Study On The Fermentation Process Of Marine Fungus Schizochytrium Sp For DHA Oil Production

Docosahexaenoic acid(DHA), an important ω-3 polyunsaturated fatty acid, has many physiological functions such as reducing blood fat, improving eyesight, promoting brain development and boosting body immunity. As a new generation of functional factor, DHA is widely used in food, pharmaceutical and other industries. Marine fungus Schizochytrium isrich in DHA and has the potential for commercial DHA production due to its advantages of rapid growth, short fermentation period and easiness for large-scale culture. In this thesis, the fermentation process of Schizochytrium sp. DP-16 for DHA oil production was optimized,and quorum sensing effect of Schizochytrium during fermentation process was studied.A strain of Schizochytrium sp. DP-16 was used for DHA oil production. The fermentation process was optimized by single factor test, and the composition of cell fatty acids was analyzed as fatty acid methyl esters derivatives(FAMEs) by GC-MS. The cell biomass, oil production and DHA concentration reached 65.0g/L, 30.7g/L and 8.9g/L respectively at 120 h under optimized conditions, being 5.0, 8.5 and 9.8 times of those before optimization respectively. Eight fatty acids were detected in Schizochytrium sp. DP-16 cells by GC-MS, in which the main saturated fatty acids were C14:0 and C16:0 acid, and the main polyunsaturated fatty acids were DPA and DHA. The content of DHA in Schizochytrium sp.DP-16 cells accounted for 28.78% of the total fatty acids.It was found that the fermentation process of Schizochytrium sp. DP-16 contained cell proliferation period and oil accumulation period. The quorum sensing effect during fermentation process was studied. Culture supernatant of 40 h was mixed with cell precipitate of 16 h, and then cultured for 8 h. it’s the cell biomass, oil production and oil-to-biomass ratio were raised by 43.7%, 179.1% and 94.0% respectively compared to control. The culture supernatant of 40 h was extracted by ethyl acetate. The extract liquor was evaporated to driness under reduced pressure, dissolved in water, and then added to the culture of 16 h.After cultivation of 8 h, the oil production and oil-to-biomass ratio were raised by 100.0%and 58.8% respectively compared to control. The results preliminarily indicated the quorum sensing effect existed in fermentation process of Schizochytrium for DHA oil production, andthe quorum sensing signal molecules existed in the culture supernatant, which could be extracted by ethyl acetate and promoted the biosynthesis of DHA oil.