A Comprehensive Investigation of Ochratoxin A in the Nigerian Coffee and Cocoa Value Chains: Occurrence, Exposure Assessment, and Mitigation

Ochratoxin A is a nephrotoxic and possibly carcinogenic mycotoxin produced by Aspergillus and Penicillium species in improperly stored and processed coffee and cocoa, two significant export commodities from South West and South South Nigeria. European Union regulations impose strict maximum limits on ochratoxin A in these commodities, and non-compliance results in shipment rejections that impose significant economic costs on Nigerian exporters. Despite this, systematic ochratoxin A occurrence data and exposure assessments calibrated to the Nigerian value chain context are absent. This thesis presents a comprehensive multi-phase investigation of ochratoxin A occurrence, dietary exposure, and mitigation across Nigerian coffee (Coffea robusta) and cocoa (Theobroma cacao) value chains. Phase one conducted a multi-season occurrence study across coffee and cocoa value chains in Ogun, Ondo, Cross River, and Akwa Ibom states, analysing 384 samples by ultra-high performance liquid chromatography with fluorescence detection. Phase two conducted a probabilistic dietary exposure assessment integrating occurrence data with beverage consumption data from two national dietary surveys. Phase three evaluated the efficacy of fermentation optimisation, drying temperature control, and activated carbon fining as mitigation strategies through controlled trials. Phase four developed and piloted a technology-transfer programme with sixty commercial cocoa processors in Cross River State. Ochratoxin A exceedance of EU limits was observed in 26.4 percent of green coffee and 18.8 percent of cocoa bean samples, with post-harvest rain interruption as the primary risk factor. Optimised fermentation combined with forced-air drying reduced ochratoxin A by 74 percent in cocoa. Keywords: ochratoxin A, cocoa, coffee, value chain, Nigeria.