Biorefinery Potential of Microalga Haematococcus pluvialis to Produce Astaxanthin and Biodiesel Under Nitrogen Deprivation

Biorefining of Haematococcus pluvialis can be employed through the integration of different bio-product production from the same feedstock. In this regard, the present study evaluated the potential of utilizing microalga H. pluvialis to produce biodiesel without being constricted to astaxanthin under nitrogen deprivation. Hence, the impact of nitrogen limitation was investigated on the growth parameters, photosynthetic pigments, astaxanthin, and biochemical composition as well as the fatty acid (FA) profile of H. pluvialis. Finally, the physical/chemical features of biodiesel produced from H. pluvialis were assessed. Nitrogen deprivation (0 mg /L) decreased the cell number (/mL), biomass (g/ L), cell size, growth rate (mu), and biomass productivity (g/ L/ d) of H. pluvialis during 40 days of the experiment. Additionally, a remarkable reduction was found in chlorophyll content (pg/cell) under nitrogen deprivation over the culture period, whilst astaxanthin (mu g/cell) was found to be four times higher on the 40th day. Following treatment for 40 days, the carbohydrate and protein contents of the control culture (nitrogen-rich culture) were highest, while the lipid content of H. pluvialis did not change significantly under nitrogen stress. Besides, saturated fatty acids (SFAs) accounted for 75% of the total FAs under nitrogen starvation. Hence, the high SFAs level and the lowest level of C18 FAs determined the suitability of H. pluvialis grown in nitrogen-free culture for the production of biodiesel. Accordingly, cellular stresses, such as nitrogen limitation, increase the production of astaxanthin in H. pluvialis simultaneously by changes in the quality and quantity of biochemical composition, such as FAs.