Medicinal, Nutritional and Anti-Nutritional Properties of Cassava (Manihot esculenta): A Review

Abstract

The use of plant foods for therapeutic purposes represents one of the biggest human uses of the natural flora of the world. Cassava is any of several tropical plants belonging to the genus Manihot, of the family Euphorbiaceae and species esculenta or dulcis. They exist in varieties as Manihot esculenta (Bitter cassava) and Manihot dulcis (Sweet cassava) cultivated for their tuberous roots, which yield important food products. It is also used in the performance of various rituals and rites as well as for therapeutic purposes. Manihot esculenta Crantz, popularly known as cassava is one of the plants with various medicinal properties. Many studies showed that, due to presence of different phytochemicals cassava become remedy for different ailments like diabetes, celiac diseases, bone and neurological health, cardiovascular diseases, prostate problems and allergies, GIT problems and blood pressure etc., given that, it is important to remember cassava can be very poisonous if not prepared, processed, or cooked properly, Cassava produces cyanide and other toxicants, which are extremely poisonous compound to humans. The commonly occurring anti-nutrients in plants include; cyanide, Phytates, nitrates and nitrites, phenolic compounds and oxalates among others. As much as cassava contains various beneficial nutrients (carbohydrates, vitamins and minerals, proteins, fiber and essential amino acids), it also has anti-nutritional and toxic substances, which impair nutrient uptake and absorption of nutrients. However, it has been documented in that various processing methods reduce the levels of some of these toxic substances in cassava. Manihot esculenta Crantz is not so commonly used in herbal medicine, but indigenous people do employ it for various purposes. Because some of its potentially toxic components, sometimes it is considered as non-edible and toxic in various parts of the world. But, it is definitely one of the most useful medicinal plants. Various phytochemicals presents in this plant, numerous medicinal uses and detoxification mechanism of this neglected plant have been highlighted in this review.

Full text

Academic Journal of Nutrition 8 (3): 34-46, 2019
ISSN 2309-8902
© IDOSI Publications, 2019
DOI: 10.5829/idosi.ajn.2019.34.46
Corresponding Author: Temesgen Zekarias, Ethiopian Institute of Agricultural Research, Addis Ababa,
Ethiopia P.O. Box: 2003. Tel: +251912844964.
34
Medicinal, Nutritional and Anti- Nutritional Properties of
Cassava (Manihot esculenta): A Review
Temesgen Zekarias, Bakalo Basa and Tamirat Herago
1 23
Ethiopian Institute of Agricultural Research, Addis Ababa, Ethiopia
1
Livestock and Fisheries Development Office, Ofa Woreda, Wolaita Zone, Ethiopia
2
Ethiochicken, AGP Poultry PLC, Hawassa, Ethiopia
3
Abstract: The use of plant foods for therapeutic purposes represents one of the biggest human uses of the
natural flora of the world. Cassava is any of several tropical plants belonging to the genus Manihot, of the
family Euphorbiaceae and species esculenta or dulcis. They exist in varieties as Manihot esculenta
(Bitter cassava) and Manihot dulcis (Sweet cassava) cultivated for their tuberous roots, which yield important
food products. It is also used in the performance of various rituals and rites as well as for therapeutic purposes.
Manihot esculenta Crantz, popularly known as cassava is one of the plants with various medicinal properties.
Many studies showed that, due to presence of different phytochemicals cassava become remedy for different
ailments like diabetes, celiac diseases, bone and neurological health, cardiovascular diseases, prostate problems
and allergies, GIT problems and blood pressure etc., given that, it is important to remember cassava can be very
poisonous if not prepared, processed, or cooked properly, Cassava produces cyanide and other toxicants,
which are extremely poisonous compound to humans. The commonly occurring anti-nutrients in plants include;
cyanide, Phytates, nitrates and nitrites, phenolic compounds and oxalates among others. As much as cassava
contains various beneficial nutrients (carbohydrates, vitamins and minerals, proteins, fiber and essential amino
acids), it also has anti-nutritional and toxic substances, which impair nutrient uptake and absorption of
nutrients. However, it has been documented in that various processing methods reduce the levels of some of
these toxic substances in cassava. Manihot esculenta Crantz is not so commonly used in herbal medicine, but
indigenous people do employ it for various purposes. Because some of its potentially toxic components,
sometimes it is considered as non-edible and toxic in various parts of the world. But, it is definitely one of the
most useful medicinal plants. Various phytochemicals presents in this plant, numerous medicinal uses and
detoxification mechanism of this neglected plant have been highlighted in this review.
