Opportunities for improving maize quality and reducing post harvest losses through effective aflatoxin
management
Opportunities for improving maize quality and reducing post harvest losses through effective aflatoxin
management
Kerstin Hell IITA, Benin
Pascal Fandohan INRAB, Benin
Ousmane Coulibaly IITA, Benin
Ranajit Bandyopadhyay IITA, Ibadan
Outline Introduction
Factors that influence aflatoxin
Prevalence of mycotoxins in Africa
- contamination on different commodities
- distribution across agroecological zone
Mycotoxin management
- systems management
- resistance breeding
- biocontrol
- awareness campaign
Conclusions + Perspectives
Food security
Food Security exists when all people, at all times, have physical and economic access to sufficient, safe and nutritious food to meet their dietary needs and food preferences for an active (productive) and healthyhealthy life.
Food safety: microbial contaminants and chemical toxicants below tolerance levels.
Children are most prone to ill-effects of unsafe food.
Important food (per caput kg/year) in African diet
Commodity 1961 2000 Change (%)
Cassava 111.8 103.1 - 8%
Maize 31.8 40.1 + 26%
Banana/plantain 30.5 28.5 - 7%
Yams 19.6 28.2 + 44%
Milk 27.9 27.1 - 3%
Sorghum 32.2 23.7 - 26%
Millet 22.4 17.4 - 22%
Meat 12.7 11.4 - 10%
Aflatoxin problem
Fungi attack cereals under favorable environmental conditions.
Three species of Aspergillus produce aflatoxins : Aspergillus flavus Link ex Fries, Aspergillus parasiticus Speare and Aspergillus nomius (Kurtzman et al. 1987).
Aflatoxin cause illness to humans and animals
• Cause liver cancer, affects body's immune system and cause growth retardation.
• Associated with malnutrition syndrome, and can lead to many other disorders and even death
• Blood tests show high human exposure in Asia and Africa (99% children)
Animal health impact of aflatoxin
Livestock and poultry losses
– liver damage including cancer
– recurrent infection due to immune system suppression
– reduced growth rate
– losses in feed efficiency
– decreased milk and egg yield
– embryo toxicity (reduced reproductivity)
– death (cattle, turkey, poultry, swine..)
Tolerance level of animal species
vary for different mycotoxins
Fungal growth and toxin development
For fungal growth and subsequent toxin production a suitable
substrate is required.
Factor(s) that initiate toxin formation: water stress, high-
temperature stress, insect damage of the host plant, specific crop
growth stages, poor fertility, high crop densities, and weed
competition.
Aflatoxin formation is also affected by associated growth of other
molds or microbes.
The occurrence of aflatoxins is influenced by environmental factors ; hence the extent of contamination will vary with geographic location, agricultural and agronomic practices, and the susceptibility of commodities to fungal invasion during preharvest, storage, and/or processing periods. .
Factors influencing fungal growth and toxin development Pre Harvest
- Growth cracks, mechanical injury and damage by pests to the
plant parts or seeds leads to infestation by fungi.
- Toxins are produced under high temperatures, drought, high
insect activity and terminal water stress prior to harvest.
Post Harvest
- Fungi continue to grow and produce aflatoxins under high
moisture and warm temperatures.
- This process is enhanced if drying is delayed. Damage by
insect or rats can also facilitate mold invasion and toxin
production during storage.
Habitat management options
Protect harvested cobs from rain
Sorting of kernels with insect damage + discoloration:
from 3 to 7% aflatoxin; while unsorted from 7 to 13%
Cobs with 10% insect damage averaged 388 - 515 ppb
Maize stored in bags have more aflatoxin (particularly
w/o insect control) in West Africa
Significant reduction in aflatoxin levels of maize samples
treated with Mycosorb® shown in lab tests
Drying maize and aflatoxin content
If not < 17% grain moisture after 72h from
harvest, significantly high aflatoxin risk
Drying on black plastic sheets or cemented dry
areas lead to safe moisture levels after approx. 5
days while drying maize cobs in ground needs
minimum 10 days.
