Breaking the silica barrier: optimising carotenoid extraction from diatoms

Diatoms are a rich source of bioactive carotenoids, but their rigid silica frustules limit solvent penetration, reducing extraction efficiency and concealing the true carotenoid content. This study aimed to optimise the removal of silica from Chaetoceros calcitrans, Nannofrustulum shiloi, and Cylindrotheca fusiformis to enhance carotenoid extraction the efficiency. A combination of physical treatments (Ultraturrax, ultrasonication, bead milling) and chemical treatments (acid, alkaline, surfactants, and chelating agents) was tested to disrupt the silica structure while preserving carotenoids. Additionally, enzymatic extraction was explored as a complementary technique. The effectiveness of each treatment was assessed through scanning electron microscopy (SEM) to evaluate silica disruption, Fourier-transform infrared spectroscopy (FTIR) to analyze chemical modifications in the silica structure, spectrophotometry for total carotenoid quantification, and high-performance liquid chromatography with diode-array detection (HPLC- DAD) for carotenoid profiling. Results demonstrated that disrupting the silica frustule significantly increased carotenoid extraction yields, confirming that the rigid cell wall conceals a substantial fraction of these bioactives. FTIR analysis further revealed structural changes in the silica matrix, including the reduction of silica-related peaks and the appearance of new bands associated with altered chemical bonds, providing insights into the effectiveness of different treatments. However, some chemical treatments were too aggressive, reducing carotenoid yields by more than 50%, highlighting the importance of selecting optimal conditions for silica removal without compromising carotenoid stability. These findings provide an optimised strategy for enhancing the bioavailability of diatom-derived carotenoids, with potential applications in functional foods, nutraceuticals, and natural colourants. By unlocking the full potential of these diatoms, this study contributed to the development of sustainable and bioactive-rich extracts with diverse applications in biotechnology and natural product industries.