Key words: Anti-nutrients Cassava Medicinal value Nutrients
INTRODUCTION needs [3]. Similarly Ethiopian traditional medicine is
Since ancient times of civilization, people of the world of plants, animal products and minerals as well as magic
have been relying on medicinal plants, plant extracts and and superstition. Though most practices and treatments
their natural constituents as either prophylactic or in herbal medicine require specialists or professionals
therapeutic remedy to restore and maintain health or as an which are referred generally to as herbalists, to use plants
alternative treatment for various diseases including which are common in Ethiopia [4]. Even though, there is
analgesia and inflammatory process of diverse organs significant role of medicinal plants in supporting the
[1, 2]. Despite the immense technological advancement in Ethiopian national primary health care, little work has so
modern medicine, many people in Africa (Approximately far been made to properly document the associated
75% of the population) still rely on traditional healing knowledge and promote its practices. On the other hand,
practices and medicinal plants for their daily healthcare medicinal plants and the associated knowledge are being
composed of a number of specific skills, namely; the use

Acad. J. Nutr., 8 (3): 34-46, 2019
35
seriously depleted due to deforestation, environmental produced by the body, peripheral organ systems and
degradation and acculturation that have been taking place extremities are guaranteed a healthy flow of blood and
in the country for quite a long time. So, urgent ethno oxygen to keep those cells healthy and operating at their
botanical studies and subsequent conservation measures optimal levels. Cellular re-growth and maintenance is
are needed to salvage the medicinal plants and the improved, which means that wound healing and energy
associated knowledge from further loss [5]. levels are also increased [10].
Among medicinal plants which are used so far in
ancient times, cassava (Manihot esculenta Crantz) is one Effect of Cassava on Gastrointestinal Tract Problems:
which is a dicotyledonous plant, belonging to the family One of the other bonuses of tapioca is the wealth of
Euphorbiaceae [6]. The crop is an important source of dietary fiber it contains. Fiber has been directly linked to
carbohydrate for humans and animals, having higher improving a number of conditions within the human body,
energy than other root crops, 610 kJ/100 g fresh weight in but the most obvious is in terms of digestion. Fiber bulks
addition to remedy for various inflammatory, analgesic up stool, which helps to move it through the digestive
and carcinogenic conditions. Cassava is also significantly tract, thereby eliminating constipation, bloating, intestinal
rich in calcium, manganese, beta carotene, vitamin C and pain and even more serious conditions like colorectal
vitamin A. In spite having toxic cyanide, cassava is cancer. Furthermore, fiber helps to boost heart health by
remedy for number of ailments if prepared properly; such scraping excess cholesterol off the walls of arteries and
as digestive disorders (Gastritis, gastroduodenal ulcer, blood vessels, thereby helping to eliminate
constipation and colitis), liver disease, celiac disease and atherosclerosis and associated issues like heart attacks
diabetes [7]. Therefore, the objectives of this paper are to and strokes [11].
review on medicinal properties, nutritional composition,
anti-nutritional components and detoxification methods of Effect of Cassava on Blood Pressure: Tapioca also
cassava (Manihot esculenta). contains potassium, yet another essential mineral that the
Medicinal Values of Cassava: Plants with various that it reduces the tension and stress of blood vessels
medicinal properties have been source of attraction for and arteries. This can increase the flow of blood to parts
many scientists all over the world since thousands of of the body and reduce the strain on the cardiovascular
years. Millions of plants have been studied extensively system. This means a reduction in atherosclerosis and a
since ancient times for various phytochemicals and their much smaller chance of blood clots getting stuck and
possible medicinal uses in various disease conditions in causing fatal events like heart attacks or strokes.
human beings. Even modern day treatment strategies do Furthermore, potassium is key for fluid balance in the
not underestimate potential of herbs for various chronic body and when it is in proper balance with sodium, all of
illnesses [8]. Recently there has been a tremendous the fluid exchanges in the body can be smooth, further
increase in the use of plant based health products in boosting metabolic efficiency and energy [12].
developing as well as developed countries resulting in an
exponential growth of herbal products globally. In the Effect of Cassava on Celiac Disease: Absence of the
present era of drug development and in discovery of allergenic protein -- gluten -- makes cassava flour a good
newer drugs, molecules of many plant products are substitute for rye, oats, barley and wheat. Persons
evaluated on the basis of their traditional uses. Manihot diagnosed with celiac disease and other gluten-based
esculenta Crantz, popularly known as cassava is also one allergies can find relief in consuming foods made using
of these plants with various medicinal properties [9]. tapioca or cassava flour. Although baking cakes, bread
Effects of Cassava on Cardiovascular Diseases: One of size, it can be substituted with guar and xanthan gum [13].
the most valuable mineral contributions of tapioca is iron.
Iron is essential for the normal functioning of the human Bone and Neurological Health: Tapioca is a rich source of
body and perhaps its most significant roles are in the vitamin K, calcium and iron, all of which play important
creation of new red blood cells. Together with copper, roles in the protection and development of bones.
which tapioca also contains, iron increases the amount of Bone mineral density decreases as we age, resulting in
red blood cells in the body, thereby preventing anemia conditions like osteoporosis, osteoarthritis and general
and related conditions. With more red blood cells being weakness and lack of flexibility. If tapioca is regularly
human body requires. Potassium is a vasodilator, meaning
and other foods requires gluten to enable them to swell in

Acad. J. Nutr., 8 (3): 34-46, 2019
36
consumed, then our bones can be protected and search for new classes of drugs to combat this disorder.
developed and also maintained as we get older. The To this effect, many substances from plant source have
wealth of vitamin K does more than promote osteotrophic been found to possess anti-diabetic activity with minimal
activity, it is also important for our mental health. It has side effects and the search is on-going [17].
