Effects of eggshell powder addition on the extrusion behaviour of rice

The study was conducted to investigate the effects of eggshell powder on the extrusion behaviour and extrudate properties of rice in a co-rotating twin-screw extruder. A reduction in feed rate was observed with 1% eggshell powder added while feed rate increased as eggshell powder added up to 2% or more. Increase in specific mechanical energy (SME) was proportional to increase in pH with the levels of eggshell powder added being up to 2%. When eggshell powder added more than 2%, no significant change in pH value but decrease in SME were observed. Microstructure of eggshell powder added extrudates showed a fine and friable texture with thinner cell walls and more cell numbers. With increase in levels of eggshell powder could increase L∗ values but decrease b∗ values of extrudates. However, no significant change in a∗ values of extrudates was observed. Adding eggshell powder increased water solubility index (WSI) of extrudates. Increasing the levels of eggshell powder could decrease moisture content (MC) and cross-sectional expansion (CE) but increase longitudinal expansion (LE) of extrudates. The addition of eggshell powder also could increase specific volume (SV) and decrease shear force (SF) of extrudates; moreover, the highest SV and the lowest SF of extrudates were observed as 1% eggshell powder added.