh refers to essential minerals as well as toxic elements such as heavy metals.fLancaster and others (1982).gOn a fresh weight (dry matter) basis (adapted from Gil and Buitrago 2002).

Table 3 --- Nutritional composition of different kinds of foods (100 g) for comparison to cassava root.a

Water Energy Energy Protein Total Ash Carbohydrate by Dietary SugarsFood (g) (kcal) (kj) (g) lipid (g) (g) difference (g) fiber (g) (g)

Cassava, raw root 59.68 160 667 1.36 0.28 0.62 38.06 1.8 1.7Potato, raw 79.34 77 321 2.02 0.09 1.08 17.47 2.2 0.78CerealsWheat flour, unenriched 11.92 364 1523 10.33 0.98 0.47 76.31 2.7 0.27Bread, wheat 35.74 266 1115 10.91 3.64 2.2 47.51 3.6 5.75Rice, white, unenriched 12.89 360 1506 6.61 0.58 0.58 79.34 --- ---Corn, sweet, white, raw 75.96 86 358 3.22 1.18 0.62 19.02 2.7 3.22Corn, yellow 10.37 365 1527 9.42 4.74 1.2 74.26 7.3 0.64Sorghum 9.2 339 1418 11.3 3.3 1.57 74.63 6.3 ---Vegetables (raw)Green beans 90.27 31 129 1.82 0.12 0.66 7.13 3.4 1.4Carrots 88.29 41 173 0.93 0.24 0.97 9.58 2.8 4.74Spinach 94 14 59 1.5 0.2 1.8 2.5 --- ---Lettuce, green leaf 95.07 15 61 1.36 0.15 0.62 2.79 1.3 0.78Soybeans, green 67.5 147 614 12.95 6.8 1.7 11.05 4.2 ---Animal productsRaw egg (white) 87.57 52 216 10.9 0.17 0.63 0.73 0 0.71Cheese, Cheddar 36.75 403 1684 24.9 33.14 3.93 1.28 0 0.52Milk (whole) 88.32 60 252 3.22 3.25 0.69 4.52 0 5.26Raw fish (trout) 71.42 148 619 20.77 6.61 1.17 0 0 0aAll values were obtained from the USDA Natl. Nutrient database for standard references (http://www.nal.usda.gov/fnic/foodcomp/search/). Nutrient values and weights are for the edibleportion.

are high during sun-drying of cassava flours (more than 50%) andduring medua-me-mbong preparation (66% lost) (Favier 1977).

Nutritional Value of Cassava Leaves

Protein and carbohydratesThe nutrient composition of cassava leaves varies in both qual-

ity and quantity depending on the variety of cassava, the ageof the plant, and the proportional size of the leaves and stems(Gil and Buitrago 2002). Cassava leaves are rich sources of pro-tein, minerals, vitamins B1, B2, and C, and carotenoids (Adewusiand Bradbury 1993). Comparison of Table 2 and 3 shows thatthe crude protein content (5 to 7 g/100 g), the crude fat (1 to2 g/100 g), and minerals (2 g/100 g) of cassava leaves surpassthose of the legumes and leafy legumes, except for soybean. Cas-sava leaf protein ranges from 14% to 40% of DM in differentvarieties (Eggum 1970). The crude protein content is compara-ble to that of fresh egg (10.9 g/100 g) and the amino acid pro-file of cassava leaf protein is well balanced compared to that ofthe egg (Jacquot 1957) except for methionine, lysine, and maybeisoleucine. Indeed, Table 8 indicates a deficit in methionine, anexcess of lysine, and a low content of isoleucine for cassava leavesin comparison with the egg. Futhermore, cassava leaves have anessential amino acid content higher than soybean protein andFAO’s recommended reference protein intake (FAO/WHO 1973;Okigbo 1980; West and others 1988).

The carbohydrate content in cassava leaves (7 to 18 g/100 g)is comparable to that of green-snap beans (7.1 g/100 g), car-rots (9.6 g/100 g), or green soybeans (11.1 g/100 g), and it ishigher than those of leafy vegetables such as green leaf lettuce(2.8 g/100 g) and New Zealand spinach (2.5 g/100 g). The car-bohydrates in cassava leaves are mainly starch, with amylosecontent varying from 19% to 24% (Gil and Buitrago 2002).

Minerals and vitaminsCassava leaves are rich in iron, zinc, manganese, magnesium,

and calcium (Wobeto and others 2006). The following varia-tions in mineral content for cassava leaf meal (CLM) have been



Table 4 --- Amino acid profile of cassava.a

Content in roots Content in leaves

% wet % dry % % wet % dry %Amino acid wt wt proteinb wt wt proteinb

Arginine 0.10 0.29 11.0 0.30 1.48 5.30Histidine 0.02 0.07 2.60 0.13 0.66 2.30Isoleucine 0.01 0.03 1.00 0.33 1.67 5.90Leucine 0.11 0.31 11.70 0.54 2.72 9.70Lysine 0.02 0.07 2.60 0.37 1.87 6.70Methionine 0.01 0.03 1.00 0.07 0.36 1.30Phenylalanine 0.01 0.03 1.00 0.18 0.92 3.30Threonine 0.01 0.03 1.00 0.27 1.35 4.80Tryptophan – 0.29 0.50 0.05 0.24 0.80Valine 0.01 0.04 1.50 0.20 0.99 3.50Alanine 0.05 0.15 5.70 0.34 1.70 6.10Aspartic acid 0.04 0.13 4.90 0.49 2.44 8.70Cysteine 0.003 0.01 0.40 0.04 0.21 0.70Glutamic acid 0.05 0.15 5.70 0.40 1.99 7.10Glycine 0.003 0.01 0.40 0.35 1.73 6.20Proline 0.01 0.03 1.00 0.18 0.88 3.10Serine 0.01 0.04 1.50 0.34 1.68 6.00Tyrosine 0.003 0.01 0.40 0.18 0.89 3.20aAdapted from Gil and Buitrago (2002).bContent of total protein (%).

reported: from 61.5 to 270 mg iron/kg DM, 30 to 63.7 mg zinc/kgDM, 50.3 to 263 mg manganese/kg DM, 6.2 to 50 mg copper/kgDM, 2.3 to 3 g sulfur/kg DM, 2.6 to 9.7 g magnesium/kg DM,0.4 to 16.3 g calcium/kg DM, and 8 to 16.9 g potassium/kgDM (Barrios and Bressani 1967; Gomez and Valdivieso 1985;Nwokolo 1987; Ravindran and others 1992; Aletor and Adeo-gun 1995; Awoyinka and others 1995; Chavez and others 2000;Madruga and Camara 2000). Cassava leaf meal is rich in iron in

