Process Intensification for Green Extraction of C-Phycocyanin Protein From Limnospira platensis (Spirulina) Microalgae Through Natural Deep Eutectic Solvents and Membrane Contactor

Abstract

This research explores the potential of Natural Deep Eutectic Solvents (NADESs) as sus-tainable and efficient alternatives for extracting C- phycocyanin (C-PC); a valuable blue pig-ment-protein, from the microalga Limnospira platensis (commonly known as Spirulina). Thirty-three terpene- based NADESs were synthesised and tested in aqueous two-phase systems (ATPS) under batch extraction conditions. Among them, the combinations of acetic acid:thy-mol (DES 1) and decanoic acid:thymol (DES 2), and levulinic acid:thymol (DES 3) showed the highest extraction performances, achieving 79.87%, 78.21%, and 73.60% extraction efficiency, respectively, with partition coefficients ranging from 2.5 to 3.9. These results suggest favoura-ble interactions driven by solvent polarity and hydrogen bonding. Following the batch trials, the three most promising solvents DES 1, DES 2, and DES 3 were further evaluated in a continuous extraction setup using membrane-based contactors. Two configurations were used: a flat-sheet polyethersulfone (PES) membrane module and a hollow fiber membrane

contactor, both tailored for high molecular weight species. Although continuous operation led to slightly reduced efficiencies i.e. 59.80% (DES 1), 51.32% (DES 2), and 53.23% (DES 3), this was expected given the limitations of mass transfer experienced in membrane processes which is not modified specifically to cater C-PC extraction. Moreover, the hollow fiber module delivered superior and more stable performance, owing to its higher interfacial contact area. Interfacial tension measurements revealed significant reductions (up to 73%) when C-PC solutions contacted DES 2 and DES 3, indicating strong interfacial affinity. Importantly, FTIR spectroscopy confirmed that the protein’s secondary structure remained intact after ex-traction, reinforcing the biocompatibility of these solvents.