Accumulation and antioxidant activity of secondary carotenoids in the aerial microalga Coelastrella striolata var. multistriata

The growth and nitrate uptake of the aerial microalga Coelastrella striolata var. multistriata, which was isolated from the surface of rocks, were characterized under a variety of conditions in this study. The maximum specific growth rate of the alga, having prominent inorganic nitrogen uptake in the fresh medium, was 0.30 d⁻¹, as calculated in the growth logarithmic phase. It was also shown that the alga had abilities to be reddish orange to green colour (depending on the nitrogen source concentration in the medium) and to synthesize very high amounts of a complex mixture of carotenoids, such as canthaxanthin, astaxanthin and β-carotene. The reddish orange cells of the alga could accumulate 56.0 mg of major secondary carotenoids per g biomass. In the content of carotenoids, canthaxanthin, astaxanthin and β-carotene in the cells were 47.5, 1.5, and 7.0 mg/g dwc, respectively. Additionally, it was shown that the algal extract containing those carotenoids had an antioxidant potential in lipid foods. In the near future, the aerial microalga C. striolata var. multistriata will be used as a functional material in a variety of commercial applications, such as feed supplements, natural antioxidants and food dyes.