LRMS and HRMS-based metabolite profiling of Scenedesmus almeriensis produced under variable salinity

This study evaluated the phytochemical profile of Scenedesmus almeriensis , a freshwater microalga that can also be produced using seawater, with particular attention to phenolic compounds and pigments. To the best of the authors knowledge, this is the first study providing a comparative and molecular-level characterisation of the phenolic composition of S. almeriensis under freshwater and seawater production conditions. After optimising the ultrasound-assisted extraction process (using a methanol-water mixture at a ratio of 80:20 v/v for 10 min), a UHPLC-QqQ method was validated for quantifying molecules such as trans-ferulic acid (104 μg kg −1 ), syringic acid (27 μg kg −1 ), catechin (12 μg kg −1 ) and sinapic acid (12 μg kg −1 ). Untargeted analysis using HRMS (Q-Orbitrap), multivariate modelling (PCA, OPLS-DA, VIP >1.5) and univariate analysis led to the tentative identification of 58 compounds, of which seven were confirmed as metabolites using reference standards. This approach goes beyond conventional colorimetric methods commonly applied in previous studies on Scenedesmus , allowing a detailed molecular profiling of phenolic constituents. Production using seawater promoted the selective accumulation of antioxidant compounds and pigments without significantly affecting biomass productivity or photosynthetic efficiency, highlighting seawater acclimatisation as a viable strategy to modulate the phytochemical composition of freshwater microalgae for biotechnological applications.