Influence of light absorption rate by Nannochloropsis oculata on triglyceride production during nitrogen starvation

• Radiation properties of N. oculata were measured during sudden nitrogen starvation.
• Light absorption rate by N. oculata decreases during sudden nitrogen starvation.
• Triglyceride TG-FA productivity correlates with light absorption rate by cells.
• A critical light absorption rate should be exceeded for large TG-FA accumulation.
• Conclusions were valid for both sudden and progressive nitrogen starvation.

This study aims to understand the role of light transfer in triglyceride fatty-acid (TG-FA) cell content and productivity from microalgae during nitrogen starvation. Large amounts of TG-FA can be produced via nitrogen starvation of microalgae in photobioreactors exposed to intense light. First, spectral absorption and scattering cross-sections of N. oculata were measured at different times during nitrogen starvation. They were used to relate the mean volumetric rate of energy absorption (MVREA) per unit mass of microalgae to the TG-FA productivity and cell content. TG-FA productivity correlated with the MVREA and reached a maximum for MVREA of 13 μmolhνμmolhν/g s. This indicated that TG-FA synthesis was limited by the photon absorption rate in the PBR. A minimum MVREA of 13 μmolhνμmolhν/g s was also necessary at the onset of nitrogen starvation to trigger large accumulation of TG-FA in cells. These results will be instrumental in defining protocols for TG-FA production in scaled-up photobioreactors.

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