Biodiversity of Aspergillus Species and Aflatoxin Contamination in Stored Cereals and Legumes in Cameroon

Abstract

In cereal and legume grains, the presence of Aspergillus spp. and their aflatoxins induce huge economic losses, health problems and environmental problems during storage.  Thanks to their mycotoxins, Aspergillus, Penicillium and Fusarium cause losses of up to 25% of agricultural production worldwide, and 50% in developing countries. The aim of this work is to identify Aspergillus spp. isolated from maize, soybean, rice and peanut grains in storage, while examining their aflatoxin contamination levels. To this end, 25 composite samples of each grain were systematically collected from the five agro-ecological zones (AEZ) of Cameroon. Morphological characterization of Aspergillus spp. isolates was carried out using various specific culture media. Aflatoxin determination was carried out using standard aflatoxin extraction and ELISA strip quantification. The results show that, of the 100 composite samples collected, 99% were contaminated by a wide variety of molds, with a prevalence of 334/745 or 44.83% of Aspergillus spp. Of the Aspergillus spp. isolates obtained, 21.85% were derived from peanuts, 27.84% from rice, 21.56% from maize and 28.74% from soybeans. Aspergillus prevalence varied with agro-ecological zones (AEZs), and the most affected zones were AEZ V with 31.73% Aspergillus spp. isolates, and AEZ III with 28.14% Aspergillus spp. isolates. Aspergillus diversity according to AEZs shows that section Flavi is the most represented with 33% of isolates, successively followed by sections Nigri, Fumigati, Terrei, Candidi and Circumdati with 27%, 16%, 6%, 6% and 6% respectively. Examination of the total aflatoxin contamination levels of the various grains showed that, irrespective of the foodstuffs and AEZs, aflatoxin contamination was 100%. However, the highest mean concentration of aflatoxin was recorded in AEZ V (9.63 µg/kg). By commodity, samples of maize (9.46 µg/kg) followed by rice (8.92 µg/kg) showed the highest aflatoxin levels in Cameroon. In the end, all the foodstuffs showed a very high diversity of Aspergillus, and all the aflatoxin levels exceeded the regulatory thresholds in force.