Abstract – Light management can optimize algal biomass and biochemical composition, but responses vary based on growth stage and harvesting time. A 2^2 factorial design along with 3 center point runs was used to investigate the effects of light intensity (50, 100, and 150 umol photon m-2 s-1) and exposure time (10.5, 16, and 21.5 h) on lipid, protein, carbohydrate, and pigments content, density, and productivity of Spirulina platensis. By analyzing trends in cellular content, the time each key metabolite reached its maximum was chosen as its best harvesting time. Low factor levels during the mid-exponential phase resulted in the highest protein content, while high levels at the very early exponential phase showed the most carbohydrates. Low light intensity favored the accumulation of lipids, chlorophyll, and carotenoids at the end of exponential phase. The highest phycobiliproteins were obtained at intermediate factor levels during the late exponential phase. Harvesting at high levels of factors at the end of exponential phase led to the highest component density. The maximum productivities were observed at high factor levels. These findings emphasize the importance of carefully selecting the harvesting time in different light conditions to achieve the desired biochemical content, density, and productivity in Spirulina applications.

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