Extrusion studies starch

While starch copolymers are typically prepared by batch polymerization methods, reactive extrusion of starch has been studied. Mixtures of starch, polystyrene, styrene, sodium hydrogen carbonate, citric acid and water were extruded at temperatures between 100°C and 200°C.118 It was reported that expanded graft copolymers... 

The extrusion of starch with relatively low water contents (15 - 25% w/w) was extensively studied by the food industry [43]. One of the first commercial products of starch that achieved very good results was the expanded starch used for protection and as a shock absorber in packages, as a replacement for expanded polystyrene. These materials were patented by the National Starch Chemical Investment Corporation [44]. 

As in the initial extrusion study, extrudate properties correlated with radical production, or in this case scavenging, in the extrudates. As radical scavenging by cysteine increased, expansion ratio, cell size, and cell wall thickness all decreased (3) (Figure 9) because the crosslinked protein network that provided both structure and extensibility to the dough had been disnq)ted. Microscopy with differential staining of proteins and stoch revealed mesh-like protein structures with starch dispersed within in control extrudates with added cysteine the mesh structure was replaced by thin aligned strands of protein (Schaich, unpublished). 

Besides rheology, there are other aspects to consider in the extrusion of starch which have already been widely studied and are important to emphasize. 

Surfactants have been, reprotedly, used to prevent extensive puffing of extruded cereal products. It was found in these studies that surfactants could effectively inhibit gelatinization of cereal starch. However, effect of surfactants on protein texturization has not been reported. Two types of surfactants, sodium stearoyl-2-lactylate and calcium stearoyl-2-lactylate (at levels of 0.2 and 0.4% based on the weight of the flour), were mixed with soy flour prior to extrusion. A yeast protein (Torutein, manufactured by Amoco Inc.), claimed to be an extrusion helper although its function is not known, was added. 

Extrusion is a cost effective manufacturing process. Extrusion is popularly used in large scale production of food, plastics and composite materials. Most widely used thermoplastics are processed by extrusion method. Many biopolymers and their composite materials with petroleum-based polymers can also be extruded. These include pectin/starch/poly(vinyl alcohol) (Fishman et al. 2004), poly(lactic acid)/sugar beet pulp (Liu et al. 2005c), and starch/poly(hydroxyl ester ether) (Otey et al. 1980), etc. In this study, composite films of pectin, soybean flour protein and an edible synthetic hydrocolloid, poly(ethylene oxide), were extruded using a twin-screw extruder, palletized and then processed into films by compression molding process or blown film extrusion. The films were analyzed for mechanical and structural properties, as well as antimicrobial activity. 

Most of the data on hpid-starch interactions was derived during studies on dough making and extrusion, wherein the material studied contained, in addition to starch, proteins, also easily interacting with lipids. 

Zardetto Dalla Rosa in 2006 studied the evaluation of the chemical and physical characteristics of fresh egg pasta samples obtained by using two different production methodologies extrusion and lamination. Authors evaluated that it is possible to discriminate the two kinds of products by using FT-NIR spectroscopy. FT-NIR analysis results suggest the presence of a different matrix-water association, a diverse level of starch gelatinization and a distinct starch-gluten interaction in the two kinds of pasteurised samples. 

In spite of the number and diversity of studies on multilayer flows and stability, only a few articles [MAR 01b, MAR 02, WAN 00] and patents [AVE04a] have reported on the use of plasticized starch in co-extmsion. Various different stratified stractures have been obtained by co-extrusion with different polyesters such as PQ., PBSA, PLA, PBAT or PHAs [AVE 04a, MAR 02, MAR 01b, WAN 00],... 

As an alternative to these materials the objective in this research will be to produce starch based resilient thermoplastic foams based totally on native potato starch. This is done in two steps the production of expandable thermoplastic starch beads by extrusion and foaming of the expandable beads after conditioning in a successive foaming step. The properties of these foams will be studied as a function of processing parameters and material composition. A further objective is to determine the ultimate properties of pure starch based foams. 

Dimethylacetamide (DMAc) with lithium bromide was used by Wasserman and Timpa to study the effect of extrusion on the molecular weight of corn starch (39). The instrument has an on-line viscometric detector and is run at 80°C. 

Myllymaki et al. studied the depolymerization of barley starch during its extrusion in the presence of a mixture of water and glycerol [107]. They observed a correlation between the depolymerization of the starch chains and both the water/glycerol concentration and, to a minor extent, the screw speed. 

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