Optimization Of Seed Cultivation And DHA Production From Schizochytrium Limacinum SR21 Fermentation

Docosahexaenoic acid(DHA)is a polyunsaturated fatty acid with important physiological works such as brain-enhancing,anticancer,and antitumor.Studies has shown that Schizochytrium has been used as a strain to produce DHA.The DHA produced by fermentation of Schizochytrium still has problems such as unclear culture stage,no guidance of kinetic model,and no automatic control of fermentation.In this study,dividing the fermentation into three stages: seed growth stage,bacterial growth stage,fatty acid and DHA collection stage,by analyzing the model of Schizochytrium.Setting up a reliable dynamic model by optimizing the three stages,it can provide theoretical guidance for continuous fermentation,automated control and scale-up culture.The specific research content is as follows:Single factor experiment to design the concentration of potassium dihydrogen phosphate,the type and concentration of nitrogen source,pH value and inoculum to find out the model conditions for seed growth of Schizochytrium.The results indicate that there is no ammonium acetate,yeast extract concentration is 20 g/L,inoculated 20 % and pH 7.5 is most helpful for the seeds growth.Finally,we inoculate 10 %,because of the large volume of seed fermentation broth needed for industrial scale and inoculum 5 % the seed grows slowly.Compared with the control group,the cell density increased by 36 % at 24 h.To confirm the model total nitrogen(TN)concentration in the growth,fatty acid and DHA collection stages of Schizochytrium,we set up the kinetic equation based on the basal medium.The results showed that the concentration of TN in the fermentation broth was above 1.0 g/L before 48 h,and reduced to about 0.6 g/L from 48 h to 60 h,and maintained in the following.According to the experimental data obtained under this condition,the dry weight of Schizochytrium is 136 g/L and the DHA content is 16.70 %.The fermentation and kinetic equations identified in this paper could guide developing continuous fermentation and fermentation scale up.New ideas have been proposed for realizing automated control and reduction of fermentation costs.