Docosahexaenoic Acid Production By Schizochytrium Sp.ATCC 20888 Using Inulin As Raw Material

Docosahexaenoic acid(DHA),a member of?-3 long-chain polyunsaturated fatty acids,has drawn worldwide increasing attention due to its beneficial physiological functions for humans.Schizochytrium sp.,a marine fungus,can accumulate large amounts of single cell oil(SCO)with high proportion of DHA,it is considered as a promising alternative commercial source of DHA,but the production is hindered by the high feedstock cost.As a reserve carbohydrate,inulin present in plants represents a cheap,abundant and readily available bioresource.In this study,aiming at developing a practical and economical process for DHA production by Schizochytrium sp.ATCC 20888 using inulin as raw material.Schizochytrium sp.ATCC 20888 was cultured in fermentation medium with pure glucose,fructose or inulin powder as carbon source respectively,after 72 h of growth on glucose,16.81 g/L of total lipids was obtained,with the lipid content in biomass of 42.97%.Growth on fructose produced 16.54 g/L of total lipids after 96 h,with the lipid content in biomas of38.17%.Inulin was used as a carbon source with low biomass and low oil yield,and then determined it could not utilize inulin directly for growth and lipid production and therefore inulin needs be hydrolyzed to fermentable sugars prior to fermentation.Inulin was hydrolyzed by HCl or endo-inulinase or exo-inulinase,then thin-layer chromatography method was used for analysis,and the hydrolysates were used as carbon sources for fermentation,the results showed that fructose was the main carbohydrate in the acidic hydrolysate by HCl or enzymatic hydrolysates by exo-inulinase,and could be consumed by Schizochytrium sp.for cell grown and lipid production,the main carbohydrates in the hydrolysate by endo-inulinase were inulooligosaccharides,it could not be utilized by Schizochytrium sp.for fermentation.Finally,it was determined that the enzymatic hydrolysate by exo-inulinase was the most suitable for the fermentation by Schizochytrium sp.Single factor experiment was used to optimize the process conditions of enzymatic hydrolysis of inulin by exo-inulinase.Up to 97.8%of hydrolysis yield was obtained at 80 g/L of inulin,enzyme loading of 2g/kg substrate,40 ~oC,p H 7.0 for 12 h.The resulting hydrolysate was used for the microalgal cultivation,the lipid content in biomass of 45.26%and lipid productivity of 0.22 g/L·h were achieved,and meanwhile the DHA content in total fatty acids reached 35.59%,and the fermentation results are comparable to that of glucose as a carbon source.This study described the suitability of inulin as a low-cost and non-food feedstock for Schizochytrium sp.ATCC 20888 for DHA production.