Date

2015

Author

Doğan, Önay Burak

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Aflatoxins are highly mutagenic toxins with carcinogenic effects produced as secondary metabolites by fungal species Aspergillus flavus and Aspergillus parasiticus under certain conditions. Chronic or acute consumption of aflatoxins found in food and feed products possesses great health risks. It is particularly an important problem in animal feed from food waste and by-products. Therefore there is growing need to eliminate aflatoxins from contaminated products. In this study, first the optimum growth conditions of gram-positive, aerobic bacterium Rhodococcus erythropolis, which is known to be degrading aflatoxin, were determined in synthetic media. One factor at a time approach was adopted to determine the most effective carbon and nitrogen sources for growth. Plackett Burman design was used to screen other variables (temperature, pH, liquid culture volume, agitation speed and concentrations of nitrogen and carbon sources) vi important for growth. Three variables determined as significant by Plackett-Burman design was then further evaluated with Box-Behnken response surface optimization method and optimum conditions were defined for growth of R. erythropolis. For better understanding of aflatoxin degrading ability of R. erythropolis, viable cells and crude extracellular enzymes were compared. Process conditions for detoxification of Aflatoxin B1 were optimized by Box-Behnken response surface method with three variables (solid concentration, inoculum volume and time). Decrease in toxicity of treated groundnut meal was assessed by sheep liver glutathione-S-transferase (GST) assay. The results showed that peptone and glucose are the best nitrogen and carbon sources for growth of R. erythropolis, respectively. Optimal culture conditions were found as 22.5 °C of temperature, pH 7, 100 mL of liquid volume in 500 mL flasks, 1% (v/v) of inoculum volume, 135 rpm of agitation speed, 5 g/L of glucose concentration and 5 g/L of peptone concentration. Viable cells were found to be more effective for Aflatoxin B1 degradation and used for rest of the study. It was observed that R. erythropolis cells and extracellular enzymes are able to degrade aflatoxin even when grown in absence of the toxin. It was observed that viable cell cultures of R. erythropolis performed better detoxification activity than extracellular enzymes. Optimum conditions for detoxification were found as 27.4 %(w/v) of solid concentration, 4.88 %(v/v) of inoculum volume and 24 h of time by Box-Behnken response optimization. At these conditions maximum reduction in AFB1 was predicted as 92.2% and verified as 87.3% Toxicity of treated groundnut meal extracts were found to be decreased significanty by GST assay. Treated samples inhibited the enzyme activity 64.5% and untreated samples inhibited 86.6%. As a result, viable cell cultures of R. erythropolis was suggested as an effective detoxification agent for aflatoxin contaminated groundnut meal used for animal feed.

Subject Keywords

Peanuts., Aflatoxins., Mycotoxins., Rhodococcus erythropolis.

URI

http://etd.lib.metu.edu.tr/upload/12619082/index.pdf
https://hdl.handle.net/11511/24984

Collections

Graduate School of Natural and Applied Sciences, Thesis