The proteins, peptides, and amino acids vary with the algal species as well as the habitat and the season (Arasaki and Arasaki,1983). In general, the protein content is relatively low in brown algae but is higher in green and red algae. Proteins may indeed represent 35-45% of dry matter in macroalgae (Holdt and Kraan, 2011) and even 60%-70% in microalgae (Babadzhanov, Abdusamatova et al., 2004; Samarakoon and Jeon, 2012). These levels are com­parable to those found in high-protein vegetables (e. g., soybeans), in which proteins account for up to 40% of their dry mass (Murata and Nakazoe, 2001).

Most algal species contain all essential amino acids and are in particular a rich source of aspartic and glutamic acids (Fleurence, 1999). The levels of some amino acid residues are actually higher than those found in terrestrial plants—for example, threonine, lysine, trypto­phan, cysteine, methionine, and histidine (Galland-Irmouli, Fleurence et al., 1999). Brown al­gae proteins have been reported as good sources of threonine, valine, leucine, lysine, glycine, and alanine but poor sources of cysteine, methionine, histidine, tryptophan, and tyrosine (Dawczynski, Schubert et al., 2007). Red algae possess high quantities of glutamic and aspartic acids but lower levels of basic amino acids compared to the other two algal groups (Fleurence, 1999).

Bioactive proteins and peptides have been found in micro — and macroalgae that possess a nutraceutical potential (DeFelice, 1995), as is the case of their role in reducing the risk of cardiovascular diseases (Erdmann, Cheung et al., 2008). Several other bioactivities are presented in Table 10.3.