Influence of pre-soaking conditions on ultrasonic extraction of Spirulina platensis proteins and its recovery using aqueous biphasic system

Ultrasonic aqueous extraction of proteins from dry Spirulina platensis at acidic (ACSU), alkali (ALSU), and neutral (NSU) conditions and its recovery using aqueous biphasic system (ABS) was studied. S. platensis was soaked in the solvent for 12 h prior to extraction. Neutral condition showed a higher protein release of 18.6 mg/ml at optimum conditions (solid–liquid ratio 1:20, 80% ultrasound amplitude, 100% ultrasound duty cycle, and 4ºC). The Box–Behnken design (BBD) suggested optimum conditions for ABS (PEG 6000, pH 8, and 5% NaCl) and gave 84.1% recovery. Although microscopic observations indicated structural changes, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Fourier-transform infrared spectroscopy (FTIR) analyses confirmed that the proteins are intact.