The Effect of Extrusion Operating Conditions on the Apparent Viscosity and the Properties of Extrudates in Twin-Screw Extrusion Cooking of Maize Grits

Abstract

Maize grits were extrusion-cooked in a CM45 conical, counter-rotating twin screw extruder with varied feed rate (47 to 60 kg/h), product temperature (150 to 160°C), feed moisture content (13 to 17 g/100g wet basis), and die length (115 to 185 mm). The specific mechanical energy (SME), the starch gelatinizatiion degree, the apparent melt viscosity, the radial expansion ratio and extrudate bulk density were measured. The apparent viscosity, SME, and product properties, were found to be most dependent on the feed moisture content. Increasing moisture content decreased the SME, the degree of gelatinization, the apparent viscosity, and the radial expansion ratio, giving products with greater density. The apparent viscosity was used in the modelling of the extrudate properties. The apparent viscosity was found to affect the radial expansion ratio but not the extrudate bulk density.