Mycotoxigenic fungi at high levels when drying
on stalk or on ground
Traditional processing methods on aflatoxin from contaminated corn
Roasting and treatment
with alkali reduce level of
aflatoxin
Boiling and soaking of
corn in lime-water could
eliminate or greatly
reduce the levels of
aflatoxin in the final
product
Selective removal or
isolation of contaminated
portions of the food
commodity is the most
widely used physical
method for aflatoxin
decontamination
Research still needed on
others to minimize risks
Survey results - commodities
Maize
44% of the samples aflatoxin positive
mean of positive samples116 ppb
highest prevalence in the SGS and SS Yam chips
17% > 20 ppb (WHO); 75% >4 ppb (EU) Cowpea
all aflatoxin and fumonisin positive (N=30)
mean of 5.92 ppb Groundnut
3-20ppb 2.9%, >20ppb 1.7%
Mycotoxin risk areas in Africa
High aflatoxin risk zones: moist savannas (with bimodal rainfall patterns) and hot dry savannas
Fusarium toxin risk zones: humid forest and mid-altitudes
Aflatoxin contamination increases with storage time especially in drier savanna
Drier savannaMoist savannaHumid forestMoist midaltitudeDrier midaltitudeHigh altitude
Development of aflatoxin management strategies in maize Host plant resistance
Fertilizer use
Biological control
Time of harvest
Threshing method
Grain drying method
Storage structure
Storage form
Sorting
Insect control
Contaminated Healthy
Reducing the Risk of Aflatoxin Contamination in Maize Pre harvest
Plant maize hybrids with first possible rains and harvest crop at
correct maturity.
Remove dead plants and plants showing severe stress due to pest
or pathogen attack.
Remove weeds and protect crop from corn borer damage.
Avoid continuous planting of maize under conservation tillage.
Avoid excessively high plant populations and excessive
application of nitrogen.
Visually inspect cobs for fungal infections/damage on the grain
and discard the affected cobs.
Reducing the Risk of Aflatoxin Contamination in Maize Post harvest
Avoid mechanical damage to seed during harvesting, drying and
storage.
Protect harvested cobs from rain
Sorting of kernels with insect damage + discoloration: from 3 to
7% aflatoxin; while unsorted from 7 to 13%
Maize stored in bags have more aflatoxin (particularly w/o insect
control) in West Africa
Clean grain bins/storage areas before putting the new crop.
Stock cobs or seeds in bags on wooden plank and store them in
well aerated waterproof area.
Avoid stacking of harvested crop with cobs intact.
Drying maize and aflatoxin content
If not < 17% grain moisture after 72h from harvest,
significantly high aflatoxin risk
Rapidly dry the grain down to 13.5% moisture content
and store the seeds.
Drying on black plastic sheets or cemented dry areas
lead to safe moisture levels after approx. 5 days while
drying maize cobs in ground needs minimum 10 days.
Mycotoxigenic fungi at high levels when drying on stalk or
on ground
Management Practices (IITA research)
Late planting increased toxin contamination (Borgemeister et al.
2001)
Late harvesting increased the risk of toxin contamination (Hell et
al. 1996)
Removal of insect damaged cobs at harvest (Hell et al. 2000)
Rapid drying outside the field and off the ground, drying over
fire very effective (Yetondji et al. 2000)
Decision making system for insect and fungi, differs for climatic
zones (Meikle et al. 2002)
Sorting prior to consumption (reduced by 15%) (Hell et al. 2005)
Aflatoxin management
Training farmers in major
maize growing areas in
Benin (FFS approach)• Good agronomic
practices
• Proper harvesting and drying of grain
• Maintaining grain quality
• Hygiene and sanitization of grain handling and storage structures
Other Management Options of Aflatoxins
• Regulatory Control
• Detoxification Strategies• Physical methods of separation, thermal
inactivation, microbial inactivation, and fermentation
• Chemical methods e.g. ammoniation
• Modification of Toxicity by Dietary Chemicals• Food and feed additives (e.g. antibiotics and
preservatives).
• Alteration of Bioavailability by Aflatoxin chemosorbents• Inorganic sorbent materials (HSCAS).
