Occurrence of mycotoxins in cassava (Manihot esculenta
Crantz) and its products
Yann Adjovi, B. J. G. Gnonlonfin, Sylviane Bailly, Jean-Denis Bailly, Souria
Tadrist, Olivier Puel, Isabelle Oswald, A. Sanni
To cite this version:
Yann Adjovi, B. J. G. Gnonlonfin, Sylviane Bailly, Jean-Denis Bailly, Souria Tadrist, et al.. Occurrence
of mycotoxins in cassava (Manihot esculenta Crantz) and its products. International Journal of Food
Safety, Nutrition and Public Health, 2015, 5, pp.217-247. 10.1504/IJFSNPH.2015.070157. hal01594243
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Int. J. Food Safety, Nutrition and Public Health, Vol. 5, Nos. 3/4, 2015
Occurrence of mycotoxins in cassava (Manihot
esculenta Crantz) and its products
Yann C.S. Adjovi*
Research Centre in Food Toxicology,
INRA, UMR1331, Toxalim,
F-31027 Toulouse, France
and
Universite de Toulouse III,
INP, Toxalim, F-31076 Toulouse, France
and
Laboratoire de Biochimie et de Biologie Moleculaire,
04, P.O. Box 0320, Cotonou, Benin, Africa
Email: yann.adjovi6@gmail.com
*Corresponding author
Benoit J.G. Gnonlonfin
Biosciences, Eastern and Central Africa,
International Livestock Research Institute,
12, P.O. Box 30709, Old Naivasha Road, Nairobi, Kenya
Email: bgnonlonfin@yahoo.fr
Sylviane Bailly, Jean-Denis Bailly,
Soraya Tadrist, Olivier Puel and
Isabelle P. Oswald
Research Centre in Food Toxicology,
INRA, UMR1331, Toxalim,
F-31027 Toulouse, France
and
Universite de Toulouse III,
ENVT, INP, Toxalim, F-31076 Toulouse, France
Email: s.bailly@envt.fr
Email: jd.bailly@envt.fr
Email: souria.tadrist@toulouse.inra.fr
Email: Olivier.Puel@toulouse.inra.fr
Email: ioswald@toulouse.inra. fr
Ambaliou Sanni
Laboratoire de Biochimie et de Biologie Moleculaire,
04, P.O. Box 0320, Cotonou, Benin, Africa
Email: ambaliou.sanni@gmail.com
Copyright © 2015 Inderscience Enterprises Ltd.
217
218
Y.C.S. Adjovi et al.
Abstract: Contamination of foods with mycotoxins represents an important
limit to the income of farmers and a major public health concern especially in
tropical countries. Cassava represents an important part of the diet of
many people in this part of the word and the most important smallholder
crop in Africa. Fungal contamination of cassava products can occur at
pre-harvest level or after, during processing, according to the conditions
(moisture, temperature, competition with other microorganisms). Such fungal
contamination can also lead to mycotoxin accumulation. The most common
fungi found in cassava products belong to genera Rhyzopus, Aspergillus,
Fusarium, Phoma and Penicillium. Their corresponding mycotoxins could also
be found in cassava. However, until now, the correlation between the presence
of Aspergillus flavus and its toxins aflatoxins remains unclear. In this review,
we broadly report data about mycotoxins contamination of cassava (Manihot
esculenta Crantz) and its derivatives, with a special emphasis on aflatoxins.
Keywords: cassava; mycotoxin; aflatoxins; tropical region.
Reference to this paper should be made as follows: Adjovi, Y.C.S.,
Gnonlonfin, B.J.G., Bailly, S., Bailly, J-D., Tadrist, S., Puel, O., Oswald, I.P.
and Sanni, A. (2015) ‘Occurrence of mycotoxins in cassava (Manihot esculenta
Crantz) and its products’, Int. J. Food Safety, Nutrition and Public Health,
Vol. 5, Nos. 3/4, pp.217–247.
Biographical notes: Yann C.S. Adjovi is a Research Assistant, PhD and
specialist of biochemistry and molecular biology applied to food security.
Benoit J.G. Gnonlonfin is a PhD and specialist of sampling strategy and
aflatoxin analysis.
Sylviane Bailly is a DVM and specialist of fungal eco-physioloy and
morphological analysis.
Jean-Denis Bailly is a DVM, PhD, and Professor in Food Hygiene at the
National Veterinary School of Toulouse.
Soraya Tadrist is a technician and specialist in purification of fungal
metabolites and mycotoxin analysis.
Olivier Puel is a research engineer, PhD and specialist of molecular analysis of
mycotoxin biosynthesis and fungal metabolome.
Isabelle P. Oswald is an agronomist, PhD and specialist of mycotoxin toxicity
and on their impact on immune function. She is the leader of the team
Biosynthesis and Toxicity of Mycotoxins within Toxalim unit.
Ambaliou Sanni is a biochemist and molecular biologist, Professor, head of
Biochemistry and Molecular Biology unit and head of PhD School in
University of Abomey-Calavi (Benin).
Occurrence of mycotoxins in cassava (Manihot esculenta Crantz)
1
219
Introduction
Mycotoxins are toxic secondary metabolites of filamentous micromycetes. Exposure to
mycotoxins can lead to both acute and chronic toxicities ranging from death to
deleterious effects on the central nervous, cardiovascular, pulmonary and digestive
systems. Mycotoxins may also be carcinogenic, mutagenic, teratogenic and
immunosuppressive (FAO, 2001). Some, such as aflatoxin B1, also have synergistic
effect with the hepatitis B virus in the etiology of liver cancer and probably interact with
HIV/AIDS (Williams et al., 2004).
Problems caused by mycotoxins have consequences on trades and economy. On
domestic and international markets, economic losses due to the existence of regulations
occur at various levels along the processing chain, from the producers to the commodity
brokers, processors and the animal producers (FAO, 2004).
Different foods such as cereals, spices and dried crops can be contaminated by
mycotoxins. Cereal products (corn and wheat), peanuts, cottonseeds and mixed feeds
appeared to be the most commonly contaminated foodstuffs. In tropical areas, aflatoxins
could be found at high levels in several crops such as maize [30–920 |ag/kg (Rustom,
1997) and 24 |ag/kg in 2006 in Kenya (Johnni et al., 2011)] but also in dried fish, dried
chili peppers, corn and peanuts in Thailand, at levels of 772, 996, 2,700, and over
12,000 ^g/kg, respectively (Shank et al., 1972). In temperate areas, the most common
mycotoxins are deoxynivalenol (DON) and its derivatives found in cereal grains and
animal feeds, fumonisins that are frequent contaminants of maize, zearalenone (ZEA) in
the cereals and silage. These three kind of toxins are produced in the fields, before
harvest of grains. Patulin can also contaminate apple and its derivates (Marczuk et al.,
2012).
Within this context, the quality and safety of agricultural products and food are
surveyed to limit consumer exposure.
Cassava (Manihot esculanta Crantz) is the staple food and source of nourishment for
more than one billion people worldwide (FAO, 2011) especially in Africa, Asia and
South America. Because of its high water contain, cassava must be transformed into
various derivatives to ensure its availability outside harvest periods and to reduce
post-harvest losses. The cassava products can be fermented, dried or roasted, and the
most common form is chips. This product serves as food for both human and animals and
can be maintained up to one year (Wareing et al., 2001).
However, tropical climate of some geographical areas of cassava production may
contribute to fungal development of many species and subsequent toxinogenesis on such
raw material (Bankole and Adebanjo, 2003). Moreover, the processing conditions and
storage premises are not always well adapted to protect cassava products from secondary
contamination and/or fungal development.
Considering the importance of this crop in developing countries and subsequent
possible fungal toxin production, various studies have attempted to evaluate cassava
products contamination with moulds and mycotoxins. A number of potentially
mycotoxigenic fungi have been isolated from cassava products and mycotoxins
contamination of cassava has been documented but the potential sanitary risk of such
contamination was not fully assessed (Westby, 2002).
The goal of this review is to report the available data regarding the contamination of
cassava products by moulds and mycotoxins.
220
2
Y.C.S. Adjovi et al.
Mycotoxins and toxinogenic fungi
2.1 Definition and health impacts
Mycotoxins are highly toxic substances. They can contaminate agricultural commodities
before or after harvest (Cole et al., 2003). Their presence in foods and feeds is linked to
cancers, immune system defects, growth retardations, liver diseases and death. Adverse
effects of mycotoxins poisoning have been well documented over the years (Wu, 2004).
The presence of mycotoxins also limits incomes of farmers due to existing export trade
restrictions. Factors that contribute to mycotoxins contamination of foods and feeds are
mainly related to environmental conditions and especially humidity and temperatures that
may favour fungal proliferation and toxinogenesis.
2.2 Toxinogenic species
Mycotoxins are secondary metabolites of fungi that are microorganisms lacking
chlorophyll production and depend on substrate to grow. They may act as saprophytes
that breakdown non-living organic materials and transport available nutrients to the
growing hyphae or parasites attacking and exhibiting pathogenic effect on both plants and
animals (Adaku et al., 2012). Fungi have a worldwide distribution, and are able to grow
in a wide type of environments, including deserts, hyper saline environments (Sancho
et al., 2007), deep sea (Hawksworth, 2006), rocks (Mueller and Schmit, 2006), and under
a broad range of conditions such as extremely low and high temperatures. They have
been shown to be able to survive to intense ultra violet and cosmic radiations encountered
during space travel (Alexopoulos et al., 1996).
Many fungi are pathogens of plants, while a smaller number are pathogenic for
animals, including human beings. They attack and destroy raw and manufactured
products for post-harvested steps resulting in great economic losses (Atanda et al., 2011).
Food fungi were classified into three groups namely: field, storage and advanced
decay fungi.
Field fungi invade developing and mature seeds before harvest. They include species
belonging to Alternaria, Fusarium, Helminthosporium, Cladosporium, Chaetomium and
Curvularia genera by decreasing order of predominance (Jarvis, 1971; Magro et al.,
2010). All field fungi require high moisture content between 20% to 25% to grow and are
therefore referred as hygrophilic fungi (Jesenska et al., 1993; Magro et al., 2010). The
same authors gave the representative species of field fungi as Alternaria alternata,
Cladosporium herbarum, Fusarium graminearum, Rhizppus nigricans and Trichoderma
lignorum. The latest is ranked in the top 10 of plant pathogens in the world (Dean et al.,
2012).
The fungi that invade grains after harvest and during storage mainly belong to
Aspergillus, Penicillium, Phoma, Sporendonema genera and some species of Fusarium
(Jarvis, 1971; Elegbede, 1978; Rasch et al., 2010; Magro et al, 2010). They are able to
grow on substrates in which the moisture content has been reduced to 13% to 18%,
equivalent to an equilibrium relative humidity of 70% to 85% (Jarvis, 1971; Codex
Alimentarius, 2012). This group, known as mesophilic storage fungi, has the following
representative species: Aspergillus flavus, A. fumigatus, A. terreus, Paecilomyces varioti,
Penicillium aurantiogriseum, P. citrinum and P. viridicatum. Others are Aspergillus
ochraceus and A. versicolor (Lillehoj, 1973; Codex Alimentarius, 2012). The main
221
Occurrence of mycotoxins in cassava (Manihot esculenta Crantz)
factors influencing their development are moisture content in stored food, temperature,
storage length, degree of invasion before arrival at the storage site, amount of foreign
material and insects and mites activities (Ominski et al., 1994; Codex Alimentarius,
2012). According to fungal physiology, mycotoxins contamination may start in fields,
and ultimately cuts across the value chain, affecting farm families, traders, markets and
finally, consumers. There are more than 400 mycotoxins produced by a plethora of fungi.
Toxin profiles differ across crops, countries and regions within countries (Cole et al.,
2003). Among the fungal genera, Fusarium, Aspergillus and Penicillium are considered
as the most important because of their ability to produce mycotoxins such as fumonisin
(FB), aflatoxin (AF), ochratoxin (OTA), ZEA and trichothecenes (DON, T-2 toxin,
nivalenol) (Adaku et al., 2012). Table 1 shows major mycotoxins and their producers.
Table 1
Mycotoxins, fungi and toxicity
Mycotoxins
Aflatoxins
Citrinin
Fungal species
Toxicity
Aspergillus section Flavi: Hepatotoxic, Carcinogenic, and
A. flavus;
other harmful effects to human,
poultry, pigs and cattle can be
A. parasiticus
noticed.
References
Wu (2004)
Penicillium citrinum;
P. expansum
Nephrotoxic
Peraica et al.