been shown that vitamin K can reduce the chances of There is a trend towards using natural products to
developing Alzheimer’s disease by stimulating neuronal control hyperglycemia and associated pathologies.
activity in the brain. Alzheimer's often occurs due to a lack Cassava has been rediscovered as a medicinal agent.
of activity or mental stagnation; vitamin K keeps neural Cassava has been reported to have a broad spectrum of
pathways active and engaged and free of free radicals that biological activities; the anti-oxidant, oxygen radical
can cause a breakdown of brain tissues [14]. scavenging activity of cassava (And its extracts) is
Effect of Cassava on Prostate Problems and Allergies: The beneficial effects of cassava in diabetes have been
The long-term observations on the medicinal effect of confirmed by a number of studies in experimental animals
Manihot esculenta are related to prostate problems [7].
and allergies. Several decades of observations in
Western European countries and a few clinical tests have Nutritional Value of Cassava: Composition of cassava
shown cassava to be effective in treating prostate depends on the specific tissue (root or leaf) and on
problems ranging from infections and swelling to cancer several factors, such as geographic location, variety, age
[15]. It appears that consumption of cassava in large of the plant and environmental conditions. The roots and
quantities in the diet has no biochemically evident leaves, which constitute 50% and 6% of the mature
therapeutic benefit in castration-resistant prostate cancer. cassava plant, respectively, are the nutritionally valuable
A single case may not be adequate to test a hypothesis. parts of cassava [18]. The nutritional value of cassava
However in the absence of scientific publications about roots is important because they are the main part of the
the effects of cassava on prostate cancer, this plant consumed in developing countries. In Table 3, the
scientifically tested case would act as a basis of proximate mineral and vitamin compositions of cassava
evidence that can be used by health care workers who roots and leaves are reported.
look after patients with castration-resistant prostate
cancer as well as by patients with the disease until Nutritional Value of Cassava Roots
further research is done and better evidence is available Macronutrients: Cassava root is an energy-dense food.
[16].
Effect of Cassava on Diabetes: In modern medicine no
satisfactory effective therapy is still available to cure
diabetes mellitus, which is a syndrome resulting from a
variable interaction of hereditary and environmental
factors and characterized by abnormal insulin secretion
(Type- 1) or insulin receptor or post-receptor (Resistance,
Type- 2) events affecting metabolism involving
carbohydrates, proteins and fats in addition to damaging
â-cells of pancreas, liver and kidney in some cases.
Several attempts have been made to tackle hyperglycemia
and comorbidities (Cardiovascular, renal, hepatic,
ophthalmic, neurological and osteopathic-, endothelial-
and sexual-dysfunction, etc.) that come with increased
blood glucose level. To this effect drugs like sulfonylurea
that stimulate insulin secretion by the islets and
-glucosidase inhibitors that augment glucose utilization
and suppress glucose production have been developed.
Despite the limited efficacy of these therapies, it is also
not devoid of side effects, therefore necessitating the
mainly due to the presence of phenolics and flavonoids.
In this regard, cassava shows very efficient carbohydrate
production per hectare. It produces about 250000
calories/hectare/d, which ranks it before maize, rice,
sorghum and wheat [18]. The root is a 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
percent of the carbohydrates produced are starch [19].
83% is in the form of amylopectin and 17% is amylase [20].
Roots contain small quantities of sucrose, glucose,
fructose and maltose [21].
Cassava has bitter and sweet varieties. In sweet
cassava varieties, up to 17% of the root is sucrose with
small amounts of dextrose and fructose [17, 18]. Raw
cassava root has more carbohydrate than potatoes and
less carbohydrate than wheat, rice, yellow corn and
sorghum on a 100-g basis (Table 1). The fiber content in
cassava roots depends on the variety and the age of the
root. Usually its content does not exceed 1.5% in fresh
root and 4% in root flour [19]. The lipid content in
cassava roots ranges from 0.1% to 0.3% on a FW basis.

