*3.2. Protein and Amino Acids*

Protein content in seaweed varies by species, season, and geographic location, and can be as high as 45% DW. The contents of peptides, proteins, or amino acids in seaweed are affected by seasonal fluctuations and habitat; in general, red algae have larger concentrations (up to 47%) than green algae (around 9 and 26%), while brown algae have low amounts (3–15%) [77]. The difference in the amounts of proteinas and amino acids in some seaweeds are illustrated in Tables 3 and 4. All essential and non-essential amino acids are found in the proteins of the three macroalgae groups [78]. Seaweed protein and bioactive peptides have a variety of health benefits as well as significant antioxidant activity, especially through compounds with low molecular weight compounds that are far secure than produced substances or have less adverse impacts [79,80].

**Table 3.** Different proteins accumulation of some seaweeds.


ND: Not detected; SfL: *Solieria filiformis* lectin; Cf-hGP: *Capsosiphon fulvescens* hydrophilic glycoproteins; UPGP: *Undaria pinnatifida* glycoprotein.



Various seaweeds contain amino acids such as valine, leucine, isoleucine, or taurine which have potential biological action as antioxidants [92,93]. Acidic amino acids aspartic acid or glutamic acid is abundant in most seaweed species, and they comprise most essential amino acids [94]. While algal proteins were being thought to consist of threonine, tryptophan, sulfur amino acids (cysteine and methionine), lysine, or histidine-limiting amino acids, their overall levels are larger than in terrestrial plants [95]. Furthermore, amino acids are required for the production of hormones and nitrogenous low molecular weight compounds, both of which are important biologically. Amino acids can be used to help treat some disorders since they have distinct physiological roles. Supplementing with methionine, for example, can help people with multiple sclerosis [96]. Despite the fact that seaweed proteins contain low amounts of some essential amino acids, these seaweeds could be introduced to cereal foods such as pasta to enhance the amino acid composition [97].

Macroalgal species such as *Chlorella* sp., *Dunaliella tertiolecta*, *Aphanizomenon flosaquae* and *Spirulina plantensis*, due to their high protein content or nutritive quality, are often used as human food sources [98]. Endogenous (threonine, serine, aspartic acid, proline, glutamic acid, or glycine) and exogenous (histidine, lysine, isoleucine, methionine, phenylalanine, leucine, valine or threonine) amino acids are abundant in some algae species [43]. Ulva spp. has glutamic or aspartic acid (26–32% amino acid), *Ulva australis* has taurine or histidine, *Himanthalia elongata* (sea spaghetti) *Palmaria palmata* (Dulse) and have a lot of glutamic acid, serin or alanine, and *Sargassum vulgare* has lot of methionine [99]. Several applications of seaweeds protein are illustrated in Table 5.


**Table 5.** Seaweeds proteins and their roles in medicinal.
