Influence of light absorption rate on the astaxanthin production by the microalga Haematococcus pluvialis during nitrogen starvation

Abstract

Large amounts of astaxanthin (about 4% DW) can be produced under nitrogen starvation of Haematococcus pluvialis in photobioreactors (PBRs) exposed to high light to induce a light stress. However, in PBR, the large biomass concentration usually achieved leads to strong light attenuation conditions, which makes complex the analysis of this “light stress”. This study aims then to elucidate the role of light transfer in astaxanthin cell content and productivity from the microalga Haematococcus pluvialis during nitrogen starvation. In order to obtain several light attenuation conditions in the culture volume, H. pluvialis was cultivated in a flat-panel PBR in sudden nitrogen starvation conditions with different initial biomass concentrations (Cx0) of 0.21, 0.52, 1.39 and 2.21 kg m− 3 in batch mode and exposed to an incident photons flux density (PFD) of 250 µmolhν m− 2 s− 1. First, spectral mass absorption cross-sections of H. pluvialis were measured at different times during nitrogen starvation. They were then used to relate the mean rate of photons absorption (MRPA) to the astaxanthin productivity and cell content. A minimum initial MRPA of 7000 µmolhν kgx−1 s− 1 was found necessary at the onset of nitrogen starvation to trigger large accumulation of astaxanthin in H. pluvialis cells, up to 3.21% DW. The results also demonstrated the existence of a relation between the MRPA and the daily astaxanthin productivity of H. pluvialis cultures, introducing then the MRPA as a physical quantity of interest for a rational optimization of the light culture conditions in PBRs.