Aflatoxins are secondary fungal metabolites that frequently contaminate food crops such as maize and peanuts. They are well known to cause liver cancer; however, multiple studies have also found aflatoxin to be immunotoxic. Studies also show that aflatoxin and fumonisin (another mycotoxin) may have synergistic toxicological effects. This dissertation determines the prevalence of these two mycotoxins in Nigerian maize and maize products, explores if lactic acid bacteria (LAB) fermentation effectively reduces these mycotoxins in a popular commercially produced maize cereal in Nigeria and evaluates the immunotoxicological risk of aflatoxin in southwest Nigerian children and adults. Our hypothesis was that aflatoxin and fumonisin occur and co-occur at multiple stages of the southwest Nigerian maize value chain. We analyzed the occurrence and co-occurrence of aflatoxin and fumonisin from harvest to postharvest storage to processing and final food and feed products in the marketplace (chapter 2). Some of the samples collected form farmers’ storage contained alarming levels of total aflatoxins (> 400 ppb) which could potentially cause acute aflatoxicosis in humans. About 52% of the samples exceeded the Nigerian standards for aflatoxins and 13% of the samples contained fumonisin levels that exceeded the US regulatory limit. The co-occurrence was found to be at multiple stages along the maize value chain. Next, we examined if lactic acid fermentation significantly reduces aflatoxin and fumonisin concentrations in commercially produced ogi which is a popular cereal produced from maize in Nigeria (chapter 3). Ogi is consumed by potentially vulnerable populations such as young children and the elderly or ill, so it is important to consider the risk of mycotoxins in this food. Our hypothesis was that lactic acid bacteria (LAB) fermentation can significantly reduce mycotoxin level in commercially produced ogi. We have analyzed the levels of aflatoxin and fumonisin before and after LAB fermentation using LC-MS/MS and found it to reduce both mycotoxins after processing. However, the reduction was statistically significant only for fumonisins (P<0.05). As aflatoxin is a genotoxic carcinogen, international risk assessment bodies have never established a non-carcinogenic tolerable daily intake (TDI) for aflatoxin since there is no threshold assumption made for cancer. There is substantial evidence in the literature that aflatoxin may have immunotoxin effects. Hence, we have determined a range of TDI of aflatoxin (0.017 to 0.082 μg/kg BW/day), based on the existing data surrounding aflatoxin and biomarkers of immune suppression (chapter 4). Finally, we have conducted a quantitative risk assessment on immunosuppressive endpoint of aflatoxin in southwest Nigerian children and adults based on our calculated TDI and dietary aflatoxin exposure through maize and groundnut consumptions (chapter 5). Our hypothesis was that the rural populations in southwest Nigeria are at great risk from aflatoxin-induced immunosuppression. Our risk assessment indicates a reasonable risk of aflatoxin-induced immunosuppression in children residing in the rural settings of southwest Nigeria. The risk is comparatively lower in children living in the urban sector with a chance of possible risk. Adults living in rural sector are also at possible risk. On the other hand, the adult population residing in the urban sector does not seem to be at risk from aflatoxin-induced immunosuppression. Taken together, the results presented in this dissertation advance understanding of the exposure, risks and impacts of mycotoxins in high-risk populations in Southwest Nigeria.
Read