Table 5 --- Mineral content of 100 g of various foods for comparison to cassava root.a

Cab Fe Mg P K Na Zn Cu Mn SeFood mg mg mg mg mg mg mg mg mg μg

Cassava, raw root 16 0.27 21 27 271 14 0.34 0.1 0.384 0.7Potato, raw 12 0.78 23 57 421 6 0.29 0.108 0.153 0.3

CerealsWheat flour, unenriched 15 1.17 22 108 107 2 0.7 0.144 0.682 33.9Bread, wheat 142 3.46 48 155 184 521 1.21 0.159 1.123 28.8Rice, white, unenriched 9 0.8 35 108 86 1 1.16 0.11 1.1 ---Corn, sweet, white, raw 2 0.52 37 89 270 15 0.45 0.054 0.161 0.6Corn, yellow 7 2.71 127 210 287 35 2.21 0.314 0.485 15.5Sorghum 28 4.4 --- 287 350 6 --- --- --- ---

Vegetables (raw)Green beans 37 1.04 25 38 209 6 0.24 0.069 0.214 0.6Carrots 33 0.3 12 35 320 69 0.24 0.045 0.143 0.1Spinach 58 0.8 39 28 130 130 0.38 0.093 0.639 0.7Lettuce, green leaf 36 0.86 13 29 194 28 0.18 0.029 0.25 0.6Soybeans, green 197 3.55 65 194 620 15 0.99 0.128 0.547 1.5

Animal productsRaw egg (white) 7 0.08 11 15 163 166 0.03 0.023 0.011 20Cheese, Cheddar 721 0.68 28 512 98 621 3.11 0.031 0.01 13.9Milk, whole 113 0.03 10 91 143 40 0.4 0.011 0.003 3.7Fish, trout, raw 43 1.5 22 245 361 52 0.66 0.188 0.851 12.6aAll values were obtained from the USDA Natl. Nutrient database for standard references (http://www.nal.usda.gov/fnic/foodcomp/search/). Nutrient values and weights are for theedible portion.bCa = calcium; Fe = iron; Mg = magnesium; P = phosphorus, K = potassium, Na = sodium; Zn = zinc; Cu = copper; Mn = manganese; Se = selenium.

comparison with liver (121 mg/kg FW) and egg yolk (58.7 mg/kgFW), although the iron from plant origin is generally less bioavail-able than iron from animal food sources. Iron and zinc contentin CLM are comparable to those reported for sweet potato leavesand peanut leaves (Table 9). Calcium content is comparable tothose of peanut and broccoli, and magnesium content surpassesthat of broccoli but is below those of peanut and sweet potato.Thus, mineral content of CLM is comparable with that of otherleaves (Wobeto and others 2006).

The vitamin content of cassava leaves (Table 2) is richer inthiamin (vitamin B1, 0.25 mg/100 g) than legumes and leafylegumes, except for soybeans (0.435 mg/100 g). The leaves havemore thiamin than several animal foods including fresh egg,cheese, and 3.25% fat whole milk (Table 6). The riboflavin (vi-tamin B2) content of cassava leaves (0.60 mg/100 g) surpassesthat of legumes, leafy legumes, soybean, cereal, egg, milk, andcheese (Table 6). The niacin content (2.4 mg/100 g) is comparableto that of maize (2 mg/100 g), and surpasses those reported forlegumes and leafy legumes, milk, and egg (Table 6). The vitaminA content of cassava leaves is comparable with that of carrotsand surpasses those reported for legumes and leafy legumes. Thevitamin C content (60 to 370 mg/100 g) of cassava leaves is highcompared to values reported for other vegetables (Table 6). Thus,the overall vitamin content of the leaves is comparable and incertain cases better than those reported for most legumes, leafylegumes, cereals, egg, milk, and cheese.

FiberThe fiber content of cassava leaves is high (Table 2) compared

to the fiber content of legumes and leafy legumes reported inTable 3 and ranges between 1 and 10 g/100 g FW. Dietary fiberis considered part of a healthy diet and can reduce problems ofconstipation. Although recent evidence is mixed, fiber may helpprevent colon cancer (Rock 2007). The rich fiber of cassava mayassist intestinal peristalsis and bolus progression (Favier 1977),but if fiber content from any source is too high, it will have



Table 6 --- Vitamin composition for 100 g of various foods for comparison to cassava root.a

Vitamin Pantothenic Vitamin Folate Vitamin Vitamin Vitamin VitaminCb Thiamin Riboflavin Niacin acid B6 total B12 A Retinol E K

Food mg mg mg mg mg mg μg μg μg RAE μg mg μg

Cassava, raw root 20.6 0.087 0.048 0.854 0.107 0.088 27 0 1 0 0.19 1.9Potato, raw 19.7 0.08 0.032 1.054 0.296 0.295 16 0 0 0 0.01 1.9

CerealsWheat flour, 0 0.12 0.04 1.25 0.438 0.044 26 0 0 0 0.06 0.3

unenrichedBread, wheat 0.2 0.373 0.311 5.19 0.82 0.119 85 0 0 0 0.19 4.9Rice, white, 0 0.07 0.048 1.6 1.342 0.145 9 0 0 0 --- ---

unenrichedCorn, sweet, 6.8 0.2 0.06 1.7 0.76 0.055 46 0 0 0 0.07 0.3

white, rawCorn, yellow 0 0.385 0.201 3.627 0.424 0.622 19 0 11 0 0.49 0.3Sorghum 0 0.237 0.142 2.927 --- --- --- 0 0 0 --- ---

Vegetables (raw)Green beans 16.3 0.084 0.105 0.752 0.094 0.074 37 0 35 0 0.41 14.4Carrots 5.9 0.066 0.058 0.983 0.273 0.138 19 0 841 0 0.66 13.2Spinach 30 0.04 0.13 0.5 0.312 0.304 15 0 220 0 --- ---Lettuce, green leaf 18 0.07 0.08 0.375 0.134 0.09 38 0 370 0 0.29 173.6Soybeans, green 29 0.435 0.175 1.65 0.147 0.065 165 0 9 0 --- ---

Animal productsRaw egg (white) 0 0.004 0.439 0.105 0.19 0.005 4 0.09 0 0 0 0Cheese, Cheddar 0 0.027 0.375 0.08 0.413 0.074 18 0.83 265 258 0.29 2.8Milk, whole 0 0.044 0.183 0.107 0.362 0.036 5 0.44 28 28 0.06 0.2Raw fish (trout) 0.5 0.35 0.33 4.5 1.94 0.2 13 7.79 17 17 0.2 0.1aAll values were obtained from the USDA Natl. Nutrient database for standard references (http://www.nal.usda.gov/fnic/foodcomp/search/). Nutrient values and weights are for theedible portion.bVitamin C = total ascorbic acid; Vitamin A is represented as retinol activity equivalents (RAE) and retinol refers to vitamin A in the preform; vitamin E = α-tocopherol; vitaminK = phylloquinone.

