Multi-Stress Induction of Astaxanthin Accumulation in Haematococcus lacustris: A Taguchi-Designed Experimental Study

Multi-stress induction represents a promising strategy for enhancing astaxanthin accumulation in Haematococcus lacustris; however, productivity optimization requires balancing cellular enrichment with biomass formation. This study investigates the main effects of three critical process variables, namely temperature, CO2 supplementation, and salinity, on the induction of astaxanthin in autotrophic cultivation. A Taguchi L9 orthogonal-array design elucidated how the combined variation in the above factors, across three levels each, affected biomass formation, astaxanthin biosynthesis and biochemical composition under nitrogen and phosphorus deprivation and continuous illumination. Duplicate cultures were incubated for 12 days in 500 mL bottles sparged daily with CO2–air mixtures until target outlet concentrations were reached and sealed afterwards. The response-specific main-effect analysis indicated that CO2 governed biomass and volumetric astaxanthin production, whereas salinity dominated in astaxanthin and lipid content regulation. Maximum values attained for the set engineering objectives included 4.23 wt.% for astaxanthin content and 2.49 g/L for biomass concentration. Model R2 ranged from 87.97% to 97.57%, while predicted R2 exceeded 80% for all responses except protein content. An independent validation experiment at the model-predicted optimum (28 °C, 9% CO2, and 6 g/L NaCl) yielded 101.0 mg/L astaxanthin, supporting the model’s utility within the investigated factor levels.