Moisture and Aflatoxin Contents of Kenyan Market Peanuts and Decontamination with Water, Lime and Ultraviolet Radiation Treatments

In the recent past, aflatoxin in peanuts and products has been a subject of controversy in Kenya. In the early 2019, some brands of locally manufactured peanut butter were withdrawn from the market shelves on account of containing aflatoxin higher than the national tolerance. It has been established that Kenyan market peanuts contain high levels of aflatoxin. Roasting is reported to have little effect on the aflatoxin content. This study was designed to assess the effect of specific treatments prior to roasting in reducing the aflatoxin levels to below the tolerance. This would then ensure compliance of the toxin levels in the roasted peanuts and the products with the national tolerance. The treatments included soaking in water, in lime, and UV irradiation. The peanut samples were collected from 20 vendors in the Main Cereal Market in Nairobi and brought to the laboratory of the Kenya Bureau of Standards (KEBS). They were analysed for moisture and aflatoxin content. Each sample was subjected to the treatment and reduction was evaluated in aflatoxin to the tolerance. The moisture content of the peanuts varied from 5.2 – 8.4% with mean of 6.5%. Moisture almost complied with the optimum for storage of 8.0%. The total aflatoxin contents varied from 3.3 – 38.5 ppb with mean of 14.8 ppb. Up to 45% samples had aflatoxin above tolerance of 10 ppb.

There was positive and significant (p < 0.01) correlation between aflatoxin levels and moisture content. Treatment of the peanuts with water (cold & warm) and warm lime and irradiation with UV all managed to reduce the aflatoxin contents to below the tolerance, in the order lime>warm water>cold water>UV irradiation. The study concluded that the moisture content of the market peanuts in Kenya, almost complies with recommended optimum for storage the tolerance, but the mean aflatoxin content was well above the tolerance. However, the aflatoxin levels can be lowered effectively by soaking in water, lime, and by irradiation with UV.