Radical scavenger, cysteine added

To test this Working Hypothesis, 0%, 0.5%, 1% and 2% cysteine were added to wheat flour as a radical scavenger during extrusion (3). The original Bouncer flour (14% protein) was extruded at process moisture 16% (w/w), constant die temperature 185 C, 225 g/min mass flow rate, and screw speed 500 rpm conditions that provided optimum wheat flour expansion, flavor and textural quality in the earlier experiments. 

Figure 6. EPR signals of wheat four extruded with varying levels of cysteine added as a radical scavenger. Adapted from (3) with permission. Copyright American Assoc, of Cereal Chemists, 1996.

Figure 7. Protein solubility increases in wheat flour extrudates as a junction oj level of cysteine added as a free radical scavenger during extrusion. From Koh (3), used with permission. Copyright American Association oJ Cereal Chemists, 1996.

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in control extrudates with added cysteine the mesh structure was replaced by thin aligned strands of protein (Schaich, unpublished). 

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