초록
<P><B>Abstract</B></P> <P>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 CO<SUB>2</SUB> capture. In this study, four robust microalgal strains, already known as starch-accumulating strain, were investigated: <I>Chlorella sorokiniana</I>, <I>Scenedesmus vacuolatus</I>, <I>Dunaliella tertiolecta</I>, and <I>Tetraselmis chuii. C. sorokiniana</I> was selected as the best starch producer in the biorefinery context, and the role nitrogen and CO<SUB>2</SUB> concentration had on the starch production was investigated. For light irradiance of 300μmolm<SUP>−2</SUP> s<SUP>−1</SUP> the optimal nitrogen concentration for growth and starch accumulation resulted 32mgL<SUP>−1</SUP>. The CO<SUB>2</SUB> 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 <I>C. sorokiniana</I> 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.</P> <P><B>Highlights</B></P> <P> <UL> <LI> <I>C. sorokiniana</I> was selected as robust strain for starch production in biorefinery context. </LI> <LI> At 300μmolm<SUP>−2</SUP> s<SUP>−1</SUP>, the optimal N and CO<SUB>2</SUB> concentration for starch production were 32mgL<SUP>−1</SUP> and 2%. </LI> <LI> The highest starch content of 38%DW was reached after the first day of N-depletion (early N-depletion). </LI> <LI> The optimal harvesting time for starch recovery and biorefinery applications was the early N-depletion. </LI> </UL> </P>