Optimization And Metabolic Control Of DHA Fermentation

DHA has attracted great interest and got extensive application due to its distinctive physiological function. Owing to its noticeable advantage, DHA production by microorganism has become one of hotspots in research field of the world. From the initial strain, Thraustochytrium aureum ATCC34304, the optimizing of medium components and culture condition, breeding of high DHA yield strain, metabolic regulation and control of DHA fermentation and scale-up culture in bioreactor was mainly studied in this dissertation.DHA fermentation was conducted by five different initial strains. By comparing biomass, fatty content, DHA content and feasibility of industry production, T. aureumATCC34304 was selected to investigate due to its high biomass and DHA content. T. aureum ATCC34304 is a kind of heterotrophic fungi from sea, has short fermentation period, easy to culture and regulate and control its metabolism.T. aureum can use many different carbon sources. Corn starch is optimal carbon source for DHA fermentation by T. aureum. The suitable concentration of corn starch is 25~30g/L.The maximal biomass and DHA production could be got when T. aureum was cultured in medium in which the yeast extract was used as nitrogen source. So the yeast extract was chosen as the nitrogen source for DHA production from T. aureum. The suitable C/N ratio is from 15/1 to 20/1.When the initial pH of medium is 7.0, the maximal biomass was obtained. But it is not suitable for DHA accumulation. The fatty and DHA content is highest in medium with initial pH 6.0. The optimal initial pH, 6.0, was confirmed by comprehensively considering.The optimal addition concentration for corn starch, 30g/L, yeast extract, 1.72g/L, and initial pH, 6.5,were determined by orthogonal experiment.Through single factor analyses, the optimal culture condition was fixed: the culture time for seeds is 48 hour; inoculum volume is 10%; the changing temperature...