Sequential optimization for biomass and fucoxanthin enriched carotenoid production of Isochrysis galbana

Microalgae are promising sources of high-value bioactive compounds, offering renewable, low-waste, and environmentally friendly alternatives to synthetic chemicals. This study focuses on optimizing the cultivation conditions of Isochrysis galbana to enhance biomass and carotenoid production, with particular emphasis on enhancing fucoxanthin, a potent antioxidant with diverse biological activities. A sequential optimization strategy combining one-factor-at-a-time (OFAT) screening and response surface methodology (RSM) was employed to identify and refine key physicochemical variables. Optimal conditions for biomass production were 2.75 mM nitrate, 0.32 mM phosphate and 23 μE m⁻² s⁻¹ light intensity, whereas total carotenoids and fucoxanthin yields were maximized at 2.43 mM nitrate, 0.28 mM phosphate, and 28 μE m⁻² s⁻¹. Under optimized conditions, biomass reached 1.40 ± 0.05 g L⁻¹ (volumetric productivity: 0.05 g L⁻¹ d⁻¹), total carotenoids increased to 98.67 ± 1.43 mg g⁻¹ (4.34 mg L⁻¹ d⁻¹), and fucoxanthin content was enhanced to 31.36 ± 1.55 mg g⁻¹ (1.38 mg L⁻¹ d⁻¹). These values represent 4.83, 4.47, and 4.24-fold increases, respectively, compared to the unoptimized conditions. The results demonstrate that I. galbana cultivation under optimized conditions is a viable and sustainable approach for the large-scale production of fucoxanthin and other carotenoids. This work supports the potential integration of I. galbana-based systems into biotechnological pipelines targeting functional foods, nutraceuticals, and pharmaceutical applications.