Comprehensive Growth Analysis to Detect Optimal Time Point for Carotenoid Production: A Comparative Study in Spirulina subsalsa and Chlorella pyrenoidosa

Abstract This study investigated the growth dynamics of Spirulina subsalsa and Chlorella pyrenoidosa under standardized phototrophic cultivation conditions to determine the optimal harvest time for maximum carotenoid yield. Both species were maintained at temperature (28℃-35℃), relative humidity (52%-55%), light intensity (2.5-3.5 klx) and a photoperiod of (10:14 h) light/dark cycle. Growth dynamics were assessed by monitoring cell density, biomass productivity, protein content, chlorophyll and carotenoid content over a defined cultivation period. S. subsalsa showed rapid growth, reaching peak cell density with in a shorter duration of 12 days, compared to C. pyrenoidosa which showed longer duration of 27 days. The biomass productivity was higher (186.36 ± 0.029 mg/L/day) in Spirulina compared to Chlorella (12.98 ± 0.546 mg/L/day). S. subsalsa showed higher protein content on day 6 (33.634 ± 0.97 mg/g fresh weight (FW)), higher chlorophyll on day 8 (1.25 ± 0.034 mg/g FW) and higher carotenoid on day 12 (0.379 ± 0.003 mg/g FW) compared to C. pyrenoidosa with maximum protein (3.374 ± 0.039 mg/g FW), maximum chlorophyll (0.252 ± 0.002 mg/g FW) and maximum carotenoid (0.054 ± 0.001 mg/g FW) on day 27. The protein, chlorophyll, and carotenoid levels showed decrease in both the algae at the end of the experiment. Harvesting S.subsalsa on day 12 and C. pyrenoidosa on day 27 will result in increased carotenoid yield and enhance the efficiency of carotenoid extraction. The study provides a base for sustainable large-scale cultivation of two microalgal species with targeted harvesting of natural carotenoids to meet industrial demand.