Optimization Of Culture Condition For DHA Production And In Situ Ethyl-transesterification Of Lipid Of Schizochytrium Sp. 20888

In this paper, in order to enhance the DHA productivity of Schizochytrium sp. 20888,the cultivation time, culture temperature, carbon and nitrogen sources and their concentration were optimized with single-factor experiment and orthogonal optimization design. And then an alcohol dehydration process was used to dry the cell biomass after the expand culture. Finally, the in situ ethyl-transesterification of Schizochytrium sp. 20888 was studied and the optimal process conditions were confirmed by the single-factor experiments, Box-Behnken design(BBD) and response surface methodology(RSM). The main research contents and results are as follows:(1) The cultural conditions of DHA high productivity with Schizochytrium sp. 20888 were investigated. The cultivation time, carbon and nitrogen sources and their concentrations and culture temperature were studied through the “one-factor-at-a-time”experimentation to observe the influence on dry cell mass, total lipid content and the percentage of DHA. After that, the medium composition and concentrations of carbon and nitrogen sources were further optimized and determined by the orthogonal optimization test. The results showed that the optimal cultivation time was 4 d, the proper incubation temperature was 23 ℃, the optimal carbon sources were glucose and glycerol and their concentrations were 65 g/L and 80 g/L respectively while the optimal nitrogen sources were peptone, yeast extract and sodium glutamate and their concentrations were 6 g/L, 4g/L and 8 g/L respectively. In this case, the DHA yield was reached the maximum of33.68%.(2) The alcohol dehydration was studied based on the wet cells. The results showed that it was feasible to dehydrate Schizochytrium cell by the new process, and the moisture of the cell biomass could be reduced to or below the level that the spray drying could reach.The results also show that the moisture of the cells can be reduced from 68.62% to 0.90%while dehydrating twice with 1.5 times of 95% ethanol and following one time with 1.5times of absolute ethanol. With this method, the residual glycerol and some pigments in the cell biomass could be removed and the extracted lipid from the dry cell mass dehydrated by new process exhibited clear, golden and had good fluidity which was better than the the lipid from cells dried by oven, so it became more convenient for its subsequent processing.(3) The in situ ethyl-transesterification was researched. In order to transesterify the cellular lipid directly into fatty acid methyl ester(FAEE), the in situ ethyltransesterification of Schizochytrium sp. 20888 was investigated and the optimal process conditions were confirmed by the “one-factor-at-a-time” experiments, BBD and RSM. The results showed that the reaction time and the content of absolute ethanol were two statistically significant factors, and the optimal in situ ethyl-transesterification process conditions with 0.50 g dry cells was as following: the absolute ethanol content, 11.76 mL;the concentrated sulfuric acid content, 0.41 mL; the reaction temperature, 75.5 ℃; the reaction time, 2.24 h. Under these conditions, the transesterification rate of DHA reached the highest level of 85.43%.