ABSTRACT
Extrusion cooking is one of the most relevant innovations of the 20th century and has been extensively used for the production of savory snacks. These technologies have gradually gained acceptance because they are a continuous process, energy-efficient, environmentally friendly, and save labor as well as industrial floor space. The main advantage of extrusion technologies is their versatility. Extrusion cooking technologies are widely used for production of many grain-based snacks. There are basically two major categories of extrusion processes: direct extrusion, which yields second-generation expanded puffs, and production of half products or pellets for the manufacturing of third-generation snacks. When the two processes are compared, the requirements of raw materials, formulations, tempering or conditioning, and processing conditions are quite different. Direct extruded puffs are produced with a single or twin extruder and are usually baked or fried after extrusion and then flavored with liquid or powdered seasonings. On the other hand, most pellets or half-products are obtained after two sequential extrusion stages named cooking and forming, where two separate extruders are employed, however, novel units can perform both steps. The resulting pellets are carefully dehydrated and then expanded by frying, high-temperature, or microwave baking. The two main novel extrusion technologies are coextrusion and supercritical CO2 extrusion (SCFX). The first one allows the production of extrudates with two different materials, yielding snacks with inner fillings, whereas the SCFX technology produces expanded extrudates with unique texture at lower operational temperatures, preserving nutritional and functional compounds.
