Effect of zein extrusion and starch type on the rheological behavior of gluten-free dough

Previous research has shown that zein, above its glass transition temperature, may adopt molecular structures that are able to form doughs with viscoelastic properties comparable to those of wheat gluten. It is hypothesized that extrusion can promote molecular changes in zein and favor interactions with starch that enhance dough viscoelasticity. Thus, the effects of extruding zein at 90-160 degrees C on the rheological properties of doughs prepared with potato, rice, and maize starches were determined. Formulations were optimized to provide similar mixing profiles to that of a standard wheat dough. For all zein samples, creep-recovery tests demonstrated that doughs prepared with maize and potato starches were less elastic when compared to doughs prepared with rice starch. Zein doughs produced using rice starch were comparable to wheat-dough. Extensional tests showed that zein extruded at 160 degrees C provided a larger increase in strain-hardening behavior, which is important for bread production. These samples also exhibited larger extensional stresses. Gel electrophoresis of zein extruded at 160 degrees C revealed an increase in protein aggregates and the presence of smaller peptides when compared to samples subjected at lower extrusion temperatures. Scanning electron micrographs of doughs containing zein showed starch granules embedded within an amorphous material and fibrous structures, which is attributed to elongated zein.