Prevalence of aflatoxin along the maize

value chain in Kenya.

George Mahuku (CIMMYT) & Henry

(H. Sila) Nzioki (KARI)

Mycotoxin producing fungi

• Weak parasite

• Very susceptible

to ecological

conditions

• Optimum

conditions differ

for growth &

toxin production

• Mycotoxins

production

elicited by stress

AF

A. Flavus

FB

F. verticillioides

DON

F. graminierum

Temp 25° 35° 30°

aw 0.98 0.78 0.96

Mycotoxins in Maize and effect on

human health

Fungus Mycotoxin International

limits (vary)

Health Effects

Aspergillus

flavus and A.

parasiticus

Aflatoxin B1 (0 – 50 ppb)

Kenya (10 ppb)

Carcinogen, affecting the liver,

reduced efficiency of the

immunological system, retards

growth and development of

children

Fusarium

verticillioides

Fumonisin B1 4 ppb Asociated with esophageal cancer,

and neural tube defects leading to

abortion

Fusarium

graminearum

Zearalenone Not established Properties of estrogen hormones

F.

graminearum

Deoxynivalenol 1 ppm Reduced efficiency of the

immune system

Penicillium

verrucosum

Ochratoxin A Not established Chronical renal diseases

Variation in acceptable aflatoxin levels

Aflatoxin

• are naturally occurring mycotoxins

produced by the fungi Aspergillus

flavus and A. parasiticus.

• not all A. flavus strains are toxigenic

• grow on maize, peanuts ,wheat, beans

and rice.

• are a problem particularly in warm and

humid, tropical countries.

• drought conditions are ideal for growth

and proliferation of fungi.

Aflatoxin affected major crops

• Cereals: Maize, Sorghum, Pearl millet

• Oil seeds: Groundnuts, Soybean, Sunflower

• Spices: Chillies, Black pepper, Turmeric

• Tree nuts: Pistachio, Almonds, coconut

Aspergillus and aflatoxin

• Aspergillus flavus – opportunistic pathogen

• Superior adaptability

– Survives in a wide range of environments: soil, plant debris, dead insects

and seeds

• Fungus does not need a live host to survive

• Complex environmental and ecological factors affect A. flavus

infection and aflatoxin contamination.

• Aflatoxin contamination is:

– unavoidable under the present production, processing and storage of

crops & commodities.

• Infection and aflatoxin contamination can occur at pre-harvest,

harvest, post-harvest, process, storages, transit stages

Factors affecting Aflatoxin contamination

of Maize

Distribution Detection/diversion

Animal Products

Humans Animals

Processing &

Storage -Structure;

-Moisture; -Temperature

Harvesting - Crop maturity

- Temperature

- Moisture

-Handling

Environmental Factors

-Temperature

- Moisture availability

- Mechanical injury

-Insect/ bird damage

Biological Factors

-Susceptible crop

- Compatible toxigenic fungi

Aflatoxin in the Food Chain

FEED

Response to different concentrations of aflatoxin

Increasing concentration of aflatoxin

zero

Objectives

• Understand the incidence and prevalence of aflatoxin

along the maize value chain in selected study areas.

• Identify critical points where intervention

technologies are mostly likely to be more effective

Maize Sampling Sites

• Lower Eastern – Machakos County: Machakos, Kathiani Kangundo and

Matungulu Districts

– Makueni County: Mbooni East and Makueni Districts

• Upper Eastern – Embu County: Mbeere North, Embu North and Embu

West Districts

• South Western Kenya – Homabay County: Homabay and Rongo Districts

– Kisii County: Kisii Central District

Methodology

• Along identified critical points along the market

chains, samples were collected:

• Pre-harvest – physiological maturity while in the field

• Harvest, handling and processing for storage

• Storage by farmers (30 day interval)

• Markets (30 day interval)

• Assemblers

• Wholesalers

• Retailers

• Consumers of products

Information / Data collected

• Farmer / Actor name

• GPS coordinates

• Maize variety

• Source of maize

• Moisture content

• I kg maize sample for analysis (following a standard protocol: Aflacontrol website)

Maize samples collected from farmer

fields (pre-harvest)

Year

Region 2009 2010 2011 Total

Lower Eastern (LE) 30 167 143 340

Upper Eastern (UE) 10 41 40 91

South Western (Homabay/Rongo [HR})

- 153 99 252

South Western (Kisii

Central [KC]) - 78 41 119

Total 40 439 323 802

Maize samples collected from farmer

stores (post-harvest / storage)

Year

Region 2009 2010 2011 Total

Lower Eastern 87 276 156 519

Upper Eastern 59 253 44 356

South Western (Homabay/Rongo)

- 368 101 469

South Western (Kisii Central) 30 214 39 283

Total 176 1111 340 1627

Maize samples collected from

markets

Year

District 2009 2010 2011 Total

Lower Eastern 152 535 219 906

Upper Eastern 126 232 38 396

South Western (Homabay/Rongo)

- 345 92 437

South Western (Kisii

Central) 52 154 40 246

Total 330 1266 389 1985

Total Samples analyzed = 4,414

Maize samples from farmer fields & Stores with aflatoxin levels above and below 10ppb (2009)

Farmer Fields Farmer Stores

0

20

40

60

80

100

120

UE(N=10)

LE(N=30)

UE(N=58)

LE (N=87)

KC(N=30)

#Samples <10 (μg/kg)

% Samples >10 (μg/kg)

