The extrusion process can be used to transform wheat or legume protein – e.g. from soy, peas or lupines – into a fibrous structure similar to that of meat. If fat, aromas and/or colorings are added, the texturized vegetable protein generated in this way can be processed after soaking in water in order to make stand-alone meat substitutes or various ingredients or extenders used in the food industry. The aim of the extrusion process is to manufacture a product with a consistent color and texture. After being soaked in water, a subtly laminar or fibrous structure should be visible or tangible. The texture of the product must not be too soft, and should be very similar to “original” meat in a tactile or kinesthetic sense. These requirements are fulfilled if the protein is effectively solubilized, and if the starch is completely and consistently embedded in the protein matrix. The Coperion ZSK food extruder offers the ideal conditions for this.
The process
Vegetable protein is texturized with the aid of the ZSK food extruder by means of a typical hot extrusion cooking process. During this process, a protein-rich powder mixture or a vegetable protein concentrate – which usually has around 70% protein content – is mixed with water in the ZSK food extruder and hydrated. The mass is subsequently pulped, melted and denatured in the process section of the ZSK. The fiber and starch components are finely dispersed and worked in. These help to loosen up the texture of the extrudate. The temperatures in the process section are usually very high in order to achieve a well-texturized structure, yet not so high that they brown the product excessively.
The set-up
Powdery vegetable proteins or premixes – and also additives if these are required – are fed into the feeding barrel of the ZSK process section via Coperion K-Tron gravimetric feeders. The water required for the process is injected into the extruder’s process section via injection nozzles, which are also gravimetrically controlled by Coperion K-Tron loss in weight technology. It is possible to assist the thermomechanical extrusion process by directly injecting steam into the ZSK process section. In this manner, particular textures can be achieved, and the process can be run more economically.
Initially, the water and powder are mixed together to form a paste before the mass is warmed up by means of mechanical energy consumption. During this process, the starches are gelatinized, the proteins are denatured, and the entire mixture is worked to form a consistent product. Additional liquids such as aromas or other components can be added to the process section further downstream and worked into the product mass. At the end of the ZSK food extruder, the hot protein mass is discharged through a shaping nozzle in such a way that oriented, fine fibers develop. The product expands as it escapes from the nozzle, causing it to get its light and foamy, fibrous or laminar structure. Using Coperion’s ZGF centric pelletizer the textured product is shaped and cut to the desired size at the nozzle plate itself.
