Ultrasound-assisted processing of Chlorella vulgaris for enhanced protein extraction

The green microalga Chlorella vulgaris is a promising source of proteins of high nutritional value for the food industry. The present study aims to improve the recovery of proteins and umami free amino acids from C. vulgaris by exploring the use of ultrasound following multiple approaches including ultrasound-assisted single solvent extraction, ultrasound-assisted sequential solvent extraction and ultrasound-assisted enzymatic extraction. Ultrasound-assisted single solvent extraction using an alkaline solvent during 10 min provided equivalent protein recoveries to those obtained in control experiments macerating the biomass during 18 and 24 h. Ultrasound-assisted sequential solvent extraction using 0.4 M NaOH followed by 0.4 M HCl achieved a protein recovery of 79.1 ± 5.3%, 1.32-fold higher than the control experiments without ultrasound for 1 h. Ultrasound-assisted enzymatic extraction using lysozyme resulted in protein recoveries ranging from 33 to 42%, and these extracts also contained a high percentage of umami free amino acids. Ultrasound-assisted enzymatic extraction with protease enhanced the recovery of proteins (58–82%), although the extracts had low percentage of umami free amino acids. The scanning electron microscopy imaging revealed that ultrasound-assisted solvent extraction and ultrasound-assisted enzymatic extraction significantly changed the morphology of the cell surface.