Figure 2 --- Different processingtechniques for whole cassava root.The edible forms of cassava root areshaded in gray (adapted from Favier1977).



Table 7 --- Nutritional value after processing 100 g of cassava root.a

Whole Peeled Boiled Baton or Flour (retting Flour (retting Washedroot root root Chikwangue Gari and no peel) and peel) cooked

Wet root (g) 100 77.0 87.6 49.2 38.5 25.3 to 29.6 27.9 to 34.0 66.8Dry matter (g) 40.0 32.3 28.3 21.6 29.7 21.3 to 25.6 20.8 to 28.7 19.0Calories 157 127 112 86 119 85 to 102 83 to 115 76Protein (g) 1.0 0.48 0.38 0.18 0.37 0.16 to 0.22 0.26 to 0.51 0.16Fat (g) 0.1 0.1 0.04 0.02 0.2 0.04 to 0.06 0.04 to 0.12 0.03Carbohydrates (g) 37.9 31.0 27.4 21.2 28.8 20.9 to 25.1 20.3 to 28.1 18.8Fiber (g) 1.3 0.6 0.5 0.4 0.6 0.4 0.3 to 0.6 0.3Ash (g) 0.90 0.57 0.46 0.21 0.34 0.16 to 0.19 0.24 to 0.50 0.06Calcium (mg) 26 13 12 7 10 6.0 to 8.0 7.0 to 15.0 11Phosphorus (mg) 47 39 31 13 18 9.0 to 11.0 10.0 to 21.0 7Iron (mg) 3.5 0.4 0.4 3.1 1.5 0.2 to 0.7 0.8 to 11.9 0.2Thiamin (μg) 72 31 20 10 18 6.0 to 12.0 13 3Riboflavin (μg) 34 18 16 21 15 10.0 to 12.0 8.0 to 21.0 6Niacin (mg) 0.73 0.52 0.41 0.16 0.33 0.11 to 0.18 0.17 to 0.37 0.03Vitamin C (mg) 33 20 1 1 2 0 0 0aAdapted from Favier (1977).

Table 8 --- Comparison of the amino acid profile of cassavawith egg, on a 16 g N basis (adapted from Favier 1977).

Cassava leavesbEgg Cassava

Amino acid proteina Jamaica Brazil rootc

% on a basis of 16 g NTryptophan 1.5 1.5 2.1 –Threonine 4.9 2.8 4.9 4.7Isoleucine 8.0 5.0 4.8 1.8Leucine 9.2 8.9 8.8 2.9Lysine 3.9 7.2 6.3 7.2Methionine 4.1 1.7 1.7 1.0Cysteine 2.4 1.4 1.0 –Phenylalanine 6.3 5.8 5.5 2.1Tyrosine 4.5 4.2 3.9 1.6Valine 7.3 5.8 5.6 2.6Arginine 6.4 5.3 6.1 14.9Histidine 2.1 2.2 2.6 1.7a Mitchell and Block (1946).b Rogers and Milner (1963).c Busson (1965).

negative effects in humans. Fiber can be a nutritional concernbecause it can decrease nutrient absorption in the body (Baerand others 1996). Excess fiber will increase fecal nitrogen, causeintestinal irritation, and reduce nutrient digestibility, in particularprotein digestibility (Favier 1977; Baer and others 1996). It isimportant to optimize the utilization of nutrients from cassavabecause nutrient deficiencies are more prevalent in regions wherecassava is used as a staple food.

Comparison of Nutritional Value of Cassava Rootsand Cassava Leaves

Table 2 compares the proximate, vitamin, and mineral compo-sitions of cassava leaves and roots. The roots are twice as rich asthe leaves in carbohydrates, but the leaves contain more protein,lipid, minerals, vitamins, and fiber. The total protein content incassava leaves is 5 to 10 times higher than in roots and is com-parable with the protein content of egg (Jacquot 1957) based ongrams of nitrogen. The protein content of cassava leaves is sim-ilar to those of sweet potato leaves and peanut leaves (Table 9)(Wobeto and others 2006). There is a significant deficit in me-thionine for both cassava leaves and roots. Cassava roots also

Table 9 --- Comparison of sweet potato leaf and peanutleaf nutrients with cassava leaf meal (CLM).a

Nutrient (100 g dry weight) CLM Sweet potato Peanut

Protein (g) 28.1 30.6 26.6β-Carotene (mg) 88.0 75 113.3Vitamin C (mg) 90.2 141.7 293.3Iron (mg) 16.7 14.7 16Zinc (mg) 5.08 3.33 5.33Manganese (mg) 14.1 --- ---Magnesium (mg) 229.3 493.3 676.7Calcium (mg) 1509.4 623.3 1236.7aAdapted from Wobeto and others (2006).

have important deficits in cysteine and tryptophan, and have rel-atively low concentrations of isoleucine, leucine, phenylalanine,tyrosine, and valine (Jacquot 1957). The leaves have tryptophanconcentrations comparable to those found in eggs, but the cys-teine content in leaves is only about half that of the egg (Jacquot1957).

Cassava roots have a large excess of arginine, while the argininecontent of leaves is relatively low and comparable to that ofeggs. Both leaves and roots have an excess of lysine, which isapproximately twice as high as what has been observed in eggs(Jacquot 1957) on a basis of 16 g nitrogen. Although cassavaroots do not have a well-balanced amino acid profile and are oflower nutritional value because of low protein quantity, cassavaleaves have good protein content. Therefore, cassava leaf proteinscould be used to improve the nutritional value of a diet primarilymade up of cassava roots. However, methionine and cysteinewould still be limiting amino acids (Gil and Buitrago 2002), so amethionine and cysteine source should be added to the diet tosupplement these 2 sulfur-containing amino acids.

