This study reports the fungal and bacterial metabolites associated with natural contamination of 38 composite samples of locally processed rice from five agro-ecological zones of Nigeria (AEZs). The samples were evaluated for the presence of microbial metabolites by LC-MS/MS. Among the identified metabolites, 63 fungal and 5 bacterial metabolites were measured at varying concentrations and occurrence levels. Fusarium toxins had the highest incidence of 79%, but occurred in low amounts with fumonisin B1 (FB1) having the highest percentage incidence of 39.5% and a mean of 18.5 µg/kg. Among the Aspergillus toxins, aflatoxins (AFs) occurred in 36.9% of the rice samples, with aflatoxin B1 (AFB1) having the highest occurrence level of 18.4% and a mean value of 5 µg/kg. About 12 metabolites had incidence levels > 50%, including beauvericin (BEA) and tryptophol, which had occurrence levels of 100%. Among the emerging toxins under evaluation by international organisations such as the European Food Safety Authority (EFSA) and the Food and Agriculture Organisation of the United Nations (FAO), citrinin, sterigmatocystin (STER) and beauvericin were detected with maximum values of 207, 125 and 131 μg/kg, respectively. This paper also reports the first documented evidence of the contamination of Nigerian rice by bacterial and Alternaria metabolites, nivalenol, kojic acid, STER, moniliformin, fusaric acid, fumonisin B3, citrinin, 3-nitropropionic acid, andrastin A, cytochalasins, emodin and physicon.
Keywords: LC-MS/MS; aflatoxin; beauvericin; mycotoxin; rice; zearalenone.