Junie 2014
70
Aflatoxins inmaize’spotential
impact on consumers
A
flatoxins are naturally occurring poisonous substances
producedby the fungi
Aspergillus flavus
and
A. parasiticus
which infect and contaminatemaize andgroundnut grains.
flatoxins are potentially problematic in seasons favourable for
plant infection or contamination of stored grains. In unfavourable
seasons levels of aflatoxins may be negligible with minor potential
mycotoxicotic effects on humans and animals that consume
thegrain.
A previous study carried out during the 2005/2006 and 2006/2007
seasons on aflatoxin contamination of maize and groundnut
samplesproducedbysubsistence farmers inLimpopo,Mpumalanga,
KwaZulu-Natal and the Eastern Cape provinces, indicated that
aflatoxin contamination is sporadic, but it can reach levels as high
as 49 parts per billion (ppb) in a singlemaize sample and be absent
inother samplescollected from thesamearea, e.g. Jozini innorthern
KwaZulu-Natal.
Themaximum allowable limit for aflatoxins in human food in South
Africa is 10ppb (tenparts per billion is the same as onepinchof salt
in 10 tons of potato chips or one second in 22 years).
Maize is a major staple food in South Africa with the average daily
intake being 300 g or more per capita. Exposure to human food or
animal feed contaminatedwith aflatoxins through ingestion, results
in reducedperformance, depressed immunity and sicknessor death
inhumans and animals.
High aflatoxin levels can be lethal in livestock, particularly young
pigs, pregnant sows, calves and young poultry. Contamination
of crops with aflatoxins is often most severe in rural areas where
subsistence farmers are unaware of their existence, and follow
agricultural practices that might contribute to the production of
aflatoxins. The quality of maize consumed, thus determines the
qualityof human and animal life.
Contamination ofmaizewith
Aspergillus
fungi and aflatoxin
Aflatoxins are produced during both pre-harvest and post-harvest
stages of grain production by
Aspergillus
species which survive
onmaize debris and infect maize ears through the silk. The fungus
grows from the ear tip (silk) towards thebase.
Hot and humid conditions favour the growth of
Aspergillus
species.
Drought stress, temperatures between 26°C - 30°C aswell as insect
and physical grain damage are factors that contribute to aflatoxin
production in the field.Aflatoxinproductionmayalso increaseduring
storagewhere relativehumidity, grainmoistureand temperatureare
favourable for aflatoxin contamination.
Subsistence farming, aflatoxin
contamination andmaize production
Subsistence farmers often lack the necessary resources to ensure
productionof qualitygrain from fieldplantings to consumption.
With restricted access to resistant hybrid seed, fertilisers and
pesticides, the yield and product quality of subsistence farmers is
often severely affected by poor soil fertility, fungal infections and
pest damage.
Most grain isharvestedand storedon farmor in silos formedium- to
long-term storage, generally under conditions with poor aeration,
poormoisture and temperature control, which are factors known to
influence aflatoxinproductionduring storage.
Prevention strategies for the reduction of
aflatoxin contamination
Control of stalkborersusing chemicals suchasBulldock® (beta-
cyfluthrin).
PlantingBtmaize hybrids that reduce stalk borer levelswhich in
turn reduce aflatoxin contamination by indirectly reducing the
disseminationof
Aspergillus
spores.
Early harvesting and rapid drying of maize to moisture levels
below 12% reduces aflatoxinproduction.
Avoid mixing damp and dry grain during storage because an
isolatedpocket of dampgrain supports fungal growthwhich can
spread to the surroundingdrygrain.
Optimum conditions for storage are temperatures below 12°C,
relative humidity below 85%, and grain moisture content
below 12%.
Storage facilities must be regularly monitored to ensure early
detection and control of insect and fungal infestations. Oldgrain
residue must not be mixed with new grain and storage areas
must be sanitisedbeforenewgrain is stored.
Sorting of grain to remove discoloured grain before use for
human consumptionwill assist in reducing aflatoxin levels.
Contaminated grain should preferably be destroyed as aflatoxin
has a way of finding its way back into the food chain via
contaminatedmilk ormeat.
Research on storage practices of
subsistence farmers at theARC-GCI
The researchers at the ARC-GCI are involved in a follow-up study
to determine the effect of storage systems on contamination by
aflatoxins andother fungalmycotoxins (fumonisins, deoxynivalenol,
nivalenol and zearalenone) in maize produced by subsistence
farmers innorthernKwaZulu-Natal.
Since storage systems are important sources of contamination and
aflatoxin accumulation in rural areas, grain is collected after harvest
and after grainhas been in storage for three to fourmonths.
Results indicate that one sample each from Vryheid (1,23 ppb) and
Mbazwana (0,09 ppb) were positive for aflatoxin while a sample
from Jozini had aflatoxin levels of 44,9ppb.
Since the maximum allowable limit for aflatoxin in human food in
SouthAfrica is 10 ppb, some farmers, such as the one in Jozini, are
still exposed to dangerously high levels of aflatoxins. This indicates
that the nature of contamination is sporadic, but potentially very
ON FARM LEVEL
Aflatoxins /Maize / Subsistence farmers / Impact
Pest control
Subsistence farmers–NorthernKwaZulu-Natal:
EDSONNCUBE
and
SYLVIAPHOKANE;
ARC-GrainCrops Institute
