Toxigenic fungi and aflatoxins associated with marketed rice grains in Uganda

The natural contamination of rice grains from Ugandan locally grown crop or imported from Pakistan by toxigenic fungi and aflatoxins was investigated and assessed. Twenty four samples of each type of rice were obtained from various markets within 3 different districts. Contaminating fungi were enumerated by direct plating method on three isolation media including pentachloronitrobenzene rose-bengal yeast extract sucrose agar (PRYES), pentachloronitrobenzene potato sucrose agar (PCNB-PSA) and Aspergillus flavus/ parasiticus agar (AFPA). Fungi including toxigenic Penicillium, Fusarium and aflatoxigenic Aspergillus spp. were isolated and identified to species level and the percentage contamination levels were calculated. Locally grown rice had a comparatively narrower species spectrum of Penicillium, Fusarium and Aspergillus genera, whereby it recorded 5, 5 and 7 species respectively while the imported rice recorded 8, 6 and 11 species respectively. Among the Penicillium, P. chrysogenum, P. novae-zeelandiae, P. oxalicum, P. pinophilum and P. purpurogenum occurred on both types of rice grains while among the Fusarium, F. graminearum, F. verticillioides and F. oxysporum also occurred on the two grains. Similarly occurring on the two types of rice were Aspergillus flavus, A. candidus, A. fumigatus, A. niger, A. oryzae and A. terreus. Aspergillus parasiticus was recorded on only the local rice but A. candidus was the most frequent Aspergillus on both types of rice grains. Penicillium oxalicum was among the most frequent Penicillium species on the local rice while P. chrysogenum and P. citrinum were prevalent on the imported rice. F. solani was the most frequent Fusarium species on the local rice whereas the imported rice recorded scarce contamination by Fusarium spp. The locally grown rice recorded a comparatively lower incidence of aflatoxins whereby, 44.4 % of its samples were contaminated while 77.8 % of the imported rice samples were contaminated. Similarly, the local rice had comparatively lower moisture contents, in which, 14.60 % was its highest level while 15.5 % was the highest level for the imported rice. A half of the imported rice samples had moisture content above the recommended level for safe storage of milled rice while for the local rice only 12.5 % of the samples moisture content were above this level. A significantly positive correlation coefficient existed between incidence of aflatoxigenic Aspergillus spp. and moisture content of the rice grain samples screened for aflatoxin contamination.