# Plant-Based Fish Analogs--A Review
## 4 Technologies Used for Plant-Based Fish and Meat Analogs Production
### Other Technologies  
Electrospinning is a technique that allows the production of very thin fibrils with a high aspect ratio. In the spinning process, placing a high voltage over a polymer solution produces fibrils. The protein solution is pushed through the nozzle and electrically accelerated by the electric potential gradient from the ground electrode. Consequently, the fine stream exiting the nozzle, shaped like a Tylor cone, becomes a fine fiber. At the same time, the solvent evaporates and is finally collected on the manifold connected to the electrode. For electrospinning to occur, the spun proteins must be in an unfolded conformation or internally unstructured. Vegetable proteins are usually spherical in their native state, so they should be unfolded (usually using heating) prior to electrospinning, avoiding the formation of insoluble aggregates. In order to obtain structures resembling animal proteins, an acidic solution of spirulina protein [18, 25, 124].  
One of the new technologies that can find industrial application in producing meat and fish analogs is wet spinning [18]. In this process, the protein solution is forced into a coagulation bath containing a solvent that lowers the solubility of the protein or promotes cross-linking and fiber formation. The solvent can cause the protein to precipitate, and with the force of the nozzle, they align the proteins, forming fibers. Binders, e.g., Ca\({}^{2+}\), are added to the solvent to allow the proteins to cross-link. It is also possible to change the acidity of the solution, which favors the formation of inter- and intra-molecular chemical bonds between the protein chains. The products obtained this way are then purified from the solvent [25, 125]. For this technology to be introduced to the food industry, new solvents are constantly being sought that will be safe for both products and the environment [126]. Therefore, the production of wet spinning fibers also uses raw materials such as soy, wheat, oka protein, and zein [125].  
Directional freezing is based on the use of the freezing process to obtain multilayer protein structures. The process involves producing microstructures from two-phase systems (aqueous or organic solutions, suspensions, and slurries). Variable solution concentrations and the directional freezing rate regulate the shape of the protein structures. In this method, soy proteins can be used to prepare protein products [127, 128].  
The shear cell technology is another technique in which a combination of shear and heat is used to form plant-based meat and fish analogs with layered fibrous structures that resemble the mouthrefel and texture of real animal products [36]. The shear device used in this technology is called a shear chamber, where intense shear can be applied. There are two types of shear cells: conical cells based on cone-plate rheometer and cylindrical shape--Couette cells, which can be used on an industrial scale. The shear cell technology is characterized by a lower variation in product quality compared to extrusion. Examples of proteins that can be subjected to this process are dairy proteins (calcium caseinate), soy protein isolate, and vital wheat gluten [85, 129, 130, 131].