Quantitative analysis on photon numbers received per cell for triggering β-carotene accumulation in Dunaliella salina

Accumulation of β-carotene in Dunaliella salina is highly dependent on light exposure intensity and duration, but quantitative analysis on photon numbers received per cell for triggering β-carotene accumulation is not available so far. In this study, experiment results showed that significant β-carotene accumulation occurred after at least 8 h illumination at 400 µmol photons·m^-2·s^-1. To quantify the average number of photons received per cell, correlations of light attenuation with light path, biomass concentration, and β-carotene content were, respectively, established using both Lambert-Beer and Cornet models, and the latter provided better simulation. Using Cornet model, average number of photons received per cell (APRPC) was calculated and proposed as a parameter for β-carotene accumulation, and constant APRPC was maintained by adjusting average irradiance based on cell concentration and carotenoids content changes during the whole induction period. It was found that once APRPC reached 0.7 µmol photons cell^-1, β-carotene accumulation was triggered, and it was saturated at 9.9 µmol photons cell^-1. This study showed that APRPC can be used as an important parameter to precisely simulate and control β-carotene production by D. salina.