Fermentation Production And Component Analysis Of DHA-rich Lipid By Schizochytrium Sp.

Docosahexaenoic acid（DHA）,an importantω-3 polyunsaturated fatty acid,has many physiological functions of promoting the development of brain cells,enhancing vision,preventing andtreating cardiovascularandcerebrovasculardiseases,preventing arteriosclerosis,and preventing cancer.As a new generation of functional factor,it is widely used in the food and pharmaceutical industry.Schizochytrium sp.is a marine fungus rich in DHA,which has the advantages of rapid growth,easy culture,and high intracellular lipid content.It is an ideal strain for commercial production of DHA.In this thesis,DHA was produced from a strain of Schizochytrium sp.DP-16,and the fermentation medium was optimized,and the composition of DHA-rich lipid was analyzed.In this work,response surface methodology（RSM）was used to optimize the fermentation medium for DHA-rich lipid production by marine fungus Schizochytrium sp.DP-16 to increase DHA-rich lipid production and provide reference for the industrial production of DHA-rich lipid.Based on single factor experiments results of carbon sources,nitrogen sources and exogenous additives,glucose,yeast extract and monosodium glutamate were determined as the major influencing factors.Then the fermentation medium for DHA-rich lipid production was optimized using response surface methodology.Under optimal conditions,the maximum response value predicted by the experimental model was 21.511g·L^-1.The actual test result is 21.391 g·L^-11 with good reliability.The pre-optimized lipid yield was 20.467 g·L^-1,and the optimized fermentation medium increased the DHA-rich lipid production by 4.5%.Compositional analysis of DHA-rich lipid produced by Schizochytrium sp.DP-16 showed that the lipid composition included glycerides,phospholipids,and unsaponifiables.Among them,glycerides include triglycerides（TG）,diglycerides（DG）and glycerol monoester（MG）;phospholipids include phosphatidic acid（PA）,hemolytic phosphatidyl ethanolamine（LPE）and phosphatidyl ethanolamine（PE）,hemolytic phosphatidyl choline（LPC）,phosphatidyl inositol（PI）,phosphatidyl choline（PC）and phosphatidyl glycerol（PG）,unsaponification material including squalene,cholesterol,paraffin and alkanes.The results indicated that lipid accumulation of Schizochytrium sp.DP-16 is an energy storage process.When the nitrogen and carbon sources are sufficient,the cells proliferate,and the content of phospholipids in cell lipid is high.After the nitrogen source is exhausted,the cell division stops and the synthesis of lipid starts.The accumulated lipid is mainly glyceride.Phospholipids have a high content of unsaturated fatty acids during the fermentation process.In the unsaponifiables,the content of squalene increases,and the cholesterol content increases first and then decreases.After 96 hours fermentation,the contents of squalene and cholesterol were 0.0123 g·L^-11 and0.755 mg·L^-1respectively.