(1999)
Cyclopiazonic
acid
Penicillium cyclopium,
Peniccillium camemberti
Aspergillus flavus
Induces hyperemia and
ulceration of proventriculus;
focal necrosis in the liver and
spleen; increased weight of
pancreas and kidney.
Dorner et al.
(1983), Gentles
et al. (1999)
Deoxynivalenol
Fusarium graminearum;
F. culmorum
Provokes barley acute human
toxicosis, internal disturbances,
growth inhibition in pigs.
Pestka (2008)
Diacetoxyscirpe
nol
Fusarium
sporotrichioides;
F. poae
Provokes ill-thrift, decrease
feed consumption, slow
growth, diarrhea and abortion.
Pronk et al.
(2002)
Ergot alkaloids
Claviceps purpurea
Responsible for
vasoconstriction, neural
disorders, skin necrosis and
agalactia.
Dyer (1993),
Cross (2003)
Fumonisins
Ochratoxin A
Patulin
Fusarium moniliforme; F. Suspected to cause esophageal
verticillioides;
cancer in human pulmonary
edema in pigs and
F. proliferatum
leukoencephalomalacia
inequines.
Marasas (2001)
A. ochraceus;
A. carbonarius;
Penicillium verrucosum
May be carcinogenic, kidney
damage and other harmful
effects in pigs and poultry.
Gentles et al.
(1993)
P. expansum;
A. clavatus
Neurotoxic; responsible for
haemorrhages of lung and
brain.
Peraica et al.
(1999)
Notes: The most dangerous mycotoxin is aflatoxin B1 and the principal producer is
Aspergillus flavus. The toxicity of other mycotoxins is tested in animals and its
consequences on human health are studying.
222
Y.C.S. Adjovi et al.
Table 1
Mycotoxins, fungi and toxicity (continued)
Mycotoxins
Fungal species
Toxicity
References
Peniccillic acid
Peniccilium viridicatum
sterigmatocystin
Aspergillus
nidulanellusnidulellus, A.
glaucus, A. sydowii, A.
versicolor
Carcinogenic (group 2B),
hepatotoxic; causes toxemia.
IARC (1987),
Sun et al. (2002)
Fusarium
sporotrichioides;
F. poae
Alimentary aleucy toxic;
reduces inflammatory response
and inhibits protein DNA,
RNA synthesis in poultry.
Sokolovic et al.
(2008)
T-2 toxin
Tenuazonic acid
Zearalenone
Alternaria alternata
Fusarium. culmorum;
F. graminearum
Toxic to kidneys and liver; can Pandiyan et al.
cause abortion; reduces growth (1990), Bernhoft
et al. (2004),
rate and immunity.
Keblys et al.
(2004)
Causes hematological disorder Steyn and Rabier
in human (onyaalai); collapse (1976), Zhou and
in cardiovascular system,
Qiang (2008)
dysplasia, nausea in mouse and
rat.
Estrogenic toxin causes
infertility in animals;
JECFA (2001)
Notes: The most dangerous mycotoxin is aflatoxin B1 and the principal producer is
Aspergillus flavus. The toxicity of other mycotoxins is tested in animals and its
consequences on human health are studying.
2.3 Human and animals toxicity with regulatory consequences
Mycotoxins concerns have grown during the last few decades because of their
implications in human and animal health, productivity, and the cost of their management
for trades.
This has significant consequences in both developed and developing countries.
Worldwide, the primary concern with mycotoxins contamination of the food supply chain
is human health (Shier et al., 2005; Wild, 2007; Shephard, 2008b; Bryden, 2012)
followed by the impact on animal health and production (Shier et al., 2005).
2.3.1 Human toxicity
The implications of ingestion or absorption of mycotoxins on human health include
immunosuppression, impaired growth, various cancers and death depending on the type,
the period of exposure and the amount of toxins ingested. Moreover, a synergistic effect
between mycotoxins exposure and some important diseases in the African continent such
as malaria, kwashiorkor, hepatitis B and HIV/AIDS have been suggested (Williams et al.,
2004; Wagacha and Muthomi, 2008). The most toxic and dangerous mycotoxins are
aflatoxins. Indeed, aflatoxin B1 (AFB1) is the most potent hepatic carcinogen known in
mammals and has been classified by the International Agency for Cancer Research in the
group I of molecules that are carcinogenic for both human and animals (IARC, 1993).
AFB1 also displays immunosuppressive properties (Meissonnier et al., 2008) and is
involved in growth impairment observed in children (Gong et al., 2004; Khlangwiset
Occurrence of mycotoxins in cassava (Manihot esculenta Crantz)
223
et al., 2011). Exposure to aflatoxin in Sub-Saharan Africa is very frequent. In some areas,
99% of tested children display aflatoxin residues in their blood (Gong et al., 2002) and
this high exposure contributes to appearance of chronic hepatomegaly in children (Gong
et al., 2012). Contamination of food by very high levels of aflatoxin can also lead to fatal
consequences such as the death of 125 people in Kenya (Lewis et al., 2005; Probst et al.,
2007).
Some studies on fumonisins, that appear to be the second most important mycotoxin
family in tropical countries, have found their major role in the etiology of human
oesophageal cancers in regions where this ailment is abnormally highly prevalent. A role
in neurological diseases in human population can also be probably considered. Due to the
structural similarity between fumonisins and sphingosine which is a principal constituent
of cell membranes, fumonisins are the first known naturally occurring inhibitors of
sphingolipid biosynthesis (Gamal et al., 2012).
2.3.2 Animal toxicity
Mycotoxin-contaminated feeds reduce animal growth, productivity and may lead to
death. AFB1 is the most toxic aflatoxin, followed in decreasing order by AFM1, AFG1
and AFB2 to AFG2. The toxicity of aflatoxin G1, G2 and B2 are respectively 50%, 80%
and 90%. In animals, AFB1 causes liver necrosis at centro-lobular level.
The effects of aflatoxins on animal health vary according to the species. Animals such
as veals, chicken, duckling, guinea pigs and porks are sensitive to AFB1 whereas goats,
sheeps, rats and mices are relatively resistant (Patterson and Allcroft, 1970). Among
birds, the susceptibility varies according to the species. In turkeys, the disease known as
‘Turkey X disease’ resulted in the death of 20,000 turkeys after renal dilatation and
congestion in England in 1960 (Stevens et al., 1960). Cats are particularly sensitive, with
death occurring between 48 and 72 hours. This sensitivity is also noted in ducklings when
exposed to AFB1 with a LD50 of 0.56 mg/kg. There may be a reduction in income from
poultry, pigs and cattle as a result of death due to either carcinogenesis or aflatoxicosis by
aflatoxin B1 (Nyathi et al., 1987).
In Africa, the second most common mycotoxin is fumonisin B1. The prevalence of
fumonisins has been reported to be 100% or close to it in all surveillance data that have
been reported on maize from different parts of Africa (Bankole et al., 2006). Fumonisins
have been implicated in a number of animal diseases such as leucoencephalomalacia in
equines, which involves a massive liquefaction of the cerebral hemisphere of the brain
with neurological manifestations such as abnormal movement, aimless circling, and
lameness. These toxins are also responsible for porcine pulmonary edema, rat liver cancer
and haemorrhage in the brain of rabbits (Marasas, 1995).
Fumonisin B1 is followed by ZEA. This mycotoxin acts as a xenoestrogen and is
considered as an endocrine disruptor (Schoevers et al., 2012) that could significantly
damage thymus and spleen of mice (Liang et al., 2010).
In temperate regions DON toxicity studies in animals have targeted a specific
toxicological outcome or mechanism, and thus provided insight into potential hazards
(Pestka and Smolinski, 2005). Many studies of host resistance, mitogen-induced
lymphocyte proliferation, and humoral immune response have yielded a common theme
that trichothecenes are both immuno-stimulatory and immunosuppressive depending on
dose, exposure frequency and timing relative to functional immune assay (Pestka et al.,
2004).
224
Y.C.S. Adjovi et al.
Table 1 shows the important mycotoxins (aflatoxins, fumonisins, desoxynivalenol,
ZEA, and patulin) and effect on health.
2.4 Economicals consequences
Mycotoxins importance as public health issue has led various countries to setup
maximum tolerated limits for these compounds in foods. The existence of such
regulations can represent a strong limit to international trades and lead to important
economic losses.
In the case of Africa, the European Union regulation on aflatoxins costs $670 million
each year due to limitation of exports of cereals, dried fruits, and nuts (Annan, 2001).
Food products rejected for exportation are consumed locally and can lead to exposure to
high concentrations of toxins. For instance, the greatest recorded fatal
mycotoxins-poisoning outbreak caused by mycotoxin (aflatoxin) occurred in Africa in
2004 (Wu, 2004).
In developed economies, where mycotoxins contamination in foods and feeds chains
is tightly regulated to reduce human and animal exposure, the additional costs to meet the
economic burden of regulating the foods and feeds supply is supported by the producer
and/or the consumer. In a study of Wu (2004), an empirical economic model for
mycotoxins impact suggests that, if a regulation limit of fumonisins in foods of 2 mg/kg
would be adopted internationally, the export losses for USA, China and Argentina would
range between $20 and $40 million annually, with a total loss of about $100 million. If a
more stringent fumonisin regulations, such as the formerly proposed EU standard of
0.5 mg/kg, is adopted as a worldwide norm, the estimated losses linked to limitation of
corn export would rise to $170 million in the USA, $60 million in China, and $70 million
in Argentina for a total of about $300 million each year.
This could also have consequences on animal health and production (Shier et al.,
2005; Bryden, 2012). Indeed, those developing regulations for the risk management of
mycotoxins seek to balance the need to protect human health with economic concerns
that requires a very detailed risk assessment process (Kuiper-Goodman, 2004).
Another difficulty could result from the long period that is often required for
transportation of crops from rural and commercial farmers of the commodity to the
distribution centre of the importing country. Inappropriate transporting and storage
conditions may offer considerable opportunities for moulds to grow, leading to alteration
and/or mycotoxin appearance. Economic losses related to fungal and mycotoxin
contamination are also a result of the decreased yields associated with mould infection of
plants, costs incurred by inspection, sampling and analysis before and after shipment,
losses attributed to compensation paid in case of claim, farmers subsidies to cover losses,
research training and extension program costs and costs of detoxification (Sibanda
et al., 2010).
As a result, mycotoxins appear as important contaminants with significant impacts on
human and animal health, but that also have also economic and international trade
implications (Wu, 2004; Bryden, 2007; Wild, 2007; Wild and Gong, 2010). The supply
of meat, milk and eggs, the human food products of animal production, can also be
adversely affected by mycotoxins due to their adverse effects on breeding performances.
Occurrence of mycotoxins in cassava (Manihot esculenta Crantz)
3
225
Importance of cassava
3.1 Production of cassava in the world
Ranked 10th among the top 20 agricultural commodities produced in the world, and third
most important food crop in tropical regions after rice and maize (FAO, 2011), cassava
represents an important part of the diet of almost one billion people or who it represents
one main source of energy. Its global production is estimated at 250 million tons (FAO,
2011). Figure 1 shows the geographic distribution of cassava production and exporting
countries in the world. Among producing regions, Africa accounts for more than half
(150 Mt) of the global supply. Nigeria, which alone accounts for about a third of the
production of Africa (45 Mt), is also by far the world’s largest producer followed by the
Democratic Republic of Congo (DRC) with about 15 Mt, Angola and Ghana (12 Mt
each) and Mozambique (9 Mt). Asia contributes to about one third of world’s production,
60% being produced by Thailand (about 25 Mt) and Indonesia (22 Mt). China and
Vietnam appear as increasing producers and each of these countries produces between
9 and 8 million tons per year since 2008. India, now the third largest producer of cassava
in Asia, also displays a continuous growing production with more than 30% of increase
between 2006 and 2010. In Latin America and the Caribbean, the production is relatively
stable between 2006 and 2009 at about 35 Mt, which represents nearly 20% of world
supply. Brazil dominates with about 70% of regional production (Gamal et al., 2012).
The other two significant producers are Paraguay (approximately 5 Mt) and Colombia
(1.5 to 1.7 Mt) (UNCTAD, 2012).
Cassava production is primarily used for human consumption. It represents staple
food and a major contributor to food security in producing areas and Africa consume
almost its entire production. Cassava products, fermented or not, are also devoted to
foodstuff (Akoroda, 2007). Cassava can be used for animal feed but this is done mainly
in Brazil and Colombia where about half of the production is devoted to such use. The
remainder is dedicated to food of local population and exportation to Nigeria, China, the
Netherlands and Spain.
