Physico-chemical properties, phytochemicals and DPPH radical scavenging activity of supercritical fluid extruded lentils

A powder blend comprised of lentil flour and pre-gelatinized potato starch was processed using supercritical fluid (carbon dioxide) extrusion (SCFX). The blend was extruded at temperature of 95-99.5 degrees C and screw speeds of 40, 80 and 120 rpm. The physical properties of the extruded products such as porosity, rehydration rate, expansion ratio, and crispness improved as the screw speed increased. Furthermore, the density, water solubility index, brittleness, and hardness of the products decreased as the screw speed increased. SCFX increased the transition temperature of starch and protein in lentil flour. Increased screw speed led to increased gelatinization in the starch. Unlike traditionally cooked lentils, no retrogradation of starch was observed for the extruded red lentil products stored at room temperature for 60 days. Compared to raw lentil, SCFX increased the total phenolic and DPPH radical scavenging activity of lentils by 30% and 18%, respectively. In addition, SCFX decreased the trypsin inhibitor content in the lentil flour. Higher screw speeds led to a greater reduction in the trypsin inhibitor content. The SCFX process rendered red lentil flour into a snack-type whole grain product with a more balanced nutritional and antioxidant composition.