Starch Extrusion Cooking

A different form of starch gelatinization is extrusion cooking technology [37], As described by Conway in 1971 [38], extrusion cooking and forming are characterized by sufficient work and heat being applied to a cereal-based product to cook all the ingredients to obtain a crunchy 

It has been demonstrated that an extrusion-cooked starch can be solubilized without any formation of maltodextrins and that the extent of solubilization depends on exttusion temperature, moisture content of the starch before extrusion and amylose/amylopectin ratio. For instance, Mercier et al. [39] determined the properties of different types of starch and considered the influence of the following parameters in a short twin-screw extrader moisture content between 10.5 and 28%, barrel temperature between 65 and 250 °C, residence time between 20 seconds and 2 minutes. It was demonstrated that com starch, after extrusion cooking, gave a solubility lower than 35%, while potato starch solubility was up to 80%. 

Hanna et al. [42] observed that the degree of gelatinization of ordinary com (30% amy-lose) and waxy corn (1% amylose) decreased with increasing moisture content but increased with increasing temperature. Corn starches were extruded between 17.8 and 42.2% moisture contents and extruder barrel temperatures of 116, 120, 140, 160 and 164 °C. Screw speeds of 93.5, 1(X), 130, 160 and 166.5 rpm were used to generate different residence times. 

In the patent literature, the terminology destructurized starch [46-65] refers to a form of thermoplastic starch described as molecularly dispersed [56]. Destracturization of starch is defined as melting and disordering of the molecular structure of the starch granules as a molecular dispersion [55,56]. It means that, at the same time, the native crystallinity of starch 

This is achieved by heating the starch above the glass transition temperature (Tg) and the melting temperatures (Tm) of its components, until they undergo endothermic transitions under shear, temperature and pressure for a time sufficient to destroy also the granular sttucture. As already stated, the water volume fraction required has to be below 0.45 and preferably below 0.28 [27]. 

---

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. 

Flory-Huggins approach, may be somewhat low even with highly crystalline preparations of A- or B-type starch lintners (DP —15). Despite its theoretical limitations, the Flory analysis (as illustrated in Figure 8.10 inset) can be used to simulate the melting behavior of starch in practical applications (e.g. extrusion cooking, baking) and to compare the thermal stability of different starch materials under dynamic heating at various moisture conditions.20,25 240 337... 

Qu, D., and Wang, S. S. (1991a). Kinetics of formation of gelatinized and melted starches at extrusion-cooking conditions. IFT Annual Meeting, Chicago, IL, Abstract 43. 

Colonna, P., Doublier, J.L., Melcion, J.P., de Monredon, F., and Mercier, C. (1984). Extrusion cooking and drum drying of wheat starch. Cereal Chemisty, 61, 538-543. 

The thermoplastic amorphous starch is produced using the extrusion cooking technology,... 

During extrusion cooking, no perceptible changes occur because the process is very fast and the temperature sufficient for enzyme inactivation is attained in less than 1 min. The content of extractable lipids may be affected by lipid-starch interactions (see Chapter 18). The maximum temperature is usually too low to initiate oxidation reactions, but partial destruction of natural antioxidants does occur. 

Mercier, C., Comparative modifications of starch and starchy products by extrusion cooking and drum-drying, in Pasta and Extrusion Cooked Foods, Mercier, C. and Cantarelli, C., eds., Elsevier Applied Science, London, U.K., 1987, p. 120. 

Chinnaswamy, R., Hanna, M.A. and Zobel, H.F. (1989) Microstmctural, physiochemical, and macro-molecular changes in extrusion-cooked and retrograded com starch. Cereal Foods World, 34,417-422. 

Orford, P.D., Parker, R. and Ring, S.G. (1993) The functional properties of extrusion-cooked waxy-maize starch. Journal of Cereal Science, 18, 277-286. 

The procedure is now illustrated by an example. Wheat starch and poly (styrene) (PS) are blended together. To this blend, citric acid and sodium bicarbonate is added. Citric acid acts as the oxidizing agent and sodium bicarbonate is the substance for degrading the starch. This blend is extrusion-cooked at a temperature of 140°C and a pressure of approximately 20 M Pa. 

Despite the fact that TPS is considered a new material in technological terms, its basic features and processes are in fact the same as those relative to extrusion-cooking starch used in the food industry since the 1960s. This kind of processing is therefore briefly described briefly in the heading, given its importance in the development of TPS. 

Mercier C., Charbonniere R., Grebaut J. et al. Formation of amylose-lipid complexes by twin-screw extrusion cooking of manioc starch. Cereal Chem., 57, 1980, 4-9. 

Merder C., Effect of extrusion-cooking on potato starch using a twin-screw French extruder, Starke, 29, 1977, 48-52. 

This article reviews the main results obtained in the fields of starch-filled plastics and thermoplastic starch, with particular attention to the concepts of gelatinization, destructurization, extrusion cooking, and the complexation of... 

Della Valle, G. Quillien, L. Gueguen, J. Relationships between processing conditions and starch and protein modifications during extrusion-cooking of pea flour. J. Sci. Food Agric. 1994, 64, 509-517. 

Grossman, M.V.E. El-Dash, A.A. Carvalho, J.F. Extrusion cooking of cassava starch for ethanol production. Starch/Stdrke 1988, 40, 300-307. 

---