2001 AACC Annual Meeting Charlotte, North Carolina October 14-18, 2001 Charlotte Convention Center

The hydrophobic zein protein of corn disperses from protein bodies during extrusion cooking and influences extrudate physical properties. Our objective was to investigate changes in glass transition temperature (Tg) of extrudates in relation to physical properties. Dynamic mechanical thermal analysis (DMTA) was used to determine Tg's of extruded samples. The Warner-Bratzler (WB) method with a Universal Testing Machine has shown that added zein protein bodies influence the extrudate physical properties. At bone-dry moisture condition, WB results showed that zein-added starch extrudates needed lower force (kg) to break than the extruded starch samples, indicating brittleness. At intermediate moisture level (equilibration at 58% RH), the WB test demonstrated that zein-added starch extrudates maintained their brittleness, while starch extrudates became pliable. Although all extrudates were pliable when equilibrated at high moisture level (98% RH), results showed that added zein still provided some degree of strength to the extrudates. DMTA results showed that the above observations are related Tg changes due to zein addition. DMTA of bone-dry samples showed melting point only and no Tg's due to the absence of water. The addition of zein protein to starch extrudates increased Tg's substantially (20 to 25 C increase) for samples equilibrated (at 58% RH) to an intermediate moisture level. No similar trends were observed at high moisture samples (equilibrated at 98% RH). Our studies suggest that zein protein could be utilized to alter Tg's of starch-based products to achieve desired physical properties.