Astaxanthin is a keto-carotenoid responsible for the pinkish color of some fish, crustaceans, and birds and is used as a
pigmentation agent in aquaculture and as a potent antioxidant for human health2003). The green microalga Haematococcus pluvialis is the best known source of natural astaxanthin. A common strategy for the production of astaxanthin in H. pluvialis is to sustain rapid growth under favorable culture conditions(green stage) and then stress the cells by introducing high light and/or nutrient depletion to
induce astaxanthin production (“red stage”). Although this
“two-stage” batch mode has been adopted by the Haematococcus
industry and research community persisting, largely ignored problem associated with this common practice is that considerable cell death occurs upon transferring H. pluvialis from the green stage to the red stage. The cell mortality rate may range from 20 to 80 % of total cells subjected to stress, depending on strains, bioreactors, and stress conditions under which H. pluvialis cells are maintained. As a result, overall astaxanthin productivity in H. pluvialis cultures is low. For example, an average astaxanthin production rate of 2.2 mg L−1
day−1 was obtained from the outdoor cultivation of H.pluvialis in a 75,000-L photobioreacto.High light or high light in combination with nutrient depletion are the major factors that stimulate astaxanthin synthesis in H. pluvialis in a photoautotrophic culture mode, but they may also cause severe photoinhibition of photosynthesis or photooxidative damage of the cells. It is imperative