3.2 Economic importance
On the economic front, 10% of the world production of cassava is traded. In recent years,
flows to Asia were strongly accelerated to such an extent that Asia accounts for 98% of
world imports and 97% of exports. It was in 2001 that, for the first time, imports of
cassava in developing countries have surpassed developed countries. Since then,
international flows focused on Asia, especially China.
The Asiatic continent is the largest importer of cassava roots with 6.247 Mt out of a
total of 6.392 Mt in 2010. China alone imports more than 92% of Asian importations, and
purchases have tripled since 2001. This interest in cassava is explained by the dynamism
of the ethanol industry: China is now the third largest producer of ethanol after the USA
and Brazil. Beijing’s decision in 2007 not to use grain to produce biofuels in order to
preserve their food security has undoubtedly boosted demand for cassava. Currently, 50%
of ethanol production is from cassava and sweet potato (FAO, 2010).
226
Y.C.S. Adjovi et al.
Main destination for world exports of cassava for a long time, mainly as pellets for
animal feed, the European Union, which applies for annual tariff quotas for imports of
cassava and tapioca starch, became a minor player with volumes that fluctuate according
to the European grain market (FAO, 2010). Since 2009, the abundance of community
supplies of feed grains has contributed to the decline of cassava importations (UNCTAD,
2012).
Figure 1
Cassava production and exportation flux in the world
Notes: Africa is the first cassava producer with in order: Nigeria, Democratic Republic of
Congo, Angola, Ghana and Mozambique. Asia is in second ringed with: Thailand,
Indonesia, Vietnam, China and India. The third position is occupied by America
Caribbean: Brazil, Paraguay and Colombia. Other low producers are also
encountered on the continents mentioned above.
For commercialisation, Asia accounts for 97% of world exports. Thailand leading
with 4–4.5 Mt per year followed by Cambodia, Vietnam, Indonesia, Costa Rica
Paraguay and Uganda.
Thailand is a leading exporter of cassava and dominates the market. It exports annually
about 4 Mt of roots, and approximately 4.5 million tons of chips, of which 4.4 Mt to
China (UNCTAD, 2012). Volumes are also relatively stable in Indonesia with
145,000 tons of cassava exported while Vietnam and to a lesser extent Cambodia
recorded a significant increase in exports: Vietnam went from 304,000 tons in 2006 to
1 Mt in 2010. On the same way, Cambodia, virtually non-existent before 2008, when the
country embarked on the production of ethanol, amounted to 345,000 tones in 2009 and
128,000 tons in 2010 (UNCTAD, 2012).
Occurrence of mycotoxins in cassava (Manihot esculenta Crantz)
227
Outside Asia, Costa Rica exported 92,000 tons in 2010 mainly towards the US market
(70% of the exports) while Paraguay devotes all of its exports to Brazil (UNCTAD,
2012).
In Africa, Uganda is the only African country that is distinguished by its exports to
Burundi, Rwanda and the Democratic Republic of Congo (UNCTAD, 2012).
Like many other commodities, the export prices of flour and starch in Thailand
(Bangkok FOB), have been appreciated especially during the second half of the last
decade. Over the last 11 years, they have been multiplied by more than three and went
from $146.15 per ton in January 2000 to $509.21 per ton in May 2011, with a highest
cost recorded in August 2010 at $630 per ton following a poor harvest in Thailand. Since
then, prices are ranging between $500 and $600 a ton.
3.3 Nutritional importance
The drive for attainment of foods self-sufficiency in developing countries requires total
exploitation of all potential sources of nourishment. Hence, the search for an alternative
will go a long way in solving the problem of competition. Cassava (Manihot esculenta
Crantz) is rich in carbohydrates but low in protein. The food crisis of 2008 has
strengthened African Governments in their policy development of cassava cultivation and
promotion of consumption, especially by mixing flour of cassava and wheat to make
bread. Besides its own favourable characteristics such as high yields per hectare, low
input requirement or tolerance to drought, cassava has the advantage of being able to stay
in the ground for over one year and then be harvested in case of food shortages or rising
grain prices. Cassava makes a greater contribution to total calorie intake in Africa than
maize or sorghum. The roots are normally processed or consumed while the peels are
being discarded as waste. However, these parts could be also used in animal feeding.
Cassava leaves, as by-products of roots harvest, are (depending on the varieties) rich in
proteins, minerals, vitamins B, C and carotenes (Ravindrian and Blair, 1992; Adewusi
and Bradbury, 1993; Aletor and Adeogun, 1995). The only handicap remains fragility
and once harvested they cannot be easily transported.
Regarding peels, Iyayi and Tewe (1994) reported that cassava peel meal could make
up to 40% of the diet of fryer rabbits without any deleterious effects on performance.
Cassava peels, leaves, petioles and stems have been incorporated at different levels in
livestock feeds (Ikwelle, 1999; Tewe and Kasali, 1986). The main factor limiting the use
of cassava roots is their cyanide content that affects nutrient utilisation in livestock
animals. Agunbiade et al. (2002) reported the hydrocyanic content of cassava peel meal
to be 27 mg/kg. Symptoms of cyanide toxicity include increased respiratory rhythm,
increased pulse rate and spasmodic muscular movements (Oke, 1969). Several processing
methods like cooking, sun drying and roasting have been used to reduce the cyanide
content of cassava products and improve cassava utilisation in practical livestock
nutrition (Iyayi and Tewe, 1994; Oguntimein, 1992; Omole, 1977).
3.4 Cassava derivatives
In Africa, Caribbean and Pacific (ACP), cassava is consumed as fresh roots or products
of primary processing after being peeled, grated or soak into water to ferment (attieke,
lafun) and as wet mash (fufu) or varied dry products (tapioca, gari, chip/crumbs/chunks,
228
Y.C.S. Adjovi et al.
or milled into flour) (Akoroda, 2007); it is also a source of income in urban areas.
Cassava consumption was about 115 kg per capita in 2010 in the ACP countries against
18 kg for the rest of the world (UNCTAD, 2012). Ugwu and Ay (1992) has classified
cassava products into nine groups as follows: S cooked fresh roots; S – cassava flour:
fermented and unfermented; from chips or lafun; S granulated roasted cassava (gari); S
granulated cooked cassava (attieke, kwosai); S fermented pastes; S sedimented starches; S
drinks (with cassava components); S leaves (cooked as vegetable); S medicines. Their
processes are presented in Figure 2(a).
Cassava products can be subdivided into two groups: fermented and non-fermented
products.
Fermentation corresponds to the chemical transformation of organic substances into
simpler compounds under the action of enzymes that are produced by microorganisms
such as moulds, yeasts, or bacteria. Enzymes act by hydrolysing, a breaking down or
predigesting phenomenom, complex organic molecules to form smaller (and in the case
of foods, more easily digestible) compounds and nutrients (Steinkraus, 1997). Fermented
foods are food substrates that are invaded or overgrown by edible microorganisms whose
enzymes, particularly amylases, proteases, and lipases hydrolyse the polysaccharides,
proteins and lipids to non-toxic products with flavours, aromas and textures pleasant and
attractive for the human consumer (Steinkraus, 1997). The longer the fermentation
period, the stronger is the sour taste (FAO, 2005).
In this group the following products can be found: gari, fermented chips, fufu, lafu,
attieke; and in non-fermented group, cooked roots, tapioca and leaves.
Gari is the most consumed product in West Africa. Demand increases and its
processing capacity is reinforcing across the region. The second derivative, fufu, is a
popular staple in Ghana, Nigeria, Sierra Leone and other parts of West Africa. Fufu is the
second most consumed/sold cassava product in West Africa. Fufu is traditionally made
from fresh cassava that is pounded. In recent years, the demand for instant fufu flour has
increased since it is faster to prepare and its conservation is longer.
Other traditional products: lafun, granuled products tapioca and attieke are popular
processed products made from cassava in West Africa (Padonou et al., 2009; FAO,
2005). Most African traditional products were obtained after a sun-drying step.
Purpose of drying foods is to reduce the amount of free water in the substrate since
free water is available for the growth of microorganisms. A significant reduction of water
content in a food contributes to curb the proliferation of microorganisms (El Adlouni
et al., 2006). Sun-drying is probably the oldest and most common way to reduce the
moisture of any crop. It utilises solar energy from the sun directly. The sun’s heat allows
the free water contained in the food to evaporate and wind causes the water vapour. The
air above the product is never saturated with water vapour, which facilitates drying
(El Adlouni et al., 2006).
In Africa, cassava is sun-dried on virtually any surface in the open air such as a large
flat rock in the field, on the sides of a paved road, on tops of flat roofs, in a flat basket, or
on bare ground (FAO, 2005). This traditional mode of solar drying often leads to poor
quality products, since they are usually not protected during the drying process, nor
against dust, rain and wind or against insects, birds, rodents and pests. This can result in
fouling products, exposure to micro-organisms, mycotoxins formation and infection by
pathogens (Her and Ankila, 1995).
Occurrence of mycotoxins in cassava (Manihot esculenta Crantz)
Figure 2
Different cassava products process, (a) principal product derivate from cassava
(b) production of different cassava chips
(a)
(b)
229
230
Y.C.S. Adjovi et al.
Another cassava product is starch, used in the processing of many food products, such as
glucose and alcohol, and as an industrial product in the chemical, textile, paint, adhesive
glues and laundry industries. Nigeria has sizeable plants average and important
manufacture of starch from cassava, exporting their production to large multinational
food companies such as Cadbury and Nestle (Djoko, 1995; FAO, 2004).
Flour is the most widely used cassava product in Africa and it is processed in various
ways. Drying and milling are the most essential steps. Flours from unfermented cassava
roots are more common in areas where sweet cassava varieties dominate. Indeed, because
of its high water content, this process is used as a way of preservation. Flour is produced
by grinding cassava chips (FAO, 2004, 2005).
The conditions of production and storage of cassava and its derivatives in developing
countries, may lead to mould contamination and development. Previous studies have
demonstrated the importance of fungal contamination in processed and stored cassava
products (Westby and Twiddy, 1991; Kaaya and Eboku, 2010).
4
Fungi and mycotoxins in cassava products during processing
Due to its economical and nutritional importance, it appears necessary to ensure safety of
cassava products and limit the presence of contaminants that may be hazardous for
human health among which moulds are of special importance. An uncontrolled mould
development may result in discoloration, quality deterioration, reduction in commercial
value and production and accumulation of toxic secondary metabolites in contaminated
foods (Krogh, 1992). The potential mycotoxins risk of cassava products is not really
evaluated.
The variation of mycotoxins in the cassava chips is greatly depending on production
and storage conditions as well as storage duration. Nonetheless a study in Ghana had
identified toxins of Aspergillus (patulin, sterigmatocystin, cyclopiazonic acid),
Penicillium (penicillic acid), Phoma or Alternaria (tenuazonic acid) species (Wareing
et al., 2001). Most of the samples of this study were unpeeled cassava, washed and
sun-dried before storage in house.
In cassava chips flour from Uganda and Ivory Coast, Westby et al. (1994) identified
neosolaniol, T-2 toxin and diacetoxyscirpenol (Fusarium sp), patulin, cyclopiazonic acid,
penicillic acid. In 2009, Manjula et al. (2009) detected low level of aflatoxin (0.3–4.4 ppb
in chips and flour; 0.1–13 Mg/kg in stored chips) in cassava samples from Tanzania and
Congo, and traces of fumonisins. In this study, the samples corresponded to several form
of cassava: fresh, stored, dried, just dried, stored-smoked, non-smoked, and fermented.
No relationship between production process and aflatoxin contamination was found.
Another survey conducted in Tanzania, found no aflatoxin contamination of cassava
flour from Tanzanian villages produced following a direct drying process (Muzanila
et al., 2000). Similarly, works done in Ghana by Wareing et al. (2001), in Nigeria by
Jimoh and Kolapo (2008), in Benin by Gnonlonfin et al. (2008, 2012) and Adjovi et al.
(2013) also showed that fully direct processed cassava chips samples were not
contaminated by aflatoxins.
Table 2
Chips
Unfermented/sundried
and smoked
Fresh product and
storage
Cladosporium sp, Aspergillus
(A. flavus, A. candidus,
A. versicolor, A. wentii,
A. niger, A. ochraceus),
Penicillium sp, Fusarium sp,
Rhyzppus sp
Chips
Unfermented/sundried
During processing
and storage
Chips
Unfermented/sundried
Chips
Unfermented
Chips
Fermented
Chips
Fermented and
unfermented/sundried
and smoked
Major fungi
Mycotoxins
(contaminated tested)
Countries
References
Sterigmatocystin (10/125),
patulin (4), ACP (4),
penicilic Ac (5), tenuazonic
Ac (3). AFB1-
Ghana
Wareing et al.