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Table 1: Maximum recorded yield and food energy of important tropical staple crops (Source: [25]
Crop Annual yield (tons/hectare) Daily energy production (kJ/hectare)
Fresh cassava root 71 1045
Maize grain 20 836
Fresh sweet potato root 65 752
Rice grain 26 652
Sorghum grain 13 477
Wheat grain 12 460
Banana fruit 39 334
Table 2: Amino acid profile of cassava [19]
Content in roots Content in leaves
---------------------------------------------------------------------- ---------------------------------------------------------------------
Amino acid % wet weight % dry weight % protein % wet weight % dry weight % protein
Arginine 0.10 0.29 11.0 0.30 1.48 5.30
Histidine 0.02 0.07 2.60 0.13 0.66 2.30
Isoleucine 0.01 0.03 1.00 0.33 1.67 5.90
Leucine 0.11 0.31 11.70 0.54 2.72 9.70
Lysine 0.02 0.07 2.60 0.37 1.87 6.70
Methionine 0.01 0.03 1.00 0.07 0.36 1.30
Phenylalanine 0.01 0.03 1.00 0.18 0.92 3.30
Threonine 0.01 0.03 1.00 0.27 1.35 4.80
Tryptophan – 0.29 0.50 0.05 0.24 0.80
Valine 0.01 0.04 1.50 0.20 0.99 3.50
Alanine 0.05 0.15 5.70 0.34 1.70 6.10
Aspartic acid 0.04 0.13 4.90 0.49 2.44 8.70
Cysteine 0.003 0.01 0.40 0.04 0.21 0.70
Glutamic acid 0.05 0.15 5.70 0.40 1.99 7.10
Glycine 0.003 0.01 0.40 0.35 1.73 6.20
Proline 0.01 0.03 1.00 0.18 0.88 3.10
Serine 0.01 0.04 1.50 0.34 1.68 6.00
Tyrosine 0.003 0.01 0.40 0.18 0.89 3.20
This content is relatively low compared to maize and exception of soybeans. The calcium content is relatively
sorghum, but higher than potato and comparable to rice. high compared to that of other staple crops and ranges
The lipids are either non polar (45%) or contain different between 15 and 35 mg/100 g edible portion. The vitamin
types of glycolipids (52%). The predominant fatty acids C (Ascorbic acid) content is also high and between 15 to
are palmitate and oleate [22]. The protein content is low at 45 mg/100 g edible portions [18, 14]. Cassava roots
1% to 3% on a DM basis and between 0.4 and 1.5 g/100 g contain low amounts of the B vitamins, that is; thiamin,
FW [23]. riboflavin and niacin and part of these nutrients is lost
In contrast, maize and sorghum have about 10 g during processing. Usually the mineral and vitamin
protein/100 g FW. The content of some essential amino contents are lower in cassava roots than in sorghum and
acids, such as methionine, cysteine and tryptophan, is maize. The protein, fat, fiber and minerals are found in
very low (Table 2). However, the roots contain an larger quantities in the root peel than in the peeled root.
abundance of arginine, glutamic acid and aspartic acid However, the carbohydrates, determined by the
[19]. About 50% of the crude protein in the roots nitrogen-free extract, are more concentrated in the peeled
consists of whole protein and the other 50% is free amino root (Central cylinder or pulp) [19].
acids (Predominantly glutamic and aspartic acids) and
non-protein components such as nitrite, nitrate and Nutritional Value of Cassava Leaves
cyanogenic compounds. The presence of cyanogenic Protein and Carbohydrates: The nutrient composition of
compounds, which predominate in bitter varieties and cassava leaves varies in both quality and quantity
processes to reduce them were recently reviewed by depending on the variety of cassava, the age of the plant
Montagnac et al. [24]. and the proportional size of the leaves and stems [19].
Minerals and Vitamins: Cassava roots have calcium, iron, vitamins B1, B2 and C and carotenoids [26]. Cassava leaf
potassium, magnesium, copper, zinc and manganese protein ranges from 14% to 40% of DM in different
contents comparable to those of many legumes, with the varieties [27]. The crude protein content is comparable to
Cassava leaves are rich sources of protein, minerals,

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38
that of fresh egg (10.9 g/100 g) and the amino acid profile those reported for most legumes, leafy legumes, cereals,
of cassava leaf protein is well balanced compared to that egg, milk and cheese [31].
of the egg [28] except for methionine, lysine and may be
isoleucine. Furthermore, cassava leaves have an essential Fiber: The fiber content of cassava leaves is high
amino acid content higher than soybean protein and compared to the fiber content of legumes and leafy
FAO’s recommended reference protein intake [18]. legumes and ranges between 1 and 10 g/100 g FW.
The carbohydrate content in cassava leaves (7 to 18 g/100 Dietary fiber is considered part of a healthy diet and can
g) is comparable to that of green-snap beans (7.1 g/100 g), reduce problems of constipation. Although recent
carrots (9.6 g/100 g), or green soybeans (11.1 g/100 g) and evidence is mixed, fiber may help prevent colon cancer
it is higher than those of leafy vegetables such as green [32]. The rich fiber of cassava may assist intestinal
leaf lettuce (2.8 g/100 g). The carbohydrates in cassava peristalsis and bolus progression but, if fiber content from
leaves are mainly starch, with amylase content varying any source is too high, it will have negative effects in
from 19% to 24% [19]. humans. Fiber can be a nutritional concern because it can
Minerals and Vitamins: Cassava leaves are rich in iron, increase fecal nitrogen, cause intestinal irritation and
zinc, manganese, magnesium and calcium [10]. The reduce nutrient digestibility, in particular protein
following variations in mineral content for cassava leaf digestibility [31].
meal (CLM) have been reported: from 61.5 to 270 mg
iron/kg DM, 30 to 63.7 mg zinc/kg DM, 50.3 to 263 mg Anti-Nutritional Properties of Cassava
manganese/kg DM, 6.2 to 50 mg copper/kg DM, 2.3 to 3 g Anti-Nutrients in Cassava Leaves and Roots: Despite the
sulfur/kg DM, 2.6 to 9.7 g magnesium/kg DM, 0.4 to many benefits of eating tapioca in various forms, it is
16.3 g calcium/kg DM and 8 to 16.9 g potassium/kg DM important to remember that cassava can be very
[29, 30]. poisonous if not prepared, processed, or cooked properly.