0
200
400
600
800
1000
1200
1400
1600
1800
Afl
ato
xin
(p
pb
)
TZ
MI1
02
13
68
18
23
TZ
M1
04
TZ
MI5
02
Inbred Lines
Field-03 Field-04 KSA
Aflatoxin resistance in maize inbreds
Aflatoxin resistance in maize
Collaboration with USDA
Resistance evaluation by
lab (US) and field tests
(Nigeria)
Many inbreds being tested
for resistance
Promising sources of
resistance identified in lab
and field evaluations
Synthetics being
constituted.
0
200
400
600
800
1000
1200
1400
1600
1800
Afl
ato
xin
(n
g/g
)
TZMI1
0213
93
TZMI3
0550
12
1368
-150
5718
23
TZM10
4
TZMI5
02
Inbreds
Ibadan USA
Mean fumonisin in selected elite inbred lines evaluated at Ibadan under artificial infection with F. verticillioides
Fumonisin 2003 2004 (ppm)
(1368/S.A. Pub Lines36/1368)-2-2-2-B 2.5 0.8 (CIM 116 x TZMi 302 x CIM 116)-2-2-B 3.3 3.7 KU1414xICAL 36-1xKU1414-6-1-B 4.7 3.5 Obantapa-9-3-1-1-B 5.9 6.5 Obantapa-33-5-1-B 5.9 4.7 Obantapa-31-1-1-B 5.9 0.3 PIONEER SEEDS-26-2-1-B 32.4 37.1 ((KU1414 x 9450) x 9450)-24-2-1-B 43.5 25.4 P43SRC9FS100-1-1-8-#1-B1-4-B 55.0 21.6 1368xINV 534-1x1368-7-1-B 62.0 58.6 4205 63.5 99.2 1368xICAL 224-1x1368-2-2-B 87.2 25.0 Mean 28.9 17.1 SE 4.2 3.3
Biological control of aflatoxin
Ability to produce aflatoxin in A. flavus
strains varies
Some strains produce a lot (toxigenic), and
others little aflatoxin (atoxigenic)
Competitive exclusion (one strain competing
to exclude another) as biocontrol principle in
final stages of approval in the US
24 atoxigenic from 6 locations plus four
toxigenic strains being field-tested
Toxigenic
Atoxigenic
Awareness campaign to sensitize the population on aflatoxin risk
At least 3278 people in Ghana, Togo and Benin benefited directly
8 national scientists trained in aflatoxin monitoring
792 maize farmers, 820 traders, 1180 consumers, 200 poultry farmers and 140 animal feed producers received information about aflatoxin.
137 stakeholders involved in campaign
Awareness campaign to sensitize people on aflatoxin risk
Aflatoxin-aware farmers increased
by 46% and 39% in Benin and
Togo.
The percentage of informed
traders was significantly 10.3 and
3.2 times higher in Togo and
Benin
33% more traders believed the
campaign messages.
More than 10 million people in
Benin, Togo and Ghana are now
aware of the dangers of aflatoxin-
contaminated feed/foods.
Incentives to Farmers
Aflatoxin management
practices not only minimizes
the contamination, but also
contributes to increased yields
Fetches higher remuneration
Safe to eat “aflatoxin” free
food
Reduction of postharvest
losses
Potential for direct buying by
export oriented industries –
higher dividend
EUROPEAN UNION (EU)
2004: REJECTIONS ACCORDING TO IDENTIFIED RISK
SOURCE: EU Rapid Alert System For Food and Feed (RASFF, 2005)
Conclusions
Mycotoxins in food and feed pervasive in Africa.
Negative impact overlooked – chronic, unseen.
Serious effect on children’s growth & development.
Export potential of primary raw material unrealized.
Institutions related to food safety very weak.
New approaches, tools and coalition to manage mycotoxin are needed.
Management options are possible to manage toxins
Aflatoxin received most attention; studies needed on other mycotoxins as well.
Future research directions at IITA
Food basket survey for multiple mycotoxins,
Bio-ecological aspects of mycotoxin
production,
Deployment of biological control,
Proteomics and resistance ,
Resistance breeding,
Strategies to reduce impact of mycotoxins
in trade,
impact of aflatoxin management options and/or nutritional improvement
on children’s growth and health ,
R&D network to deal with mycotoxins, food safety and trade.