| Schizochytrium is marine microalgae rich in DHA,and the high production cost limits its wide application.Exploring the low-cost production strategy of DHA is an important strategy to accelerate the development of its industrial production.The annual output of Chinese liquor lees is high,but the utilization is low,and the stacking will cause environmental pollution.In this paper,using distiller’s grains to replace the nitrogen source of the traditional medium,a new low-cost fermentation process of Schizochytrium was established,the feasibility of recycling fermentation waste liquid was explored,and the non-sterile fermentation process conditions were determined.（1）Using the sauce-flavor distilled grains as the research material,pretreated as the nitrogen source of the medium for Schizochytrium,to explore the effect of the distiller’s grains treatment solution replacing the traditional nitrogen source on the production of DHA by the fermentation of Schizochytrium.Comparing the distiller’s grains treatment solution with commercial nitrogen sources tryptone,yeast powder and beef extract,it was found that the biomass of Schizochytrium was 26.28%higher than that of the distiller’s grains treatment solution only under the condition of tryptone.Based on the lipid morphology comparison and free amino acid composition analysis of Schizochytrium in distiller’s grains treated liquid and tryptone culture conditions,the feasibility of distiller’s grains treated liquid as nitrogen source for Schizochytrium sp.S31 medium was determined.The fermentation process parameters were optimized by a single factor experiment,and the optimal fermentation process conditions were determined as follows:the ratio of dry matter and water of distiller’s grains is 1:9,the amount of glucose added is 70 g·L-1,the fermentation temperature is 28°C,and the amount of distiller’s grains treatment liquid is added 70%,the initial p H was 7.0,under these conditions,the biomass of shake flask culture could reach 22.14 g·L-1,the lipid yield was 8.88 g·L-1,and the DHA yield was 2.85 g·L-1.（2）To explore the effect of fermentation waste liquid addition amount and cycle times on the growth and DHA synthesis of Schizochytrium sp.S31.When the waste liquid addition amount is 15%,the biomass of the three cycles is 27.97 g·L-1,25.15 g·L-1 and 20.92 g·L-1,respectively.In one cycle,the DHA yield reached 4.27 g·L-1,which was 33.26%higher than that without waste liquid recycling.The fed-batch fermentation experiment was carried out in a 7.5 L stirred fermenter,and the biomass and lipid production reached the maximum at the same time at 108 h,which were 63.46 g·L-1 and 27.23 g·L-1,respectively.The method improves the production efficiency of DHA while reducing the cost of waste liquid treatment and provides a new idea for the resource utilization of fermentation waste liquid.（3）To explore the non-sterile fermentation process with distiller’s grains treated liquid as the nitrogen source of the medium.Considering that Schizochytrium can grow actively in high salt concentration medium,the sea crystal concentration and inoculum amount were optimized to reduce bacterial contamination.The optimal conditions were determined:the concentration of sea crystal was 47.5 g·L-1,and the inoculation amount was 15%.The biomass,lipid yield and fatty acid quality of Schizochytrium sp.S31 under the optimized non-sterile conditions were compared under the sterilization conditions.It is only 0.05%lower than that.Combined with microbial community analysis,the dominant position of Schizochytrium sp.S31 in the fermentation process was determined,which provided a theoretical basis for reducing energy consumption through non-sterile fermentation. |
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