"Physical and microstructural properties of native corn starch-soy protein concentrate (CS-SPC) extrudates were investigated in relation to the macromolecular changes in starch during extrusion. The effects of extruder screw speed (230 and 330 rpm) and SPC concentration (0%, 5%, 10%, 15%, 20%) on the above-mentioned parameters were determined. Increasing screw speed resulted in higher specific mechanical energy (SME) and expansion, and lower mechanical strength. On the other hand, addition of 5-20% SPC led to lower SME and expansion, and higher mechanical strength. X-ray micrographs showed smaller yet more cells, and cell wall thickening with SPC addition. Water absorption index increased and water solubility index decreased with increase in screw speed and SPC level," wrote N.J.E. Demesa and colleagues, Kansas State University.
The researchers concluded, "Increasing screw speed resulted in a slight shift toward smaller molecular weight fractions of starch, as determined by gel permeation chromatography."
Demesa and colleagues published their study in the Journal of Food Engineering (Soy protein-fortified expanded extrudates: Baseline study using normal corn starch. Journal of Food Engineeringg, 2009;90(2):262-270).
For additional information, contact N.J.E. Demesa, Kansas State University, Dept. of Grain Science & Ind, 201 Shellenberger Hall, Manhattan, KS 66506, USA.
From the December 5, 2008, Prepared Foods e-Flash