The effect of barrel temperature and feed moisture content on deamidation and volatile formation in extruded soy flour

Extrusion has been widely used in the food industry to produce uniquely textured and flavored foods. The chemical changes and reactions which occur during extrusion processing such as the Maillard reaction, and protein deamidation are not yet fully understood and play a major role in the final flavor of the foodstuff being produced. One goal of this research was to determine the effect of barrel temperature and moisture content on deamidation of soy protein during the extrusion of defatted soy flour. Additionally, another goal of this research was to determine volatile formation during the same extrusion conditions.; Defatted soy flour extrudates were generated under different temperatures (140-180{dollar}spcirc{dollar}C) and moisture contents (20-30%). Deamidation of the extrudates was measured by an ammonia electrode after a purge and trap method for sample clean-up. Upon analysis of the residual amide content for the extrudates, it was found that deamidation occurred during the extrusion processing of defatted soy flour and that at higher temperature and greater moisture contents the levels of deamidation increased.; Deamidation in extruded soy flour may have also had an effect on the volatiles produced. The level of pyrazines was shown to increase as the level of deamidation increased which may be partially attributed to the ammonia liberated by the deamidation reaction.; The volatiles generated during extrusion were determined by a short path thermal desorption methodology that concentrated the volatiles on an adsorbent substrate prior to desorption into a GC-MS for isolation and identification. The samples extruded at higher temperatures had higher levels of pyrazines and lipid oxidation products. Samples extruded at higher feed moisture contents had slightly higher levels of pyrazines than samples extruded at lower feed moisture contents.; Absorbance at 420 nm and an L*a*b* color space analysis using a chromometer was used to measure the browning and color change in the extrudates. The brown color and {dollar}Delta{dollar}E values of soy flour increased at higher extrusion temperatures and moisture contents. Additionally, HPLC methodology was used to determine the mono- and disaccharides present in the extrudates. Sucrose and maltose levels decreased as the temperature of extrusion increased.