High Density Culture Of Crypthediunm Cohnni And Studies On Oil Modification

Docosahexaenoic Acid(DHA) plays a important role in the development of brain and eyes for infants, and it is beneficial for cardiovascular disease , and it can improve body immunity. DHA is accumulated in the cell lipid of Crypthecodinium cohnni (C.cohnni), and EPA is almost not existed in it, so it is a good DHA source for infants and pregnant women. The variables with the biggest effect on the growth and lipid and DHA accumulation are medium compositions and culture conditions, optimized environmental factors, such as carbon source , nitrogen source, pH, dissolved O₂ etc, were gotten. When C.cohnni was grown on different carbon and nitrogen source changes of enzyme acitivities shed light on some aspects of the biochemistry of this microalgae. The optimal extraction terms of cell oil was got by supercritical fluid CO₂ extraction (SCF-CO₂), and the acylation of cell oil was modified by enzyme-catalysis with caprylic acid.In the culture of C.cohnni, the optimized inoculums was 6X 105 cell per ml at the beginning of the fermentation. The optimal culture medium composition by shaken flasks was: 20g/Lglucose, 2g/L yeast extract and KNO₃(the ratio of them is 1:2 , mol/mol), 9g/L NaCl, 0.8g/L KH₂PO₄, 12mmol/L Mg²⁺, 10^-5g/L V_B12,10^-5g/LV_H.Nitrogen-limiting was not obvious in the oil accumulation of C.cohnni. when nitrogen was not limited, lipid content increased with the enlargement of ratio of carbon to nitrogen. When pyruvic acid and citric acid and malic acid were added at the beginning of fermentation, they were favorable for growth, but adverse to lipid accumulation, they had different effect on DHA content: pyruvaic acid was favorable for DHA content, DHA content was up to maximum when citric acid added was 2g/L, malic acid added decreased DHA content. When they were added at 60h of cultivation, DHA content increased with the pyruvic acid added, the citric acid and malic acid added enhanced lipid and DHA content. It was also found that the cell of C.cohnni has aggregation phenomena, aggregated cell have higher biomass.