World Mycotoxin Journal: Use of peanut meal as a model matrix to study the effect of composting on aflatoxin decontamination

The Food and Agriculture Organization estimated that 25% of the world's crops are affected by aflatoxins each year. Crop contamination with aflatoxins remains a primary cause of post-harvest losses in developing countries. The European Union's regulation on aflatoxins costs Africa $750 million annually in reduced export of cereals, dried fruit, and nuts. African economies lose about $450 million annually to aflatoxin contamination, out of a global estimation of $1.2 billion. Peanut husks produced in Northern Ghana are often used as mulching materials around rural households. They are also used with other peanut wastes, such as shells, for organic soil amendment in agricultural production fields. However, the use of peanut meal as a soil amendment introduces aflatoxins and aflatoxin-producing mould into subsequent farming seasons. This research evaluated the effectiveness of composting as a means of aflatoxin decontamination using highly-contaminated peanut meal as a model matrix at 40°C for 6 weeks. The composting methods caused a significant reduction in the levels of aflatoxin B1, B2, G1, and G2 in peanut meal. Aspergillus flavus and Aspergillus parasiticus counts and total mould counts decreased from 103-105 to <10 colony forming units/g. Composting time and the type of starters used significantly influenced aflatoxin content, while the presence of accelerator did not affect aflatoxin levels. The highest level of toxin decontamination occurred in the first week when compost temperature and ammonia concentration were high. Micronutrient contents of resulting composts were within the accepted range for fertilizers, except for calcium. Heavy metal content was below the maximum allowable levels except nickel in one of the samples. Aflatoxin reduction was also observed in an up-scale experiment using contaminated agriculture waste as raw materials. Results suggest that composting could be employed to decontaminate aflatoxin-containing agricultural waste in developing countries. The nutrient quality and heavy metal content of the resulting compost as crop fertilizers were also evaluated. The study used aflatoxin-contaminated peanut meal as a model matrix and evaluated the effectiveness of composting as a means of aflatoxin decontamination. Three different commercial starters were used either alone or in combination with a commercial accelerator. The samples were stirred continuously for 3 min to ensure a uniform mixture and then placed in a water bath at 40°C under a fume hood for 6 weeks. The temperature, pH, and ammonia concentration of the same samples were documented twice a day, before and after stirring the composts during the entire 6-week composting process. Quantitative analysis of aflatoxins in compost using HPLC was done through a commercial service provided by J. Leek International based on AOAC method 991.31. Aflatoxins in composted peanut meal were extracted with methanol:deionised water (60:40, v/v) and NaCl (5%) at 1:5 mass/volume ratio. The peanut meal/methanol-water mixture was blended in a high-speed blender for 1 min. After blending, the sample was filtered with a P8 filter paper. Filtered peanut meal extract was mixed with deionised water in a ratio 1:2 and then filtered again through a G6 glass filter.