enhancement of β-carotene biosynthesis in microalga dunaliella salina: mixotrophic cultivation and static magnetic field treatment

Carotenoids, such as β-carotene and astaxanthin, are the most important photosynthetic metabolites found in microalgae. they have several properties such as antioxidant and antidiabetic activities. β-carotene is one of the precursors of vitamin a possessing useful applications in the food industry, cosmetics, and pharmaceuticals. the microalga dunaliella salina is known as one of the biological producers of this valuable pigment, thanks to the lack of a rigid cell wall and shorter cultivation time. the optimization of culture medium for d. salina through the application of appropriate operational conditions such as static magnetic fields, can significantly impact biomass and carotenoids production. in this study, mixotrophic cultivation of d. salina was examined by adding different organic carbon sources, including glucose, fructose, acetate, malonate, glycerol, and starch, each at two levels of concentration. the inhibitory effect of malonate and glycerol on both growth and β-carotene production was observed. starch demonstrated higher biomass production (1.22 g l−1) and β-carotene accumulation (10.12 mg l−1) compared to other carbon sources. based on its superior performance, the optimization process was continued using 7.0 g l−1 of starch as the optimum concentration. subsequently, static magnetic fields with two intensities (10 and 30 mt) were applied to the mixotrophic samples at various exposure times (1 and 24 h day−1). the results revealed that the 24-hour treatment with both intensities improved biomass production (2.18 g l−1) and β-carotene concentration (6 mg l−1) by up to 25% in the culture of d. salina enriched with an organic carbon source.