Cassava leaf meal is rich in iron in comparison with Cassava produces cyanide, which is an extremely
liver (121 mg/kg FW) and egg yolk (58.7 mg/kg FW), poisonous compound to humans and animals. Therefore,
although the iron from plant origin is generally less while tapioca that you buy in a store is perfectly healthy
bioavailable than iron from animal food sources. Iron and to eat, don’t attempt to process or eat tapioca grown or
zinc content in cassava leaf meal are comparable to those found in the wild, unless you are instructed by someone
reported for sweet potato leaves and peanut leaves. who is very familiar with a healthy way of processing it
Calcium content is comparable to those of peanut and [33].
broccoli and magnesium content surpasses that of Anti-nutrients are also referred to as nutritional
broccoli but is below those of peanut and sweet potato. stress factors. These factors may either be in the form
Thus, mineral content of cassava leaf meal is comparable of synthetic or natural compounds and they impede
with that of other leaves [10]. nutrient absorption. The commonly occurring anti
The vitamin content of cassava leaves is richer in nutrients in plants includes; cyanide, phytates, nitrates
thiamin (Vitamin B1, 0.25 mg/100 g) than legumes and and nitrites, phenolic compounds and oxalates among
leafy legumes, except for soybeans (0.435 mg/100 g). others. As much as cassava contains various beneficial
The leaves have more thiamin than several animal nutrients, it also has anti-nutritional and toxic substances,
foods including fresh egg, cheese and 3.25% fat whole which impair nutrient uptake and absorption of nutrients.
milk. The riboflavin (Vitamin B2) content of cassava However, it has been documented in that various
leaves (0.60 mg/100 g) surpasses that of legumes, leafy processing methods reduce the levels of some of these
legumes, soybean, cereal, egg, milk and cheese. The toxic substances in vegetables [34].
niacin content (2.4mg/100 g) is comparable to that of maize Generally Cassava contains anti-nutrients, such as
(2 mg/100 g) and surpasses those reported for legumes phytate, nitrate, polyphenols, oxalate and saponins that
and leafy legumes, milk and egg. The vitamin A content of can reduce nutrient bioavailability. However, some of
cassava leaves is comparable with that of carrots and these compounds can also act as anti-carcinogens
surpasses those reported for legumes and leafy legumes. and antioxidants depending on the amount ingested.
The vitamin C content (60 to 370 mg/100 g) of cassava Phytate interferes with the absorption of divalent
leaves is high compared to values reported for other metals, such as iron and zinc, which are essential
vegetables. Thus, the overall vitamin content of the nutrients. The aqueous and ethanolic extracts of raw
leaves is comparable and in certain cases better than cassava tuber contain alkaloids, flavonoids, tannins and
decrease nutrient absorption in the body. Excess fiber will

Acad. J. Nutr., 8 (3): 34-46, 2019
39
Table 3: Nutritional composition of cassava roots and leaves Source: [23]
Proximate composition Cassava roots Cassava leaves
Food energy (kcal) 100-149 91
Moisture (g) 45.9-85.3 64.8-88.6
Dry weight g) 29.8-39.3 19-28.3
Protein (g) 0.3-3.5 1.0-10.0
Lipid (g) 0.03-0.5 0.2-2.9
Total carbohydrate (g) 25.3-35.7 7-18.3
Dietary fiber(g) 0.1-3.7 0.5-10.0
Ash (g) 0.4-1.7 0.7-4.5
Vitamins
Thiamin (mg) 0.03-0.28 0.06-0.31
Riboflavin (mg) 0.03-0.06 0.21-0.74
Niacin (mg) 0.6-1.09 1.3-2.8
Ascorbic acid (mg) 14.9-50 60-370
Vitamin A ( g) 5.0-35.0 8300-11800
Minerals
Calcium (mg) 19-176 34-708
Phosphorus (mg) 6-152 27-211
Iron (%) 0.3-14.0 0.4-8.3
Potassium (%) 0.25-0.72 0.35-1.23
Magnesium (ppm) 0.03-0.08 0.12-0.42
Copper (ppm) 2.00-6.00 3.0-12.0
Zinc (ppm) 14.00-41.00 71.0-249.0
Sodium (ppm) 76.00-213.00 51.0(177)
Manganese (ppm) 3.00-10.00 72.0-152.0
anthocyanosides, anthraquinone, phlobatinnins and
saponins but, do not contain cardiac glycosides. The
cassava leaves contain lot of antinutrients, such as
tannins, oxalate, phytate and trypsin inhibitors [35].
Cassava leaves are nutritious but it contains more
anti-nutrients that cause toxicity unless processed [36].
Phytates: Phytate is an anti-nutrient that controls the
intracellular signaling and forms the phosphate storage
part in plant seeds; although it binds proteins and
minerals in the gastrointestinal tract making them
unavailable for absorption and utilization by the body.
In particular, phytate has a binding effect on multivalent
metal ions, including zinc, iron and calcium, all of which
are important nutrients. This leads to formation of salts
that are highly insoluble and minerals that are less
bioavailability [37].
