|Title:||A Study on Ochratoxin A and Toxigenic Fungi on Coffee and Selected Cereal Grains Consumed in Ethiopia|
|???metadata.dc.contributor.*???:||Dr. Dawit Abate|
|Keywords:||Aspergillus Spp;Aflatoxins;Toxigenic Fungi;Coffee;Mycotoxin;Ochratoxin;ELISA;HPLC-VWD;Teff;wheat;Defect Count|
|Publisher:||Addis Ababa University|
|Abstract:||Ochratoxin A (OTA) is toxic fungal secondary metabolite produced by some filamentous fungi belonging to the genus Aspergillus and Penicillium. This mycotoxin is commonly found in coffee and cereal grains and total removal of the toxin by various food processing methods is not possible. The aim of this research is to study ochratoxin A and toxigenic fungi in coffee and cereal grains. This dissertation contains five major chapters in which background information, the rationale for the study and research objectives are presented in the first chapter. The second chapter is dedicated to reviewing the available literature on the properties of OTA, the producing fungi, occurrence of OTA in foods, biosynthesis of OTA, analytical methods, toxicity in human and animals, mechanisms of action and prevention strategy. This section also addresses production and processing of coffee and some selected cereal grains. The remaining three chapters are the main experimental part of this study. The third chapter focuses on the occurrence of toxigenic fungi and OTA in Ethiopian coffee for local consumption. In this chapter, fungal incidences in coffee samples and OTA contamination levels in coffee were evaluated using various mycological techniques and ELISA method for toxin analysis. The identities of fungal isolates were revealed using species-specific primers and DNA sequencing techniques. The result indicated that total fungal incidence mounted up to 87%. The predominant fungal genera were Aspergillus (79 %), Fusarium (8 %) and Penicillium (5 %). Ochratosin A producing species of A. westerdijkiae, A. ochraceus, A. melleus, and A. steynii were identified for the first time using molecular techniques from locally sold coffee in Ethiopia. A. westerdijkiae and A. ochraceus were found to be the predominant OTA producers. The median OTA level in the locally sold Ethiopian coffee was 1.53 μg/kg. Although samples from wet processing resulted in low median levels of OTA, they were not significantly different from other processing types (p < 0.306). Significant differences in fungal incidences were observed between the different coffee processing types (p < 0.001), coffee sample types (p < 0.005), and storage materials (p < 0.03). An in vitro assessment of OTA and Aflatoxins (AFs) production potential of all Aspergillus isolates reviled that A. westerdijkiae isolates were clearly the most potent producers of OTA while AFs were only produced by two A. flavus isolates. This chapter is published in Food Control 69 (2016) 65-73. The fourth experimental chapter deals with the association of coffee bean defects with Ochratoxin A contamination in the beans: A possible implication for visual judgment of OTA contaminated coffee beans. In this chapter coffee bean defects were investigated based on Ethiopian coffee quality and liquoring manual and Specialty Coffee Association of American (SCAA). The predominant coffee bean defects encountered in this study in descending order were black beans (47.5 %), cherry (13.5 %), immature bean (8.1 %), sour bens (7.9%), insect infested (7.9 %), moldy beans (4.4 %), and broken beans (3.7%). Ochratoxin A contamination levels in coffee beans were positively correlated with black beans (r = 0.33, p < 0.03), visible mold overgrowth (r = 0.80, p < 0.00), beans damaged by insects (r = 0.71, p < 0.00), and presence of husk (r = 0.67, p < 0.00). These types of defects could be used as a possible visual marker for OTA presence in locally sold coffee. The fifth chapter deals with High Performance Liquid Chromatography Variable Wavelength Detector (HPLC-VWD) method of detection and quantification of Ochratoxin A in teff (Eragrostis teff) and wheat (Triticum spp.) flour samples intended for local consumption. In this section, HPLC method was developed and validated to detect and quantify OTA in teff and wheat flour samples. Based on this validated method teff and wheat four samples were analyzed for OTA contamination using HPLC-VWD apparatus. The results indicate that 20% of the teff and 50 % of the wheat flour samples were contaminated with median OTA level of 0.99 μg/kg (LOD = 0.78) and 6.76 μg/kg (LOD = 0.58 μg/kg) respectively. This validated method for OTA detection and quantification in teff and wheat using HPLC-VWD detector generates meaningful data that satisfy performance criteria set by European Commission, EC 401, 2006 and Eurachem Guideline validation requirements. Moreover, an insight into the occurrence of OTA in teff is very valuable because the cereal might provide a low OTA risk alternative for wheat in Ethiopia.|
|Description:||A Dissertation Submitted to the School of Graduate Studies of Addis Ababa University in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Applied Microbiology|
|Appears in Collections:||Thesis- Microbial, Cellular and Molecular Biology|
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