Study On Theγ-linolenic Acid Production By Cunninghamella Echinulata Fermentation

Theγ-linolenic acid (GLA) is a kind of polyunsaturated fatty acids (PUFAs) which play an important role in the metabolism control of human physiology. In order to explore the low-cost PUFA-producing processes by Cunninghamella echinulata (labled FR), potato starch-industrial wastes (PSW) were used as a cheap nutrient source in this thesis.It was found that the pellet diameter of FR mycelia was important to the control of liquid culture. The better condition for controlling liquid culture was shown as below. Firstly, PDA medium was used for culturing the FR for 6 days. Secondly, the cultured spores were used to inoculate 100 mL of PDY medium in 250 mL round flask with the final concentration of 10 8/mL. The contents of the flask were incubated at 28℃for 48 h on a reciprocal shaker (150 r/min) with six glass beads ( diameter 4-5 mm). Finally, we got the pellet mycelium with the diameter from 0.5mm to 2mm.By improving the culture condition, we found that the best condition for dissolving oxygen in the medium is culturing the microorganisms in the 150 mL PSW medium of 500 mL round flask on a reciprocal shaker (150 r/min). By developing the C/N ratio and feeding methods, it was suggested that the optimal nitrogen resource were the mixture of (NH4) 2SO4 and soybean with the ratio 3:7. The total nitrogen atoms concentration and the glucose concentration were 0.238 % and 7.128 %, respectively. After 4.2 days culturing, the 4.67 % glucose was added to medium for feeding fermentation. The final biomass, oil yield and GLA content reached 35.6 g/L,11.81g/L and 10.36 %, respectively. Besides, the kinetics model had been established.In the process of bioreactor fermentation, the parameter of different controlling methods were studied and optimized. During the first 4 days of the fermentation, the best culture temperature is 28℃and the optimized pH value is 6. During the last 3 days, the best condition for lipid accumulation and GLA synthesis is fermenting at 18℃and pH 5. The best fermenting condition for dissolving oxygen was by culturing organisms at the rotate speed of 200 r/min in the second day and the last 4 days, without shaking in the first day and the third day. During the whole process, the air feed speed kept at 400 L/h. The best feeding methods was adding 1 % glucose each day from the second day to the sixth day, and making the final feeding glucose concentration to 5 %. These methods greatly increased the biomass, oil content and the proportion of GLA in the oil, which reached 38 g/L, 13.46 g/L and 10.12 % .respectively.