(2001)
A. flavus, Mucor sp, Fusarium
verticillioides, Rhy%ppus sp,
Nigrospora sp
AFB1-; FB1-(0/100)
Benin
Gnonlonfin
et al. (2008)
Storage/marketed
Rhyzppus sp, Chrysonilia sp,
Nigrospora sp, Aspergillus
(A. flavus, A. niger, A.
ochraceus, A. candidus)
AFB1- (0/60)
Benin
Gnonlonfin
et al. (2012)
During different
processing and
storage
Rhyzppus sp, Penicillium sp,
Aspergillus flavus Fusarium sp,
Mucor sp
AFB1+ (30%) (high
moisture, drying
bareground drying, storage
on floor and old containers)
Uganda
Kaaya and Eboku
(2010)
Processing and
storage
Aspergillus (A. flavus,
A. clavatus, A. versicolor,
A. fumigatus, A. niger,
A. ochraceus, A. nomius,
A. parasiticus, A. tamarii,
A. terreus)
AFB1+ (18/72); correlate:
pH, moisture, processing,
storage condition and
duration, type of chips,
level of contamination.
AFB1+ (high moisture,
fermented, humidity in
storage); AFB- (smoked)
Cameroon
Essono et al.
(2007, 2009)
AFB1- (tarpaulin drying)
Occurrence of mycotoxins in cassava (Manihot esculenta Crantz)
Storage or fresh
product
Fungal and mycotoxins contamination of cassava products
Production
Derivates
Notes: AFB1: Aflatoxin B1; AFB2: Aflatoxin B2; OTA: Ochratoxin A; FB1: fumonisin B1.
231
Aspergillus (A. flavus,
A. parasiticus)
AFB1- (0/10)
Uganda
Westby et al.
(1995b)
-
Aspergillus sp
AFB- (0/10)
Mozambique;
Uganda
Essers (1995)
Stored
Rhizppus nigricans, Fusarium
oxysporum, Aspergillus
(A. flavus, A. niger)
AFB-
Nigeria
Jimoh and Kolapo
(2008)
AFB-
Nigeria
Bankole and
Mabekoje (2004)
AFB- (100%)
Benin
Adjovi et al. (2013)
AFB1 (100%) Zearalenone
(8%)
Vietnam
Nguyen et al.
(2007)
Chips
Fermented/sundried
Stored
Chips
Fermentation
Chips
Chips
-
Stored
Chips
Unfermented/sundried
Fresh and stored
products
Chips for
animal
Dried
Stored
Chips and
flour
Unfermented/sundried
and smoked
Fresh products
and storage
Aspergillus flavus; Fusarium sp
AFB1 + (fresh not
processed and storage;
sundried and storage
4 months; smoked after
sundried) Tanzania,
AFB1- (Congo)
Tanzania and
Congo
Manjula et al.
(2009)
3 types
Aspergillus sp, Fusarium sp
OTA (2/33) with 32, 65
Brazil
Soares and
Rodriguez-Amaya
(1989)
Aspergillus sp
OTA
Brazil
Pohland et al.
(1992)
Flour
Flour
Aspergillus flavus, Aspergillus
parvisclerotigenus, Aspergillus
novoparasiticus
Notes: AFB1: Aflatoxin B1; AFB2: Aflatoxin B2; OTA: Ochratoxin A; FB1: fumonisin B1.
Y.C.S. Adjovi et al.
References
Major fungi
Fungal and mycotoxins contamination of cassava products (continued)
Countries
Storage or fresh
product
232
Table 2
Mycotoxins
(contaminated tested)
Production
Derivates
Production
Major fungi
Aspergillus niger, Aspergillus
flavus, Rhizppus stolonifer,
Mucor racemosus and Fusarium
oxysporium
Stored
-
Countries
References
Nigeria
Kolawole et al.
(2009)
AFB+ (18/18) with 16 ppb
Uganda
Kitya et al. (2010)
Fumonisin B1 (421 ig/kg),
AFB2 (< LOQ8 ig/kg), AF
B1 (< LOQ9 ig/kg),
diacetoxyscirpenol
(< LOQ6 ig/kg) and
zearalenone (< LOQ12ig/kg)
Cameroon
Njumbe et al.
(2011)
Flour
-
Flour
Dried
Flour for
bread
Dried
-
Penicillium oxalicum,
Aspergillus flavus, Fusarium spp
AFB1 (1.91Mg / kg)
Ghana
Adegoke et al.
(1993)
Bread
Fermented and waved
-
No fungi
AFB1 (0.03|ag / kg)
Ghana
Adegoke et al.
(1993)
Meal
-
Stored (exported)
Aspergillus (A. flavus,
A. parasiticus)
AFB1 (0.7 ng/kg);
Zearalenone (90^g/kg)
Indonesia
Bottalico et al.
(1980)
Meal
-
Stored (exported)
Aspergillus (A. flavus,
A. parasiticus); Fusarium sp
AFB1 (9 ng/kg);
zearalenone (3 mg/kg)
Thailand
Bottalico et al.
(1980)
Gari
Fermented and
roasted
Fresh product
Aspergillus flavus,
A. parasiticus
AFs-
Ghana
Cotty (2002)
Gari
Fermented
Stored
Aspergillus (A. niger, A. repens,
A. flavus), lemenniera aquatica
Nigeria
Osho et al. (2010)
Gari
Fermented
Stored
-
OTA (3.28–22.73^g/kg
Nigeria
Makun et al. (2013)
Attieke
Fermented and
roasted
-
-
AFs-, DON-(0/5); OTA
(0.2 ig/kg)
Ivoiry cost
Kastner et al.
(2010)
Cassava
feeds
-
Stored
-
AFs-
Fiji and
Tonga island
Lovelace and
Albersberg (1989)
233
Notes: AFB1: Aflatoxin B1; AFB2: Aflatoxin B2; OTA: Ochratoxin A; FB1: fumonisin B1.
Fungal and mycotoxins contamination of cassava products (continued)
Stored
Mycotoxins
(contaminated tested)
Occurrence of mycotoxins in cassava (Manihot esculenta Crantz)
Flour
Storage or fresh
product
Table 2
Derivates
234
Y.C.S. Adjovi et al.
Recently, several studies aimed to establish prevalence of key mycotoxins in Africa have
been initiated, although only a few have been carried out in Tanzania, Benin, and all have
focused on aflatoxins and fumonisins. In Benin, Adjovi et al. (2013) have shown the
presence of toxigenic strains of Aspergillus of the Flavi section in cassava chips produced
and sold in Benin, but no presence of aflatoxins was observed. This study also revealed
the presence of new species of genus Aspergillus which are aflatoxigenic:
Aspergillusparvisclerotigenes and Aspergillus novoparasiticus. Table 2 shows different
types of fungi and mycotoxins found in cassava products.
Cassava products contamination begins at pre-harvest and may also occur later,
depending on transformation processes and storage conditions.
4.1 Pre-harvest and harvest conditions
Pre-harvest fungal contamination is due to cultural practices including crop rotation,
cropping pattern, irrigation, planting and harvesting (Kumar and Kumari, 2010). During
this stage some fungi can grow on plants and produce mycotoxins (Cwalina-Ambroziak,
2004). The surface of tubers can be contaminated by various soil fungi that penetrate into
the tissues through injuries caused by devastators (Jesenska et al., 1993). The main fungi
found at pre-harvest stage are Fusarium sp. with species such as F. graminearum, F.
oxysporum, F. avenaceum, F. moniliformes that are met in potatoes, maize and wheat;
Alternaria sp. with Alternaria solani and Alternaria alternata in potatoes, Alternaria
infectoria in maize (Jesenska et al., 1993; Cwalina-Ambroziak and Czajka, 2000;
Sorensen et al., 2010), Phoma sp. with Phoma exigua in potatoes and Phomapomorum in
maize (Sorensen et al., 2010). Among pre-harvest fungi the most important mycotoxin
producers are Fusarium and Alternaria (Sorensen et al., 2010). During pre-harvest, the
microorganisms of soil and the insects attack may also cause damage on cassava crops.
As for other crops, the principal genera that contaminate cassava are Aspergillus,
Fusarium and Alternaria (Sorensen et al., 2010; Atanda et al., 2011).
The proximity of cassava and cereals culture can be responsible for
cross-contamination by cereals’ fungi.
Field fungi invade developing and mature seeds before harvesting. These kinds of
mycobiota were found in cassava chips sold in Benin (Gnonlonfin et al., 2008, 2012).
As for cereals, cultural practices and pre-harvest conditions also contribute to
microbial contamination of cassava crops. The drying season, the rapid variation of
temperature, the presence of insects and the previous usage of the soil by another culture
can favour high microbial contamination (Wicklow, 1994).
4.2 Processing and storage of cassava and derived products
Without special precautions, cassava roots are not conserved beyond 3 or 4 days. But
there are some techniques to prolong the fresh root storage time until about 2–8 weeks.
To achieve conservation of several months, it is essential to transform the roots of
durable products such as chips, gari, etc. Due to their perishable nature, storage of fresh
cassava roots is little practiced in Africa. Traditional methods to prolong the shelf life
include the practice of pruning the plant three weeks before harvest, store in pits, pack
them and water them, coat them with mud or stored under water. Even in this case, the
roots will deteriorate after a few days. Many farmers prefer to leave while cassava in the
fields until they need it (FAO, 2000).
Occurrence of mycotoxins in cassava (Manihot esculenta Crantz)
235
After harvest, the aim is to reduce the time to process or use. Considering the
distances between the production areas and the main places of consumption, it is very
difficult to avoid substantial losses. That is why there is a major interest, economic point
of view, to prolong the shelf life of cassava.
Among the preservation techniques used include:
•
storage in silo pits is covered with a thatched roof
•
storage in moist sawdust
•
immersed in a fungicide and bagging polyethylene
•
coating with wax
•
refrigerated storage
•
storage under plastic sheeting roots soaked in water.
All methods may include the retention period of one or two weeks. But these methods
still have some drawbacks such as cost (fungicides, refrigeration), lack of ability to
control the quality of the roots and the possibility of attacks by rodents (FAO, 2000).
The fact that cassava roots quickly rot is one of two principals reasons of the common
cassava processing wherever it is grown and consumed. The second reason is related to
the need to make consumables roots man removing cyanogenic glycosides. To increase
the shelf life, it is necessary to reduce the water content, either by drying or by roasting.
The two dry goods processing the most popular-cassava are the chips (root dried pieces)
and Gari, a fermented cornmeal. Chips and Gari easily keep bags in a cool, dry-in rights
for about a year. However, it should inspect the products regularly (at least once a month)
in order to monitor the quality as they are hygroscopic (meaning they absorb water) and
that the chips be little wind attacked by storage pests (FAO, 2000). The studies on
cassava products mainly interested on chips (fermented or not) in Africa and few
concerned attieke, meal and flour. The contamination of cassava products by fungi is
studied according to different process applied to chips production and mostly the
presence or absence of fermentation step.
4.3 Production of fermented and non-fermented products
Fermented products often contain mixed microbial populations because of the lack of
sterility and the use of natural (spontaneous) fermentation or mixed-culture fermentation
starters. In Asia, fungi are used for their enzymatic ability to degrade polymeric
substances, as well as for texture forming properties. The main fungi encountered in
Asian fermented food are Rhizopus sp. (in tempeh), Monascus sp. (in fermented rice),
Actinomucor sp. (Ac. elegans in fermented sojae) and Aspergillus sp. (A. oryzae, A. sojae
in soy sauce). In Africa, the use of mycelial fungi for fermentation is less common in the
fermentative detoxification of bitter cassava roots (Nout and Aidoo, 2010).
In fermented cassava derivatives, the fermentation can be accomplished by two ways:
stacking in heaps or soaking in water for a certain period. The fermentation process,
whether in water or in heaps, influences the taste of the final product (FAO, 2005).
Generally, the microorganisms associated with cassava fermentation are mostly lactic
acid bacteria (Lactobacillus plantarum, Streptococcus faecium and Leuconostoc
mesenteroides) and spore-forming bacteria such as Bacillus sp. (Bokanga, 1989;
236
Y.C.S. Adjovi et al.
Nwankwo et al., 1989; Okafor et al., 1984; Ngaba and Lee, 1979). Nevertheless, the most
important microorganisms are fungi belonging to genus Rhizopus, Mucor, Actinomucor,
and Neurospora (Steinkraus, 1997).
