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.
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.
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.