Extraction, purification, and bioactivity evaluation of phycobiliproteins and sulphated galactans from Bostrychia scorpioides (Hudson) Mont.

Marine macroalgae represent a promising and sustainable source of high-value biomolecules with applications in the pharmaceutical, cosmetic, nutraceutical, and biotechnology industries. However, in order to maximise biomass utilisation and reduce the non-valorised residues, it is necessary to promote new integrated biorefinery methods capable of extracting more efficiently and more bioactive compounds with the same biomass. In this study, we aimed to develop and optimise a sequential extraction technique for the co-extraction and valorisation of two functionally distinct classes of biomolecules from the red alga Bostrychia scorpioides : phycobiliproteins (PBPs), which are commonly utilised as natural pigments and bioactive substances, and sulphated galactans (SGs), which are known for their pharmaceutical and biomaterial properties. A combination extraction strategy incorporating maceration, sonication, and freeze-thaw cycles was used to improve cell wall disintegration, as confirmed by scanning electron microscopy. Total antioxidant activity testing revealed that the combined extraction strategy had the highest radical-scavenging efficiency (EC₅₀ = 0.345 ± 0.002 mg mL⁻¹), exceeding both separate extraction procedures and the Trolox reference standard. The sequential procedure allowed for the selective recovery of PBPs from the supernatant, while SGs were collected from the leftover biomass, resulting in best resource utilisation. PBPs were then semi-purified using dialysis, followed by DEAE-Sepharose ion-exchange chromatography and Amicon ultrafiltration (10–100 kDa). UV-Vis spectrophotometry, ATR-FTIR spectroscopy, SDS-PAGE, and native PAGE analysis were used to characterise the purified fractions. Electrophoretic profiles showed a distinct protein band about 10.5 kDa, with purification factors exceeding 3.5-fold. Stability experiments indicated that PBP functional characteristics may be preserved for up to eight months in storage. Furthermore, cytotoxicity testing with peripheral blood mononuclear cells validated the biocompatibility of the separated fractions. Overall, this integrated biorefinery strategy proven the efficient co-recovery of stable, bioactive PBPs and SGs from B. scorpioides , highlighting the species as a valuable marine feedstock for the long-term production of multifunctional compounds with significant pharmaceutical, cosmetic, and biotechnological applications.