Food safety experts and farmers have warned Nigerians not to eat dark-stained yams, saying some types of discolouration could mean the yams had gone bad and could cause major health problems.
The warning was given in separate interviews with the News Agency of Nigeria in Lagos on Sunday by the Lagos State All Farmers Association of Nigeria and a public health specialist.
Some yams, they said, can turn black and still be OK to eat but soft black areas, bad smells and obvious mould can mean they have gone bad.
The stakeholders identified numerous plausible causes of yam discolouration and deterioration such as the usage of fertiliser, rodent attacks, accidental injuries while weeding and possible microbial contamination.
The Lagos State AFAN Chairman, Mr Sakin Agbayewa, said the colour of yam could be a function of the type of fertiliser used in farming.
He also said elements that could impair yam quality include fertiliser application, rodent assaults and inadvertent cuts to tubers during weeding.
He said rodents occasionally attack yam tubers planted in heaps and consume chunks of the tubers without the farmers recognising the damage.
Farmers may conceal holes in yam piles with earth not knowing that rodents have harmed the tubers. This will cause the affected yams to deteriorate as they grow.
Agbayewa also said that cutlasses used in weeding could accidentally cut yam tubers and make them liable to deterioration.
Prof Tanimola Akande, a public health expert, said the safety of dark-stained yam depends on the origin and the extent of the discolouration.
He said yam could colour naturally when exposed to air, but it could still be safe to eat, unless it showed other signs of rotting.
But Akande said that soft dark spots, bad aromas and apparent mould could be signs of decomposition due to bacterial or fungal activity.
He said that eating rotten yam could expose the consumers to hazardous micro-organisms or toxins, which could lead to stomach cramps, nausea, vomiting, fever and diarrhoea.
He warned people to avoid eating tubers which exhibit signs of deterioration and to inspect yams thoroughly before cooking them. Akande said it was crucial to differentiate natural darkening from discolouration due to deterioration to reduce food safety hazards.
The warning comes amid growing concerns in Lagos about the spread of discoloured yams, often termed “chocolate yam”. Discolouration has been found only after cutting open the tubers, which has led to financial loss and loss of appetite, say consumers.
A Festac resident, Ms Divine-Favour Johnson, said she was angry after buying the yams with the afflicted tubers. “You don’t know the agony of chocolate yams. “Consumers lose money and lose their taste,” she remarked.
“Imagine you save to buy yam and you use your money to buy yam. Then you cut up the yam and you find that it’s chocolate inside, like a spoilt yam”.
Mr Samuel Arowojolu, a diesel operator in Oshodi, said he has seen yam discolouration severally, adding that the problem was getting prevalent.
“If you go to a market where they sell yam, you might find that out of five different places you might try to purchase from you might get two that will bring out discolouration,” he added.
The worries have also seen the Environmental Health Officers Association of Nigeria, Lagos State Chapter, directing environmental health officers to increase enforcement against alleged chemical adulteration of staple foods.
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