The lipid content is 10 times higher in leaves than in roots. Al-though the lipids and lipid-soluble components such as chloro-phyll, resin, and xanthophylls are much more concentrated inleaves, some of them, such as volatile fatty acids, chlorophyll,and resin, do not bring significant energy to the diet. Therefore,the energy density of the lipid is lower in leaves than in roots (Giland Buitrago 2002).

The mineral content of cassava leaves is 2 to 5 times higherthan that of the roots. The roots typically have more phospho-rus, but the leaves have a greater concentration of calcium (Gil



and Buitrago 2002). The calcium content in the leaves is 100times higher than in roots and the phosphorus content is 2 to 3times higher in roots than in the leaves. Cassava leaves are moreconcentrated than the roots in vitamins and the minerals iron,potassium, magnesium, copper, zinc, and manganese. Indeed,thiamin and niacin contents are 4 to 5 times higher in leaves thanin roots, and riboflavin and vitamin C are 10 to 12 times higherin the leaves. Cassava leaves have a high quantity of vitamin A inthe form of provitamin A carotenoids. Vitamin E, however, is lowin both the leaves and roots (Gil and Buitrago 2002).

Thus, cassava roots are of lower nutritional value regardingmineral, vitamin, lipid, and protein contents, but the leaves arewell provided in these, and should be added to a diet consistingmainly of roots. Cassava leaves are typically served boiled andmixed with other vegetables, such as okra and beans. The fibercontent of leaves is greater than that of roots (3.5 times more), andso, it may limit the absorption of minerals, vitamins, and proteinsby the body and may be a restricting nutritional factor.

Cassava and Selected AntinutrientsAnalyzing the nutritional value of cassava, it appears that cas-

sava roots are a good carbohydrate source and cassava leaves aregood mineral, vitamin, and fiber sources for humans. However,cassava contains antinutrients and toxic substances that interferewith the digestibility and the uptake of some nutrients. Neverthe-less, depending on the amount consumed, these substances canalso bring benefits to humans.

Cyanide is the most toxic factor restricting the consumption ofcassava roots and leaves. Indeed, cassava, particularly its bitter va-rieties, has a cyanide level higher than the FAO/WHO (1991) rec-ommendations, which is < 10 mg cyanide equivalents/kg DM, toprevent acute toxicity in humans. Cassava leaves have a cyanidecontent ranging from 53 to 1,300 mg cyanide equivalents/kg ofDW (Siritunga and Sayre 2003; Wobeto and others 2007), andcassava root parenchyma has a range of 10 to 500 mg cyanideequivalents/kg DM (Arguedas and Cooke 1982; Dufour 1988;Siritunga and Sayre 2003); both of these are much higher thanwhat is recommended. Several health disorders and diseases havebeen reported in cassava-eating populations. Consumption of 50to 100 mg of cyanide has been associated with acute poisoningand has been reported to be lethal in adults (Halstrom and Moller1945). The consumption of lower cyanide amounts are not lethalbut long-term intake could cause severe health problems suchas tropical neuropathy (Osuntokun 1994), glucose intolerance,konzo (spastic paraparesis) (Ernesto and others 2002), and, whencombined with low iodine intake, goiter and cretinism (Delangeand others 1994).

In addition, the nitrate content in cassava leaves ranges from43 to 310 mg/100 g DM (Correa 2000; Wobeto and others 2007).Cassava-eating populations ingesting cyanide and high amountsof nitrates and nitrites have the risk of developing stomach cancer.Cassava-eating individuals tend to have a high amount of thio-cyanate in the stomach due to cyanide detoxification by the body,which may catalyze the formation of carcinogenic nitrosamines(Mirvish 1983; Maduagwu and Umoh 1988; Onyesom and Okoh2006).

Phytate (inositol hexakisphosphate) is another compoundfound in high abundance in cassava, with approximately624 mg/100 g in roots (Marfo and others 1990). Phytic acid isable to bind cations such as magnesium, calcium, iron, zinc, andmolybdenum and can, therefore, interfere with mineral absorp-tion and utilization which may affect requirements (Hambidgeand others 2008). It may also bind proteins preventing their com-plete enzymatic digestion (Singh and Krikorian 1982). However,phytic acids also have antioxidant and anticarcinogenic proper-

ties. Indeed, phytic acids can reduce free ion radical generationand thus peroxidation of membranes by complexing iron, andphytate may protect against colon cancer (Graf and others 1987).Phytate was able to reduce serum cholesterol and triglycerides inan animal model fed a cholesterol-enriched diet (Jariwalla 1999).Dephosphorylation of phytate occurs during processing of cas-sava, especially during fermentation when > 85% of phytate isremoved (Marfo and others 1990). The possibility of genetic mod-ification of cassava to reduce phytate concentrations has not yetbeen investigated (Montagnac and others 2009).

The polyphenol content (tannins) in cassava leaves is increasedwith the maturity of the plant. Cassava leaf meal has a polyphe-nol content of 2.1 to 120 mg/100 g DM (Wobeto and others2007). Polyphenols can form insoluble complexes with divalentions such as iron, zinc, and copper. They can also inactivatethiamin, bind certain salivary and digestive enzymes, and en-hance secretion of endogenous protein. Consequently, they in-hibit nonheme-Fe absorption, reduce thiamin absorption and thedigestibility of starch, protein (Silva and Silva 1999), and lipids,and also interfere with protein digestibility (Bravo 1998). How-ever, tannins also have antioxidant and anticarcinogen proper-ties that can benefit humans (Chung and others 1998; Chen andChung 2000; Alessio and others 2002; Matuschek and Svanberg2002; Nakagawa and others 2002). Catechins (catechin, cate-chin gallate, gallocatechin) and flavone 3-glycosides (rutin andkaempferol 3-rutinoside), suggested to have cardiovascular healthbenefits, have been identified in cassava roots (Buschmann andothers 2000). Anthocyanidins (cyanidin and delphinidin) havebeen identified in cassava leaves (Reed and others 1982). Pro-cessing cassava leaves reduces the polyphenol content, but 50%to 60% is retained; again, it has been suggested that geneticmodifications might well reduce total polyphenol content (Fasuyi2005).