During the production of cassava-fermented chips, the use of ferment (starter) likely
occurs as a result of the carryover of these ferments contained in the water used during
the soaking process. Some studies demonstrate that bacteria that are present in the
fermented foods could prevent the contamination with mycotoxins. It is the case during
the fermentation of Meju by Bacillus subtilis which reduces the production of aflatoxin B
and G by Aspergillus parasiticus (Park et al., 2003). A study of Essono et al. (2007) on
fermented chips produced in Cameroon, demonstrated that the predominant fungi isolated
from the analysed samples belong to the genus Aspergillus and especially to the
following species: A. clavatus, A. flavus, A. niger and Aspergillus versicolor. Other
species of the genus Aspergillus were identified in this study. They belonged to the Flavi
section: A. nomius, A. tamarii and A. parasiticus; and to other sections as well:
A. aculeatus, A. candidus, A. flavipes, A. fumigatus, A. ochraceus, and A. terreus. This
study correlates the presence of aflatoxin B1 to fermentation and high moisture of
cassava chips (Essono et al., 2009). Essers (1995) noted the absence of aflatoxin B1 in
fermented cassava chips with low moisture. In another study, cassava fermented product
like gari, which is fermented and roasted with low moisture content, and despite the
presence of Aspergillus flavus and Aspergillus parasiticus, once again no aflatoxins were
detected (Westby, 2001). By contrast, in the study of Kastner et al. (2010) on Attieke,
ochratoxin A (OTA) has been detected (0.2 ug/kg). In cassava flour, Njumbe et al. (2011)
have detected fumonisin B1 (421 ug/kg). The presence of mycotoxins does not depend
only on fermentation process but also on other parameters like moisture content,
temperature, drying process and conditions.
In the case of non-fermented cassava, after peeling, cassava is washed with fresh
water and transformed directly. During non-fermented chips production the peeled roots
may be sliced to reduce the size of the pieces before drying (Kaaya and Eboku, 2010).
The drying is done on roof or on bare ground, rock surface, tarpaulin, iron sheets and
mats [Figure 2(b)] (Gnonlonfin et al., 2008; Kaaya and Eboku, 2010). A survey on
cassava chips processing areas in Benin, Ghana and Nigeria (Gnonlonfin et al., 2008;
Wareing et al., 2001) has indicated that, despite low moisture of chips, the most common
fungi were Rhizopus sp. and Aspergillus sp. In these studies, authors have detected the
presence of sterigmatocystin, patulin, cyclopiazonic acid, penicillic acid, tenuazonic acid
(Wareing et al., 2001), but not aflatoxin B1 and fumonisin B1 (Gnonlonfin et al., 2008)
despite the presence of Aspergillus flavus and Fusarium sp. In case of high moisture
associated with inadequate drying condition, aflatoxin B1 has been detected in cassava
chips (Kaaya and Eboku, 2010). Table 2 shows cassava products processing and
relationship with contamination by fungi and mycotoxins.
4.3.1 Sun-dried products
During the drying, some moulds can develop such as Penicillia (Flannigan, 1970) [and
produce ochratoxin A (OTA)] (El Adlouni et al., 2006), Aspergillus sp. and Alternaria sp.
(Jackson and Al-Taher, 2008). In cassava derivatives, fungi proliferate when the moisture
content exceeds 14%. And then, a relationship between drying process and mould
contamination was observed. The influence of drying process on the sensitivity to
Occurrence of mycotoxins in cassava (Manihot esculenta Crantz)
237
aflatoxin contamination has also been reported for other products such as figures (Ozer
et al., 2012).
A study of Wareing et al. (2001) has reported that fire-dried cassava gave counts of
10 to 102 cfu/g less than sun-dried. When the dried chips were obtained after
fermentation process, moulds observed on products were white, black, or orange (Kaaya
and Eboku, 2010). The presence of greenish moulds could also occur and could be
attributed to insufficient first surface drying step.
In Uganda, Kaaya and Eboku (2010) reported that the majority of farmers dry the
cassava products on bare ground or bare rocks and this method exposes the crop to
contamination with soil, dust, moulds because the soil is the primary source of moulds
(Diener et al., 1987).
4.3.2 Storage of cassava products
Storage fungi include all species of Aspergillus, Fusarium and Penicillium genera. The
growth of fungi during storage is governed by moisture and temperature, but also biotic
factors like competition or the presence of insects (Atanda et al., 2011).
Indeed, storage fungi are much more frequent in lots infested by insects, because
insects generate moisture and distribute fungi spores in the commodity. Storage fungi
require a relative humidity of, at least, 65% (or a water activity of aw = 0.65), which is
equivalent to an equilibrium moisture content of 13% in grains and cassava chips (Atanda
et al., 2011; Gnonlonfin et al., 2012). They grow at temperature ranging from 10 to 40°C
(Atanda et al., 2011).
Storage of harvested grains at > 10% moisture content and for prolonged period in
poor storage facilities may cause proliferation of moulds on grains (Ominski et al., 1994;
Abdalla, 1998; Ahmed et al., 2009). Similarly unwholesome practice of mixing grains of
different grades in order to improve the quality of contaminated grains, especially when
one contains a large number of fungi spores, will provide inoculum for the good grade
and probably contaminate the toxin-free grain (Wagacha and Muthomi, 2008). Other
compelling factors adduced by the authors that worsen the fungi and mycotoxins burden
in Africa are: public ignorance of the existence of the toxins; complete absence or lack of
enforcement of regulatory limits and introduction of contaminated food into the food
chain, which has become inevitable due to shortage of food supply caused by drought,
wars and other socio-economic and political insecurity.
4.4 Particular case of aflatoxin contamination
Among all moulds and mycotoxins found in cassava, only Aspergillus flavus and
aflatoxin contamination remain blurred. Indeed, previous studies (Brudzynski et al.,
1977; Bottalico et al., 1980; Adegoke et al., 1993) that focused on the contamination of
cassava by aflatoxin, mentioned its presence revealed by thin layer chromatography
whereas a compound of cassava, scopoletin was interfering the dosage. Indeed, this
molecule has the same retention time as aflatoxin. So the first studies have long assumed
that cassava products were contaminated with aflatoxin. With the development of new
analytical methods for the determination of mycotoxins, some features have permitted to
identify exactly the presence aflatoxin in cassava products.
238
Y.C.S. Adjovi et al.
Surveys that have studied the contamination of cassava by aflatoxin were most
interested in chips. So the development of the following paragraph is based on data
regarding both fermented and non-fermented cassava chips.
4.4.1 Relationships between aflatoxin concentration and processing practices
The peeling of cassava suppresses its protection and makes it more vulnerable to attack
by moulds and possibly subsequent contamination by mycotoxins.
The form of cassava pieces can result in uneven drying which can lead to increase
moulds contamination. The direct sun drying of cassava products is likely to shorten the
drying period since drying is started immediately after peeling and chipping the cassava
roots. Drying on tarpaulin and drying on paved surface were associated with no
contamination by aflatoxin. The duration of drying affects the moisture and, in
association with temperature that favour fungal growth, may influence aflatoxin
production (Kaaya and Eboku, 2010). An experimental quick drying of in-shell Brazil
nuts (70–102°C during 48 hours) reduced fungal contamination and decreased production
of aflatoxin from 11.13 to 4.8 ug/kg (Pacheco and Scussel, 2006).
Essers et al. (1994) and Kaaya and Eboku (2010) have noted that, in Uganda, the
fermented cassava chips are more contaminated by moulds than non-fermented ones. In
that case, level of mycotoxins contamination and specifically aflatoxins contamination is
related to the degree of mouldiness.
4.4.2 Aflatoxin in cassava stored products
A. flavus produces highest aflatoxin levels at water activity of 0.996 and temperature of
30°C between 5–15 days of storage (Gqaleni et al., 1997). Additionally cassava chips are
hygroscopic and tend to pick up moisture during storage, which promotes moulds and
other deterioration agents (Knoth, 1993). The storage in the huts is known to expose the
product to rain, which causes the dry pieces to become wet. Usually, cassava products
with 12% moisture can be stored for long time but moisture content greater than 12%
allows microbial growth. For instance, Kaaya and Eboku (2010) have reported an
aflatoxin contamination on cassava products contaminated by A. parasiticus in Uganda,
at 40% moisture.
The cassava chips can be stored from one week to one year. A short storage period
averaging 8–12 weeks reported in the study of Wareing et al. (2001) in Ghana, reduce the
risk of contamination by aflatoxins. The storage of cassava product for a long time is one
important factor predisposing the products to aflatoxin contamination (Kaaya and Eboku,
2010; Wareing et al., 2001).
Kaaya and Eboku (2010) reported that storing cassava in Jerricans would lead to a
34 times higher contamination while storage in polypropylene bags and heaping on bare
floor would lead to 19 to 16 times increased contamination compared to other conditions.
Storage of cassava chips with other agricultural commodities prone to mould
contamination promotes cross-contamination (Bankole and Eseigbe, 2004).
The chips are most often stored with grain crops especially corn which can be heavily
contaminated with A. flavus and aflatoxin. This proximity may contribute to the transfer
of toxigenic mould spores on cassava chips.
Occurrence of mycotoxins in cassava (Manihot esculenta Crantz)
5
239
Conclusions
Cassava is a highly nutritious substrate favouring the growth of microorganisms. Its
transformation into different derivatives, though ensuring the availability of the food
during welding does not guarantee the absence of the development of moulds.
Consequently, studies have revealed in cassava products, a diverse mycobiota
according to the area of production. But the predominance of the genus Aspergillus is
however noted. Moulds found can produce mycotoxins in the processed cassava such as
ZEA, fumonisins, penicillic acid, patulin and ochratoxin A. In several studies, the
absence of aflatoxin in cassava was highlighted. Yet, the few studies that have found this
mycotoxin show that its presence is related to the manufacturing process, production and
storage conditions that accelerate the physiological deterioration (fermentation) and
degradation. Adjovi et al. (2013) have proved the existence of anti-aflatoxin property in
fresh cassava, independently of geographical origins. This data suggest that cassava
compounds have the ability to block toxinogenesis leading to Aspergillus secondary
metabolites. However, this property was lost after processing: heating, sun drying and
freezing.
References
Abdalla, A.E. (1998) An Evaluation of the Durability of Sorghum Grains in Traditional and
Modified Underground Pits in Central Sudan, PhD thesis, University of Gezira, Wad Medani,
Sudan.
Adaku, C.C., De Kock, S., Zanele, P.Z., Mwanza, M., Egbuta, M.A. and Dutton, M.F. (2012)
‘Fungal and mycotoxin contamination of South African commercial maize’, J. Food Agric.
Environ., Vol. 10, No. 2, pp.296–303.
Adegoke, G.O., Adegoke, G.O., Akinnuoye, D.E. and Akanni, A.O. (1993) ‘Effet de la
transformation sur la mycoflore et teneur en aflatoxine B1 de manioc sur les produits’,
Nutrition ursine Human Foods, Vol. 43, No. 3, pp.191–196.
Adewusi, S.R.A. and Bradbury, J.H. (1993) ‘Carotenoid in cassava: comparison of open column
and HPLC methods of analysis’, J. Sci. Food Agric., Vol. 62, No. 4, pp.375–383.
Adjovi, Y.C.S., Bailly, S., Gnonlonfin, B.J.G., Tadrist, S., Querin, A., Sanni, A., Oswald, I.P.,
Puel, O. and Bailly, J.D. (2013) ‘Analysis of the contrast between natural occurrence of
toxigenic Aspergillii of the Flavi section and aflatoxin B1 in cassava’, J. Food Microbiol.,
Vol. 38, pp.151–159.
Agunbiade, J.A., Adeyemi, O.A., Fashina, O.E. and Bagbe, S.A. (2002) ‘Fortification of cassava
peels in balanced diets for rabbit’, Nigeria J. Anim. Prod., Vol. 28, No. 1, pp.167–173.
Ahmed, N., Abdalla, E., Adam, A.E. and Betjowck, Y.S. (2009) ‘Fungi and mycotoxins associated
with Sorghum grains in major storage systems in Gedarif, Sudan’, A Paper submitted to the
17th Board of Directors Meeting of the National Council for Mycotoxins, December, Sudanese
Standards and Measurements Organisation, Sudan.
Akoroda, M.O. (2007) ‘Cassava consumption and marketing in West-Africa’, Atelier ‘Potentialites
a la transformation du manioc en Afrique de l’Ouest’ – Abidjan, 4–7 June, pp.2–23.
Aletor, V.A. and Adeogun, O.A. (1995) ‘Nutrients and anti-nutrient components of some tropical
leafy vegetables’, Food Chem., Vol. 54, No. 4, pp.375–379.
