Study On The Fermentation And Purification Of Docosahexaenoic Acid

Docosahexaenoic acid(DHA)is an important polyunsaturated fatty acid,which has significant effect on human health and huge economic value.At present,DHA is used as additives in many foods and nutrition productions,and its production processes are widely studied.Two alternative methods are applied for the production of DHA.The first method depends on the fish oil in deep ocean,but being restricted by quantity and cost.Moreover,the purity of DHA can not be assured from this method and extraction process also pollutes the ocean.Due to these reasons,the fermentation method attracts more and more attention.Schizochytrium sp.is a marine fungiand produces DHA in high quantities,which can be cultivated for production of DHA quickly and easily,with a product with high content of DHA and healthy to human and animals,so it is very promising.In this study,the production of DHA by Schizochytrium sp.is systematically studied,with comprehensive investigation of the purification process of DHA from dried Schizochytrium sp.,and a more advanced production process for DHA is obtained with high promising in industrial application.At first,a lab scale purification method for DHA is built,and the method for quantification of DHA is also developed.The DHA is extracted from fermentation broth or mushroom residue step by step,then esterified and quantified on liquid chromatography by external standard method with acetonitrile and methanol as mobile phase.In order to increase the production rate of DHA and decrease cost,the parameters of fermentation processes are optimized systematically,especially the growth environment of bacteria.In the experiments,the addition of sea crystal in culture medium,the increase of initial sugar content and oxygen have positive effect on the growth of Schizochytrium sp.and production of DHA.Finally,the pilot plant test is carried out to obtain a suitable production process for DHA,resulting in good results both in fermentation and purification processes.The best conditions of fermentation in pilot scale are shown below: 10% inoculum amount,the pH at 3 for early stage and 4 for later stage,6% sugar concentration,with bacteria concentration as 385 g/L and 8.5 g/L per unit.