Aflatoxin and fumonisin contamination of yam flour from markets in Nigeria

The natural occurrence of aflatoxins (AFs) and fumonisins (FBs) in yam flour samples (n=100) obtained in south-western Nigeria was evaluated. AFs were determined by HPLC with fluorescence detection and FBs by HPLC coupled with mass spectrometry. Aflatoxin B ₁ (AFB ₁) and aflatoxin G ₁ (AFG ₁) were found in 57% and 21% of flours from white yam with concentrations ranging from <0.02 (limit of detection, LOD) to 3.2μgkg ^-1 (mean=0.4μgkg ^-1) and from <0.05 to 3.5μgkg ^-1, respectively. AFB ₁ was the only aflatoxin detected in samples from water yam, contaminating 32% of the samples with values ranging from <LOD to 0.6μgkg ^-1 (mean=0.1μgkg ^-1). Fumonisin B ₁ was found in 32% of the white yam samples (<0.5 (LOD) to 91μgkg ^-1; mean=5μgkg ^-1) and in 5% of water yam samples (<LOD to 2μgkg ^-1). AFs and FBs were significantly higher (P<0.05) in white yam flours compared to water yam flours. Preparation of amala from naturally-contaminated yam flour resulted in reduction of AFB ₁ and AFG ₁ by 44% and 51% respectively. From this study, only 7% of the samples contained AFs above the European standard limits for cereals intended for direct human consumption, while all the FBs-positive samples were well below the limits. The occurrence of ochratoxin A, zearalenone and deoxynivalenol was also evaluated in 20 samples; these mycotoxins were never detected.