Alexopoulos, C.J., Mims, C.W. and Blackwell, M. (1996) Introductory Mycology, p.17, John Wiley
and Sons, ISBN 0471522295, p.17.
240
Y.C.S. Adjovi et al.
Annan, K. (2001) Third United Nations Conference on the Least Developed Countries
[online] http://www.globalpolicy.org/socecon/un/unctad/2001/anna0514.htm
(accessed December 2003).
Atanda, S.A., Pessu, P.O., Agoda, S., Isong, I.U., Adekalu, O.A., Echendu, M.A. and Falade, T.C.
(2011) ‘Fungi and mycotoxins in stored foods’, Afr. J. Micro. Res., Vol. 5, No. 25,
pp.4373–4382.
Bankole, S., Schollenbeger, M. and Drochner, W. (2006) ‘Mycotoxin contamination in food
systems in Sub-Saharan Africa’, Mykotoxin Workshop Hrsg.: Bydgosczz (Polen), 29–31 May,
Vol. 28, p.37.
Bankole, S.A. and Adebanjo, A. (2003) ‘Mycotoxins in food in West Africa: current situation and
possibilities of controlling it’, Afr. J. Biotech., Vol. 2, No. 9, pp.254–263.
Bankole, S.A. and Eseigbe, D.A. (2004) ‘Aflatoxins in Nigerian dry-roasted groundnuts’, Nutr.
Food Sci., Vol. 34, No. 6, pp.268–271.
Bankole, S.A. and Mabekoje, O.O. (2004) ‘Mycoflora and occurrence of aflatoxinB1 in dried yam
chips from markets in Ogun and Oyo States, Nigeria’, Mycopathologia, Vol. 157, No. 1,
pp.111–115.
Bernhoft, A., Keblys, M., Morrison, E., Larsen, H.J. and Flaoyen, A. (2004) ‘Combined effects of
selected Penicillium mycotoxins on in vitro proliferation of porcine lymphocytes’,
Mycopathologia, Vol. 158, pp.441–450.
Bokanga, M. (1989) Microbiology and Biochemistry of Cassava Fermentation, PhD thesis, Cornell
University, Ithaca, NY, USA.
Bottalico, A., Lerario, P. and Frisullo, S. (1980) ‘Occurrence of aflatoxins, zearalenone and
aflatoxigenic strains of Aspergilli in samples of cassava meal’, J. Zoo. Nutr. Anim., Vol. 6,
No. 3, pp.209–214.
Brudzynski, A., Van Pee, W. and Kornaszewski, W. (1977) ‘The occurrence of aflatoxin B1 in
peanuts, corn and dried cassava sold at the local market in Kinshasa, Zaire; its coincidence
with high hepatoma morbidity among the population’, Zesz. Probl. Postepow Nauk. Roln.,
Vol. 189, pp.189–117.
Bryden, W.L. (2007) ‘Mycotoxins in the food chain: human health implications’, Asia Pac. J. Clin.
Nutr., Vol. 16, Suppl. 1, pp.95–101.
Bryden, WL. (2012) ‘Mycotoxin contamination of the feed supply chain: implication animal
productivity and feed security’, Anim. FeedSci. Tech., Vol. 173, pp.134–158.
Codex Alimentarius (2012) Discussion Paper on Fungi and Mycotoxins in Sorghum, Codex
Committee on Contaminants in Foods; FAO/WHO Food Standards Program, Sixth Session
Maastricht, The Netherlands, 26–30 March.
Cole, R.J., Scheweikert, M.A. and Jarvis, B.B. (2003) Handbook of Secondary Fungal Metabolites,
Vols. 1–3, Acad. Press, CA, USA.
Cotty, P.J. (1992) ‘Use of native Aspergillus flavus strains to prevent aflatoxin contamination’, US
Patent, Vol. 5, pp.171–686.
Cross, D.L. (2003) ‘Clavicipitacean fungi: evolutionary biology, chemistry, biocontrol and cultural
impacts. Ergot alkaloid toxicity’, in White Jr., J.F., Bacon, C.W., Hywel-Jones, N.L. and
Spatafora, J.W. (Eds.): Mycology, pp.475–494, Marcel-Dekker Inc, New York and Basel.
Cwalina-Ambroziak, B. (2004) ‘Diseases of potatoes and fungi colonizing potato stem bases in
dependence on different nitrogen fertilization’, Actafyto. Zoo., Vol. 7, Special Number,
Proceedings of the XVI, Slovak and Czech, Plant Protection Conference organised at Slovak
Agricultural University in Nitra, Slovakia.
Cwalina-ambroziak, B. and Czajka, W. (2000) ‘Potato stems infection by Rhhi%octonia solani and
Colletotrichum coccodes in different crop rotation’, Phytopathol. Pol., Vol. 20, pp.155–163.
Dean, R., Van Kan, J.A., Pretorius, Z.A., Hammond-Kosack, K.E., Di Pietro, A., Spanu, P.D.,
Rudd, J.J., Dickman, M., Kahmann, R., Ellis, J. and Foster, G.D. (2012) ‘The Top 10 fungal
pathogens in molecular plant pathology’, Mol. Plant Path., Vol. 13, No. 4, pp.414–430.
Occurrence of mycotoxins in cassava (Manihot esculenta Crantz)
241
Diener, U.L., Cole, R.J., Sanders, T.H., Payne, G.A., Lee, L.S. and Klich, M.A. (1987)
‘Epidemiology of aflatoxin formation by Aspergillusflavuf, Ann. Rev. Phyt., Vol. 25,
pp.249–270.
Djoko, S.D. (1995) Food Processing in Indonesia: The Development of Small-Scale Industries,
Bogor Research Institute for Food Crops Biotechnology, Agency for Agricultural Research
and Development, pp.9–10.
Dorner, J.W., Cole, R.J., Lomax, L.G., Gosser, H.S. and Diener, U.L. (1983) ‘Cyclopiazonic acid
production by Aspergillus flavus and its effects on broiler chickens’, Appl. Environ.
Microbiol., Vol.46, No. 1, pp.698–703.
Dyer, D. (1993) ‘Evidence that ergovaline acts on serotonin receptors’, Life Sci., Vol. 53,
pp.223–228.
El Adlouni, C., Tozlovanu, M., Natman, F., Faid, M. and PfohlLeszkowicz, A. (2006) ‘Preliminary
data on the presence of mycotoxins (ochratoxin A, citrinin and aflatoxin B1) in black table
olives ‘greek style’ of Moroccan origin’, Mol. Nutr. Food Res., May, Vol. 50, pp.507–512.
Elegbede, J.A. (1978) Fungal and Mycotoxin Contamination of Sorghum During Storage, MSc
Thesis submitted to Department of Biochemistry, Ahmadu Bello University, Zaria.
Essers, A.J.A. (1995) Removal of Cyanogens From Cassava Roots: Studies on Domestic
Sun-Drying and Solid Substrate Fermentation in Rural Africa, PhD Thesis, Wageningen
Agricultural University, The Netherlands.
Essers, A.J.A., Witjes, C.M.J.W., Schurink, E.W. and Nout, M.J.R., (1994) ‘Role of fungi in
cyanogens removal during solid substrate fermentation of cassava’, Biotechnol. Lett., Vol. 16,
pp.755–758.
Essono, G., Ayodele, M., Akoab, A., Foko, J., Filtenborg, O. and Olemboe, S. (2009)
‘Aflatoxin-producing Aspergillus spp. and aflatoxin levels in stored cassava chips as affected
by processing practices’, Food Cont., Vol. 20, No. 7, pp.648–654.
Essono, G., Ayodele, M., Akoa, A., Foko, J., Olembo, S. and Gockowski, J. (2007) ‘Aspergillus
species on cassava chips in storage in rural areas of southern Cameroon: their relationship with
storage duration, moisture content and processing methods’, Afr. J. Micro. Res., May, Vol. 1,
pp.1–8.
FAO (2000) ‘Les richesses du sol. Les plantes a racines et tubercules en Afrique: une contribution
aux technologies des recoltes et apres recoltes’, in Bell, A., Muck, O. and Schuler, B. (Eds.):
Archives Documents de la FAO, GTZ, Allemagne, [online]
http://www.fao.org/wairdocs/x5695f/x5695f00.htm (accessed October 2014).
FAO (2001) ‘2001/2003 manual on the application of the HACCP system in mycotoxin, prevention
and control’, FAO Food Nutr. Paper, Vol. 73, pp.1–124 [online]
http://www.fao.org/docrep/005/y1390e/y1390e00.HTM (accessed December 2012).
FAO (2004) ‘The global cassava development Strategy and implementation plan’, Proceeding of
the Validation Forum on the Cassava Development Strategy, Food and Agriculture
Organization of the United Nations [online] http://www.fao.org.
FAO (2005) Food Supply Situation and Crop Prospects in Sub-Saharan Africa: Global Information
and Early Warning System (GIEWS), Vol. 3, pp.1–69, Africa Report, Food and Agriculture
Organization of the United Nations, Rome, Italy.
FAO (2010) ‘Une nouvelle variete de manioc part a l’assaut de la faim en Afrique’, Senegal
Business, 30 Aout 2010 [online] http://www.fao.org/ag/ags/gestion-apres-recolte/racines-ettubercules /fr (Accessed December 2012)
FAO (2011) ‘Global information and early warning system on food and agriculture’, FAO Food
Outlook: Global Market Analysis, November.
Flannigan, B. (1970) ‘Mycoflora of dried barley grain’, Trans. Br Myco. Soc., Vol. 53, pp.371–379.
Gamal, A.S., Esam, M. and El-Shishtawy, M. (2012) ‘Fumonisin lung toxicity: gross and
microscopic changes are dose and time dependent’, J. Amer. Sci., Vol. 8, No. 9, pp.729–736.
242
Y.C.S. Adjovi et al.
Gentles, A., Smith, E.E., Kubena, L.F., Duffus, E., Johnson, P., Thompson, J., Harvey, R.B. and
Edrington, T.S. (1999) ‘Toxicological evaluations of cyclopiazonic acid and ochratoxin A in
broilers’, Poultry Science, Vol. 78, No. 1, pp.1380–1384.
Gentles, A.B., Small, M.H., Smith, E.E., Phillips, T.D., Duffus, E. and Braithwaite, C.E. (1993)
‘Teratogenic effects of orally administered diacetoxyscirpenol in mice’, Toxicologist, Vol. 13,
p.208.
Gnonlonfin, G.J.B., Adjovi, C.S.Y., Katerere, D.R., Shephard, G.S., Sanni, A. and Brimer, L.
(2012) ‘Mycoflora and absence of aflatoxin contamination of commercialized cassava chips in
Benin, West Africa’, Food Cont., Vol. 23, No. 2, pp.333–337.
Gnonlonfin, G.J.B., Hell, K., Fandohan, P. and Siame, A.B. (2008) ‘Mycoflora and natural
occurrence of aflatoxins and fumonisin B1 in cassava and yam chips from Benin, West
Africa’, Int. J. Food Micro., Vol. 122, Nos. 1–2, pp.140–147.
Gong, Y., Hounsa, A., Egal, S., Turner, P.C., Sutcliffe, A.E., Hall, A.J., Cardwell, K. and
Wild, C.P. (2004) ‘Postweaning exposure to aflatoxin results in impaired child growth: a
longitudinal study in Benin, West Africa’, Env. Hea. Pen., Vol. 112, No. 13, pp.1334–1338.
Gong, Y.Y., Cardwell, K.F. Hounsa, A., Egal, S., Turner, P.C., Hall, A.J. and Wild, C.P. (2002)
‘Dietary aflatoxin exposure and impaired growth in young children from Benin and Togo: a
cross-sectional study’, Brit. Med. J., Vol. 325, No. 7354, pp.20–21.
Gong, Y.Y., Egal, S., Hounsa, A., Turner, P.C., Hall, A.J., Cardwell, K.F. and Wild, C.P. (2003)
‘Determinants of aflatoxin exposure in young children from Benin and Togo, West Africa; the
critical role of weaning’, Int. J. Epi., Vol. 32, No. 4, pp.556–562.
Gong, Y.Y., Wilson, S., Mwatha, J.K., Routledge, M.N., Castelino, J.M., Zhao, B., Kimani, G.,
Kariuki, H.C., Vennervald, B.J., Dunne, D.W. and Wild, C.P. (2012) ‘Aflatoxin exposure may
contribute to chronic hepatomegaly in Kenyan school children’, Env. Hea Pers., Vol. 120,
No. 6, pp.893–896.
