Comparison of extraction methods to obtain high-purity protein concentrate from green microalgae Nannochloropsis oceanica

Nannochloropsis oceanica is a promising and sustainable source of high-value protein. This study compared various extraction methods to implement an optimal protocol for obtaining high-purity protein concentrate. These methods included non-defatting protocols using ultrasound and high-pressure homogenization, as well as solvent-based defatting with chloroform, ethanol, isopropanol, and acetone. The most effective protocol involved acetone defatting, followed by alkaline extraction at pH 12.0 and acid precipitation at pH 2.0, obtaining 86% protein content by dry weight. This protocol outperformed non-defatting methods, which achieved only 42% protein content by dry weight. The higher effectiveness of the acetone-defatting process was attributed to its capacity to break down cell walls and remove lipids and pigments, including chlorophyll a. These findings establish that acetone defatting is an effective method for obtaining high-purity protein concentrate from N. oceanica and could support further research and applications in protein extraction from this and other microalgal species.