Effects of nitrogen source and growth phase on proximate biochemical composition, lipid classes and fatty acid profile of the marine microalga Isochrysis galbana

The marine microalga Isochrysis galbana was cultured in nitrate, nitrite or urea media to examine changes in the gross biochemical composition, with special emphasis on the growth phase associated changes in the compositions of the lipid classes and fatty acids. The gross biochemical composition was affected more by the growth phase than by the nitrogen source. Protein was higher during exponential growth (about 37–45% AFDW) but the pattern changed as the cultures aged, and lipids were the main algal constituents on all nitrogen sources in the late stationary phase. In all cultures, the relative abundance of neutral lipid increased in the late stationary phase concomitant with a proportional reduction in phospholipids, whereas galactolipids only slightly changed during the growth of the cultures. Total fatty acid content was affected by nitrogen source and growth phase. Maximal PUFA values were obtained at the early stationary phase and decreased throughout the stationary phase. The highest fatty acid contents in the early stationary phase were produced in urea cultures; these cultures also had higher PUFA content, with EPA and DHA contents of 27.66% and 14.13% of total fatty acids, respectively.