Gametophyte phase of commercial kelps, the potential food supplements for essential fatty acids and n‐3 polyunsaturated fatty acids

For heteromorphic algae with alternating generations, the thallus and gametophyte phases are different morphologies in free‐living life history. The thalli are popular used as traditional vegetables and herbal drugs, whereas the gametophyte phases are little involved. To better understand the functional lipids in the gametophyte phase of three commercial kelps, Saccharina japonica, Undaria pinnatifida, and Costaria costata, the contents of total lipids (TLs), fatty acid (FA) profiles, and transcriptomic analysis were performed. For the studied kelps, the TL contents in gametophyte phase were always almost twice more than those in the thallus, and the kelp species, their life stage, and the gender were critical factors affecting lipid accumulation. The gametophyte phases of U. pinnatifida and C. costata were rich in essential FA C18:2 n − 6 and C18:3 n − 3. The S. japonica gametophyte phase contained abundant C20:5 n − 3 and C18:4 n − 3, possessed an ideal ratio of n − 6/n − 3 polyunsaturated fatty acid below 1.0, and was supported by the transcriptome data which showed that the key sjD12/15 (n − 3) gene of gametophyte partially upregulated than sporophyte. The results suggested that S. japonica gametophyte phase was the worthiest of further development and utilization as a functional food. Practical Application It is the first report on the fatty acid characteristics of three gametophyte phases of Saccharina japonica, Undaria pinnatifida, and Costaria costata and find that the S. japonica was worthy of further development and utilization as a functional food owing to its satisfactory fatty acid composition.