Using an In‐Line Slit‐Die Viscometer to Study the Effects of Extrusion Parameters on Corn Melt Rheology

Abstract

An in‐line slit‐die viscometer (SDV) was used to measure the viscosity of a melt extrudate independently of the extruder operating conditions. The melt produced by extrusion of the corn grits followed a power law rheological model. The viscosity of the melt and extrusion parameters such as specific mechanical energy (SME), torque, and die pressure decreased with increasing moisture content. The degree of starch gelatinization increased when barrel temperature increased from 90 to 130°C. At temperatures higher than 130°C, most of the starch had gelatinized. The increase in barrel temperature, however, resulted in small changes in the apparent viscosity of the melt, until a maximum of ≈130°C. At a constant feed rate, SME increased and torque decreased when screw speed increased due to the shear thinning behavior of the melt. At a constant screw speed, the torque increased and SME decreased with increasing feed rate. This was due to a decrease in apparent viscosity of the melt at higher feed rates. SME is not an independent extrusion variable and should be used with caution either when predicting the effect of thermomechanical treatment of the product or as the key and only variable for controlling the food extrusion process.

Rheological behavior of corn and soy mix as feed ingredients

“…The utilization of the Power Law model to describe the flow behavior of cereal grains has been confirmed by several authors (LI;CAMPANELLA;HARDACRE, 2004;CARVALHO;ASCHERI;MITCHELL, 2004;ALAVI;CHEN;RIZVI, 2002;SINGH;SMITH, 1999;BAGLEY;DINTZIS;CHAKRABARTI, 1998;PADMANABHAN;BHATTACHARYA, 1991;SENOUCI;SMITH, 1988).…”

“…It is known that extruded foods behave as non-Newtonian fluids, and their viscosity can be described by the Power Law model (CARVALHO; ASCHERI; MITCHELL, 2004;LI;CAMPANELLA;HARDACRE, 2004;SINGH;SMITH, 1999;EERIKAINEN;LINKO, 1998;RAO;ANANTHESWARAN 1982;REMSEN;CLARK, 1978). However, little is known about the rheological behavior of ingredients submitted to the characteristic processes in the feed industry.…”

System parameters and product properties response of soybean protein extruded at wide moisture range

“…The in-line viscosity at die of each treatment was calculated according to the method described by Li et al (2004) using the formula below, where g is the apparent viscosity (Pa s), s the shear stress (Pa), c the shear rate (s À1 ), DP the die pressure drop (Pa), H, L and B the known geometries of viscometer channel (mm), and s the velocity of extrudate coming out from the die (mm/s)…”

Shear and elongational viscosities of a complex starchy formulation for extrusion cooking

“…Different techniques have long been used to carry out these measurements. They vary from off-line determinations mainly through capillary rheometers (Parker, Lai-Fook, Ollet & Smith, 1989;Madeka & Kokini, 1992;Sandoval & Barreiro, 2007), to the most popular in use, on-line measurements at the extruder die (e.g., Harper, Rhodes & Wanninger, 1971;Bhattacharya & Padmanhabhan, 1992;Vergnes, Della Valle, & Tayeb, 1993;Drozdek & Faller, 2002;Li, Campanella, & Hardacre, 2004 for instance). Using the latter, Cho and Rizvi (2009) recently showed that whey protein addition slightly decreased viscosity of starch based melts for extrusion, and that it could affect cellular structure.…”