Natural occurrence of moulds and aflatoxin B1 in melon seeds from markets in Nigeria

Shelled melon seeds (Colocynthis citrullus L.) were purchased from markets in randomly selected villages and towns in three states in each of the rain forest (Ogun, Oyo and Osun) and Northern guinea savanna (Kaduna, Niger and Bauchi) zones of Nigeria. The seed samples were analysed for incidence of visibly diseased seeds, moisture content, moulds and aflatoxin B1 contamination. The incidence of diseased seeds ranged from 6.4% to 50.4% in the forest, and 4.3% to 34.3% in the savanna, and the moisture content was 5.6% to 12.6% and 4.5% to 10.3%, respectively. Mould evaluation revealed that Aspergillus was the most frequent genus, followed by Penicillium, Botryodiplodia, Cladosporium and Rhizopus in decreasing sequential order. Aspergillus flavus had the highest individual count in melon seed from both zones. Aflatoxin B1 was detected at levels above 5 μg/kg in 32.2% of samples, while only 3.5% of the samples contained the toxin above the 20 μg/kg Nigerian tolerance level in food. The percentage of samples contaminated with aflatoxin B1 was statistically comparable for the pooled data of villages and towns. The median level of aflatoxin B1 was less than 5 μg/kg in the seed samples, while the mean aflatoxin B1 levels was 14.1 μg/kg in the forest and 13.0 μg/kg in the savanna samples.