Essential polyunsaturated fatty acids from 14 species of diatom (Bacillariophyceae)

The lipid class and total fatty acid compositions of 14 species of diatom (class Bacillariophyceae) were examined. The major lipid class in these microalgae was polar lipid (50.1-90.8%), although in some species, triacylglycerols (0.3-47.7%) and free fatty acids (0-29.2%) were also abundant in the logarithmic phase cultures. The major fatty acids in most species were 14:0, 16:0, 16:1 (n-7) and 20:5(n-3). The polyunsaturated fatty acids 16:2(n-4), 16:3(n-4), 16:4(n-1), 18:4(n-3) and 22:6(n-3) also comprised a significant proportion (>4% each) of the total fatty acids in some species. The characteristic fatty acid composition of diatoms is readily distinguishable from those of other classes of microalgae. The mean proportion of 22:6(n-3) was significantly higher in representatives from the order Centrales (4.9%) than the Pennales (1.6%), but there was no consistent difference in the proportions of the other fatty acids. Four of the pennate diatoms contained significant proportions of arachidonic acid, 20:4(n-6) (3.5-5.6%), but most species examined contained very low proportions of (n-6) polyunsaturated fatty acids. Based on the lipid compositions, all of the diatom species studied are potentially suitable sources of some of the longer chain polyunsaturated fatty acids.