International Journal of Aquaculture, 2025, Vol.15, No.5, 248-254 http://www.aquapublisher.com/index.php/ija 249 rank among the top in seaweed, making seaweed an important source of high-quality protein for vegetarians (Arakaki et al., 2023). The amino acid composition of seaweed protein is balanced, and the essential amino acids are complete and the proportions are appropriate. A study and comparison of the protein composition of seaweed in different harvest periods was found that the ratio of total amino acids and essential amino acids of seaweed was the highest during the peak growth period (Mohammed et al., 2021). In addition, seaweed is rich in amino acid derivatives such as taurine, which helps to improve nutritional value and has health effects such as regulating metabolism. 2.2 Carbohydrates and dietary fiber Carbohydrates are another major component of the dry weight of seaweed, and the content is usually between 30% and 50%, of which a considerable proportion exists in the form of dietary fiber (Gonçalves et al., 2021). Among them, water-soluble dietary fiber (such as seaweed polysaccharide) is rich in content, which helps maintain intestinal health and reduces cholesterol absorption. Seaweed polysaccharide is the most distinctive carbohydrate in seaweed. Its main chain consists of alternating galactose and 3,6-dehydrated galactose, and has a sulfate group attached to some galactose residues. It is a typical sulfate polysaccharide (Mei et al., 2024). As dietary fiber, seaweed polysaccharides have the effects of absorbing water and promoting intestinal peristalsis, and also exhibit a variety of biological activities. In addition, seaweed also contains a small amount of soluble sugars, but the overall fat content is extremely low, and energy mainly comes from carbohydrates and proteins. This high-fiber, low-fat ingredient feature makes seaweed a healthy food choice. 2.3 Vitamin and mineral distribution Seaweed is rich in a variety of vitamins and minerals and is a natural "nutrition treasure house". Seaweed is a few plant sources that contain vitamin B12, and intake is moderate to help prevent anemia caused by deficiency of this vitamin. In addition, seaweed provides rich antioxidant vitamins such as vitamins A, C, E, etc., which helps improve the body's immunity and antioxidant defense (Kaur and Kaushik, 2025). In terms of minerals, the content of iodine, iron, calcium, magnesium, potassium and other elements in seaweed is outstanding (Alda et al., 2023). Among them, iodine is an essential element for the synthesis of thyroid hormones, and eating seaweed can prevent iodine deficiency (such as goiter). Iron in seaweed is beneficial to improve iron deficiency anemia, and calcium and magnesium help maintain bone and nerve health. However, it is necessary to note that the iodine and sodium content in seaweed is high, and it is necessary to eat it in moderation. 3 Functional Compounds of Nori 3.1 Polyphenol compounds Polyphenols are one of the important active ingredients in seaweed, giving seaweed strong antioxidant ability and various biological activities. Seaweed contains a variety of polyphenol compounds such as phenolic acids, flavonoids and brominated polyphenols unique to marine algae. Among them, bromine polyphenols have higher antioxidant activity due to their presence of bromine atoms and are considered to be a key ingredient for the health care effects of seaweed (Goya and Mateos, 2024). In vitro experiments showed that the seaweed polyphenol extract showed significant effects in free radical scavenging such as DPPH and ABTS and inhibiting cellular lipid peroxidation. Xu et al. (2022) extracted the saphi polyphenol and found that it had a significant inhibitory effect on the proliferation of human liver cancer HepG2 cells (Xu et al., 2022). It can be seen that seaweed polyphenols are one of the main contributors to seaweed's antioxidant and other biological activities. 3.2 Carotenoids and phycobilide proteins Nori contains carotenoids such as beta-carotene and lutein. It not only gives nori a unique color, but also an important source of antioxidants and vitamin A, which helps protect vision and improve immunity. Seaweed is also rich in phycobilidin (especially R-phycoerythrin), and the photosynthetic pigment protein unique to this type of red algae is also biologically active. Some studies have pointed out that phycoerythrin has antioxidant, antitumor and immune regulation activities. Phycoerythrin can not only be used as a natural food coloring, but also has application value in the field of biotechnology. Carotenoids and phycobilidin in seaweed together improve their nutritional and functional value (Chen et al., 2017).
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