Optimization of arachidonic acid production by fed-batch culture of Mortierella alpina based on dynamic analysis

Arachidonic acid is an essential fatty acid in human nutrition. Improvement of arachidonic acid production by fungus Mortierella alpina was investigated. The time courses of fungal biomass, lipid and arachidonic acid production with different initial glucose concentrations were examined to study dynamic characteristics of arachidonic acid production on a shaker flask scale. Results showed that low initial concentrations of glucose were good for fungal growth at the early days of cultivation. When residual glucose concentration was under 10 g/L, fungi stopped growing because of inefficient energy source and carbon source needed for their growth. Meanwhile, the lipids were still accumulated for a period even though fungi stop growing. A great increase of arachidonic acid content in lipids occurred after the glucose was exhausted. To obtain high arachidonic acid yield, a fed-batch process was developed according to the dynamic analysis. Glucose and nitrate were included in the feed medium. Low initial glucose concentration (50 g/L) and nitrate concentration (3 g/L) were used to shorten the lag phase of fungal growth. Twenty grams per liter per day glucose and 1.5 g/(L day) nitrate were fed to the medium at the 3rd, 4th and 5th days of cultivation. A good arachidonic acid yield (7.74 g/L) on the 8th day was obtained, which was a great improvement over that of batch cultures.