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Graphical abstract:

Flavonoids are the secondary metabolites synthesized by microalgae and have diverse applications in various fields. The present study compares among two microalgal strains, Chlorella vulgaris(CV) and Chlorella pyrenoidosa(CP), for the production of flavonoids and lipids, which were cultivated in mixotrophic as well as autotrophic modes. This study also focuses on the role of l-phenylalanine as a supplement to enhance flavonoids. The current work establishes the relation between nitrates, external carbon, and l-phenylalanine for enhanced production of flavonoids and lipids. The extracted flavonoids were found to be maximum in CP-autotrophic mode followed by CV-mixotrophic mode with 138 μg/ml and 118 μg/ml, respectively. The common flavonoids observed with both the microalgal strains were quercetin, catechin, and p-coumaric acid. In comparison, the production of the maximum lipid of 23.7% was reported with mixotrophic operation in CV, followed by CP (19.4%). The scavenging activity of the extracted flavonoids was determined using a hydrogen peroxide assay and was found to be in the range of 63–73% at all experimental conditions. CP was found to produce more flavonoids in autotrophic mode, whereas mixotrophic mode showed maximum production of lipids and flavonoids in the CV. The simultaneous production of high value-added products, viz., flavonoids and lipids, not only paves a pathway for the biorefinery approach but also elevates the commercial potential during scale-up.