During the second stage of cultivation which is the red stage, carotenogenesis (formation of beta carotene) is achieved by subjecting the algae to stress conditions – higher sunlight, higher salinity (120‰) and nitrogen deficiency. Under these conditions, Dunaliella salina produces beta carotene and glycerol as a protective factor for surviving under such harsh conditions.
As the beta carotene content reaches the required level inside the algae cell, harvesting stage is carried out.
The time taken for green Dunaliella algae to produce excess beta carotene and turn red is around one week, and the total cultivation period lasts around three weeks. At the end of three weeks, harvesting is carried out.