Effects of die temperature, alkalized cocoa powder content and CO2 gas injection on physical properties of extruded cornmeal

The extrusion process with CO2 gas injection has been successfully developed for the production of cornmeal-based extrudates with unique porous structure and texture. The die temperature (95, 110, and 120 °C), alkalized cocoa powder (ACP) content (0%, 6%, and 12%), and CO2 gas injection flow rate (0 and 200 mL/min) were critical to control the expansion and texture of the final product. Extrudates containing high level of ACP without CO2 gas injection were denser, less expanded, and harder than those with CO2 gas injection. An increase in ACP content from 0% to 12% significantly (p < 0.05) increased the specific mechanical energy input and reduced the lightness, redness, yellowness, water absorption index, and water solubility index of extrudates. The peak, breakdown, and final viscosity significantly (p < 0.05) reduced with increasing die temperature and ACP content. The finding showed that the use of CO2 gas can help to produce extudates with uniform cellular texture. The use of ACP as ingredient using CO2 gas injection prevented cell collapse and increased expansion indexes of extruded cornmeal at higher die temperature.

► The extrusion with CO2 injection has been successfully produced cocoa-fortified cornmeal snacks. ► The CO2 injection and the addition of alkalized cocoa powder increased expansion with increasing temperature. ► The extrudates with uniform pore, low density and low breaking were obtained at temperature below 100 °C with CO2 injection. ► An increase in alkalized cocoa powder reduced cell collapse at higher temperature with CO2 injection.