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Evaluation and optimization of microbial oil production using synthetic sugars

Gürel, Nermin
Oleaginous microorganisms produce microbial oil that can be a solution to sustainable oil production. Lipomyces starkeyi DSM70295 and Rhodosporidium toruloides DSM4444 yeasts were chosen to produce microbial oil in this study. Synthetic sugars, glucose, galactose,xylose, fructose and 1:1(w/w) combinations of sugars with glucose were used in fermentation medium. Nitrogen is an important criterion for yeast growth and lipid accumulation. To test effects of nitrogen on yeast growth and lipid production, C/N ratio of fermentation medium was at 50 and 110. It was observed that both yeasts were grown more efficiently at 50 C/N ratio whereas lipid contents of yeasts were higher at C/N=110. Biomass, reducing sugar and lipid content analysis proved Rhodosporidium toruloides to be more efficient than Lipomyces starkeyi in oil production. To determine optimum conditions, Rhodosporidium toruloides was grown in media with different C/N ratio and pH. The results of response surface method(RSM) gave the highest microbial lipid yield at C/N ratio of 125 and pH 5.0. Lipid content of R.toruloides was measured as 60.6%. The coefficient of determination (R2=97.0), insignificant lack of fit (p=0.23>0.05) showed that model fitted well to experimental data. The results confirmed that R.toruloides was more efficient microbial oil producer than L.starkeyi under tested conditions with the highest lipid yield in glucose:galactose containing medium. In future study, food wastes such as whey can be used as fermentation medium to reduce costs.