Valorization of sugar industry byproducts for cost-effective Chlorella vulgaris MU-22 production: assessment of bioactive extracts and biofertilizer potential on bell pepper (Capsicum annuum)

Abstract Microalgae have garnered increasing attention due to their diverse applications in biotechnology, agriculture, and environmental sustainability. However, the high cost of microalgal cultivation remains a significant barrier to large-scale utilization. This study aimed to reduce the production cost of freshwater-isolated Chlorella vulgaris MU-22 by supplementing Bold Basal Medium (BBM) with hydrolyzed molasses, a low-cost byproduct of sugarcane and sugar beet processing. The effects of molasses supplementation on the growth performance and biochemical composition of C. vulgaris MU-22 were evaluated under mixotrophic conditions. Molasses supplementation significantly improved C. vulgaris MU-22 growth, increasing maximum cell density from 274 × 10⁴ cells mL⁻¹ (control) to 929 × 10⁴ cells mL⁻¹ at 1.0 g glucose L⁻¹ and raising optical density to 2.459 at 2.0 g glucose L⁻¹. Photosynthetic efficiency remained high under all treatments (Fv/Fm = 0.770–0.785), indicating enhanced biomass production without detrimental effects on photosynthetic performance. The biochemical profile of C. vulgaris MU-22 showed enriched levels of proteins, lipids, carbohydrates, chlorophylls, carotenoids, total flavonoids, and phenolic compounds. Furthermore, the bioactive extracts of the cultivated microalga were assessed for their antibacterial, antioxidant, insecticidal, antigenotoxic, cytotoxic, and biofertilizer properties, particularly in relation to the growth and health of Capsicum annuum L . The findings highlight the potential of molasses as a sustainable carbon source for cost-effective microalgal cultivation and support the multifunctional application of C. vulgaris biomass in agriculture and biocontrol.