Effect of extruding wheat flour at lower temperatures on physical attributes of extrudates and on thiamin loss when using carbon dioxide gas as a puffing agent

Wheat flour with 0.3% (w/w) thiamin was extruded on a twin-screw laboratory-scale extruder (19-min barrel) at lower temperatures and expanded using carbon dioxide (CO2) gas at 150 psi. Extrusion conditions were die temperature of 80 degrees C and screw speed range of 300-400 rpm. Control samples were extruded at a die temperature of 150 degrees C and screw speed range of 200-300 rpm. Dough moisture content was 22% in control samples and 22 and 25% in CO2 samples. Expansion ratio, bulk density, WAI, and %WS1 were compared between control and treatment. CO2 injection did not significantly increase expansion ratio. Bulk densities in the CO2 extruded samples decreased when feed moisture decreased from 25 to 22%. The products using CO2 had lower WAI values than products puffed without CO2 at higher temperatures. The mean residence time was longer in CO2 screw configurations than in conventional screw configurations. Thiamin losses were 10-16% in the control samples. With CO2, thiamin losses were 3-11% at 22% feed moisture, compared with losses of 24-34% at 25% moisture. Unlike typical high-temperature extrusion, thiamin loss in the low-temperature samples decreased with increasing screw speed. Results indicate that thiamin loss at lower extrusion temperatures with CO2 injection is highly dependent on moisture content.