Oxalates are antinutrients affecting calcium and magnesiumbioavailability (Massey 2007) and form complexes with proteins,which inhibit peptic digestion (Oboh 1986). Oxalate contentranges from 1.35 to 2.88 g/100 g DM for cassava leaf meal (Fon-seca 1996; Correa 2000; Wobeto and others 2007). The negativeeffect of oxalates on humans depends on the level of both oxalateand calcium in the cassava leaves. Wobeto and others (2007) re-ported that the calcium-to-oxalate ratio of 5 cassava cultivarswas greater than 0.44%, which means that oxalate levels foundin cassava leaf meal do not diminish the uptake of calcium.

Saponins are plant glycosides that are studied for their potentialhealth benefits, particularly those derived from ginseng and soy(Bachran and others 2008; Yin and others 2008). Saponins areconsidered the bioactive component of ginseng responsible forits metabolic and potential health effects (Yin and others 2008;Christensen 2009). They have antitumor properties and may of-fer synergistic effects when used in combination with drug ther-apy (Bachran and others 2008). Saponins can also act on thecentral nervous system of humans with potential therapeutic ef-fects (Nah and others 2007). Cassava leaf meal has a steroidalsaponin content ranging from 1.74 to 4.73 g/100 g DM (Wobetoand others 2007), which compares to those found for soybeans(0.07 to 5.1 g/100 g DM) (Fenwick and Oakenfull 1983; Irelandand Dziedzic 1985; Schiraiwa and others 1991), but is lowerthan those observed in alfalfa (5.6 g/100 g DM) and beet leaves(5.8 g/100 g DM) (Fenwick and Oakenfull 1983). Saponin con-tent increases in cassava leaf meal with plant maturity (Wobetoand others 2007).

Cassava leaf meal has a trypsin inhibitor content of 3.79 in-hibited trypsin unit (ITU)/mg DM at the starch accumulationphase (17-mo-old plant) and of 11.14 ITU/mg DM at the leafdevelopment phase (12-mo-old plant) (Correa and others 2004).Trypsin inhibitor has adverse effects on the pancreas. Indeed,



Liener (1977) has demonstrated that for species with a pancreascomprising more than 0.3% of the body weight, trypsin inhibitorfeeding in these species will produce an enlargement of the pan-creas. Unheated soybean trypsin inhibitor decreases the activityof rat, monkey, human, bovine, porcine, and mink trypsins at arate of 90% to 100% and rat, monkey, and human total prote-olytic activity by up to 40% (Struthers and Macdonald 1983).However, protease inhibitors may suppress carcinogenesis (Parkand others 2007).

Biofortification and Processing Methods to Improve theNutritional Value of Cassava

Cassava is a target for biofortification because of its impor-tance as a staple crop. The Bill and Melinda Gates Foundationhas supported a global effort to develop cassava germplasm en-riched with bioavailable nutrients since 2005 (BioCassava Plus[http://biocassavaplus.org/]). This initiative is called BioCassavaPlus and has 6 major objectives: to increase the minerals zincand iron, increase protein, increase vitamins A and E, decreasecyanogen content, delay postharvest deterioration, and developvirus-resistant varieties.

Biofortified cassava and protein valueCassava roots, with a crude protein content of about 1.5%, are

low in protein and some essential amino acids. To date, severaldifferent strategies have been investigated to improve the proteincontent and the amino acid composition of cassava ready-to-eat products. To engineer improved storage proteins with bal-anced amino acid composition in cassava tubers, Zhang andothers (2003a) successfully transferred a 284 bp synthetic gene(ASP1) coding for a 11.2 kDa-storage protein rich in essentialamino acids (80%) into embryonic suspensions of cassava usingAgrobacterium. They observed stable integration and expressionof ASP1 in cassava leaves and primary roots. However, contraryto the results obtained for transgenic sweet potatoes (Egnin andothers 2001) and tobacco lines (Kim and others 1992) whereASP1 had been over-expressed, no significant differences in pro-tein content and in the overall amino acid composition of cassavaleaves were observed between transgenic and wild-type cassavalines (Zhang and others 2003a). Nonetheless, analysis of 1-y-oldcassava plants from the 2nd vegetative generation grown undergreenhouse conditions showed an increase in protein contentand essential amino acid composition in storage roots of sev-eral transgenic lines (Zhang and others 2004). Two cassava rootspecific promoters related to vascular expression and secondarygrowth were identified (Zhang and others 2003b), which repre-sent valuable candidates for targetting the protein ASP1 in storageroots for genetic improvement. Currently, studies to improve thelevels of expression and accumulation of the ASP1 protein intocassava tubers are underway (Zhang and others 2004).

Researchers have also tried to improve the nutritional valueof cassava by crossbreeding wild-type varieties. Two hybridsshowed promising results regarding protein content comparedto typical cassava cultivars. The interspecific hybrid of cassava(UnB 033) and Manihot dichotoma showed higher protein con-tent (26.4%) in its leaves compared to cassava cultivars (24.25%)(Nassar and others 2004). This hybrid also resulted in a 5-timeshigher content of manganese and zinc than those of typical cas-sava cultivars (EB01). The leaf cyanide content was moderate, thatis, 128.5 ± 11.7 mg cyanide/kg FW (Nassar and others 2004). A2nd valuable hybrid was achieved by crossing with Manihot oli-gantha (Nassar and Dorea 1982). Protein content in the roots wastwice that of typical cassava cultivars. For peeled tuber, the inter-specific hybrid had a protein content of 4.5%, while the proteincontent observed in cassava cultivars ranged from 0.9% to 1.4%.

Moreover, this cassava hybrid also had richer protein contentin the peel (8.06%) than typical cassava cultivars (from 1.11% to2.09%) (Nassar and Dorea 1982). Further research has continuedto indicate the feasibility of selecting interspecific hybrids that arerich in both crude protein and amino acids to improve the proteinvalue (Nassar and Souza 2007). This interspecific cassava hybridhas an improved amino acid profile with 10 times more lysineand 3 times more methionine than the common cultivar.

Transgenic approaches to reduce cyanogen in cassava havefocused on suppressing cyanogen synthesis or acceleratingcyanogen breakdown (Siritunga and Sayre 2007). One poten-tial benefit of lowering cyanogen content is the facilitation of freecyanide assimilation into amino acids (Siritunga and Sayre 2007).Thus, reducing toxic cyanogens would have the added benefit ofimproving the protein value of the roots.

