Comparison between drum and pulverized air dried distillers grain extrudates using single screw extruder

Abstract

Corn distillers dried grains (DDG) were extruded in a corn meal base using single screw extruder at various levels of extruder die temperature, DDG content, screw speed, moisture content, and sodium bicarbonate(NaHCO3) content. Physical properties of extrudate, such as radial expansion, bulk density, peak load, and color of extrudate strands were measured. Pulverized air-dried (PDA) DDG extrusion results were compared with Drum dried DDG extrusion results. Results revealed that pulverized air-dried DDG expanded more than drum dried DDG even when all parameters were held constant. It was observed that there was decrease in radial expansion from 8.31 mm for PDA DDG at 0% and 150 °C to 7.7 mm for drum dried DDG at 0% and 150 °C. A decrease in protein and subsequent increase in starch appears to be reason for increase in extrudate expansion. High temperature results in burning of product. Bulk density increased with increase in DDG content. Highest expansion was obtained at 0% DDG. Highest expansion was achieved at 15% moisture content. NaHCO3 was added to see whether it releases carbon dioxide when heated which will cause the product to expand more. A central composite design was used to determine effects of three independent variables on physical properties of extrudates. Using response surface methodology, it is possible to achieve optimum point for higher radial expansion. R2 value was 89.72%, which revealed that there exists strong correlation between variables and the model was appropriate.