博士 / 國立臺灣大學 / 農業化學研究所 / 90 / Abstract
The effect of culture conditions on docosahexaenoic acid (DHA) production, fatty acids profiles and secreted acids in the broth by the oleaginous yeast Schizochytrium sp. S31 were studied in flasks on an orbital shaker. DHA was the main omega-3 polyunsaturated fatty acid. Monosaccharides, glucose and fructose, and yeast extract were the suitable carbon and nitrogen source. Microbes consumed their own reserve fatty acids in the cell and secreted acids in the broth. Based on the one-factor-a-time, the optimal culture conditions for DHA production (352 mg L-1) were pH7.0 with 20 g glucose L-1, 0.4% (w/v) yeast extract and 3.0 % (w/v) NaCl for 4 days. The higher syntheses of lipid and DHA would have the C/N ratio higher than 75 g g-1.
The optimum of concentrations of nutrients (glucose and yeast extract) and cultivation conditions (concentration of sodium chloride, pH and incubation time) on docosahexaenoic acid (DHA) production by Schizochytrium sp. S31 in flasks under 30oC was studied by experimental design. It employed fractional factorial design, path of steepest ascent, central composite design and response surface methodology (RSM). The empirical model developed by RSM was adequate to describe the relationships between the studied factors and the response of DHA production. Based on contour plots and canonical analysis, the optimal conditions for maximizing DHA production (516 mg L-1) were at glucose, 27.98 g L-1; yeast extraction, 4.52 g L-1; sodium chloride, 24.82 g L-1; pH 6.96 and incubation 4 days under 30oC. Experimental checking the optimal conditions achieved about 97% of the predicted DHA production that indicated the model adequately. Based on the optimal conditions for maximizing DHA production, the production of DHA under the cultivation in a 5 L fermentor was 1400 mg L-1. The result was four times to the result from the one-factor-at-a-time method and also 2.8 times to the result from the optimal condition of response surface methodology.
The effect of culture conditions, different nitrogen source, carbon fed-batch cultivation and oxygen availability, on the production of docosahexaenoic acid (DHA) and succinic acid in the broth by the oleaginous microorganism, Schizochytrium sp. S31, were investigated in 5 L fermentor. Carbon fed-batch cultivation increased the biomass formation, lipid, DHA and succinic acid production. Yeast extract was a better nitrogen source than ammonium chloride that the production of DHA and succinic acid were 1.2 g L-1 and 9 g L-1, respectively. Under oxygen-limiting conditions, cell growth and synthesis of lipid and DHA decreased. The production of succinic acid was influenced slightly by oxygen limitation. From the results indicated that Schizochytrium sp. S31 would have the potential to produce DHA and succinic acid.
Key Words: DHA, docosahexaenoic acid, fatty acids, response surface methodology, experimental design, optimization, Schizochytrium sp. S31.
| Identifer | oai:union.ndltd.org:TW/090NTU00406038 |
| Date | January 2002 |
| Creators | Wu, Shwu-Tzy, 吳淑姿 |
| Contributors | Liang-Ping Lin, 林良平 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 141 |
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