Postharvest processing to enhance proteinAnother approach that increases the protein content and qual-

ity of ready-to-eat cassava products is the development of posthar-vest processing techniques. Crude protein of cassava root andleaf by-products can be increased by solid-state fermentation viaAspergillus niger (Iyayi and Losel 2001), while also decreasingcyanogen content by up to 95% (Birk and others 1996). Smith andothers (1986) reported a significant increase in the protein con-tent of cassava roots by solid-state fermentation via Sporotrichumpulverulentum. This fungus was able to produce 30.4 g of high-quality protein per 100 g of dry cassava in 48 h at 45 ◦C. Theprotein bioavailability of fermented cassava leaves was similar tothat of soybean pressed cake diets delivered to ruminants, and,therefore, fermented cassava leaves can replace soybean as asource of protein (Bakrie and others 1996).

The development of cassava leaf protein concentrates with lowfiber could enhance the protein value of cassava meals. Crudeprotein content of cassava leaf protein concentrate is twice (42%to 43%) that of cassava leaf meal (22%) (Castellanos and others1994). Indeed, Fasuyi and Aletor (2005) reported that cassavaleaf protein concentrates had crude protein, fat, and gross energycontent higher than those of cassava leaf meals and lower crudefiber and ash contents. Table 10 shows the proximate composi-tion of cassava leaf meal and cassava leaf protein concentrate.Although methionine (2.48 g/16 g N) and cysteine were limitedin concentrates, the amino acid analysis determined that lysine(6.80 g/16 g N), leucine (9.65 g/16 g N), valine (6.30 g/16 g N),and tryptophan (2.31 g/16 g N) exceeded those of soybean, fish,and egg reported by the FAO/WHO (1973). In addition, the wa-ter absorption capacity (181.5% ± 45.4%), the fat absorption

Table 10 --- Comparison of cassava leaf protein concen-trate and cassava leaf meal on a nutritional basis.a

Variety

Cassava leafCassava leaf protein

meala concentratesb

Proximate composition 1 2 1 2

Crude protein (g/kg DM) 343.0 363.0 500.0 493.0Crude fiber (g/kg DM) 127.0 115.0 18.0 14.0Ether extract (g/kg DM) 75.0 70.0 216.0 224.0Ash (g/kg DM) 72.0 69.0 93.0 79.0Nitrogen free extract (g/kg DM) 383.0 382.0 115.0 141.0Gross energy (MJ/kg) 47.1 47.2 53.6 50.1Digestible energy (MJ/kg) --- --- 46.7 47.6aAdapted from Fasuyi (2005).bAdapted from Fasuyi and Aletor (2005); Fasuyi (2006).



capacity (19.2% ± 1.2% to 40.8% ± 1%), the emulsion capacity(32.5% ± 8.3%) and stability (42.9% ± 2.9%), the least gelationconcentration (12.5% ± 3.4%), the foaming capacity (32.1% ±7.7%) and stability (10.2 ± 4.1 cm3), and the solubility of cas-sava leaf protein concentrates in acid and alkaline media supportthe nutritive potential of cassava leaf protein concentrate (Fasuyiand Aletor 2005). These properties of cassava leaf protein con-centrate allow formulation into viscous products such as soups,protein-rich carbonated beverages, and curds; or as additives forgel formation in food products. They also show the ability of cas-sava leaf protein concentrate to form and stabilize emulsions infood products (Fasuyi and Aletor 2005). Therefore, cassava leafprotein concentrate is a good alternative protein for human andanimal nutrition, but due to the few limiting amino acids it shouldnot be the exclusive source of protein. Growth bioassays in ratsshowed that cassava leaf protein concentrate should be fed alongwith another viable protein source, because the concentrate withand without dl-methionine supplements did not support growth(Fasuyi 2005).

Regarding techniques to produce protein concentrates, ultra-filtration is more efficient than that of acidic thermocoagulation(Table 11) (Castellanos and others 1994). Indeed, ultrafiltrationprovides a better protein efficiency ratio (1.81), protein digestibil-ity in vitro (85%), and the availability of lysine (90%). It also in-creases the amino acid content, especially of lysine (5.05 g/100 gprotein), threonine (4.15 g/100 g protein), tryptophan (0.7 g/100 gprotein), and sulfur-containing amino acids. However, sulfur-containing amino acids and tryptophan are still deficient afterprocessing compared with FAO’s recommendations.

Biofortified cassava and energy densityAlthough cassava root has one of the highest rates of CO2

fixation (43 μmol CO2/m2/s) and of sucrose synthesis for a C3plant, carbohydrate yield is below its full potential. Therefore, ithas been hypothesized that cassava plants can be engineered toenhance their starch yield. The catalyst of the first dedicated, rate-limiting step of starch synthesis is ADP-glucose pyrophosphory-lase (AGPase). Its activity is a key factor for the enhancementof starch production. Muller-Rober and others (1992) observedseverely reduced starch production and accumulation of sucroseand glucose in potato tubers as a result of inhibiting AGPase ex-pression. Because bacterial AGPase activity is several hundred-folds higher than that of the cassava plant, Ihemere and others(2006) hypothesized that AGPase activity of cassava roots could

Table 11 --- Comparison of ultrafiltration and thermocoagulation processes on nutritional value of cassava leaf proteinconcentrates.a

Casein Cassava AcidicProximate analysis reference leaf Ultrafiltration thermocoagulation

Crude protein contentb (%) 22.00 43.92 42.92Lipids (%) 16.00 12.99 13.03Ash (%) 5.74 6.00 8.74Crude fiber (%) 13.19 1.06 1.72Carbohydrates (%) 43.07 36.03 33.59Cyanide content (ppm) 375 12 45Protein digestibility (%) 92 --- 85 80Available lysine (%) --- 92c 90 83Protein efficiency ratio (%) 2.50 --- 1.81 1.60Protein efficiency ratio (% of casein) 100 --- 72.4 60.0Carotene content (ppm) --- 50d 235 180aAdapted from Castellanos and others (1994).b(N ∗ 6.25).cLyophilized cassava leaf.dFresh cassava leaf.

be increased with addition of a modified bacterial AGPase. Thiswould theoretically enhance cassava root starch production. Un-der greenhouse conditions, Ihemere and others (2006) observedan AGPase activity 70% higher than that of wild types (pH 7.5,25 ◦C) and a 2.6-fold increase in total tuberous root biomassfor transgenic cassava plants. Although the density of starch wasnot modified between the transgenic and wild-type lines, an in-crease in tuberous root size and number (biomass) resulted in anincrease in total starch.

