FATTY-ACID CONTENT AND CHEMICAL-COMPOSITION OF FRESH-WATER MICROALGAE

Fatty acid (FA), total lipid, protein, amino acid, carbon, nitrogen, and phosphorus content was analyzed in 24 samples of freshwater microalgae. The samples originated from batch, continuous, or mass cultures in various growth phases and from net samples from lakewater. FA were analyzed quantitatively by using an internal standard in a GLC system and expressed as mg.g-1 dry weight (DW). The FA of one group of blue-greens (e.g. Oscillatoria and Microcystis) were similar to those of the greens with higher amounts of 18C acids of the omega-3 type compared to the omega-6 type, whereas the other group (e.g. Anabaena and Spirulina) contained mostly omega-6 acids. The flagellates, a taxonomically diverse group, were characterized by high amounts of long-chained (20-22 C) polyunsaturated FA (PUFA), particularly of the omega-3 type. The omega-3/omega-6 ratio appears to be highest in algae in the exponential growth phase. The increased lipid content in stressed algae was mostly due to increased saturated fatty acids and omega-6 acids, whereas the valuable omega-3 acids were unchanged or even decreased. Amino acid composition (% of total amino acids) did not vary much between species, but when analyzed quantitatively (mg.g-1 DW), varied considerably between species and within species in different growth phases. The nitrogen and phosphorus contents were variable in all three algal groups. The relationship between PUFA and phosphorus content differed among the algal groups. The data suggest that PUFA in the phospholipids consist mostly of omega-3 acids.