Effect of L-cysteine on the rheological properties of wheat flour

Extrudate expansion of cereal-based products is largely dependent on the mo lecular interactions and structural transformations that proteins undergo d ining extrusion processing. Such changes strongly influence the characteris tic rheological properties of the melt. It is possible to modify rheologica l properties of wheat flour during extrusion processing, in particular shea r viscosity, with cysteine. The objective of this work was to further devel op an understanding of the molecular interactions and structural transforma tions of wheat flour from dynamic oscillatory rheological measurements. Tem perature and frequency sweeps were conducted in the linear viscoelastic ran ge of the material. Changes in the storage moduIus (G '), the loss moduIus (G ") and the loss tangent (tan delta) of 25% moisture wheat flour disks as a function of cysteine concentration (0-0.75%) were monitored. Molecular w eight between cross-links (M-c) and the number of cross-links (N-c) per glu tenin molecule were determined from frequency sweep data. Increasing cystei ne concentration broke crosslinks by decreasing G ' maximum and increasing tan delta values. Molecular weight between cross-links increased and the nu mber of cross-links decreased. G ' values from temperature sweeps showed a similar trend. This information leads to a better understanding of the visc oelastic behavior of wheat flour doughs during extrusion cooking and elucid ation of protein-protein reaction mechanisms and other interactions in extr uded cereal-based snack foods.