LC-QTOF-MS/MS for tentative identification of antioxidant peptides in defatted Spirulina platensis cakes obtained by supercritical CO2 extraction

This work tackles a supercritical fluid extraction (SFE) of microalga spirulina (Arthrospira platensis) to recover potential products from a nutritional and bioactive point of view. The execution of a response-surface model (RSO) through Box-Behnken design yielded 86% defatting, which significantly contrasts traditional Soxhlet extraction (9%). Contrarily to most of the reported works in the literature that focused on the analysis of the recovered oil, this study points out the added value of the remaining cakes after processing (spirulina residues). Namely, protein content determined by the DUMAS method concluded that a noted increase in the SFE cake was produced with respect to the raw material (from 69.2 to 74.4 g/100 g). In this regard, a tentative identification of antioxidant peptides through LC-QTOF-MS/MS was carried out. More deeply, 14 peptide sequences containing specific amino acids with potential antioxidant capacity were found in the SFE remaining cakes, of which the peptide sequences "SIVNADAEARYLSPGELDRIK" and "RYLSPGELDRIKSFVT" were only detected in these cakes and not in the Soxhlet solids. In addition, 4 short amino acid groups associated with potential antioxidant capacity were also identified in both cases ("EL", "RY", "RYL", and "YL"). ICP-MS served to determine the mineral profile in these materials, with most of them remaining in the cakes after SFE and Soxhlet extractions. With respect to oils, they were rich in Mg, P, K, and Fe minerals. The SFE oil extract had a much higher antioxidant capacity, phenolic content, chlorophyll A, and carotenoid content than the Soxhlet extract. Overall, this study presents an advanced extraction technique that efficiently recovers bioactive compounds and nutrients with potential food applications.