2.1 Reverse micelle extraction
As a promising extraction technology for protein extraction from soy, reverse micelle is a nanometer-sized aggregate that is formed by a surfactant, an organic solvent, and a small amount of aqueous solution (Bu, 2014). It takes various shapes such as spherical, oval, and rod. Surfactants dissolve in non-polar organic solvents and form reverse micelle when their concentration exceeds the critical micelle concentration. There are many different surfactants used to prepare micelles, including anionic (such as AOT and SDS), cationic (such as CTAB), zwitterionic, non-ionic (such as Spans and Tweens), and mixed surfactants (Lépori, 2016). Bis (2-Ethylhexyl) sodium sulfosuccinate (AOT), an anionic surfactant, has received a lot of attention because AOT-based reverse micelle does not require co-surfactants and can encapsulate large amounts of water in their aqueous core (Fuglestad, 2016). As shown in Fig. 1 , in the reverse micelle, the non-polar groups of the surfactant are in contact with the organic solvent on the outside, while the polar groups are arranged on the inside, forming an aqueous core. The size, shape, and internal structure of aqueous cores, the number of aggregations, and microviscosity are critical to the solubility of the biomolecules in the micelle core. A considerable number of hydrophilic biomolecules can be dissolved in the aqueous cores of the reverse micelle, such as proteins, amino acids, enzymes, nucleic acids, short peptides, and DNA. These biomolecules are protected from denaturation by organic solvents inside the aqueous cores (Hong SC, 2015).