Tannins/Phenolics: Flavonoids form a set of compounds
that are referred to as polyphenolics, such as tannins,
which are anti-nutritional agents. Data on polyphenols
found in cassava leaves is expressed by researchers as
tannin equivalents while employing a non-specific assay
[33, 38]. Polyphenols, which are antioxidants, bind various
minerals in food, reducing its bioavailability. In addition,
they impair the functionality of digestive enzymes, thus
slowing digestion and in some cases cause proteins
precipitation [39]. The levels in plants vary and may be
influenced by factors like; germination, storage and
processing time. Increase phenolic compounds levels are
known to decrease fertility among women of reproductive
age by altering the levels of hormones, hence affecting
the early pregnancy stages [40].
Cyanide: The cyanide, which occurs as cyanogenic
glucosides, is a toxic compound that has been associated
with adverse health outcomes among humans. The level
of cyanide in cassava surpasses 10 mg/kg dry weight,
which is the recommended maximum consumption level by
the World Health Organization and the Food and
Agricultural Organization. This makes cassava leaves
highly toxic for consumption by humans. The content of
cyanide in cassava roots is much lower (10 times lower)
as compared to the leaves, an aspect that explains its
utilization for methodological standardization [41].
The level of cyanide is cassava is defined by the type of
cassava of reference, with each variety exhibiting different
levels of this toxic compound. Excessive intake of cyanide
is known to cause cretinism and goiter which are
associated with iodine deficiency [42]. This is as a result
of the production of thiocyanate as a by-product of
cyanide metabolism, which restricts the uptake of iodide
by thyroid gland [43]. As such, prior to consumption, it is
important for cassava leaves to be properly processed in
view of reducing the content of cyanide [44].
Oxalates: Oxalates are di-carboxylic acids that are present
in plant-based foods such as cassava, which have a
negative impact on the bioavailability of magnesium and
calcium. These anti-nutritional agents bind calcium,
leading to formation of crystals or excretion through urine.
The crystals that form (Calcium oxalate) majorly contribute
to kidney stones. It is highly advisable to reduce oxalates
intake and promote the intake of calcium among
individuals who are risk of kidney stones [45]. Cassava
leaves have an oxalate concentration of between 1.35 and
2.88 g/100 g of total dry weight [33].
Less attention had been given towards the
importance of the levels of oxalates in foods until recently,
as it was believed that only 10% of the calcium excreted
daily was due to dietary calcium [45]. The impact that
oxalates have on the health of humans is highly
dependent on the calcium available and the oxalate levels
consumed. According to Wobeto et al. [33] cassava’s
calcium-to-oxalate ratio is a high of 5, which surpasses the

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40
Table 4: The anti-nutrient levels of Manihot esculenta in mg/100 g of wet
weight
Manihot esculenta Phytates Oxalates Tannins Cyanide Nitrates
191.25 15.74 0.65 25.69 3.58
recommended 0.44%, below which calcium uptake is
endangered. As such, the level of oxalates in cassava
leaves have no negative impact on calcium uptake.
Nevertheless, groups that consume cassava leaves
should consider breeding different varieties of cassava to
obtain types that have lower levels of oxalates and
enhanced calcium. Other anti-nutrients including nitrates,
phytates, oxalates, polyphenols and saponins also reduce
the bioavailability of nutrients. The anti-nutrient
compounds also act as antioxidants and anti-carcinogens
depending on amounts consumed [31].
Nitrates and Nitrites: Nitrates occur naturally in most
soils and water sources; hence they are taken up by
growing plants. Leafy vegetables are the main
contributors of nitrates in diets and contribute about 75%
of the total foods ingested. Nitrates in themselves are not
toxic at the levels present in most foods but the toxicity
occurs when the nitrates are reduced to nitrites [46].
When high levels of nitrates in vegetables are ingested,
they are changed to nitrite. This can result in the
development of blue-baby disease, metheamoglobinemia,
or cancer [47]. However, since nitrates and nitrites are
water soluble, some amounts may be lost through
leaching during the preparation process. Further, most of
the nitrites present are oxidized to nitrate and upon
cooking, they leach out of the vegetable [48]. Green leafy
vegetables with increased levels of nitrates include;
spinach, radishes, lettuce, beets and celery, among others
[49].
Detoxification Properties of Cassava
Detoxification of Cassava Cyanogens
Biotechnology and Conventional Breeding: The presence
of toxic cyanogenic glycosides in cassava constitutes a
critical limiting factor to its use, together with other
considerations such as deficiency in some essential
nutrients and high deterioration rate. Detoxification
through breeding/genetic engineering and processing
offers an opening to scaling this debacle that confronts
economic and social prospects of the plant. This reduces
the exposure to cyanogenic compounds and thus lowers
or eliminates the risk of cyanide intoxication [50].
Autolysis of linamarin is extensively relied on in
detoxifying cassava (especially during processing) for
human consumption. This is triggered by maceration or
cell disruption, which results in bringing linamarase
into contact with the glycosides and hydrolyses them.
