FUNGAL SPECIES AND AFLATOXIN CONTAMINATION IN PEANUTS

Abstract

Aflatoxins are a group of mycotoxins mainly produced by Aspergillus flavus and A. parasiticus mostly on cereals and peanuts. Aflatoxins adversely affect food and feed safety thereby affecting human and animal health as well as trade. Conditions for growth of fungal contaminants and production of mycotoxins vary from region to region and among different products. This study investigated levels of fungal and aflatoxin contamination in marketed peanuts in Kericho and Eldoret towns. A total of 228 samples were collected using stratified systematic sampling from both towns: 140 from formal (raw: 30; roasted coated: 66; roasted de-coated: 44) and 88 (raw: 48; roasted coated: 35; roasted de-coated: 5) from informal markets. Diversity and populations of fungal species contaminating peanuts were determined by culturing ground samples on Modified Dichloran Rose Bengal Agar. Aflatoxin levels were quantified using indirect competitive enzyme-linked immunosorbent assay. Correlation between the incidence of major aflatoxin-producing fungal species and aflatoxin contamination levels was also established. Seven major fungal species and strains isolated from peanut samples were Aspergillus flavus L strain, A. flavus S strain, A. parasiticus, A. tamarii, A. caelatus, A. alliaceus and A. niger. Other isolated fungal genera were Fusarium, Penicillium, Mucor and Rhizopus. Aflatoxin levels averaged 146.8 µg/kg (range: 0 to 2345 µg/kg) for raw, 56.5 µg/kg (range: 0 to 382 µg/kg) for roasted coated and 19.9 µg/kg (range: 0 to 201 µg/kg) for roasted de-coated peanut samples. The level of aflatoxin contamination differed significantly (p ≤ 0.05) between raw peanut samples from formal and informal markets, both in Eldoret and Kericho towns. There was no significant difference (p ≥ 0.05) in aflatoxin contamination levels of roasted de-coated peanut samples from formal and informal market outlets. Overall, the total aflatoxin levels in 43% of peanuts and peanut products exceeded the 10 μg/kg regulatory limit set by the Kenya Bureau of Standards. Raw peanuts were the most contaminated with more than 50% of the samples having aflatoxin levels above10 μg/kg. There was a positive and significant correlation (R2 = 0.63; p ≤ 0.05) between aflatoxin levels and the population of major aflatoxin producing fungal species (Aspergillus flavus L and S strain and A. parasiticus combined) in raw peanuts sampled from formal market outlets in Eldoret. Total aflatoxin in raw peanut samples from Kericho informal market outlets was positively and significantly correlated (R2 = 0.81; p ≤ 0.05) with the population of Aspergillus flavus (L and S strains). In roasted coated peanut samples from formal market outlets in Eldoret, aflatoxin levels correlated positively and significantly with Aspergillus flavus S strain (R2=0.37; p ≤ 0.05). Roasted de-coated peanuts were the least contaminated with only 40% and 22% of samples exceeding Kenya Bureau of Standards threshold in informal and formal markets, respectively. Roasting, de-coating and packaging of peanuts reduced the incidence of aflatoxin-producing fungi and aflatoxin production. There is need to create awareness among peanut traders and the public on proper handling of peanuts and health risks associated with consuming unsafe peanut products. v