Fatty acid yield and composition in the diatom Craspedostauros sp. Effects of pre-treatment, preservation, and storage

Abstract

Diatoms are unicellular microalgae that produce silicified cell walls, called frustules, a sustainable alternative to high-purity industrial silica, conventionally synthesized from mined quartz sand, the second most used non-renewable resource and primary source of industrial silica. Diatoms also accumulate substantial lipid fractions including polyunsaturated fatty acids (PUFAs) with nutraceutical value and triacylglycerols suitable for biodiesel. Co-producing both would improve resource efficiency and strengthen the economics of microalgal biorefining, yet the practical feasibility in industrial conditions remains largely unexplored. This study characterizes the fatty acid (FA) profile of Craspedostauros sp., a previously uncharacterized production strain, while evaluating the influence of pre-treatment method (untreated control, dilute acid at 1 % H2SO4, and probe ultrasonication), preservation strategy (freeze-drying and refrigerated wet storage), and storage duration (up to 4 months) on FA yield and composition. FAs were extracted using a modified Folch-based solvent method and evaluated against the traditional Folch method by gas chromatography-mass spectrometry (GC-MS). The two extraction methods were found to return similar average yields but with performance dependent on pre-treatment. Frustule integrity was assessed by scanning electron microscopy (SEM), showing no visible frustule breakage following dilute acid treatment in either fresh or freeze dried biomass. Total extractable FA content ranged from 0.70 to 8.72 % dry weight (6.95 to 87.16 µg mg⁻¹ dry weight) across treatments, with a profile notably rich in the PUFAs EPA and ARA. The highest yield was recovered from freeze-dried biomass after 4 months of room temperature storage following dilute-acid pre-treatment, indicating that FA content depleted over 3 months (90.6 % loss relative to immediate extraction in untreated biomass) can be substantially recovered. These findings provide the first baseline FA characterization for Craspedostauros sp. and identify practical pre-treatment and storage combinations relevant to frustule and lipid co production at industrial scale.