Postharvest technique to enhance energy densityAnother strategy to enhance the energy density of cassava by-

products is to add amylase. In the case of weaning food products,Treche and others (1994) demonstrated that the energy densityof cassava gruels would double, and would maintain an ac-ceptable consistency when plant amylase sources such as flourfrom malted cereals are added. The alpha-amylases hydrolyzethe starchy component of cassava gruel into maltose and dex-trins of low molecular weight and of low water-binding capac-ity, which allows a reduction in the viscosity of cassava liquidgruel.

Biofortified cassava and vitamin AVitamin A is a fat-soluble vitamin playing an important role

in vision, bone growth, reproduction, and in the maintenance ofhealthy skin, hair, and mucous membranes (FAO/WHO 2002).Identified as a widespread public health problem in 37 countriesworldwide, vitamin A deficiency is the most common cause ofchildhood blindness. It is estimated that 228 million children areaffected and 500000 children become partially or totally blindevery year as a result of vitamin A deficiency (WHO/FAO 2003).The geographical areas most affected by vitamin A deficiencyare tropical areas where cassava is a staple crop, for example,Brazil, Africa, and Asia (Shrimpton 1989). Biofortification of sta-ple crops with provitamin A carotenoids is an emerging strategyto address the vitamin A status of the poor (Tanumihardjo 2008;Tanumihardjo and others 2008).

Cassava root contains small amounts of β-carotene, a provita-min A carotenoid, which can be converted as needed into retinal,reduced to retinol, and stored in the liver esterified to fatty acids.The bioconversion of β-carotene to vitamin A in the body is nat-urally regulated and therefore β-carotene has little potential fortoxicity compared with high intake of vitamin A-fortified foods(Tanumihardjo 2008). Fortified foods, such as sugar in Guatemala



(Dary and Mora 2002) and Nicaragua (Ribaya-Mercado and oth-ers 2004), and supplements contain highly bioavailable pre-formed vitamin A and uptake is not regulated like bioconversion.Utilizing biofortified cassava with enhanced β-carotene (Figure 3)would be a sustainable strategy to reduce the prevalence of vi-tamin A deficiency in areas where cassava is a staple food. Inaddition, β-carotene can act as an antioxidant to protect cellsand tissues from the damaging effects of free radicals and singletoxygen species (Paiva and Russell 1999). For example, in Mongo-lian gerbils fed biofortified carrots or vitamin A supplements, theantioxidant status of the carrot groups was higher than the sup-plement group (Mills and others 2008). However, β-carotene’srole in cancer prevention is not completely understood; smokerstaking daily β-carotene supplements had a greater risk of lungcancer and cardiovascular disease than those not taking supple-ments (Goodman and others 2004).

Cassava also contains other interesting carotenoids that are notprovitamin A, such as the carotene lycopene and the xanthophyllslutein and zeaxanthin. Lycopene appears to be particularly effi-

Figure 3 --- Boiling the cream-colored biofortified cassavareveals the β-carotene through the deepening of color toyellow. The outer brown peel was removed before boil-ing. The underlying white peel, which is sometimes usedin livestock feed, was removed after freeze-drying andbefore flour preparation for an animal study (Howe andothers 2009).

cient at quenching the destructive potential of singlet oxygen (DiMascio and others 1989). Red cassava with substantial lycopeneis currently being distributed to small-scale farmers throughoutBrazil (Nassar 2007). Lutein and zeaxanthin might act as antioxi-dants in the macular region of the human retina (Snodderly 1995;Pauleikhoff and others 2001). The possible role of lutein in pre-venting age-related eye disease is currently under investigation.

Screening, selecting, and crossbreeding varieties of cassavawith high content of carotene is currently underway and showspotential as a dietary source (Nassar and others 2005). A broaddistribution of carotene concentrations in cassava leaves androots has been observed. Carotene content is 100 times higherin cassava leaves (ranging from 12 to 97 mg/100 g FW) thanin roots (ranging from 0.102 to 1.069 mg/100 g FW) (Iglesiasand others 1997; Chavez and others 2003). The color intensityof the cassava root and the carotene concentration are posi-tively correlated (Iglesias and others 1997). The carotene con-centration was 0.13 mg/100 g in white cassava roots, and 0.39mg/100 g, 0.58 mg/100 g, 0.85 mg/100 g, and 1.26 mg/100 gin cream, yellow, deep yellow, and orange cassava roots, respec-tively. Moreover, 5 orange cassava genotypes have been foundwith β-carotene contents ranging from 2.04 to 2.55 mg/100 gFW in the Amazonian region of Brazil and Colombia (Iglesiasand others 1997). These results are encouraging because usingconservative conversion factors of 12 μg β-carotene to 1 μg vi-tamin A proposed by the Inst. of Medicine, Food and NutritionBoard (2001), this level of β-carotene would result in 170 to210 μg vitamin A. This range of vitamin A includes the esti-mated average requirement for a young child 1 to 2 y old (thatis, 210 μg vitamin A) and represents about 40% of the estimatedaverage requirement for a woman of childbearing age (that is,485 μg vitamin A). Yellow and orange cassava roots are a viablealternative for delivering provitamin A carotenoids to vitamin A-deficient populations that consume cassava. Considering the highdaily intakes of cassava in several African countries (FAO 2006)(Figure 1B), cassava biofortified with β-carotene could readilyimpact the prevalence of night blindness due to vitamin A defi-ciency in women if widely adopted (WHO 2008) (Table 12).

However, the stability of β-carotene during different process-ing techniques needs to be further evaluated. Carotene stability isgenotypically dependent and cassava genotypes with the highestcarotene content in fresh roots are not the ones with the high-est carotene content after processing (Iglesias and others 1997).For example, comparing cream and yellow cassava root clonesafter processing, the yellow roots lost more β-carotene (Chavezand others 2004). Carotene concentration and availability is af-fected by heat-processing treatments. Iglesias and others (1997)reported that boiling, oven-drying, and sun-drying fresh cassavaroot parenchyma reduced carotene content by 34%, 44%, and73%, respectively. Chavez and others (2004) pointed out thatlyophilization and production of gari from fresh cassava root re-duced the initial β-carotene content by 25% and 80%, respec-tively. Therefore, lyophilization and boiling were most effectiveat retaining β-carotene, and sun-drying and gari production theleast.

