Thermoplastic extrusion direct expanded

There are basically two families of snack items obtained with thermoplastic extruders the direct expanded snacks and the third-generation snacks produced from pellets or half-products obtained after the sequential cooking and forming extrusion steps. The direct extruded types are subdivided into baked puffs and fried puffs (Rooney and Sema-Saldivar 2003, Serna- Saldivar et al. 2008). 

Second-generation snacks These are the most important snack category. Second-generation snacks are simple shaped products such as com and tortilla chips, puffed curls, and all directly expanded snacks generally produced via thermoplastic extrusion. 

Thermoplastic extrusion Name of the continuous extrusion process in which raw materials, generally refined milled fractions, are cooked and plasticized due to heat and pressure occurring inside the extruder barrel. The starch is gelatinized, and the exiting extrudate is usually formed into predetermined shapes. This process is widely used to produce direct-expanded-products and pellets or intermediate products used for production of many breakfast cereals and snacks. 

The combination of starch with a water soluble polymer such as PVOH and/or polyalkylene glycols has been widely considered since 1970 [157]. Recently, the system, thermoplastic starch/PVOH has been studied mainly for producing starch-based loose fillers as a substitute for expanded PS [158-164], As an example, Lacourse and Altieri developed a technology based on hydroxy propylated high amylose starch containing small amounts of PVOH for improving foam resiliency and density [158-162]. In this case loose fill was produced directly by a twin-screw extruder. Recently more advanced processes and alloys have been developed which have resulted in foams with lower foam densities (8-6 kg/m ) and better performance [165-167]. Other applications of modified starch/PVOH can be in the sector of sheet extrusion/thermoforming. 

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