*3.3. Fatty Acids*

Fatty acids (FAs) are required for all organisms to function normally. FAs are components of plasma membranes that serve as energy storage materials as well as signal molecules that control cell development and differentiation as well as gene expression. Elongation and desaturation can change the structure of FAs [121,122]. The quantity of unsaturated bonds in FA molecules determines their biological effects. Additionally, lipids are essential to transport and absorb fat-soluble vitamins (i.e., A, E, D or K). PUFAs (25–60% of total lipids), glycolipids, phytosterols, phospholipids, or fat-soluble vitamins are all found in low concentrations (1–5% of dry weight) in seaweed lipids (vitamin A, D, E or K, carotenoids) [1]. Several seaweeds have a greater total lipid concentration above 10% of dry weight; however, 50% of these lipids are in the form of extractable fatty acids in the brown alga *Spatoglossum macrodontum*. In addition, *S. macrodontum* showed the maximum fatty acid concentration (57.40 mg g−<sup>1</sup> DW) and a fatty acid profile rich in saturated fatty acids with a higher concentration of C18:1, making it an excellent biofuel feedstock. Similarly, the green seaweed *Derbesia tenuissima* possesses significant quantities of fatty acids (39.58 mg g1 DW), but with a greater amount of PUFA (n-3) (31% lipid) that can be used as nutraceuticals or fish oil substitutes [123]. The lipid algae concentration is low (1–5%), with neutral lipids and glycolipids dominating. Because algae generate long-chain polyunsaturated fatty acids, including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), the amount of

essential fatty acids in algae is greater than in terrestrial plants [124]. In general, red algae have higher concentrations of EPA, palmitic acid, oleic acid, and arachidonic acid than brown algae, which have greater amounts of oleic acid, linoleic acid, and α-linolenic acid but lower amounts of EPA. Green algae have more linoleic acid and α-linolenic acid, as well as palmitic, oleic, and DHA [125]. Both red and brown algae contain omega-3 and omega-6 fatty acids [126]. The different in the amounts of lipid in different seaweeds are illustrated in Table 6.


**Table 6.** Lipids accumulation of some seaweeds.

EPA: eicosapentaenoic acid; DHA: docosahexaenoic acid.
