Process optimization for antioxidant enriched sorghum flour and apple pomace based extrudates using liquid CO2 assisted extrusion

•Liquid CO2 instead of supercritical CO2 reduces the cost of processed products.•It also produces the similar quality of product with retaining its nutritive values.•Improved quality with higher inclusion of apple pomace were obtained below 100 °C.•Replacement of supercritical CO2 by liquid CO2 will enhance the feasibility at industrial level.

Extrusion as a thermal process renders nutritional and bioactive compounds losses in final extruded products. To overcome this issue, in the present study, blend of corn flour and hydrodynamic cavitated sorghum flour, apple pomace was extruded in the presence of CO2 to retain total phenolic content and antioxidant activity in extrudates. CO2 extruded products had 12% and 7% more total phenolic content and antioxidant activity, respectively as compared with control extrudates at optimum conditions of 30% apple pomace ratio, 25 g/100 g feed moisture, 97 °C temperature and 100 rpm screw speed. Though expansion ratio decreased after CO2 extrusion, 59% less hardness and 70% more crispness were observed in CO2 extrudates compared with control extrudates. Low water absorption index and higher water solubility index were observed in CO2 extrudates, however extrusion with CO2 decreased in-vitro starch digestibility and total dietary fiber by 3% and 4%, respectively. The color (L*, a*, b*) results proved that the Maillard's reaction rates decreased when CO2 was injected during extrusion process. The high inclusion of apple pomace using CO2 injection produced extrudates with improved antioxidant, textural and functional properties below 100 °C extrusion temperature.