The activity of linamarase, however decreases a few days
after harvest [51]. The reasons responsible for this
lowered activity is not certain, but has been related to the
formation of enzyme inhibiting compounds such as
polyphenols [52].
The hindrance to attaining optimal use of cassava
can best be achieved when cyanide-free strains are
obtained from breeding programmes because they do not
occur naturally [23]. Cyanide-free strains would make
cassava reliably safe, more acceptable and marketable and
reduce cyanide effluent from cassava processing plants
[53]. Genetic engineering, using antisense technology,
has been used to block the synthesis of linamarin,
resulting in cyanide-free cassava. Dramatically reduced
linamarin content in leaves and roots of wild-types has
also been achieved by genetic manipulation [53-55].
The downside to this development, however, is the
likelihood of having reduced plant yield as a result of
stalling the synthesis of linamarin [56]. The resulting
transgenic plant could not produce roots because of a
lack of ammonia, which is produced by the roots using
linamarin as its source. Obstructing the synthesis of
linamarin also leaves the plant vulnerable to animal and
insect attack since linamarin is used in a defensive
mechanism [57]. Besides these technical and research
issues, controversy and skepticism surrounding
genetically modified organisms [58] may pose a challenge
to the introduction and use of transgenic “strains” in part
of the world. Genetic transformation and molecular
biology techniques have not made any commercially
remarkable impact even though they present great
potential. Conventional methods of breeding, which
involves selection and crossing varieties to yield
desirable traits, have also been applied in a bid to reduce
the cyanogen content in cassava. Previous studies by
Iglesias et al. [59] showed reduced cyanogen content in
some clones compared to their parental variety. The low
vegetative multiplication rate and the fact that several
factors affect the quality of planting material; however,
complicates and makes this method quite difficult to
implement [60].
Processing: Aside of genetic/breeding interventions
embarked upon to obtain significantly reduced cyanogens
content in cassava, biological detoxification methods
such as enzyme and bacteria action and physical methods
such as processing present suitable options to attaining

Acad. J. Nutr., 8 (3): 34-46, 2019
41
a similar goal. These methods have resulted in favours contact of the enzymes with its substrate. In the
tremendous and significant economic gains as far as the case of submerged fermentation, this process synergises
use of cassava is concerned. Detoxification essentially with leaching of cyanogen to detoxify the cassava roots
involves two separate treatments; first is one that [73].
enhances the contact between linamarase and its Three major types of fermentation are widely
substrates (Cyanohydrins) followed by a second that practiced in different parts of Africa; these are the grated
volatilizes the HCN produced as a result of contact root fermentation, mould fermentation of roots in
between the enzyme and its substrates. Processing largely heaps and fermentation of roots under water [61].
promotes these conditions that are required for adequate Fermentation of cassava roots is largely acidic (pH 3.8)
detoxification. Cassava processing improves shelf-life, while that for leaves is alkaline (pH 8.5) with lactic acid
detoxifies the roots, facilitates transport and enhances bacteria dominating the microbiota [74]. Some lactic
consumer acceptability [61, 62]. acid bacteria and yeast possess linamarase activity and
The short coming of processing as a detoxification are recognized for significantly contributing to
method, conversely, is that a lot of them result in loss of cyanogenic glycoside breakdown during fermentation of
nutrients [63]. Enzymatic removal of cyanogens is cassava [75].
commonly accomplished by treating samples with These microorganisms are capable of utilizing the
enzymes isolated from bacteria to breakdown cyanogenic cyanogens and their degradation products [76] thereby
compounds into acetone cyanohydrins, which ridding their substrate of these noxious substances and
decomposes spontaneously to HCN or by treating with rendering the substrate safe. Previous reports have
plant cell wall-degrading enzymes such as cellulolytic and shown a remarkable reduction in cyanogenic potential of
pectolytic enzymes to enhance the release of linamarin cassava following fermentation. More than 50 % and 35 %
and allow for more contact time with linamarinase [64]. reduction in cyanogen levels has previously been
The latter principle has been exploited in the production achieved in the production of gari and fermented cassava
of cassava starch [65]. The HCN produced is flour respectively [77, 78] have also reported up to 41%
subsequently dissolves readily in water or is released into reduction in cyanide levels during fermentation. Other
the air [63, 66]. researchers have also reported varying levels of decline
The enzyme hydrolyses of the cyanogens is in cyanogen potential after fermentation [79]. Indeed
sensitive to changes in pH [67] with pH > 5 favoring the reduction in cyanide level in all cases depends on the
breakdown. Certain species of Bacillus,Pseudomonas initial cyanide levels of the raw material.
and Klebsiella oxytoca have been reported to utilize
cyanide as the only source of nitrogen under aerobic and Soaking: Soaking cassava roots usually precedes
anaerobic conditions thus breaking it down into non-toxic fermentation, cooking or drying. Retting, followed by sun
compounds [68]. Bacillus subtilis KM05 isolated from drying is exploited as a method of processing cassava
cassava peels has been used to detoxify cassava flour roots in some parts of Africa. This technique of long
[63] by degrading linamarin into HCN and subsequently soaking cassava roots in stagnant or slow running ponds
releasing ammonia. In another study by Nwokoro and and causes the breakdown of tissues and extraction of the
Anya [69] cassava flour samples treated with linamarinase starchy mass [80]. The water softens the cells of the
enzyme isolated from L.delbrueckii resulted in an 89.5% cassava roots, provides a larger medium for fermentation
reduction in cyanide content. and facilitates leaching of cyanogenic glycosides.