Gqaleni, N., Smith, J.E., Lacey, J. and Gettinby, G. (1997) ‘Effects of temperature, water activity
and incubation time on production of aflatoxins and cyclopiazonic acid by an isolate of
Aspergillus flavus in surface agar culture’, App. Env. Micro., Vol. 63, No. 1037,
pp.1048–1053.
Hawksworth, D.L. (2006) ‘The fungal dimension of biodiversity: magnitude, significance, and
conservation’, Myco. Res., Vol. 95, No. 6, pp.641–655.
Her, M. and Ankila, O. (1995) ‘Manuel du Sechage Solaire au Maroc’, Food Nutr. Library,
Vol. 2.2, German Agency for Technical Cooperation (GTZ) [online] http://www.nzdl.org.
IARC (1987) IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Suppl. 7,
Overall Evaluations of Carcinogenicity: An Uptading of IARC Monographs, Vols. 1–42,
pp.83–87, IARC Press, Lyon.
Ikwelle, M. (1999) Annual Review and Planning Workshop of the National Root Crop Research
Institute, 2 February, Ibadan, Nigeria.
International Agency for Research on Cancer (IARC) (1993) ‘Some naturally occurring substances:
food items and constituents, heterocyclic aromatic amines and mycotoxins’, IARC
Monographs on the Evaluation of Carcinogenic Risks to Humans, IARC, Lyon, France,
Vol. 56, p.489.
Iyayi, E.A. and Tewe, O.O. (1994) ‘Cassava feeding in small holder livestock units’, ACTA
Horticulturae, in International Workshop on Cassava Safety, ISHS No. 375 (Eds.:
M. Bokanga, A.J.A. Essers, N. Poulter, H. Rosling and O. Tewe), Ibadan, Nigeria, 1–4 March
1994, pp.261–269.
Jackson, L.S. and Al-Taher, F. (2008) ‘Factors affecting mycotoxin production in fruits’, in
Barkai-Golan, R. and Paster, N. (Eds.): Mycotoxins in Fruits and Vegetables, pp.75–104,
Elsevier, California, USA.
Jarvis, B. (1971) ‘Factors affecting the production of mycotoxins’, J. App. Bact., Vol. 34, No. 3,
pp.199–213.
Occurrence of mycotoxins in cassava (Manihot esculenta Crantz)
243
JECFA (2001) Safety Evaluation of Certain Mycotoxins in Food, FAO/WHO Expert Committee on
Food Additives, WHO Food Additives Series 47 and FAO Food and Nutr. Paper, Vol. 74,
p.701.
Jesenska, Z., Pieckova, E. and Bernat, D. (1993) ‘Heat resistance of fungi from soil’, Int. J. Food
Micro., Vol. 19, No. 3, pp.187–192.
Jimoh, K.O. and Kolapo, A.L. (2008) ‘Mycoflora and aflatoxin production in market samples of
some selected Nigerian foodstuffs’, Res. J. Micro., Vol. 3, No. 3, pp.169–174.
Johnni, H., Daniel, J.H., Lewis, L.W., Redwood, Y.A., Kieszak, S., Breiman, R.F., Flanders, W.D.,
Bell, C., Mwihia, J., Ogana, G., Likimani, S., Straetemans, M. and McGeehin, M.A. (2011)
‘Comprehensive assessment of maize aflatoxin levels in Eastern Kenya, 2005–2007’, Env.
Hea. Pers., Vol. 119, No. 12, pp.1794–1799.
Kaaya, A.N. and Eboku, D. (2010) ‘Mould and aflatoxin contamination of dried cassava chips in
Eastern Uganda: association with traditional processing and storage practices’, J. Bio. Sci.,
Vol. 10, No. 8, pp.718–729.
Kastner, S., Kandler, H., Hotz, K., Bleisch, M., Lacroix, C. and Meile, L. (2010) ‘Screening for
mycotoxins in the inoculum used for production of attieke, a traditional Ivorian cassava
product, LWT’, Food Sci. Tech., Vol. 43, No. 7, pp.1160–1163.
Keblys, M., Bernhoft, A., Hofer, C.C., Morrison, E., Larsen, H.J. and Flaoyen, A. (2004). ‘The
effects of the Penicillium mycotoxins citrinin, cyclopiazonic acid, ochratoxin A, patulin,
penicillic acid, and roquefortine C on in vitro proliferation of porcine lymphocytes’,
Mycopathologia, Vol. 158, pp.317–324.
Khlangwiset, P., Shephard, G.S. and Wu, F. (2011) ‘Aflatoxins and growth impairment: a review’,
Crit. Rev. Tox., Vol. 41, No. 9, pp.740–755.
Kitya, D., Bbosa, G.S. and Mulogo, E. (2010) ‘Aflatoxin levels in common foods of South Western
Uganda: a risk factor to hepatocellular carcinoma’, Eur. J. Canc. Care, Vol. 19, pp.516–521.
Knoth, J. (1993) Traditional storage of yams and cas- sava and its improvement, Deutsche
Gesellschaft fur Technische Zusammenarbeit (GTZ) GmbH.
Kolawole, O.M., Adeyemi, B.J., Kayode, R.M.O. and Ajibola, T.B. (2009) ‘The drying effect
of colour light frequencies on the nutrient and microbial composition of cassava’, African
Journal of Agricultural Research, Vol. 4, No. 3, pp.171–177.
Krogh, P. (1992) ‘Adverse effect of mycotoxin on human health’, in Mathur, S.B. and Jorgensen, J.
(Eds.): Seed Pathology, Proceedings the Seminar, Copenhagen, Denmark, 20–25 June 1988,
pp.149–157.
Kuiper-Goodman, T. (2004) ‘Risk assessment and risk management of mycotoxins in food’, in
Magan, N. and Olsen, M. (Eds.): Mycotoxins in Food, Detection and Control, p.7, Woodhead
Publishing Limited, Cambridge, UK.
Kumar, A.C. and Kumari, P. (2010) ‘Management of mycotoxin contamination in pre-harvest and
post-harvest crops: present status and future prospects’, J. Phy., Vol. 2, No. 7, pp.37–52.
Lewis, L., Onsongo, M., Njapau, H., Schurz-Rogers, H., Luber, L., Kieszak, S., Nyamongo, J.,
Backer, L., Dahiye, A.M., Misore, A., DeCock, K., Rubin, C. and The Kenya Aflatoxicosis
Investigation Group (2005) ‘Aflatoxin contamination of commercial maize products during an
outbreak of acute aflatoxicosis in eastern and central Kenya’, Env. Hea. Pers., Vol. 113,
No. 12, pp.1763–1767.
Liang, Z-s., Ma, Y-j., Liu, C-y., Deng, X-b., Yan, H-k. and Fan, X-l. (2010) ‘In vivo toxicity of
zearalenone in immune organs of mice’, Chin. Vet. Sci., No. 3, pp.279–283.
Lillehoj, E.B. (1973) ‘Feed sources and conditions conducive for production of aflatoxin
ochratoxin, Fusarium toxins and Zearalenone’, J. Amer. Vet. Med. Ass., Vol. 163, No. 2,
pp.1280–1283.
Lovelace, C.E. and Albersberg, W.G. (1989) ‘Aflatoxin levels in foodstuffs in Fiji and Tonga
islands’, Plant Food Hum. Nutr., Vol. 39, No. 4, pp.393–399.
244
Y.C.S. Adjovi et al.
Magro, A., Matos, O., Bastos, M., Carolino, M., Lima, A. and Mexia, A. (2010) ‘The use of
essential oils to protect rice from storage fungi’, Julius-Kiihn-Archiv., Vol. 425, pp.542–547.
Makun, H.A., Adeniran, A.L., Mailafiya, S.C., Ayanda, I.S., Mudashiru, A.T., Ojukwu, U.J.,
Jagaba, A.S., Usman, Z. and Salihu, D.A. (2013) ‘Natural occurrence of ochratoxin A in some
marketed Nigerian foods’, Food Control, Vol. 31, No. 2, pp.566–571.
Manjula, K., Hell, K., Fandohan, P., Abass, A. and Bandyopadhyay, R. (2009) ‘Aflatoxin and
fumonisin contamination of cassava products and maize grain from markets in Tanzania and
Republic of the Congo’, Tox. Rev., Vol. 28, No. 2, pp.63–69.
Marasas, W.F.O. (1995) ‘Fumonisins: their implications for human and animal health’, Nat. Tox.,
Vol. 3, pp.193–198.
Marasas, W.F.O. (2001) ‘Discovery and occurrence of the fumonisins: a historical perspective’,
Env. Hea. Pers. Supp., Vol. 109, No. 4, p.2.
Marczuk, J., Obremski, K., Lutnicki, K., Gajęcka, M. and Gajęcki, M. (2012) ‘Zearalenone and
deoxynivalenol mycotoxicosis in dairy cattle herds’, Pol. J. Vet. Sci., Vol. 15, No. 2,
pp.365–372.
Meissonnier, G.M., Pinton, P., Laffitte, J., Cossalter, A.M., Gong, Y.Y, Wild, C.P., Bertin, G.,
Galtier, P. and Oswald, I.P. (2008) ‘Immunotoxicity of aflatoxin B1: Impairment of the
cell-mediated response to vaccine antigen and modulation of cytokine expression’, Tox. App.
Phar., Vol. 231, No. 2, pp.142–149.
Mueller, G.M. and Schmit, J.P. (2006) ‘Fungal biodiversity: what do we know? What can we
predict?’, Biod. Cons., Vol. 16, No. 7, pp.1–5.
Muzanila, Y.C., Brennan, J.G. and King, R.D. (2000) ‘Residual cyanogens, chemical composition
and aflatoxins in cassava flour from Tanzanian villages’, Food Chem., Vol. 70, No. 1,
pp.45–49.
Ngaba, J.R. and Lee, J.S. (1979) ‘Fermentation of cassava (Manihot esculenta Crantz)’, J. Food
Sci., Vol. 44, No. 4979, pp.1570–1571.
Nguyen, M.T., Tozovanu, M., Tran, T.L. and Pfohl-Leszkowicz, A. (2007) ‘Occurrence of
aflatoxin B1, citrinin and ochratoxin A in rice in five provinces of the central region of
Vietnam’, Food Chemistry, Vol. 105, No. 1, pp.42–47.
Njumbe, E.E., Di Mavungu, J.D., Monbaliu, S., Van Peteghem, C. and De Saeger, S. (2011) ‘A
validated multianalyte LC_MS/MS method for quantification of 25 mycotoxins in cassava
flour, peanut cake and maize samples’, J. Agr. Food Chem., Vol. 59, No. 10, pp.5173–5180.
Nout, M.J.R. and Aidoo, K.E. (2010) ‘Asian Fungal fermented foods’, in Hofritcher, M. (Ed): The
Mycota X, Industrial Application, 2nd ed., Springer-Verlag, Berlin, Heidelberg.
Nwankwo, D., Anadu, E. and Usoro, R. (1989) ‘Cassava fermenting organisms’, Mircen. J., Vol. 5,
No. 2, pp.169–179.
Nyathi, C.B., Mutiro, C.P., Hasler, J.A. and Chetsanga, C.J. (1987) ‘A survey of urinary aflatoxin
in Zimbabwe’, International Journal of Epidemiology, Vol. 16, pp.516–519.
Oguntimein, G.B. (1992) ‘Processing cassava for animal feeds’, in Helm, S.K., Reynolds, S.I.L.
and Egbunike, G.N. (Eds.): Proceedings on Cassava in Livestock Feed, 14–18 November,
IITA/ILCA, Ibadan, Nigeria.
Okafor, N., Ijioma, B. and Oyolu, C. (1984) ‘Studies on the microbiology of cassava retting for
foo-foo production’, J. App. Bact., Vol. 56, No. 1, pp.1–13.
Oke, O.O. (1969) ‘The role of hydrocyanide in nutrition’, Wor. Rev. Nutr. Diet., Vol. 11,
pp.170–198.
Ominski, K.H., Marquardt, R.R., Sinha, R.N. and Abramson, D. (1994) ‘Ecological aspects of
growth and mycotoxin production by storage fungi’, in Miller, J.D. and Trenholm, H.L.
(Eds.): Mycotoxins in Grains. Compounds other than Aflatoxin, pp.287–305, Eagen Press,
USA.
Omole, T.A. (1977) ‘Cassava in the nutrition of layers’, in Nestle, B. and Graham, M. (Eds.):
Cassava as Animal Feed, pp.51–55, Ottawa, Canada.
