Extrusion of wheat gluten plasticized with glycerol: Influence of process conditions on flow behavior, rheological properties, and molecular size distribution

Gluten-glycerol dough was extruded under a variety of processing conditions using a corotating self-wiping twin-screw extruder. Influence of feed rate , screw speed, and barrel temperature on processing parameters (die pressur e, product temperature, residence time, specific energy) were examined. Use of flow modeling was successful for describing the evolution of the main f low parameters during processing. Rheological properties of extruded sample s exhibited network-like behavior and were characterized and modeled by Col e-Cole distributions. Changes in molecular sizes of proteins during extrusi on were measured by chromatography and appeared to be correlated to molecul ar size between network strands, as derived from the rheological properties of the materials obtained. Depending on operating conditions, extrudates p resented very different surface aspects, ranging from very smooth-surfaced extrudates with high swell to completely broken extrudates. The results ind icated that extrudate breakup was caused by increasing network density, and some gliadins may have acted as cross-linking agents. Increasing network d ensity resulted in decreasing mobility of polymeric chains, and "protein me lt" may no longer have been able to support the strain experienced during e xtrusion through the die. Increasing network density was reflected in incre ased plateau modulus and molecular size of protein aggregates. Increasing n etwork structure appeared to be induced by the severity of the thermomechan ical treatment, as indicated by specific mechanical energy input and maximu m temperature reached.