Most of the figures published in the literature on concentrations of algal proteins, dominantly enzymatic proteins, are based on estimations of so called crude protein, commonly used in evaluating food and feed. This figure is obtained by hydrolysis of the algal biomass and estimation of the total nitrogen. Since besides protein also other constituents of micro-algae as for instance nucleic acids, amines, glucosamides, and cell wall materials contain nitrogen, this calculation results in an overestimation of the true protein content. According to reported figures the content of non-protein nitrogen amounts to 12% in Scenedesmus obliquus, 11.5% in Spirulina and 6% in Dunaliella.
Proteins are composed of different amino acids and hence the nutritional quality of a protein is determined basically by the content, proportion and availability of its amino acids.
Selected data on the amino acid profile of various algae are compiled in Table 2 and compared with some basic conventional food items and a reference pattern of a well-balanced protein, recommended by WHO/FAO (1973). It can be seen that the amino acid pattern of almost all algae compares favourable with that of the reference and the other food proteins (Becker, 2004).