3.5. The mechanism of aqueous enzymatic extraction of protein and oil bodies
The mechanism of the protein and oil body extraction through the enzymatic hydrolysis of the peanut cell wall is presented schematically in Fig. 8. Proteins and oils are present in peanut cotyledon cells in the form of protein bodies and oil bodies. The cell wall, which is composed of cellulose, hemicellulose, and pectin, maintains the cell structure and inhibits the release of proteins and oils. In the aqueous enzymatic extraction process, mechanical crushing is an important step that destroys the peanut cell wall and promotes the release of proteins and oil bodies. We used the conventional dry crushing in this study to break the chain structure of the cell wall and decrease the peanut particle size. However, dry crushing destroyed only a part of peanut cells, and therefore not all protein and oil bodies were released. In contrast, Viscozyme® L degraded sufficiently the structure of the cell wall by acting on the C-O stretching, C-C stretching, and CH2 symmetrical bending of cellulose, the C-O stretching and O-C-O asymmetrical bending of hemicellulose, and the C-O stretching and C-C stretching of pectin, and thus facilitated the release of oil bodies and proteins from peanut cells. After centrifugation of the extract, which contained proteins, oil bodies, and the enzymatic hydrolysate of cell wall polysaccharides, oil bodies exist in the upper layer of the aqueous phase, while proteins and enzymatic hydrolysate are in the aqueous phase.