Extrusion starch

Rate Limited by Discharge Temperature and Torque for Starch Extrusion... 

We extended the methodology developed for molecular characterization of cotton fiber to analysis of other polysaccharides. In this report, we present the results obtained from MWDs determined by SEC for various complex carbohydrate samples dissolved in DMAC-LiCl. Applications include cotton fiber, corn and wheat starch flours, and avocado cell walls. Relationships are evaluated between the respective MWDs and cotton fiber development, variety, inheritance, textile processing, and strength starch extrusion conditions and stage of ripening in avocado. 

Starch PoIy(ethyIene-vinylalcohol) copolymer, 56% VA waxy maize, native com and high-amylose starches extrusion-blended x-ray, DSC, SEM, TEM Phase separated starch domains. Oriented droplets, 0.05-5 jm in length (waxy maize), 0.05-1.2 pm domains (native com), <0.25 pm (high amylose) (81)... 

The term TPS describes an amorphous or semi-crystalline material composed of gelatinized or destructurized starch containing one or a mixture of plasticizo-s. TPS can be repeatedly softened and hardened so that it can be moulded/shaped by the action of heat and shear forces, allowing its processing to be conducted with the techniques commonly used in the plastic industry. The following sections are devoted to a brief description of the basics of starch extrusion and processing and to the more relevant applications of TPS [50, 57, 73-75, 79-81]. TPS or destructurized starch are also known as PLS [82], because of the inevitable presence of non-volatile plasticizers in their composition. TPS is however the predominant term used for these materials. 

Extrusion effects on starch are significant since starchy cereals and tubers provide the bulk of calories consumed by most people, particularly those living in less-developed nations. Gelatinization occurs at lower moisture levels (12—22%) than is possible with other food processing methods. Qu and Wang (1994) hypothesized that waxy com starch extrusion is dominated by melting, which follows a zero order kinetics, rather than gelatinization, a first order reaction. 

Caudwell, R. W. Gatehouse, A. G. Formulation of grasshopper and locust enomopathogens in baits using starch extrusion technology. Crop Protection. 1996, 15,33-37. 

The problems associated with starch extrusion are increased when starch nanocomposites are processed using hydrophilic fillers. As it was explained before, although these fillers are compatible with starch and glycerol, they tend to clump together obstructing their dispersion in the matrix. 

All of the starch types investigated were found to show lower SME values with increasing glycerol contents in the mixtures (Figure 7.8). The lowest SME values were obtained for potato starch extrusion, the highest for wheat starch processing. Differences in SME values were also detected for potato starch with varied amylose contents. The highest SME values were found for potato starch with 24% amylose, the lowest for starch with 22.1% amylose content... 

Thermoplastic starch extrusion-cooking is associated with a rather low energy input 0.07 kWh kg on average. The extruder power required for extrusioncooking of TPS depends on material composition an increase in the glycerol content in a mixture causes the process energy consumption to decrease. 

The SME value also depends on the type of starch. The lowest SME values were obtained during potato starch extrusion, whereas the highest were found for wheat starch processing. It was also found that there are differences in SME values for potato starch of varying amylose contents. 

Scaling-up of thermoplastic starch extrusion suffers from the same general problems that are encountered in many other processes in the process industry ... 

Similarity in residence times means equal residence times in the small-scale and the large-scale equipment. This is not a requirement that is often fulfilled in extrusion processes, and in thermoplastic starch extrusion this can only be achieved if the scahng-up is adiabatic. 

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