Effects of Different Screw Configurations on Physicochemical Properties and Reconstitutability of Extruded Corn Flour

To investigate the effects of different screw configurations on the physicochemical properties and reconstitutability of extruded corn flour, this study set up different screw configurations by varying the number of kneading element groups, the distance between the kneading elements and the die head (kneading-die distance), and the kneading element spacing. The specific mechanical energy was taken to reflect the shear strength of the screw. The paste, hydration, textural properties and microstructure of extruded corn flour were measured as well as its reconstitutability. The results showed that different screw configurations caused changes in specific mechanical energy; compared with that of non-extruded corn flour (NCF), the specific mechanical energy of extruded corn flour was elevated with increasing number of kneading elements and with decreasing kneading-die distance or kneading element spacing, and the starch and water molecules in extruded corn flour formed a highly porous gel structure. When two sets of kneading elements were used and the kneading element spacing was 5 L/D (G6), the peak pasting viscosity and gel hardness of corn flour decreased by 57% and 64.94%, respectively. The relative crystallinity of starch decreased by 62.76%, the water absorption index and water solubility index increased by 1.83 and 2.10 folds, respectively and the agglomeration rate of extruded corn flour decreased by 77.91%, indicating significantly improved reconstitution stability. Correlation analysis showed that the specific mechanical energy of extruded corn flour was significantly and positively correlated with the content of amylose, stability coefficient, water absorption index and water solubility index, but significantly and negatively correlated with the relative crystallinity, agglomeration rate and centrifugal sedimentation rate. The relative crystallinity was significantly and negatively correlated with the water absorption index, water solubility index and stability coefficient, but significantly and positively correlated with the agglomeration rate and centrifugal sedimentation rate. In conclusion, increasing the number of kneading elements and decreasing the element spacing can effectively enhance the physicochemical properties and reconstitutability of extruded corn flour, providing a theoretical basis for the selection of screw configuration for improved reconstitutability of extruded corn flour.