Process design for augmentation and spectrofluorometric quantification of neutral lipid by judicious doping of pathway intermediate in the culture of marine Chlorella variabilis for biodiesel application

•Lipid enhancement without starving cell in Chlorella variabilis was demonstrated.•Citric acid can be replaced by orange peel extract as low cost substitution.•Orange peel extract supplemented medium showed better growth than the citric acid.•Supplemented media yielded desired fatty acid composition for biodiesel production.•Both supplemented media showed non deleterious effect on cell growth.

Over the past few years microalgae have emerged as the most promising feedstock for biodiesel production. However, enhancing lipid content remains a major scientific challenge. Many studies irrationally rely upon nitrogen starvation for improving lipid content at the cost of biomass. In this study, strategic enhancement of neutral lipid without compromising with biomass production was achieved in marine Chlorella variabilis by supplementing the culture with triacylglycerol pathway intermediate, citric acid (1 g L−1 pure and 0.5 g L−1 orange peel extract as a low cost substitute). The microalga accumulated 17% and 34% (on dry cell weight basis) more neutral lipid, when cultivated in with citric acid and orange peel extract as supplements respectively, without any adverse effect on growth. The medium supplemented with orange peel extract stimulated better growth than that supplemented with citric acid. Gas chromatography studies validated that both the supplemented media yielded desired fatty acid composition for biodiesel production.