Fermentation: Fermentation as a method of processing but has little effect on bound cyanide. Soaking peeled or
primarily enhances nutritional properties through unpeeled cassava roots is practiced in the northern and
biosynthesis of vitamins, essential amino acids and central regions of Malawi [62] to produce ‘waluwa’ and
proteins, by improving protein quality and fiber ‘kanyakaska’ which are dried and pounded into flour
digestibility as well as the enhancement of micronutrient and used to prepare a local delicacy called ‘kodowole’.
bioavailability and degradation of anti-nutritional factors The cassava roots come out of the process having lost
[70, 71] Fermentation of cassava, both aerobic and between 31.0% and 49.9% (For unpeeled and peeled roots
anaerobic, favors the hydrolysis of linamarin into HCN. respectively) of their cyanogenic potential. Other studies
Even though details of the mechanism involved are have resulted in remarkably significant reduction in
unclear [72] fermentation softens the cells of the roots and cyanogenic glycosides after soaking [81].
The method removes a substantial amount of free cyanide

Acad. J. Nutr., 8 (3): 34-46, 2019
42
Cooking: Boiling cassava roots, which is often for direct becomes immobilized thus preventing its interaction with
consumption with accompaniments such as soups and linamarase in the drying medium [52, 87]. Extending the
stews, is commonplace in most areas where cassava is period of drying with higher moisture levels have been
produced for culinary purposes. Cooking is processing observed to result in enhanced linamarin breakdown, thus
cassava roots by this method is preceded by peeling, explaining the fact that fast drying rates result in lower
cutting into11 chunks/dicing and washing. Disruption of detoxification while slower rates result in higher cyanogen
cell membrane during cooking largely occurs between removal [52]. Cyanohydrin levels remain high in the
60 and 70°C and not long after that linamarase is product during drying because of the enzyme hydrolysis
destroyed, making contact with its substrate inadequate that takes place, especially when root pieces are humid.
for thorough detoxification. This causes a possible Their levels could be reduced further by thorough drying
retention of cyanogenic glycoside levels [82]. well below 12 or 13% moisture. HCN levels conversely
Cyanohydrins from aldehydes, may also exist even after remain low during drying because it volatilizes as a result
cooking because they are thermo-stable [50]. As a result, of its exposure to heat [87].
boiling is often criticized and an ineffective standalone
method of detoxifying cassava roots and hence is CONCLUSION AND RECOMMENDATIONS
preferred as a method of processing sweet cassava,
although the heat favors rapid evaporation of HCN Phytochemical and pharmacological investigations
produced [83]. studied out in the plant Manihot esculenta in various
Indeed, the extent of reduction of cyanogenic literature sources reveal its multidisciplinary usage. It is
glycosides has been related to the cooking time [82, 84] very essential to have a proper documentation of
have reported cooking to reduce cyanogen potential by medicinal plants and to know their potential for the
50 -70% in Southern Asia [85]. Introduced a soaking and improvement of health and hygiene through an eco-
squeezing stage prior to cooking and achieved a friendly system. Manihot esculenta Crantz, most
remarkable reduction in cyanogenic potential of up to popularly known as cassava is one of the most forgiving
70%. Boiling/cooking has also been applied to process and adaptable plants. It is not so commonly used in herbal
cassava leaves and resulted in 75 % reduction [84] and in medicine, but indigenous people do employ it for various
some cases more than 90% reduction in cyanide level [86]. purposes. Because of some of its potentially toxic
Roasting Drying: Cassava roots have been processed in it is considered as non-edible and toxic in various parts of
to a lot of dried products. Drying is widely accepted as an the world but, it is definitely one of the most useful
efficient processing method for cassava roots as it results medicinal plants. Therefore, based on the above
in products that are shelf-stable with relatively reduced conclusion the following recommendations are forwarded:
cyanide content. In as much as advanced systems of further pharmacological experiments should be performed
drying exist, sun drying is the most adopted method in in the plant to extend to the next level of clinical trial to
cassava processing regions of Africa and as such generate novel drugs. Processing cassava into ready-to-
sun-dried cassava products are the most common [61]. eat products is necessary to remove cyanogens and other
Dried cassava pieces can be processed further into other anti-nutrients. In addition to genetically engineering and
preferred forms. Drying or roasting cassava is usually traditionally breeding cassava to contain higher amounts
preceded by peeling, chipping, chunking or grating before of macronutrients, it is necessary to process cassava to
spreading out in the sun to dry. Detoxification is achieved reduce toxic cyanide and improve protein content and
by the drying mechanism in itself does not play any energy density. Continued efforts to improve its
significant role in the detoxification process but the tissue nutritional value are important because cassava is staple
disruption that precedes drying. The efficiency of cyanide food for many people in developing countries.
removal during drying is dependent on moisture content
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