Abstract
Red macroalgae represent an underexplored yet promising resource due to their rich composition in proteins, pigments, and bioactive compounds with potential uses in nutraceutical, pharmaceutical, and agricultural industries. However, despite their abundance in coastal regions many species remain neglected and the development of efficient extraction and valorisation methods is still limited. This work assesses the optimization of protein and phycoerythrin extraction from three abundant red macroalgae species, Grateloupia lanceola , Asparagopsis taxiformis , and Nemalion elminthoides collected in Madeira island. Its major objective was to study a new biorefinery concept. The response surface methodology (RSM) results indicate that G. lanceola , harvested from offshore fish farms, exhibits the highest concentrations of both protein (2967 mg L −1 ) and phycoerythrin (212 mg L −1 ) when subjected to specific extraction parameters such as higher biomass weight (400 g) and increased number of cycles (18) using the Solid–Liquid Extraction system. In contrast, A. taxiformis and N. elminthoides demonstrated varied extraction patterns, with A. taxiformis producing substantial protein concentrations (328 mg L −1 ) but lower phycoerythrin yields (11 mg L −1 ). Sequential biorefinery methods were also employed to obtain bioactive compounds, and polysaccharides extracts. G. lanceola yields the highest concentration of soluble proteins (6.25 ± 0.59 g (100 g) −1 dw) and polysaccharides (11.13 ± 4.85 g (100 g) −1 dw), while N. elminthoides showed superior bioactive extract concentration (11.81 ± 0.31 g (100 g) −1 dw). The phenolic content in bioactive extracts has also been assessed using the Folin Ciocalteu method, finding a significant variation in total phenolic content among the species (1.38 ± 0.22 and 5.16 ± 0.06 mg GAE g −1 dw). The chromatographic analysis, formed by a Waters HPLC system and a photodiode array detector (Waters 2996) allowed to detect phenolic compounds within the bioactive extract, which include protocatechuic acid, hydroxybenzoic acid, epicatechin, p-coumaric acid and ferulic acid. Furthermore, the agronomic potential of the biorefinery residues was explored, revealing high nitrogen and phosphorus contents in liquid and solid residues, suggesting their potential to be used as biofertilizers. These findings contribute to the development of sustainable extraction processes for bioactive compounds from red macroalgae, enhancing the efficiency of biorefinery strategies and promoting the marine biomass valorization.