Study On The Fermentation Technology Of Docosahexaenoic Acid (DHA)

Docosahexaenoic acid (DHA) is an omega-3polyunsaturated fatty acid(omega-3PUFA)with important physiological functions and high ecomomic value.DHA is not synthesized in adequate amounts to meet metabolic demands of thehuman body,thus must be obtained from dietary sources. The traditional sourcesof DHA are fish oils.However,conventional fish oils may not be suitable to meetthe increasing market for DHA owing to their poor quality and low quantity.Schizochytrium sp. is a kind of marine fungi with rich DHA, which is an idealsource for production of DHA because it contains high content and good quality oflipid and it is easy to cultivate and purify. At present, in Japan, the United Statesand some European countries, Schizochytrium sp.has been applied toindustrialized production of DHA. However, in domestic, the technology for DHAproduction is still in its infancy. The current domestic production of DHA in thefermentation is facing strain degeneration and low DHA content. Therefore,improvement of DHA production of Schizochytrium sp.by using varioustechnology and biological methods is particularly important. This paper carriedout the work as follows:First of all, the initial strain is rejuvenatied and naturally separated.Throughscreening, rescreening and generational stability test,we obtained strain Sc-16asthe initial strain,which followed by UV mutation breeding. Considering thepotency of fermentation, and generational stability, strain UV-28is selected asthe starting strain of follow-up experiments. Here, the fermentation titer of strainUV-28reached4261μg/mL, which is1.28times higher than the initialfermentation titers. Also, the cryopreservation of glycerol tube method isinvestigated to be the best preservation method for Schizochytrium sp..Then, we optimized the initial slant medium, seed medium, fermentationmedium and their culture conditions.By optimizing experiments, we got the bestfermentation medium formula（g/100mL）: Glucose12.6, Zhenyuan peptone1.7,tryptone0.5, sea salt1.2, trace elementsⅠ0.2, vitamins0.2, trace elementsⅡ0.1, monosodium0.1.And we obtained the optimum culture conditions: pH5.6,shaking bottled liquid volume35mL/250mL, inoculum18%, rotation speed240rpm, cultivation temperature25℃, cultivation cycle120h. Final fermentationtiter is7459μg/mL,which is2.25times improved than the initial strain potency.Finally,we adopt the new culture medium and culture conditions to carry onthe optimization of fermentation tank process, and draw the fermentationmetabolic curve, which lay a foundation for the subsequent fermentation tankamplification and industrial production.