| Summary: | 碩士 === 元培科技大學 === 食品科學研究所 === 99 === Biodiesel produced from microbial lipids has become an alternative biofuel to replace petroleum fuel because of it could reduce the use of energy crops. Many oleaginous microorganisms were considered as the potential candidate for biodiesel production. In this study some potential yeasts for lipid production, including Cryptococcus sp., Moesziomyces spp., and Pseudozyma spp., were selected for furture production of microbial lipids. In the first section, glucose or sucrose was used as the sole carbon source in the nitrogen-limited media to select the candidate for lipid production. Among strains tested, Cryptococcus sp SM5S05 accumulated highest levels of intracellular lipids no matter which dextrose or sucrose-based culture medium was utilized. The lipid content increased with the yeast biomass at fixed concentration of glucose; however, lipid content was not associated with the yeast biomass at fixed concentration of nitrogen sources. Accumulation of lipids strongly depended on the C/N ratio and nitrogen concentration. The highest content of lipids was measured at a C/N ratio of 60-90, glucose concentrations of 4-6% and a nitrogen concentration of 0.1%. Under the maximum conditions the yields of lipid and lipid content of the dry biomass were 6.1-5.2 g/L and 60-57%, respectively, in the batch fermentation. In the fed-batch culture, we designed two initial concentrations of 4% and 6% and feeding 2% glucose at 48 h of fermentation. In the fed-batch fermentation using initial glucose concentration of 4% and supplementing 2% glucose, the yields of yeast biomass and ethanol were 6.4 g/L and the lipid content of 56.1%, which is 7% higher than that of batch fermentation. The contents of oleic acid methyl ester and linoleic acid methyl ester, analyzed by GC after transesterification, were 60.9 % and 27.3 %, respectively. The lipids from Cryptococcus sp. contained mainly long-chain unsaturated fatty acids with 16 and 18 carbon atoms.
The second section is focused on using cellulosic corncob wastes to replace glucose for the production of biomass and lipid. After corncob was pretreated by the hydrolysis with 1.0% sulfuric acid and autoclaved at 121℃ for 15 min, the cellulosic residue was then hydrolyzed by commercial enzymes. After 48 h of hydrolytic reaction, overall reducing sugar and glucose concentrations reached 0.61 and 0.36 g/g dried substrate, respectively. Batch cultures using cellulosic hydrolysatebased media demonstrated that there was little inhibitory effect with a reducing sugar concentration of up to 60 g/ l. Batch cultures were run for 4 days and reached a dry biomass and cellular lipid content of 6.3 g l-1 and 52.4%, respectively. Furthermore, in the fed-batch fermentation using the hydrolysate containing 6% reducing sugar and feeding 2% glucose after 48 h of fermentation, the yields of yeast biomass and ethanol were 5.9 g/L and the lipid content of 45.8%. Based on the results, the cellulosic hydrolysate could be used for the production of microbial lipid. The lipid yields of Cryptococcus sp. under maximum conditions of fermentation is meaningful for scale-up process. The microbial lipid will be the potential alternative resource for biodiesel production.
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