Identification of an industrial microalgal strain for starch production in biorefinery context: The effect of nitrogen and carbon concentration on starch accumulation

The recent trends in microalgal cultures are focused on the biorefinery of the biomass components. Some of them are not completely valorised, for example starch. Since there is a wide market for starch products in food and non-food industries, the exploitation of microalgal starch fractions could improve the economic sustainability of microalgae production. In this perspective, the optimization of nitrogen and carbon source uptake for starch accumulation is a critical point for reducing the nitrogen requirement footprint and to increase CO2 capture. In this study, four robust microalgal strains, already known as starch-accumulating strain, were investigated: Chlorella sorokiniana, Scenedesmus vacuolatus, Dunaliella tertiolecta, and Tetraselmis chuii. C. sorokiniana was selected as the best starch producer in the biorefinery context, and the role nitrogen and CO2 concentration had on the starch production was investigated. For light irradiance of 300 μmol m−2 s−1 the optimal nitrogen concentration for growth and starch accumulation resulted 32 mg L−1. The CO2 concentration clearly does not influence the starch accumulation, but concentrations distant from 2% negatively influence microalgal growth, affecting the final starch productivity. The biomass composition during the batch growth of C. sorokiniana was also analysed in order to explicitly characterise the dynamic of starch accumulation during the different growth phases. Protein content decreased during N-depletion, carbohydrates were mainly produced during the early N-depletion, followed by the accumulation of lipids in the late depletion.