Effect of screw configuration, moisture content and particle size of corn grits on properties of extrudates

Abstract

Extrusion is a modern procedure for processing different types of raw materials and production of wide range of food products, where the corn grits are often used as main raw materials. Therefore the aim of this study was to determine the effect of screw configuration (4:1 and 1:1), moisture content (15% and 20%) and particle size of corn grits (>500 µm and <500 µm) on properties of extrudates. Samples were extruded in the laboratory single screw extruder Brabender 19/20 DN, at temperature profile 135/170/170 °C, using die with 4 mm diameter. Physical and rheological properties, digestibility and starch damage of the obtained extrudates were determined, and results were compared with control samples of non-extruded corn grits. Lower moisture content and usage of screw with compression ratio 4:1 increased expansion ratio and fracturability, but decreased bulk density and hardness of extrudates, regardless of granularity. After extrusion process water absorption index increased, but peak, hot and cold viscosity of all samples decreased, with more pronounced effect in grits extruded with lower moisture content and with screw 4:1. Extrusion caused a reduction of the resistant starch content and increase starch damage of all samples.