The development of each technology was and is driven by the process required to meet consumer needs and deliver certain product characteristics such as texture, nutrition, and quality. Extrusion cooking of protein-based foodstuffs permits a wide range of protein sources to be continuously cooked by a combination of mechanical and thermal energy. The macromolecules in the proteinaceous ingredients lose their native, organized structure and form a continuous, viscoelastic mass. As functional proteins pass through the extruder barrel and die, they can align in the direction of flow. This realignment exposes bonding sites which lead to cross-linking and a reformed, expandable structure which can have fibrous striations and be meat-like in nature if it is not hindered by fat, starch, and fiber components in sufficient quantities.
In addition to texturing and restructuring plant and animal proteins, the extrusion cooking process also performs several other important functions including:
• Denaturing protein – Proteins are effectively denatured during the moist, thermal process of extrusion. Denaturation of protein reduce water solubility and improves digestibility while destroying the biological activity of enzymes.
• Deactivate residual heat labile growth inhibitors – Growth inhibitors are inherent in some vegetable proteins and can exert harmful physiological effects on humans or animals as revealed by growth or metabolism studies. By deactivating these growth inhibitors, the harmful physiological effects can be dramatically reduced or eliminated altogether.
• Control raw or bitter flavors – Many of these undesirable flavors are volatile in nature and are eliminated through the extrusion and decompression of the protein at the extruder die. The use of preconditioning and atmospheric venting devices in the design of the extrusion system also assists in volatilization and removal of off flavors.
• Provide a homogeneous, irreversible, bonded dispersion of all micro-ingredients throughout a protein matrix – This not only ensures uniformity of all minor ingredients throughout the product, but also provides a means whereby micro-ingredient can be intimately associated with potential reaction sites promoting cross-linking or other desirable chemical and physical modifications.
• Shape and size the final extruded product – Makes protein-based foodstuffs convenient and in transportable portions for packaging in the retail or institutional marketplace.
Early in the market cycle, the most popular raw material for production of textured plant-based protein was solvent extracted defatted soy flour with approximately 50 percent protein. For over 30 years, soy flour was considered the preferred ingredient for extrusion because of availability, price, and nutritional density and these textured soy proteins were largely manufactured on single screw extrusion systems.