| DHA (Docosahexaenoic acid,22:6△4.7.10.13.16.19) is a very important kind of long-chain unsaturated fatty acids that belongs to omega-3 fatty acid, which has a series of biological and physiological functions, including improving and enhancing infants intelligence and memory, reducing blood fat, preventing arteriosclerosis, anti-aging and so on. Therefore, DHA is widely popular with the market. Schizochytrium sp.FJU-512, as a kind of marine fungi, has some industrial production conditions, but it’s on the yield, quality and cost of production has yet to be further improved.This paper is studied with Schizochytrium sp.FJU-512 which has been shown to be excellent DHA producers. Firstly, its fermentation medium was optimized. Trough one-factor-at-a-time experiments, glucose and sodium glutamate yeast extract were obtained as the optimum carbon and nitrogen sources for Schizochytrium sp.FJU-512 on DHA production, Subsequently, the best ratio of carbon and nitrogen source was selected by orthogonal experiment. At last, a homogeneous experiment was designed to optimize inorganic salts in fermentation medium. Results indicated that the optimal fermentation medium formula of DHA production was:glucose 120 g/L, yeast extract 5.0 g/L, sodium glutamate 20 g/L, (NH4)2SO40.25 g/L, sea salt 25.00 g/L, KH2PO4 4.0 g/L, MgSO4·7H2O 0.5 g/L, CaCO 35.0 g/L, Na2SO4 3.0 g/L, FeSO4·7H2O 20 mg/L, vitamin B1 0.005 g/L, vitamin B1 20.005 g/L. By using the optimized medium, DHA yield of 13.83 g/L was achieved, the cost of medium was reduced by 35% or so.Secondly, This paper investigated the influence of nitrogen source limitation and temperature stress to Schizochytrium sp.FJU-512 fermentation respectively. The results showed that the best carbon and nitrogen ratio of nitrogen source limitation is 80, meanwhile, when beganning to limit nitrogen source after 84h, DHA production reached 17.25 g/L, which increased by 59.2% compared with the control group. In addition, through the experiment, it found that the optimal control technology of fermentation temperature is 28℃ during 0-96 h and 15℃ during 96-120 h. On this condition, the proportion of DHA in total oil reached 47.29%, and its yield compared to the entire 28℃ increased by 11.11%. Then the influence of the use of superposition technique to Schizochytrium sp.FJU-512 fermentation was discussed. Results showed that, compared with the single temperature control technology, the proportion of DHA in total oil obtained slightly promotion, and the amount is 2.16%.Afterward, based on the results of batch fermentation, four kinds of flow process were studied, It turned out that when flows sodium glutamate and triple feeding medium concentrate (excluding sodium glutamate) with a variable speed, the growth of Schizochytrium sp.FJU-512 and the accumulation of DHA were best, and the biomass, oil content and the production of DHA respectively were 114.33 g/L,48.02 g/L and 19.21 g/L, meanwhile, the fermentation time was shortened 24 h, the average yield of DHA reached 200.1 mg/(L.h), up 14.3% compared with before optimization.Finally, in order to further optimize the downstream production technology and improve the oil yield, this paper discussed the effect of the compound breakage method on Schizochytrium sp.FJU-512 cell broken, through combined high pressure homogeneous broken and enzymatic broken, indicated that after 80 Mpa high-pressure homogeneous treatment under the enzyme solution, the cell broken degree is best. Then further optimized the conditions of enzymatic hydrolysis. The optimal conditions to achieve the highest cell disruption rate was as follow:2% of enzyme, temperature 55℃, pH 10, hydrolysis time 2 h. Under these conditions, the oil extraction amount reached 26.81 g/L, up 47.3% compared with before optimization. |
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