Cooking: Is it enough?
Izelle Theunissen, MRC News
Mention the word 'phutu' or 'pap' and any South African would know what you
mean. Scientists from the MRC's PROMEC Unit recently investigated whether the
cooking process is enough to destroy naturally occurring fumonisins in this
traditional South African dish. They also argue that international fumonisin
exposure guidelines should take into account more details about maize
consumption.
Fumonisms
Fumonisins are secondary metabolites produced in maize mainly by the fungus Fusarium
verticillioides. The most abundant fumonisins are FB1, with FB2 and FB3
occurring in lesser amounts.
FB1 has been linked to various diseases in animals, such as
leuko-encephalomalacia in horses and pulmonary oedema in swine. But it also has
carcinogenic properties: research has shown that it causes kidney and liver
cancer in male rats and liver cancer in female mice.
"We have also associated the fumonisins with the high incidence of
oesophageal cancer in the Transkei region of the Eastern Cape Province,"
says Dr Gordon Shephard, a Chief Specialist Scientist in the MRC's PROMEC Unit.
So it's no small wonder that fumonisin levels are of international concern, with
guidelines stipulating their maximum levels already in place in some countries.
The recent 56th meeting of the Joint FAO/WHO Expert Committee on Food Additives
(JECFA) determined a group provisional maximum tolerable daily intake (PMTDI) of
2 µg/kg bodyweight/day.
"Although these guidelines are designed to protect consumers in the
developed countries where maize consumption is low, much lower tolerance levels
of 200 µg/kg would be required to protect subsistence farming communities that
consume maize as a staple diet in developing countries - such as the communities
in the Transkei region," Dr Shephard says.
Research work has shown that maize consumption in this region is as high as 460
g per person per day - in contrast to developed countries where consumption is
no higher than 7 g per person per day.
The Unit's research in the region showing high exposure to fumonisins has always
been performed on uncooked home-grown maize. "But we also wanted to
investigate whether exposure could be lowered through preparation of the
traditional stiff porridge. This is a typical meal in these rural
communities," Dr Shephard explains.
Cooking test
Following a traditional recipe, the scientists prepared the maize and analysed
the contents. At first glance, the results are encouraging. In general,
fumonisin levels were lowered by 23% through the cooking process. "But this
doesn't constitute a decontamination procedure - communities reliant on maize as
their staple diet are indeed at risk of fumonisin exposure in their daily
consumption of this porridge," says Dr Shephard.
According to him, some studies have shown fumonisins to be heat-stable. "So
the fumonisins that are apparently lost during the preparation of the porridge
could merely have been rendered impossible to extract by binding to the starch
matrix or by the formation of various sugar adducts - thus giving a different
result," he explains.
Making provision for different communities
Dr Shephard believes that the setting of the PMTDI has highlighted the potential
exposure of various world communities to fumonisins. In addition to the Transkei
region, various South and Central American communities also have high levels of
consumption. "For instance, one reference from Mexico reports consumption
as high as 510 g/person/day," says Dr Shephard.
There are also differences in the way maize dishes are prepared. "In Mexico
maize is consumed mainly as tortillas, following a lime treatment which leads to
a reduction in fumonisin levels by hydrolysis," he explains.
"Risk assessment takes into account both hazard and exposure assessment.
International concerns over fumonisin exposure and the consequent hazard
assessment have resulted in the establishment of the PMTDI of 2 µg total
fumonisin/kg bodyweight/per day by JECFA. But we believe accurate and
comprehensive exposure assessments require detailed knowledge of maize
consumption in various populations - taking into account whether maize is a
staple food of a population," says Dr Shephard.
Article courtesy of the MRC news
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