Occurrence of mycotoxins in cassava (Manihot esculenta Crantz)
245
Osho, A., Mabekoje, O.O. and Bello, O.O. (2010) ‘Comparative study on the microbial load of
Gari, Elubo-isu and Iru in Nigeria’, Afr. J. Food Sci., Vol. 4, No. 10, pp.646–649.
Ozer, H., Oktay, B., Hatice, I. and Ozay, G. (2012) ‘Mycotoxin risks and toxigenic fungi in
date, prune and dried apricot among Mediterranean crops’, Phyt. Medit., Vol. 51, No. 1,
pp.148–157.
Pacheco, A.M. and Scussel, V.M. (2006) ‘Effects of processing and factory storage on aflatoxin
contamination of in-shell Brazil nuts’, 9th International Working Conference on Stored
Product Protection: Microorganisms, Mycotoxins and Other Biological Contaminant,
pp.159–164.
Padonou, W.S., Nielsen, D.S., Hounhouigan, J.D., Thorsen, L., Nago, M.C. and Jakobsen, M.
(2009) ‘The microbiota of Lafun, an African traditional cassava food product’, International
Journal of Food Microbiology, Vol. 133, Nos. 1–2, pp.22–30.
Pandiyan, V., Nayeem, M., Nanjappan, K. and Ramamurti, R. (1990) ‘Penicillic acid as Na+, K+
and Ca2+ channel blocker in isolated frog's heart at toxic levels’, Indian J. Exp. Biol., Vol. 28,
pp.295–296.
Park, K.Y., Jung, K.O., Rhee, S.H. and Choi, Y.H. (2003) ‘Antimutagenic effects of doenjang
(Korean fermented soypaste) and its active compounds’, Mutat Research, Vols. 523–524,
pp.43–53.
Patterson, D.S. and Allcroft, R. (1970) ‘Metabolism of aflatoxin in susceptible and resistant animal
species’, Food Cosmet Toxicol., Vol. 8, pp.43–53.
Peraica, M., Radic, B., Lucic, A. and Pavlovic, M. (1999) ‘Toxic effects of mycotoxins in humans’,
Bull. World Health Organ., Vol. 77, pp.754–766.
Pestka, J.J. (2008) ‘Mechanisms of deoxynivalenol-induced gene expression and apoptosis’, Food
Addit. Contam. Part A Chem. Anal. Control Expo. Risk Asse., Vol. 25, No. 1, pp.1128–1140.
Pestka, J.J. and Smolinski, A.T. (2005)‘Deoxynivalenol: toxicology and potential effects on
humans’, Journal of Toxicol Environ Health B Crit Rev., Vol. 8, No. 1, pp.39–69.
Pestka, J.J., Zhou, H-R., Moon, Y. and Chung, Y.J. (2004) ‘Cellular and molecular mechanisms for
immune modulation by deoxynivalenol and other trichothecenes: unraveling a paradox’,
Toxicol. Lett., Vol. 153, No. 1, pp.61–73.
Pohland, A.E., Nesheim, S. and Friedman, L. (1992) ‘Ochratoxin A: a review’, Pure and Appl.
Chem., Vol. 64, No. 1, pp.1092–1046.
Probst, C., Njapau, H. and Cotty, P.J. (2007) ‘Outbreak of an acute aflatoxicosis in Kenya in 2004:
identification of the causal agent’, App. Env. Micro., Vol. 73, No. 8, pp.2762–2764.
Pronk, M.E.J., Schothorst, R.C. and van Egmond, H.P. (2002) Toxicology and Occurrence of
Nivalenol, Fusarenon X, Diacetoxyscirpenol, Neosolaniol and 3- and 15-Acetylnivalenol: A
Review of Six Trichothecenes, p.75, RIVM Report 388802024, Bilthoven, Netherlands.
Rasch, C., Kumke, M. and Lohmannsroben, H-G. (2010) ‘Sensing of mycotoxin producing fungi in
the processing of grains’, Food Biop. Tech., Vol. 3, No. 6, pp.908–916.
Ravindrian, V. and Blair, R. (1992) ‘Feed resources for poultry production in Asia and the pacific.
II. Plant protein sources’, Wor. Pou. Sci., Vol. 48, No. 3, pp.205–231.
Rustom, I.Y.S. (1997) ‘Aflatoxin in food and feed: occurrence, legislation and inactivation by
physical methods’, Food Chem., Vol. 59, No. 1, pp.57–67.
Sancho, L.G., de la Torre, R., Horneck, G., Ascaso, C., de Los Rios, A., Pintado, A., Wierzchos, J.
and Schuster, M. (2007) ‘Lichens survive in space: results from the 2005 LICHENS
experiment’, Astrob., Vol. 7, No. 3, pp.443–454.
Schoevers, E.J., Santos, R.R., Colenbrander, B., Fink-Gremmels, J. and Roelen, B.A.J. (2012)
‘Transgenerational toxicity of Zearalenone in pigs’, Rep. Tox., Vol. 34, No. 1, pp.110–119.
Shank, R.C., Wogan, G.N., Gibson, J.B. and Nondasuta, A. (1972) ‘Dietary aflatoxins and human
liver cancer: Aflatoxins in market foods and foodstuffs of Thailand and Hong Kong’, Food.
Cosmet. Tox., Vol. 10, No. 1, pp.61–69.
246
Y.C.S. Adjovi et al.
Shephard, G.S. (2008a) ‘Determination of mycotoxins in human foods’, Chem. Soc. Rev., Vol. 37,
No. 11, pp.2468–2477.
Shephard, G.S. (2008b) ‘Risk assessment of aflatoxins in food in Africa: food additive contaminant
part A’, Chem. Anal Cont. Expo Risk Assess., Vol. 25, No. 10, pp.1246–1256.
Sibanda, L., Marovatsanga, L.T. and Pestka, J.J. (1997) ‘Review of mycotoxin work in sub-Saharan
Africa’, Food Control, Vol. 8, No. 647, pp.21–29.
Shier, W.T., Abbas, H.K., Wearer, M.A. and Horn, B.W. (2005) ‘The case for monitoring
Aspergillus flavus aflatoxinogenicity for food safety as asses countries’, in Abbas, H.K. (Ed.):
Aflatoxin and Food Safety, pp.291–311, CRC Press, Boka Raton.
Soares, L.M. and Rodriguez-Amaya, D.B. (1989) ‘Survey of aflatoxins, ochratoxin A, zearalenone,
and sterigmatocystin in some Brazilian foods by using multi-toxin thin-layer chromatographic
method’, J. Ass. Off. Anal. Chem., Vol. 72, No. 1, pp.22–26.
Sokolovic, M., Garaj-Vrhovac, V. and Mpraga, V. (2008) ‘T-2 toxin: incidence and toxicity in
poultry’, Arh Hig Rada Tok., Vol. 59, No. 11, pp.43–52.
Sorensen, J.L., Aveskamp, M.M., Thrane, U. and Andersen, B. (2010) ‘Polyphasic characterization
of Phoma pomorum isolated from Danish maize’, Int. J. Food Micro., Vol. 136, No. 3,
pp.310–317.
Steinkraus, K.H. (1997) ‘Classification of fermented foods: worldwide review of household
fermentation technique’, Food Cont., Vol. 8, Nos. 5–6, pp.311–317.
Stevens, A.J., Saunders, C.N., Spence, J.B. and Newham, A.G. (1960) ‘Investigation into disease of
turkey poults’, Veterinary Records, Vol. 75, pp.627–628.
Steyn, P.S. and Rabie, C.J. (1976) ‘Characterization of magnesium and calcium tenuazonate from
Phoma sorghina’, Phyt., Vol. 15, No. 12, pp.1977–1979.
Sun, X-M., Zhang, X-H., Wang, H-Y., Cao, W-J., Yan, X., Zuo, L-F., Wang, J-L. and Wang, F-R.
(2002) ‘Effects of sterigmatocystin, deoxynivalenol and aflatoxin g1on apoptosis of human
peripheral blood lymphocytes in vitro’, Biomedical And Environmental Sciences, Vol. 15,
pp.145–152.
Tewe, O.O. and Kasali, O.B. (1986) ‘Effect of cassava peel processing on the performance, nutrient
utilization and physiopathology of the African giant rat (Cricetomys gambianus Waterhouse)’,
Trop. agr. (Trinidad), Vol. 63, No. 2, pp.125–128.
Ugwu, B.O. and Ay, P. (1992) Seasonality of Cassava Processing in Africa, COSCA Working
Paper No. 9, Collaborative Study of Cassava in Africa, International Institute of Tropical
Agriculture, Ibadan, Nigeria.
UNCTAD (2012) CNUCED Fiche Produit: Manioc [online]
http://www.unctad.info/fr/Infocomm/Produits-AAACP/FICHE-PRODUIT—Manioc/)
(accessed March 2013).
Wagacha, J.M. and Muthomi, J.W. (2008) ‘Mycotoxin problem in Africa: current status,
implications to food safety and health and possible management strategies’, Int. J. Food
Micro., Vol. 124, No. 1, pp.1–12.
Wareing, P.W., Westby, A., Gibbs, J.A., Allotey, L.T. and Halm, M. (2001) ‘Consumer preferences
and fungal and mycotoxin contamination of dried cassava products from Ghana’, Int. J. Food
Sci. Tech., Vol. 36, No. 1, pp.1–10.
Westby, A. (1991) ‘Importance of fermentation in cassava processing’, Proceedings of the Ninth
Symposium of the International Society for Tropical Root Crops, Accra, Ghana,
20–26 October.
Westby, A. (2002) ‘Cassava utilisation, storage and small-scale processing’, in Hillocks, R.,
Tresh, J. and Bellotti, A. (Eds.): Cassava: Biology, Production and Utilization, pp.281–300,
CABI Publishing, Wallingford, UK.
Westby, A. and Twiddy, D.R. (Eds.) (1991) ‘Role of microorganisms in the reduction of cyanide
during traditional processing of African cassava products’, International Foundation for
Science (IFS) Proceedings. Workshop on Traditional African Foods: Quality and Nutrition,
Stockholm, Sweden, Vols. 25–29, pp.127–131.
Occurrence of mycotoxins in cassava (Manihot esculenta Crantz)
247
Westby, A. Ikwning, E.P., Gibbs, J.A. and Dallin, S.M. (1995a) ‘Formation of aflatoxins by
Aspergillus flavus and A. parasiticus isolates from cassava products: transformation
Alimentaire du Manioc’, Agbor Egbe, T., Brauman, A., Griffon, D. and Treche, S. (Eds.):
ORSTOM.
Westby, A., Wareing, P., Gibbs, J. and Dallin, S. (1995b) ‘Formation of aflatoxins by Aspergillus
flavus and A. parasiticus isolates from cassava products’, in Agbor Egbe, T., Brauman, A.,
Griffon, D. and Treche, S. (Eds.): Transformation Alimentaire du Manioc, pp.375–381,
Orstom, Paris.
Westby, A., Wareing, P.W. and Gibbs, J.A. (1994) ‘Ability of cassava products to support
mycotoxin formation’, Paper and poster presented at the 10th Triennal Symposium of the
International Society for Tropical Root Crops, Brazil, November 1994.
Wicklow, D.T. (1994) ‘Preharvest origins of toxigenic fungi in stored grain’, in Highley, E.,
Wright, E.J., Banks, H.J. and Champ, B.R., (Eds.): Stored Product Protection: Proceedings of
the Sixth International Working Conference on Stored-Product Protection, CAB International,
Wallingford, UK, pp.1075–1081.
Wild, C.P. (2007) ‘Aflatoxin exposure in developing countries: the critical interface of agriculture
and health’, Food Nutr. Bull., Vol. 28, No. 2, Suppl., pp.372–380.
Wild, C.P. and Gong, Y.Y. (2010) ‘Mycotoxins and human disease: a largely ignored global health
issue’, Carc., Vol. 31, No. 1, pp.71–82.
Williams, J.H., Phillips, T.D., Jolly, P.E., Stiles, J.K., Jolly, C.M. and Aggarwal, D. (2004) ‘Human
aflatoxicosis in developing countries: a review of toxicology, exposure, potential health
consequences, and interventions’, Amer. J. Clin. Nutr., Vol. 80, No. 5, pp.1106–1122.
Wu, F. (2004) ‘Mycotoxin risk assessment for the purpose of setting international regulatory
standards’, Env. Sci. Tech., Vol. 38, No. 15, pp.4049–4055.
Zhou, B. and Qiang, S. (2008) ‘Environmental, genetic and cellular toxicity of tenuazonic acid
isolated from Alternaira alternate’, Afr. J. Bio. Vol. 7, No. 8, pp.1151–1156.