Ultrasound-assisted extraction of phycobiliproteins from Spirulina (Arthrospira) platensis using protic ionic liquids as solvent

A new method that combines ultrasonic assisted extraction (UAE) with ionic liquids (ILs) was proposed to extract phycobiliproteins from the microalgae Spirulina (Arthrospira) platensis. Extraction of the pigments was carried out in an ultrasonic bath at 25 °C and at a frequency of 25 kHz. The effects of pH and solvent:biomass ratio were evaluated through a central rotational composite design and response surface methodology were used to determine the best extraction conditions. Solvents used were protic ionic liquids (PILs) 2-hydroxy ethylammonium acetate (2-HEAA), 2-hydroxy ethylammonium formate (2-HEAF), their equimolar mixture (2-HEAA+2-HEAF) (1:1 v/v) and the commercial ionic liquid, 1-butyl-3-methylimidazolium chloride [Bmim][Cl] and sodium phosphate buffer (0.1 M) as a control. Results showed that the PILs were able to extract the phycobiliproteins from microalgae. The pH was the most significant variable. Solvent:biomass ratio was also significant in the extraction process. The highest concentrations of phycobiliproteins were observed using 2-HEAA +2-HEAF as solvent at pH 6.50 and solvent:biomass ratio 7.93 mL·g−1 within 30 min of extraction. Allophycocyanin was the pigment extracted in greater quantity (6.34 mg·g−1), followed by phycocyanin (5.95 mg·g−1) and phycoerythrin (2.62 mg·g−1). Scanning electron microscopy (SEM) revealed that the ultrasound affect the cellular structure of the microalgae.