Palm Kernel: A Potential Substrate for Rapid Detection of Aflatoxigenic Fungi

Palm kernel is a cheap natural resource which is abundantly available in the tropics, parts of Asia and South and Central America. A culture medium was developed by incorporating fresh palm kernel extract for the detection of aflatoxigenic fungi. Aflatoxin positive isolates of Aspergilliexhibited a characteristic blue or blue green fluorescence of agar under long wave UV light against a pink background which was confirmed by thin layer chromatography. As compared to conventional desiccated coconut agar, the fluorescent nature of the medium, the intensity and diffusion of the hot water soluble fluorescent compounds of the fungus was unique on this medium. The optimal pH and temperature conditions of aflatoxin production were 7 and 30 ºC respectively. Additives (synthetic and natural) either had no effect or adversely affected the fluorescence of the medium. Aflatoxin detection was possible within 36h in palm kernel broth compared to 40 h in coconut broth. The optimal time of production of fluorescence was 44 h on palm kernel agar compared to 48 h on the conventional medium. Further tests with isolates from different sources showed that yellow pigmentation, fluorescence and aflatoxins were complementary thus obviating the need for UV light. It is thus possible to presumptively identify aflatoxin positive isolates.