5 6 7 8 9 10 11 pH (before extrusion)

Figure 2. (a) Influence of pH adjustment on Warner-Bratzler shear values of extruded soy protein; (b) influence of pH adjustment on sensory response of extruded soy protein. Source: Adapted with permission from Ref. 20.

flour (33). The peak force measured using a Ottawa texture machine was found to correlate well with protein solubility, as illustrated in Figure 3. The higher barrel and low die temperature resulted in a better texture for both materials.

Although most research has been on soy proteins because of the potential to simulate meat products, some research has evaluated the properties of other high-protein materials after extrusion. These included studies of the effect of extrusion on glandless cottonseed flour and soy meal mixtures (34,35) and on cowpea meal (36) and the effect of process temperature, screw speed, moisture content, and pH on the WAC and nitrogen solubility index of cowpea, mung bean, defatted soybean, and air-classified mung bean (37). Protein type and amount were found to affect properties. Results from extrusion of blends of corn and soy proteins have been reported (22,38-40). Increasing the amount of soy protein in the corn-soy mixture led to products with better textural and functional properties.


Much literature is available on extrusion cooking of starch-based materials. Reference 41 is an excellent review of

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