Region Range (μg/kg) STDev

FF

Upper Eastern (UE) 0 - 9091.8 2874.9

Lower Eastern (LE) 0 - 273.8 68.9

FS

Upper Eastern (UE) 0 - 27393.7 4188

Lower Eastern (LE) 0 - 3180.7 422

Kisii Central (KC) 0 - 5.4 1.6

Maize samples from market with aflatoxin levels above and below 10ppb (2009)

0

10

20

30

40

50

60

KC (N=52) LE (N=152) UE (N=126)

% Samples <10 (μg/kg)

% Samples >10 (μg/kg)

Region Range (μg/kg) STDev

Upper Eastern (UE) 0 - 12000 2160

Lower Eastern (LE) 0 - 9302 166.4

Kisii Central (KC) 0 – 3442.2 2160

Proportion of Maize samples from the farmer stores with aflatoxin levels

above 10 ppb (2009)

0

10

20

30

40

50

60

70

80

90

Makueni Embu MbeereNorth

Kisii

1 month PH

2 months PH

3 months PH

Proportion of Maize samples from the market with aflatoxin levels above 10 ppb (2009)

0

10

20

30

40

50

60

70

80

90

100

Makueni Embu MbeereNorth

Kisii

1 month PH

2 months PH

3 months PH

Maize samples from farmer fields & Stores with aflatoxin levels above and below 10ppb (2010)

0

10

20

30

40

50

60

70

80

90% Samples <10 (μg/kg)

% Samples >10 (μg/kg)

Region Range (μg/kg) STDev

FF

Upper Eastern (UE) 0 - 252 52.7

Lower Eastern (LE) 0 – 1454.8 139.1

Hbay/Rongo (HB) 0 – 722.2 66

Kisii Central (KC) 0 – 558.7 77.5

Upper Eastern (UE) 0 – 22641.7 253.5

FS

Lower Eastern (LE) 0 – 1978.3 234.5

Hbay/Rongo (HB) 0 – 1511.2 123.6

Kisii Central (KC) 0 – 611.8 77.2

Farmer Fields Farmer Stores

Maize samples from the first and second seasons with aflatoxin levels above 10ppb

(2010)

0

5

10

15

20

25

30

35

40

45

50

Lower Eastern(N=149)

Upper Eastern(N=41)

Hbay/Rongo(N=153)

Kisii Central(N=79)

October-November

March - May

Proportion of samples collected from

farmer stores with aflatoxin levels above

10 μg/kg (2010)

July - August harvest February – March harvest

0

10

20

30

40

50

60

70

80

1 month 2 months 3 months

KisiiCentral

Homabay / Rongo

Lower Eastern

Upper Eastern

0

10

20

30

40

50

60

70

80

1 month 2 months

Maize samples from markets with aflatoxin levels above and below 10ppb, (2010)

0

10

20

30

40

50

60

70

80

90

LowerEastern(N=535)

UpperEastern(N=232)

Hbay/Rongo(N=345)

Kisii Central(N=154)

% Samples <10 (μg/kg)

% Samples >10 (μg/kg)

Region Range (μg/kg) STDev

Upper Eastern (UE) 0 – 1632.9 184.7

Lower Eastern (LE) 0 – 2076.7 188.4

Hbay/Rongo (HB) 0 – 379.5 42

Kisii Central (KC) 0 – 1308.8 148.9

Maize samples from farmer fields & Stores with aflatoxin levels above and below 10ppb (Jan – May

2011)

Farmer Fields Farmer Stores

Region Range (μg/kg) STDev

FF

Upper Eastern (UE) 0 – 581.5 94.4

Lower Eastern (LE) 0 – 354.6 49.8

Hbay/Rongo (HB) 0 – 20.2 3.6

Kisii Central (KC) 0 – 63.1 9.8

Upper Eastern (UE) 0 – 248.5 49.1

FS

Lower Eastern (LE) 0 – 685.6 92.9

Hbay/Rongo (HB) 0 – 41.6 5.6

Kisii Central (KC) 0 – 357.2 57

0

20

40

60

80

100

120% samples < 10ppb

% samples >10 ppb

Maize samples from markets with aflatoxin levels above and below 10ppb, (Jan – May, 2011)

Region Range (μg/kg) STDev

Upper Eastern (UE) 0 – 1679.6 286.2

Lower Eastern (LE) 0 – 3568.3 335.9

Hbay/Rongo (HB) 0 – 36.8 5.9

Kisii Central (KC) 0 – 60.7 9.7

0

10

20

30

40

50

60

70

80

90

100

H/R (N=92) KC (N=40) LE (N=219) UE (N=38)

% samples < 10ppb

% samples >10 ppb

Conclusion

• Occurrence of aflatoxins in maize is a complex series of interaction between G x E x Pathogen x Farmers practices. This complexity poses difficulties in achieving control.

• We did not find differences in aflatoxin levels among varieties / hybrids grown by farmers.

• Contamination starts from the field

– Need to factor in environmental conditions

• Aflatoxin is not homogeneously distributed in contaminated lots. Sampling poses a major challenge, hence the fluctuations between sampling times.

• Aflatoxin contaminated maize samples were found from both South western and Eastern Kenya regions

• This is the first systematic study looking at aflatoxin contamination along the maize value chain

Acknowledgements

• Partners: Ministry of Agriculture extension

staff, Farmers, Traders, KARI – Katumani

staff: Centre Director, crop protection and

support staff

• ICRISAT for aflatoxin analysis

• ACDI/VOCA

• Financial support

– Bill and Melinda Gates Foundation