Study Of Docosahexaenoic Acid Production By Crypthecodinium Cohnii

DHA is a polyunsaturated fatty acid that belongs to theω-3 group. In recent years, DHA has attracted much attention because it plays an important role in human health. Crypthecodinium cohnii is extraordinary in DHA and it can be grown heterotrophically on organic substrates without light. It is a prolific producer of DHA.The effects of temperature and temperature shift on the biomass and oil content of Crypthecodinium cohnii were investigated. Over the entire range of temperatures we have studied, form 15℃to 35℃, the microalga can grew well. High temperature is good for growth and the highest biomass is 25.25g/L at 30°C. In contrast, low temperature is good for the accumulation of oil and the formation of polyunsaturated fatty acids and the highest oil content is 40 percent. A shift from high temperature to low temperature at a later stage of cultivation was also attempted. A temperature shift from 28℃(for 5 days) to 22℃(for 2 days) resulted in an increase in oil which was reach up to 8.28g/L. When medium pH was 6.5~7.0, the highest cell dry weight concentration were obtained.The content of glucose, sodium glutamate and yeast extract of fermentation medium was optimized using Design Expert 7.1 software. The optimum levels of these important factors were 68g/L, 30g/L and 6.5g/L respectively. Under the optimum medium, the production of DHA was reach up to 2.41g/L, which is highest of all.The breaking of cell wall of Crypthecodinium cohnii by supersonic treatment, enzymatic procession and temperature-difference was evaluated separately in the article. The results showed that all methods were effective to the wall-broken efficiency and oil extraction rate. Better results appeared if we combined the enzymatic procession (for 5 hours, first) and the supersonic treatment (for 1 hour, second), as the rate of wall broken could be up to 91.7% and the oil extraction rate increased 21.7%.