Processing cassava increases the cis-β-carotene isomer con-tent significantly (Thakkar and others 2007; Howe and others2009). The percentage of cis content after processing was 30% to52%, which was observed for 10 genotypes of processed cassava(Thakkar and others 2007). The vitamin A value of cis-β-caroteneis generally accepted to be less than the trans isomer and is re-ported to be 23% to 61% for 9-cis-β-carotene and 48% to 74%for 13-cis-β-carotene in gerbil and rat models (Deming and oth-ers 2002). However, the bioconversion factor for β-carotene wassimilar in Mongolian gerbils fed different percentages of cis-β-carotene, that is 48% and 2.5% of total β-carotene as cis from



Table 12 --- The impact of biofortified cassava with 2 mg β-carotene/100 g fresh weight on intake of vitamin A inseveral cassava-eating African countries. Considering that the estimated average requirement of women is 485 μg/d,biofortified cassava could positively impact the prevalence of night blindness.

Prevalence of Consumption β-Carotene β-Carotene Estimated retinolCountry night blindnessa g/db content mg retainedc mg equivalentsd μg

Congo, Democratic Republic 5.4% to 9.5% 820 16.4 10.8 900 to 1800Mozambique 1.6% to 8.2% 680 13.6 9.0 750 to 1500Ghana 4.6% to 12.8% 600 12 7.9 660 to 1300Benin 4.1% to 14.7% 430 8.6 5.7 480 to 950Guinea 7.9% to 21.3% 360 7.2 4.8 400 to 800Rwanda 4.8% to 11.5% 350 7 4.6 380 to 770Madagascar 1.7% to 15.3% 320 6.4 4.2 350 to 700Nigeria 4.9% to 11.1% 310 6.2 4.1 340 to 680aThe range of prevalence in different communities of night blindness (a serious sequela of vitamin A deficiency) in women of childbearing years (WHO http://www.who.int/vmnis/vitamina/data/database/countries/en/index.html).bFAOSTAT agricultural data (database) Rome, Italy: FAO http://faostat.fao.org/site/609/default.aspx#ancor.cAn optimistic retention factor of 66% was used as reported for boiled cassava (Iglesias and others 1997).dEstimated retinol equivalents were calculated using conversion factors of 6 μg β-carotene (FAO/WHO 2002) and 12 μg β-carotene to 1 μg retinol (Inst. of Medicine 2001) to encompass arange of predicted equivalencies.

cassava (Howe and others 2009) and carrots (Mills and others2007), respectively. Bioefficacy studies in humans fed bioforti-fied cassava need to be done to determine the influence of cis-β-carotene content formed during processing on the vitamin Avalue.

Measures of β-carotene absorption efficiency and conversionto vitamin A from cassava are important parameters to studyto support the development of carotenoid-biofortified cassava.Carotenoid-biofortified cassava root (yellow cassava) was as effi-cient as β-carotene supplements in maintaining vitamin A statusin a Mongolian gerbil model (Howe and others 2009). Indeed, nodifferences were observed for total vitamin A content in the liversof gerbils fed white cassava with daily β-carotene supplementsor 45% high β-carotene cassava flour. Moreover, β-carotene wasalso found in the livers of gerbils supplemented with β-carotenein oil or fed 45% high β-carotene cassava, which implies thatthe gerbils had adequate vitamin A status. In addition, vitamin A-depleted gerbils fed about 15% and 30% high-β-carotene cassavaflour had similar vitamin A liver content, but more β-carotene wasstored in the livers of the group fed 30% high-β-carotene cassava(Howe and others 2009).

Regarding the bioavailability of carotene from cassava leaves,Wistar rats fed synthetic β-carotene or cassava leaf powder hadsimilar growth and tissue weight (Siqueira and others 2007).However, β-carotene absorption was lower from cassava leafpowder than from synthetic β-carotene. This might be due tocomplexation of β-carotene with cassava leaf proteins and to thestorage form of β-carotene within the cassava leaf matrix (Siqueiraand others 2007).

ConclusionsThe cassava plant is a valuable source of carbohydrate, pro-

tein, and vitamins. However, these macro- and micro-nutrientsare not well distributed in the plant. Cassava roots are rich incarbohydrates but poor in vitamins and protein, while cassavaleaves are an excellent source of protein and vitamins. Becausesome strains of cassava produce substantial quantities of cyanide,which makes them toxic for humans and animals, processing cas-sava into ready-to-eat products is necessary to remove cyanogensand other antinutrients. However, processing reduces cassava’snutritional value, especially when the peel is removed. In addi-tion to genetically engineering and traditionally breeding cropsto contain higher amounts of macronutrients, protein content andenergy density of cassava can be increased through processing.Research to improve the provitamin A content of cassava culti-

vars is currently underway, especially on β-carotene stability afterprocessing. Carotenoid-biofortified cassava is effective in main-taining vitamin A status in an animal model. Continued efforts toimprove its nutritional value are important because cassava is astaple food for many people in developing countries.

AcknowledgmentsThis study is in partial fulfillment of the requirements for JAM to

obtain the Diplome d’Ingenieur Agronome (equivalent to a mas-ter’s degree of Agronomic Engineering) from the Ecole NationaleSuperieure Agronomique of Montpellier SupAgro, France. Theauthors thank Julie Howe (Auburn Univ., Ala., U.S.A.) while atthe Univ. of Wisconsin-Madison for encouraging JAM during thethesis preparation stages and Harold Furr for assistance in edit-ing the manuscript. We also thank Bussie Maziya-Dixon (IITA,Ibadan, Nigeria) for providing the maps of utilization and con-sumption; Bonnie McClafferty (HarvestPlus, Washington, D.C.,U.S.A.) and JV Meenakshi (HarvestPlus, New Delhi, India) for en-couragement and coordination; and Christine Hotz (HarvestPlus,Ottawa, Canada) for helpful insights. This review was sponsoredin part by HarvestPlus contract nr 8037 and Hatch WisconsinAgricultural Experiment Station WIS04975.

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