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.