The green halophilic alga Dunaliella is the best natural source of p-carotene. This microalgae is marketed in several countries, such as the United States, Australia, and Israel. The biopigment p-carotene is extracted from microalgal biomass and used as a food supple­ment or a natural pigment added to foods, or the dry biomass is marketed in tablets (Wood, 1998).

The biomass of the microalga Dunaliella has demonstrated several biological activities, such as being antihypertensive, bronchodilator, analgesic, muscle relaxant, and anti-edema. The natural p-carotene contains many essential nutrients that are not present in the same pigment produced synthetically (Yousry, 2002). The human body converts p-carotene to vitamin A without forming toxins in the liver. p-carotene has antioxidant activity while avoiding the effects of free radicals.

This microalga is grown in high salinity, with optimal growth in 22% of NaCl. Under these cultivation conditions the microalga culture is axenic and thus poses no problems of contam­ination when kept in open ponds (Wood, 1998).

The concentration of p-carotene accumulated in the cells of Dunaliella overcomes the traditional source of this pigment, and about 14% of the compound may be extracted.

Dunaliella is a eukaryotic green algae that grows in saline sites. Halophilic representatives of microalga have an osmotic mechanism that is different from halophilic bacteria. Dunaliella, which has no cell wall, can be developed with high salt concentration in the cytoplasm by the synthesis of glycerol. This microalga also responds to osmotic stress with the synthesis of glycerol if the high salinity is caused artificially by polyols.

The amount of glycerol produced by the microalga when exposed to saline stress is pro­portional to the concentration of NaCl in the culture.