Chlorella spp. are simple, nonmotile, unicellular, aquatic green microalgae. They were one of the first algae to be isolated as a pure culture. The Chlorella microalga measures between 5 and 10 micrometers and, under an optical microscope one, can observe its green color and spherical shape.

Compared to higher plants, Chlorella has a high concentration of chlorophyll and photo­synthetic capacity. The microalga Chlorella is classified as a species according to the shape of the cells, characteristics of chlorophyll, and other variables. There are 20-30 species, some of which are Chlorella vulgaris, Chlorella pyrenoidosa, and Chlorella ellipsoidea. The species are differentiated within the group, known as strains (Illman et al., 2000).

The first pure culture of microalga to be scientifically proven was Chlorella vulgaris in 1890 by the microbiologist M. W. Beijerinck. In 1919, Otto Warburg published articles on the use of this microalga in culture to study its physiology. After years of research with Chlorella and other microalgae, he found that these microorganisms grow under specific conditions and can be used to produce compounds with nutritional benefits to human health.

One of the most important characteristics of Chlorella is its protein content. Depending on the culture conditions, this microalga can provide 60% of protein with essential amino acids for human consumption. Chlorella has approximately three times more protein than the same amount of red meat, which is one of the most concentrated sources of protein. Due to its high protein concentration, Chlorella is used as a food supplement. This microalga has 23% carbo­hydrates, 9% fat, and 5% minerals (Henrikson, 1994).

Chlorella is also rich in B vitamins, especially B12, which is vital in the formation and re­generation of blood cells. Because it also has a high iron content, this microalga is a product indicated for the treatment and prevention of anemia. In order for its nutrients to be fully uti­lized by the body, cells of Chlorella, which are protected by a cell wall, must be disintegrated during the drying process to enable its nutrients to be fully absorbed by the metabolism (Henrikson, 1994).