Enhanced carotenoid production in Chlorococcum humicola via two-stage cultivation in synthetic wastewater under white light stress conditions

Abstract

Carotenoids are high-value pigments widely used in nutraceutical and pharmaceutical applications due to their antioxidant properties. This study investigates the effect of white light intensity on carotenoid biosynthesis in Chlorococcum humicola cultivated in synthetic domestic wastewater using a two-stage process in a 10-L airlift photobioreactor. The first stage (green phase) supported optimal biomass growth at 3,500 Lux, followed by a stress-induced red phase under nitrogen depletion with elevated light intensities ranging from 3,500 to 60,000 Lux. Biomass, chlorophyll, fatty acids, and carotenoids were analyzed, and β-carotene was identified using HPLC. At 20,000–40,000 Lux, cells preferentially accumulated fatty acids up to 26.69 ±0.14 percent of dry weight, indicating a metabolic shift toward energy storage. Exposure to 60,000 Lux significantly enhanced carotenoid production, reaching 1.69 ± 0.03 mg L−1, with β-carotene accounting for 17.16 ± 0.04 percent of total carotenoids. Statistical analysis confirmed significant differences among treatments (p < 0.05). The stable chlorophyll-to-biomass ratio suggests metabolic reallocation rather than pigment degradation. These findings demonstrate the photoadaptive capacity of C. humicola and highlight white light as an eco-friendly strategy for enhancing carotenoid production in scalable systems.