## 4 Preparation of Single-Cell Protein (SCP) for Use in Food
### Cell Disruption
The electric field generated by the voltage induces an increase in the cytoplasmatic membrane permeability (electro-poration), facilitating the intracellular compounds release, whereas HVED produces an arc discharge through an intense electrical field from a needle electrode to one ground. Cell damage is caused by pressure shock waves, bubble cavitation, and high liquid turbulence [86, 87]. [PERSON] et al. [87] demonstrated that PEF is an effective procedure for extracting proteins from _Haematococcus pluvialis_ and _C. vulgaris_, [PERSON] et al. [88] applied PEF to release monoproteins to the extracellular medium, and [PERSON] et al. [89] extracted soluble proteins from _S. cerevisiae_. Furthermore, in various studies, HVED was indicated to be a more favorable technique than PEF due to its higher efficiency [90, 91, 92, 93]. It may be explained by the fact that the PEF treatment affects the rupture of cell membranes, but HVED can cause more extensive damage by acting on both cell walls and membranes [89]. In chemical methods, different reagents (alkali or acid, organic solvents, deep eutectic solvents, detergents, and ionic liquids) can be utilized for the permeabilization or lysis of cells. These methods are based on the relative selectivity of chemicals with the specific components of the membrane, enabling proteins to pass through the cell wall. The type of chemical is determined by the target compound and its location in the microbial cell [82]. One of the most used chemical procedures to extract _S. cerevisiae_ protein is alkaline precipitation. [PERSON] et al. [94] stated that pretreatment with lithium acetate (LiAc), described as a cell wall permeabilization enhancer, can improve the protein yields. It was also examined that the use of ionic liquids to destroy cell walls did not alter the properties of the extracted protein [95]. Furthermore, the combination of ultrasonication and alkali treatment revealed the higher cell disruption efficiency, and the total extracted proteins from microalgae (_Chlorella sorokoniana_ and _Chlorella vulgaris_) in comparison to the use of each method separately [96]. However, in spite ease of scaling up and low energy inputs requirements, chemical treatments may cause the degradation of some intracellular compounds and introducing contamination to the system, resulting in more downstream operations. Additionally, some chemical substances are characterized by low selectivity, high cost, and toxicity, which makes them difficult to use [82]. Another promising mild disruption method is enzymatic degradation, which involves attacking the mannoprotein complex and glucan backbone of the cell wall by autolysis or lytic enzymes without destroying the cell integrity [97]. Enzymes provide a very gentle and specific means of disrupting cells thanks to their intrinsic catalytic activity and substrate specificity. Enzymatic methods enable one to prevent serious damage being inflicted upon the intracellular compounds, the use of toxic chemicals, or aggressive physical conditions such as high shear stress. In addition, they are effective, highly biologically selective, and operate at low temperatures with low energy demand. Enzymes are also easily controlled biological materials and commercially available, making the scale-up of this method relatively easy [86]. Moreover, the enzymatic degradation can be combined with other mechanical or non-mechanical methods. For example, [PERSON] et al. [98] developed a combination of enzymatic and bead-milling techniques for the extraction of proteins, lipids, and carbohydrates from microalgae C. _vulgaris_ with the use of lipase, cellulase, protease, and phospholipase. In the study, 88% of lipids, 74% of carbohydrates, and 68% of proteins were recovered without loss of any products, reducing the residence time and avoiding corrosive solutions.