Maximizing beta-carotene production from Dunaliella salina using different concentrations of ferrous sulfate and potassium nitrate under in situ and induced cultivation conditions

Natural beta-carotene, a valuable antioxidant and food additive, is conventionally derived from vegetables and microalgae such as Dunaliella salina (D. salina). Growing concerns over the safety of synthetic carotenoids and increasing demand for natural alternatives in food, nutraceutical, and cosmetic industries have accelerated the development of controlled cultivation systems. However, unstable environmental conditions in outdoor production systems can hinder consistent carotenoid yields. In this context, D. salina is recognized as a promising candidate for beta-carotene production through indoor cultivation, which allows for precise control over key growth parameters and reduces dependency on fluctuating environmental factors. This study investigated how nitrogen availability and ferrous ion supplementation affect the growth and beta-carotene accumulation of D. salina under both in situ and stress-induced conditions. Results show that nitrogen supports robust biomass accumulation, while ferrous ions stimulate beta-carotene synthesis via oxidative stress. Notably, the combined application of these two nutrients produced a synergistic effect, achieving both high cell density (2.4079 ± 0.00432 × 10⁷ cells mL^-1) and elevated beta-carotene content (27.12 ± 1.41 pg cell^-1) after 20 days of induced two-stage cultivation in a 15 L indoor culture system. These findings contribute to the development of optimized cultivation strategies for sustainable, high-yield beta-carotene production.