SA Grain June 2017

Research strategy aims to eliminate

mycotoxins in South African grains

n South Africa, the supply of high quality, healthy maize is a na-

tional priority since maize represents the staple food of many

South Africans. Moreover, maize is of great importance as feed-

stock in the animal and poultry i dustry.

In nature most cereal grains, oil seeds, tree nuts, fruits and dehydrat-

ed fruits are susceptible to contamination by mycotoxin-producing

fungi during the pre-harvest (production), post-harvest (storage) and

processing stages.

These fungi have the ability to produce some hazardous toxins,

called mycotoxins such as the fumonisins, aflatoxins, zearalenone,

ochratoxins, trichothecenes (deoxynivalenol [DON] and nivalenol

[NIV]) and diplodiatoxins (diplonine).

Fortunately, the hepatocarcinogenic aflatoxins occur extremely

rarely on South African commercial maize, reducing their signifi-

cance locally as a potential health threat. The fumonisins, mainly

produced by

Fusarium verticillioides

and

Fusarium proliferatum

represent the most important mycotoxin threat to the local maize

industry.

Mycotoxins pose an enormous threat to the international trade in

foods and feeds. Post-harvest losses in the developing world, in

particular, are severe because of inadequate storage facilities and

the consequent poor quality of the produce. It is claimed that ap-

proximately 60% of Africa’s grain supplies are at risk owing to

fungal contamination and mycotoxin formation, thereby contributing

to food insecurity.

The more than 300 known mycotoxins comprise small-molecular-

weight compounds, derived from the secondary metabolism of

several fungi, including members of the genera

Aspergillus, Penicil-

lium, Fusarium, Claviceps, Stenocarpella

and

Alternaria

These compounds are thermally stable and cannot be eliminated

during food processing. Mycotoxins induce powerful and dissimi-

lar biological effects in humans and animals. Some are carcinogenic

(aflatoxins, ochratoxins and fumonisins), mutagenic (aflatoxins and

sterigmatocystin), teratogenic (ochratoxins), oestrogenic (zearale-

none), haemorrhagic (trichothecenes), immunotoxic (aflatoxins and

ochratoxins), nephrotoxic (ochratoxins), hepatotoxic (aflatoxins,

ochratoxins and phomopsins), dermatoxic (trichothecenes) and

neurotoxic (ergotoxins, penitrems, lolitrems and paxilline), whereas

others display antitumor, cytotoxic and antimicrobial properties.

The global health threat of mycotoxins to mankind is based on well-

documented human mycotoxicoses such as ergotism, alimentary

toxic aleukia in Russia, acute aflatoxicoses in South and East Asia,

and human primary liver cancer in Africa and South East Asia.

The fumonisins are implicated in the aetiology of the high incidence

of oesophageal cancer among the inhabitants of the former Tran-

skei region of South Africa, China and Iran and with clusters of birth

defects, i.e. neural tube defects such as anencephaly and spina

bifida, occurring in different parts of the world such as on the Texas-

Mexico border.

Although the role of mycotoxins in diseases among domestic ani-

mals is better established, diagnosis of the mycotoxicosis is ex-

tremely difficult owing to the numerous pharmacological effects of

the causative toxins, for example aflatoxins (Turkey-X disease), fu-

monisins (leukoencephalomalacia in horses and pulmonary oedema

in swine), ochratoxins (nephropathy in swine [Danish porcine ne-

phropathy]), phomopsin A (lupinosis in sheep), sporidesmin A (facial

eczema in sheep) and zearalenone (hyperoestrogenism, vulvovagi-

nitis and abortion in swine). Outbreaks of diplodiosis amongst farm

animals are linked to feeds contaminated with

Stenocarpella maydis

Since the discovery of aflatoxins during the 1960s, an increasing

number of countries have legislated maximum tolerated levels for

an increasing number of mycotoxins with the aim of protecting both

human and animal populations from the harmful effects of myco-

toxin exposure.

June 2017

ON FARM LEVEL

Integrated pest control

Research / Mycotoxin-producing fungi

PROF PIET STEYN,

consultant to the Maize Trust

1a - 1c: An example of

Fusarium verticillioides

Photos: Dr Belinda J van

Rensburg, ARC-Grain Crops