EFFECT OF EXTRUDER RETENTION TIME ON CAPILLARY FLOW OF SOY DOUGH¹

Abstract

Soy dough (defatted soy flakes), at 120° C and 30% moisture, was extruded through a series of dies of differing length (L) and radius (R). Rlots of pressure (P) were linear with the length to radius ratios (L/R) of the dies at constant output rate (Q) and R. The intercepts of the P versus (L/R) plots on the P = O axis give the end corrections (e) for capillary flow at each output rate. For soy dough, these end corrections were surprisingly large at low output rates and generally decreased rapidly with increasing output rate. This is contrary to the normal behavior of viscoelastic fluids, such as thermoplastics, where the end correction increases with increasing output rate. Both the end correction, which is a measure of the elastic properties of the soy dough, and the viscosity of the soy dough depended on the output rate as expected and also on the retention time of the material in the system.

Measurement of rheological and ultrasonic properties of food and synthetic polymer melts

“…Various authors have used such equipment to study food dough and polymer rheology [1][2][3]. Instead of a piston-driven rheometer, other workers have used screw extruders to feed capillary dies of various length to diameter ratios [4][5][6][7][8].…”

An experimental study of food melt rheology

“…The importance of time and shear history in calculating viscosities of food materials has been emphasised by Remsen and Clark [14] and Jasberg et al [15] who used capillary rheometers. Other workers have used an extruder-fed die to obtain shear rheological properties [16,17] although comparatively few data exist for use in models.…”

Comparison of the extrusion cooking of a soya isolate and a soya flour

“…Clearly it would have been desirable to evaluate n by making measurements at different shear rates, achieved by altering the flow rate. There are, however, difficulties in analysing the data from such an approach, since viscosity will also depend on the retention time (Jasberg, Mustakas & Bagley, 1982).…”