Proper post-harvest handling will save grain from aflatoxins

Jul 24, 2020

It is also found in decaying vegetation, hay and grains undergoing microbiological deterioration.

FARMING  |  AGRIBUSINESS

On June 7, Uganda marked the World Food Safety Day. One major discussion of the day was poisonous foods, mainly due to poor post-   harvest handling.

For instance, ‘‘some of the foodstuff meant for COVID-19 relief was not fit for human consumption, because it was contaminated," an official from the Uganda National Bureau of Standards (UNBS) said.

According to UNBS, the flour contained aflatoxins. They are naturally occurring toxins that are produced by a fungi.

Now that the harvest of dry grains for the first season has started, farmers must ensure good post-harvest handling to avoid the risk of their produce being contaminated with aflatoxins.

"Despite the increase in production and consumption, of major staple crops such as cereals, legumes and oil seeds, quality and safety is still a major challenge," explains Vincent Ssempijja, the agriculture minister.

Ssempijja pointed out that the ministry has embraced aflatoxins mitigation as part of its food safety interventions under the Agriculture Sector Strategic Plan (ASSP).

How aflatoxins spread

According to a ministry handbook on management of aflatoxins in Uganda, the native habitat of the fungi that cause aflatoxins is in the soil. It is also found in decaying vegetation, hay and grains undergoing microbiological deterioration.

The fungi invades all types of organic substrates whenever conditions are favourable for its growth. Favourable conditions include high moisture content (at least 7%).

Aflatoxins can attack and contaminate grain before harvest or during storage.

Host crops, which include maize, barley, sorghum, soya and groundnuts, are particularly susceptible to infection by fungi following prolonged exposure to a high-humidity environment or damage from poor handling and conditions such as drought.

Affects quality feeds

Results from a comprehensive animal feed quality survey processed in Uganda done in 2015, revealed that the aflatoxin concentration in broiler starter, broiler finisher, layer mash and dairy meal was 40.5 ppb, 42.8 ppb, 67.5 ppb, 6.4 ppb.

The survey was done by Dr Swidiq Mugerwa, now director of the National Livestock Resources Research Institute (NaLIRRI).

Ppb (parts per billion) is a unit of measure for minute substances that are so small to be expressed in grams.

The recommended aflatoxin concentration in animal feed is 20 ppb. This means that in every one billion units of animal feed, there should be not more than 20 units/parts of aflatoxin.

UNBS, in collaboration with other bureaus of standards from the East African Community, has set a limit of 10 ppb for all foods and feeds, but only currently certifies products intended for export.

Other countries have different maximum tolerable levels of aflatoxin contamination with the European Union having the most stringent standards, at 4ppb.

However, UNBS says it is not easy to monitor the levels of aflatoxins in Uganda because most of the produce is traded informally.

Dr Jolly Kabirizi, a livestock nutrition scientist, explains that when animals are given feeds with aflatoxins, their development will retard and sometimes accelerate other diseases that may cause death.

"If it is a milking cow, it will gradually reduce production leading to losses," she says.

According to Mugerwa, ingestion of feed contaminated with aflatoxins not only undermines animal performance and productivity, but also present huge health risks to consumers of livestock tissues and products.

Humans can also acquire toxins by consuming contaminated foods such as maize and sorghum. The International Agency for Research on Cancer ranks aflatoxin as Group 1 possible cancer causers. In children, they reduce growth, leading to stunting and kwashiorkor.

Mugerwa pointed out that despite their importance in sustaining food and nutritional security, the productivity and profitability of intensive dairy and poultry industries in Uganda is undermined by the detrimental effects of aflatoxicosis.

This is despite the economic development and poverty eradication benefits. Aflatoxicosis is the syndrome resulting from ingestion of feeds contaminated with aflatoxins.

Ingestion of feeds by animals containing such alarming levels of aflatoxins is associated with growth depression. This is caused by a decline in feed quality as well as intake induced by aflatoxins.

This affects nutrient utilisation and decline in feed quality. It is estimated that with each mg/kg increase of aflatoxins in the diet, the growth rate for broiler birds would be reduced by at least 5%.

In laying birds, aflatoxicosis reduces egg production and egg size by 10% and 5% respectively, in addition to impairing semen quality.

Aflatoxins are immune suppressants and aflatoxicosis has been noted to escalate the susceptibility of birds to infectious diseases, such as Newcastle.

"Because of these toxins, when you immunise chicken from diseases such as Newcastle, there is no effect because of the toxins," Mugerwa says.

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